Abstract:
Apparatus and methods are described, included a method for detecting uterine contractions in a pregnant woman. The method includes sensing motion of the woman without contacting the woman, generating a signal corresponding to the sensed motion, and analyzing the signal to detect presence of labor contractions. Other applications are also described.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 14/454,300 to Halperin, filed Aug. 7, 2014, which is a continuation of U.S. patent application Ser. No. 14/150,115 to Pinhas (issued as U.S. Pat. No. 8,840,564), filed Jan. 8, 2014, which is: 
     (i) a continuation of U.S. patent application Ser. No. 13/921,915 to Shinar (issued as U.S. Pat. No. 8,679,030), filed Jun. 19, 2013, which is a continuation of U.S. patent application Ser. No. 13/107,772 to Shinar (issued as U.S. Pat. No. 8,491,492), filed May 13, 2011, which: 
     is a continuation-in-part of U.S. patent application Ser. No. 11/782,750 to Halperin (issued as U.S. Pat. No. 8,403,865), filed Jul. 25, 2007; and 
     is a continuation-in-part of U.S. patent application Ser. No. 11/552,872 to Pinhas (published as US 2007/0118054), filed Oct. 25, 2006, now abandoned, which claims the benefit of (a) U.S. Provisional Patent Application 60/731,934 to Halperin, filed Nov. 1, 2005, (b) U.S. Provisional Patent Application 60/784,799 to Halperin filed Mar. 23, 2006, and (c) U.S. Provisional Patent Application 60/843,672 to Halperin, filed Sep. 12, 2006; and 
     (ii) a continuation-in-part of U.S. patent application Ser. No. 13/863,293 to Lange, published as US 2013/0245502, now abandoned, which is a continuation of U.S. patent application Ser. No. 11/552,872 to Pinhas (published as US 2007/0118054), filed Oct. 25, 2006, now abandoned, which claims the benefit of (a) U.S. Provisional Patent Application 60/731,934 to Halperin, filed Nov. 1, 2005, (b) U.S. Provisional Patent Application 60/784,799 to Halperin filed Mar. 23, 2006, and (c) U.S. Provisional Patent Application 60/843,672 to Halperin, filed Sep. 12, 2006. 
     All of the above-mentioned applications are incorporated herein by reference. 
    
    
     FIELD OF EMBODIMENTS OF THE INVENTION 
     Some applications of the present invention relate generally to predicting and monitoring physiological conditions. Specifically, some applications relate to methods and apparatus for monitoring a subject by monitoring the subject&#39;s respiration rate and/or the subject&#39;s heart rate. 
     BACKGROUND 
     Chronic diseases are often expressed by episodic worsening of clinical symptoms. Preventive treatment of chronic diseases reduces the overall dosage of required medication and associated side effects, and lowers mortality and morbidity. Generally, preventive treatment should be initiated or intensified as soon as the earliest clinical symptoms are detected, in order to prevent progression and worsening of the clinical episode and to stop and reverse the pathophysiological process. Therefore, the ability to accurately monitor pre-episodic indicators increases the effectiveness of preventive treatment of chronic diseases. 
     Many chronic diseases cause systemic changes in vital signs, such as breathing and heartbeat patterns, through a variety of physiological mechanisms. For example, common respiratory disorders, such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF), are direct modifiers of breathing and/or heartbeat patterns. Other chronic diseases, such as diabetes, epilepsy, and certain heart conditions (e.g., congestive heart failure (CHF)), are also known to modify cardiac and breathing activity. In the case of certain heart conditions, such modifications typically occur because of pathophysiologies related to fluid retention and general cardiovascular insufficiency. Other signs such as coughing and sleep restlessness are also known to be of importance in some clinical situations. 
     Many chronic diseases induce systemic effects on vital signs. For example, some chronic diseases interfere with normal breathing and cardiac processes during wakefulness and sleep, causing abnormal breathing and heartbeat patterns. 
     Breathing and heartbeat patterns may be modified via various direct and indirect physiological mechanisms, resulting in abnormal patterns related to the cause of modification. Some respiratory diseases, such as asthma, and some heart conditions, such as CHF, are direct breathing modifiers. Other metabolic abnormalities, such as hypoglycemia and other neurological pathologies affecting autonomic nervous system activity, are indirect breathing modifiers. 
     Asthma is a chronic disease with no known cure. Substantial alleviation of asthma symptoms is possible via preventive therapy, such as the use of bronchodilators and anti-inflammatory agents. Asthma management is aimed at improving the quality of life of asthma patients. 
     Monitoring of lung function is viewed as a major factor in determining an appropriate treatment, as well as in patient follow-up. Preferred therapies are often based on aerosol-type medications to minimize systemic side-effects. The efficacy of aerosol type therapy is highly dependent on patient compliance, which is difficult to assess and maintain, further contributing to the importance of lung-function monitoring. 
     Asthma episodes usually develop over a period of several days, although they may sometimes seem to appear unexpectedly. The gradual onset of the asthmatic episode provides an opportunity to start countermeasures to stop and reverse the inflammatory process. Early treatment at the pre-episode stage may reduce the clinical episode manifestation considerably, and may even prevent the transition from the pre-clinical stage to a clinical episode altogether. 
     Two techniques are generally used for asthma monitoring. The first technique, spirometry, evaluates lung function using a spirometer, an instrument that measures the volume of air inhaled and exhaled by the lungs. Airflow dynamics are measured during a forceful, coordinated inhalation and exhalation effort by the patient into a mouthpiece connected via a tube to the spirometer. A peak-flow meter is a simpler device that is similar to the spirometer, and is used in a similar manner. The second technique evaluates lung function by measuring nitric-oxide concentration using a dedicated nitric-oxide monitor. The patient breathes into a mouthpiece connected via a tube to the monitor. 
     Efficient asthma management requires daily monitoring of respiratory function, which is generally impractical, particularly in non-clinical or home environments. Peak-flow meters and nitric-oxide monitors provide a general indication of the status of lung function. However, these monitoring devices do not possess predictive value, and are used as during-episode markers. In addition, peak-flow meters and nitric-oxide monitors require active participation of the patient, which is difficult to obtain from many children and substantially impossible to obtain from infants. 
     CHF is a condition in which the heart is weakened and unable to circulate blood to meet the body&#39;s needs. The subsequent buildup of fluids in the legs, kidneys, and lungs characterizes the condition as congestive. The weakening may be associated with either the left, right, or both sides of the heart, with different etiologies and treatments associated with each type. In most cases, it is the left side of the heart which fails, so that it is unable to efficiently pump blood to the systemic circulation. The ensuing fluid congestion of the lungs results in changes in respiration, including alterations in rate and/or pattern, accompanied by increased difficulty in breathing and tachypnea. 
     Quantification of such abnormal breathing provides a basis for assessing CHF progression. For example, Cheyne-Stokes Respiration (CSR) is a breathing pattern characterized by rhythmic oscillation of tidal volume with regularly recurring periods of alternating apnea and hyperpnea. While CSR may be observed in a number of different pathologies (e.g., encephalitis, cerebral circulatory disturbances, and lesions of the bulbar center of respiration), it has also been recognized as an independent risk factor for worsening heart failure and reduced survival in patients with CHF. In CHF, CSR is associated with frequent awakening that fragments sleep, and with concomitant sympathetic activation, both of which may worsen CHF. Other abnormal breathing patterns may involve periodic breathing, prolonged expiration or inspiration, or gradual changes in respiration rate usually leading to tachypnea. 
     SUMMARY OF EMBODIMENTS 
     For some applications of the present invention, a subject&#39;s respiration rate is monitored for a duration of time of greater than two hours. A parameter of the subject&#39;s respiration rate over the time duration, such as the median respiration rate, the mean respiration rate, the maximum respiration rate, and/or a pattern of the respiration rate is determined. The parameter is compared to the same parameter as determined on a previous day during a time period that overlaps with (e.g., is substantially the same as, or partially overlaps with) the time period based upon which the parameter of respiration was determined on the present day. For example, the parameter is compared to the same parameter as determined on a previous day for the same time duration and at the same period (e.g., the same time) of the day. For example, the mean respiration rate over a time duration of three hours, between the times of 8 pm and 11 pm on the present day, may be compared with the mean respiration rate over a time duration of three hours between the times of 8 pm and 11 pm on the previous day. In response thereto, the likelihood of the subject subsequently undergoing an adverse clinical event is determined. Typically, it is determined that the subject is likely to undergo an adverse clinical event by determining that the difference between the parameter of respiration (e.g., the mean respiration rate) of the present day and of the previous day is greater than a threshold amount, e.g., by determining that the parameter of respiration of the present day and that of the previous day are substantially different. Typically, in response to determining that the subject is likely to undergo an adverse clinical event, an alert is generated. 
     For some applications, the techniques described in the above paragraph with respect to the subject&#39;s respiration rate are applied with respect to the subject&#39;s heart rate and/or with respect to the subject&#39;s respiration rate and the subject&#39;s heart rate. For example, it may be determined that the subject is likely to undergo an adverse clinical event by determining that the difference between a parameter of the subject&#39;s cardiac cycle (e.g., the mean heart rate over a time duration of greater than two hours at a given period of the day) of the present day and of a previous day is greater than a threshold amount, e.g., by determining that the parameter of the cardiac cycle of the present day and that of the previous day are substantially different. Or, it may be determined that the subject is likely to undergo an adverse clinical event by determining that the difference between a parameter of the subject&#39;s cardiac cycle of the present day and of a previous day is greater than a threshold amount, and the difference between a parameter of the subject&#39;s respiration of the present day and of a previous day is greater than a threshold amount. 
     For some applications of the present invention, a subject&#39;s motion is monitored for a duration of time of greater than two hours. A parameter of the subject&#39;s motion, such as total duration that the subject is in motion, or percentage of time that the subject is in motion, over the time duration is determined. The parameter is compared to the same parameter as determined on a previous day during a time period that overlaps with (e.g., is substantially the same as, or partially overlaps with) the time period based upon which the parameter of respiration was determined on the present day. For example, the parameter is compared to the same parameter as determined on a previous day for the same time duration and at the same period (e.g., the same time) of the day. For example, the total time that the subject is in motion, or percentage of time that the subject is in motion over a time duration of three hours, between the times of 8 pm and 11 pm on the present day, may be compared with the total time that the subject is in motion, or percentage of time that the subject is in motion over a time duration of three hours between the times of 8 pm and 11 pm on the previous day. In response thereto, the likelihood of the subject subsequently undergoing an adverse clinical event is determined. Typically, it is determined that the subject is likely to undergo an adverse clinical event by determining that the difference between the parameter of motion of the present day and of the previous day is greater than a threshold amount, e.g., by determining that the parameter of motion of the present day and that of the previous day are substantially different. Typically, in response to determining that the subject is likely to undergo an adverse clinical event, an alert is generated. 
     For some applications, the threshold of the cardiac cycle (described hereinabove) is set responsively to a detected respiration rate, and/or responsively to a detected parameter of the subject&#39;s motion. Alternatively or additionally, the threshold of the parameter of the subject&#39;s respiration (described hereinabove) is set responsively to the detected heart rate, and/or responsively to a detected parameter of the subject&#39;s motion. Further alternatively or additionally, the threshold of the parameter of the subject&#39;s motion (described hereinabove) is set responsively to the detected heart rate, and/or responsively to the detected respiration rate. 
     In some embodiments, the present invention includes systems and methods for monitoring uterine contractions, for example, for predicting the onset of preterm labor. Such systems may include a motion acquisition module, a pattern analysis module, and an output module. Aspects of this invention may be used for monitoring uterine contractions and predicting the onset of preterm labor, for example, without viewing or touching the pregnant woman&#39;s body, for instance, without obtaining compliance from the woman. 
     Another embodiment of the invention is a method for detecting uterine contractions in a pregnant woman, the method comprising sensing motion of the woman, for example, without contacting the woman, and generating a signal corresponding to the sensed motion; and analyzing the signal to detect presence of labor contractions. In one aspect, sensing motion of the women comprises sensing motion in the lower abdomen, the pelvis, and the upper abdomen of the women and generating a motion-related signal for the lower abdomen, the pelvis, and the upper abdomen to detect the presence of labor contractions. 
     Another embodiment of the invention is an apparatus for detecting uterine contractions in a pregnant woman, the apparatus comprising at least one motion sensor adapted to detect motion of the woman, for example, without contacting the woman, and generate at least one signal corresponding to the sensed motion; and a signal analyzer adapted to analyze the at least one signal to detect the presence of labor contractions. 
     There is therefore provided, in accordance with some applications of the present invention, apparatus, including: 
     a mechanical sensor configured to detect a physiological signal of a subject without contacting or viewing the subject or clothes that the subject is wearing; 
     a control unit configured to:
         receive the physiological signal from the sensor over a time duration of at least two hours at a given period of at least one first baseline day,   determine a physiological parameter of the subject based upon the received physiological signal of the first baseline day;   receive the physiological signal from the sensor over a time duration of at least two hours at a given period of a second day, the period over which the subject&#39;s physiological signal is detected on the second day overlapping with the period over which the subject&#39;s physiological signal is detected on the first baseline day;   determine a physiological parameter of the subject based upon the received physiological signal of the second day;   compare the physiological parameter based upon the received physiological signal of the second day to the baseline physiological parameter of the subject; and   generate an alert in response to the comparison; and an output unit configured to output the alert.       

