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Biomedical subjects

R R Burton

Publications and source records attributed to R R Burton.

At least 55 records · Page 3Linked to original sources
PubMed1986

Influence of inspired oxygen concentration on acceleration atelectasis.

The USAF is developing an On Board Oxygen Generation System (OBOGS) for use in fighter aircraft. This study was conducted to determine the inert gas dilution requirements of the OBOGS necessary to prevent acceleration atelectasis. Human subjects were exposed to either 21, 50, 70, 82.5, 95 or 100% inspired oxygen, along with an increased +Gz Simulated Aerial Combat Maneuver (SACM) profile using the USAF School of Aerospace Medicine human centrifuge. The SACM profile utilized four +4.5z peaks (136 s at this +Gz) superimposed on a +3 Gz baseline, representing a total ride time of 276 s. A significant reduction in vital capacity (VC) occurred at inspired oxygen concentrations of 70% and greater. The addition of 5% argon (a natural product of OBOGS) to pure oxygen did not reduce the magnitude of acceleration atelectasis observed, nor the severity of breathing symptoms. A 30-s exposure to positive pressure breathing at 30 mm Hg during the end of the SACM reduced the level of VC reduction caused by subjects breathing 100% oxygen during +Gz.

Acceleration↗
PubMed1986

A conceptual model for predicting pilot group G tolerance for tactical fighter aircraft.

A static model based on eye-heart vertical distance has been developed which predicts group mean G tolerances relative to the application of any of the following anti-G methods and/or physiologic responses: a) anti-G suit, b) reclined seat, c) anti-G straining maneuver (AGSM), d) positive pressure breathing (PPB), e) gradual onset of G, f) isometric muscular contraction, and g) leg elevation. This model was validated with published data. A variation of this model (derived equation) predicts the amount of AGSM (in mm Hg) required, in combination with any of the anti-G methods/responses at any G level. This calculated effort of AGSM can be equated to level of fatigue and performance decrements. A level of 50 mm Hg or an increase of 2 G in the upright seat was the maximum AGSM recommended for routine use as an anti-G method for operational fighter pilots.

Aircraft↗
PubMed1985

The effectiveness of specific weight training regimens on simulated aerial combat maneuvering G tolerance.

To assess the effectiveness of muscle-strength (weight training) on simulated aerial combat maneuvering (SACM) G tolerance, seven young men were exposed to a 12-week program of whole-body weight training in which were measured, strengths of various muscle groups, body circumferences, body mass, and the percentage of body fat. The magnitudes of the weights used in training were used to measure muscle strength and were compared and correlated with each subject's SACM tolerance--defined as the total time that a subject could withstand continuous exposure to a 4.5 and 7.0 + Gz centrifuge profile using fatigue as his voluntary endpoint. Chest and biceps circumferences increased 4.2% and 3.1%, respectively; abdomen and thigh circumferences did not significantly change; body fat decreased 16.8%; and body mass increased 2.3%. Abdominal (sit ups) and biceps (arm curl) strengths increased 99% and 26.2%, respectively, and were highly correlated with SACM tolerance time (p less than 0.01); leg (leg press) and chest strengths (bench press) made less significant contributions to the SACM tolerance time. A net increase in SACM tolerance times of 53% resulted from weight-training. Multiple regression analysis of all four muscle groups between weeks 1 and 12 with the SACM tolerance had a correlation of determination of 0.61.

Acceleration↗
PubMed1985

Operational G-induced loss of consciousness: something old; something new.

Loss of consciousness (LOC) during exposure to +Gz occurs in aircrew flying high-performance aircraft. This phenomenon is responsible for several USAF aircraft losses with accompanying loss of life. It has been recognized as a potential flying problem since 1938. Acceleration-induced LOC results in 15-to 20-s periods of aircrew total incapacitation, amnesia, and clonic spasms. It can occur at relatively low G levels and without symptoms of loss of light (blackout). Operational anti-G equipment and methods are not completely effective in preventing LOC. Considering the present status of G protection, a deficiency in the anti-G straining maneuver is considered to be the primary cause of G-induced LOC. This deficiency usually can be corrected with proper centrifuge training. Our present understanding of G protection suggests that the elimination of LOC as a serious problem for USAF high-performance aircraft operations must include the supination of aircrew to a minimum seat back angle of 60 degrees to 65 degrees.

Acceleration↗
PubMed1982

The influence of differential physical conditioning regimens on simulated aerial combat maneuvering tolerance.

