Abstract:
A method and system for delivering a gas containing carbon dioxide to a patient are described. The method comprises measuring a physiological parameter of breathing stability in the patient; determining an optimal gas delivery parameter based on the physiological parameter of breathing stability; and delivering the gas to the patient in accordance with the optimal gas delivery parameter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35USC§119(e) of U.S. provisional patent application 61/432,371 filed Jan. 13, 2011 and is related to U.S. patent application Ser. No. 12/837,259 filed on Jul. 15, 2010 and published on Mar. 24, 2011 as US 2011/0067697, the specifications of which are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a device and method for the delivery of gas containing carbon dioxide (CO 2 ) to a patient and more particularly to a controlled delivery based on the detection of a breathing disorder. 
       BACKGROUND OF THE ART 
       [0003]    Sleep disordered breathing (SDB) is characterized by irregular breathing both in rate and depth (amplitude). SDB can include periodic hypopnea (overly shallow breathing or an abnormally low respiratory rate) and periodic apnea (no breathing). It is established that SDB has two main causes: 1) obstructive abnormalities, which are associated with an obstruction of the pharyngeal airway and 2) central sleep disorders, which stem from a failure of the sleeping brain to generate regular rhythmic neural signals needed by the respiratory muscles. 
         [0004]    Obstructive abnormalities can usually be treated using positive airway pressure (PAP) therapy, where a breathing gas is introduced in the airways of the patient at a pressure slightly higher than the atmospheric pressure. However, central sleep disorders are not treated effectively with PAP, even with the administration of oxygen-enriched breathing gases (oxygen therapy). 
         [0005]    Disturbed sleep usually results in chronic fatigue, and impairs the patient&#39;s daytime cognitive functions and quality of life. SDB is frequently observed in patients with heart failure. For these patients, central sleep apnea is a serious condition that is believed to aggravate cardiac arrhythmia and to increase the occurrence of strokes and myocardial infarctions. Unfortunately, there exist no approved methods for the treatment of central sleep apnea. 
         [0006]    The most well-known central sleep disorder is the Cheyne-Stokes respiration (CSR) where a patient experiences a succession of hyper- and hypoventilation periods. This type of disorder is mainly experienced late at night, during nights where obstructive apnea/hypopnea episodes were observed in the early hours of sleep. CSR can also be observed at any time of the night and even during wake time in advanced forms of heart failure. The prevalence of CSR in the population with congestive heart failure is estimated at between 15 and 35%. 
         [0007]    The central respiratory function is a complex system that comprises multiple feedback mechanisms based on chemical receptors sensing carbon dioxide (CO 2 ), oxygen (O 2 ) and blood acidity (pH). When the feedback signals are not sufficiently intense, the central rhythmic neural signals to the respiratory muscles are perturbed or can stop completely. Hyperventilation associated with unstable breathing also contributes to lower the blood concentration of CO 2 . 
         [0008]    It has been shown that increasing the concentration of CO 2  in the breathing air has a stabilizing effect on patients with CSR, because of the increased CO 2  feedback signal. However, no practical methods for administering CO 2  to a patient are commercially available. 
         [0009]    A prior art method of administering CO 2  relies on the accepted PAP technique. PAP requires leak-proof masks that are uncomfortable because they need to be secured tightly over the patient&#39;s face. PAP gases with low humidity content also contribute to the drying of the respiratory passageways and the patient&#39;s discomfort. One should note that the administration of a continuous flow of CO 2 , such as is proposed in this prior art method, is a significant medical expense due to the large quantities of gas used. 
         [0010]    An alternate prior art method utilizes a dead space in an external breathing apparatus as a simple way to increase the fractional concentration of inspired CO 2  (FICO2). This method has the disadvantages of requiring a leak-proof mask and demanding an increased respiratory effort to move the gases in the external breathing circuit. 
       SUMMARY 
       [0011]    According to one broad aspect of the present invention, there is provided a method for delivering a gas containing carbon dioxide to a patient. The method comprises measuring a physiological parameter of breathing stability in the patient; determining an optimal gas delivery parameter based on the physiological parameter of breathing stability; and delivering the gas to the patient in accordance with the optimal gas delivery parameter. 