     For some applications, the physiological sensor is configured to detect the physiological signal of the subject by detecting a respiration rate of the subject. 
     For some applications, the physiological sensor is configured to detect the physiological signal of the subject by detecting a heart rate of the subject. 
     For some applications, the physiological sensor is configured to detect the physiological signal of the subject by detecting a parameter of motion of the subject. 
     There is further provided, in accordance with some applications of the present invention, apparatus, including: 
     a sensor configured to detect a respiration signal indicative of a respiration rate of a subject; and 
     a control unit configured to:
         receive the detected respiration signal from the sensor over a time duration of at least two hours at a given period of at least one first respiration-rate baseline day;   determine a baseline parameter of the subject&#39;s respiration based upon the received respiration signal of the first respiration-rate baseline day;   receive the detected respiration signal from the sensor over a time duration of at least two hours at a given period of a second day, the period over which the subject&#39;s respiration is detected on the second day overlapping with the period over which the subject&#39;s respiration is detected on the first respiration-rate baseline day;   determine a parameter of the subject&#39;s respiration based upon the received respiration signal of the second day;   compare the parameter of the subject&#39;s respiration based upon the received respiration signal of the second day to the baseline parameter of the subject&#39;s respiration; and   generate an alert in response to the comparison; and an output unit configured to output the alert.       

     For some applications, the control unit is configured to determine the baseline parameter of respiration by determining a baseline respiration pattern based upon the received respiration signal of the first respiration-rate baseline day, and the control unit is configured to determine the parameter of the subject&#39;s respiration based upon the received respiration signal of the second day by determining a respiration pattern based upon the received respiration signal of the second day. 
     For some applications: 
     the control unit is configured to determine the baseline parameter of respiration by determining a parameter selected from the group consisting of: a mean respiration rate, a maximum respiration rate, and a median respiration rate, based upon the received respiration signal of the first respiration-rate baseline day, and 
     the control unit is configured to determine the parameter of the subject&#39;s respiration based upon the received respiration signal of the second day by determining a parameter selected from the group consisting of: a mean respiration rate, a maximum respiration rate, and a median respiration rate, based upon the received respiration signal of the second day. 
     For some applications, the control unit is configured to: 
     receive a heart-rate signal from the sensor indicative of a heart rate of the subject over a time duration of at least two hours at a given period of at least one first heart-rate baseline day; 
     determine a baseline parameter of the subject&#39;s cardiac cycle based upon the received heart-rate signal of the first heart-rate baseline day; 
     receive a heart-rate signal from the sensor indicative of a heart rate of the subject over a time duration of at least two hours at the given period of the second day, the period over which the subject&#39;s heart rate is detected on the second day overlapping with the period over which the subject&#39;s heart rate is detected on the first heart-rate baseline day; 
     determine a parameter of the subject&#39;s cardiac cycle based upon the received heart-rate signal of the second day; and 
     compare the parameter of the subject&#39;s cardiac cycle based upon the received heart-rate signal of the second day to the baseline parameter of the cardiac cycle, and 
     generate the alert by generating the alert in response to (a) the comparison of the parameter of the subject&#39;s respiration based upon the received respiration signal of the second day to the baseline parameter of the subject&#39;s respiration, and (b) the comparison of the parameter of the subject&#39;s cardiac cycle based upon the received heart-rate signal of the second day to the baseline parameter of the subject&#39;s cardiac cycle. 
     For some applications, the control unit is configured to: 
     receive a motion signal from the sensor indicative of motion of the subject over a time duration of at least two hours at a given period of at least one first motion-parameter baseline day; 
     determine a baseline parameter of the subject&#39;s motion based upon the received motion signal of the first motion-parameter baseline day; 
     receive a motion signal from the sensor indicative of motion of the subject over a time duration of at least two hours at the given period of the second day, the period over which the subject&#39;s motion is detected on the second day overlapping with the period over which the subject&#39;s motion is detected on the first motion-parameter baseline day; 
     determine a parameter of the subject&#39;s motion based upon the received motion signal of the second day; and 
     compare the parameter of the subject&#39;s motion based upon the received motion signal of the second day to the baseline parameter of motion, and 
     generate the alert by generating the alert in response to (a) the comparison of the parameter of the subject&#39;s respiration based upon the received respiration signal of the second day to the baseline parameter of the subject&#39;s respiration, and (b) the comparison of the parameter of the subject&#39;s motion based upon the received motion signal of the second day to the baseline parameter of the subject&#39;s motion. 
     For some applications, the control unit is configured to compare the parameter of the subject&#39;s respiration based upon the received respiration signal of the second day to the baseline parameter of the subject&#39;s respiration by determining whether the parameter of the subject&#39;s respiration based upon the received respiration signal of the second day differs from the baseline parameter of the subject&#39;s respiration by more than a threshold amount. 
     For some applications, the control unit is configured to: 
     receive a heart-rate signal from the sensor indicative of a heart rate of the subject; and 
     set the threshold in response to the detected heart-rate signal. 
     For some applications, the control unit is configured to: 
     receive a motion signal from the sensor indicative of a motion of the subject; and 
     set the threshold in response to the detected motion signal. 
     There is additionally provided, in accordance with some applications of the present invention, apparatus, including: 
     a sensor configured to detect a heart-rate signal indicative of a heart rate of a subject; and 
     a control unit configured to:
         receive the detected heart-rate signal from the sensor over a time duration of at least two hours at a given period of at least one first heart-rate baseline day;   determine a baseline parameter of the subject&#39;s cardiac cycle based upon the received heart-rate signal of the first heart-rate baseline day;   receive the detected heart-rate signal from the sensor over a time duration of at least two hours at a given period of a second day, the period over which the subject&#39;s heart rate is detected on the second day overlapping with the period over which the subject&#39;s heart rate is detected on the first heart-rate baseline day;   determine a parameter of the subject&#39;s cardiac cycle based upon the received heart-rate signal of the second day;   compare the parameter of the subject&#39;s cardiac cycle based upon the received heart-rate signal of the second day to the baseline parameter of the subject&#39;s cardiac cycle; and   generate an alert in response to the comparison; and an output unit configured to output the alert.       

