Respiratory Muscle Failure and Respiratory Failure

Abstract

It is well known that respiratory muscle weakness causes respiratory failure in neuromuscular disease. More recently, we have come to appreciate that respiratory muscle dysfunction contributes significantly to carbon dioxide retention in most of the disorders that predispose to hypercapnic respiratory failure. This is especially so for obstructive diseases of the upper and lower airways, restrictive diseases of the chest wall, and the many conditions other than neuromuscular disease that impair respiratory muscle contractility. To elucidate the mechanisms by which respiratory muscle failure leads to hypercapnic respiratory failure, we address three issues in this article. The section "Respiratory Muscle Failure" reviews the relationship between muscle weakness and fatigue, as well as the concept of "incipient fatigue." Because it is difficult to distinguish among these conditions in the clinical setting, we use the term "failure" to signify any form of impaired respiratory muscle contractility. The section "Respiratory Muscle Failure and the Pattern of Breathing" summarizes evidence to show that respiratory muscle failure causes rapid, shallow breathing. This occurs even though central neural drive is maintained and there is no overt muscle fatigue. The final section indicates that a reduction in tidal volume is the final common pathway linking respiratory muscle failure to hypercapnic respiratory failure.