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Biomedical subjects

J R Allan

Publications and source records attributed to J R Allan.

At least 19 recordsLinked to original sources
PubMed1989

Effect of head or neck cooling used with a liquid-conditioned vest during simulated aircraft sorties.

The effectiveness of head or neck cooling in reducing head sweating and increasing subject comfort when used in conjunction with a liquid-conditioned vest during simulated sorties in the European Fighter Aircraft was investigated. Six subjects underwent three 2-h exposures at 40 degrees C wearing Aircrew Chemical Defence clothing and one of three combinations of liquid-conditioned garments. In all three exposures, a liquid-conditioned vest was worn and, in two exposures, either a head-cooling cowl or a neck-cooling collar was worn in addition to the vest. All six subjects reported increased comfort and decreased head sweating with head cooling, a result supported by the data collected.

Adult↗
PubMed1989

Detectability of emergency lights for underwater escape.

The time to detect each of three underwater lights by six subjects was measured in clear and turbid (attenuation coefficient = 4.2.m-1) water, at distances of 1.54 m and 3.1 m, from two viewing angles, straight ahead (0 degrees) or 65 degrees to one side, and under three levels of ambient illumination. The lights were viewed either through a window, to simulate the use of a face mask, or with the subjects immersed. All lights were detected rapidly (less than 1 s) when viewed through the window in clear water. In turbid conditions, none of the lights was seen at 3.1 m by any subject. At a 1.54 m viewing distance, reliable detection by immersed subjects was found only in the clear water under the two darker ambient illuminations. In turbid water, detection was unreliable. We conclude that the design of underwater escape lighting should not rely on visibility over distances greater than 1.5 m, and that an illuminated guide-bar might provide valuable assistance in directing escape from aircraft.

Accidents, Aviation↗
PubMed1986

The thermal performance of partial coverage wet suits.

A wet-suit worn external to normal clothing and covering the trunk and arms only has been assessed as a method for providing short-term immersion protection for helicopter passengers in offshore oil field operations. Manikin measurements of effective insulation in water give a mean figure of 0.54 togs for the areas covered by the suit and 0.09 togs for uncovered areas. These figures were used to obtain model predictions of survival time for 'thin' and 'average' men which suggest that the suit can give adequate protection for 1 h at 5 degrees C subject to care in fitting. Direct measurements of heat flux have demonstrated the presence of water flushing beneath the suit and the potentially serious loss of insulation that can result.

Body Temperature Regulation↗
PubMed1985

The effect of leakage on the insulation provided by immersion-protection clothing.

The effect of controlled, incremental water leakage on the thermal insulation provided by three immersion-protection assemblies has been measured using a thermal manikin. The results show an average loss of 30% of the initial insulation for a leak of 500 g, 40% for a leak of 1000 g, and nearly 60% for a leak of 3000 g. The assemblies differed only in the thermal insulation layer which consisted of: A. A single thickness of wool (initial immersed insulation 0.63 clo) B. A double thickness of wool (initial immersed insulation 0.79 clo) and C. A layer of polypropylene batting between nylon covers (initial immersed insulation 0.76 clo). Differences between the assemblies in loss of insulation with leakage were small and no evidence was found to support claims that the insulating properties of polypropylene are more resistant to wetting than those of wool. It is considered that the substantial loss of insulation even with small leaks makes it essential that tests of the water-excluding performance of immersion suits are undertaken in realistic conditions rather than in calm water.

Body Temperature Regulation↗
PubMed1985

Immersion cooling: effect of clothing and skinfold thickness.

Accidental immersion often involves the threat of death due to hypothermia. Clothing to control heat loss in water is generally selected to minimize bulk while providing the necessary protection. While water temperature (Tw) and possible immersion time are often considered, another relevant variable is the insulation provided by subcutaneous fat. This paper describes the use of a sophisticated computer model to explore the interactions among skinfold thickness (6-20 mm mean weighted value), clothing insulation (0.06-0.23 clo, immersed), and Tw (0-20 degrees C), in producing critical hypothermia (arterial temperature less than or equal to 34 degrees C). Results indicate that subcutaneous fat strongly affects heat loss even with heavy clothing. Discussion includes examples of the possible use of skinfold data to improve specification of protective clothing for groups and allow special clothing prescription for individuals.

Adult↗
PubMed1981

Heat stress in front and rear cockpits of F-4 aircraft.

