Ambulatory monitoring of the impedance cardiogram.

The growing need for more advanced ambulatory monitoring has led to the development of an ambulatory monitor for impedance cardiography (VU-AMD). This paper presents two studies addressing the validity of the VU-AMD. In the first study, the cardiovascular responses of 25 subjects during various conditions were simultaneously recorded with the VU-AMD and a standard laboratory impedance device. Correlations between the responses of the ambulatory and laboratory devices were high, both inter- and intraindividually, except for stroke volume and cardiac output during exercise. In the second study, 26 subjects underwent 24-hr monitoring with the VU-AMD. The values obtained with the VU-AMD were realistic and varied in a predictable way over activity and posture. It is concluded that the VU-AMD is a valid device for the measurement of systolic time intervals in real-life situations, but its applicability for absolute stroke volume and cardiac output determination remains to be established.