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Biomedical subjects

T M Gibson

Publications and source records attributed to T M Gibson.

18 recordsLinked to original sources
PubMed1984

Hyperventilation in flight.

Hyperventilation in flight may be caused by environmental, psychological, pharmacological, and pathological factors. The effects are discussed and two case histories are presented, illustrating the development and effect of hyperventilation in training or aircrew under stress. Investigation of in-flight hyperventilation is technically very difficult, but positive acceleration, hypoglycaemia, and anxiety are important contributory factors. The incidence of hyperventilation must be reduced by educating aircrew in its aetiology, early recognition, and treatment.

Aerospace Medicine↗
PubMed1981

Prediction of oesophageal temperatures from core temperatures measured at other sites in man.

Transient changes in core temperature were induced in seven subjects by immersion in a hot, then a cold, bath and by light intermittent exercise. Measurements of core temperature were made at four sites: the external auditory canal, the oesophagus, the rectum and the gastrointestinal tract. A mathematical model was derived to enable prediction of oesophageal temperature from measurements made at any one of the other sites. The equations for auditory canal and rectal temperatures were very similar to those previously derived in the Institute of Aviation Medicine; use of an equation to predict oesophageal temperatures from gastrointestinal tract temperatures measured in the field using a radio-pill would therefore appear to be reasonable.

Aerospace Medicine↗
PubMed1981

Effect of saline loading during heat acclimatization on adrenocortical hormone levels.

Six male subjects were acclimatized to heat; once they were given sufficient 1% saline to prevent the occurrence of a salt deficit during acclimatization, and another time they were given no saline. Plasma aldosterone (PA), plasma cortisol (PC), plasma renin activity (PRA), and plasma electrolytes were measured before, during, and after and sweat electrolytes before and after the 11-day acclimatization program. PRA and PA were significantly increased by the acute stress of heat and exercise but were unaffected by acclimatization. These increases were attenuated, but not prevented, by drinking saline, whereas sweat [Na] and PC were reduced by acclimatization but were unaffected by saline. Thus adrenocortical activity has been shown not to be increased after heat acclimatization, and mineralocorticoid activity, although potentiated by a Na deficit, appears to be determined primarily by the acute stress of heat and of exercise. Hence, the increased Na conservation with acclimatization is likely to be a normal response to heat and exercise even in the absence of a negative Na balance.

Acclimatization↗
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

Investigation of a simple, retrospective test for in-flight hyperventilation.

The experiment was designed to study the feasibility of using a single rebreathing estimate of mixed venous carbon dioxide tension (PvCO2) was a simple field test for hyperventilation in pilots. The results confirmed that the fall of end tidal carbon dioxide tension (P(ET)CO2) during hyperventilation and rise during recovery was exponential. The results also showed that the relationships between PvCO2 and P(ET)CO2 values during the unsteady states of carbon dioxide washout and accumulation may be described as a loop which encloses the theoretically derived line for the steady-state relationships. The deviation from the steady-state line appears on theoretical consideration to be directly proportional to carbon dioxide elimination rate, and indirectly proportional to cardiac output. Because of the exponential recovery, and because one value of PvCO2 could correspond to a range of values of P(ET)CO2, it is concluded that a field test for hyperventilation based on a single rebreathing estimate of PvCO2 would not be of value. The finding of a low value of PvCO2 would, however, be an indication that hyperventilation had taken place.

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

Hyperventilation in aircrew: a review.

The causes and effects of hyperventilation, relevant to the flight environment, have been reviewed and one case history is presented. Methods of investigating in-flight hyperventilation are discussed.

Aerospace Medicine↗
PubMed1979

Cockpit thermal stress and aircrew thermal strain during routine Jaguar operations.

Thermal data have been obtained from Jaguar aircraft flying routine, warm-weather operations in Sardinia. These data have been analysed in terms of the ambient and cockpit wet bulb globe temperatures (WBGT) and the mean body temperature (Tb) of the pilot. In contrast to similar data previously obtained from Harrier and Buccaneer aircraft, no interrelationships could be demonstrated between ambient WBGT at ground level and either cockpit WBGT or pilot Tb. Relationships which could be described by equations of negative slope were obtained between Tb and sortie time and between cockpit WBGT and sortie time. A model has been derived for predicting aircrew thermal strain in the Jaguar from cockpit temperature and sortie time.

Aerospace Medicine↗
PubMed1979

Prediction of body temperatures during exercise in flying clothing.

A mathematical model has been used to describe experimental results for core and skin temperatures in subjects undergoing a rest/activity cycle in two aircrew clothing assemblies at two environmental temperatures (wet bulb, globe temperature (WBGT) indices of 25.9 and 28.9 degrees C). The model presented compares well with published data for subjects in standard aircrew equipment assemblies. Aircrew flying at a WBGT of 28.9 degrees C in chemical defence clothing may reach an unacceptable level of mean body temperature within 40 min and deep body temperature will rise at 1 degree C.hr-1. To prevent deterioration in flying performance during repeated sorties, an alteration in the work/rest activity pattern or the introduction of effective cabin or personal conditioning systems may be required,

Aerospace Medicine↗
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↗
PubMed1978

Effects of hypocapnia on psychomotor and intellectual performance.

Nine subjects performed five psychomotor tasks (two motor, two intellectual, and one combined motor and short-term memory) at three levels of PACO2 (38.5, 25.0 and 15.0 torr) with voluntary hyperventilation at 20 l/min. There were no performance decrements at PACO2 levels of 38.5 and 25.0 torr. At a PACO2 of 15.0 torr, there were no decrements of intellectual performance but there were highly significant decrements in motor performance. It is suggested that a lack of regional cerebral hypoxia, arising from compensating changes in regional cerebral blood flow, could be responsible for the preservation of intellectual performance at a PACO2 of 15 torr.

Adult↗