Thoracic bioimpedance measurement of cardiac response to maximal cycle exercise

Changes in thoracic electrical impedance are related to stroke volume, and measurement of these alterations provides a noninvasive means of estimating cardiac output. The use of bioimpedance techniques during exercise has previously been limited by interference resulting from body motion and ventilation artifact. A bioimpedance monitor designed to minimize this interference was utilized to record cardiac responses to maximal cycle exercise in 21 healthy college men. Satisfactory peak values of cardiac output, stroke volume, and heart rate were recorded in 18 (86%) of the subjects. Cardiac output was closely related to oxygen consumption (mean r = 0.93). Mean resting and peak cardiac output values (6.85 and 33.75 L min,-1 respectively) were consistent with results using other methodologies in this subject population. The pattern of stroke volume changes with progressive workloads also mimicked that of previous reports. These findings indicate that cardiac output can be accurately recorded during maximal cycle exercise using measurement of thoracic bioimpedance. This technique offers a safe, convenient means of assessing cardiovascular responses to exercise stress.