Patent Publication Number: US-9833154-B2

Title: Suprasystolic measurement in a fast blood-pressure cycle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of and claims priority to U.S. Non-Provisional application Ser. No. 12/650,984, now U.S. Pat. No. 8,840,561, filed on Dec. 31, 2009, and titled “Suprasystolic Measurement in a Fast Blood-Pressure Cycle”, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This application is directed to systems and methods for monitoring a patient, and in particular, to a suprasystolic measurement in a fast blood-pressure cycle. 
     BACKGROUND 
     Traditional non-invasive blood pressure monitoring devices operate by inflating a cuff to a pressure well above a patient&#39;s systolic blood pressure. Because the systolic pressure is usually not know prior to inflation, the cuff must be inflated to such a high pressure to ensure that the patient&#39;s arterial blood flow is completely occluded. Once well above systole, the cuff is deflated and the systolic and diastolic pressures are calculated based on signals provided during cuff deflation. 
     Some methods have been developed to estimate blood pressures during cuff inflation. These methods, however, are generally inaccurate and/or slow. Consequently, such methods cannot provide a commercially useful determination of systolic pressure that must meet certain regulatory standards. 
     More recently, a suprasystolic measurement technique has been developed, as described by U.S. Pat. No. 6,994,675. This technique includes inflating a cuff to a “suprasystolic pressure,” about 10-40 mmHg above a patient&#39;s systolic pressure. Suprasystolic pressure can be maintained while signals from the occluded artery are collected. These signals are processed to determine a number of hemodynamic parameters, such as, for example, aortic compliance. 
     Current suprasystolic methods require determining a patient&#39;s systolic blood pressure prior to inflating the cuff because the suprasystolic pressure is directly proportional to the systolic pressure. As described above, current methods for accurately determining systolic pressure rely on inflating and then deflating a cuff. Thereafter, the cuff is re-inflated to a suprasystolic pressure (i.e., about 10-40 mmHg above systole). Such repeated inflation and deflation of the cuff takes additional time and exposes the patient to the additional discomfort. 
     The present disclosure is directed to systems and methods for providing a suprasystolic measurement in less time and with less patient discomfort than prior techniques. In one exemplary embodiment, a patient&#39;s systolic pressure can be determined during cuff inflation. Following inflation, the cuff can be maintained at a suprasystolic pressure determined by the systolic pressure. During this suprasystolic phase, signals from the patient can be measured and analyzed to determine one or more hemodynamic parameters. Thus, data obtained during an inflationary, or dynamic phase, of a pressure cycle may be used in real time to determine if and how a suprasystolic measurement should be conducted. Combining a systolic pressure determination and suprasystolic measurement into a single pressure cycle can reduce cycle time and minimize patient discomfort. 
     SUMMARY 
     A first aspect of the present disclosure includes a system for monitoring a patient having a cuff configured to inflate to at least partially occlude an artery of the patient and a cuff controller configured to inflate the cuff and generally maintain inflation of the cuff at about a target pressure. The system also includes a sensor configured to receive a signal associated with the at least partially occluded artery and generate an output signal based on the received signal, and a cuff control module configured to determine the target pressure during the dynamic phase and based on the output signal, and control the cuff controller during the dynamic phase and the static phase. 
     A second aspect of the present disclosure includes a method of determining a hemodynamic parameter of a patient that includes providing a cuff configured to at least partially occlude a vessel of the patient. The method includes inflating the cuff to a target pressure during a dynamic phase, wherein the target pressure can be determined during the dynamic phase, maintaining the inflatable cuff at about the target pressure during a static phase, and determining the hemodynamic parameter during the static phase. 
     A third aspect of the present disclosure includes a processor configured to transmit a first signal to inflate a cuff to at least partially occlude an artery of a patient and receive a signal from the cuff representative of vibrations from the at least partially occluded artery. The processor can further determine a target pressure during cuff inflation based on the received signal, and transmit a second signal to generally maintain cuff inflation at about the target pressure. 
