Chronic alveolar hypoventilation has been considered in terms of its pathogenesis. Distinction has been made betweengeneralalveolar hypoventilation, which arises from failure of the ventilatory apparatus, andnetalveolar hypoventilation which is secondary to bronchopulmonary disease. Examples are presented to ifiustrate the pathogenesis ofgeneralalveolar hypoventilation in various disorders of the ventilatory apparatus. The common end-points for all of these are arterial hypoxaemia and hypercapnia; these abnormalities in the blood gases are responsible for the cardiorespiratory failure of chronic alveolar hypoventilation. However, the clinical expression of these abnormal blood gases is modified by the pathogenetic background: in failure of the respiratory centre, the consequences of arterial hypoxaemia and hypercapnia are manifest in the purest forms, free of the complications of abnormal lungs or mechanics of breathing; in severe kyphoscoliosis, the compressed distorted lung restricts the pulmonary hypertension andcor pulmonale; in obesity, the hypermetabolic and hypervolemic states provide a background of left ventricular, as well as right ventricular overload, for the consequences of arterial hypoxaemia and hypercapnia. The clinical importance of recognizing the syndrome ofgeneralalveolar hypoventilation lies in its reversibility following adequate relief of the hypoxaemia and hypercapnia.
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