Heat stress can be a serious problem in aircraft flown at low altitudes in warm-to-hot environments. Data are reported here on 36 flights by F-4 aircraft at Eglin AFB, FL. Ground dry-bulb temperatures (Tdb,g) were 19-33 degrees C (mean 28 degrees C) with psychrometric wet-bulb temperatures (Twb) 14-24 degrees C (mean 20 degrees C). Environmental and physiological data were recorded in both front and rear cockpits at 2-min intervals throughout each mission, which simulated low-level ground attack and lasted 94-126 min. Data were analyzed for four phases. A) preflight taxi, B) low-level flight, C) ordnance delivery, and D) postflight taxi. Cockpit dry-bulb temperature (Tdb,c) exceeded Tdb,g during ground operations; the front cockpit cooled in flight, while the rear remained hot. Linear relationships appeared for Tdb,c vs. Tdb,g in the four mission phases, and for globe temperature vs. Tdb,c. Aircrew mean skin temperature was significantly related to Tdb,c, and core (ear canal) temperature rose slightly with heat stress. Sweat rates reflected both Tdb,c and clothing worn. Discussion covers differences in air conditioning in the two cockpits and possible consequences of the observed heat stress and physiological strain.

Adult↗
PubMed1980

Effect of direction and rate of change of deep body and skin temperatures on performance of a rotary pursuit task.

Performance at a pursuit rotor task has been studied during the overshoot of core temperature caused by sudden cooling after heating, and the undershoot caused by sudden heating after cooling. Conditions were chosen so that effects of the absolute levels of core and skin temperature could be discounted. The results showed that the direction of change of core and skin temperature, rates of change of core temperature between -0.07 and +0.06 degrees C/min, and rates of change of skin temperature between -1.0 and +1.0 C/min did not affect performance; particular circumstances of this experiment, expecially the short duration of the changes in direction studied, make this conclusion tentative. Comparison with earlier studies indicates that the major determinants of performance at elevated body temperatures are absolute levels of mean skin temperature, with the absolute level of core temperature having a less significant role.

Adult↗
PubMed1979

Effect of induced cyclic changes of deep body temperature on task performances.

Performance of three tests was studied during induced cycles of deep body temperature between limits of 37.8 degrees C and 38.9 degrees C. During heating phases skin temperature was 38.8 degrees C and during cooling it was 36.1 degrees C. A verbal transformation test, performed at the midpoint of each temperature cycle, showed no significant effect from the large differences in skin temperature and subjective comfort between heating and cooling. The test was considered to be insufficiently difficult. A pursuit rotor test and a colour/word interference test, performed at the end of the heating and cooling phases, showed mean decrements in performance of 15% and 4%, respectively. These results are related to the measured levels of deep body and skin temperature and to subjective assessments of comfort.

Adult↗
PubMed1979

Effect of cockpit temperature gradients on the validity of single-point measurements.

Dry bulb temperature was measured at six sites throughout seven sorties in F4E aircraft in a study of vertical and lateral cockpit temperature gradients designed to determine the validity of single-point measurements. The results show that both vertical and lateral gradients exist in F4E aircraft and that single-point measurements of Tdb close to the right shoulder show a bias of up to 4 degrees C in relation to mean cockpit dry bulb temperature derived from measurements at five sites. This bias may be removed by using the predictive relationships developed in this study. The relationship between black globe and dry bulb temperatures is also given for F4E aircraft flown in warm, sunny conditions.

Aerospace Medicine↗
PubMed1979

Separation of the effects of raised skin and core temperature on performance of a pursuit rotor task.

Performance of a pursuit rotor task was studied during induced cycles of core temperature between limits of 37.9 degrees C and 38.5 degrees C. At each level of core temperature tested (37.9 degrees C, 38.5 degrees C, and 38.5 degrees C) performance was significantly worse during heating, when skin temperatures were high, than during cooling. The observed decrements were 13.6% at 37.9 degrees C, 16.0% at 38.2 degrees C and 18.1% at 38.5 degrees C. While it may be true that the performance changes were caused by changes in the level of skin temperature, the direction and rate of change of both core and skin temperatures may be important determinants of performance. The results are discussed in relation to current arousal theory.

Adult↗
PubMed1979

Effect on performance of cycling deep body temperature between 37.0 and 37.6 degrees C.

Previous experiments (1.2) showed that performance of of a pursuit rotor task is worse during heating than during cooling at deep body temperatures of 37.9-38.5 degrees C. Performance of the same task and of a manikin task has now been studied in a similar experiment while core temperature was cycled between 37.0 and 37.6 degrees C. No change in performance was observed between heating and cooling. It is concluded that decrements in performance during heating only develop above a critical absolute level of deep body temperature. The critical level of deep body temperature, above which performance of the rotary pursuit task is degraded, is 37.6-37.9 degrees C, and this can be related to affective thermal sensation.

Adult↗