     For some applications, the control unit is configured to: 
     receive a motion signal from the sensor indicative of motion of the subject over a time duration of at least two hours at a given period of at least one first motion-parameter baseline day; 
     determine a baseline parameter of the subject&#39;s motion based upon the received motion signal of the first motion-parameter baseline day; 
     receive a motion signal from the sensor indicative of motion of the subject over a time duration of at least two hours at the given period of the second day, the period over which the subject&#39;s motion is detected on the second day overlapping with the period over which the subject&#39;s motion is detected on the first motion-parameter baseline day; 
     determine a parameter of the subject&#39;s motion based upon the received motion signal of the second day; and 
     compare the parameter of the subject&#39;s motion based upon the received motion signal of the second day to the baseline parameter of motion, and 
     generate the alert by generating the alert in response to (a) the comparison of the parameter of the subject&#39;s cardiac cycle based upon the received heart-rate signal of the second day to the baseline parameter of the subject&#39;s cardiac cycle, and (b) the comparison of the parameter of the subject&#39;s motion based upon the received motion signal of the second day to the baseline parameter of the subject&#39;s motion. 
     For some applications, the control unit is configured to compare the parameter of the subject&#39;s cardiac cycle based upon the received heart-rate signal of the second day to the baseline parameter of the subject&#39;s cardiac cycle by determining whether the parameter of the subject&#39;s cardiac cycle based upon the received heart-rate signal of the second day differs from the baseline parameter of the subject&#39;s cardiac cycle by more than a threshold amount. 
     For some applications, the control unit is configured to: 
     receive a respiration signal from the sensor indicative of a respiration rate of the subject; and 
     set the threshold in response to the detected respiration signal. 
     For some applications, the control unit is configured to: 
     receive a motion signal from the sensor indicative of a motion of the subject; and 
     set the threshold in response to the detected motion signal. 
     There is further provided, in accordance with some applications of the present invention, apparatus, including: 
     a sensor configured to detect a motion signal indicative of motion of a subject; and 
     a control unit configured to:
         receive the detected motion signal from the sensor over a time duration of at least two hours at a given period of at least one first motion-parameter baseline day;   determine a baseline parameter of the subject&#39;s motion based upon the received motion signal of the first motion-parameter baseline day;   receive the detected motion signal from the sensor over a time duration of at least two hours at a given period of a second day, the period over which the subject&#39;s motion is detected on the second day overlapping with the period over which the subject&#39;s motion is detected on the first motion-parameter baseline day;   determine a parameter of the subject&#39;s motion based upon the received motion signal of the second day;   compare the parameter of the subject&#39;s motion based upon the received motion signal of the second day to the baseline parameter of the subject&#39;s motion; and   generate an alert in response to the comparison; and an output unit configured to output the alert.       

