[Changes in heart rate and blood pressure under push pull maneuver simulated on a tilt table].

Objective. Push-pull maneuver (PPM) was simulated using a tilt table to assess detailed cardiovascular responses and the simulation model. Method. Ten healthy fighter pilots were exposed to 3 times transition of body position of head-up tilt (HUT) for 1 min-->head-down tilt (HDT) for 10 s, 15 s and 20 s respectively-->HUT for 1 min in randomized sequences. The rate of tilt table rotation was 45 degrees /s. Heart-level arterial blood pressure was monitored with 4 s intervals, and HR was continuously monitored by ECG. Result. HR and BP fell significantly during HDT compared with those during HUT; upon subsequent HUT, HR and BP were significantly less than those during previous HUT, except BP at 11-15 s. Conclusion. Cardiovascular responses to PPM can be simulated with a tilt table. It is suggested that the tilt table model is valid in simulating the PPM.

[Assessment of autonomic nervous function during orthostatic stress in pilots with history of syncope].

OBJECTIVE: To assess the role of autonomic nervous function during orthostatic tolerance tests (OTT) in pilots with history of G-induced loss of consciousness (G-LOC) or vasovagal syncope (VVS). METHOD: The relation between heart rate variability (HRV) and outcome of OTT result were compared among 3 groups of cases: 1) 30 patients with history of syncope and positive OTT as patient group (PG); 2) 20 cases with history of syncope but negative OTT result as negative group (NG); 3) 15 age-, sex-, flight plane model-, flight time-matched healthy pilots as healthy control (HC). OTT results and HRV, heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP) before and after OTT and their time and frequency domain were compared and analyzed among the three groups. RESULT: HR, SBP, and DBP were not significantly different (P>0.05) among the three groups before OTT. But during OTT, HR in PG was higher than those in NG and HC (P<0.01), SBP and DBP in PG were lower than those in NG and HC (P<0.01). 24 h continuous RR interval standard difference (SDNN), HRV triangle index (HRVI), and interval average value in PG were significantly lower than those in NG and HC; Power spectrum analysis of mean 1 h value for low frequency part (LF) and high frequency part (HF) were not significantly different among three groups, but LF/HF ratio in PG was higher than that in NG or HC (P<0.05). CONCLUSION: It is suggested that G-LOC and VVS may be due to increase in sympathetic tone and decrease in parasympathetic tone during orthostatic stimulation, as resulted from autonomic nervous dysfunction.