This disclosure relates generally to methods of using a pulmonary artery pressure signal and, more particularly, to using a pulmonary artery pressure signal to detect and/or monitor physiological parameters, physiological status, and aspects of disorders and diseases, amongst other things.
Cardiopulmonary diseases afflict millions of people each year. In particular, diseases of the heart remain the leading cause of death in the United States. Monitoring patients' physiological state is an important aspect in the diagnosis, management and treatment of various diseases and disorders, including cardiopulmonary diseases. For this reason, significant efforts have been directed at improving monitoring and detection technologies. In specific, significant efforts have been directed at improving monitoring and detection technologies for cardiopulmonary diseases and related diseases that affect cardiopulmonary parameters.
Implantable medical devices can be advantageous as monitoring devices because the monitoring can be performed as desired, without regard to the physical location of the patient. In addition, the use of implantable medical devices for patient monitoring eliminates problems associated with patient compliance. However, many existing techniques for monitoring patients' physiological state cannot be implemented well in the context of implantable medical devices.
For at least these reasons, a need exists for methods of gathering physiological data regarding a patient with an implantable medical device. A need also exists for methods of detecting, diagnosing, predicting, and/or monitoring cardiopulmonary diseases and other conditions that affect cardiopulmonary parameters.
Embodiments of the invention are related to methods and systems for using a pulmonary artery pressure signal to detect and/or monitor physiological parameters, physiological status, and/or aspects of disorders and diseases, amongst other things. In an embodiment, the invention includes a method of measuring a pulmonary function parameter of a patient including chronically implanting a pulmonary artery pressure sensor, obtaining a pulmonary artery pressure signal from the pressure sensor, and processing the signal to obtain the pulmonary function parameter.
In an embodiment, the invention includes a method of detecting a sleeping disorder including measuring a pulmonary artery pressure signal with a pressure sensor, and monitoring the pulmonary artery pressure signal to identify a breathing pattern indicative of a sleeping disorder.
In an embodiment, the invention includes a method of tracking sleep characteristics of a patient including monitoring a pulmonary artery pressure signal for a change to a cardiopulmonary parameter indicative of a sleep event, and
recording an occurrence of the sleep event if a change to the cardiopulmonary parameter indicative of the sleep event occurs.
This summary is an overview of some of the teachings of the present application and is not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details are found in the detailed description and appended claims. Other aspects will be apparent to persons skilled in the art upon reading and understanding the following detailed description and viewing the drawings that form a part thereof, each of which is not to be taken in a limiting sense. The scope of the present invention is defined by the appended claims and their legal equivalents.
The invention may be more completely understood in connection with the following drawings, in which:
While the invention is susceptible to various modifications and alternative forms, specifics thereof have been shown by way of example and drawings, and will be described in detail. It should be understood, however, that the invention is not limited to the particular embodiments described. On the contrary, the intention is to cover modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
Monitoring a patient's physiological condition is an important aspect in the diagnosis, management and treatment of various diseases. One approach to monitoring the physiological state of patients is the use of an implantable medical device that can detect physiological conditions. The use of an implantable medical device as a monitoring device can be advantageous because the monitoring can be performed as frequently as desired, without regard to the physical location of the patient. In addition, patient monitoring with an implanted medical device eliminates or reduces problems associated with patient compliance.
One aspect of physiological status is the pressure of fluids, such as blood, at various points in the vasculature of a patient. Frequently, blood pressure is indirectly estimated based on readings taken by care providers during clinical visits using a sphygmomanometer. During sphygmomanometry, typically, an occluding cuff is inflated to a pressure level above arterial pressure as indicated by obliteration of the pulse. Then, the cuff is gradually deflated and the pressures are noted at which sounds produced by the arterial pulse waves (Korotkoff sounds) appear and disappear again as flow through the artery resumes. While sphygmomanometry is minimally invasive, it is less than ideal because of limited accuracy and reproducibility and because of its inability to measure blood pressure in remote embedded blood vessels within the circulatory system where pressure is different than the normal left sided systemic blood pressure. As such, direct measurement of fluid pressure within various parts of the heart and lungs is beneficial for purposes of both diagnosis and treatment.