The influence of physical conditioning on tolerance to a centrifugation profile called the Simulated Aerial Combat Maneuvering (SACM)--was determined using 24 young men as subjects. These subjects were assigned to groups as controls (no physical training, C), runners (R), and weight trainers (W). They followed a 12-week protocol of specified physical training. During this study, tolerance to the SACM, maximum oxygen consumption, muscle strength, and body composition were periodically determined. SACM tolerance was defined as the total time that a subject could withstand continuous exposure to a 4.5 and 7.0 +Gx centrifugation profile as determined by his voluntary endpoint of fatigue. The +Gx tolerance of the runners and controls increased at an average rate of 4 s/week during the course of the experiment. On the other hand, the weight trainers increased their G tolerance at an average rate of 15 s/week. The difference between group W compared with groups C and R was statistically significant at the 5% level. Fatigue scores indicate that group W subjects take longer to reach a given level of fatigue than did the subjects of the other groups. It appears therefore that a physical conditioning program of weight training will improve human tolerance to aerial combat maneuvers.

Aerospace Medicine↗
PubMed1980

Human responses to repeated high G stimulated aerial combat maneuvers.

Five subjects wearing standard USAF anti-G suits and seated at a 65 degrees back angle were exposed to a simulated aerial combat maneuver (SACM) which was repeated 5 times with 4-min 1-G rests between each SACM exposure. The SACM was 122 s in duration with 10 s acceleration peaks of 10, 8, and 6 G; between these peaks, the subject was at 4 G for 15 s. This series of repeated SACM exposure fatigued four of the five subjects. Heart rate and rhythm, arterial oxygen saturation, expired gases, lactate, pyruvate, glucose, CPK enzymes and isoenzymes, blood volume, subjective fatigue measurements, and subject performance were examined relative to the development of fatigue, the energy cost of the M-1, and tolerance to the SACM. All physiologic-metabolic parameters were significantly affected by the repeated SACMs. However, only heart rate changes appeared to be correlated with developing fatigue. A significant amount of energy is required to perform the M-1. Subjects whose energy-metabolic and cardiovascular states are least disturbed by high G exposure are those persons who will perform best and become least fatigued during repeated aerial combat maneuvers.

Aerospace Medicine↗
PubMed1980

Human tolerance to aerial combat maneuvers.

An acceleration profile was developed on the USAF School of Aerospace Medicine's 6.1-m radius centrifuge to measure human tolerance to the Aerial Combat Maneuver (ACM). The ACM profile is a continuous repetitive, 4.5 G for 15 s to 7 G for 15 s, cyclic G exposure which is terminated by the subject at his fatigue endpoint. ACM tolerances using this type of G profile were determined for seven subjects at four different seatback angles; i.e. 13 degrees, 30 degrees, 55 degrees, and 65 degrees from the vertical. Group (mean +/- S.E.) tolerances for the ACM were 170 +/- 17 s at 13 degrees and 541 +/- 48 s at 65 degrees. These tolerances were not usually correlated with relaxed gradual onset G tolerances. The subjective fatigue endpoint was physiologically verified using heart rate, heart rhythm, and performance criteria at the four seatback angles. The potential value of the ACM profile is considered as a measure of the effectiveness of anti-G equipment and methods in the aerial combat environment.

Acceleration↗
PubMed1979

Physiological effect of high, sustained +Gz forces on man.

Two studies were conducted to evaluate physiological responses and possible tolerance to high sustained +Gz forces at the USAF School of Aerospace Medicine, using the 20-ft (6.10 m) radius Human Centrifuge. In the first study (A), 14 human volunteer subjects--fully protected with an anti-G suit and performing the M-1 or L-1 straining maneuver--were exposed to +Gz forces. These forces began at +6.5 Gz, and increased weekly in 0.5 G increments to +9.0 Gz, for a duration of 45 sec at each level. Physiological performance was based mostly on the subjects' ability to maintain clear vision during the 45 sec exposure. Of the 14 subjects, 9 were able to maintain vision and remain at the +9 Gz level for 45 sec. In the second study (B), 12 human volunteer subjects--also protected with anti-G suits and using the straining maneuvers--were exposed to levels of +1, 3, 6, and 8 Gz, for 60 sec at each level. Extensive physiologic parameters were recorded in order to detect objective criteria which could be used as determinants for a medical tolerance endpoint to the particular level of +Gz stress. In both studies, the reasons for stopping the runs at levels exceeding +7.5 Gz included: fatigue, cardiac arrhythmias, blackout, and one occurrence of ventricular tachycardia. Other physiological responses to the sustained +Gz stress (such as heart rate, arterial blood pressure, central venous blood pressure, arterial oxygen saturation, gastric pressure, and ankle venous pressure) did not furnish specific information that could be used as "physiological tolerance limit" criteria.

Acceleration↗
PubMed1979

Influence of the ambient acceleration field upon acute acceleration tolerance in chickens.