     Additional objects and advantages of the present disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present disclosure. The objects and advantages of the present disclosure will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure, as claimed. 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the present disclosure and together with the description, serve to explain the principles of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a monitoring system, according to an exemplary embodiment. 
         FIG. 2  illustrates a pressure pulse applied by the monitoring system, according to an exemplary embodiment. 
         FIG. 3  illustrates a first flow chart, according to an exemplary embodiment. 
         FIG. 4  illustrates a second flow chart, according to another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein are patient monitoring systems and methods of using such systems. In particular, the present disclosure provides a suprasystolic measurement in a fast blood-pressure cycle. Both blood-pressure determination and suprasystolic measurement are generally completed in less time than a typical blood pressure assessment alone, such as, for example, about 25 seconds. The time is reduced in part because cuff re-inflation can be avoided. 
     The present disclosure also permits the use of real time data collected during inflation in a subsequent suprasystolic measurement. For example, an accurate suprasystolic pressure can be based on a systolic pressure determined during inflation. Further, if a suprasystolic measurement should occur, the duration of a suprasystolic measurement, or what sort of signal analysis should be performed during suprasystolic measurement can be determined during inflation. 
     In some embodiments, the combined blood-pressure determination and suprasystolic measurement can provide dynamic information to a decision tree or algorithm to determine a particular hemodynamic parameter. For example, a suprasystolic measurement might be conducted on patients having certain physiological indicators, such as, weight, heart rate, or blood pressure. A patient&#39;s physiological indicators may be determined during inflation. If one or more of these indicators fails to meet certain criteria, the suprasystolic measurement could be cancelled and the patient notified. Thus, various indicators could be tested during inflation to ensure suitable suprasystolic measurement. 
     In yet other embodiments, the present system can permit rapid analysis of hemodynamic data gathered from unloaded, partially loaded, or fully loaded vessels. Before inflation, the patient&#39;s vessels are unloaded and blood flow is not restricted. During inflation, termed a “dynamic phase,” the patient&#39;s vessels are progressively loaded, reducing blood flow. At suprasystolic pressure, the patient&#39;s vessels are completely loaded or occluded, termed a “static phase.” Data gathered during these different conditions may be compared and contrasted to determine one or more hemodynamic parameters. For example, a beat-to-beat time during the dynamic phase, when the vessel is partially occluded, may be compared with a beat-to-beat time during the static phase, when the vessel is completely occluded. Such data comparison can provide an indication of irregular heart beat timing. Two or more separate conditions could also be used to attenuate signal noise using various de-noising algorithms. 
       FIG. 1  illustrates a system  10 , according to an exemplary embodiment of the present disclosure. System  10  can be configured to monitor a patient, and in some embodiments, to determine a hemodynamic parameter of the patient. 
     System  10  can include a cuff  12  configured to at least to partially occlude the movement of blood through a vessel of patient  14 . In some embodiments, cuff  12  can be configured to completely completely occlude an artery of patient  14 . Although shown in  FIG. 1  surrounding the upper arm of patient  14 , cuff  12  may be adapted for placement on any suitable part of patient  14 , including, for example, a wrist, a finger, an upper thigh, or an ankle. In addition, one or more cuffs  12  could be placed at different locations about patient  14  for use with system  10 . 
     Cuff  12  can include an inflatable device, wherein the pressure or volume within cuff  12  may be controlled by a cuff controller  16  operably associated with cuff  12 . Cuff controller  16  can include a pump or similar device to inflate cuff  12 . For example, cuff controller  16  could supply cuff  12  with a fluid to increase the pressure or volume of cuff  12 . In other embodiments, cuff controller  16  could include mechanical, electrical, or chemical devices configured to control vessel occlusion of patient  14  via cuff  12 . 
