Bronchial response of asthmatic patients in an atmosphere-changing chamber. 2. Effects of exercise at high altitude

Asthma in medium altitude--exercise-induced bronchoconstriction in hypobaric environment in subjects with asthma

BACKGROUND

Hypoxic gas inhalation has been reported to enhance airway responsiveness and results in bronchoconstriction in animal models and in humans with asthma. However, the data have so far been conflicting. The aim of the present study was to examine the effect of reduced barometric pressure on exercise-induced bronchoconstriction (EIB) in subjects with asthma.

METHODS

Twenty subjects (10-45 years old, male symbol/female symbol = 13/7) with asthma (at least 10% reduction in forced expiratory volume in 1-second postexercise) participated in exercise testing in barometric pressure corresponding to altitudes of 200 (normobaric) and 2500 (hypobaric) m above sea level in random order on separate days. Lung function was measured before and after exercise, as well as after inhalation of salbutamol. Heart rate, oxygen uptake (), arterial oxygen saturation (S(p)O(2)), respiratory gas exchange ratio (RER) and minute ventilation () were measured during exercise.

RESULTS

There was no difference in lung function after exercise. The and HR(peak) during exercise did not differ. The RER(peak) was higher (P = 0.04) in hypobaric environment. The decreased 10.1% (7.2-13.0) [mean (95% confidence intervals)] (P < 0.001) from normobaric to hypobaric environment. At the same time, S(p)O(2) at decreased from 94.4 (92.2-96.6) to 85.6% (82.8-88.4) (P < 0.001).

CONCLUSIONS

A barometric pressure corresponding to altitude of 2500 m did not increase EIB in subjects with asthma. The reduction in is most probably due to the lower S(p)O(2) in hypobaric environment.

Pulmonary function testing and extreme environments

Millions of people worldwide engage in leisure or occupational activities in extreme environments. These environments entail health risks even for normal subjects. The presence of lung disease, or other conditions, further predisposes to illness or injury. Patients who have lung conditions should, but often do not, consult with their pulmonary clinicians before traveling. Normal subjects, including elderly or deconditioned adults, may be referred to pulmonologists for evaluation of risk prior to exposure. Other patients may present for consultations after complications occur. Pulmonary function testing before or after exposure can assist physicians counseling patients about the likelihood of complications.

Lung disease at high altitude

The lungs are a delicate interface between the atmosphere and our bodies across which oxygen diffuses from the air we breathe to the blood which carries oxygen to the cells and mitochondria. In healthy lungs at sea level where there is a surfeit of oxygen, this process occurs easily, whereas, in lungs with disease it becomes a task which may not be fully successful and hypoxemia may ensue or worsen. At high altitude where the barometric pressure (Pb) and thus the supply of oxygen is lower, the job of getting oxygen to the blood, even in the healthy lung is more difficult, and in the diseased lung it may be impossible. This presentation will review the lungs' responses to high altitude, with emphasis on the abnormal. Both acute and chronic responses of patients with pre-existing lung disease will be reviewed. Pulmonary diseases encountered at high altitude in previously healthy people, such as high altitude pulmonary edema and chronic mountain sickness will be touched on only as they pertain to other patients. Pre-existing lung disease (with and without hypoxemia at sea level) such as obstructive lung diseases (asthma, COPD, emphysema), and restrictive lung diseases (sarcoid, asbestosis, interstitial pulmonary fibrosis) will be discussed in terms of gas exchange, lung mechanics, and treatment at high altitude. Disorders of ventilatory control; e.g., obesity-hypoventilation syndrome and sleep apnea, may present formidable problems, and guidelines for their treatment will be discussed. Infectious lung diseases; e.g., pneumonia, cystic fibrosis, and pulmonary vascular disorders such as chronic mountain sickness, primary pulmonary hypertension, and congenital absence of the pulmonary artery are important disorders that require special attention because of the accentuated hypoxic pulmonary vascular response encountered at high altitude. The purpose therefore, is to provide the medical practitioner with the insight into prevention, recognition, and treatment of pulmonary problems encountered specifically at high altitude, as well as guidance on how best to advise patients with lung disease who want to fly in airplanes and/or ascend to high altitude for work or pleasure.