     For some applications, the control unit is configured to compare the parameter of the subject&#39;s motion based upon the received motion signal of the second day to the baseline parameter of the subject&#39;s motion by determining whether the parameter of the subject&#39;s motion based upon the received motion signal of the second day differs from the baseline parameter of the subject&#39;s motion by more than a threshold amount. 
     For some applications, the control unit is configured to: 
     receive a respiration signal from the sensor indicative of a respiration rate of the subject; and 
     set the threshold in response to the detected respiration signal. 
     For some applications, the control unit is configured to: 
     receive a heart-rate signal from the sensor indicative of a heart rate of the subject; and 
     set the threshold in response to the detected heart-rate signal. 
     There is additionally provided, in accordance with some applications of the present invention, a method including: 
     detecting a respiration rate of a subject over a time duration of at least two hours at a given period of at least one first respiration-rate baseline day; 
     determining a baseline parameter of the subject&#39;s respiration based upon the detected respiration rate for the first respiration-rate baseline day; 
     detecting a respiration rate of the subject over a time duration of at least two hours at a given period of a second day, the period over which the subject&#39;s respiration is detected on the second day overlapping with the period over which the subject&#39;s respiration is detected on the first respiration-rate baseline day; 
     determining a parameter of the subject&#39;s respiration based upon the detected respiration rate on the second day; 
     comparing the parameter of the subject&#39;s respiration based upon the detected respiration rate on the second day to the baseline parameter of the subject&#39;s respiration; and 
     generating an alert in response to the comparison. 
     There is further provided, in accordance with some applications of the present invention, a method including: 
     detecting a heart rate of a subject over a time duration of at least two hours at a given period of at least one first heart-rate baseline day; 
     determining a baseline parameter of the subject&#39;s cardiac cycle based upon the detected heart rate for the first heart-rate baseline day; 
     detecting a heart rate of the subject over a time duration of at least two hours at a given period of a second day, the period over which the subject&#39;s heart rate is detected on the second day overlapping with the period over which the subject&#39;s heart rate is detected on the first heart-rate baseline day; 
     determining a parameter of the subject&#39;s cardiac cycle based upon the detected heart rate on the second day; 
     comparing the parameter of the subject&#39;s cardiac cycle based upon the detected heart rate on the second day to the baseline parameter of the subject&#39;s cardiac cycle; and 
     generating an alert in response to the comparison. 
     There is additionally provided, in accordance with some applications of the present invention, a method including: 
     detecting motion of a subject over a time duration of at least two hours at a given period of at least one first motion-parameter baseline day; 
     determining a motion parameter of the subject&#39;s respiration based upon the detected motion for the first motion-parameter baseline day; 
     detecting motion of the subject over a time duration of at least two hours at a given period of a second day, the period over which the subject&#39;s motion is detected on the second day overlapping with the period over which the subject&#39;s motion is detected on the first motion-parameter baseline day; 
     determining a parameter of the subject&#39;s motion based upon the motion detected on the second day; 
     comparing the parameter of the subject&#39;s motion based upon the motion detected on the second day to the baseline parameter of the subject&#39;s motion; and 
     generating an alert in response to the comparison. 
     There is further provided, in accordance with some applications of the present invention, a method including: 
     detecting a physiological signal of a subject over a time duration of at least two hours at a given period of at least one first baseline day, without contacting or viewing the subject or clothes that the subject is wearing; 
     determining a physiological parameter of the subject based upon the detected physiological signal for the first baseline day; 
     detecting the physiological signal of the subject over a time duration of at least two hours at a given period of a second day, the period over which the subject&#39;s physiological signal is detected on the second day overlapping with the period over which the physiological signal is detected on the first baseline day; 
     determining a physiological parameter of the subject based upon the detected physiological signal on the second day; 
     comparing the physiological parameter based upon the detected physiological signal on the second day to the baseline physiological parameter of the subject; and 
     generating an alert in response to the comparison. 
     The present invention will be more fully understood from the following detailed description of embodiments thereof, taken together with the drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a system for monitoring a chronic medical condition of a subject, in accordance with some applications of the present invention; 
         FIG. 2  is a schematic block diagram illustrating components of a control unit of the system of  FIG. 1 , in accordance with some applications of the present invention; 
         FIGS. 3A-D  are graphs showing the results of experiments conducted, in accordance with some applications of the present invention; 
         FIG. 4  is a graph illustrating breathing rate patterns of a chronic asthma patient, which is the same as FIG. 4 of U.S. Pat. No. 7,077,810 to Lange, which is incorporated herein by reference; 
         FIGS. 5 and 6  are graphs of exemplary baseline and measured breathing rate and heart rate nighttime patterns, respectively, which are generally similar to  FIGS. 6 and 7  of U.S. Pat. No. 7,314,451 to Halperin, which is incorporated herein by reference; and 
         FIG. 7  is a graph of baseline and breathing rate nighttime patterns, respectively, which is the same as FIG. 23 of U.S. Pat. No. 7,314,451 to Halperin. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference is made to  FIG. 1 , which is a schematic illustration of a system  10  for monitoring a chronic medical condition of a subject  12 , in accordance with some applications of the present invention. System  10  typically comprises a mechanical sensor  30  (e.g., a motion sensor), a control unit  14 , and a user interface  24 . For some applications, user interface  24  is integrated into control unit  14 , as shown in the figure, while for other applications, the user interface and control unit are separate units. For some applications, motion sensor  30  is integrated into control unit  14 , in which case user interface  24  is either also integrated into control unit  14  or remote from control unit  14 . 
       FIG. 2  is a schematic block diagram illustrating components of control unit  14 , in accordance with some applications of the present invention. Control unit  14  typically comprises a motion data acquisition module  20  and a pattern analysis module  16 . Pattern analysis module  16  typically comprises one or more of the following modules: a breathing pattern analysis module  22 , a heartbeat pattern analysis module  23 , a cough analysis module  26 , a restlessness analysis module  28 , a blood pressure analysis module  29 , and an arousal analysis module  31 . For some applications, two or more of analysis modules  20 ,  22 ,  23 ,  26 ,  28 ,  29 , and  31  are packaged in a single housing. For other applications, the modules are packaged separately (for example, so as to enable remote analysis by one or more of the pattern analysis modules of breathing signals acquired locally by data acquisition module  20 ). For some applications, user interface  24  comprises a dedicated display unit such as an LCD or CRT monitor. Alternatively or additionally, user interface  24  includes a communication line for relaying the raw and/or processed data to a remote site for further analysis and/or interpretation. 
     For some applications of the present invention, data acquisition module  20  is adapted to non-invasively monitor breathing and heartbeat patterns of subject  12 . Breathing pattern analysis module  22  and heartbeat pattern analysis module  23  are adapted to analyze the respective patterns in order to (a) predict an approaching clinical event, such as an asthma attack or heart condition-related lung fluid buildup, and/or (b) monitor the severity and progression of a clinical event as it occurs. For some applications, breathing pattern analysis module  22  and heartbeat pattern analysis module  23  are adapted to analyze the respective patterns in order to determine a likelihood of an approaching adverse clinical event without necessarily identifying the nature of the event. User interface  24  is adapted to notify subject  12  and/or a healthcare worker of the predicted or occurring event. Prediction of an approaching clinical event facilitates early preventive treatment, which generally reduces the required dosage of medication, and/or lowers mortality and morbidity. When treating asthma, such a reduced dosage generally minimizes the side-effects associated with high dosages typically required to reverse the inflammatory condition once the event has begun. 
     For some applications of the present invention, pattern analysis module  16  combines parameter data generated from two or more of analysis modules  20 ,  22 ,  23 ,  26 ,  28 ,  29 , and analyzes the combined data in order to predict and/or monitor a clinical event. For some applications, pattern analysis module  16  derives a score for each parameter based on the parameter&#39;s deviation from baseline values (either for the specific patient or based on population averages). Pattern analysis module  16  combines the scores, such as by taking an average, maximum, standard deviation, or other function of the scores. The combined score is compared to one or more threshold values (which may be predetermined) to determine whether an event is predicted, currently occurring, or neither predicted nor occurring, and/or to monitor the severity and progression of an occurring event. For some applications, pattern analysis module  16  learns the criteria and/or functions for combining the individual parameter scores for the specific patient or patient group based on personal history. For example, pattern analysis module  16  may perform such learning by analyzing parameters measured prior to previous clinical events. 
     Although system  10  may monitor breathing and heartbeat patterns at any time, for some conditions it is generally most effective to monitor such patterns during sleep at night. When the subject is awake, physical and mental activities unrelated to the monitored condition often affect breathing and heartbeat patterns. Such unrelated activities generally have less influence during most night sleep. For some applications, system  10  monitors and records patterns throughout all or a large portion of a night. The resulting data set generally encompasses typical long-term respiratory and heartbeat patterns, and facilitates comprehensive analysis. Additionally, such a large data set enables rejection of segments contaminated with movement or other artifacts, while retaining sufficient data for a statistically significant analysis. 
     Reference is again made to  FIG. 2 . Data acquisition module  20  typically comprises circuitry for processing the raw motion signal generated by motion sensor  30 , such as at least one pre-amplifier  32 , at least one filter  34 , and an analog-to-digital (A/D) converter  36 . Filter  34  typically comprises a band-pass filter or a low-pass filter, serving as an anti-aliasing filter with a cut-off frequency of less than one half of the sampling rate. The low-passed data is typically digitized at a sampling rate of at least 10 Hz and stored in memory. For example, the anti-aliasing filter cut-off may be set to 5 Hz and the sampling rate set to 40 Hz. 
     Reference is again made to  FIG. 1 . Typically, motion sensor  30  detects one or more physiological signal of the subject without contacting or viewing the subject or clothes that the subject is wearing. For some applications of the present invention, motion sensor  30  comprises a pressure gauge (e.g., a piezoelectric sensor) or a strain gauge (e.g., a silicon or other semiconductor strain gauge, or a metallic strain gauge), which is typically adapted to be installed in, on, or under a reclining surface  37  upon which the subject lies, e.g., sleeps, and to sense breathing- and heartbeat-related motion of the subject. “Pressure gauge,” as used in the claims, includes, but is not limited to, all of the gauges mentioned in the previous sentence. Typically, reclining surface  37  comprises a mattress, a mattress covering, a sheet, a mattress pad, and/or a mattress cover. For some applications, motion sensor  30  is integrated into reclining surface  37 , e.g., into a mattress, and the motion sensor and reclining surface are provided together as an integrated unit. For some applications, motion sensor  30  is adapted to be installed in, on, or under reclining surface  37  in a vicinity of an abdomen  38  or chest  39  of subject  12 . Alternatively or additionally, motion sensor  30  is installed in, on, or under reclining surface  37  in a vicinity of a portion of subject  12  anatomically below a waist of the subject, such as in a vicinity of legs  40  of the subject. For some applications, such positioning provides a clearer pulse signal than positioning the sensor in a vicinity of abdomen  38  or chest  39  of the subject. For some applications, motion sensor  30  comprises a fiber optic sensor, for example, as described by Butter and Hocker in Applied Optics 17: 2867-2869 (Sep. 15, 1978). 
     For some applications, the pressure or strain gauge is encapsulated in a rigid compartment, which typically has a surface area of at least 10 cm^2, and a thickness of less than 5 mm. The gauge output is channeled to an electronic amplifier, such as a charge amplifier typically used with piezoelectric accelerometers and capacitive transducers to condition the extremely high output impedance of the transducer to a low impedance voltage suitable for transmission over long cables. The strain gauge and electronic amplifier translate the mechanical vibrations into electrical signals. Alternatively, the strain gauge output is amplified using a Wheatstone bridge and an amplifier such as Analog Device Module Numbers 3B16, for a minimal bandwidth, or 3B18, for a wider bandwidth (National Instruments Corporation, Austin, Tex., USA). 
     For some applications of the present invention, motion sensor  30  comprises a grid of multiple pressure or strain gauge sensors, adapted to be installed in, on, or under reclining surface  37 . The use of such a grid, rather than a single gauge, may improve breathing and heartbeat signal reception. 
     Breathing pattern analysis module  22  is adapted to extract breathing patterns from the motion data, and heartbeat pattern analysis module  23  is adapted to extract heartbeat patterns from the motion data. Alternatively or additionally, system  10  comprises another type of sensor, such as an acoustic or air-flow sensor, attached or directed at the subject&#39;s face, neck, chest and/or back. 
     For some applications of the present invention, the subject&#39;s respiration rate is monitored for a duration of time of greater than two hours (e.g., greater than three hours, greater than four hours, greater than five hours, or greater than six hours). Breathing pattern analysis module  22  determines a parameter of the subject&#39;s respiration rate over the time duration, such as the median respiration rate, the mean respiration rate, the maximum respiration rate, and/or a respiration rate pattern. Module  22  compares the determined parameter to the same parameter as determined on a previous day during a time period that overlaps with the time period based upon which the parameter of respiration was determined on the present day. For example, the parameter is compared to the same parameter as determined on a previous day for the same time duration and at the same period (e.g., the same time) of the day. 
     For example, the mean respiration rate over a time duration of three hours, between the times of 8 pm and 11 pm on the present day, may be compared with the mean respiration rate over a time duration of three hours between the times of 8 pm and 11 pm on the previous day. In response thereto, the likelihood of the subject subsequently undergoing an adverse clinical event is determined. Typically, it is determined that the subject is likely to undergo an adverse clinical event by determining that the difference between the parameter of respiration (e.g., the mean respiration rate) of the present day and of the previous day is greater than a threshold amount. Typically, in response to determining that the subject is likely to undergo an adverse clinical event, an alert is generated by user interface  24 . 
     For some applications, the period of to the day which is compared to the same period of the previous day is a time period, e.g., between 8 pm and 11 pm, as described hereinabove. Alternatively, the period may be defined with respect to the subject&#39;s circadian clock, e.g., the period may be the first three hours of the subject&#39;s sleep, or from the beginning of the second hour of the subject&#39;s sleep to the end of the fifth hour of the subject&#39;s sleep. 
     For some applications, heartbeat pattern analysis module  23  applies generally similar analysis to the subject&#39;s heart rate to that described hereinabove with respect to the breathing pattern analysis module  22 . For example, module  23  may determine that the subject is likely to undergo an adverse clinical event by determining that the difference between a parameter of the subject&#39;s cardiac cycle (e.g., the mean heart rate over a time duration of greater than two hours at a given period of the day) on the present day and that of a previous day is greater than a threshold amount. For some applications, control unit  14  determines that the subject is likely to undergo an adverse clinical event by determining that the difference between a parameter of the subject&#39;s cardiac cycle on the present day and that of a previous day is greater than a threshold amount, and the difference between a parameter of the subject&#39;s respiration on the present day and that of the previous day is greater than a threshold amount. 
     As described hereinabove, for some applications, breathing pattern analysis module  22  and heartbeat pattern analysis module  23  are adapted to analyze the respective patterns in order to determine a likelihood of an approaching adverse clinical event without necessarily identifying the nature of the event. Thus, for some applications, in response to determining that the subject is likely to undergo an adverse clinical event, the user interface generates a generic alert signal, in order to indicate to a healthcare professional that an adverse clinical event is imminent. 
     For some applications, system  10  applies generally similar analysis to a different physiological parameter of the subject to that described hereinabove with respect to the breathing pattern analysis module  22 . For example, the system may apply the analysis to a parameter of the subject&#39;s motion, such as the total time that the subject is in motion, or percentage of time that the subject is in motion over a given time duration. 
     Reference is now made to  FIGS. 3A-D , which are graphs showing the results of experiments conducted, in accordance with some applications of the present invention. Earlysense Ltd. (Israel) manufactures the EverOn™ system, which is a contact-less piezoelectric sensor placed under a subject&#39;s mattress that provides continuous measurement of heart rate and respiration rate of the subject, generally in accordance with the techniques described hereinabove. 
     A non-interventional study was conducted in two internal medicine departments (Sheba Medical Center and Meir Medical Center, both in Israel). Patients who were admitted due to an acute respiratory condition were enrolled on the study. Patients were monitored by the EverOn™ sensor and followed for major clinical episodes. A major clinical event was defined as death, transfer to ICU, or intubation and mechanical ventilation on the floors. Out of 149 patients included in the study, 96 patients had a length of stay that allowed at least one comparable time window. Ten major clinical events were recorded for these patients. Retrospective analysis of continuous respiratory and heart signal recording was performed. The median respiration rate and heart rate over 6-hour time durations (00-06, 06-12, 12-18, and 18-24) were compared to the median respiration rate and heart rate over a corresponding 6-hour time duration on the previous day. Similarly, the maximum respiration rate and heart rate over 6-hour time durations (00-06, 06-12, 12-18, and 18-24) were compared to the maximum respiration rate and heart rate over a corresponding 6-hour time duration on the previous day. Retrospective receiver operating characteristic (ROC) curve analysis was applied to the results to determine the sensitivity, specificity, positive predictive value, and negative predictive value of using respective thresholds (i.e., thresholds for the difference between median or maximum respiration rate or heart rate and those of the previous day) for determining the likelihood of a subject undergoing (a) any adverse clinical event, i.e., either a major or a moderate clinical event (such as a non-major respiratory event requiring immediate intervention, e.g., bilevel positive airway pressure (BIPAP) or continuous positive airway pressure (CPAP)), or (b) a major clinical event. 
     Table 1 (shown below) shows the results of the ROC curve analysis of respective combinations of median heart rate and respiration rate thresholds (i.e., thresholds for the difference between median heart rate and respiration rate and those of the previous day) with respect to determining the likelihood of a subject undergoing any adverse clinical event, i.e., either a major or a moderate clinical event. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Threshold Heart 
                   