     In some embodiments, cuff controller  16  can generally maintain cuff  12  at about a target pressure. For example, once a target pressure has been determined, as explained in detail below, cuff controller  16  could control cuff  12  to provide patient  14  with a generally constant pressure. While the present disclosure refers to a target pressure, it should be understood that the actual pressure applied by cuff  12  may vary. As such, the pressure applied to patient  14  may generally remain within appropriate limits, such as, for example, with 2%, 5%, 10%, or 20% of the target pressure. 
     System  10  can further include a sensor  18  configured to receive a signal associated with patient  14 . In some embodiments, sensor  18  can be configured to receive a signal associated with an at least partially occluded vessel of patient  14 . Such an input signal can arise from blood movement through a partially occluded vessel or from a signal associated with an occluded blood vessel. Sensor  18  could sample multiple times at various intervals. In yet other embodiments, sensor  18  could provide an indication of blood vessel movement, such as, for example, oscillations arising from vascular expansion or contraction. For example, sensor  18  could be configured to detect a pressure or volume of cuff  12  that may vary periodically with the cyclic expansion and contraction of an artery of patient  14 . In particular, sensor  18  could determine a blood pressure or other hemodynamic parameter associated with patient  14 —using an oscillometric method. 
     In some embodiments, sensor  18  could detect a volume or a pressure associated with cuff  12 . For example, sensor  18  could include a pressure sensor and may be located within or about cuff  12 . System  10  could further operate with a plurality of sensors  18 , and may include a high-resolution sensor or pneumatic sensor designed to operate in conjunction with cuff  12 . 
     Sensor  18  can further be configured to generate an output signal. The output signal may be generated based on an input signal received from patient  14 . In one aspect, the output signal can include a representation of an input signal associated with cuff  12  and/or patient  14 . 
     Cuff  12 , cuff controller  16 , and sensor  18  may be operably associated with a cuff control module  20 . Specifically, cuff control module  20  could include one or more processors configured to control one or more operations of cuff  12 , cuff controller  16 , or sensor  18 . For example, cuff control module  20  can control inflation of cuff  12  via control of cuff controller  16 . 
     In some embodiments, cuff control module  20  can calculate a target pressure. This calculation may be based on an output signal from sensor  18 , as described above. Cuff control module  20  may also control inflation of cuff  12 , inflation of cuff  12  to the target pressure, or generally maintaining inflation of cuff  12  at about the target pressure. 
     In operation, cuff control module  20  could calculate a target pressure during inflation of cuff  12 . Such a calculation could take less than about 15 seconds. Cuff control module  20  could then generally maintain cuff  12  at about the target pressure for a defined time period, such as, for example, less than about 10 seconds. In other embodiments, the target pressure could be generally maintained for a defined number of cardiac cycles, such as, for example, six, eight, or ten cycles. Unlike current suprasystolic techniques, such cardiac cycle data may be available upon reaching the target pressure. This availability can reduce the need to ignore or discount one or more of the first several cardiac cycles from any suprasystolic measurement. Cuff compression using current techniques can cause conscious or unconscious muscle movement, affecting signals obtained during the first few beats at a suprasystolic pressure. Such data may be unsuitable for parameter determination, thereby prolonging the static phase. A more gradual compression of a patient&#39;s limb or arteries up to a suprasystolic pressure can reduce or eliminate the effects of these unwanted movements. 
     As shown in  FIG. 1 , system  10  can optionally include a signal analysis module  22 , a communication module  24 , or an accelerometer  26 . These components may operate with one or more of the components of system  10  as described above. 
     Signal analysis module  22  may be configured to analyze one or more signals using one or more processors. Such analysis may be based on the output signal of sensor  18 . For example, signal analysis module  22  can include one or more filters configured to filter a signal associated with sensor  18  or cuff control module  20 . Such filters can include band-pass, high-pass, or low-pass filters. 
