Pulmonary responses of asthmatic and normal subjects to different temperature and humidity conditions in an environmental chamber

Abstract

Determining the possible adverse health effects of air pollutants can be complicated by differences in the environmental conditions of temperature and humidity. To evaluate the potentially confounding effects of differences in temperature and humidity, we exposed 8 normal male subjects and 8 male subjects with asthma to the extremes in temperature and humidity that could be maintained in an environmental chamber. We performed serial pulmonary function tests for these subjects before and during 6 hr exposure periods on 5 separate occasions: cold, dry (10 degrees C, 10% relative humidity); cold, humid (10 degrees C, 50% relative humidity); normal ambient (22 degrees C, 40% relative humidity); hot, dry (37 degrees C, 15% relative humidity); and hot, humid (37 degrees C, 60% relative humidity). The exposure period included a 12 min exercise on a cycle ergometer. We found no significant change in spirometry, airways resistance, or diffusing capacity for either group of subjects at rest alone over the 6 hr period of exposure for any exposure condition. However, there were changes in spirometry and airways resistance as a result of the 12 min period of exercise. The subjects with asthma had significant decreases in forced expiratory volume in 1 sec (FEV1) (20-21%) and increases in specific airways resistance when exercising in conditions of cold and dry, cold and humid, and hot and dry. The normal subjects had an average increase in FEV1 of approximately 6% when exercising in the hot and humid conditions. We found significant correlations for the changes in FEV1 with the water content of the exposure conditions for both groups of subjects. We also found that the work performance (expressed as the external work performed divided by the oxygen consumed) was decreased for the subjects in both groups at the conditions of the higher temperature (37 degrees C) compared with the lower temperature (10 degrees C). These results confirm that controlling for the conditions of temperature and humidity is essential in chamber studies, field studies, or epidemiologic evaluations determining the adverse effect of an air pollutant.

Models and mechanisms of exercise-induced asthma

“…Thus, the mechanisms that contribute to the aetiology of AIB in humans may not be unique to individuals with asthma. Exercise-induced bronchoconstriction in asthmatics and bronchodilation in normal subjects correlate with inspired water content [73]. This confirms the tendency of normal human airways to narrow in response to hyperventilation [118][119][120].…”

Bronchial reactivity of healthy subjects: 18–20 h postexposure to ozone

“…In addition, desquamation and disruption of airway epithelial membranes by O 3 would increase accessibility of MCh and other inhaled irritants and cellular mediators to epithelial sensory nerves and the bronchial musculature (8). In support of this mechanism, our laboratory previously reported that ϳ1 day after exposure of healthy subjects to O 3 there is a loss of epithelial integrity and an increase in airway permeability (14).…”

“…It has been previously demonstrated that exposure to FA at moderate differences in ambient temperature (20-30°C) did not alter spirometric indexes of airway function; however, when normal subjects exercised under hot, humid conditions (37°C and 60% relative humidity), lung function improved significantly (8). However, the benefit of ambient heat on airway function appears to be lost when heat stress is combined with a high effective concentration of O 3 .…”

Humidity: A review and primer on atmospheric moisture and human health

“…Indirect effects of humidity on respiratory disease include the role of moist indoor environments in promoting the growth of mold and the reproduction of mites (Hayes et al, 2013;Richardson et al, 2005;Williamson et al, 1997) and the effects of humidity on pollen dispersal and pollen-related allergens (Bartkova-Scevkova, 2003). In a series of controlled climate chamber studies on exercise performance (Eschenbacher et al, 1992), asthma patients exhibited significantly greater bronchoconstriction after exercise than non-asthmatic subjects as RH decreased.…”