Patent Publication Number: US-2020288989-A1

Title: Measuring cardiovascular pressure based on patient state

Description:
TECHNICAL FIELD 
     The disclosure relates to medical device systems, more particularly, measurement of cardiovascular pressure by medical device systems. 
     BACKGROUND 
     Various implantable medical devices have been clinically implanted or proposed for therapeutically treating or monitoring one or more physiological conditions of a patient. Such devices may be adapted to monitor or treat conditions or functions relating to heart, muscle, nerve, brain, stomach, endocrine organs or other organs and their related functions. Advances in design and manufacture of miniaturized electronic and sensing devices have enabled development of implantable devices capable of therapeutic as well as diagnostic functions such as pacemakers, cardioverters, defibrillators, biochemical sensors, and pressure sensors, among others. Such devices may be associated with leads to position electrodes or sensors at a desired location, or may be leadless, with the ability to wirelessly transmit data either to another device implanted in the patient or to another device located externally of the patient, or both. 
     By way of illustrative example, implantable miniature sensors have been proposed and used in blood vessels to measure directly the diastolic, systolic and mean blood pressures, as well as body temperature and cardiac output. As one example, patients with chronic cardiovascular conditions, particularly patients suffering from chronic heart failure, may benefit from the use of implantable sensors adapted to monitor blood pressures. As another example, subcutaneously implantable monitors have been proposed and used to monitor heart rate and rhythm, as well as other physiological parameters, such as patient posture and activity level. Such direct in vivo measurement of physiological parameters may provide significant information to clinicians to facilitate diagnostic and therapeutic decisions. If linked electronically to another implanted therapeutic device (e.g., a pacemaker), the data can be used to facilitate control of that device. Such devices also, or alternatively, may be wirelessly linked to an external receiver. 
     SUMMARY 
     In general, this disclosure is directed to techniques for measuring cardiovascular pressure. The example techniques may include measuring cardiovascular pressure of a patient within a predetermined window of time during the day. A medical device may also determine the state, e.g., posture, activity level, and/or heart rate, of the patient at the time of each cardiovascular pressure measurement. The measurement of cardiovascular pressure may be stored or discarded based on whether the state of the patient at the time of the cardiovascular pressure measurement was a target state, e.g., target posture. In some examples, the cardiovascular pressure measurements taken when the patient is in the target state may be used to evaluate the condition of the patient. 
     As one example, the disclosure is directed to a method for monitoring a cardiovascular pressure in a patient, the method including measuring, by pressure sensing circuitry of an implantable pressure sensing device, the cardiovascular pressure of the patient. The method further includes transmitting, via wireless communication circuitry of the implantable pressure sensing device, the measured cardiovascular pressure to another device. The method further includes determining, by processing circuitry of the other device, whether a posture of the patient at a time of the measured cardiovascular pressure was a target posture for cardiovascular pressure measurements. The method further includes determining, by the processing circuitry of the other device, whether to store or discard the transmitted cardiovascular pressure based on determining whether the posture was the target posture. 
     A medical device system for monitoring a cardiovascular pressure in a patient, the medical device system including an implantable pressure sensing device including wireless communication circuitry and pressure sensing circuitry configured to measure the cardiovascular pressure of the patient. The implantable pressure sensing device further includes processing circuitry configured to control the pressure sensing circuitry to measure the cardiovascular pressure of the patient. The processing circuitry of the implantable pressure sensing device is further configured to transmit the measured cardiovascular pressure to another device via the wireless communication circuitry. The medical device system further includes the other device including processing circuitry configured to determine whether a posture of a patient at the time of the measured cardiovascular pressure was a target posture for cardiovascular pressure measurements. The processing circuitry of the other device is further configured to determine whether to store or discard the transmitted cardiovascular pressure based on determining whether the posture was the target posture. 
     As another example, the disclosure is directed to a method for monitoring a cardiovascular pressure in a patient, the method including determining, by processing circuitry of an implantable monitoring device, that a time of day is within a predetermined window for cardiovascular pressure measurements. The method further includes sensing, with sensing circuitry of the implantable monitoring device, posture of the patient during the predetermined window in response to the determination. The method further includes determining, by the processing circuitry of the implantable monitoring device, that the sensed posture of the patient is a target posture for cardiovascular pressure measurements. The method further includes sending a trigger signal, via wireless communication circuitry of the implantable monitoring device, to an implantable pressure sensing device, wherein the implantable pressure sensing device measures the cardiovascular pressure of the patient using pressure sensing circuitry in response to the trigger signal. The method further includes receiving, by the processing circuitry of the implantable monitoring device, the measured cardiovascular pressure of the patient from the implantable pressure sensing device via the wireless communication circuitry of the implantable monitoring device. 
     As another example, the disclosure is directed to a medical device system for monitoring a cardiovascular pressure in a patient, where the medical device system comprises an implantable monitoring device comprising wireless communication circuitry, processing circuitry configured to determine that a time of day is within a predetermined window for cardiovascular pressure measurements, and sensing circuitry configured to sense a posture of the patient during the predetermined window in response to the determination. The processing circuitry is further configured to determine that the sensed posture of the patient is a target posture for cardiovascular pressure measurements. The wireless communication circuitry is configured to send a trigger signal to an implantable pressure sensing device. The medical device system further comprises the implantable pressure sensing device comprising wireless communication circuitry configured to receive the trigger signal and pressure sensing circuitry configured to measure the cardiovascular pressure of the patient in response to the trigger signal. The wireless communication circuitry of the implantable pressure sensing device is further configured to transmit the measured cardiovascular pressure of the patient to the implantable monitoring device. 
     As another example, the disclosure is directed to a method for monitoring a cardiovascular pressure in a patient, the method comprising determining, by processing circuitry of an implantable pressure sensing device, that a time of day is within a predetermined window for cardiovascular pressure measurements. The method further includes measuring, by pressure sensing circuitry of the implantable pressure sensing device, the cardiovascular pressure of the patient in response to the determination. The method also includes transmitting, via wireless communication circuitry of the implantable pressure sensing device, the measured cardiovascular pressure to another device. The method includes determining, by processing circuitry of the other device, whether a posture of the patient at the time of day was a target posture for cardiovascular pressure measurements, wherein the target posture comprises a supine posture, a right-side-down posture when the implantable pressure sensing device is implanted in the left pulmonary artery, or a left-side-down posture when the implantable pressure sensing device is implanted in the right pulmonary artery. The method further includes determining, by the processing circuitry of the other device, whether to store or discard the transmitted cardiovascular pressure based on determining whether the posture was the target posture. 
     This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the apparatus and methods described in detail within the accompanying drawings and description below. The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The details of one or more examples of this disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of this disclosure will be apparent from the description and drawings, and from the claims. 
         FIG. 1A  is a conceptual drawing illustrating an example medical device system in conjunction with a patient. 
         FIG. 1B  is a conceptual diagram illustrating another example medical device system in conjunction with a patient. 
         FIG. 2A  illustrates a side profile view of an example sensor assembly. 
         FIG. 2B  illustrates a side profile view of another example sensor assembly. 
         FIG. 3A  illustrates a bottom perspective view of the example sensor assembly of  FIG. 2A . 
         FIG. 3B  illustrates a side cross-sectional view of the example sensor assembly of  FIG. 2A . 
         FIG. 4A  is an exploded perspective view of example configurations of an example sensor assembly. 
         FIG. 4B  is an exploded perspective view of example configurations of an example sensor assembly. 
         FIG. 5  is a conceptual drawing illustrating an example configuration of an insertable cardiac monitor. 
         FIG. 6  is a functional block diagram illustrating an example configuration of an implantable medical device. 
         FIG. 7  is a functional block diagram illustrating an example configuration of implantable pressure sensing device. 
         FIG. 8  is a functional block diagram illustrating an example system that includes external computing devices. 
         FIG. 9  is a block diagram illustrating another example system that includes external computing devices. 
         FIG. 10  is a flowchart illustrating an example technique that may be implemented by implantable medical device, in accordance with this disclosure. 
         FIG. 11  is a flowchart illustrating an example technique that may be implemented by an implantable pressure sensing device, in accordance with this disclosure. 
         FIG. 12  is a flowchart illustrating an example technique that may be implemented by devices of a medical device system, in accordance with this disclosure. 
         FIG. 13  is a flowchart illustrating an example technique that may be implemented by devices of a medical device system, in accordance with this disclosure. 
     
    
    
     The drawings and the description provided herein illustrate and describe various examples of the inventive methods, devices, and systems of the present disclosure. However, the methods, devices, and systems of the present disclosure are not limited to the specific examples as illustrated and described herein, and other examples and variations of the methods, devices, and systems of the present disclosure, as would be understood by one of ordinary skill in the art, are contemplated as being within the scope of the present application. 
     DETAILED DESCRIPTION 
     Cardiovascular pressure, such as pulmonary artery pressure (PAP), may be significantly affected by body position or orientation during the pressure measurement. Consequently, PAP is traditionally clinically measured with the patient at rest, awake, and supine (i.e., lying on their back). An implantable pressure sensing device may unobtrusively take measurements under similar conditions by being configured to measure PAP (or other cardiovascular pressure measurements) at night, e.g., between midnight and 4 am, when the patient is more likely to be at rest and supine. 
     However, a patient may not necessarily be asleep at night when the automatic pressure measurements are scheduled and, if asleep, may not be in the supine posture. Posture (e.g., body position or orientation) may significantly affect the cardiovascular pressure value measured by an implantable pressure sensing device due to changes in cardiac output and the hydrostatic blood column above sensing device. For example, in an experiment using a porcine model, the pressure in the left pulmonary artery increased by 12 mmHg when the position was changed from dorsal down recumbency to left lateral recumbency. 
     This disclosure describes example techniques related to measuring cardiovascular pressure within a predetermined window of time during the day. The measurements may be matched with concurrent measurements of patient state, e.g., posture, activity level, and/or heart rate, where the cardiovascular pressure measurements are discarded or stored based on the patient state measurements. As a result, the stored cardiovascular pressure measurements may form a dataset with similar patient state, allowing a practitioner to better evaluate the condition of the patient, e.g., whether the condition of the patient changed from over time. In the following description, references are made to illustrative examples. It is understood that other examples may be utilized without departing from the scope of the disclosure. 