     In some embodiments, signal analysis module  22  may determine a hemodynamic parameter. A hemodynamic parameter can include an indication of cardiac or vascular health, such as, for example, an indication of cardiac, circulatory, or vascular functionality. Specifically, a hemodynamic parameter can include a heart rate, a blood pressure, a vessel compliance, an aortic index, an augmentation index, reflected wave ratio, or an indication of treatment. Blood pressure can include systolic, diastolic, or mean atrial pressure. An indication of treatment can include a parameter reflecting the affect of a drug treatment, or one or more treatments of a disease state. 
     In some embodiments, a hemodynamic parameter can be determined based on a suprasystolic measurement. In other embodiments, a hemodynamic parameter can be determined based on a first set of data obtained during inflation of cuff  12  and a second set of data obtained during general maintenance of cuff  12  at about the target pressure, as explained below in detail. The first or second sets of data can include various data associated with a signal waveform associated with patient  14  and/or cuff  12 , and may include amplitude, frequency, morphology, feature, or mathematically derived data. Data can be derived from a derivative, integration, or frequency analysis, such as, for example, a fast-Fourier transform. Data may also be derived from various algorithms, including curve fitting, neural network, filtering, smoothing, or data processing. 
     System  10  can further include an accelerometer  26  to detect movement. Accelerometer  26  can be configured to detect movement in one, two, or three dimensions. For example, accelerometer  26  could be used to detect movement of patient  14  or movement of the arm of patient  14 . 
     A signal arising from accelerometer  26  could be used to provide additional information to another module. For example, if movement of patient  14  is sufficient to interfere with sensor  18 , a signal from accelerometer  26  may be transmitted to cuff control module  20  to halt the pressure cycle. In-addition, a signal from accelerometer  26  may be transmitted to signal analysis module  22  to cancel or reset a calculation. Data obtained from sensor  18  could be combined with data from accelerometer  26  to determine if an irregular signal may be caused by a motion artifact. Various data from accelerometer  26  may be processed to provide additional data to determine one or more hemodynamic parameters. 
     System  10  can further include a communication module  24  configured to provide communication to patient  14  or one or more operators. For example, communication module  24  could include a display configured to display one or more hemodynamic parameters. In other embodiments, communication module could include a transmitter configured to transmit data to a remote location. Communication module  24  may further include audio output to communicate with patient  14  and/or an operator of system  10 . 
     In addition to the components outlined above, system  10  may include various other components as required, such as, for example, a memory, a power source, and a user input. One or more components described herein may be combined or may be separate and operate with wireless or wired communication links. Moreover, the various components of system  10  could be integrated into a single processing unit or may operate as separate processors. In operation, one or more processors can be configured to operate in conjunction with one or more software programs to provide the functionality of system  10 . 
       FIG. 2  shows a cuff pressure waveform  28  as applied to a patient over a period of time, according to an exemplary embodiment. For example, waveform  28  may be applied to patient  14  using system  10  as indicated in  FIG. 1 . In some embodiments, waveform  28  can include a dynamic phase  30  and a static phase  32 . 
     Dynamic phase  30  can include a generally increasing pressure. For example, as indicated in  FIG. 2 , dynamic phase  30  can include a continuously increasing linear pressure curve. In other embodiments, dynamic phase  30  can include a step wise pressure increase, a curved pressure increase, an exponential pressure increase, a gradual, or a rapid pressure increase. 
     During dynamic phase  30 , one or more sets of data may be obtained using one or more sensors. Such data may be analyzed, as described in detail below, to determine a target pressure  34 . Target pressure  34  can be greater than systolic pressure or about equal to systolic pressure. In some embodiments, target pressure  34  can be about equal to a suprasystolic pressure. 
     Static phase  32  can include generally maintaining a cuff pressure at about target pressure  34 . In operation, a target pressure can be determined during dynamic phase  30  and applied during static phase  32 . Target pressure  34  can include a generally constant pressure. In some embodiments, target pressure  34  can fluctuate within a range of values. For example, target pressure  34  can include values within about ±2%, ±5%, ±10%, or ±20%. 
