Journal of Applied Physiology, Vol 41, Issue 1 52-56, Copyright © 1976 by American Physiological Society
Systolic time intervals during +Gz acceleration
T. B. Graboys and E. D. Michaelson
Systolic time intervals (STI) were recorded in 8 healthy male volunteers
before, during, and after 30-s exposures to +3 Gz, +5 Gz, and +7 Gz
acceleration. Heart rate (HR) increased at all +Gz levels, as did the HR
corrected QSIc interval, left ventricular ejection time (LVETc),
preejection period (PEPc) and PEP/LVET. These changes in STI were also
proportional to the +Gz level. At the higher +Gz levels, PEPc and PEP/LVET
continued to increase early in the recovery period, but HR and all STI
returned to control after 60 s of recovery. Although physiological
variables other than myocardial contractility, such as preload and
afterload may influence STI during +Gz the effects of +Gz on stroke volume
(SV) and cardiac output (CO) were estimated using previously described
relationships between STI and invasively determined indices of
cardiovascular function. In general CO increased as SV decreased. During
recovery, HR and CO fell and CO remained slightly below control levels,
primarily because estimated SV remained low. This study demonstrates the
feasibility of using STI to estimate noninvasively the transient changes in
cardiovascular function during +Gz acceleration.
