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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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What is claimed is: 1. A method, comprising: providing an implantable cardiac device configured to sense transthoracic impedance and make an activity measurement; implantably computing an index indicative of pulmonary function using the sensed transthoracic impedance by computing a ratio of multipl

What is claimed is: 1. A method, comprising: providing an implantable cardiac device configured to sense transthoracic impedance and make an activity measurement; implantably computing an index indicative of pulmonary function using the sensed transthoracic impedance by computing a ratio of multiple respiration parameters; implantably computing a patient activity level using the activity measurement; and detecting an episode of dyspnea based on a parameter of the computed pulmonary function index exceeding an index value of a pulmonary function index versus activity level profile, the index value associated with an activity range of the pulmonary function index versus activity level profile which the patient activity level is calculated to be within, wherein the pulmonary function index versus activity level profile comprises a plurality of index values associated with different ranges of patient activity levels. 2. The method of claim 1, wherein the index value for detecting the dyspnea episode is based on the pulmonary function index versus activity level profile. 3. The method of claim 1, wherein the pulmonary function index versus activity level profile is formed by trending 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 method of claim 1, wherein the pulmonary function index versus activity level profile is formed by trending a plurality of pulmonary function index values and their associated patient activity levels, wherein the threshold for detecting the dyspnea episode is based on the pulmonary function index versus activity level profile. 5. The method of claim 1, wherein computing the pulmonary function index comprises computing a ratio of a respiratory rate value and a tidal volume value for the patient. 6. The method of claim 1, comprising: adapting a cardiac therapy for the patient based on the computed index indicative of pulmonary function of the patient; and delivering the adapted cardiac therapy to the patient. 7. The method of claim 1, comprising determining a patient's sleep-state at least in part using the pulmonary function index. 8. The method of claim 1, comprising alerting a physician in response to a pulmonary function index value being beyond the index value. 9. The method of claim 1, comprising alerting a physician in response to a trend of the patient's calculated index indicative of pulmonary function.