Respiratory response to exercise in postpolio patients with severe inspiratory muscle dysfunction

To evaluate the limiting factors of exercise performance and to analyze the respiratory strategies adopted during exercise in postpolio patients with severe inspiratory muscle dysfunction.

Five patients with prior poliomyelitis associated with scoliosis and with respiratory muscle dysfunction (mean vital capacity, 1.74L [range, 1.1 to 2.4]) were studied at rest and during leg or arm cycle exercise.

Gas exchange was examined by arterial blood gases and mass spectrometry of expired air. Ventilatory mechanics were studied by measurement of esophageal and gastric pressures.

Blood gases at rest were normal, except for subnormal PO2 levels in three patients. In all but one patient, ventilatory insufficiency was the limiting factor for exercise. A compensatory breathing pattern with abdominal muscle recruitment during expiration was present already at rest in three of the patients. The pressures generated by the diaphragm were below fatiguing margins, ie, levels that in healthy subjects can be sustained for at least 45 minutes.

The extent of ventilatory dysfunction was not evident in blood gas values at rest; however, it was revealed by blood gas values during the exercise test. Diaphragm fatigue seems to be avoided at the cost of impaired blood gases.