Gas Exchange in Severe Chronic Obstructive Lung Disease in Relation to Inspired Oxygen and Increased Carbon Dioxide Fraction, Physical Exercise and Body Posture

Abstract

Pulmonary gas exchange (Douglas bag), arterial blood gas tensions and acid-base balance (electrode technique), were studied in 25 patients with severe chronic obstructive lung disease and a ventilatory capacity (MVV_F) ≤35% of predicted normal values. Comparisons were made, in the habitual state, between patients with earlier periods of manifest respiratory insufficiency (R-group) and a group of patients (C = comparison) with the same ventilatory impairment, but no such periods of insufficiency.

During ambient air breathing at rest, in the supine posture, the means and ranges of arterial blood gas tensions were not significantly different in the R- and C-groups, but standard bicarbonate and base excess were more elevated in the R-group. P_aO2 ranged from 37 to 73 and P_aO2 from 36 to 63 mmHg. The elevated V_D/V_T was not consistently different at rest in the supine and sitting body postures, but in the supine posture most of the ventilatory variables were lower in both groups and P_aO2 was higher in the R-group. In the C-group some of the ventilatory variables remained lower during exercise in the supine posture. During supine exercise V_DV_T decreased in the C-, but not in the R-group.

The habitual P_aO2 level and acid-base status were important factors for ventilatory changes during hypoxia, hyperoxia and induced hypercapnoea. Also the habitual P_aO2 influenced these changes. R-group female patients and two C-group male patients with secondary polycythemia seemed to be most adapted to chronic hypercapnoea.