       FIG. 1A  is a conceptual drawing illustrating an example medical device system  8 A in conjunction with a patient  2 A. Medical device system  8 A is an example of a medical device system configured to implement the techniques described herein for monitoring cardiovascular pressure and other physiological parameters of patient  2 A, such as blood pressure and body position or posture, patient motion or activity, and/or heart rate, and determining whether to store or discard a measurement of cardiovascular pressure based on the state of patient  2 A at the time of the cardiovascular pressure measurement. In the illustrated example, medical device system  8 A includes an implantable medical device (IMD)  15 A, also referred to as implantable monitoring device  15 A or an implantable hub device, in communication with external device  14 A. Medical device system  8 A also includes implantable pressure sensing device  12 A, also referred to as sensor device  12 A or sensor device  12 A. For purposes of this description, knowledge of cardiovascular anatomy is presumed and details are omitted except to the extent necessary or desirable to explain the context of the techniques of this disclosure. 
     As shown in  FIG. 1A , implantable sensor assembly  10 A may be implanted within pulmonary artery  6 A of heart  4 A. In some examples, pulmonary artery  6 A of heart  4 A may comprise a left pulmonary artery, and pulmonary artery  6 B may comprise a right pulmonary artery. Although  FIG. 1A  depicts sensing device  12 A positioned in a descending branch of the left pulmonary artery, sensing device  12 A may positioned elsewhere with the left pulmonary artery, in the right pulmonary artery, or any suitable region of the patient&#39;s cardiovascular system. For the sake of clarity, a fixation assembly for sensor assembly  10 A is not depicted in  FIG. 1A . A suitable fixation assembly configured to secure sensor assembly  10 A within pulmonary artery  6 A will be discussed below with respect to  FIGS. 2A-4B . 
     In the illustrated example, IMD  15 A is an insertable cardiac monitor (ICM) capable of sensing and recording cardiac electrogram (EGM) signals from a position outside of heart  4 A via electrodes, and will be referred to as ICM  15 A hereafter. In some examples, ICM  15 A includes or is coupled to one or more additional sensors, such as accelerometers, that generate one or more signals that vary based on patient motion and/or posture, blood flow, or respiration. ICM  15 A may monitor a physiological parameter indicative of patient state, such as posture, heart rate, activity level, heart rate, and/or respiration rate, and ICM  15 A may measure the physiological parameter(s) at times when sensor device  12 A is measuring cardiovascular pressure. ICM  15 A may include processing circuitry to determine whether the measured posture of patient  2 A is a target posture for cardiovascular pressure measurements, wherein the target posture may include a supine posture, i.e., lying on one&#39;s back. ICM  15 A may be implanted outside of the thorax of patient  2 A, e.g., subcutaneously or submuscularly, such as the pectoral location illustrated in  FIG. 1A . ICM  15 A may be positioned near the sternum near or just below the level of heart  4 A. In some examples, ICM  15 A may take the form of a Reveal LINQ™ ICM, available from Medtronic plc, of Dublin, Ireland. 
     Sensor device  12 A may be implanted, as one example, within a pulmonary artery of patient  2 A and may include pressure sensing circuitry configured to measure the cardiovascular pressure of patient  2 A. In some examples, sensor device  12 A may be a part of sensor assembly  10 A. Each of sensor device  12 A and ICM  15 A may include a timer and processing circuitry configured to determine a time of day based on the timer value. If sensor device  12 A determines that the current time is within a predetermined window that may be stored in memory of sensor device  12 A, sensor device  12 A may measure and transmit the cardiovascular pressure of patient  2 A to ICM  15 A. In some examples, sensor device  12 A may include wireless communication circuitry configured to receive a trigger signal from ICM  15 A. The pressure sensing circuitry of sensor device  12 A may be configured to measure the cardiovascular pressure of patient  2 A in response to receiving the trigger signal. In this manner, ICM  15 A may dictate the times at which sensor device  12 A measures cardiovascular pressure, and sensor device  12 A may enter a low-power mode such as sleep mode until the wireless communication circuitry of sensor device  12 A receives a trigger signal. 
     ICM  15 A may transmit posture data, and other physiological parameter data acquired by ICM  15 A, to external device  14 A. ICM  15 A may also transmit cardiovascular pressure measurements received from sensor device  12 A to external device  14 A. For example, ICM  15 A may transmit any data described herein related to cardiovascular pressure, posture, heart rate, activity level, respiration rate, and/or other physiological parameters to external device  14 A. In some examples, the processing circuitry of ICM  15 A may first determine whether to store or discard the cardiovascular pressure measurements based on the posture or other state of patient  2 A at the time of each cardiovascular pressure measurement. In some examples, processing circuitry of ICM  15 A may send all pressure measurements received from sensor device  12 A, along with patient state measurements made by ICM  15 A, to external device  14 A, and the external device or another networked computing device may determine whether to store or discard the cardiovascular pressure measurements based on the posture or other state of patient  2 A at the time of each cardiovascular pressure measurement. For purposes of this disclosure, a cardiovascular pressure measurement may include one or more numerical values such as a systolic value and/or a diastolic value, a waveform of the cardiovascular pressure, and/or any other data relating to cardiovascular pressure. 
     External device  14 A may be a computing device, e.g., used in a home, ambulatory, clinic, or hospital setting, to communicate with ICM  15 A via wireless telemetry. External device  14 A may be coupled to a remote patient monitoring system, such as Carelink®, available from Medtronic plc, of Dublin, Ireland. External device  14 A may be, as examples, a programmer, external monitor, or consumer device, e.g., smart phone. In some examples, external device  14 A may receive time-stamped data from ICM  15 A. The time-stamped data may include measurements of cardiovascular pressure, the posture of patient  2 A, and other parameters such as heart rate and respiration rate. The remote patient monitoring system may correlate and assess the time-stamped data as described further herein. 
     External device  14 A may be used to program commands or operating parameters into ICM  15 A for controlling its functioning, e.g., when configured as a programmer for ICM  15 A. External device  14 A may be used to interrogate ICM  15 A to retrieve data, including device operational data as well as physiological data accumulated in IMD memory. The interrogation may be automatic, e.g., according to a schedule, or in response to a remote or local user command. Programmers, external monitors, and consumer devices are examples of external devices  14 A that may be used to interrogate ICM  15 A. Examples of communication techniques used by ICM  15 A and external device  14 A include radiofrequency (RF) telemetry, which may be an RF link established via Bluetooth, WiFi, or medical implant communication service (MICS). 
     Medical device system  8 A is an example of a medical device system configured to monitor the cardiovascular pressure of patient  2 A. The techniques described herein may be performed by processing circuitry of medical device system  8 A, such as processing circuitry of one or more of ICM  15 A, sensor device  12 A, and external device  14 A, individually, or collectively. The techniques include determining a time of day and determining whether the time is within a predetermined window for cardiovascular pressure measurements. The pressure sensing circuitry of sensor device  12 A may measure the cardiovascular pressure of patient  2 A in response to determining that the time is within the predetermined window. The wireless communication circuitry of sensor device  12 A may transmit the measured cardiovascular pressure to ICM  15 A. 
     The processing circuitry of ICM  15 A may determine whether a posture of patient  2 A at the time of the cardiovascular pressure measurement was a target posture for cardiovascular pressure measurements. The processing circuitry of ICM  15 A may determine whether to store or discard the transmitted cardiovascular pressure based on determining whether the posture of patient  2 A was the target posture at the time of the cardiovascular pressure measurement. In some examples, the processing circuitry of sensor device  12 A or ICM  15 A may determine the time of day and whether the time is within the predetermined window. If the processing circuitry of ICM  15 A determines whether the time is within the predetermined window, ICM  15 A may send a triggering signal to sensor device  12 A, and sensor device  12 A may measure and transmit the cardiovascular pressure to ICM  15 A in response to receiving the triggering signal. In some examples, the communication between ICM  15 A and sensor device  12 A may be radio frequency communication, tissue conductive communication, and/or any other suitable form of communication. 
     Another example medical device system that may be configured to implement the techniques is described with respect to  FIG. 1B . Although described herein primarily in the context of implantable medical devices monitoring cardiovascular pressure, a medical device system that implements the techniques described in this disclosure may additionally or alternatively include an external medical device, e.g., external cardiac monitor, and/or external pacemaker, cardioverter and/or defibrillator, configured to process measurements of cardiovascular pressure and other parameters. 
       FIG. 1B  is a conceptual diagram illustrating another example medical device system  8 B in conjunction with a patient  2 B. In the illustrated example, medical device system  8 B includes a sensor assembly  10 B implanted, for example, in the patient&#39;s pulmonary artery  6 B through which blood flows from the heart  4 B to the lungs, and another IMD  15 B. Medical device system  8 B is another example of a medical device system configured to implement the techniques described herein for monitoring cardiovascular pressure and other physiological parameters of patient  2 B, such as blood pressure and body position or posture, patient motion or activity, and/or heart rate, and determining whether to store or discard a measurement of cardiovascular pressure based on the state of patient  2 B at the time of the cardiovascular pressure measurement. The sensor device  12 B, IMD  15 B, and external device  14 B in  FIG. 1B  may provide substantially similar functionality, e.g., with respect to the techniques described herein for monitoring cardiovascular pressure and other physiological parameters of a patient, as the like numbered device described above with respect to  FIG. 1A . 
     IMD  15 B may have one or more leads  18 ,  20 ,  22  including electrodes that are placed on or near selected portions of the cardiac anatomy in order to perform the functions of IMD  15 B as is well known to those skilled in the art. For example, IMD  15 B may be configured to sense and record cardiac EGM signals via the electrodes on leads  18 ,  20 ,  22 . IMD  15 B may also be configured to deliver therapeutic signals, such as pacing pulses, cardioversion shocks, or defibrillation shocks, to heart  4 B via the electrodes. In the illustrated example, IMD  15 B may be a pacemaker, cardioverter, and or defibrillator. 
     In some examples, this disclosure may refer to IMD  15 B, particularly with respect to its functionality as part of a medical device system that monitors cardiovascular pressure and other physiological parameters of a patient  2 , as an implantable monitoring device or implantable hub device. In some examples, IMD  15 B includes or is coupled to one or more additional sensors, such as accelerometers, that generate one or more signals that vary based on patient motion and/or posture, blood flow, or respiration. IMD  15 B may monitor a physiological parameter indicative of patient state, such as posture, heart rate, activity level, heart rate, and/or respiration rate, and ICM  15 B may measure the physiological parameter(s) at times when sensor device  12 B is measuring cardiovascular pressure. IMD  15 B may include processing circuitry to determine whether the measured posture of patient  2 B is a target posture for cardiovascular pressure measurements, wherein the target posture may include a supine posture, i.e., lying on one&#39;s back. The target posture may also include lying on one&#39;s right side when sensor device  12 B is implanted in the left pulmonary artery, referred to as a right supine posture, or lying on one&#39;s left side when sensor device  12 B is implanted in the right pulmonary artery, referred to as a left supine posture. 
