Richert, Malie L Ceridon

Introduction Optivol (Medtronic Inc.) thoracic impedance (ZT) provides preemptive disease status information in heart failure (HF). It remains unclear how pulmonary‐capillary blood volume (Vc), lung volume (Lvol), and interstitial fluid influence ZT. Hypothesis Positional change and exercise result in increased Vc and/or lung interstitial fluid and ZT tracks fluctuation in these variables. Methods 12 HF patients (age 63±8yr, LVEF 41±14%) were recruited. Measures were taken at rest, exercise, recovery. This included: spirometry, ZT, diffusing capacity of the lungs for CO and NO (DLCO, DLNO), alveolar‐capillary conductance (Dm, interstitial fluid index), and Vc. Inspiratory capacity was obtained to provide consistent lung volumes for assessing ZT. Results Positional change (upright‐supine) resulted in an increased ZT (5±4%, p<0.01), while the change in Lvol (RV‐TLC) resulted in a 7±2 ohm swing in ZT (0.2±0.1ohm change/100ml change in Lvol). After 30min supine, Vc increased 28±39% (p<0.05) while Dm/Vc and Lvol decreased (29±11% and 17±3%, p<0.05). During exercise compared to baseline, Vc increased 56±44% (p<0.01), DmCO/Vc decreased 25±7% (p<0.05), and ZT did not change. During recovery measures normalized except DmCO/Vc. Conclusion Positional changes and fluctuations in Lvol influence ZT yet measures of lung fluid minimally impact this measure despite significant fluctuations.