                   
                   
                   
               
               
                 rate (beats per 
                   
                   
                   
                   
               
               
                 minute)- 
                   
                   
                   
                   
               
               
                 Respiration rate 
                   
                   
                   
                   
               
               
                 (breaths per 
                   
                   
                   
                   
               
               
                 minute) ) 
                 Sensitivity 
                 Specificity 
                 PPV 
                 NPV 
               
               
                   
               
             
             
               
                 14-3 
                 67 
                 82 
                 35 
                 95 
               
               
                 14-4 
                 67 
                 82 
                 35 
                 95 
               
               
                 14-5 
                 67 
                 86 
                 40 
                 95 
               
               
                 14-6 
                 58 
                 89 
                 44 
                 94 
               
               
                 16-3 
                 67 
                 87 
                 42 
                 95 
               
               
                 16-4 
                 67 
                 87 
                 42 
                 95 
               
               
                 16-5 
                 67 
                 89 
                 47 
                 95 
               
               
                 16-6 
                 58 
                 93 
                 54 
                 94 
               
               
                 18-3 
                 67 
                 89 
                 47 
                 95 
               
               
                 18-4 
                 67 
                 89 
                 47 
                 95 
               
               
                 18-5 
                 67 
                 90 
                 50 
                 95 
               
               
                 18-6 
                 58 
                 94 
                 58 
                 94 
               
               
                 20-3 
                 67 
                 94 
                 62 
                 95 
               
               
                 20-4 
                 67 
                 94 
                 62 
                 95 
               
               
                 20-5 
                 67 
                 95 
                 67 
                 95 
               
               
                 20-6 
                 58 
                 98 
                 78 
                 94 
               
               
                 22-3 
                 67 
                 94 
                 62 
                 95 
               
               
                 22-4 
                 67 
                 94 
                 62 
                 95 
               
               
                 22-5 
                 67 
                 95 
                 67 
                 95 
               
               
                 22-6 
                 58 
                 98 
                 78 
                 94 
               
               
                   
               
             
          
         
       
     
     Table 2 (shown below) shows the results of the ROC curve analysis of respective combinations of median heart rate and respiration rate (i.e., thresholds for the difference between median heart rate and respiration rate and those of the previous day) thresholds with respect to determining the likelihood of a subject undergoing a major clinical event. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Threshold (Heart 
                   
                   
                   
                   
               
               
                 rate (beats per 
                   
                   
                   
                   
               
               
                 minute)- 
                   
                   
                   
                   
               
               
                 Respiration rate 
                   
                   
                   
                   
               
               
                 (breaths per 
                   
                   
                   
                   
               
               
                 minute) ) 
                 Sensitivity 
                 Specificity 
                 PPV 
                 NPV 
               
               
                   
               
             
             
               
                  -3 
                 80 
                 83 
                 35 
                 97 
               
               
                 14-4 
                 80 
                 83 
                 35 
                 97 
               
               
                 14-5 
                 80 
                 86 
                 40 
                 97 
               
               
                 14-6 
                 70 
                 90 
                 44 
                 96 
               
               
                 16-3 
                 80 
                 87 
                 42 
                 97 
               
               
                 16-4 
                 80 
                 87 
                 42 
                 97 
               
               
                 16-5 
                 80 
                 90 
                 47 
                 97 
               
               
                 16-6 
                 70 
                 93 
                 54 
                 96 
               
               
                 18-3 
                 80 
                 90 
                 47 
                 97 
               
               
                 18-4 
                 80 
                 90 
                 47 
                 97 
               
               
                 18-5 
                 80 
                 91 
                 50 
                 98 
               
               
                 18-6 
                 70 
                 94 
                 58 
                 96 
               
               
                 20-3 
                 80 
                 94 
                 62 
                 98 
               
               
                 20-4 
                 80 
                 94 
                 62 
                 98 
               
               
                 20-5 
                 80 
                 95 
                 67 
                 98 
               
               
                 20-6 
                 70 
                 98 
                 78 
                 97 
               
               
                 22-3 
                 80 
                 94 
                 62 
                 98 
               
               
                 22-4 
                 80 
                 94 
                 62 
                 98 
               
               
                 22-5 
                 80 
                 95 
                 67 
                 98 
               
               
                 22-6 
                 70 
                 98 
                 78 
                 97 
               
               
                   
               
             
          
         
       
     
     It is noted with respect to Tables 1 and 2 that the greatest sum of sensitivity and specificity is for thresholds of 20 or 22 for median heart rate in combination with a threshold of 5 for median respiration rate, both for predicting all adverse clinical events (i.e., major and minor adverse clinical events), and for predicting major clinical events. 
     Thus, for some applications of the present invention, a subject&#39;s heart rate and respiration rate are monitored. The median (or mean, or maximum) heart rate and respiration rate over a time duration of more than two hours and less than eight hours (e.g., greater than three hours, greater than four hours, greater than five hours, or greater than six hours) is determined and is compared to the median (or mean, or maximum) heart rate and respiration rate over a similar time duration at a similar period of the day (e.g., at the same time of day) on at least one previous day (e.g., the previous day). In response to determining (a) that the median (or mean, or maximum) heart rate on the present day differs from that of the previous day by a threshold amount of more than 15 beats per minute, e.g., more than 18 beats per minute, and (b) that the median (or mean, or maximum) respiration rate of the present day differs from that of the previous day by a threshold amount of more than 3 breaths per minute, e.g., more than 4 breaths per minute, then an alert is generated in order to indicate that an adverse clinical event is likely to occur. 
     Table 3 (shown below) shows the results of the ROC curve analysis of respective maximum heart rate thresholds (i.e., thresholds for the difference between the maximum heart rate and that of the previous day) with respect to determining the likelihood of a subject undergoing a major or a moderate clinical event. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Heart rate 
                   
                   
                   
               
               
                   
                 threshold 
                   
                   
                 Sum of 
               
               
                   
                 (beats per 
                   
                   
                 Sensitivity and 
               
               
                   
                 minute) 
                 Sensitivity 
                 Specificity 
                 Specificity 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0.00 
                 1.00 
                 0.00 
                 1.00 
               
               
                   
                 0.25 
                 1.00 
                 0.01 
                 1.01 
               
               
                   
                 1.00 
                 1.00 
                 0.02 
                 1.02 
               
               
                   
                 3.00 
                 0.92 
                 0.07 
                 0.99 
               
               
                   
                 4.00 
                 0.83 
                 0.11 
                 0.94 
               
               
                   
                 4.50 
                 0.83 
                 0.17 
                 1.00 
               
               
                   
                 5.00 
                 0.83 
                 0.19 
                 1.02 
               
               
                   
                 6.00 
                 0.75 
                 0.25 
                 1.00 
               
               
                   
                 7.00 
                 0.75 
                 0.32 
                 1.07 
               
               
                   
                 8.00 
                 0.75 
                 0.38 
                 1.13 
               
               
                   
                 8.50 
                 0.67 
                 0.46 
                 1.13 
               
               
                   
                 9.00 
                 0.67 
                 0.48 
                 1.14 
               
               
                   
                 10.00 
                 0.67 
                 0.54 
                 1.20 
               
               
                   
                 11.00 
                 0.67 
                 0.62 
                 1.29 
               
               
                   
                 11.50 
                 0.67 
                 0.70 
                 1.37 
               
               
                   
                 12.00 
                 0.67 
                 0.71 
                 1.38 
               
               
                   
                 13.00 
                 0.67 
                 0.75 
                 1.42 
               
               
                   
                 13.50 
                 0.67 
                 0.79 
                 1.45 
               
               
                   
                 14.00 
                 0.67 
                 0.80 
                 1.46 
               
               
                   
                 15.00 
                 0.67 
                 0.82 
                 1.49 
               
               
                   
                 16.00 
                 0.67 
                 0.85 
                 1.51 
               
               
                   
                 17.00 
                 0.67 
                 0.86 
                 1.52 
               
               
                   
                 18.00 
                 0.67 
                 0.87 
                 1.54 
               
               
                   
                 19.00 
                 0.67 
                 0.89 
                 1.56 
               
               
                   
                 20.00 
                 0.67 
                 0.90 
                 1.57 
               
               
                   
                 21.00 
                 0.67 
                 0.92 
                 1.58 
               
               
                   
                 22.00 
                 0.67 
                 0.93 
                 1.60 
               
               
                   
                 22.75 
                 0.58 
                 0.93 
                 1.51 
               
               
                   
                 25.00 
                 0.58 
                 0.94 
                 1.52 
               
               
                   
                 27.00 
                 0.50 
                 0.95 
                 1.45 
               
               
                   