     IMD  15 B also may have wireless capability to receive and transmit, by telemetry, signals relating to operation of the device, and to receive programming commands. IMD  15 B may communicate wirelessly to an external device such as external device  14 B or to another implanted device such as a sensor device  12 B of the sensor assembly  10 B. For sake of clarity, sensor assembly  10 B is shown without a fixation assembly in  FIG. 1B . The sensor device  12 B also may communicate wirelessly with external device  14 B to provide in vivo data for selected physiological parameters to an external site to inform clinicians of the patient&#39;s status. In some examples, sensor device  12 B may communicate wirelessly and directly with external device  14 B, rather than communicating with external device  14 B through IMD  15 B. In a similar way, sensor device  12 A of  FIG. 1A  may communicate wirelessly and directly with external device  14 A. 
     Medical device system  8 B is an example of a medical device system configured to monitor the cardiovascular pressure of patient  2 B. The techniques described herein may be performed by processing circuitry of medical device system  8 B, such as processing circuitry of one or more of IMD  15 B, sensor device  12 B, and external device  14 B, individually, or collectively. The techniques include determining a time of day and determining whether the time is within a predetermined window for cardiovascular pressure measurements. The pressure sensing circuitry of sensor device  12 B may measure the cardiovascular pressure of patient  2 B in response to determining that the time is within the predetermined window. The wireless communication circuitry of sensor device  12 B may transmit the measured cardiovascular pressure to IMD  15 B. 
     The processing circuitry of IMD  15 B may determine whether a posture of patient  2 B at the time of the cardiovascular pressure measurement was a target posture for cardiovascular pressure measurements. The processing circuitry of IMD  15 B may determine whether to store or discard the transmitted cardiovascular pressure based on determining whether the posture of patient  2 B was the target posture at the time of the cardiovascular pressure measurement. In some examples, the processing circuitry of sensor device  12 B or IMD  15 B may determine the time of day and whether the time is within the predetermined window. If the processing circuitry of IMD  15 B determines whether the time is within the predetermined window, IMD  15 B may send a triggering signal to sensor device  12 B, and sensor device  12 B may measure and transmit the cardiovascular pressure to IMD  15 B in response to receiving the triggering signal. 
       FIGS. 2A-4B  illustrate examples of sensor assemblies adapted for minimally invasive placement in a patient&#39;s blood vessel, the assembly being shown in its expanded, deployment configuration. Turning first to  FIGS. 2A-2B , side profile views of example configurations of sensor assembly  10 A and sensor assembly  10 B (individually “sensor assembly  10 ” or collectively “sensor assemblies  10 ”) are depicted. Each of sensor assemblies  10  includes a sensor  12  coupled to fixation members  30 A,  30 B (collectively “fixation assembly  30 ”). The fixation assembly  30  and sensor  12  are arranged to enable the sensor assembly  10  to be provided in a delivery configuration that enables it to be navigated to an implant location where it can be deployed into the deployment configuration. As described in this disclosure, it should be understood that the delivery configuration defines a pitch, width or diameter that is narrower, in relation to the deployment configuration, along a common plane. Upon release, the fixation assembly expands into the deployment configuration so as to be in physical contact with the wall of the blood vessel to maintain the positional integrity of sensor device  12 . In one example, the fixation assembly will engage the interior wall of the vessel defining the blood flow lumen. The sensor device  12  is attached to the fixation assembly  30  in a manner such that the sensing element  32  of the sensor device  12  is spaced from the wall of the vascular lumen to minimize adverse obstruction to blood flow through the lumen and to position the sensing element  32  of the sensor device  12  to be fully exposed to the blood in the vessel, without obstruction from the housing of the sensor or the vessel wall. 
       FIG. 3A  illustrates a bottom perspective view of the sensor assembly  10 A and  FIG. 3B  illustrates a side cross-sectional view of the sensor assembly  10 A. The sensor device  12  includes a capsule  34  that forms a hermetically sealed housing that encloses the operational components such as the electronic circuitry of the sensor assembly  10 A. The capsule  34  defines longitudinal walls e.g., LW 1 , LW 2 , that extend from a first lateral side wall SW 1  to a second lateral sidewall SW 2 . The longitudinal walls define the longitudinal axis of the sensor device  12 . As will be described in more detail with reference to  FIG. 4 , the fixation members  30 A,  30 B are coupled to an exterior of the capsule  34  such as the first and second sidewalls, respectively. 
       FIGS. 4A and 4B  are exploded perspective views of example configurations of the example sensor assemblies  10 A and  10 B, respectively. The capsule  34  of the sensor device  12  may include an elongate body that defines an interior cavity. The interior cavity of the capsule  34  is sized and shaped to contain the battery  40 , and electronics and sensor components  42  of the sensor device  12 . The capsule  34  is preferably designed with shapes that are easily accepted by the patient&#39;s body while minimizing patient discomfort. For example, the body of capsule  34  may be formed in a cylindrical shape with cylindrical sidewalls. Other non-cylindrical configurations may be employed, however, in which case the corners and edges may be designed with generous radii to present a capsule having smoothly contoured surfaces. In the depicted example, the body of capsule  34  is formed as a generally rectangular structure, which means that the outline of the shape of capsule  34  resembles a rectangle with the edges and corners that are contoured. 
     The capsule  34  is preferably formed having two sections  36 ,  38 , one of which ( 36 ) can contain the sensing element  32 , such as a pressure sensing diaphragm, of sensor device  12 , while the other section ( 38 ) can contain the battery  40 , and electronics and sensor components  42  of the sensor device  12 . 
     The capsule  34  is formed from one or more biocompatible materials that can be hermetically sealed when the sections  36 ,  38  are joined. A number of such biocompatible materials may be employed, as will be understood by those familiar with the art, including metals and biocompatible plastics. For example, the sections  36 ,  38  may be formed from unalloyed titanium with an American Society for Testing and Materials (ASTM) grade 1 to grade 4 or an alloyed titanium (grade 5) that includes aluminum and vanadium. In some examples, section  36  may be formed from sapphire. For examples in which the sections are metal, the metal material of the capsule  34  may optionally be selected to be compatible with the fixation assembly  30  material so as to permit the fixation assembly  30  to be securely-coupled to the capsule  34 . In other examples, the capsule  34  along with the fixation assembly  30  may be integrally formed from one or more of the same or distinct materials. In some examples, the capsule  34 , as well as some portions of the fixation member  30 , may be encapsulated in a biologically inert dielectric barrier material such as a film of silicone or polyp-xylylene) polymer sold under the trademark PARYLENE. 
     As shown in  FIG. 4A , capsule  34  may include fasteners F 1 , F 2  that define channels for reception of a segment of the fixation assembly  30 . In the example of  FIG. 4B , capsule  34  may include fasteners F 3 , F 4  that define channels for reception of a segment of the fixation assembly  30 . The received segment may include a portion along a length of the fixation assembly  30  or a free end of the fixation assembly  30 . The fasteners F 1 -F 4  are coupled to an exterior of the capsule  34 , or in alternative examples, formed integrally with the capsule  34 . For example, as shown in the example of  FIG. 4A , the fasteners F 1 , F 2  are provided at an exterior of the capsule  34  at the lateral sidewalls SW 1 , SW 2 , respectively. In the alternative example of  FIG. 4B , the fasteners F 3 , F 4  are provided at spaced apart locations on an exterior of one or more of the longitudinal walls of the capsule  34 , such as the bottom longitudinal wall LW 2 . 
     In some examples, the fasteners are formed as pairs of tabs that are arranged to define one or more channel(s) for receiving one or more segment(s) of the fixation assembly  30 . Each fastener can include a pair of tabs that are aligned longitudinally as described, for example, in U.S. Pat. No. 8,864,676 to Beasley et al. which is incorporated herein by reference in its entirety. The fasteners may be coupled to the capsule  34  through welding, for example. Alternatively, the fasteners may be formed integrally with the capsule  34 , preferably on opposing ends of the capsule. However, the description of the fasteners F 1 -F 4  is not intended to be limiting, and rather, it is provided to explain the context of the invention. 
     In the examples of  FIGS. 4A-4B , the fasteners F 1 -F 4  are formed as tubular structures that define channels that are sized to receive a segment of each of the fixation members  30 A,  30 B. In some examples, the fasteners F 1 -F 4  may be formed as discrete components, such as tubes, for example, that can be coupled to the capsule  34  through coupling techniques such as welding or bonding agent such as glue or crimping. Alternatively, the fasteners may be formed integrally with the capsule  34 . As will be described in more detail below, the fixation assembly  30  is coupled to the fasteners F 1 -F 4  by any suitable coupling technique such as welding, crimping, bonding agent such as glue, frictional fit, etc. 
     The channels of fasteners F 1 -F 4  may optionally be defined to receive a segment of the fixation members  30 A,  30 B in a snug fit arrangement to prevent relative movement between the capsule  34  and the fixation assembly  30 . By way of dimensional example, the thickness of a cross section of fixation assembly  30  may be on the order of 0.006 inch for a round shape or 0.005 inch by 0.010 inch for a rectangular shape. In comparison, the diameter (or width) of the channel of each of the fasteners may be on the order of 0.010 inch to 0.025 inch. 
     The free ends of each of the fixation members  30 A,  30 B may be oriented in opposing directions. For example, a first of the free ends may be oriented downward in relation to the lateral sidewall SW 1 , SW 2 , while the other end may be oriented upward in relation to the lateral sidewalls SW 1 , SW 2  as shown in  FIG. 4A . Among other things, such an orientation can provide a degree of load cancellation that minimizes load transfer to the sensing element  32 . 
     In alternative examples, one of the fixation members e.g.,  30 A may be coupled along a lateral sidewall such as SW 1  as shown in  FIG. 4A , and the other of the fixation members e.g.,  30 B may be coupled to a longitudinal wall such as LW 1  or LW 2  as shown in  FIG. 4B . 
