A new source for vestibular illusions in high agility aircraft.

The enhanced maneuverability aircraft of the future will expose pilots to combinations of conventional translational accelerations as well as extraordinary angular accelerations. This flight regime, combined with the intense concentration required for combat maneuvering, will make motion-induced illusions more perilous than in existing aircraft. Although there are many causes for disorientation, theoretical analysis indicates two in particular, the "G-excess" and "cross-coupling" illusions, may be invoked by a new and distinctly different stimulus. These two illusions, which are both typically induced by motion of the pilot's head, may in addition be created by rotation of the aircraft with respect to its flight path. After comparing typical pilot head movements to projected decoupled angular motion capabilities of supermaneuverable aircraft, we conclude that the potential exists for G-excess or cross-coupling illusions in a high agility aircraft independent of pilot head motion with respect to the aircraft.

Positive pressure breathing for acceleration protection and its role in prevention of inflight G-induced loss of consciousness.

That pressure breathing for G protection (PBG) can improve both tolerance and endurance to high sustained +Gz acceleration is now well established. It is not surprising, therefore, that the undoubted potential benefits of PBG in an operational environment have been greeted with enthusiasm by aircrew and their commanders. In some quarters, the use of positive pressure breathing (PPB) during periods of high sustained +Gz acceleration is being hailed as a potential cure for the problem of G-induced loss of consciousness (G-LOC). We believe, however, that confidence in the technique for this purpose in modern, highly agile fighter aircraft is misplaced. This article reviews PPB's background and present use as protection against +Gz acceleration, and summarizes the physiologic basis for its effectiveness, before relating it to its undoubted role in support of other anti-G strategies. From theoretical considerations supported by published evidence, we conclude that while PPB, if used correctly and when combined with other strategies, can enhance tolerance to +Gz acceleration, its principal influence on the occurrence of G-LOC will be by virtue of its ability to increase endurance by decreasing aircrew fatigue.

Rapid decompression to 50,000 feet: effect on heart rate response.

Interest in Molecular Sieve Oxygen Generation Systems (MSOGS) for use in military aircraft has demonstrated a need to study physiological effects of MSOGS product gas in the worst case scenario, a rapid decompression (RD). In this paper we report the heart rate (HR) response to positive pressure breathing (PPB) during and after RD from 6,096 to 15,239 m (20,000 to 50,000 ft) in a hypobaric chamber while breathing gas mixtures that simulate the product gas from MSOGS. Interbeat (R-R) intervals were recorded in 10 subjects while they breathed either Aviators' Breathing Oxygen (ABO), that is 99.5% oxygen, or 93% oxygen at two regulator settings: dilution and non-dilution. Additional experimental profiles on six subjects isolated the effects of hypoxia, anxiety, and PPB on HR changes after RD. Anxiety appeared to have the greatest effect. Most of the subjects showed increased HR and reduced HR variability after the onset of pressure breathing (immediately after decompression). As the exposure continued, HR variability increased as the HR began to decline. No consistent change in the HR response could be attributed to the modest increase in hypoxia produced by substitution of 93% oxygen for ABO.

Maximal aerobic power in women cadets at the U.S. Air Force Academy.

A sample of 17 women cadets of the U.S. Air Force Academy's Class of 1980 was assessed to determine their maximal oxygen consumption and percent body fat. The sample was selected using the ponderal index to insure a stratified sample of body types. The Short Balke protocol was used to determine Vo2 max, and the Siri and the Keys and Brozek equations were used to find percent body fat. The Katch and McArdle equation was employed to determine body density. The average Vo2 max for the women cadets was 46.1 ml/kg/min (S.D. = 4.0). Correcting for altitude, this value compares quite favorably with other reported values. The 24.8% mean body fat places these subjects well within the normal range for college age females. The female cadets of the Class of 1980 appear to be above their contemporaries in civilian life in circulo-respiratory fitness.

Effects of equivalent sea-level and altitude training on VO2max and running performance.

Twelve middle-distance runners, each having recently completed a competitive track season, were divided into two groups matched for maximal oxygen uptake (VO2max), 2-mile run time and age. Group 1 trained for 3 wk at Davis, PB = 760 mmHg, running 19.3 km/day at 75% of sea-level (SL) VO2max, while group 2 trained an equivalent distance at the same relative intensity at the US Air Force Academy (AFA), PB = 586 mmHg. The groups then exchanged sites and followed a training program of similar intensity to the group preceding it for an additional 3 wk. Periodic near exhaustive VO2max treadmill tests and 2-mile competitive time trials were completed. Initial 2-mile times at the AFA were 7.2% slower than SL control. Both groups demonstrated improved performance in the second trial at the AFA (chi = 2.0%), but mean postaltitude performance was unchanged from SL control. VO2max at the AFA was reduced initially 17.4% from SL control, but increased 2.6% after 20 days. However, postaltitude VO2max was 2.8% below SL control. It is concluded that there is no potentiating effect of hard endurance training at 2,300-m over equivalently severe SL training on SL VO2max or 2-mile performance time in already well conditioned middle-distance runners.

The consequences of physiological resistances on metabolite removal from the patient-artifical kidney system.

A diffusion limited, multicompartment patient-artifical kidney transport model has been developed. The physiological transport parameters have been clincially elevated for radiosotopically tagged urea, creatinine, uric acid, vitamin B12, and inulin with anuric, chronic uremic patients. Concomitant hemodialysis simulations illustrate that a 3 compartment patient model is adequate to characterize physiological transport. However, because of the high value of the transcapillary mass transfer coefficient, it is concluded that a 2 compartment (intracellular/extracellular) model is adequate to define mass transfer in the patient-artifical kidney system: a single pool may be assumed for very low hemodialyzer (less than 20 ml/min) clearances. Dialysis simulations also demonstrate that a point of diminshing returns is reached with respect to increasing mass removal from the patient, via increasing dialyzer clearance for middle molecules. In a 5 hr hemodialysis simulation the system becomes limited by physiological mass transfer resistances for dialyzer clearances greater than 100 ml/min. It is concluded that physiological transport resistances significantly impeded the removal of middle molecules from the patient-artifical kidney system. As a result, a single, well mixed pool assumption is not generally adequate to describe solute transport. A consequence of this conclusion is that the M2-hr hypothesis, which is based on a single pool assumption, cannot be generally utilized to accurately adjust hemodialysis treatment schedules for equivalent middle molecule removal. We are currently analyzing the patient-artifical kidney system to define improved adjustments modes for equivalent mass removal employing a 2 pool patiemt model.