[Physiopathology of chronic respiratory insufficiency]

The use by West et al. of gases with different solubilities and of appropriate models has indicated that impairment of gas exchange in patients with chronic obstructive pulmonary disease and respiratory failure resulted essentially from altered ventilation/perfusion ratios. To understand why some patients do not appear to be capable of compensating this impairment and become hypercapnic, it is necessary to examine the other components of the respiratory system (control of ventilation, respiratory muscles) and their interactions. The measurement of occlusion pressure and of average inspiratory flow, and analysis of the timing of the respiratory cycle provides interesting information on the output of the control system and the efficiency of respiratory muscles. Electromyography of respiratory muscles also affords useful information on the degree of fatigue of these muscles. The use of this data should help to clarify the problem that has remained unanswered for many years: is the patient with hypercapnia someone who does not want to, or cannot, increase his ventilation? Other studies in the same group of patients during sleep have supplied evidence for the presence of numerous episodes of arterial oxygen desaturation with marked effects on the cardiovascular system. Pathophysiology should also consider this aspect of respiratory failure which occurs in the third of our lifetime devoted to sleep.