The use of impedance cardiography in the young and elderly during postural stress.

Impedance cardiography was used to measure postural changes of the indices of stroke volume and cardiac output in 20 elderly and 18 young subjects of either sex. In both the young and elderly subjects the reproducibility of the technique was high. All young subjects showed a fall in the index of cardiac output and increase in peripheral resistance when subjected to a 60 degree head-up tilt, but some elderly subjects showed either no change or an increase in cardiac output and fall in peripheral resistance on tilting. It is suggested that these abnormalities were the result of either an impaired autonomic nervous system or an increased peripheral arterial rigidity.