         [0012]    In one embodiment, the gas containing carbon dioxide is a mixture of gases including carbon dioxide. 
         [0013]    In one embodiment, the method further comprises repeating the step of measuring the physiological parameter of breathing stability in the patient, after the delivering the gas, to determine an effect of the delivering on the physiological parameter. 
         [0014]    In one embodiment, the method further comprises repeating the steps of determining the optimal gas delivery parameter and delivering the gas to adjust the delivering consequently to the effect. 
         [0015]    In one embodiment, the optimal gas delivery parameter is selected from the group consisting of a fraction of carbon dioxide in the gas and a flow rate of the gas during the delivering. 
         [0016]    In one embodiment, the method further comprises issuing an alarm if the physiological parameter is measured to be outside of a predetermined threshold. 
         [0017]    In one embodiment, the physiological parameter is the breathing pattern for the patient, the breathing pattern including at least the respiratory amplitude. 
         [0018]    In one embodiment, the physiological parameter is analyzed to obtain a breathing pattern index for the patient and the determining the gas delivery parameter is carried out using the breathing pattern index. 
         [0019]    In one embodiment, the physiological parameter further includes at least one parameter selected from the group consisting of arterial hemoglobin oxygen saturation, respiratory rate, respiratory amplitude, chest movement pattern, end tidal CO 2  (ETCO 2 ) level, Rapid Eye Movement (REM) pattern, rate of apnea, rate of hypopnea, rate of desaturation, respiratory rate variability, heart rate variability, heart rate synchrony and snoring noise level. 
         [0020]    According to another broad aspect of the present invention, there is provided a system for delivering a gas containing carbon dioxide to a patient. The system comprises a physiological sensor for measuring a physiological parameter of breathing stability in the patient; a controller receiving the physiological parameter from the physiological sensor for determining an optimal gas delivery parameter based on the physiological parameter of breathing stability; and a gas delivery sub-system having a gas source and a gas delivery controller for delivering the gas to the patient in accordance with the optimal gas delivery parameter received from the controller. 
         [0021]    In one embodiment, the gas containing carbon dioxide is a mixture of gases including carbon dioxide. 
         [0022]    In one embodiment, the optimal gas delivery parameter is selected from the group consisting of a fraction of carbon dioxide in the gas and a flow rate of the gas during the delivering and wherein the gas delivery controller uses the gas delivery parameter to deliver the gas from the source. 
         [0023]    In one embodiment, the system further comprises an alarm sub-system including an alarm emitter and an alarm controller, the alarm controller having a predetermined threshold, the alarm controller receiving the physiological parameter from the controller and controlling the alarm emitter to issue an alarm if the physiological parameter is measured to be outside of the predetermined threshold. 
         [0024]    In one embodiment, the physiological parameter is the breathing pattern for the patient, the breathing pattern including at least the respiratory amplitude. 
         [0025]    In one embodiment, the system further comprises a breathing pattern index calculator for analyzing the physiological parameter to obtain a breathing pattern index for the patient and wherein the controller uses the breathing pattern index to determine the gas delivery parameter. 
         [0026]    In one embodiment, the physiological parameter further includes at least one parameter selected from the group consisting of arterial hemoglobin oxygen saturation, respiratory rate, respiratory amplitude, chest movement pattern, end tidal CO 2  (ETCO 2 ) level, Rapid Eye Movement (REM) pattern, rate of apnea, rate of hypopnea, rate of desaturation, respiratory rate variability, heart rate variability, heart rate synchrony and snoring noise level. 