The pulmonary artery is one place where fluid pressure can be measured in order to provide cardiopulmonary status information to the clinician. While the vasculature commonly referred to as the “pulmonary artery” includes the pulmonary trunk (or main pulmonary artery) and the right and left pulmonary arteries, “pulmonary artery” is used in this invention to mean any artery supplying blood to the lungs.
Pulmonary artery pressure can be a useful indication of a patient's condition both directly and indirectly. For example, pulmonary artery pressure is useful because many diseases can result in elevated pulmonary artery pressure and therefore can be detected by monitoring pulmonary artery pressure. Pulmonary artery pressure is also useful because it is related to the pressure in other parts of the vasculature. For example, pulmonary artery pressure is related to the pressure in the left ventricle. Specifically, the pulmonary artery end-diastolic pressure (PAEDP) can be used to estimate left ventricle end-diastolic pressure (LVEDP), which is an important parameter of cardiopulmonary status. Left ventricle end-diastolic pressure (LVEDP) can also be referred to as left ventricle filling pressure or left ventricle pre-load. At the end of expiration during the respiratory cycle, intrathoracic pressure has little impact on pulmonary artery pressure. Therefore, LVEDP can be estimated based on the PAEDP as measured at the end of expiration.
The range of hemodynamic information that can be obtained with a coronary artery pressure sensor can include many different parameters. By way of example, hemodynamic information that can be obtained with a coronary artery pressure sensor can include the systolic pulmonary artery pressure at end-expiration, the diastolic pulmonary artery pressure at end-expiration, the mean pulmonary artery pressure, the systolic duration, the diastolic duration, the slew rate of the pulmonary artery pressure, dP/dt, the amplitude, duration and timing of the dicrotic notch, heart rate, and heart rate variability, among others.
In addition to this hemodynamic information, it has been discovered that a pulmonary artery pressure signal can be processed in order to determine or estimate one or more parameters of pulmonary function (“pulmonary function parameters”). Pulmonary artery pressure is modulated by intrathoracic pressure, which changes with inspiration and expiration. Specifically, intrathoracic pressure is increased during expiration and decreased during inspiration. The relationship between pulmonary artery pressure and intrathoracic pressure can be used in a method in order to derive one or more pulmonary function parameters. In an embodiment, the invention includes a method of measuring a pulmonary function parameter of a patient using a pulmonary artery pressure signal.
By way of example,
Many different pulmonary function parameters can be calculated or estimated by processing a pulmonary artery pressure signal. For example, such pulmonary function parameters can include respiration waveforms (both inspiration and expiration), respiration rate, respiratory rate variability, respiratory excursion, breath interval, inspiration slope, expiration slope, tidal volume, relative tidal volume, minute ventilation, relative minute ventilation, pulmonary vascular resistance, relative pulmonary vascular resistance, forced expiration volume in one minute (FEV1), relative forced expiration volume in one minute (FEV1), forced vital capacity (FVC), relative forced vital capacity (FVC), ratio of FEV1 to FVC, total lung capacity (TLC), relative total lung capacity (TLC), and the like.
Referring now to
Respiration line 104 illustrates a roughly sinusoidal respiratory artifact that is superposed on pulmonary artery pressure and is caused by changes in intrathoracic pressure during the respiration cycle. Respiration line 104 can be calculated based on the pulmonary artery pressure signal 100 using various techniques. For example, the respiration line 104 can be calculated by tracking the fluctuation of the pulmonary artery pressure peaks over time. As another example, the respiration line 104 can be calculated by tracking the fluctuation of the pulmonary artery pressure valleys over time. In some embodiments, filtering can be used to separate the respiration and cardiac components of pulmonary artery pressure signal 100. For example, a lowpass filter with a cutoff frequency of approximately 0.5 Hz would substantially pass the respiratory component of the pulmonary artery pressure signal 100, thus creating respiration line 104, while significantly attenuating the cardiac component. Further, filtering pulmonary artery pressure signal 100 with a high pass filter with a cutoff frequency of approximately 0.75 Hz would substantially pass the cardiac component of the pulmonary artery pressure signal 100, while significantly attenuating the respiratory component. To improve respiratory and cardiac signal separation, the cutoff frequencies of the lowpass and highpass filters may be decreased and increased with decreasing and increasing respiratory and/or cardiac rates respectively.
