The Respiratory Muscles

Abstract

THE respiratory system consists essentially of two parts: a gas-exchanging organ — the lungs—and a pump that ventilates the lungs. The pump consists of the chest wall, the respiratory muscles that displace it, the centers in the nervous system that control the muscles, and the nerves connecting the centers to the muscles. Both parts of the system are vital. In general, failure of the gas-exchanging function due to lung disease results in hypoxemia with normocapnia or hypocapnia, whereas failure of the pump (which also causes hypoxemia) leads to hypoventilation and hypercapnia, which is the hallmark of ventilatory failure (Fig. 1). . . .