Abnormal responses of wasted ventilation fraction (VD/VT) during exercise in patients with pulmonary vascular abnormalities.

The finding of a rise in VD/VT or failure of VD/VT to fall during exercise has been proposed as a useful noninvasive indicator of pulmonary vaso-occlusive disease in patients with unexplained dyspnea. However, we previously reported a normal fall in VD/VT during exercise in patients with pulmonary hypertension at rest and/or during exercise due to collagen vascular disease. To investigate further the relationship between pulmonary vascular abnormalities and VD/VT responses to exercise, we studied 4 subjects with severe hypoxemia due to cirrhosis or diffuse telangiectasia. We found an abnormal VD/VT response to exercise in these subjects despite normal pulmonary hemodynamics which effectively excluded hemodynamically significant pulmonary vascular obstruction. These findings provide further support for the lack of utility of the VD/VT measurement at rest and during exercise as a screening method for detecting pulmonary vaso-occlusive disease, since the VD/VT cannot only fall appropriately during exercise in patients with pulmonary hypertension but can also remain unchanged or rise during exercise in patients with normal pulmonary hemodynamics.