         [0027]    In one embodiment, the system further comprises an analysis module for analyzing the measured physiological parameter and determined gas delivery parameter to detect a trend for the patient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a example embodiment thereof and in which 
           [0029]      FIG. 1  is a schematic illustration of an example embodiment; 
           [0030]      FIG. 2  is a functional block diagram of the main components of an example embodiment; 
           [0031]      FIG. 3  is a graph of an example breathing pattern plotted against the time; 
           [0032]      FIG. 4  is a graph of an example expired CO 2  concentration plotted against the time; 
           [0033]      FIG. 5  is a flowchart illustrating the main steps of an example method for delivering the CO 2  to a patient with the example system shown in  FIG. 1 ; 
           [0034]      FIG. 6  includes  FIG. 6A  and  FIG. 6B , wherein  FIG. 6A  is a graph of an example breathing pattern with some low amplitude respirations plotted against the time and  FIG. 6B  is a graph of an example delivery of CO 2  in response to the breathing pattern shown in  FIG. 6A ; and 
           [0035]      FIG. 7  includes  FIG. 7A  and  FIG. 7B , wherein  FIG. 7A  is a graph of an example expired CO 2  concentration with some low end tidal CO 2  (ETCO 2 ) values plotted against the time and  FIG. 7B  is a graph of an example delivery of CO 2  in response to the respiratory pressure shown in  FIG. 7A . 
       
    
    
       [0036]    It will be noted that throughout the appended drawings, like features are identified by like reference numerals. 
       DETAILED DESCRIPTION 
       [0037]    The present invention proposes an adaptive system and method where CO 2  is delivered based on the patient physiological data with the aim to stabilize, or at least improve, the breathing pattern. The physiological parameter detected is therefore indicative, in some respect, of breathing stability. 
         [0038]    A closed control loop is used to deliver CO 2  intermittently in response to respiratory abnormalities or patterns, thereby helping to reduce central apnea and hypopnea. The quantity of CO 2  used in the proposed method and system is reduced with respect to existing systems which deliver CO 2  since the CO 2  is administered according to delivery parameters (flow rate, time and duration) determined using measured physiological data. In most cases the administration of CO 2  will be intermittent, thus greatly reducing the amount of delivered CO 2  compared with a continuous delivery. 
         [0039]      FIG. 1  is a schematic illustration of an example system  101  used to administer gaseous CO 2  from a CO 2  source  103  to a patient  105  by means of a nasal cannula  107  affixed to the patient&#39;s nose  109 . The quantity of CO 2  delivered to the patient  105  from the source  103  is controlled using the integrated system  111 . 
         [0040]    Sensors are used to provide physiological signals that can be utilized by the integrated system  111  to change the amount of CO 2  administered to the patient  105 . At least one breathing pattern sensor  115 , for example an accelerometer, detects the breathing pattern (depth (amplitude) of breath, rate, presence or absence of breath, etc.) of the patient and sends its signal to the integrated system  111 . The breathing pattern could only detect amplitude of breath but typically detects both amplitude and rate. The integrated system  111  uses this physiological signal to adjust the delivery of CO 2 . 
         [0041]    The nasal cannula  107  can optionally include a pressure sensor and can also optionally include an end tidal CO 2  (EtCO 2 ) sensor as will be depicted in  FIG. 2 . A blood oxygen sensor (oxymeter or SpO 2  sensor)  113  can also optionally be used with the system. The physiological signals acquired by the optional pressure sensor, EtCO 2  sensor and oxymeter can also be used by the integrated system  111  to adjust the delivery of CO 2 . 
         [0042]      FIG. 2  is a functional illustration of an example system  201  used to administer gaseous CO 2  from a source  203  to a patient  205  by means of a nasal cannula  207  affixed to the patient&#39;s nose  209 . The quantity of CO 2  delivered to the patient  205  from the source  203  is controlled using a motorized proportional valve  211  commanded by a controller  213 . 
         [0043]    The motorized proportional valve  211  has an actuator (not shown) which allows a displaceable portion of the valve  211  to be moved between a closed position and an open position to allow the flow of CO 2  to be sent to the patient  205  from the source  203 . As will be readily understood, a partial opening is also possible to control the flow of CO 2 . The valve  211  may or may not provide feedback information regarding its degree of opening to the controller, which may differ from the commanded value. 
