ESTIMATION OF CARDIAC-OUTPUT BY ELECTRICAL-IMPEDANCE DURING ARM EXERCISE IN WOMEN

The feasibility of using the transthoracic impedance cariogram (ZCG) of women to determine cardiac output (.ovrhdot.QZCG) and stroke volume (.DELTA.V) during upper body exercise where chest movements could distort the ZCG was calculated. As a frame of reference, .ovrhdot.QZCG values were compared with cardiac output values obtained by CO2 rebreathing (.ovrhdot.QCO2). Ten women (mean age = 29 yr) completed a discontinuous, progressive-intensity exercise test using an arm-crank ergometer. Exercise at each power output level of 60, 120 and 180 kp[pound]m.cntdot.min-1 was 10 min in duration followed by 10 min of rest. The ZCG was recorded during steady-state exercise and during a 15-s exercise pause when subjects remained motionless. .ovrhdot.QZCG and .ovrhdot.QCO2 were similar during exercise at each power output level. However, .ovrhdot.QZCG at each pause was lower than .ovrhdot.QZCG or .ovrhdot.QCO2 during exercise because of an immediate fall in heart rate with no change in .DELTA.V. Evidently, arm exercise can be stopped momentarily to obtain an artifact-free ZCG without compromising the calculation of .DELTA.V. The exercise pause .DELTA.V must be multiplied by the steady-state exercise heart rate to avoid an underestimation of the exercise .ovrhdot.QZCG.