Arterial Carbon Dioxide Changes During Voluntary Hyperventilation in Chronic Obstructive Pulmonary Disease

Factors influencing the degree of arterial Pco2 (Paco2) change with voluntary hyperventilation (VHV) were investigated in 32 chronic obstructive pulmonary disease (COPD) patients. Arterial blood gases, breathing frequency, expired gas composition and volume were measured during quiet breathing and during VHV. The decrease in Paco2 correlated best with the wasted ventilation ratios (VD/VT) during VHV with the lowest VD/VT being associated with the greatest decrease in Paco2 (p < .001). The degree of perfusion of overventilated lung regions rather than breathing pattern accounted for the differences in VD/VT during VHV. Neither control Paoo2 nor control VD/VT related to the change with VHV. Increase in metabolic cost of VHV related negatively (p < .01) and minute volume during VHV related positively to the Paco2 decrease (p < .01). Maximal voluntary ventilation and FEV1.0 as estimates of mechanical flow limitation correlated least well with the decrease in Paco2 (p ≤ .05). It was concluded that in COPD change in ventilation perfusion relationships during VHV is the major mechanism determining the magnitude and direction of Paco2 change.