Respiration line 104 (or the “respiration signal”) can, in turn, be used to calculate many different pulmonary parameters. The contours of the respiration line 104 over time can be referred to as the respiration waveform. The slope of the respiration line 104 as it is rising (as during expiration) and as it is falling (as during inspiration) can be tracked and recorded. In this manner, both the inspiration slope and expiration slope can be calculated.
The time for each cycle of respiration (both expiration and inspiration) can be determined by measuring the amount of time 106 in between successive peaks (or valleys) of the respiration line 104. The amount of time between successive peaks can be referred to as the breath interval. The respiration rate can then be calculated simply by dividing the desired time period, such as one minute, by the breath interval (time for each cycle of respiration). For example, if the time for each cycle is found to be two seconds, then the respiration rate would be thirty breaths per minute. The respiration rate can be calculated in real-time. The respiration rate can also be recorded and tracked over a period of time. In this manner, respiratory rate variability can be calculated.
The amplitude 114 of the respiration line 104 corresponds to how deep or shallow the breathing of the patient is. The term “tidal volume” refers to the amount of air breathed in or out during normal respiration. As such, the amplitude 114 of the respiration line 104 can be used to estimate relative tidal volume. The tidal volume can be estimated in real time and/or recorded over a period of time. By way of example, in an embodiment, a baseline value for the net amplitude of the respiration line 104 from peak to valley can be established for a given patient and then measurements in real time can be compared with the baseline value to derive a relative tidal volume value. This method can be used to assess whether the tidal volume of the patient is increasing or decreasing over time.
In some embodiments, the baseline value can simply be based on historical data derived from the pulmonary artery pressure signal. In other embodiments, the baseline value can be calibrated by using data from another instrument. As one example, during a calibration procedure, a patient can be prompted to blow into an air flow meter while the pulmonary artery pressure signal is being recorded. Data from the air flow meter can be used to accurately calculate the actual tidal volume. The recorded pulmonary artery signal can then be calibrated to the actual tidal volume as indicated by the air flow meter. Estimates of the actual tidal volume can be made in real time by applying this calibration data to the pulmonary artery pressure signal.
The relative tidal volume can in turn be used to estimate other parameters. For example, minute ventilation is defined as the tidal volume multiplied by the respiration rate (in breaths/minute). As such, the relative tidal volume, as calculated above, can be multiplied by the respiration rate in order to derive a relative minute ventilation value.
Pulmonary vascular resistance (PVR) refers to the resistance offered by the vasculature of the lungs to the flow of blood. The units for measuring vascular resistance are dyn-s/cm5. PVR can be estimated using a pulmonary artery pressure signal by the formula: PVR=((mean pulmonary artery pressure−end-diastolic pulmonary artery pressure)/cardiac output)×80, where pressures are in mmHg and cardiac output is measured in liters per minute. Conventionally, pulmonary capillary wedge pressure is used in the formula instead of end-diastolic pulmonary artery pressure. However, it is widely accepted that end-diastolic pulmonary artery pressure can be used as an estimation of pulmonary capillary wedge pressure.
Forced expiratory volume (FEV1) refers to the amount of air that a patient can forcibly exhale in one second. This value can be estimated using a pulmonary artery pressure signal in various ways. For example, in some embodiments, a patient can be given a cue indicating that they should forcibly blow out as much air as possible. The pulmonary artery pressure signal can be captured during this forcible expiration and then processed to provide an estimation of the volume expelled during a one second span of time. For example, the pulmonary artery pressure signal can be processed into a respiration signal (such as respiration line 104 in
Forced vital capacity (FVC) refers to the total volume of air that a patient can forcibly blow out after full inspiration. This value can be estimated using a pulmonary artery pressure signal in various ways. For example, in some embodiments, a patient can be given a cue indicating that they should breathe in as much air as they can and then forcibly exhale as much air as possible. The pulmonary artery pressure signal can be captured during this forcible expiration and then processed to provide an estimation of the total volume of air expired during a one second span of time. For example, the pulmonary artery pressure signal can be processed into a signal indicative of respiration (such as respiration line 104 in
It will be appreciated that the value for FVC can be either relative or absolute. For example, the value of FVC could be in relation to the historical FVC of the patient. In other embodiments, the FVC can be absolute if, for example, the respiration signal is calibrated after implantation against a reference value. For example, a patient with an implanted device generating a pulmonary artery pressure signal could be evaluated using a spirometer. Data from the spirometer can then be used to calibrate the respiration signal.
