[Effect of dead space loading on ventilation, respiratory muscle and exercise performance in chronic obstructive...

To evaluate the effect of dead space (V(D)) loading on ventilation and respiratory muscle function, to test a novel measurement of oxygen consumption of respiratory muscle, and to analyze the effect of oxygen consumption of respiratory muscle on exercise performance.

Twenty-six patients with moderate chronic obstructive pulmonary disease (COPD) and 29 age-matched healthy control subjects underwent 30 W or 55 W constant work (CW) exercise in a standard protocol and under 300 ml (46 cm in length) dead space loading. Pulmonary function test (PFT) was measured pre- and post-exercise both in the dead space loading and unloading.

The addition of 300 ml V(D) did not significantly affect FVC, FEV(1), and FEV(1)/FVC in both COPD patients and the healthy controls at rest or after CW exercise. The values of FVC, FEV(1), and FEV(1)/FVC with V(D) loading in COPD were (3.03 +/- 0.15) L, (1.95 +/- 0.09) L and (64.9 +/- 2.5)%, respectively; after 55 W CW exercise, those values were (3.03 +/- 0.18) L, (2.00 +/- 0.13) L, and (66.3 +/- 3.2)%, respectively (P > 0.05). Minute ventilation (V.(E)) and oxygen uptake (V.O(2)) significantly went up with V(D) loading and dropped with unloading at rest and during exercise in every subject. The enhancement of V.O(2) under V(D) loading (DeltaV.O(2)) was not significantly different between COPD and the control at rest or during lower intensity CW (30 W) exercise. However, DeltaV.O(2) was significantly higher in COPD than in the control during moderate intensity CW (55 W) exercise [(272 +/- 24) ml/min vs (194 +/- 19) ml/min, P < 0.05].

Lengthening respiratory tube to 46 cm (300 ml dead space) combined with moderate constant work exercise does not worsen the airflow obstructive in COPD,or results in respiratory muscle fatigue both in the COPD patients and the healthy controls. The enhancement of V.O(2) under V(D) loading can be considered as oxygen consumption of respiratory muscle working for increased ventilation. An advantage of oxygen consumption in respiratory muscle during moderate intensity exercise in COPD implies that maintaining the balance of oxygen supplying to both respiratory and limb muscles might be the key point in performing moderate to heavy exercise.