Role of chemosensitivity during exercise in normal subjects and patients with pulmonary emphysema

In 11 normal subjects (mean age = 22.8 years) and 8 patients with pulmonary emphysema (mean age = 70.4 years), the role of chemosensitivity in determining ventilation, cardiac output, lactic acid, and cyclic AMP and GMP was evaluated quantitatively during 150 or 30 W exercise and simulated exercise. Simulated exercise was done while the subjects took a rest by regulating arterial blood gases at exercise levels in patients and at PaO2 = 65 mm Hg and PaCO2 = 48 mm Hg in normal subjects. In normal subjects, the role of arterial blood gases in determining exercise ventilation, cardiac output, cyclic AMP and GMP are large, while those contributed much less to lactic acid. In patients, PaO2 contributed only half of the exercise ventilation. It accounted for a negligibly small portion of exercise cardiac output, lactic acid, and cyclic GMP. These results indicate, by deduction, that either augmentation of chemosensitivity, pH, or humoral factors is responsible for about half of the changes of exercise ventilation in patients with pulmonary emphysema. These factors seem to influence cardiac output, lactic acid, and cyclic AMP and GMP more strongly than PaO2 alone in exercising patients.