     In order to reduce patient discomfort, the duration of dynamic phase  30  and static phase  32  should be less than about 60 seconds. In some embodiments, the duration of phases  30 ,  32  can be less than about 45 seconds. In some embodiments, the duration of phases—; ˜3.0,  32  can be less than about 30 seconds. In particular, the duration of dynamic phase  30  can be less than about 15 seconds and the duration of static phase  32  can be less than about 10 seconds. Although  FIG. 2  shows dynamic phase  20  and static phase  32  juxtaposed, in some embodiments these phases may be separated by one or more other phase of differing cuff pressure and/or duration. 
       FIGS. 3 and 4  illustrate flow charts of two exemplary embodiments according to the present disclosure. As described above with regard to  FIG. 1 , various modules can include one or more hardware components and one or more software components that operate to control an operation of system  10 . Each step described below can be understood as corresponding to one or more computational instructions. These computational instructions can operate based on hardware and/or software components of system  10 , and may operate on one or more processors. 
       FIG. 3  includes a process  100  according to an exemplary embodiment of the present disclosure. Step  110 , labeled “Start,” may include one of more steps required to initiate an operation of system  10 . For example, system  10  may be turned on, a calibration protocol may be started, a cuff may be placed about a patient&#39;s arm, an operator may enter information to identify a patient, or information could be extracted from a database. Further, various components of system  10  may be calibrated or tested to ensure proper functioning. These operations could include a check of cuff integrity, if sufficient power is available, a calibration of one or more sensors, or confirmation of proper processor functioning. Also, other information may be entered into system  10 , such as a patient identification, weight, gender, height, or other suitable data. 
     After system  10  has completed start  110 , cuff  12  may be inflated (Step  112 ). This step may be considered the start of dynamic phase  30 . In some embodiments, Step  112  could be initiated as part of Step  110 . 
     As described above with regard to  FIG. 1 , cuff controller  16  may operate to inflate cuff  12 . During inflation, sensor  18  may detect one or more signals. These signals may be analyzed by cuff control module  20  to determine if sufficient information has been obtained (Step  114 ). Sufficient information can refer to providing one or more algorithms with information sufficient to determine when cuff inflation should be terminated. For example, an algorithm could determine a target pressure for cuff inflation. In other embodiments, an algorithm could determine a time to stop cuff inflation. 
     In one embodiment, an algorithm may use oscillometric pulse data obtained during dynamic phase  30 . The data may be analyzed in real time until such a point that an algorithm deems the data sufficient for a reading determination. Such data can relate to the maturity of the pulse envelope or the amount of envelope found during inflation. The collected pulse data can be filtered and/or conditioned. In other embodiments, a model curve can be fit to the data. In yet other embodiments, data can be submitted to a trained network of mathematical routines. Such analysis can be used to determine a systolic pressure or a diastolic pressure. 
     For example, the SureBP algorithm could be used to determine a systolic pressure. Such an algorithm is described in “Clinical evaluation of the Welch Allyn SureBP algorithm for automated blood pressure measurement,” by Bruce Alpert, which is hereby incorporated by reference in its entirety. Such an algorithm can provide an accurate measure of systolic pressure during inflation, whereby the mean error is less than about 1 mmHg and the standard deviation of the mean error is less than about ±7 mmHg. In other embodiments, such an algorithm could provide a mean error of less than about 5 mmHg and a standard deviation of less than about ±5 mmHg. 
     If an algorithm determines that sufficient information has not yet been obtained, cuff inflation (Step  112 ) can continue until sufficient information has been obtained. One or more safety algorithms could also be used to limit cuff inflation to a maximum pressure. For example, process  100  may terminate if cuff pressure reaches about 200 mmHg. 
     After sufficient information has been obtained for an algorithm to determine a suitable stopping point for cuff inflation, a target pressure may be determined (Step  116 ). In some embodiments, the target pressure may include determining a systolic pressure. A suprasystolic pressure may then be determined based on the systolic pressure. For example, a suprasystolic pressure may be determined by adding about 10-40 mmHg to the value of the systolic pressure. The value of the target pressure may be determined based on the suprasystolic pressure. In some embodiments, the target pressure may be set to the same value as the suprasystolic pressure. 