                 28.00 
                 0.42 
                 0.95 
                 1.37 
               
               
                   
                 29.00 
                 0.33 
                 0.95 
                 1.29 
               
               
                   
                 30.75 
                 0.17 
                 0.95 
                 1.12 
               
               
                   
                 32.00 
                 0.08 
                 0.95 
                 1.04 
               
               
                   
                 33.00 
                 0.08 
                 0.96 
                 1.05 
               
               
                   
                 34.00 
                 0.08 
                 0.98 
                 1.06 
               
               
                   
                 53.00 
                 0.00 
                 0.98 
                 0.98 
               
               
                   
                 56.00 
                 0.00 
                 0.99 
                 0.99 
               
               
                   
               
             
          
         
       
     
     It is noted with respect to Table 3 that the greatest sum of sensitivity and specificity is for a heart rate threshold of 22 beats per minute, for predicting major and moderate adverse clinical events.  FIG. 3A  shows the ROC curve for a heart rate threshold of 22 with respect to predicting a likelihood of either a major or a moderate adverse clinical event. The area under the curve is 0.70 with a standard deviation of 0.11 and a p-value of 0.026. 
     Table 4 (shown below) shows the results of the ROC curve analysis of respective maximum heart rate thresholds (i.e., thresholds for the difference between the maximum heart rate and that of the previous day) with respect to determining the likelihood of a subject undergoing a major clinical event. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                 Heart rate 
                   
                   
                   
               
               
                   
                 threshold 
                   
                   
                 Sum of 
               
               
                   
                 (beats per 
                   
                   
                 Sensitivity and 
               
               
                   
                 minute) 
                 Sensitivity 
                 Specificity 
                 Specificity 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0.00 
                 1.00 
                 0.00 
                 1.00 
               
               
                   
                 0.25 
                 1.00 
                 0.01 
                 1.01 
               
               
                   
                 1.00 
                 1.00 
                 0.02 
                 1.02 
               
               
                   
                 3.00 
                 1.00 
                 0.08 
                 1.08 
               
               
                   
                 4.00 
                 0.90 
                 0.12 
                 1.02 
               
               
                   
                 4.50 
                 0.90 
                 0.17 
                 1.07 
               
               
                   
                 5.00 
                 0.90 
                 0.20 
                 1.10 
               
               
                   
                 6.00 
                 0.80 
                 0.26 
                 1.06 
               
               
                   
                 7.00 
                 0.80 
                 0.33 
                 1.13 
               
               
                   
                 8.00 
                 0.80 
                 0.38 
                 1.18 
               
               
                   
                 8.50 
                 0.80 
                 0.48 
                 1.28 
               
               
                   
                 9.00 
                 0.80 
                 0.49 
                 1.29 
               
               
                   
                 10.00 
                 0.80 
                 0.55 
                 1.35 
               
               
                   
                 11.00 
                 0.80 
                 0.63 
                 1.43 
               
               
                   
                 11.50 
                 0.80 
                 0.71 
                 1.51 
               
               
                   
                 12.00 
                 0.80 
                 0.72 
                 1.52 
               
               
                   
                 13.00 
                 0.80 
                 0.76 
                 1.56 
               
               
                   
                 13.50 
                 0.80 
                 0.79 
                 1.59 
               
               
                   
                 14.00 
                 0.80 
                 0.80 
                 1.60 
               
               
                   
                 15.00 
                 0.80 
                 0.83 
                 1.63 
               
               
                   
                 16.00 
                 0.80 
                 0.85 
                 1.65 
               
               
                   
                 17.00 
                 0.80 
                 0.86 
                 1.66 
               
               
                   
                 18.00 
                 0.80 
                 0.87 
                 1.67 
               
               
                   
                 19.00 
                 0.80 
                 0.90 
                 1.70 
               
               
                   
                 20.00 
                 0.80 
                 0.91 
                 1.71 
               
               
                   
                 21.00 
                 0.80 
                 0.92 
                 1.72 
               
               
                   
                 22.00 
                 0.80 
                 0.93 
                 1.73 
               
               
                   
                 22.75 
                 0.70 
                 0.93 
                 1.63 
               
               
                   
                 25.00 
                 0.70 
                 0.94 
                 1.64 
               
               
                   
                 27.00 
                 0.60 
                 0.95 
                 1.55 
               
               
                   
                 28.00 
                 0.50 
                 0.95 
                 1.45 
               
               
                   
                 29.00 
                 0.40 
                 0.95 
                 1.35 
               
               
                   
                 30.75 
                 0.20 
                 0.95 
                 1.15 
               
               
                   
                 32.00 
                 0.10 
                 0.95 
                 1.05 
               
               
                   
                 33.00 
                 0.10 
                 0.97 
                 1.07 
               
               
                   
                 34.00 
                 0.10 
                 0.98 
                 1.08 
               
               
                   
                 53.00 
                 0.00 
                 0.98 
                 0.98 
               
               
                   
                 56.00 
                 0.00 
                 0.99 
                 0.99 
               
               
                   
               
             
          
         
       
     
     It is noted with respect to Table 4 that the greatest sum of sensitivity and specificity is for a heart rate threshold of 22 beats per minute for predicting major adverse clinical events.  FIG. 3B  shows the ROC curve for a heart rate threshold of 22 with respect to predicting a likelihood of a major adverse clinical event. The area under the curve is 0.79 with a standard deviation of 0.11 and a p-value of 0.0024. 
     In general, in accordance with the indications provided by the data in Tables 3 and 4 and in  FIGS. 3A and 3B , a subject&#39;s heart rate is monitored. The median (or mean, or maximum) heart rate over a time duration of more than two hours and less than eight hours (e.g., greater than three hours, greater than four hours, greater than five hours, or greater than six hours) is determined and is compared to the median (or mean, or maximum) heart rate over a similar time duration at a similar period of the day (e.g., at the same time of day) on at least one previous day (e.g., the previous day). In response to determining (a) that the median (or mean, or maximum) heart rate of the present day differs from that of the previous day by a threshold amount of more than 15 beats per minute (e.g., more than 18 beats per minute, e.g., more than 20 beats per minute), and/or less than 30 beats per minute, then an alert is generated in order to indicate that an adverse clinical event is likely to occur. 
     Table 5 (shown below) shows the results of the ROC curve analysis of respective maximum respiration rate thresholds (i.e., thresholds for the difference between the maximum respiration rate and that of the previous day), with respect to determining the likelihood of a subject undergoing a major or a moderate clinical event. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Respiration 
                   
                   
                   
               
               
                   
                 rate threshold 
                   
                   
                 Sum of 
               
               
                   
                 (breaths per 
                   
                   
                 Sensitivity and 
               
               
                   
                 minute) 
                 Sensitivity 
                 Specificity 
                 Specificity 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0.00 
                 1.00 
                 0.00 
                 1.00 
               
               
                   
                 0.50 
                 1.00 
                 0.05 
                 1.05 
               
               
                   
                 1.00 
                 1.00 
                 0.06 
                 1.06 
               
               
                   
                 1.50 
                 1.00 
                 0.24 
                 1.24 
               
               
                   
                 2.00 
                 1.00 
                 0.26 
                 1.26 
               
               
                   
                 3.00 
                 1.00 
                 0.43 
                 1.43 
               
               
                   
                 3.50 
                 1.00 
                 0.58 
                 1.58 
               
               
                   
                 4.00 
                 1.00 
                 0.59 
                 1.59 
               
               
                   
                 5.00 
                 1.00 
                 0.70 
                 1.70 
               
               
                   
                 6.00 
                 0.69 
                 0.76 
                 1.46 
               
               
                   
                 6.50 
                 0.54 
                 0.83 
                 1.37 
               
               
                   
                 6.75 
                 0.54 
                 0.85 
                 1.39 
               
               
                   
                 7.00 
                 0.46 
                 0.85 
                 1.31 
               
               
                   
                 7.50 
                 0.38 
                 0.89 
                 1.28 
               
               
                   
                 8.00 
                 0.31 
                 0.89 
                 1.20 
               
               
                   
                 9.00 
                 0.23 
                 0.92 
                 1.15 
               
               
                   
                 10.00 
                 0.23 
                 0.92 
                 1.16 
               
               
                   
                 12.00 
                 0.23 
                 0.93 
                 1.16 
               
               
                   
                 16.00 
                 0.23 
                 0.97 
                 1.20 
               
               
                   
                 18.00 
                 0.15 
                 0.97 
                 1.13 
               
               
                   
                 19.00 
                 0.08 
                 0.98 
                 1.06 
               
               
                   
                 24.00 
                 0.00 
                 0.98 
                 0.98 
               
               
                   
                 35.00 
                 0.00 
                 0.99 
                 0.99 
               
               
                   
               
             
          
         
       
     
     It is noted with respect to Table 5 that the greatest sum of sensitivity and specificity is for a respiration rate threshold of 5 breaths per minute, for predicting major and moderate adverse clinical events.  FIG. 3C  shows the ROC curve for a respiration rate threshold of 5 with respect to predicting a likelihood of either a major or a moderate adverse clinical event. The area under the curve is 0.84 with a standard deviation of 0.04, and a p-value of 0.000049. 
     Table 6 (shown below) shows the results of the ROC curve analysis of respective respiration rate thresholds (i.e., thresholds for the difference between the maximum respiration rate and that of the previous day), with respect to determining the likelihood of a subject undergoing a major clinical event. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                   
                 Respiration 
                   
                   
                   
               
               
                   
                 rate threshold 
                   
                   
                 Sum of 
               
               
                   
                 (breaths per 
                   
                   
                 Sensitivity and 
               
               
                   
                 minute) 
                 Sensitivity 
                 Specificity 
                 Specificity 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0.00 
                 1.00 
                 0.00 
                 1.00 
               
