Cardiopulmonary performance at rest and during exercise in seven patients with increased transradiancy of one lung ("Macleod's syndrome").

A group of seven patients with increased transradiancy of one lung included four with chronic bronchitis. The function of the two lungs combined was assessed by measurement of the lung volumes, airway resistance, and carbon monoxide uptake at rest, and by measurement of pulmonary ventilation, gas exchange, blood gases, and cardiac output at rest and during steady state exercise. The contribution of the hypertransradiant lung to the overall functional abnormalities at rest was estimated using a radioactive gas technique. All the patients had airway obstruction. Pulmonary gas exchange was only mildly affected at rest because of equal reduction of ventilation and perfusion in the abnormal lung, but during exercise ventilation-perfusion inequality increased in some of the patients. Cardiac output was low in five patients during exercise and in four there was excessive lactate production. The greatest physiological abnormalities were seen in two of the chronic bronchitics who had abnormalities of ventilation and perfusion in both lungs. We suggest that a pulmonary vascular abnormality resulting in reduced cardiac output, as well as ventilatory impairment due to airway obstruction, may contribute to the limited exercise capacity of these patients.