Jk. Moon et al., STROKE VOLUME MEASUREMENT DURING SUPINE AND UPRIGHT CYCLE EXERCISE BYIMPEDANCE CARDIOGRAPHY, Annals of biomedical engineering, 22(5), 1994, pp. 514-523
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.