Pilot performance of the anti-G straining maneuver: respiratory demands and breathing system effects.
BACKGROUND
The anti-G straining maneuver (AGSM) is still an important part of pilot protection for G-induced loss of consciousness. The specific requirements for and the effects of breathing systems on the performance of the AGSM are essential elements to designing compatible breathing systems.


METHODS
Subject pools of 27 and 34 naval aviators were recruited and used to measure the inhalatory and exhalatory flow requirements for the AGSM and the breathing system effects of mask cavity pressure during AGSM performance on the Naval Air Warfare Center Dynamic Flight Simulator at acceleration levels up to 8 Gz.


RESULTS
The mean peak inhalatory flow was 125.5 L.min-1 (n = 135, SD = 42.1) with a maximum value of 274 L.min-1. The mean peak exhalatory flow was 154.4 L.min-1 (n = 135, SD = 49.6) with a maximum value of 308 L.min-1. For the effects of the breathing system on AGSM performance, inhalatory mask cavity pressures were not above 30 mmHg with the majority less than 10 mmHg. Exhalatory mask cavity pressures did not exceed 60 mmHg but predominated in the 20-30 mmHg range. In comparison to accepted guidelines, 67-77% of inhalatory mask cavity pressures were below and 91% of the exhalatory mask cavity pressures were above the Air Standardization and Coordination Committee (ASCC) limit of +/- 14 mmHg.


CONCLUSIONS
The difference in the peak inhalatory and exhalatory flows measured during this study and clinically can be attributed to different test conditions and performer techniques. The reduction in inhalatory flow with increasing G is consistent with the increase in breathing difficulty due to the G load and the inflation of the anti-G suit. However, exhalatory mechanics appear unaffected by the G load and the inflation of the anti-G suit. Since 23-33% of the inhalatory mask cavity pressures were above this ASCC limit, improvements in regulator performance are still needed. For exhalatory effects of the breathing system, the main contributor is the mask valve. While no pilot suffered unconsciousness or expressed complaints with the breathing systems used, these exposures were of short duration. The additional work of breathing during a combat engagement may further compromise the pilot's ability to retain consciousness with the AGSM.
Whitley
P E
PE
Department of Neurosurgery, Medical College of Pennsylvania, Philadelphia, USA.
D000337:Aerospace Medicine; D005541:Forced Expiratory Volume; D006112:Gravitation; D005676:Gravity Suits; D006801:Humans; D008397:Masks / Q000592:standards*; D010102:Oxygen Inhalation Therapy / Q000295:instrumentation*; D010366:Peak Expiratory Flow Rate; D015656:Respiratory Mechanics; D014474:Unconsciousness / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D014636:Valsalva Maneuver; D014797:Vital Capacity