The ratio of FEV1/FVC can serve as a useful diagnostic measure. In healthy adults, this ratio is approximately 0.75 to 0.80. In some embodiments, the ratio of FEV1 to FVC can be calculated by dividing FEV1 (calculated as described above) by FVC (calculated as described above). The ratio of FEV1/FVC can then be used further. For example, this ratio can be stored and then output to a care provider.
Total lung capacity (TLC) refers to the volume of gas contained in the lung at the end of maximal inspiration. TLC can also be referred to as the peak inspiratory volume. TLC is equal to the sum of forced vital capacity (FVC) plus residual volume. Where a patient forcibly blows out after full inspiration, the point of maximum inspiration defines the TLC, and the point of maximum expiration defines the residual volume. By convention, the volume between maximum inspiration and maximum expiration is the forced vital capacity (FVC), as described above. The residual volume is a value that can be calibrated using conventional techniques for measuring residual volume. As such, TLC can be estimated using pulmonary artery pressure signal by determining FVC and using a calibrated value for residual volume.
A pulmonary artery pressure signal can also be used to evaluate, detect, monitor, predict and/or identify various disease states that impact pulmonary function parameters. Cardiopulmonary diseases can include those diseases that are related to pathological structural pulmonary changes (“structural pulmonary diseases”). Pathological structural pulmonary changes can include changes to the tissue, structure, or fluid in or around the lung. In some embodiments, the invention includes a method for detecting pulmonary symptoms of a disorder including obtaining a pulmonary artery pressure signal from a pressure sensor and monitoring the pulmonary artery pressure signal to identify a change in the signal over a baseline value. In some embodiments, the invention includes a method for detecting a pathological change to a tissue, structure, or fluid volume in or around the lung, the method including establishing a baseline signal pulmonary artery pressure signal with a pressure sensor and monitoring the pulmonary artery pressure signal to identify a change in the pulmonary artery pressure signal compared to the baseline signal.
Referring now to
Specific examples of structural pulmonary diseases can include pulmonary edema, pulmonary embolism, pleural effusion, pulmonary arteriovenous malformation, combined obstructive pulmonary disease (COPD), asthma, and emphysema, amongst others. These diseases can affect various hemodynamic and/or pulmonary parameters. As described above, many hemodynamic and pulmonary parameters can be calculated or estimated based on a pulmonary artery pressure signal.
Pulmonary edema is a condition in which there is fluid accumulation in the lungs. Frequently, pulmonary edema is associated with heart failure. The accumulation of fluid in the lungs associated with pulmonary edema typically results a rapid and shallow (low tidal volume) breathing pattern. Monitoring of a pulmonary artery pressure signal can be used to identify this rapid and shallow breathing pattern. Specifically, a pulmonary artery pressure signal can be processed, as described above, in order to calculate and/or estimate both a breathing rate and a tidal volume. Values for breathing rate and tidal volume can then be evaluated to detect a breathing pattern consistent with pulmonary edema. Referring now to
In some embodiments, if pulmonary parameters are consistent with a diagnosis of pulmonary edema, the event can be flagged and logged and/or an alert can be generated. This alert can be transmitted to a care provider for further action. For example, the alert can be transmitted to a care provider during interrogation of the device, such as during an office visit. As a further example, the alert can be delivered to a care provider through an advanced patient management system such as the LATITUDE® patient management system, commercially available from Boston Scientific Corporation, Natick, Mass. Aspects of an exemplary advanced patient management system are described in U.S. Pat. No. 6,978,182, the contents of which are herein incorporated by reference. As pulmonary edema can be progressive condition, in some embodiments, monitoring can be performed over a period of time to monitor the severity of the condition. By way of example, data regarding pulmonary parameters can be stored by the system and then compared with data taken in real-time. In this manner, an indication of whether the condition is improving or worsening can be derived.
