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Cardiac monitoring and/or stimulation methods and systems employing dyspnea measurement. An implantable cardiac device may sense transthoracic impedance and determine a patient activity level. An index indicative of pulmonary function is implantably computed to detect an episode of dyspnea based on

Cardiac monitoring and/or stimulation methods and systems employing dyspnea measurement. An implantable cardiac device may sense transthoracic impedance and determine a patient activity level. An index indicative of pulmonary function is implantably computed to detect an episode of dyspnea based on a change, trend, and/or value exceeding a threshold at a determined patient activity level. Trending one or more pulmonary function index values may be done to determine a patient's pulmonary function index profile, which may be used to adapt a cardiac therapy. A physician may be automatically alerted in response to a pulmonary function index value and/or a trend of the patient's pulmonary index being beyond a threshold. Computed pulmonary function index values and their associated patient's activity levels may be stored periodically in a memory and/or transmitted to a patient-external device.

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1. An implantable cardiac device, comprising: a housing configured for implantation in a patient;an implantable sensor configured to sense transthoracic impedance;an implantable activity sensor configured to make an activity measurement indicative of patient activity;a memory provided in the housing

1. An implantable cardiac device, comprising: a housing configured for implantation in a patient;an implantable sensor configured to sense transthoracic impedance;an implantable activity sensor configured to make an activity measurement indicative of patient activity;a memory provided in the housing and configured to store at least a pulmonary function index versus activity level profile comprising a plurality of index values associated with different ranges of patient activity levels;a controller provided in the housing and coupled to the respective sensors and the memory, the controller configured to: compute an index indicative of patient pulmonary function using the sensed transthoracic impedance by computing a ratio of multiple respiration parameters; anddetect an episode of dyspnea based on a parameter of the computed patient pulmonary function index exceeding an index value of the profile stored in the memory, the index value associated with an activity range of the profile which the patient activity level is calculated to be within; andcommunication circuitry provided in the housing and configured to facilitate communication of information between the implantable cardiac device and a device external of the housing. 2. The device according to claim 1, wherein the index value for detecting the dyspnea episode is based on the pulmonary function index versus activity level profile stored in the memory. 3. The device according to claim 1, wherein the profile stored in the memory is developed by the controller configured to trend a plurality of pulmonary function index values and associating the trended pulmonary function index values with patient activity levels at which the plurality of pulmonary function index values were collected. 4. The device according to claim 1, wherein the profile stored in the memory is developed by the controller configured to trend a plurality of pulmonary function index values and their associated patient activity levels, wherein the parameter used by the controller to detect the dyspnea episode is based on the pulmonary function index versus activity level profile. 5. The device according to claim 1, wherein the controller is configured to compute the patient pulmonary function index by computing a ratio of a respiratory rate value and a tidal volume value for the patient. 6. The device according to claim 1, wherein the controller is configured to determine a patient's sleep-state at least in part by using the patient pulmonary function index. 7. The device according to claim 1, wherein the controller is configured to generate an alert in response to a pulmonary function index value being beyond the index value, the controller cooperating with the communication circuitry to transmit at least the alert to the external device. 8. The device according to claim 1, wherein the controller is configured to generate an alert in response to a trend of the patient's computed index indicative of pulmonary function, the controller cooperating with the communication circuitry to transmit at least the alert to the external device. 9. The device according to claim 1, comprising: an implantable electrode arrangement; andtherapy circuitry provided in the housing and coupled to the controller and the implantable electrode arrangement, the therapy circuitry configured to deliver a therapy via the electrode arrangement based at least in part on a computed pulmonary function index value and a measured patient activity level. 10. The device according to claim 1, comprising: an implantable electrode arrangement; andtherapy circuitry provided in the housing and coupled to the controller and the implantable electrode arrangement;wherein the controller is configured to adapt a cardiac therapy for the patient based on the computed index indicative of patient pulmonary function, and the therapy circuitry is configured to deliver the adapted cardiac therapy to the patient. 11. An implantable cardiac device, comprising: a housing configured for implantation in a patient;an implantable sensor configured to sense patient respiration;an implantable activity sensor configured to measure patient activity;a memory provided in the housing and configured to store at least a pulmonary function index versus a plurality of index values associated with different ranges of patient activity levels;a controller provided in the housing and coupled to the respective sensors and the memory, the controller configured to: compute an index indicative of patient pulmonary function using the sensed patient respiration; anddetect an episode of dyspnea based on a parameter of the computed patient pulmonary function index exceeding an index value associated with an activity range of the profile which the patient activity level is calculated to be within; andcommunication circuitry provided in the housing and configured to facilitate communication of information between the implantable cardiac device and a device external of the housing. 12. The device according to claim 11, wherein the controller is configured to compute the patient pulmonary function index by computing a ratio of the multiple respiration parameters. 13. The device according to claim 11, wherein the threshold is based on a profile developed by the controller using the plurality of patient pulmonary function index values and associated patient activity levels. 14. The device according to claim 13, wherein the controller is configured to trend a plurality of patient pulmonary function index values to determine a patient's pulmonary function index profile, and the controller or a controller external to the housing is configured to detect the dyspnea episode using the threshold that is based at least in part on the patient's pulmonary function index profile. 15. The device according to claim 13, wherein the controller is configured to trend a plurality of patient pulmonary function index values and their associated patient activity levels to develop a patient's pulmonary function index versus activity level profile. 16. The device according to claim 13, wherein the controller is configured to trend a plurality of patient pulmonary function index values and their associated patient activity levels to develop a patient's pulmonary function index versus activity level profile, and the controller or a controller external to the housing is configured to detect the dyspnea episode using the threshold that is based on the patient's pulmonary function index versus activity level profile. 17. The device according to claim 11, comprising: an implantable electrode arrangement; andtherapy circuitry provided in the housing and coupled to the controller and the implantable electrode arrangement, the therapy circuitry configured to deliver a therapy via the electrode arrangement based at least in part on a computed pulmonary function index value and a measured patient activity level. 18. The device according to claim 11, comprising: an implantable electrode arrangement; andtherapy circuitry provided in the housing and coupled to the controller and the implantable electrode arrangement, the therapy circuitry configured to deliver a cardiac therapy via the electrode arrangement that increases a pacing rate by a predetermined amount. 19. The device according to claim 11, wherein: the controller is configured to generate an alert in response to at least one of a computed patient pulmonary function index value being beyond the threshold and a trend of the patient's computed patient pulmonary function index indicative of pulmonary function; andthe controller cooperates with the communication circuitry to transmit at least the alert to the external device. 20. The device according to claim 11, wherein the device comprises a cardiac rhythm management device.