         [0044]    The controller  213  receives physiological signals from the patient and calculates the appropriate command for the valve  211 . In the example embodiment, the physiological signals can include the breathing pattern obtained from the breathing pattern sensor  225 , for example accelerometer  223 , the breathing amplitude and rate derived from pressure sensor  215 , the expired CO 2  concentration derived from CO 2  sensor  217 , as well as the arterial hemoglobin (blood) oxygen saturation measured by pulse oximetry (SpO 2 ) using O 2  sensor (oxymeter)  219  and the derived heart rate. In one example embodiment, only the expired CO 2  concentration derived from CO 2  sensor  217  is used by the controller  213  as a physiological signal. In another example embodiment, only the breathing pattern obtained from the breathing pattern sensor  225  is used by the controller  213  as a physiological signal. 
         [0045]    Examples of physiological signals that can be tracked to evaluate the quality of sleep of the patient after delivery of CO 2  include the Rapid Eye Movement (REM) pattern, breathing pattern (respiratory flow, respiratory pressure, rate of apnea, rate of hypopnea, rate of desaturation, respiratory rate variability), heart rate variability, heart rate synchrony, movement of patient, electromyogram of muscles involved in breathing (for example from nasal muscles to intercostal muscles, diaphragm of sternocleido mastoids, etc.), detection of thoracic movements by plethysmography or other suitable method, the patient&#39;s temperature and the patient&#39;s snoring noise level. A quality of sleep parameter can be obtained using these physiological signals and can be used by the controller  213  to adjust the command for the valve  211 . 
         [0046]    The CO 2  source  203  is usable for providing a gas including CO 2  to the patient  205 . In some embodiments of the invention, the gas source  203  is a CO 2  source providing a pre-determined concentration of CO 2  to the patient. This pre-determined concentration can be set to any useful concentration, for example a 100% concentration corresponds to pure CO 2 . In these embodiments, the controller  213  is usable for controlling a gas flow rate of the gases source  203 . In other embodiments of the invention, the gases source  203  provides a mixture of air and CO 2 . In these embodiments, the controller  213  is usable for adjusting a fraction of CO 2  in the gas and the gas flow rate of the gas source  203 . In some embodiments, the source of CO 2  could be the expired gas from the patient. In yet other embodiments of the invention, any other suitable gas source  203  is used. The mixture of gas delivered to the patient may or may not include oxygen. 
         [0047]    As will be readily understood, any suitable gas delivery apparatus including a facial mask, a venturi mask and eyeglasses provided with gas delivery tubes can be used instead of the nasal cannula  207 . 
         [0048]    The present invention provides an improved level of comfort for the patient. If the gas delivery apparatus is a mask, it does not have to be completely leak-proof. The comfort may be even further improved by having the patient wear a simple nasal cannula. Because the system has a retroaction via the physiological signals from sensors  215 ,  217 ,  219  and  225 , the system is able to compensate for small leaks. 
         [0049]    In the example shown, the breathing pattern sensor  225  is used to monitor the respiratory cycles and determine phases of hypo- and hyperventilation and the respiratory amplitude. Accelerometer-based respiratory monitoring is based on the observation of small rotations at the chest wall due to breathing. MEMS accelerometers worn on the torso can measure inclination changes due to breathing, from which a respiratory amplitude and/or rate can be obtained. Tri-axial accelerometer data can track the axis of rotation and obtain angular rates of breathing motion. Other types of breathing pattern sensors can include an infra-red reflector monitored by a camera, a spirometer, a belt connected to a bellows or an inductive belt. 
         [0050]      FIG. 3  is a graph  301  of the breathing pattern  303  obtained with the breathing pattern sensor  225 , plotted against the time  305 . A normal breathing pattern measured via the movements of the chest of the patient is composed of positive peaks  307  measured during inspiration when the chest stretches and negative peaks  309  measured during expiration when the chest deflates. As will be readily understood, a correlation of the measured chest displacements with the breath volumes of each patient will be necessary. The normal respiratory amplitudes during the expiratory and inspiratory phases vary according to the physical condition, level of physical effort and health condition of each person. It is possible to establish an acceptable inspiratory threshold  311  and expiratory threshold  313  for each person, for example by analyzing the breathing pattern during wake time. Using these respiratory thresholds, it is possible to classify normal or abnormal respiration. For example, the maximum value of the inspiration  315  did not reach inspiratory threshold  311 , so the inspiration  315  is considered abnormal. Hypo- and hyperventilation are defined by the occurrence of abnormal respiration for a certain number of respirations or a certain period of time. These thresholds are then optionally used by the controller  213  to adjust the delivery of CO 2 . 