A pulmonary embolism is where a blood clot lodges in the lumen (open cavity) of a pulmonary artery, occluding the artery and causing dysfunction. Pulmonary emboli (clots) often originate in the deep leg veins and travel to the lungs through blood circulation. A pulmonary embolism can be manifested by a rapid and shallow (low tidal volume) breathing pattern and, in some cases, coughing. In addition, the pressure of blood in the pulmonary artery would be expected to rapidly rise in response to a pulmonary embolism. The specific degree to which pulmonary artery pressure would rise would depend on various factors including the size of the embolus and where the embolus is lodged in the pulmonary arterial vasculature.
Monitoring of a pulmonary artery pressure signal can be used to identify a pulmonary embolism. Specifically, a pulmonary artery pressure signal can be monitored to identify a rapid and shallow breathing pattern. A pulmonary artery pressure signal can be processed, as described above, in order to calculate and/or estimate both a breathing rate and a tidal volume. Values for each of these pulmonary parameters can then be evaluated in order to detect a pulmonary embolism. Monitoring of a pulmonary artery pressure signal can also be used to identify coughing. Referring now to
In some embodiments, if pulmonary parameters are consistent with a diagnosis of a pulmonary embolism, the event can be flagged and logged and/or an alert can be generated by the system. This alert can be transmitted to a care provider for further action, such as through an advanced patient management system. Because a pulmonary embolism is usually caused by a blood clot lodging in a major pulmonary artery, the symptoms associated with a pulmonary embolism frequently appear quickly. As such, in some embodiments, the rapid onset of a rapid and shallow breathing pattern can be interpreted by the system as an indication of a pulmonary embolism.
Pleural effusion refers to a condition involving the buildup of fluid between the membranes that line the lungs and chest cavity (the pleura), causing compression of the lungs, which can lead to breathing difficulty. Pleural effusion can be manifested as a rapid and shallow (low tidal volume) breathing pattern. Monitoring of a pulmonary artery pressure signal can be used to identify this rapid and shallow breathing pattern (such as the rapid and shallow pattern illustrated in
In some embodiments, if pulmonary parameters are consistent with a diagnosis of pleural effusion, the event can be flagged and logged and/or an alert can be generated by the system. This alert can be transmitted to a care provider for further action, such as through an advanced patient management system. As pleural effusion can be progressive condition, in some embodiments, monitoring can be performed over a period of time to monitor the severity of the condition. By way of example, data regarding pulmonary parameters can be stored by the system and then compared with data taken in real-time. In this manner, an indication of whether the condition is improving or worsening can be derived.
Pulmonary arteriovenous malformation (PAVM) refers to a malformation of the vasculature resulting in direct intrapulmonary connections between the pulmonary arteries and veins without an intervening capillary bed. This causes a right to left shunt with peripheral arterial oxygen desaturation. PAVM may result in lowered blood pressure within the pulmonary artery as the resistance to blood flow normally generated by an intervening capillary bed is reduced. Monitoring of a pulmonary artery pressure signal can be used to identify a reduced amount of pressure within the pulmonary artery. Referring now to
Chronic obstructive pulmonary disease (COPD) is a disease state characterized by airflow obstruction caused by chronic bronchitis, emphysema, or both. Emphysema is a pathological condition of the lungs marked by an abnormal increase in the size of the air spaces, resulting in labored breathing and an increased susceptibility to infection. It can be caused by irreversible expansion of the alveoli or by the destruction of alveolar walls. COPD and emphysema can be manifested by a breathing pattern that is both rapid and shallow, in addition to a shortened expiration time. Referring now to
Monitoring of a pulmonary artery pressure signal can be used to identify a rapid and shallow breathing pattern. Specifically, a pulmonary artery pressure signal can be processed, as described above, in order to calculate and/or estimate both a breathing rate and a tidal volume. Values for breathing rate and tidal volume can then be evaluated to detect a breathing pattern consistent with COPD and/or emphysema. In addition, monitoring of a pulmonary artery pressure signal can be used to estimate expiration time. Expiration time can be used in conjunction with the rapid and shallow breathing pattern to suggest a diagnosis of COPD or emphysema. In some embodiments, if pulmonary parameters are consistent with a diagnosis of COPD or emphysema, the event can be flagged and logged and/or an alert can be generated by the system. This alert can be transmitted to a care provider for further action, such as through an advanced patient management system. As COPD and emphysema can be progressive, chronic conditions, in some embodiments, monitoring can be performed over a period of time to monitor the severity of the condition. By way of example, data regarding pulmonary parameters can be stored by the system and then compared with data taken in real-time. In this manner, an indication of whether the condition is improving or worsening can be derived.
