Cardiopulmonary function was studied at rest and during exercise in 17 patients with Fallot's tetralogy who had systemic-pulmonary anastomoses to determine the factors which limit their work capacity (Wmax) and produce their limiting symptoms. The patients stopped exercise at a mean work rate of 355 kg-M·min-1 because of dyspnea or leg pain. The average pattern observed in room air was: a fall in arterial pO2 from 64 mm Hg at rest to 47 mm Hg during exercise due to increased right-to-left shunting; alveolar hyperventilation at rest (arterial pCO2 = 31.6 mm Hg) and during exercise (arterial pCO2 = 35.2 mm Hg); a progressive fall in arterial pH during exercise to pH = 7.369; and increased levels of wasted ventilation (VD:VT = 50.6) during exercise. Wmax was directly related to pulmonary blood flow, anaerobic threshold, and O2 pulse, and inversely related to the size of right-to-left shunt during exercise.

Exercise response during O2 breathing in 16 patients studied showed decreased hypoxemia, decreased acidosis, and decreased minute ventilation. These results suggest that the excessive ventilation observed in these patients when they breathed room air was partly due to a chemoreceptor drive.

Exercise response in the supine posture in seven patients studied was improved with decreased dyspnea, decreased minute ventilation, and decreased wasted ventilation without changes in the right-to-left shunt. These results suggest that the excessive ventilation observed was partly due to an increased wasted ventilation. Dyspnea appeared to be related to the inappropriateness of the level of ventilation relative to the metabolic needs of exercise.

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