       FIG. 5  is a conceptual drawing illustrating an example configuration of ICM  15 A of  FIG. 1A . In the example shown in  FIG. 5 , ICM  15 A may be embodied as a monitoring device having housing  62 , proximal electrode  64  and distal electrode  66 . Housing  62  may further comprise first major surface  68 , second major surface  70 , proximal end  72 , and distal end  74 . Housing  62  encloses electronic circuitry located inside the ICM  15 A and protects the circuitry contained therein from body fluids. Electrical feedthroughs provide electrical connection of electrodes  64  and  66 . 
     In the example shown in  FIG. 5 , ICM  15 A is defined by a length L, a width W and thickness or depth D and is in the form of an elongated rectangular prism wherein the length L is much larger than the width W, which in turn is larger than the depth D. In one example, the geometry of the ICM  15 A—in particular a width W greater than the depth D—is selected to allow ICM  15 A to be inserted under the skin of the patient using a minimally invasive procedure and to remain in the desired orientation during insertion. For example, the device shown in  FIG. 5  includes radial asymmetries (notably, the rectangular shape) along the longitudinal axis that maintains the device in the proper orientation following insertion. For example, in one example the spacing between proximal electrode  64  and distal electrode  66  may range from thirty millimeters (mm) to fifty-five mm, thirty-five mm to fifty-five mm, and from forty mm to fifty-five mm and may be any range or individual spacing from twenty-five mm to sixty mm. In addition, ICM  15 A may have a length L that ranges from thirty mm to about seventy mm. In other examples, the length L may range from forty mm to sixty mm, forty-five mm to sixty mm and may be any length or range of lengths between about thirty mm and about seventy mm. In addition, the width W of major surface  68  may range from three mm to ten mm and may be any single or range of widths between three mm and ten mm. The thickness of depth D of ICM  15 A may range from two mm to nine mm. In other examples, the depth D of ICM  15 A may range from two mm to five mm and may be any single or range of depths from two mm to nine mm. In addition, ICM  15 A according to an example of the present disclosure is has a geometry and size designed for ease of implant and patient comfort. Examples of ICM  15 A described in this disclosure may have a volume of three cubic centimeters (cm) or less, one-and-a-half cubic cm or less or any volume between three and one-and-a-half cubic centimeters. In addition, in the example shown in  FIG. 5 , proximal end  72  and distal end  74  are rounded to reduce discomfort and irritation to surrounding tissue once inserted under the skin of the patient. In some examples, ICM  15 A, including instrument and method for inserting ICM  15 A is configured as described, for example, in U.S. Patent Publication No. 2014/0276928, incorporated herein by reference in its entirety. In some examples, ICM  15 A is configured as described, for example, in U.S. Patent Publication No. 2016/0310031, incorporated herein by reference. 
     In the example shown in  FIG. 5 , once inserted within the patient, the first major surface  68  faces outward, toward the skin of the patient while the second major surface  70  is located opposite the first major surface  68 . Consequently, the first and second major surfaces may face in directions along a sagittal axis of patient  2 A (see  FIG. 1 ), and this orientation may be consistently achieved upon implantation due to the dimensions of ICM  15 A. Additionally, an accelerometer, or axis of an accelerometer, may be oriented along the sagittal axis. 
     Proximal electrode  64  and distal electrode  66  are used to sense cardiac signals, e.g. ECG signals, intra-thoracically or extra-thoracically, which may be sub-muscularly or subcutaneously. ECG signals may be stored in a memory of the ICM  15 A, and ECG data may be transmitted via integrated antenna  82  to another medical device, which may be another implantable device or an external device, such as external device  14 A. In some example, electrodes  64  and  66  may additionally or alternatively be used for sensing any bio-potential signal of interest, which may be, for example, an EGM, electroencephalogram (EEG), electromyogram (EMG), or a nerve signal, from any implanted location. 
     In the example shown in  FIG. 5 , proximal electrode  64  is in close proximity to the proximal end  72  and distal electrode  66  is in close proximity to distal end  74 . In this example, distal electrode  66  is not limited to a flattened, outward facing surface, but may extend from first major surface  68  around rounded edges  76  and/or end surface  78  and onto the second major surface  70  so that the electrode  66  has a three-dimensional curved configuration. In the example shown in  FIG. 5 , proximal electrode  64  is located on first major surface  68  and is substantially flat, outward facing. However, in other examples proximal electrode  64  may utilize the three-dimensional curved configuration of distal electrode  66 , providing a three-dimensional proximal electrode (not shown in this example). Similarly, in other examples distal electrode  66  may utilize a substantially flat, outward facing electrode located on first major surface  68  similar to that shown with respect to proximal electrode  64 . The various electrode configurations allow for configurations in which proximal electrode  64  and distal electrode  66  are located on both first major surface  68  and second major surface  70 . In other configurations, such as that shown in  FIG. 5 , only one of proximal electrode  64  and distal electrode  66  is located on both major surfaces  68  and  70 , and in still other configurations both proximal electrode  64  and distal electrode  66  are located on one of the first major surface  68  or the second major surface  70  (i.e., proximal electrode  64  located on first major surface  68  while distal electrode  66  is located on second major surface  70 ). In another example, ICM  15 A may include electrodes on both major surface  68  and  70  at or near the proximal and distal ends of the device, such that a total of four electrodes are included on ICM  15 A. Electrodes  64  and  66  may be formed of a plurality of different types of biocompatible conductive material, e.g. stainless steel, titanium, platinum, iridium, or alloys thereof, and may utilize one or more coatings such as titanium nitride or fractal titanium nitride. 
     In the example shown in  FIG. 5 , proximal end  72  includes a header assembly  80  that includes one or more of proximal electrode  64 , integrated antenna  82 , anti-migration projections  84 , and/or suture hole  86 . Integrated antenna  82  is located on the same major surface (i.e., first major surface  68 ) as proximal electrode  64  and is also included as part of header assembly  80 . Integrated antenna  82  allows ICM  15 A to transmit and/or receive data. In other examples, integrated antenna  82  may be formed on the opposite major surface as proximal electrode  64 , or may be incorporated within the housing  62  of ICM  15 A. In the example shown in  FIG. 5 , anti-migration projections  84  are located adjacent to integrated antenna  82  and protrude away from first major surface  68  to prevent longitudinal movement of the device. In the example shown in  FIG. 5  anti-migration projections  84  includes a plurality (e.g., nine) small bumps or protrusions extending away from first major surface  68 . As discussed above, in other examples anti-migration projections  84  may be located on the opposite major surface as proximal electrode  64  and/or integrated antenna  82 . In addition, in the example shown in  FIG. 5  header assembly  80  includes suture hole  86 , which provides another means of securing ICM  15 A to the patient to prevent movement following insert. In the example shown, suture hole  86  is located adjacent to proximal electrode  64 . In one example, header assembly  80  is a molded header assembly made from a polymeric or plastic material, which may be integrated or separable from the main portion of ICM  15 A. 
       FIG. 6  is a functional block diagram illustrating an example configuration of an IMD  15 . IMD  15  may correspond to ICM  15 A in  FIG. 1A  and  FIG. 5 , IMD  15 B in  FIG. 1B , or another IMD configured to implement the techniques for determining whether to store or discard cardiovascular pressure measurements as described in this disclosure. In the illustrated example, IMD  15  includes processing circuitry  160  and an associated memory  170 , sensing circuitry  162 , therapy delivery circuitry  164 , one or more sensors  166 , and communication circuitry  168 . However, an IMD  15  need not include all of these components, or may include additional components. For example, ICM  15 A may not include therapy delivery circuitry  164 , in some examples. 
     Memory  170  includes computer-readable instructions that, when executed by processing circuitry  160 , cause IMD  15  and processing circuitry  160  to perform various functions attributed to IMD  15  and processing circuitry  160  herein (e.g., determining time of day, comparing time of day to a predetermined window, determining posture, comparing posture to target posture, and causing communication circuitry  168  to transmit cardiovascular pressure measurements to an external device). Memory  170  may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other digital or analog media. Memory  170  may store threshold(s) for time of day, posture, heart rate, activity level, respiration rate, and other parameters. Memory  170  may also store data indicating cardiovascular pressure measurements received from a sensor device  12 . 
     Processing circuitry  160  may include fixed function circuitry and/or programmable processing circuitry. Processing circuitry  160  may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or equivalent discrete or analog logic circuitry. In some examples, processing circuitry  160  may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to processing circuitry  160  herein may be embodied as software, firmware, hardware or any combination thereof. 
     Sensing circuitry  162  and therapy delivery circuitry  164  are coupled to electrodes  190 . Electrodes  190  illustrated in  FIG. 6  may correspond to, for example, electrodes carried on leads  18 ,  20 ,  22  of device  15 B ( FIG. 1B ), or electrodes  64  and  66  of ICM  15 A. Sensing circuitry  162  may monitor signals from a selected two or more of electrodes  190  in order to monitor electrical activity of heart, impedance, or other electrical phenomenon. Sensing of a cardiac electrical signal may be done to determine heart rates or heart rate variability, or to detect arrhythmias (e.g., tachyarrhythmias or bradycardia) or other electrical signals. In some examples, sensing circuitry  162  may include one or more filters and amplifiers for filtering and amplifying a signal received from electrodes  190 . In some examples, sensing circuitry  162  may sense or detect physiological parameters, such as heart rate, blood pressure, respiration, and the like. 
     The resulting cardiac electrical signal may be passed to cardiac event detection circuitry that detects a cardiac event when the cardiac electrical signal crosses a sensing threshold. The cardiac event detection circuitry may include a rectifier, filter and/or amplifier, a sense amplifier, comparator, and/or analog-to-digital converter. Sensing circuitry  162  outputs an indication to processing circuitry  160  in response to sensing of a cardiac event (e.g., detected P-waves or R-waves). 
     In this manner, processing circuitry  160  may receive detected cardiac event signals corresponding to the occurrence of detected R-waves and P-waves in the respective chambers of heart. Indications of detected R-waves and P-waves may be used for detecting ventricular and/or atrial tachyarrhythmia episodes, e.g., ventricular or atrial fibrillation episodes. Some detection channels may be configured to detect cardiac events, such as P- or R-waves, and provide indications of the occurrences of such events to processing circuitry  160 , e.g., as described in U.S. Pat. No. 5,117,824 to Keimel et al., which issued on Jun. 2, 1992 and is entitled, “APPARATUS FOR MONITORING ELECTRICAL PHYSIOLOGIC SIGNALS,” and is incorporated herein by reference in its entirety. 
