System for monitoring thoracic fluid levels based on impedance using an implantable medical device

摘要

Techniques are provided for monitoring thoracic fluid levels based on thoracic impedance (Z T ) and cardiogenic impedance (Z C ). In one example, the implantable device tracks the maximum time rate of change in cardiogenic impedance (i.e. max(dZ C /dt)) to detect trends toward hypervolemic or hypovolemic states within the patient based on changes in heart contractility. The detection of these trends in combination with trends in thoracic impedance allows for a determination of whether the thoracic cavity of the patient is generally "too wet" or "too dry," and thus allows for the titration of diuretics to avoid such extremes. In particular, a decrease in thoracic impedance (Z T ) in combination with a decrease in max (dZ C /dt) is indicative of the thorax being "too wet" (i.e. a fluid overload). Conversely, an increase in thoracic impedance (Z T ) in combination with a decrease in max (dZ C /dt) is indicative of the thorax being "too dry" (i.e. a fluid underload).