Asthma is a chronic respiratory disease, often arising from allergies, that is characterized by sudden recurring attacks of labored breathing, chest constriction, and coughing. Asthma can be manifested by coughing and/or reduced peak air flow. In some cases, asthmas can be manifested by lengthened expiration time.
Monitoring of a pulmonary artery pressure signal can be used to identify symptoms consistent with asthma including coughing, reduced peak air flow, and/or lengthened expiration time. Specifically, a pulmonary artery pressure signal can be processed, as described above, in order to determine whether or not a patient is coughing. Coughing can be manifested as one or more sharp rises in pressure. In addition, a pulmonary artery pressure signal can be processed, as described above, in order to estimate peak air flow and this can be compared with stored values for peak air flow in order to determine whether or not there has been a reduction. Finally, the pulmonary artery pressure signal can be processed, as described above, in order to estimate expiration time. Expiration time can be compared with inspiration time in order to determine whether expiration time is lengthened. The presence of one or more of these symptoms can be indicative of asthma.
Referring now to
It will be appreciated that detection of various abnormalities in pulmonary function may not always be specific enough to provide for differential diagnosis of the condition. However, detection of pulmonary symptoms is still of significant value even in the absence of differential diagnosis. For example, pulmonary symptoms such as rapid and shallow breathing, coughing, increases or decreases in pressure, and the like can be tracked and/or logged and later conveyed to a care provider. For example, detection of spikes in pressure characteristic of coughing can be logged and then later provided to a care provider along with a time stamp of when they occurred in order to provide information about a patient's pulmonary function.
In some embodiments, the invention includes methods or detecting, trending, and/or predicting diseases, conditions, and symptoms associated with a permanent or temporary pathological change to airflow (“airway disorders”). By way of example, such diseases, conditions, and/or symptoms can include snoring, sleep apnea, hypopnea, hyperpnea, dyspnea, tachypnea, Cheyne-Stokes syndrome and the like.
Snoring refers to breathing during sleep with a rough hoarse noise due to vibration of the soft palate. Sleep apnea refers to a group of disorders in which breathing during sleep stops for at least ten seconds during sleep. Hypopnea refers to abnormally slow or shallow breathing. Hyperpnea refers to abnormally rapid or deep breathing. Dyspnea refers to difficult or labored breathing. Tachypnea refers to abnormally rapid breathing. Cheyne-Stokes syndrome (or Cheyne-Stokes respiration) is characterized by regularly alternating periods of apnea and hyperpnea. Because these disorders include effects on respiration, monitoring of respiration as calculated from a pulmonary artery pressure signal can provide useful information on the scope, severity, and/or progression of the disorder.
In an embodiment, the invention includes a method for detecting a disorder affecting airflow including obtaining a pulmonary artery pressure signal from a pressure sensor; and monitoring the pulmonary artery pressure signal to identify a respiration pattern consistent with the disorder. By way of example, referring now to
Therapies that can be used to treat airway disorders can include continuous positive airway pressure (CPAP), bi-level positive airway pressure (BiPAP), electrical diaphragm stimulation (EDS), and the like. In some embodiments, the invention can include methods of initiating or modifying respiratory therapy based on the occurrence and/or degree of airway dysfunction. By way of example, a method can include continuously collecting cardiopulmonary information as feedback on the application of therapy and then adjusting the internal or external respiratory therapy as indicated.
