The Relationships Between Minute Ventilation, Pulmonary Gas Diffusion and Respiratory Work Measured Simultaneously During a Standared Exercise Test

¹ Cardio-Respiratory Laboratory, Toronto General Hospital and the Department of Medicine, University of Toronto

Simultaneous measurements of minute ventilation, diffusing capacity, franctional carbon monoxide uptake and the respiratory work equivalent for carbon monoxide (respiratory work per ml. carbon monoxide uptake) were made during a standared exercise on 22 normal subjects and on 40 patients with chest disease. These tests were performed in order to examine ways in which ventilatory response to exercise might be influenced by abnormalities of gas exchange and respiratory work.

Eight different groups of interrelationships between minute ventilation, diffusing capacity, fractional carbon monoxide uptake and the respiratory work equivalent for carbon monoxide were found. Normal minute ventilation during exercise occurred where gas exchange was normal (groups 1 and 2); where compensation for abnormal gas exchange was easily achieved (group 3); where the attempt to compensate for abnormal gas exchange was limited by a very high respiratory effort (group 4). Excessive hyperventilation during exercise occurred in some patients due to nervousness (groups 5 and 6). In others it occurred in an attempt to compensate for abnormal gas exchange; in some, compensation was achieved (group 7), in others it was not (group 8).

Similar basic abnormalities of respiratory function during exertion were found in patients with quite different types of pulmonary disease. For example, in group 2 there were patients with emphysema, pulmonary fibrosis, bronchitis and bronchiectasis.

Statistical analysis showed that the degree of dyspnea could be correlated with increased respiratory work especially where there was also abnormal gas exchange.