Influence of posture, breathing pattern, and type of exercise on minute ventilation estimation by a pacemaker transthoracic impedance sensor

Previous studies have shown a high correlation between transthoracic impeda nce minute ventilation (IMV) determined by a pacemaker sensor and actual mi nute ventilation (V-(E) over dot measured by standard methods. We hypothesi zed that several factors (e.g., posture, breathing pattern, and exercise ty pe) could potentially affect the calibration between IMV and V-(E) over dot in patients with Medtronic Kappa 400 pacemakers, V-(E) over dot (L/min) wa s monitored using a standard cardiopulmonary metabolic gels analysis system with simultaneous recording of IMV (ohms/min) using DR-180 extended teleme try monitors. Effects of posture and of breathing pattern at rest (19 patie nts; age 60 +/- 13 years) were evaluated by monitoring each patient under t hree conditions: (a) slow breathing, supine, (b) slow breathing, sitting, a nd (c) shallow breathing, supine. Calibration at rest was defined as the ra tio of IMV to V-(E) over dot. Effect of type of exercise on calibration com pared treadmill versus graded bicycle ergometer exercise (18 patients; age 62 +/- 14 years). Calibration during exercise was defined as: (a) "Begin " (the IMV to V-(E) over dot ratio at V-(E) over dot = 10 L/min, the typical V-(E) over dot value at beginning of exercise), and Ib) slope of the IMV/V- (E) over dot regression line. Calibration of IMV/V-(E) over dot was signifi cantly smaller for sitting versus supine position (0.7130.177, P < 0.002) a nd for shallow versus slow breathing (0.7210.373, P < 0.002), and larger fo r treadmill versus bicycle exercise (Begin: 1.240.43, P = 0.018; Slope: 1.2 60.42, P = 0.013). In conclusion, posture, breathing pattern, and type of e xercise affect the IMV estimation of the actual V-(E) over dot, possibly by altering the static or dynamic geometry (thus, the impedance) of the intra thoracic viscera.