Effect of daily intermittent rest of respiratory muscles in patients with severe chronic airflow limitation (CAL)

Hypercarbia can result from respiratory muscle fatigue when the load is no longer sustainable. Previous studies have shown that patients with CAL who were unable to develop more negative inspiratory force than -50 cmH₂O were more likely to have hypercapnia, and use of negative pressure body respirators rested their respiratory muscles by reducing their contractions. Some patients with CAL are rehospitalized for recurring hypercapnic respiratory failure without known precipitating causes. We postulated that respiratory muscle fatigue contributed to the development or worsening of hypercapnia. Resting these muscles by daily, intermittent respiratory therapy was initiated for 18 patients: 16 with CAL of whom 3 also had a fibrothorax, 1 with massive obesity had mild CAL, and 1 with kyphoscoliosis. We assessed their pulmonary function, respiratory muscle strength (PI(max) and PE(max)), and gas exchange before and after 5 months of home ventilator therapy. A functional class was assigned based on the severity of dyspnea during daily living activities before and after therapy. Daily ventilator therapy was continued and the frequency and duration of hospitalization were recorded for 2 years before and 2 years after the institution of therapy.