         [0051]      FIG. 3  could also represent a graph of the respiratory pressure  303  obtained with the respiratory pressure sensor  215  and plotted against the time since both sensors will capture a volume reading. The inspiration as detected with the pressure sensor  215  will yield a negative peak and the expiration will yield a positive peak. 
         [0052]    When the expired CO 2  concentration from the sensor  217  is used by the controller  213 , a potential issue arises depending on the location of the CO 2  sensor. The sensor could sample not only the expired gases, but also the inspired gases. The presence of CO 2  in the inspiratory phase may result in potential measurement errors of the expired CO 2  parameter by the CO 2  sensor  217 .  FIG. 4  is a graph  401  of the CO 2  concentration  403  obtained with CO 2  sensor  217 , plotted against the time  405 . During the inspiratory phase  407 , the CO 2  concentration drops to the value of the inspired air  409 . During the expiratory phase  411 , the CO 2  concentration increases to approximately 5%. The maximum value  413  reached at the end of the expiratory phase  411 , is called the end tidal CO 2  (ETCO 2 ) concentration. 
         [0053]    To reduce an impact of the potential issue of contamination of the expired CO 2  concentration measurement by inspired gases, the following algorithm can be used. Individual expiratory phases are identified and located in the CO 2  concentration versus time waveform by finding the places where the average over a typical expiratory period is maximized. Once the expiratory phases are located, the maxima of the measured values over each expiratory phase are extracted. These values correspond to the end tidal CO 2  concentrations and are free from inspired air contamination. These values are then optionally used by the controller  213  to adjust the delivery of CO 2    
         [0054]    In another embodiment, the respiratory pressure sensor  215  can also be used in addition to the CO 2  concentration sensor  217  to determine or to improve the determination of when the inspiration and expiration phases begin and end, in order to reject data acquired during the inspiratory phase. 
         [0055]    When the measurement of the blood oxygen saturation obtained using sensor  219  is used as a physiological signal, sensor  219  can take on different forms. In the example shown in  FIG. 2 , the blood oxygen saturation is obtained via a finger probe  221 . In other embodiments, the blood oxygen saturation could be obtained via different means, such as using a toe probe or by placing an oximetry probe on another vascularized location on the body. 
         [0056]    The controller  213  calculates the command to the proportional valve  211  as much as possible in real time in order to stabilize the condition of the patient shortly after a breathing anomaly or breathing pattern is detected by the controller based on the physiological data. 
         [0057]      FIG. 5  is a flowchart illustrating an example method  501  for delivering the CO 2  to a patient  205 .  FIG. 5  will be described herein in relation with the system described in  FIG. 2 . After the system is powered up and initialized  503 , the controller  213  reads at steps  505  and  507 , the available physiological parameters, obtained with sensors  215 ,  217 ,  219  and  225 . Next the controller  213  analyses  509  the available physiological parameters and derives a breathing pattern index. A breathing pattern index of 100% indicates normal breathing while a breathing pattern index of 0% indicates a completely disrupted breathing pattern. The breathing pattern index is automatically determined by the controller  213  based on the variations of the detected signals compared to the thresholds. These thresholds may have been determined for example during wake time or derived from studies and then provided to the controller during a set-up procedure. 
         [0058]    The controller  213  also calculates  511  the amount of CO 2  to administer to the patient based on the available physiological data and breathing pattern index. The valve  211  is commanded  513  to the appropriate level allowing the CO 2  to be administered to the patient  205  as long as the breathing pattern is considered to be disordered. The steps in the method  501  are iterated continuously, for example several times per minutes, until the system is turned off  515 , either by a trained person or by a system internal alarm. 
