Reproducibility of haemodynamic measurements by impedance cardiography.

Impedance cardiography was used to measure heart rate (HR), stroke index (SI), cardiac index (CI) and left ventricular ejection time (t) in four subjects at rest and in eight subjects anticipating exercise and working at loads of 49, 98 and 147 watts on a bicycle ergometer. The resting measurements were repeated five times over a 2 week period and the exercise measurements were repeated three times at weekly intervals. Analysis of variance testing indicated that none of the variables changed significantly from day to day (P greater than 0.1). All variables changed with exercise and all but t changed from subject to subject (P less than 0.01). Coefficients of variation for CI, SI, HR and t were 10, 12, 8 and 1% respectively at rest and rose to 16, 13, 5 and 6% during exercise. There was a high linear correlation between work load and CI (r = 0.96). The data indicate that noninvasive impedance cardiography can be used to obtain reproducible measurements of CI, SI, HR and t during rest and immediately after exercise.