As a specific example, continuous positive airway pressure (CPAP) is frequently used to treat obstructive sleep apneas and involves the delivery of compressed air into the nasal passage of a patient, typically via a mask. The CPAP machine blows air at a prescribed pressure (the “titrated pressure”). The necessary pressure is usually determined by a physician after review of an overnight sleep study in a sleep laboratory. The titrated pressure is the pressure of air at which most (if not all) apneas and hypopneas have been prevented, and it is usually measured in centimeters of water (cm/H2O). CPAP machine generally can deliver pressures between 4 and 30 cm. CPAP is believed to work by pneumatically splinting the upper airway, decreasing the severity of obstruction.
Although CPAP has no serious side effects in most patients with sleep apnea, there are several minor pressure related side effects that reduce patient compliance and quality of life. Side effects can include dryness, burning, and congestion of the nasal mucosa, discomfort exhaling against the pressure, chest wall discomfort, middle ear discomfort, mask and machine noise, conjunctivitis from leaks into the eyes, and air swallowing. The incidence of side effects generally goes up with increased pressure. As such, a “pressure titration” is usually performed for a given patient to find a pressure that makes a reasonable trade-off between increasing effectiveness at eliminating respiratory related events and avoiding unpleasant side effects.
Embodiments of the present invention can include methods of automatically titrating the respiratory therapy delivered. For example, methods of the invention can include adjusting the pressure of air delivered during CPAP therapy based on pulmonary information as derived from a pulmonary artery pressure signal. In some embodiments, when breathing patterns are detected that indicate the upper airway is not sufficiently open, such as apnea or hypopnea, the pressure of air delivered during CPAP therapy is automatically increased.
In some embodiments, titration can proceed by gradually increasing air pressure until symptoms, such as apnea or hypopnea, disappear. For example, referring now to
In other embodiments, titration can proceed by gradually decreasing air pressure until signs, such as apnea or hypopnea, appear. In some embodiments, titration can include both gradually increasing air pressure and gradually decreasing air pressure and monitoring for signs such as apnea or hypopnea in both circumstances.
A signal from a pulmonary artery pressure sensor can be processed by an implantable device and then information regarding the desired air pressure can be transmitted to a CPAP device. Alternatively, a signal from a pulmonary artery pressure sensor can be transmitted directly to a CPAP device which can process the pulmonary artery pressure signal in order to determine whether air pressure should be increased or not.
BiPAP is similar to CPAP but provides two levels of pressure, a higher pressure during inhalation and a lower pressure during exhalation. As such, methods of titration based on a pulmonary artery pressure signal as described above are also applicable in the context of BiPAP therapy.
Information about the cardiopulmonary status of a patient, can also be used to aid in the diagnosis and monitoring of sleeping disorders. Sleeping disorders are a significant problem affecting, by some estimates, almost 15% of the population. The broad category of sleep disorders can involve difficulties related to sleeping, including difficulty falling or staying asleep, falling asleep at inappropriate times, excessive total sleep time, or abnormal behaviors associated with sleep.
An exemplary sleeping disorder is sleep apnea. Sleep apneas are defined as conditions where breathing is interrupted by at least ten seconds during sleep. This can occur up to hundreds of times per night with incidence resulting in disturbed sleep. Sleep apneas can include both obstructive sleep apneas and central sleep apneas. Obstructive sleep apneas are where the interruption in breathing is caused by an airway obstruction. Central sleep apneas are where the interruption in breathing is caused by a problem with central nervous system control of breathing.