     Sensing circuitry  162  may also include a switch module to select which of the available electrodes  190  (or electrode polarities) are used to sense the heart activity. In examples with several electrodes  190 , processing circuitry  160  may select the electrodes that function as sense electrodes, i.e., select the sensing configuration, via the switch module within sensing circuitry  162 . Sensing circuitry  162  may also pass one or more digitized EGM signals to processing circuitry  160  for analysis, e.g., for use in cardiac rhythm discrimination. 
     In the example of  FIG. 6 , IMD  15  includes one or more sensors  166  coupled to sensing circuitry  162 . Although illustrated in  FIG. 6  as included within IMD  15 , one or more of sensors  166  may be external to IMD  15 , e.g., coupled to IMD  15  via one or more leads, or configured to wirelessly communicate with IMD  15 . In some examples, sensors  166  transduce a signal indicative of a patient parameter, which may be amplified, filtered, or otherwise processed by sensing circuitry  162 . In such examples, processing circuitry  160  determines values of patient parameters based on the signals. In some examples, sensors  166  determine the patient parameter values, and communicate them, e.g., via a wired or wireless connection, to processing circuitry  160 . 
     In some examples, sensors  166  include one or more accelerometers  167 , e.g., one or more three-axis accelerometers. Signals generated by the one or more accelerometers  167  may be indicative of, as examples, gross body movement (e.g., activity) of the patient, patient posture, heart sounds or other vibrations or movement associated with the beating of the heart, or coughing, rales, or other respiration abnormalities. Accelerometers  167  may produce and transmit signals to processing circuit  160  for a determination as to whether the patient is in a target posture during a measurement of cardiovascular pressure by a pressure sensing device. In some examples, sensors  166  include one or more microphones configured to detect heart sounds or respiration abnormalities, and/or other sensors configured to detect patient activity or posture, such as gyroscopes and/or strain gauges. In some examples, sensors  166  may include sensors configured to transduce signals indicative of blood flow, oxygen saturation of blood, or patient temperature, and processing circuitry  160  may determine patient parameters values based on these signals. Sensors  166  may gather data that includes numerical values or waveforms of patient parameters. In some examples, sensors  166  may sense a waveform of a patient&#39;s cardiovascular pressure. Data indicating the waveform may be stored in memory  170  and transmitted to another device through communication circuitry  168 . 
     Therapy delivery circuitry  164  is configured to generate and deliver electrical therapy to the heart. Therapy delivery circuitry  164  may include one or more pulse generators, capacitors, and/or other components capable of generating and/or storing energy to deliver as pacing therapy, defibrillation therapy, cardioversion therapy, other therapy or a combination of therapies. In some instances, therapy delivery circuitry  164  may include a first set of components configured to provide pacing therapy and a second set of components configured to provide anti-tachyarrhythmia shock therapy. In other instances, therapy delivery circuitry  164  may utilize the same set of components to provide both pacing and anti-tachyarrhythmia shock therapy. In still other instances, therapy delivery circuitry  164  may share some of the pacing and shock therapy components while using other components solely for pacing or shock delivery. 
     Therapy delivery circuitry  164  may include charging circuitry, one or more charge storage devices, such as one or more capacitors, and switching circuitry that controls when the capacitor(s) are discharged to electrodes  190  and the widths of pulses. Charging of capacitors to a programmed pulse amplitude and discharging of the capacitors for a programmed pulse width may be performed by therapy delivery circuitry  164  according to control signals received from processing circuitry  160 , which are provided by processing circuitry  160  according to parameters stored in memory  170 . Processing circuitry  160  controls therapy delivery circuitry  164  to deliver the generated therapy to the heart via one or more combinations of electrodes  190 , e.g., according to parameters stored in memory  170 . Therapy delivery circuitry  164  may include switch circuitry to select which of the available electrodes  190  are used to deliver the therapy, e.g., as controlled by processing circuitry  160 . 
     Memory  170  may store information relating to the predetermined window of time for cardiovascular pressure measurements. Memory  170  may also store data related to cardiovascular pressure measurements, such as the pressure values, pressure waveforms, and the corresponding times of day and patient postures. Memory  170  may also store information relating to the target posture for cardiovascular pressure measurements, such as thresholds for signals from accelerometers  167 . 
     Processing circuitry  160  may determine the time of day using timer  182 . Timer  182  may be keep a running count based on a voltage-controller oscillator or any other suitable oscillator or clock. Timer  182  may generate an alert to processing circuitry  160  when the time of day is within the predetermined window of time for cardiovascular pressure measurements. 
     Communication circuitry  168  includes any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as an external device  14  or another IMD or sensor. Under the control of processing circuitry  160 , communication circuitry  168  may receive downlink telemetry from and send uplink telemetry to an external device  14  or another device with the aid of an antenna, which may be internal and/or external. In some examples, communication circuitry  168  may communicate with a local external device, and processing circuitry  160  may communicate with a networked computing device via the local external device and a computer network, such as the Medtronic CareLink® Network developed by Medtronic, plc, of Dublin, Ireland. 
     A clinician or other user may retrieve data from IMD  15  using external device  14  or another local or networked computing device configured to communicate with processing circuitry  160  via communication circuitry  168 . The clinician may also program parameters of IMD  15  using external device  14  or another local or networked computing device. In some examples, the clinician may select times of day and target posture(s) for cardiovascular pressure measurements. 
     Communication circuitry  168  may also be configured to communicate with an implantable pressure sensing device  12 . Processing circuitry  160  may receive measured cardiovascular pressure values, e.g., PAP values, from pressure sensing device  12  via communication circuitry  168 . In some examples, processing circuitry  160  may send a trigger signal to sensing device  12  via communication circuitry  168  to control the sensing device to measure cardiovascular pressure in response to the trigger signal. 
     Although not illustrated in  FIG. 6 , communication circuitry  168  may be coupled or coupleable to electrodes  190  for tissue conductance communication (TCC) via the electrodes. In some examples, communication with sensor device  12  and external device  14  may be via RF telemetry or TCC. In one example, communication circuitry  168  may be configured for RF telemetry communication with external device  14  and TCC with sensor device  12   
       FIG. 7  is a functional block diagram illustrating an example configuration of implantable pressure sensing device  12 , hereinafter called “sensor  12 ” or “sensing device  12 .” Sensing device  12  may correspond to any of sensor device  12 A in  FIG. 1A , sensor device  12 B in  FIG. 1B , sensor device  12  in  FIGS. 2A-2B , or another pressure sensing device configured to implement the techniques for measuring cardiovascular pressure as described in this disclosure. In the illustrated example, sensing device  12  includes processing circuitry  200  and an associated memory  210 , sensing circuitry  202 , one or more sensors  206 , communication circuitry  208 , and an optional timer  212 . However, sensing device  12  need not include all of these components, or may include additional components. 
     Memory  210  includes computer-readable instructions that, when executed by processing circuitry  200 , cause sensing device  12  and processing circuitry  200  to perform various functions attributed to sensing device  12  and processing circuitry  200  herein (e.g., determining time of day, comparing time of day to a predetermined window, causing communication circuitry  208  to receive triggering signals from another device, causing communication circuitry  208  to transmit cardiovascular pressure measurements to the other device). Memory  210  may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other digital or analog media. Memory  210  may store threshold(s) for time of day and other parameters. Memory  210  may also store data indicating cardiovascular pressure measurements. 
     Processing circuitry  200  may include fixed function circuitry and/or programmable processing circuitry. Processing circuitry  200  may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or equivalent discrete or analog logic circuitry. In some examples, processing circuitry  200  may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to processing circuitry  200  herein may be embodied as software, firmware, hardware or any combination thereof. 
     Sensing circuitry  202  may monitor signals from sensors  206 , which may include pressure sensors. In some examples, sensing circuitry  202  may sense or detect physiological parameters such as blood pressure in the cardiovascular system of a patient. In some examples, sensing device  12  may be implanted in a pulmonary artery of the patient. 
     In some examples, sensors  206  include one or more pressure sensors that transduce one or more signals indicative of blood pressure, and processing circuitry  200  determines one or more patient parameter values based on the pressure signals. A capacitive pressure sensor is one example of a sensor for transducing pressure. Other example pressure sensors include piezoresistive, piezoelectric, electromagnetic, or optical pressure sensors. Patient parameter values determined based on pressure may include, as examples, systolic or diastolic pressure values, such as pulmonary artery diastolic pressure values, or other pulmonary artery pressure values. 
     Communication circuitry  208  includes any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as IMD  15  or another IMD or sensor, or external device  14 . In some examples, communication circuitry  208  may communicate with a local external device, and processing circuitry  200  may communicate with a networked computing device via the local external device and a computer network, such as the Medtronic CareLink® Network developed by Medtronic, plc, of Dublin, Ireland. In the illustrated example, communication circuitry  208  is coupled to electrodes  215 A and  215 B and configured for TCC communication, e.g., with IMD  15 , via the electrodes. In some examples, electrodes  215 A and  215 B may be integral with a housing of implantable pressure sensing device  12 , and/or may take the form of one or more of the fixation elements, e.g., fixation elements  30 , of an implantable sensor assembly  10 . In some examples, communication circuitry  208  may additionally or alternatively be configured for RF communication via an antenna (not shown). 
     Communication circuitry  208  may be configured to receive a triggering signal from another device, e.g., IMD  15 . The triggering signal may cause processing circuitry  200  to control sensing circuitry  202  and sensor(s)  206  to transduce a cardiovascular pressure signal to measure cardiovascular pressure. Communication circuitry  208  may be further configured to transmit the cardiovascular pressure measurements and/or a portion of the pressure signal waveform to another device, e.g., IMD  15 . 
     Processing circuitry  200  may determine the time of day using and optional timer  212 . Optional timer  212  may be keep a running count based on a voltage-controller oscillator or any other suitable oscillator or clock. Optional timer  212  may generate an alert to processing circuitry  200  when the time of day is within the predetermined window of time for cardiovascular pressure measurements. In some examples, the determination of the time of day may include determining whether the time falls within a predetermined window. 
       FIG. 8  is a functional block diagram illustrating an example system that includes external computing devices, such as a server  224  and one or more other computing devices  230 A- 230 N, that are coupled to IMD  15 , sensing device  12 , and external device  14  via a network  222 . In this example, IMD  15  may use its communication module  168  to, e.g., at different times and/or in different locations or settings, communicate with external device  14  via a first wireless connection, and to communication with an access point  220  via a second wireless connection. In the example of  FIG. 8 , access point  220 , external device  14 , server  224 , and computing devices  230 A- 230 N are interconnected, and able to communicate with each other, through network  222 . 