               
                   
                 0.50 
                 1.00 
                 0.05 
                 1.05 
               
               
                   
                 1.00 
                 1.00 
                 0.06 
                 1.06 
               
               
                   
                 1.50 
                 1.00 
                 0.23 
                 1.23 
               
               
                   
                 2.00 
                 1.00 
                 0.26 
                 1.26 
               
               
                   
                 3.00 
                 1.00 
                 0.42 
                 1.42 
               
               
                   
                 3.50 
                 1.00 
                 0.57 
                 1.57 
               
               
                   
                 4.00 
                 1.00 
                 0.58 
                 1.58 
               
               
                   
                 5.00 
                 1.00 
                 0.69 
                 1.69 
               
               
                   
                 6.00 
                 0.73 
                 0.76 
                 1.49 
               
               
                   
                 6.50 
                 0.55 
                 0.83 
                 1.37 
               
               
                   
                 6.75 
                 0.55 
                 0.84 
                 1.39 
               
               
                   
                 7.00 
                 0.55 
                 0.85 
                 1.40 
               
               
                   
                 7.50 
                 0.45 
                 0.89 
                 1.35 
               
               
                   
                 8.00 
                 0.36 
                 0.89 
                 1.26 
               
               
                   
                 9.00 
                 0.27 
                 0.92 
                 1.19 
               
               
                   
                 10.00 
                 0.27 
                 0.93 
                 1.20 
               
               
                   
                 12.00 
                 0.27 
                 0.93 
                 1.21 
               
               
                   
                 16.00 
                 0.27 
                 0.97 
                 1.24 
               
               
                   
                 18.00 
                 0.18 
                 0.98 
                 1.16 
               
               
                   
                 19.00 
                 0.09 
                 0.98 
                 1.07 
               
               
                   
                 24.00 
                 0.00 
                 0.98 
                 0.98 
               
               
                   
                 35.00 
                 0.00 
                 0.99 
                 0.99 
               
               
                   
               
             
          
         
       
     
     It is noted with respect to Table 6 that the greatest sum of sensitivity and specificity is for a respiration rate threshold of 5 breaths per minute for predicting major adverse clinical events.  FIG. 3D  shows the ROC curve for a respiration rate threshold of 5 with respect to predicting a likelihood of a major adverse clinical event. The area under the curve is 0.85 with a standard deviation of 0.04, and a p-value of 0.00012. 
     In general, in accordance with the indications provided by the data in Tables 5 and 6 and in  FIGS. 3C and 3D , a subject&#39;s respiration rate is monitored. The median (or mean, or maximum) respiration rate over a time duration of more than two hours and less than eight hours (e.g., greater than three hours, greater than four hours, greater than five hours, or greater than six hours) is determined and is compared to the median (or mean, or maximum) respiration rate over a similar time duration at a similar period of the day (e.g., at the same time of day) on at least one previous day (e.g., the previous day). In response to determining (a) that the median (or mean, or maximum) respiration rate of the present day differs from that of the previous day by a threshold amount of more than 3 breaths per minute (e.g., more than 4 breaths per minute), and/or less than 10 breaths per minute (e.g., less than eight, or less than six breaths per minute), then an alert is generated in order to indicate that an adverse clinical event is likely to occur. 
     For some applications, the techniques described herein are used in combination with the techniques described in one or more of the following references, both of which are incorporated herein by reference: 
     U.S. Pat. No. 7,077,810 to Lange; and/or 
     U.S. Pat. No. 7,314,451 to Halperin. 
     For example, for some applications, as is generally described in U.S. Pat. No. 7,077,810 to Lange, pattern analysis module  22  is configured to predict the onset of an asthma attack or a different clinical event, and/or monitor its severity and progression. Module  22  typically analyzes changes in breathing rate and in breathing rate variability patterns in combination to predict the onset of an asthma attack. Although breathing rate typically slightly increases prior to the onset of an attack, this increase alone is not always a specific marker of the onset of an attack. Therefore, in order to more accurately predict the onset of an attack, and monitor the severity and progression of an attack, module  22  typically additionally analyzes changes in breathing rate variability patterns. For some applications, module  22  compares one or more of the following patterns to respective baseline patterns, and interprets a deviation from baseline as indicative of (a) the onset of an attack, and/or (b) the severity of an attack in progress:
         a slow trend breathing rate pattern. Module  22  interprets as indicative of an approaching or progressing attack an increase vs. baseline, for example, for generally healthy subjects, an attenuation of the typical segmented, monotonic decline of breathing rate typically over at least 1 hour, e.g., over at least 2, 3, or 4 hours, or the transformation of this decline into an increasing breathing rate pattern, depending on the severity of the attack;   a breathing rate variability pattern. Module  22  interprets as indicative of an approaching or progressing attack a decrease in breathing rate variability. Such a decrease generally occurs as the onset of an episode approaches, and intensifies with the progression of shortness of breath during an attack;   a breathing duty-cycle pattern. Module  22  interprets a substantial increase in the breathing duty-cycle as indicative of an approaching or progressing attack. Breathing duty-cycle patterns include, but are not limited to, inspirium time/total breath cycle time, expirium time/total breath cycle time, and (inspirium+expirium time) /total breath cycle time; and   interruptions in breathing pattern such as caused by coughs, sleep disturbances, or waking. Module  22  quantifies these events, and determines their relevance to prediction of potential asthma attacks.       

     Reference is made to  FIG. 4 , which is a graph illustrating breathing rate patterns of a chronic asthma patient, and which is the same as FIG. 4 of U.S. Pat. No. 7,077,810 to Lange. Breathing of the asthma patient was monitored during sleep on several nights. The patient&#39;s breathing rate was averaged for each hour of sleep (excluding periods of rapid eye movement (REM) sleep). During the first approximately two months that the patient was monitored, the patient did not experience any episodes of asthma. A line  100  is representative of a typical slow trend breathing pattern recorded during this non-episodic period, and thus represents a baseline slow trend breathing rate pattern for this patient. It should be noted that, unlike the monotonic decline in breathing rate typically observed in non-asthmatic patients, the baseline breathing rate pattern of the chronically asthmatic patient of the experiment reflects an initial decline in breathing rate during the first few hours of sleep, followed by a gradual increase in breathing rate throughout most of the rest of the night. 
     Lines  102  and  104  were recorded on two successive nights at the conclusion of the approximately two-month period, line  102  on the first of these two nights, and line  104  on the second of these two nights. The patient experienced an episode of asthma during the second of these nights. Lines  102  and  104  thus represent a pre-episodic slow trend breathing rate pattern and an episodic slow trend breathing rate pattern, respectively. As can be seen in the graph, the patient&#39;s breathing rate was substantially elevated vs. baseline during all hours of the pre-episodic night, and even further elevated vs. baseline during the episodic night. 
     Using techniques described herein, the pattern of line  102  is compared with the baseline pattern of line  100 , in order to predict that the patient may experience an asthmatic episode. The pattern of line  104  is compared with the baseline pattern of line  100  in order to assess a progression of the asthmatic episode. 
     In accordance with the data shown in  FIG. 4 , for some applications, a subject&#39;s respiration is detected on first and second days over similar time durations and at similar time periods (e.g., during the first two, three four, five, or six hours of the subject&#39;s sleep). A parameter of the subject&#39;s respiration based upon the detected respiration rate on the second day is compared with that of the first day. An alert is generated in response to the comparison indicating that an adverse clinical event is approaching, e.g., in response to determining that the difference between the median, the mean, and/or the maximum respiration rate on the second day and that of the first day exceeds a threshold. 
     For some applications, techniques as described in U.S. Pat. No. 7,314,451 to Halperin are used in conjunction with the techniques described herein. For example, for some applications, system  10  monitors and records patterns throughout all or a large portion of a night. The resulting data set generally encompasses typical long-term respiratory and heartbeat patterns, and facilitates comprehensive analysis. Additionally, such a large data set enables rejection of segments contaminated with movement or other artifacts, while retaining sufficient data for a statistically significant analysis. 
     Although breathing rate typically slightly increases prior to the onset of an asthma attack (or a different adverse clinical event), this increase alone is not always a specific marker of the onset of an attack. Therefore, in order to more accurately predict the onset of an attack, and monitor the severity and progression of an attack, in an embodiment of the present invention, breathing pattern analysis module additionally analyzes changes in breathing rate variability patterns. For some applications, module  22  compares one or more of the following patterns to respective baseline patterns, and interprets a deviation from baseline as indicative of (a) the onset of an attack, and/or (b) the severity of an attack in progress:
         a slow trend breathing rate pattern. Module  22  interprets as indicative of an approaching or progressing attack an increase vs. baseline, for example, for generally healthy subjects, an attenuation of the typical segmented, monotonic decline of breathing rate typically over at least 1 hour, e.g., over at least 2, 3, or 4 hours, or the transformation of this decline into an increasing breathing rate pattern, depending on the severity of the attack;   a breathing rate pattern. Module  22  interprets as indicative of an approaching or progressing attack an increase or lack of decrease in breathing rate during the first several hours of sleep, e.g., during the first 2, 3, or 4 hours of sleep.   a breathing rate variability pattern. Module  22  interprets a decrease in breathing rate variability as indicative of an approaching or progressing attack. Such a decrease generally occurs as the onset of an episode approaches, and intensifies with the progression of shortness of breath during an attack;   a breathing duty-cycle pattern. Module  22  interprets a substantial increase in the breathing duty-cycle as indicative of an approaching or progressing attack. Breathing duty-cycle patterns include, but are not limited to, inspirium time/total breath cycle time, expirium time/total breath cycle time, and (inspirium+expirium time)/total breath cycle time;   a change in breathing rate pattern towards the end of night sleep (typically between about 3:00 A.M. and about 6:00 A.M.); and   interruptions in breathing pattern such as caused by coughs, sleep disturbances, or waking. Module  22  quantifies these events, and determines their relevance to prediction of potential asthma attacks.       