In an embodiment, the invention includes a method of detecting a sleeping disorder comprising measuring a pulmonary artery pressure signal with a pressure sensor; and monitoring the pulmonary artery pressure signal to identify a breathing pattern indicative of a sleeping disorder. Sleeping disorders that can be detected by can include sleep apneas, both obstructive sleep apneas and central sleep apneas. As described above with reference to
In some embodiments, data regarding sleeping disorders or disturbed breathing events such as apneas as detected through monitoring of a pulmonary artery pressure signal can be used in a closed loop system for controlling pacing therapy as delivered by an implantable cardiac rhythm management (CRM) device such as a pacemaker or another CRM device including pacing functions. While not intending to be bound by theory, it is believed that some types of sleep disorders can affect cardiac rhythm. Embodiments of the invention can include methods of controlling pacing therapy as delivered by an implantable CRM device in order to counteract changes to cardiac rhythm caused by a sleeping disorder or a disturbed breathing event. It is also believed that changes to cardiac pacing can act to ameliorate some sleeping disorders or reduce the incidence of disturbed breathing events, at least in some patients. For example, it is believed that increasing the pacing rate can have a positive effect on some patients with sleeping disorders or exhibiting disturbed breathing events. In an embodiment, the invention includes a method of providing closed loop therapy including monitoring a pulmonary artery pressure signal for changes indicative of a sleeping disorder or a disturbed breathing event and controlling pacing therapy parameters in a manner so as to respond to the sleeping disorder or disturbed breathing event. The term “closed loop”, as used herein, shall refer to a system in which therapy is regulated by system feedback without human intervention. Specifically, in some embodiments the pacing rate of a cardiac rhythm management (CRM) device can be increased in response to the detection of a sleeping disorder or a disturbed breathing event.
Information about the cardiopulmonary status of a patient, as gained through a pulmonary artery pressure signal, can be also be used to monitor sleeping habits, sleep quality, and/or sleep characteristics of patients. By way of example, a pulmonary artery pressure signal can be processed in order to derive information regarding the onset, termination, duration, stages, and quality of sleep experienced by a patient. Furthermore, this information can be trended over a period of time and can provide insight into the emotional and physical health of a patient.
The onset or termination of sleep can be manifested by various effects on cardiopulmonary parameters. By way of example, the onset or termination of sleep can affect heart rate, tidal volume, minute ventilation, blood pressure, and the like. A pulmonary artery pressure signal can be utilized to derive such cardiopulmonary parameters. Therefore, monitoring of a pulmonary artery pressure signal can be used to gather information regarding the occurrence or nature of a sleep event, such as the onset, termination, duration, stages, and quality of sleep experienced by a patient.
Referring now to
As a specific example, in some studies, heart rate has been found to decrease during the onset of sleep, attributed to a relative increase in parasympathetic tone. Heart rate can be derived from a pulmonary artery pressure signal as described above with reference to
As another specific example, in some studies, minute ventilation has been found to decrease by greater than 10% during sleep as a result of reduced tidal volume after the onset of sleep. Tidal volume and minute ventilation can be derived from a pulmonary artery pressure signal as outlined above. In some embodiments, a reduction in minute ventilation and/or a reduction in tidal volume beyond a threshold amount can be interpreted as an indicator of the onset of sleep.
For most patients, blood pressure decreases with the onset of sleep. In some embodiments, a reduction in blood pressure beyond a threshold amount can be interpreted as an indicator of the onset of sleep. In some embodiments, a reduction in pulmonary artery blood pressure beyond a threshold amount can be interpreted as an indicator of the onset of sleep.
In some embodiments, the onset or termination of sleep may be detected by combining data regarding a plurality of cardiopulmonary parameters as derived from a pulmonary artery signal. For example, in some embodiments, the reduction in pulmonary artery blood pressure beyond a threshold amount in combination with a reduction in minute ventilation and/or a reduction in tidal volume beyond a threshold amount is interpreted as an indicator of the onset of sleep.
In some embodiments, the onset or termination of sleep may be detected by combining data regarding cardiopulmonary parameters with other data or signals. By way of example, in some embodiments, sleep can be detected by combining information regarding cardiopulmonary parameters with information regarding a patient's posture, the time of day, accelerometer data, eye movement data, electroencephalogram (EEG) data, muscle tone data, body temperature data, pulse oximetry data, and the like.
It should be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
It should also be noted that, as used in this specification and the appended claims, the phrase “configured” describes a system, apparatus, or other structure that is constructed or configured to perform a particular task or adopt a particular configuration. The phrase “configured” can be used interchangeably with other similar phrases such as “arranged”, “arranged and configured”, “constructed and arranged”, “constructed”, “manufactured and arranged”, and the like.
All publications and patent applications in this specification are indicative of the level of ordinary skill in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated by reference.
This application is intended to cover adaptations or variations of the present subject matter. It is to be understood that the above description is intended to be illustrative, and not restrictive. The scope of the present subject matter should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.