     Once a target pressure has been determined (Step  116 ), cuff inflation may be continued to the target pressure (Step  118 ). Once cuff inflation reaches the target pressure, dynamic phase  30  can be considered complete and static phase  32  may begin. During static phase  32 , cuff pressure can be maintained generally about the target pressure (Step  120 ). As previously described, such maintenance can include minor fluctuations about the target pressure. 
     During static phase  32 , one or more hemodynamic parameters may be determined (Step  122 ). The hemodynamic parameters may be determined using suprasystolic analysis methods. For example, as described in U.S. Pat. No. 6,994,675 to Sharrock, large arterial vascular compliance may be determined using one of more signals obtained during static phase  32  (i.e. a suprasystolic phase). While Sharrock describes the use of a wideband acoustic transducer, signals from other pressure transducers can be used to analyze temporal or amplitude variations of signals obtained during the suprasystolic phase. U.S. Patent Application Publication No. 2006/0224070 to Sharrock et al. describes using suprasystolic measurements to determine Augmentation index, cardiac performance and cardiac stroke volume. U.S. Patent Application Publication No. 2009/0012411 to Lowe et al. describes using oscillometric techniques to analysis suprasystolic signals. Each of these references is hereby incorporated by reference in their entirety. 
     Following Step  122 , process  100  may end (Step  124 ). Termination of process  100  can include gradual or rapid cuff deflation, display of one or more hemodynamic parameters, or power shut-down. 
       FIG. 4  includes a process  200  according to another exemplary embodiment of the present disclosure. Process  200  can include various steps similar to the steps described above for process  100 . For example, Step  210 , labeled “Start,” may include one of more steps required to initiate an operation of system  10 , as previously described for Step  110 . Similarly, Steps  212 ,  214 ,  216 , and  218  can occur during dynamic phase  30 , as described above for Steps  112 ,  114 ,  116 , and  118 , respectively. Further, Steps  220  and  224  can occur during static phase  32 , as described above for Steps  120  and  124 , respectively. 
     Process  200  can include one or more additional steps during dynamic phase  30 . In some embodiments, a first set of data can be obtained during dynamic phase  30  (Step  215 ). Such data can include information obtained from an oscillometric pulse. In some embodiments, the source of the first set of data may be different to the source providing data to determine the target pressure. 
     Process  200  can also include one or more additional steps during static phase  32 . In some embodiments, a second set of data can be obtained during static phase  32  (Step  221 ). As described above, first and second sets of data can include any signal waveform data associated with patient  14  and/or cuff  12 , and may include amplitude, frequency, morphology, feature, or mathematically derived data. 
     Based on first and second data sets, a hemodynamic parameter can be determined (Step  222 ). First and second data sets can be obtained and compared and contrasted to determine one or more parameters. For example, a beat-to-beat time during dynamic phase  30  can be compared to a beat-to-beat time during static phase  32 . Such a comparison can be used to check for irregular heart beat timing. Other parameters can be determined based on comparing unloaded (i.e. dynamic phase  30 ) data with loaded (i.e. static phase  32 ) data. These two separate sample conditions can also be contrasted to determine one or more parameters using other methods known in the art. 
     In addition, analysis techniques can be used to reduce signal noise. For, example, first and second data sets may be used to remove common noise associated with both sets of data. A cleaner signal may be used to more accurately or precisely determine a hemodynamic parameter. 
     In other embodiments, one or more parameters determined during static phase  32  could be used to confirm any determinations based on data obtained during dynamic phase  30 . For example, a second determination of systolic pressure could be made based on a second set of data obtained during static phase  32 . The two values of systolic pressure could be compared to ensure that both are within acceptable limits to confirm the accuracy of any calculated parameters. If outside acceptable limits, process  200  may be terminated (Step  224 ) and repeated if desired. 
     Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure contained herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present disclosure being indicated by the following claims.