     Access point  220  may comprise a device that connects to network  222  via any of a variety of connections, such as telephone dial-up, digital subscriber line (DSL), or cable modem connections. In other examples, access point  220  may be coupled to network  222  through different forms of connections, including wired or wireless connections. In some examples, access point  220  may be co-located with the patient. Access point  220  may interrogate IMD  15 , e.g., periodically or in response to a command from the patient or network  222 , to retrieve cardiovascular pressure measurements, corresponding times of day, corresponding posture data, and/or other operational or patient data from IMD  15 . Access point  220  may provide the retrieved data to server  224  via network  222 . 
     In some cases, server  224  may be configured to provide a secure storage site for data that has been collected from IMD  15 , sensing device  12 , and/or external device  14 . In some cases, server  224  may assemble data in web pages or other documents for viewing by trained professionals, such as clinicians, via computing devices  230 A- 230 N. The illustrated system of  FIG. 8  may be implemented, in some aspects, with general network technology and functionality similar to that provided by the Medtronic CareLink® Network developed by Medtronic plc, of Dublin, Ireland. 
     In some examples, one or more of access point  220 , server  224 , or computing devices  230  may be configured to perform, e.g., may include processing circuitry configured to perform, some or all of the techniques described herein, e.g., with respect to processing circuitry  160  of IMD  15  and processing circuitry  200  of external device  14 , relating to cardiovascular pressure measurements. In the example of  FIG. 8 , server  224  includes a memory  226  to store cardiovascular pressure measurements, along with corresponding data such as time of day, posture, heart rate, activity level, and respiration rate, received from IMD  15  and/or external device  14 , and processing circuitry  228 , which may be configured to provide some or all of the functionality ascribed to processing circuitry  160  of IMD  15  and processing circuitry  200  of external device  14  herein. For example, processing circuitry  228  may determine whether the measured posture from one or more IMDs  15  was a target posture for cardiovascular pressure measurements. Processing circuitry  228  may determine whether to store or discard the cardiovascular pressure measurement based on determining whether the measured posture was the target posture. 
       FIG. 9  is a block diagram illustrating another example system that includes external computing devices, such as hospital tablet  254 , TCC external instrument  258 , patient smart device  262 , clinician smart device  266 . Implantable pressure sensing device  12  may correspond to any of sensor device  12 A in  FIG. 1A , sensor device  12 B in  FIG. 1B , sensor device  12  in  FIGS. 2A-2B , sensing device  12  in  FIGS. 7 and 8 , or another pressure sensing device configured to implement the techniques for measuring cardiovascular pressure as described in this disclosure. Implantable monitoring device (IMD)  15  may correspond to any of ICM  15  in  FIG. 1A , device  15 B in  FIG. 1B , IMD  15  in  FIG. 5 , IMD  15  in  FIG. 6 or 8 , or another IMD configured to implement the techniques for determining whether to store or discard cardiovascular pressure measurements as described in this disclosure. In the example depicted in  FIG. 9 , IMD  15  may include communication links with implantable pressure sensing device  250 , hospital tablet  254 , TCC external instrument  258 , patient care network  260 , and patient smart device  262 . 
     The system of  FIG. 9  may notify a patient or clinician of a cardiovascular pressure measurement through one or more devices. For example, TCC external instrument  258  may communicate with IMD  15  and/or implantable pressure sensing device  12  via tissue conductive communications (TCC) through the body tissue of the patient. One or both of TCC external instrument  258  and patent smart device  262  may include reference measurement  256 A, which may be a measurement of local air pressure to calibrate or adjust the cardiovascular pressure measurements taken by implantable pressure sensing device  12 . Although reference measurement  256 A is depicted as a single measurement, each of TCC external instrument  258  and patent smart device  262  may include or communicate with a separate reference measurement device. 
     Hospital tablet  254  and patient care network  260  may communicate with IMD  15  via radio frequency (RF) waves or TCC. Hospital tablet  254  may include reference measurement  256 B, which may be the same or a separate reference measurement device as reference measurement  256 A. A patient or clinician may use hospital tablet  254  or TCC external instrument  258  to obtain measurements and/or determine medication instructions. 
     Patient care network  260  may include a communication links with hospital tablet  254 , TCC external instrument  258 , patient smart device  262 , HF management web portal  264 , and clinician smart device  266 . As a result, a clinician may access a patient&#39;s cardiovascular pressure measurements through hospital tablet  254  or clinician smart device  266  when the patient is in the hospital. A clinician may access a patient&#39;s cardiovascular pressure measurements through clinician smart device  266  when the patient is not in the hospital if IMD  15  has a remote communication link with patient care network  260 . One or more of hospital tablet  254 , TCC external instrument  258 , patient smart device  262 , and clinician smart device  266  may output instructions to a clinician or a patient. In some examples, a device of  FIG. 9  may instruct a patient to take blood-pressure medication based on elevated cardiovascular pressure measurements taken by implantable pressure sensing device  12 . A device that displays medication instructions may communicate with patient care network  260  to determine the medication instructions to display to a patient. A device of  FIG. 9  may generate an alert to a clinician or patient based on abnormal or unhealthy cardiovascular pressure measurements. 
       FIG. 10  is a flowchart illustrating an example technique  300  that may be implemented by an IMD  15  in accordance with this disclosure. Technique  300  may be a specific example of technique  280 . Technique  300  may be implemented by any one of the implantable medical devices (IMDs) discussed above because each one of the IMDs is configured to include at least one accelerometer (i.e., accelerometer circuitry), as well as communication and processing circuitry (see  FIG. 6  and corresponding description) to facilitate determining patient movements. 
     The technique of  FIG. 10  includes a timer interrupt at midnight, twelve a.m., or another predetermined time of day ( 302 ). Midnight may be a predetermined time because of the likelihood that the patient is sleeping and/or lying down at midnight. In some examples, IMD  15  may store more than one predetermined time, such as eight or nine times from midnight through four a.m. local time. By using a predetermined time window, patients and clinicians may obtain automatic measurements without needing to arrange for a measurement during the day. Therefore, using a predetermined tine window may increase compliance by the patient. 
     The technique of  FIG. 10  further includes sensing the posture of the patient ( 304 ). IMD  15  may use sensing circuitry  162 , sensors  166 , and accelerometers  167  to generate and transmit signals indicating the posture to processing circuitry  160 . IMD  15  may include three accelerometers, where each accelerometer may measure the orientation of the patient along one of three axes, such as longitudinal, transverse, and sagittal. 
     The technique of  FIG. 10  further includes determining whether the patient is in a supine posture ( 306 ). Memory  170  may store data relating to threshold values for one or more accelerometer signals indicating that the patient is within the supine position. Processing circuitry  160  may compare the stored data relating to the target posture to the measured accelerometer signals. When the patient is in a supine posture, the pulmonary artery may include a hydrostatic column of blood of two or three inches above the pressure sensing device. When the patient is lying on the right side, the hydrostatic column of blood may decrease to one or two inches if the pressure sensing device is located on left side of the patient&#39;s thorax. Thus, the cardiovascular pressure measurement may decrease when the patient is lying on the right side, as compared to the supine posture, because there is less blood on top of the sensor. In contrast, when the patient is lying on the left side, the hydrostatic column of blood may increase to ten or twelve inches. For this reason, the cardiovascular pressure measurement may increase when the patient is lying on the left side, as compared to the supine posture. Furthermore, other postures such as standing or sitting may affect cardiovascular pressure measurements. 
     The supine position may be the target posture to ensure that all measurements have the same posture. For patients that sleep on their side, another posture may be used as the target posture, such as the right-supine posture. In some examples, the target posture may include multiple postures, and memory  170  may store each cardiovascular pressure measurement along with data indicating the corresponding posture. By including storing data for cardiovascular pressure measurements in a single or small group of postures, the cardiovascular pressure measurements may have been measured under the same or similar conditions and compared to each other in a meaningful way. 
     In some examples, the technique of  FIG. 10  further includes determining if the activity level of the patient is below a threshold ( 308 ). A high activity level of the patient may significantly affect the cardiovascular pressure of the patient. By filtering out times with high activity levels, the technique of  FIG. 10  may gather a more homogenous set of data. Processing circuitry  160  of IMD  15  may determine the activity level of patient based on one or more of the accelerometer signals, e.g., by comparing the accelerometer signals to one or more thresholds and/or counting threshold-crossings, zero-crossings, or inflections. 
     In some examples, the technique of  FIG. 10  further includes determining if the heart rate of the patient is below a threshold ( 310 ). A high heart rate may indicate a stressful event or some other occurrence that may also raise the cardiovascular pressure of the patient. By filtering out times with high heart rates, the technique of  FIG. 10  may gather a more homogenous set of data. 
     The technique of  FIG. 10  further includes sending a trigger signal to cause a sensing device to measure cardiovascular pressure ( 312 ). IMD  15  may send the trigger signal via TCC or RF to the sensing device, which may be implanted in the vascular system of the patient. 
     The technique of  FIG. 10  further includes receiving the cardiovascular pressure measurement from the sensing device ( 314 ). IMD  15  may receive the cardiovascular pressure measurement as a signal via TCC or RF from the sensing device. IMD  15  may store the cardiovascular pressure measurement to memory  170  before sending the cardiovascular pressure measurement to an external device. In some examples, the sensing device may transmit the cardiovascular pressure measurement directly to an external device. 
     In some examples, the technique of  FIG. 10  further includes determining whether a desired number measurements, which may be a programmable number, have been taken ( 316 ). If IMD  15  determines that a sufficient number of measurements have been taken, IMD  15  may wait until the following night to request measurements from the sensing device. If IMD  15  determines that an insufficient number of measurements have been taken, IMD  15  may request an additional measurement from sensing device when IMD  15  determines that the posture of the patient is the target posture. In this way, IMD  15  may continue to request additional measurements until there are a sufficient number of measurements for a particular period of time. In counting the number of measurements, IMD  15  may count the stored measurements and not count the discarded measurements. 
     The technique of  FIG. 10  further includes setting a timer ( 317 ). The timer may be set for a specific amount of time, such as thirty minutes. If the previous posture measurement did not match the target posture, the timer may be set for a shorter period of time to allow for additional measurements. 
     The technique of  FIG. 10  further includes sensing the posture of the patient when the timer interrupts thirty minutes later ( 304 ,  318 ). The timer interrupt may be a shorter amount of time if the previous posture measurement did not match the target posture. 
