Roles of Physiological Responses and Anthropometric Factors on the Gravitational Force Tolerance for Occupational Hypergravity Exposure.

Min-Yu Tu,Hsin-Hui Chen,Chung-Yu Lai,Chao-Chien Cheng,Je-Ming Hu,Fang-Ling Li,Chen-Shu Yang,Hsin Chu,Kwo-Tsao Chiang

doi:10.3390/ijerph17218061

Abstract

Gravity in the head-to-toe direction, known as +Gz (G force), forces blood to pool in the lower body. Fighter pilots experience decreases in blood pressure when exposed to hypergravity in flight. Human centrifuge has been used to examine the G tolerance and anti-G straining maneuver (AGSM) techniques of military pilots. Some factors that may affect G tolerance have been reported but are still debated. The aim of this study was to investigate the physiological responses and anthropometric factors correlated with G tolerance. We retrospectively reviewed the training records of student pilots who underwent high G training. Variables were collected to examine their correlations with the outcome of 7.5G sustained for 15 s (7.5G profile). There were 873 trainees who underwent 7.5G profile training, 44 trainees (5.04%) could not sustain the test for 15 s. The group with a small heart rate (HR) increase (less than 10%) during the first 1–5 s of the 7.5G profile had a nearly ten-fold higher failing chance compared with the large HR increase group (adjusted odds ratio: 9.91; 95% confidence interval: 4.11–23.88). The chances of failure were inversely related to the HR increase percentage (p for trend <0.001). Factors, including body mass index, relaxed and straining G tolerance, and AGSM, were found to be negatively correlated with the outcome.

Highlights

Modern high-performance aircraft are capable of agile maneuvers to meet the demand of acrobatic battles in the air [1]
The proportion by which the heart rate (HR) increased during training was negatively and even dose-dependently associated with the outcome
The body mass index (BMI), SGT, relaxed G tolerance (RGT), and anti-G straining maneuver (AGSM) score were significantly related to the dependent variable

Summary

Introduction

Modern high-performance aircraft are capable of agile maneuvers to meet the demand of acrobatic battles in the air [1]. Military pilots are occupationally exposed to extremely high gravity environments [2,3]. Among the six axes of gravity in flight, the direction from head to toe (+Gz, commonly called G force) is the main safety concern of experts in aerospace and occupational medicine. Because hypergravity forces the blood of the pilot to pool in the lower body, the arterial blood pressure is directly affected by G force [4,5]. If the magnitude of the G force surpasses the tolerance of the human body, pilots experience stagnant hypoxia and even suffer from G-induced loss of consciousness (GLOC). Pilots have no control over their plane, and the consequences of GLOC could be tragic [6]

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