STROKE VOLUME MEASUREMENT DURING SUPINE AND UPRIGHT CYCLE EXERCISE BYIMPEDANCE CARDIOGRAPHY

This study evaluated impedance cardiography (ZCG) estimates of stroke volume (SV) during exercise. Seven subjects were studied at rest and d uring progressive cycle exercise in supine and upright positions. SV w as determined by ZCG (SVZCG) during exercise and for the first 5 cardi ac cycles following exercise. SVZCG was compared with separate measure ments of SV by CO2 rebreathing (SVCO2). Static blood resistivity (p) w as measured at each level of exercise. No significant differences were found between supine exercise and immediate post-exercise values for the peak of the first derivative of the impedance change (dZ/dt(max)), left ventricular ejection time (LVET), or SVZCG. Small differences in dZ/dt(max) and SVZCG, but not LVET, were found in exercise to post-ex ercise cycling in the upright position. Intra-individual SVZCG and SVC O2, were moderately correlated (upright mean r = 0.64, supine r = 0.42 ) from rest to 70% of peak V-O2. Similar correlations were found betwe en Pulse-O-2 (V-O2/heart rate, used as an index to SV) and both SVZCG (upright r = 0.73, supine r = 0.57) and SVCO2 (upright r = 0.8, supine r = 0.65). The ZCG parameters dZ/dt(max) and LVET correlated better w ith Pulse-O-2 (dZ/dt(max): upright r = 0.92, supine r = 0.73; LVET: up right r = -0.9, supine r = -0.9). SVZCG calculated with the Kubicek eq uation performed as well as SVCO2. ZCG might be a superior method if t he inversely correlated parameters, dZ/dt(max) and LVET, were not expr essed as a product to calculate SV.