Impairment of pulmonary gas exchange during exercise in chronic pulmonary emphysema

Abstract

Most data dealing with the pulmonary gas exchange in chronic pulmonary emphysema have been collected on resting subjects. The purpose of this study is to clarify the causes of the fall in arterial oxygen pressure which often occurs in exercising patients with chronic pulmonary emphysema. Materials and Methods In 10 patients with severe chronic pulmonary emphysema (FEV1 /VC averaged 30%) the determinations were performed during cardiac catheterization. These subjects exercised on the bicycle ergometer with a cardiac catheter placed in the main pulmonary artery, and an indwelling arterial needle in the brachial artery. Samples of arterial blood, mixed venous blood, and expired air were collected at rest and during exercise. These measurernents were followed by nitrogen washout studies. Estimates of the distribution of the pulmonary blood flow, ventilation and the ventilation-perfusion ratio were made by the modified Briscoe's methods. Results A) Changes of blood gas The arterial oxygen pressure (Pao2) and saturation (Sao2) at rest averaged 71±6.2 mmHg and 91.9±1.6% and fell during exercise to the average value of 59±7.3 mmHg and 86.9±3.1 % respectively. Mixed venous oxygen saturation (SVo2) at rest averaged 66.7±2.8% and fell during exercise to the average value of 40.1±7.8 %. B) Oxygen uptake Oxygen uptake (Vo2) increased remarkably from 263±45.3 ml/min to 748±214.0 ml/min during exercise. C) Alveolar ventilation and turn over rate Total alveolar ventilation (VAT) increased remarkably from 4.8±0.8 L/min at rest to 16.7±3.9 L/min during exercise, and the turn over rate in fast (VA1/L1) normal (VA2/L2 ), slow-ventilated space (VA3/L3) averaged 10.38±3.91, 1.57±0.49, 0.24±0.11, respectively at rest and increased to the average value of 11.82±3.20, 2.19±0.85, 0.36±0.10 during exercise. D) Cardiac output Cardiac output increased slightly from 5.3±1, 0 L/min to 8.0±1.3 L/min during exercise. E) Ventilation-perfusion ratio Ventilation-perfusion ratio in well (fast-normal)-ventilated space (VA1, 2/Q1, 2) and slow-ventilated space (VA3/Q3) averaged 1.44±0.33 and 0.26±0.06 at rest and increased to the average value of 3.78±0.41 and 0.47±0.13 respectively during exercise. F) Changes in slow-ventilated space with particular reference to end-capillary oxygen saturation Volume fraction of slow ventilated space (L3/LT) was 68±9.6% at rest and decreased to 61±11.3% during exercise. Estimated fraction of cardiac output perfusing slow-ventilated space (L3/lT) was 44±10% and slightly increased to 48 i 1 7% during exercise, and the perfusion index (Q3/QT/L3/LT) raised from 0.64±0.17 to 0.78±0.16. The calculated end-capillary oxygen saturation of slow-ventilated space (Sc3) was 84.2±2.4% at rest and fell to 74.7±4.6% during exercise. Discussion and Conclusions In the lower range of the ventilation-perfusion ratio as seen in the patients with chronic pulmonary emphysema, the fall of mixed venous oxygen saturation appeared to account for the fall in end-capillary, and arterial oxygen saturation. Thus, arterial oxygen pressure in the patiens with emphysema was very sensitive not only to the uneven ventilation-perfusion ratio but also to changes in oxygen consumption, and cardiac output. These findings serve to emphasize that studies of the uneveness of ventilation-perfusion ratio alone are not sufficient to interpret changes in pulmonary gas exchange in emphysema especially during exercise.