     Pattern analysis modules  22  and  23  typically determine baseline patterns by analyzing breathing and/or heart rate patterns, respectively, of the subject during non-symptomatic nights. Alternatively or additionally, modules  22  and  23  are programmed with baseline patterns based on population averages. For some applications, such population averages are segmented by characteristic traits such as age, height, weight, and gender. 
     Reference is again made to  FIG. 4 , which is a graph illustrating breathing rate patterns of a chronic asthma patient, measured during an experiment conducted in accordance with an embodiment of the present invention. Using techniques described herein, breathing pattern analysis module  22  compares the pattern of line  102  with the baseline pattern of line  100 , in order to predict that the patient may experience an asthmatic episode. Module  22  compares the pattern of line  104  with the baseline pattern of line  100  in order to assess a progression of the asthmatic episode. 
     For some applications of the present invention, the deviation from baseline is defined as the cumulative deviation of the measured pattern from the baseline pattern. A threshold indicative of a clinical condition is set equal to a certain number of standard errors (e.g., one standard error). Alternatively or additionally, other measures of deviation between measured and baseline patterns are used, such as correlation coefficient, mean square error, maximal difference between the patterns, and the area between the patterns. Further alternatively or additionally, pattern analysis module  16  uses a weighted analysis emphasizing specific regions along the patterns, for example, by giving increased weight (e.g., double weight) to an initial portion of sleep (e.g., the first two hours of sleep) or to specific hours, for example as morning approaches (e.g., the hours of 3:00-6:00 a.m.). 
     Reference is now made to  FIGS. 5 and 6 , which are graphs of exemplary baseline and measured breathing rate and heart rate nighttime patterns, respectively, and which are generally similar to FIGS. 6 and 7 of U.S. Pat. No. 7,314,451 to Halperin, which is incorporated herein by reference. Lines  200  and  202  ( FIGS. 5 and 6 , respectively) represent normal baseline patterns in the absence of an asthma attack. The bars represent one standard error. Lines  204  and  206  ( FIGS. 5 and 6 , respectively) represent patterns during nights prior to an onset of an asthma attack. Detection of the change in pattern between lines  200  and  202  and lines  204  and  206 , respectively, enables the early prediction of the approaching asthma attack, or other approaching adverse clinical events. 
     For some applications of the present invention, pattern analysis module  16  is configured to predict the onset of a clinical manifestation of heart failure, and/or monitor its severity and progression. Module  16  typically determines that an episode is imminent when the module detects increased breathing rate accompanied by increased heart rate, and/or when the monitored breathing and/or heartbeat patterns have specific characteristics that relate to heart failure, such as characteristics that are indicative of apnea, Cheyne-Stokes Respiration (CSR), and/or periodic breathing. 
     In accordance with the data shown in  FIG. 5 , for some applications, a subject&#39;s respiration is detected on first and second days over similar time durations and at similar time periods (e.g., during the first two, three four, five, or six hours of the subject&#39;s sleep). A parameter of the subject&#39;s respiration based upon the detected respiration rate on the second day is compared with that of the first day. An alert is generated in response to the comparison indicating that an adverse clinical event is approaching, e.g., in response to determining that the difference between the median, the mean, and/or the maximum respiration rate on the second day and that of the first day exceeds a threshold. 
     In accordance with the data shown in  FIG. 6 , for some applications, a subject&#39;s heart rate is detected on first and second days over similar time durations and at similar time periods (e.g., during the first two, three, four, five, or six hours of the subject&#39;s sleep). A parameter of the subject&#39;s cardiac cycle based upon the detected heart rate on the second day is compared with that of the first day. An alert is generated in response to the comparison indicating that an adverse clinical event is approaching, e.g., in response to determining that the difference between the median, the mean, and/or the maximum heart rate on the second day and that of the first day exceeds a threshold. 
     In accordance with the data shown in  FIGS. 5 and 6 , for some applications, a subject&#39;s respiration rate and heart rate are detected on first and second days over similar time durations and at similar time periods (e.g., during the first two, three four, five, or six hours of the subject&#39;s sleep). A parameter of the subject&#39;s respiration based upon the detected respiration rate on the second day is compared with that of the first day, and a parameter of the subject&#39;s cardiac cycle based upon the detected heart rate on the second day is compared with that of the first day. An alert is generated in response to the comparisons indicating that an adverse clinical event is approaching, e.g., in response to determining that (a) the difference between the median, the mean, and/or the maximum respiration rate on the second day and that of the first day exceeds a threshold, and/or (b) the difference between the median, the mean, and/or the maximum heart rate on the second day and that of the first day exceeds a threshold. 
     Reference is now made to  FIG. 7 , which is the same as FIG. 23 of U.S. Pat. No. 7,314,451 to Halperin, which is incorporated herein by reference.  FIG. 7  is a graph of baseline and breathing rate nighttime patterns, respectively, measured in accordance with some applications of the present invention. A line  400  represents a normal baseline pattern in the absence of Cheyne-Stokes Respiration, and a line  402  represents a pattern during a night during CSR. The bars represent one standard error. In accordance with the data shown in  FIG. 7 , for some applications, a subject&#39;s respiration is detected on first and second days over similar time durations and at similar time periods (e.g., during the first two, three four, five, or six hours of the subject&#39;s sleep). A parameter of the subject&#39;s respiration based upon the detected respiration rate on the second day is compared with that of the first day. An alert is generated in response to the comparison indicating that an adverse clinical event is approaching, e.g., in response to determining that the difference between the median, the mean, and/or the maximum respiration rate on the second day and that of the first day exceeds a threshold. 
     For some applications, techniques described herein are used in conjunction with techniques as are generally described in US 2007/0118054 to Pinhas, which is incorporated herein by reference. For example, as is described with reference to FIG. 18 of US 2007/0118054 to Pinhas, for some applications, system  10  is adapted to monitor multiple clinical parameters such as respiration rate, heart rate, cough occurrence, body movement, deep inspirations, expiration/inspiration ratio, of subject  12 . Pattern analysis module  16  is adapted to analyze the respective patterns in order to identify a change in the baseline pattern of the clinical parameters. In some cases, this change, a new baseline that is significantly different from the previous baseline indicates, for example, a change in medication and provides the caregiver or healthcare professional with feedback on the efficacy of treatment. 
     For some applications, system  10  calculates the average respiration rate and heart rate for predefined time segments. Such time segments can be minutes, hours, or days. By analyzing the history of the patient the system can calculate the correlation of respiration rate and heart rate patterns. When an onset of an asthma attack approaches the correlation of heart rate and respiration rate pattern shows a clear change. For each night the respiration rate and heart rate in sleep during the hours of 11:00 pm to 6:00 am (or over a different time period) is averaged. For each date, a respiration vector of length N with the average respiration rate of the last N nights and a heart rate vector of length N with the average heart rate for the last N nights is defined. N is typically between 3 and 30, for example 10. The correlation coefficient of the heart rate vector and the respiration vector is calculated for each date by system  10 . A moving window of several days is used to calculate correlation coefficient changes between the respiration and heart rate vectors. A steady correlation coefficient pattern over at least several days is required to identify a significant change of correlation coefficient from one time interval to another. A significant change is defined as a change in the correlation coefficient level of a magnitude larger than the typical correlation coefficient variation in the previous time interval, e.g., a change larger than 3 standard deviations of the correlation coefficient signal in the previous time interval. System  10  identifies such a significant change as an indication of an approaching clinical event. 
     As described in US 2007/0118054 to Pinhas, for some applications, during sleep, sleep stage is identified using techniques described therein. For each identified sleep stage, the average respiration rate, heart rate and other clinical parameters are calculated. This data is compared to baseline defined for that subject for each identified sleep stage, in order to identify the onset or progress of a clinical episode. 
     For some applications, for each night, for each hour (or for longer durations of time, such as more than two hours, as described hereinabove) of sleep, counted from the onset of sleep, the average respiration rate, heart rate and other clinical parameters are calculated. This data is compared to baseline in order to identify the onset or progress of a clinical episode. 
     For some applications, for each night, for each hour (or for longer durations of time, such as more than two hours, as described hereinabove), the average respiration rate, heart rate and other clinical parameters are calculated. This data is compared to baseline in order to identify the onset or progress of a clinical episode. For example, the average respiration rate in sleep during 2:00 AM-3:00 AM is calculated and compared to baseline for that subject in order to identify the onset or progress of a clinical episode. 
     In one embodiment, pattern analysis module  16  is adapted to identify preterm labor in a pregnant woman. Preterm labor is the leading cause of perinatal morbidity and mortality in the United States. Early diagnosis of preterm labor enables effective tocolytic therapy to prevent full labor. In one embodiment, system  10  is adapted to identify the mechanical signal of contractions. In one embodiment, motion sensor  30  is adapted to include multiple sensors located in the vicinity of the legs, pelvis, lower abdomen, and upper abdomen. Pattern analysis module  16  identifies a mechanical signal that is strongest in the area of the lower abdomen and pelvis and weaker in the upper abdomen as a signal indicative of contractions. In one embodiment, system  16  is adapted to differentiate between Braxton Hicks contractions and normal contractions in order to minimize false alarms of preterm labor. In one embodiment, differentiation between regular contractions and Braxton Hicks contractions is done by comparing the frequency and strength of the contractions. In one embodiment, the strength of the contraction mechanical signal is normalized by the strength of the rhythmic heart and respiration signals. In one embodiment, the system logs the contractions and alerts the subject or a clinician upon having the number or hourly rate of contractions exceed a predefined threshold. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.