Heart Rate Analysis during Simulated Push-Pull Effect Manoeuvre

Push-pull effect is considered as an important contributing factor in G-induced loss of consciousness (G-LOC) related aircraft accidents. Research concerned with the physiology of push-pull effect, attributed it to the delay in Autonomic Nervous System (ANS) response manifested as delayed Heart Rate (HR) and Blood Pressure (BP) recovery, which in turn resulted in decreased +Gz tolerance. As the HR is an important factor depicting ANS response, this study was conducted to analyse the HR response during a simulated push-pull effect manoeuvre. 18 healthy male volunteers aged between 25-40yrs participated in this study conducted in the High Performance Human Centrifuge (HPHC). Each subject had undergone a control run of increasing +Gz epochs and a push-pull run in which each increasing +Gz epochs was preceded by a-1.5Gz exposure of 10 sec duration. The onset and offset rates were IG/sec. HR was recorded one minute before starting the run, throughout the run and one minute after the run. Minimum baseline HR (HRb-min), peak HR during +Gz (HRpeak) and minimum HR achieved in post +Gz phase (HRmin-post ) were compared between +3Gz epochs of control run and comparable epochs of push-pull run using student t test. Also the time taken to attain the HRpeak (THR-peak) from the start of +Gz plateau and time taken to attain the HRmin-post (THR-min-post ) from cessation of +Gz exposure were compared between the runs using student t test. All the three HR readings did not show any significant difference between +3Gz control run and push-pull run. However the time readings THR-peak and THR-min-post were significantly higher in push-pull run. THR-peak was 12.2 (±3.8) vs 14.8 (±2.3), p=0.01 and THR-min-post was 11.5 (±6.0) vs 20.6 (±9.3), p<0.001 for the+3Gz control run and the push-pull run respectively. HR analysis during push-pull effect did not show any difference in the peak HR or the post +Gz baseline HR when compared w ith pure +Gz run. However there were significant delay for attaining the peak HR during +Gz phase and minimum HR during post +Gz phase of push-pull run. This may be attributed to the delay in recovery of autonomic nervous system following ×Gz exposure. The ANS impairment therefore seemed to be persisting long after the push-pull exposure.