       FIG. 11  is a flowchart illustrating an example technique  320  that may be implemented by sensor device  12  in  FIGS. 1A-4B , and/or implantable pressure sensing device  12  in  FIGS. 7-9 , in accordance with this disclosure. Technique  320  may be a specific example of technique  280 . Technique  320  may be implemented by any one of the sensing devices discussed above. 
     In some examples, the technique of  FIG. 11  optionally includes sensor device  12  determining that the time of day is within a predetermined window ( 322 ). In some examples, an implantable monitoring device such as IMD  15  and/or an implantable pressure sensing device such as sensor device  12 A may determine whether the time of day is within the predetermined window, e.g., during a period of time in which a patient is likely to be asleep, such as from midnight to 4 am. Either device may determine the time using a timer based on a voltage-controlled oscillator within the device. The device may compare the current time to a predetermined time or window of time. In some examples, the device may have previously set a timer and established an interrupt sequence such that processing circuitry within the device will begin executing instructions in the interrupt sequence in response to the timer reaching a threshold that corresponds to a predetermined time. Alternatively or additionally, sensor device  12  may receive a triggering signal from another device ( 324 ). The triggering signal may be based on the other device determining that the posture of the patient is a target posture ( 323 ). In either step of the technique of  FIG. 11 , sensor device  12  is triggered to measure the cardiovascular pressure of the patient. In some examples, sensor device  12  may or may not include an internal clock/timer for tracking the time of day. 
     The technique of  FIG. 11  further includes measuring the cardiovascular pressure of the patient ( 326 ). A device such as implantable pressure sensing device  201  may use sensing circuitry  202  and sensor(s)  206  to measure the blood pressure in the vascular system of a patient. The sensing device may use sensing circuitry  202  and sensors  206  for generating, processing, and storing signals indicating the cardiovascular pressure of the patient. The device may measure the cardiovascular pressure in response to a program instruction, a timer interrupt, a triggering signal, a posture measurement, and/or any other suitable trigger or stimulus. In some examples, the device may take the measurement in response to determining that the time of day is within the predetermined window. 
     The technique of  FIG. 11  further includes transmitting the cardiovascular pressure measurement to another device ( 328 ). Sensor device  12  may transmit the cardiovascular pressure measurement via TCC to IMD  15 , which may be implanted subcutaneously near the sternum. IMD  15  may include more complex communication circuitry for transmitting the cardiovascular pressure measurement to an external device. In some examples, implantable pressure sensing device  12  may use communication circuitry  208  to transmit the cardiovascular pressure measurement to IMD  15 . IMD  15  may receive the cardiovascular pressure measurement through communication circuitry  168 . The cardiovascular pressure measurement may be transmitted between devices by radio frequency via an antenna or by TCC. 
       FIG. 12  is a flowchart illustrating an example technique  340  that may be implemented by devices of a medical device system, in accordance with this disclosure. Technique  340  may be a specific example of technique  280 . Technique  340  may be implemented by three or more devices, or by fewer than three devices by combining the functions of two devices into a single device. The division of labor depicted in  FIG. 12  may be based on the larger battery and higher number of sensors in the second device compared to the first device. The first device may be configured for implantation in the cardiovascular system of the patient. Thus, the first device may be smaller than the second device. 
     The first device of  FIG. 12  may be a pressure sensing device configured to determine that the time of day is within a predetermined window ( 342 ). The pressure sensing device may then measure the cardiovascular pressure of the patient ( 344 ). The pressure sensing device may transmit the cardiovascular pressure to a second device ( 346 ). The first device may be implemented by sensor device  12  in  FIGS. 1A-4B , and/or implantable pressure sensing device  12  in  FIGS. 7-9 . 
     The second device of  FIG. 12  may be a monitoring device or a hub device configured to determine a posture of the patient ( 348 ). The monitoring device may then store or discard the cardiovascular pressure measurement based on the determination of whether the posture is the target posture ( 350 ). If the monitoring device stores the cardiovascular pressure measurement, the monitoring device may transmit the stored cardiovascular pressure measurement to a network device ( 352 ). The second device may be implemented by IMD  15  in  FIGS. 1A-8 , device  15 B in  FIG. 1B , and/or IMD  15  in  FIG. 9 . In some examples, the second device may transmit all cardiovascular pressure measurements to the network device, along with the corresponding postures, and the network device may store, discard, process, and/or analyze the cardiovascular pressure measurements. 
     The network device of  FIG. 12  may be configured to generate an alert or instruction for the patient or clinician ( 354 ). The network device may instruct a patient to take medication for high blood pressure, or cease taking the medication if the measurement indicates low blood pressure. The network device may be further configured to determine statistics for cardiovascular pressure measurements ( 356 ). The network device may be implemented by hospital tablet  254 , TCC external instrument  258 , patient smart device  262 , or clinician smart device  266 . 
       FIG. 13  is a flowchart illustrating an example technique  360  that may be implemented by a pressure sensing device and a monitoring device, in accordance with this disclosure. Technique  360  may be a specific example of technique  280 . The first device may be implemented by IMD  15  in  FIGS. 1A-8 , device  15 B in  FIG. 1B , and/or IMD  15  in  FIG. 9 . The second device may be implemented by sensor device  12  in  FIG. 1A-4B  and/or implantable pressure sensing device  12  in  FIGS. 7-9 . 
     The pressure sensing device may be configured to operate in a low-power mode such as sleep mode or idle mode until waking up based on a triggering signal or internal timer interrupt. In some examples, the first device may determine that the time of day is within a predetermined window ( 362 ) and measure and optionally store the cardiovascular pressure of the patient ( 364 ). The first device may then transmit the pressure measurement to the second device ( 366 ). The second device may be configured to determine the posture of the patient at the time of measurement of cardiovascular pressure ( 368 ) and transmit the cardiovascular pressure measurement and the measured posture to a network device ( 370 ). IMD  15  may include sensors  166  including accelerometers  167  for generating signals based on the orientation of the patient. Memory  170  may store data indicating one or more target postures, as well as possibly storing data indicating unacceptable postures. Processing circuitry  160  of IMD  15  may determine whether the posture of the patient matches the target posture(s). 
     The network device may determine if the posture is a target posture ( 372 ). The network device may further determine whether to store or discard the cardiovascular pressure measurement based on the determined posture ( 374 ). If processing circuitry  160  determines that the posture when the pressure measurement was made was the target posture, processing circuitry  160  may store the cardiovascular pressure measurement. However, if processing circuitry  160  of IMD  15  determines that the posture was not the target posture, processing circuitry  160  may discard the cardiovascular pressure measurement and possibly request another measurement from implantable pressure sensing device  12  after a given amount of time or upon determining that the patient&#39;s posture is the target posture. In some examples, IMD  15  may transmit the cardiovascular pressure measurement received from sensor  12  and the corresponding posture determined by IMD  15  to another device, e.g., any of the computing devices described herein, which may determine whether the corresponding posture is the target posture and determine whether to store or discard the pressure measurement based on the determination of whether the posture is the target posture. 
     The flowcharts of  FIGS. 10-13  are intended to illustrate the functional operation of IMD  15 , device  16 , sensor device  12 , external device  14 , medical system  8 , and other devices and systems described herein, and should not be construed as reflective of a specific form of software or hardware necessary to practice the methods described. Methods described in conjunction with flow diagrams presented herein may be implemented in a non-transitory computer-readable medium that includes instructions for causing a programmable processor to carry out the methods described. A non-transitory computer-readable medium includes but is not limited to any volatile or non-volatile media, such as a RAM, ROM, CD-ROM, NVRAM, EEPROM, flash memory, or other computer-readable media, with the sole exception being a transitory, propagating signal. The instructions may be implemented by processing circuitry hardware as execution of one or more software modules, which may be executed by themselves or in combination with other software. 
     The example methods illustrated by  FIGS. 10-13  may be performed, by any one or more devices described herein, and may be performed, in part, by processing circuitry of any one or more devices described herein, such as by processing circuitry  160  of IMD  15 , processing circuitry  200  of implantable pressure sensing device  12 , which may correspond to sensor device  12  of  FIGS. 1A-4B , computing devices  230 A- 230 N, or any of the devices of  FIG. 9 . 
     Various aspects of the techniques may be implemented within one or more processors, including one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components, embodied in programmers, such as physician or patient programmers, electrical stimulators, or other devices. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry. 
     In one or more examples, the functions described in this disclosure may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media forming a tangible, non-transitory medium. Instructions may be executed by one or more processors, such as one or more DSPs, ASICs, FPGAs, general purpose microprocessors, or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to one or more of any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. 
     In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or units may be performed by separate hardware or software components, or integrated within common or separate hardware or software components. Also, the techniques could be fully implemented in one or more circuits or logic elements. The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including an IMD, an external programmer, a combination of an IMD and external programmer, an integrated circuit (IC) or a set of ICs, and/or discrete electrical circuitry, residing in an IMD and/or external programmer. 
     The following numbered examples demonstrate one or more aspects of the disclosure. 
     Example 1 
     A method for monitoring a cardiovascular pressure in a patient, the method including measuring, by pressure sensing circuitry of an implantable pressure sensing device, the cardiovascular pressure of the patient. The method further includes transmitting, via wireless communication circuitry of the implantable pressure sensing device, the measured cardiovascular pressure to another device. The method further includes determining, by processing circuitry of the other device, whether a posture of the patient at a time of the measured cardiovascular pressure was a target posture for cardiovascular pressure measurements. The method further includes determining, by the processing circuitry of the other device, whether to store or discard the transmitted cardiovascular pressure based on determining whether the posture was the target posture. 
     Example 2 
     The method of example 1, further including determining, by the processing circuitry of the other device, whether an activity level of the patient is below a threshold level. The method further includes determining, by the processing circuitry of the other device, whether to store or discard the transmitted cardiovascular pressure based on determining whether the activity level of the patient is below the threshold level. 
     Example 3 
     The method of any of examples 1-2 or combinations thereof, further including determining, by the processing circuitry of the other device, whether a heart rate of the patient is below a threshold rate. The method further includes determining, by the processing circuitry of the other device, whether to store or discard the transmitted cardiovascular pressure based on determining whether the heart rate of the patient is below the threshold rate. 
     Example 4 
     The method of any of examples 1-3 or combinations thereof, further including determining, by the processing circuitry of the other device, whether a respiration rate of the patient is below a threshold rate. The method further includes determining, by the processing circuitry of the other device, whether to store or discard the transmitted cardiovascular pressure based on determining whether the respiration rate of the patient is below the threshold rate. 
