Exercise testing supplements conventional pulmonary function measurements. It helps to assess fitness, interpret dyspnea, diagnose exercise-induced asthma, monitor changes in severity of disease during treatment, and provide data relating to medical-legal questions about impairment and disability. Heart rate increases linearly with exercise intensity, but ventilation increases in a nonlinear fashion due to accumulation of lactic acid, which provides excessive stimulation to ventilation. In normal subjects arterial blood gases do not change with mild or moderate exercise, but PCO 2 falls slightly at higher levels. The P(A-a)O 2 increases and V D /V T decreases with exercise. Interpretation of exercise tests requires recognition of changes from this normal pattern. The treadmill and the bicycle ergometer provide standardized workloads that can be easily changed. Workload may be maintained at a constant value during the test, or it may be altered at intervals. Interpretation of exercise tests is illustrated by the results from four patients.
Cruver et al. (Wed,) studied this question.