Ambient Heat Stress Research Articles

Thermoregulatory aspects of environmental exposure to anticholinesterase agents.

Anticholinesterase (antiChE) agents can be highly toxic to birds and mammals and constitute a major proportion of the pesticides used throughout the world. AntiChEs consist of the organophosphates (OP), which irreversibly inhibit the enzyme acetylcholinesterase (AChE), and the carbamates (CB), which reversibly inhibit AChE. AChE inhibition elicits cholinergic stimulation in the central nervous system and in peripheral tissues and organs, which can lead to marked dysfunction of homeostatic systems, including temperature regulation. The control of body temperature uses cholinergic pathways in the integration and central processing of thermal information, as well as in the control of thermoeffector responses. Hence, the cholinergic stimulation elicited from exposure to antiChEs has profound effects on body temperature at rest as well as during exercise. Ambient heat and cold stress can also modulate the animal's sensitivity to antiChE exposure. After exposure to most OPs, rodents and other small species undergo a marked hypothermic response lasting up to 24 hours. On the other hand, humans exposed to OP pesticides rarely become hypothermic but rather experience a fever that may last many days. Recent studies monitoring body temperature in OP-exposed, telemetered rats demonstrated that the initial hypothermic response is followed by a period of hyperthermia lasting several days. That the hyperthermia can be blocked with administration of sodium salicylate suggests that the hyperthermia is a fever. Thus, the antiChE-induced effects on body temperature and other physiological systems cannot be explained solely by the immediate consequences of AChE inhibition and stimulation of cholinergic systems. Research into the mechanisms of action of antiChE toxicity will be improved with a better understanding of their effects on temperature regulation.

Ultraviolet skin exposure in marathon runners

Ultraviolet (UV) skin exposure was measured in a group of 21 marathon runners during the Barcelona and Madrid marathons. This was accomplished by means of a personal dosimeter attached to the runner's chest or back. At the same time, ambient UV irradiance and heat stress index were also measured by means of a spectroradiometer and a heat versus exertion monitor, respectively. The latter is an analog of the wet bulb globe temperature. The results showed that during the races the marathoners received a mean radiation of 10 and 4.5 of the minimal erythematous dose. In spite of this high UVB dose the runners did not show unwanted acute skin responses such as sunburn. Since marathon runners can be at high risk for skin cancer, the guidelines for protection of the skin from the American Cancer Society against UV radiation are highly recommended for this group of athletes.

Heat stress and helicopter pilot errors.

Helicopter pilots are subjected to degrees of heat stress that under laboratory conditions result in decreased performance. However, the effect of heat stress on the frequency of helicopter pilot errors is uncertain. The purpose of this study is to determine whether there is an association between ambient heat stress and pilot error. The records of 500 helicopter accidents and incidents due to pilot error during the months May through October were selected at random. On the day of the event, ambient dry bulb and wet bulb temperatures were recorded and compared to temperature and humidity readings on 1000 days chosen at random over the same time period, after eliminating days where events occurred. There was a significant difference between the dry temperature distributions of the days with pilot error compared with the control group (chi 2 = 47.54, P < .0001). A dose-response relationship was found, with a significantly lower risk when ambient dry bulb temperatures were 25 to 29 degrees C (odds ratio, 0.6; 95% confidence interval, 0.5 to 0.8, P < .0001), an increased risk of 1.6 (1.3 to 2.0, P < .0001) at 30 to 34 degrees C, and the highest risk at 35 degrees C or more (6.2, 95% confidence interval, 2.1 to 21.8, P < .0002). There is a dose-response relationship between ambient heat stress and pilot error in Israel military helicopter pilots. This is the first study outside the laboratory showing a connection between heat stress and accidents due to human error. Further studies are required to substantiate our findings and to determine whether extrapolation to other settings is warranted.

Workplace measurement of respirator effects using respiratory inductive plethysmography.

A useful system to study the cardiopulmonary effects of respirators in the workplace would be reliable, portable, and lightweight and would not encumber the nose or mouth or require modification to the respirator. Twenty men using such a system (which measured ventilatory parameters by respiratory inductive plethysmography [RIP]) were studied. The subjects all performed their usual jobs which involved some work with and some without a respirator. Twelve subjects used airline respirators and eight used air-purifying respirators. The RIP equipment measurements included respiratory frequency, tidal volume (VT), minute ventilation (V), and heart rate (HR). The RIP data from 20 other subjects was lost because of equipment malfunction, primarily lead separation in those whose jobs involved climbing around large workpieces. In general, the workers' cardiopulmonary parameters increased during respirator wear, probably because of a combination of factors, including the increased exercise of most respirator-requiring tasks and the weight and heat stress associated with the respirator and protective clothing. When the ventilatory parameters with and without a respirator were compared at the same heart rates, no significant differences were noted in VT for the entire group. Respiratory frequency, however, and V increased with respirator wear. The effects of respirators alone were found to be commonly confounded in the workplace by changes in protective clothing, exercise requirements, and ambient heat stress. Further improvements in the portable RIP system are needed before it can be accepted as a reliable ventilatory measurement device in the workplace.

Enhanced fever following castration: possible involvement of brain arginine vasopressin.

Arginine vasopressin (AVP) is thought to act as an antipyretic in the ventral-septal area (VSA) of the brain. As AVP content of this area has been shown to be virtually eliminated following long-term castration, we have tested the hypothesis that castrated rats would display enhanced fevers. Four months after castration (or sham castration), male Wistar rats were given prostaglandin E1 (200 ng), purified interleukin 1 (25 U), or saline (5 microliters) into a lateral cerebral ventricle. Castrated rats displayed fevers of longer duration, reflected as significantly enhanced thermal indexes, than did age-matched sham-operated controls. Castrated rats also were less able to defend their body temperatures to ambient heat stress but not to ambient cold. AVP content of VSA and lateral septum, but not of hippocampus, of castrated rats was significantly reduced; oxytocin content of the three areas was unchanged following castration. These data support earlier studies concerning effects of castration on septal AVP content and are consistent with the possibility that AVP is an antipyretic in the VSA of the rat.