         [0059]    The valve command is calculated using, for example, numerical servo computations based on the current values of the physiological signals as well as previous values measured in the preceding minutes. The function of the controller  213  can be implemented using a personal computer, but in the example embodiment, it is embedded in compact dedicated electronics composed of one or several micro-controllers, one or several digital signal processors (DSP), one or several field-programmable gate arrays (FPGA) or a combination of two or three of these types of electronic devices. 
         [0060]    At step  511 , the gas delivery parameters can be obtained using a proportional-integral-differential (PID) controller. Gas delivery parameters are determined in order to maintain one or several of the measured physiological parameters within a predetermined interval or as close as possible to a target value. In an embodiment of the invention, the breathing amplitude is derived from the physiological data obtained. A target value of, for example, more than 95% of the expiration amplitudes are larger than the expiratory threshold is selected. This target value can be adjusted according to the patient  205  in accordance with conventional criteria. 
         [0061]      FIG. 6A  is a graph  601  showing the breathing pattern  603  obtained with the breathing pattern sensor  225 , plotted against the time  605 .  FIG. 6B  is a graph  607  showing the amount of CO 2    609  delivered by the controller  213 , plotted against the time  611 . The time scales  605  and  611  are the same. The inspiratory threshold  613  and expiratory threshold  615  are predetermined for each person. When the respiratory amplitudes are measured  617  to be lower than the thresholds for a certain period of time, the controller  213  can command the valve  211  to release a certain amount of CO 2    619 . When the respiratory amplitude returns to acceptable levels, the amount of CO 2  delivered can be nil. If a smaller deviation from the threshold is measured  621 , a smaller amount of CO 2    623  can be administered by the system by controlling the valve  211 . 
         [0062]    In another example embodiment of the invention, the measured physiological parameter is indicative of the expired CO 2  concentration in the patient and a target value of, for example, 40 mmHg is selected. This target value can be entered as a fixed parameter, adjusted according to the patient  205  in accordance with conventional criteria, including from data measured in a sleep evaluation laboratory or can be determined automatically by the controller  213  based on the acquired physiological data. 
         [0063]      FIG. 7A  is a graph  701  showing the expired CO 2  concentration  703  obtained with the CO 2  sensor  217 , plotted against the time  705 .  FIG. 7B  is a graph  707  showing the amount of CO 2    709  administered by the controller  213 , plotted against the time  711 . The time scales  705  and  711  are the same. The expired CO 2  concentration is considered normal when it is lower than the upper limit  713  and higher than the lower limit  715 . These limits are determined in accordance with conventional criteria, including from data measured in a sleep evaluation laboratory, as fixed parameters or adjusted automatically by the controller  213  based on the acquired physiological data. When the expired CO 2  concentration is measured  717  to be lower than the lower limit for a certain period of time, the controller  213  can command the valve  211  to release a certain amount of CO 2    719 . When the expired CO 2  concentration increases above the lower limit, the quantity of CO 2  delivered can be nil. When the expired CO 2  concentration is measured to be higher than the higher limit for a certain period of time, the controller  213  can trigger an alarm. 
         [0064]    In yet another example embodiment of the invention, the measured physiological parameter is the respiratory rate of the patient and a target value of, for example, less than 30/min is selected. This target value can be adjusted according to the patient  205  in accordance with conventional criteria. 
         [0065]    In yet another example embodiment of the invention, the breathing pattern index is derived from the physiological data obtained. A target value of, for example, 90% breathing pattern index is selected. This target value can be adjusted according to the patient  205  in accordance with conventional criteria. 
         [0066]    At step  513 , the valve  211  is operated so that the gas is administered to the patient in accordance with the optimal gas delivery parameters determined at step  511 . This is typically performed by regulating the gas flow from source  203  with valve  211 . Alternatively, a combination of proportional valves and on/off valves can be used to control the gas flow. 
         [0067]    Safety mechanisms to limit the flow rate of administered CO 2  can be implemented. This can be done with a passive hardware flow limiter or with an active control approach using a flowmeter and a motorized limiter or safety valve. 
         [0068]    The controller  213  determines the proper time of administration and amount of CO 2 . For maximum efficiency, the administration of CO 2  would normally occur when the respiratory amplitude (quantity of air intake) is lower and would normally stop when it is returned to normal as illustrated in  FIG. 6A  and  FIG. 6B . A dynamic and intermittent administration of CO 2  immediately proceeding and following hyperventilation is proposed. 
