Lung volumes during +Gz acceleration and the effects of positive pressure breathing and chest counter-pressure

The advent of agile fast jet aircraft has initiated the research and development of enhanced systems to protect man against high +Gz acceleration. As part of such an enhanced system, the breathing of a pressurised gas mixture under +Gz is likely to become routine during the next decade in many of the world's air forces. This procedure, termed positive pressure breathing for G protection (PBG), typically uses breathing pressures of up to 65 mmHg in order to elevate intra-thoracic arterial blood pressure. In this way the fall in head level arterial blood pressure under +Gz acceleration is minimised. Consciousness is therefore preserved, with the aim of reducing the incidence of G Induced Loss of Consciousness (G-LOC). The aim of the research reported here is to assess the viability of the experimental technique and to gather preliminary data on the changes in lung volume subdivisions under PBG (specifically VC, ERV and the VC/ERV ratio).