It has been demonstrated both in the Russian and in the American space programs that there is a progressive deconditioning of the circulatory system with exposure to weightlessness. Astronauts and cosmonauts returned to Earth have a significantly reduced orthostatic tolerance which will persist for a few days. We have measured the acceleration tolerance of domestic fowl, acutely exposed to a 6 g+z field, as the time over which a normal heart rate can be maintained. This period of circulatory accommodation ends abruptly with a marked bradycardia, which with continued treatment is terminal. For animals which have been previously chronically accelerated (e.g., physiologically adapted to a 2.5 g field) the acute acceleration tolerance is greatly increased. It appears that the influence of the ambient acceleration field in conditioning the responsiveness of the circulatory system is a general phenomenon.

Acceleration↗
PubMed1979

Evaluation of assisted positive pressure breathing on +Gz tolerance.

The effect of both assisted and unassisted positive pressure (PPB) breathing on +Gz tolerance was evaluated. A GOR (gradual onset rate = 0.1 G/s) acceleration profile was used to evaluate five different experimental conditions: 1) G-suit-only, 2) G suit + unassisted PPB, 3) G suit + PPB assisted by the English jerkin, 4) G suit + PPB assisted by the Canadian waistcoat, and 5) the Swedish counterpressure garment G suit combination. Acceleration tolerances for these experimental conditions (excluding the Swedish garment) with the subjects performing M-1 maneuvers were measured using an exhaustive ACM (Aerial Combat Maneuvers) acceleration profile. GOR tolerances were similar for both assisted and unassisted PPB with the pressure breathing experimental conditions providing a significant GOR tolerance increase over the G suit only condition. Assisted PPB increased ACM tolerances over both unassisted PPB and G suit only conditions. It appears that assisted PPB may offer a practical method for reducing the fatigue associated with exposure to high G.

Aerospace Medicine↗
PubMed1979

Responses of domestic fowl to repeated +Gz acceleration.

The responses of domestic fowl to repeated exposures of 4 min to +6Gz (8 times daily, 5 d weekly) are reported. Survivorship curves for the test group of 48 birds divided into three response categories: mode I, highly susceptible, with all individuals dying on the first day; mode II, more tolerant, with mortality occurring within the first 20 d of treatment; and mode III, highly tolerant, with mortality occurring only after 20 d of treatment. Observations of lymphocyte frequency, an index of systemic stress, and postmortem observations indicate that this heterogeniety has a biological basis.

Acceleration↗
PubMed1978

Calibration of a new ear oximeter in humans during exposure to centrifugation.

An optoelectronic ear oximeter (Hewlett-Packard, model 47201A) was evaluated as a noninvasive method for determining arterial oxygen saturation (SaO2) in human subjects during exposure to various levels of accelerative forces. This physiological calibration involved exposing five subjects, while breathing air and wearing the ear oximeter for 60 s to each of three levels of accelerative forces (3, 5, and 7 G); arterial blood samples were withdrawn concurrently. SaO2 was calculated indirectly from the oxygen tensions (PaO2) measured from the sampled arterial blood with a blood gas analyzer and corrected for pH and base excess. These data were compared, as were similar data taken from the same subjects breathing three different hypoxic gas mixtures while resitng at earth's gravity (1 G). Regression analyses of these data for both experimental groups (a, G exposure, or b, hypoxic exposure), comparing the ear-oximeter SaO2 with the calculated SaO2, showed the ear oximeter to be accurate with correlation coefficients of 0.95 and 0.98, respectively.

Adaptation, Physiological↗
PubMed1977

Stress responses of pilots flying high-performance aircraft during aerial combat maneuvers.

In aerial combat maneuvers (ACMs), at Luke AFB, Az, eight pilots flew their two F-15 aircraft against nine pilots in three F-106 aircraft. A total of nine flights, consisting of 23 ACMs, were accomplished in 5 successive days. The degrees of fatigue, stress, and sympathetic activity were quantified using both subjective analyses and the biochemical constituents in the urine of the pilots of the F-15 or F-106. Biochemical indicators, reported per 100 mg creatinine, included: epinephrine, norepinephrine, 17-OHCS, urea, inorganic phosphate, sodium, potassium, and sodium/potassium ratio. The F-106 pilots exerted more relative effort than did the F-15 pilots--effort which appeared to be associated with high-G experience. Both groups of pilots were equally fatigued following ACMs; however, only the fatigue of the F-106 pilots was directly correlated with the length of the ACM. Sympathetic and stress responses during the ACM--similar for both groups of pilots--showed postflight increases of 54% in epinephrine, 19% in norepinephrine, and 20% in 17-OHCS over preflight values, thus suggesting a moderate stress response. Resting levels of these same indicators, for days the pilots did not fly and for pre-ACM values, were similar but higher than control values previously reported for other stressful activities. By late afternoon, postflight values for these indicators had returned to near-preflight levels.

Adult↗