RESPIRATORY MUSCLE LIMITATION IN PATIENTS AFTER PNEUMONECTOMY

Exercise capacity is significantly impaired in postpneumonectomy patients who have relatively normal remaining lungs. Our objectives are to determine (1) the nature and extent of mechanical ventilatory abnormalities and oxygen cost of breathing in such patients, and (2) the efficacy of a selective respiratory muscle training program in improving ventilatory and exercise performance. A group of eight postpneumonectomy and eight normal subjects (mean ages 59 and 50 yr, respectively) were studied during steady-state exercise and resting voluntary hyperventilation. Ventilation, work of breathing, cardiac output, and oxygen costs of breathing were determined. Four postpneumonectomy and five normal subjects were studied before and after a respiratory muscle training program. In patients after pneumonectomy compared with normal control subjects, maximal oxygen uptake (VO2) was 56% lower (p < 0.001). Work of breathing was significantly higher at a given ventilation. Mechanical efficiency of ventilation was lower by 44% (p < 0.05). Near maximal VO2, 48% of any additional increment of total-body VO2 was required to sustain the associated increment in ventilatory work, compared with 28% in normal subjects (p < 0.05), suggesting that competition between respiratory and nonrespiratory muscles for oxygen delivery is a significant factor limiting exercise after pneumonectomy. After respiratory muscle training, maximal respiratory pressures improved but maximal sustained ventilation and maximal VO2 did not improve significantly, suggesting that selective respiratory muscle training is of limited utility in postpneumonectomy patients.