Changes of Tolerance and Cardiovascular Responses to Head-up Tilte Combined with LBNP Following Preceding Exposure to Head-down Tilt / 航天医学与医学工程

Objective To observe pre-syncopal limited tolerance and cardiovascular responses to head-up tilt combined with lower body negative pressure (HUT/LBNP) following exposure to head-down tilt (HDT, -1 Gz). Method Exposures to HUT/LBNP (-60 mmHg) in control session (without preceding 30 s -1 Gz treatment) and in simulated push-pull effect (PPE) session (with preceding 30 s -1 Gz treatment) were performed in 8 healthy adults. The changes of hemodynamic parameters were monitored by electrical impedance instrument during the experiments. Result The mean endurance time in presyncopal symptom limited HUT/LBNP in control session and in simulated PPE session were 8.4±2.1 min and 4.5±2.4 min, respectively, the two means were significantly different (P< 0.01). In simulated PPE session, as compared with baseline, heart rate (HR) during HDT was significantly lowered (P<0.01), while stroke volume (SV) and cardiac output (CO) were increased significantly (P<0.01). During HUT/LBNP, the increased percentage (relative to baseline) of HR in PPE session was lower than these in control session (P<0.05); the decreased percentages of SV and CO during HUT/LBNP in PPE session were both higher than those in control session (P<0.05). During HUT/LBNP, arterial pulse pressure (PP) of control session was significantly decreased than the value of baseline value (P<0.05); Total peripheral resistance (TPR) of PPE session was significantly increased than baseline value (P<0.05). Conclusion Tolerance time before the appearance of presyncopal symptoms during HUT/LBNP decreases and cardiovascular responses to HUT/LBNP are impaired, preceding exposure to HDT.

Frequency of the "Gravity Transition Effect" during Aerial Combat Mission of F-16 Aircraft, ROKAF / 항공우주의학회지

BACKGROUND: Current studies have focused mainly on the push-pull effect (PPE), the reduction of +Gz tolerance when hypergravity (>+1 Gz) preceded by hypogravity (<+1 Gz). However, the reduced G tolerance could be induced by any G-transition. The frequency and extent of maneuvers to cause G-transition effect (GTEM) have not been studied previously in fighter aircraft. METHODS: 26 HUD (head-up display) videotapes from F-16 aerial combat training missions were reviewed for the presence of GTEM. The frequency and magnitude of the +Gz profiles were analyzed. RESULTS: GTEMs were found in 34 (29.6%) of 115 engagements reviewed. PPEMs (maneuvers found to cause push-pull effect) and rPPEMs (maneuvers found to cause reversed PPE) were found in 7.8%, 11.3% respectively. Combined maneuver that rPPEM followed by PPEM consecutively was found in 10.4% of engagements. There was no difference the frequency of GTEMs between BFM and ACM engagements (28.8% vs. 30.9%). CONCLUSION: GTEMs including PPEMs and rPPEMs are present in aerial combat training missions of F-16 aircraft and represent a significant source for accidents. These findings support the necessity of continued research into the physiologic response to GTE.