         [0069]    In some embodiments of the invention, optional alarms can be issued if some of the physiological parameters are measured or calculated to be outside of predetermined intervals. Measured or calculated physiological parameters that may lead to the issuance of an alarm include, for example, respiratory amplitude and rate, expired CO 2  level, breathing pattern index, blood oxygen saturation, heart rate and temperature of the patient. 
         [0070]    Examples of alarms that can be issued by an embodiment of the controller  213  are as follows: High End tidal CO 2  level (if this sensor is used), low SpO 2  level (if this sensor is used) or respiratory pressure (if this sensor is used) not available indicating that the nasal cannula is not in place should lead to an alarm. 
         [0071]    Other examples of alarms that can be issued by an embodiment of the controller  213  are provided in the following list: 
         [0072]    If the blood oxygen saturation is less than or equal to 85% for more than 3 seconds, a message indicating that connections of the blood oxygen saturation sensor  221  should be checked is issued and the method  201  steps back to step  203 ; 
         [0073]    If the blood oxygen saturation is unmeasurable, a message indicating that connections of the blood oxygen saturation sensor  221  should be checked is issued and the desired CO 2  flow rate is set as a minimal safe flow rate, or as the last determined CO 2  flow rate; 
         [0074]    If the expired CO 2  concentration is unmeasurable, a message indicating that connections of the CO 2  sensor  215  should be checked is issued; 
         [0075]    If the expired CO 2  concentration is larger than or equal to 45 mmHg or has increased by more than 10 mmHg over the preceding hour, a message indicating the patient  205  should be closely monitored and that another CO 2  delivery technique may be preferable is issued; 
         [0076]    If the expired CO 2  concentration is larger than or equal to 55 mmHg or has increased by more than 20 mmHg over the preceding hour, a message indicating that another CO 2  delivery technique may be preferable is issued. 
         [0077]    The analysis of the data collected during periods where the CO 2  delivery system is used, for example during one night, can be performed automatically to provide a summary report of events after each operation period. It can include the amount of CO 2  delivered, a graph of the expired CO 2  concentration vs time, the number of apnea and hypopnea events, a graph of the respiratory amplitude and rate vs time, a graph of the breathing pattern index vs time, the number of desaturations (SpO 2 &lt;90%) and deep desaturations (SpO 2 &lt;80%), a graph of the blood oxygen saturation (SpO 2 ) level vs time, etc. Trends in the evolution of these parameters can also be made available for monitoring longitudinal changes in these patients. 
         [0078]    The method allows monitoring by telemetry in the patients. 
         [0079]    The proposed method and system can be used for the administration of CO 2  for a very wide range of clinical settings, in hospital setting for initial adaptations (sleep laboratory or respiratory ward) or at home from pre-hospital care to intra-hospital care (emergency department, intensive care units, respiratory/cardiology/internal medicine wards, rehabilitation units, post-anesthesia recovering rooms, for example). It can be used in portable settings, such as in ambulance vehicles, in camp sites during mountain climbing expeditions and the like. It can be used by patients at home for chronic respiratory and cardiac insufficiency and any cause resulting in breathing disorders. It can be used for adults or pediatric patients. 
         [0080]    The proposed method  201  is typically performed without mechanically assisted ventilation of the patient  205 . However, in alternative embodiments of the invention, such mechanical ventilation is used. In case of breathing disorders in mechanically ventilated patients, this technique and algorithm may be used to stabilize or help improve the breathing pattern and the resulting sleep quality. 
         [0081]    While illustrated in the block diagrams as groups of discrete components communicating with each other via distinct data signal connections, it will be understood by those skilled in the art that the illustrated embodiments may be provided by a combination of hardware and software components, with some components being implemented by a given function or operation of a hardware or software system, and many of the data paths illustrated being implemented by data communication within a computer application or operating system. The structure illustrated is thus provided for efficiency of teaching the described embodiment. 
         [0082]    The embodiments described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the appended claims.