INFLUENCE OF RESPIRATION ON STROKE VOLUME DETERMINED BY IMPEDANCE CARDIOGRAPHY

  • 1 January 1981
    • journal article
    • research article
    • Vol. 52  (7) , 394-398
Abstract
The conventional method of calculating stroke volume (SV) with impedance was to measure changes in thoracic impedance for those beats of the impedance cardiogram (IC) which cross on a specific baseline. This severely limits the number of usable beats since respiration produces oscillation of the IC around this baseline. The influence of respiration on SV calculated independent of the baseline in 7 women, 20- to 44-yr-old, was investigated in each of 3 postures: seated, supine and standing. SV was determined in 3 continuous respiratory cycles from the following beats: all; all inspiratory (I); I on baseline; all expiratory (E); E on baseline; all end-E and end-E on baseline (conventional). The absolute values for SV, heart rate (HR) and cardiac output (.ovrhdot.Q) were posture dependent. SV did not differ among the respiratory phases in the standing and seated postures; in the supine posture the smallest SV occurred at end-E on baseline. HR varied with respiration in the standing and seated postures but not in the supine posture. Despite significant changes in HR in the seated and standing postures, .ovrhdot.Q did not differ among the respiratory phases. Supine .ovrhdot.Q were significantly smaller during end-E due primarily to a small SV. When reporting .ovrhdot.Q values for supine subjects it is important to designate the respiratory phase and baseline criteria. SV calculated independent of the baseline in general agree with the more conventional method of calculation. The calculation of SV should be independent of the baseline. The reliability of the data will be increased by increasing the number of observations and SV can be determined under circumstances where it is difficult to obtain end-E beats on the baseline.