     Example 5 
     The method of any of examples 1-4 or combinations thereof, further including setting, by the processing circuitry of the other device, a timer based on determining that the posture was not the target posture. The method further includes, at an expiration of the timer, determining, by the processing circuitry of the other device, whether a posture of the patient is the target posture. The method further includes sending a trigger signal, via wireless communication circuitry of the other device, to the implantable pressure sensing device, wherein the implantable pressure sensing device measures the cardiovascular pressure of the patient using the pressure sensing circuitry in response to the trigger signal. 
     Example 6 
     The method of any of examples 1-5 or combinations thereof, further including transmitting, by wireless communication circuitry of the other device, the measured cardiovascular pressure to a third device. The method further includes transmitting, by the wireless communication circuitry of the other device, the time of day to the third device. The method further includes transmitting, by the wireless communication circuitry of the other device, the posture of the patient at the time of day to the third device. 
     Example 7 
     The method of any of examples 1-6 or combinations thereof, wherein the predetermined window includes of times of day after sunset local time and before sunrise local time. 
     Example 8 
     The method of any of examples 1-7 or combinations thereof, wherein determining whether the posture was the target posture includes measuring an accelerometer signal. The target posture includes a supine posture, a right-side-down posture when the implantable pressure sensing device is implanted in the left pulmonary artery, or a left-side-down posture when the implantable pressure sensing device is implanted in the right pulmonary artery. 
     Example 9 
     A medical device system for monitoring a cardiovascular pressure in a patient, the medical device system including an implantable pressure sensing device including wireless communication circuitry and pressure sensing circuitry configured to measure the cardiovascular pressure of the patient. The implantable pressure sensing device further includes processing circuitry configured to control the pressure sensing circuitry to measure the cardiovascular pressure of the patient. The processing circuitry of the implantable pressure sensing device is further configured to transmit the measured cardiovascular pressure to another device via the wireless communication circuitry. The medical device system further includes the other device including processing circuitry configured to determine whether a posture of the patient at a time of the measured cardiovascular pressure was a target posture for cardiovascular pressure measurements. The processing circuitry of the other device is further configured to determine whether to store or discard the transmitted cardiovascular pressure based on determining whether the posture was the target posture. 
     Example 10 
     The medical device system of example 9, wherein the other device further includes a housing containing the processing circuitry, wherein the housing is configured for implantation in the patient. 
     Example 11 
     The medical device system of any of examples 9-10 or combinations thereof, wherein the other device further includes a memory configured to store an upper bound for the predetermined window and a lower bound for the predetermined window and the posture of the patient at the time of day. 
     Example 12 
     The medical device system of any of examples 9-11 or combinations thereof, wherein the implantable pressure sensing device is configured for implantation in a vascular system of the patient, and the other device is configured for subcutaneous implantation in the patient. 
     Example 13 
     The medical device system of any of examples 9-12 or combinations thereof, wherein the processing circuitry of the other device is further configured to determine whether an activity level of the patient is below a threshold level, and determine whether to store or discard the transmitted cardiovascular pressure based on determining whether the activity level of the patient is below the threshold level. 
     Example 14 
     The medical device system of any of examples 9-13 or combinations thereof, wherein the processing circuitry of the other device is further configured to determine whether a heart rate of the patient is below a threshold rate, and determine whether to store or discard the transmitted cardiovascular pressure based on determining whether the heart rate of the patient is below the threshold rate. 
     Example 15 
     The medical device system of any of examples 9-14 or combinations thereof, wherein the processing circuitry of the other device is further configured to determine whether a respiration rate of the patient is below a threshold rate, and determine whether to store or discard the transmitted cardiovascular pressure based on determining whether the respiration rate of the patient is below the threshold rate. 
     Example 16 
     The medical device system of any of examples 9-15 or combinations thereof, wherein the processing circuitry of the other device is further configured to set a timer based on determining that the posture was not the target posture, and at an expiration of the timer, determine whether a posture of the patient is the target posture. The other device further includes wireless communication circuitry configured to send a trigger signal to the implantable pressure sensing device to cause the pressure sensing circuitry of the implantable pressure sensing device to measure the cardiovascular pressure of the patient in response to the trigger signal. 
     Example 17 
     The medical device system of any of examples 9-16 or combinations thereof, wherein the processing circuitry of the implantable pressure sensing device is further configured to determine that a time of day is within a predetermined window for cardiovascular pressure measurements, wherein the processing circuitry of the implantable pressure sensing device is configured to control the pressure sensing circuitry to measure the cardiovascular pressure in response to determining that the time of day is within the predetermined window, and wherein the other device further includes wireless communication circuitry configured to transmit the measured cardiovascular pressure to a third device, transmit the time of day to the third device, and transmit the posture of the patient at the time of day to the third device. 
     Example 18 
     The medical device system of any of examples 9-17 or combinations thereof, wherein the other device is configured for implantation in the patient, and wherein the other device further comprises sensing circuitry configured to generate a signal indicating the posture of the patient. 
     Example 19 
     The medical device system of any of examples 9-18, wherein the other device is configured to receive a signal indicating the posture of the patient from an implantable monitoring device. 
     Example 20 
     A method for monitoring a cardiovascular pressure in a patient, the method including determining, by processing circuitry of an implantable monitoring device, that a time of day is within a predetermined window for cardiovascular pressure measurements. The method further includes sensing, with sensing circuitry of the implantable monitoring device, posture of the patient during the predetermined window in response to the determination. The method further includes determining, by the processing circuitry of the implantable monitoring device, that the sensed posture of the patient is a target posture for cardiovascular pressure measurements. The method further includes sending a trigger signal, via wireless communication circuitry of the implantable monitoring device, to an implantable pressure sensing device, wherein the implantable pressure sensing device measures the cardiovascular pressure of the patient using pressure sensing circuitry in response to the trigger signal. The method further includes receiving, by the processing circuitry of the implantable monitoring device, the measured cardiovascular pressure of the patient from the implantable pressure sensing device via the wireless communication circuitry of the implantable monitoring device. 
     Example 21 
     The method of example 20, further including determining, by the processing circuitry of the implantable monitoring device, that the sensed posture of the patient is not the target posture. The method further includes refraining from sending the trigger signal via the wireless communication circuitry of the implantable monitoring device based on determining the sensed posture is not the target posture. The method further includes setting, by the processing circuitry of the implantable monitoring device, a timer. The method further includes at an expiration of the timer, with posture sensing circuitry of the implantable monitoring device, sensing posture of the patient. The method further includes determining, by the processing circuitry of the implantable monitoring device, that the sensed posture of the patient is the target posture. The method further includes sending the trigger signal, via the wireless communication circuitry of the implantable monitoring device, to the implantable pressure sensing device, based on determining the sensed posture is the target posture. 
     Example 22 
     The method of any of examples 20-21 or combinations thereof, further including determining, by the processing circuitry of the implantable monitoring device, whether a heart rate of the patient is below a threshold rate. The method further includes sending the trigger signal, via wireless communication circuitry of the implantable monitoring device, to an implantable pressure sensing device based on determining whether the heart rate of the patient is below the threshold rate. 
     Example 23 
     A medical device system for monitoring a cardiovascular pressure in a patient, the medical device system comprising an implantable monitoring device comprising wireless communication circuitry, processing circuitry configured to determine that a time of day is within a predetermined window for cardiovascular pressure measurements, and sensing circuitry configured to sense a posture of the patient during the predetermined window in response to the determination. The processing circuitry is further configured to determine that the sensed posture of the patient is a target posture for cardiovascular pressure measurements. The wireless communication circuitry is configured to send a trigger signal to an implantable pressure sensing device. The medical device system further comprises the implantable pressure sensing device comprising wireless communication circuitry configured to receive the trigger signal and pressure sensing circuitry configured to measure the cardiovascular pressure of the patient in response to the trigger signal. The wireless communication circuitry of the implantable pressure sensing device is further configured to transmit the measured cardiovascular pressure of the patient to the implantable monitoring device. 
     Example 24 
     The medical device system of example 23, wherein the processing circuitry of the implantable monitoring device is further configured to determine that the sensed posture of the patient is not the target posture. The wireless communication circuitry of the implantable monitoring device is further configured to refrain from sending the trigger signal based on determining the sensed posture is not the target posture. The processing circuitry of the implantable monitoring device is further configured to set a timer. The posture sensing circuitry of the implantable monitoring device is further configured to sense posture of the patient at an expiration of the timer. The processing circuitry of the implantable monitoring device is further configured to determine that the sensed posture of the patient is the target posture. The wireless communication circuitry of the implantable monitoring device is further configured to send the trigger signal to the implantable pressure sensing device, based on determining the sensed posture is the target posture. 
     Example 25 
     The medical device system of any of examples 23-24 or combinations thereof, wherein the processing circuitry of the implantable monitoring device is further configured to determine whether a heart rate of the patient is below a threshold rate. The wireless communication circuitry of the implantable monitoring device is further configured to send the trigger signal to an implantable pressure sensing device based on determining whether the heart rate of the patient is below the threshold rate. 
     Example 26 
     A method for monitoring a cardiovascular pressure in a patient, the method comprising determining, by processing circuitry of an implantable pressure sensing device, that a time of day is within a predetermined window for cardiovascular pressure measurements. The method further includes measuring, by pressure sensing circuitry of the implantable pressure sensing device, the cardiovascular pressure of the patient in response to the determination. The method also includes transmitting, via wireless communication circuitry of the implantable pressure sensing device, the measured cardiovascular pressure to another device. The method includes determining, by processing circuitry of the other device, whether a posture of the patient at the time of day was a target posture for cardiovascular pressure measurements, wherein the target posture comprises a supine posture, a right-side-down posture when the implantable pressure sensing device is implanted in the left pulmonary artery, or a left-side-down posture when the implantable pressure sensing device is implanted in the right pulmonary artery. The method further includes determining, by the processing circuitry of the other device, whether to store or discard the transmitted cardiovascular pressure based on determining whether the posture was the target posture. 
     Example 27 
     The method of any of examples 1-8 or combinations thereof, further including determining, by processing circuitry of the implantable pressure sensing device, that a time of day is within a predetermined window for cardiovascular pressure measurements, wherein measuring the cardiovascular pressure of the patient is in response to determining that the time of day is within the predetermined window. 
     Various aspects of this disclosure have been described. These and other aspects are within the scope of the following claims.