Impaired matching of perfusion and ventilation in heart failure detected by¹³³xenon

Abstract

In severe chronic heart failure (CHF) the ventilatory cost of CO₂ elimination during exercise (VE/VCO ₂) is increased, suggesting ventilation/perfusion (V/Q) mismatch.

The relationship of exercise VE/VCO ₂ regression slopem to deadspace ventilation was studied in 15 patients with CHF who underwent cardiopulmonary exercise testing and arterial blood gas monitoring. Regional lung ventilation and perfusion was studied, using¹³³xenon, at rest and peak exercise in a further group of 10 CHF patients and in five normal subjects.

VE/VCO ₂ slopem correlated well with deadspace ventilation at peak exercise in the 15 patients with CHF. We therefore used exercise VE/VCO ₂ slopem to categorize CHF patients undergoing¹³³xenon imaging into groups with increased (slopem>36) or normal (slopem<36) exercise deadspace ventilation. In normals, resting V/Q determined by¹³³xenon showed a gravitational gradient, which improved on exercise as a result of relative increases and of relative reductions in regional perfusion; no significant changes in regional ventilation distribution were detected. In patients with CHF who had normal slopem (n=5), rest and exercise V/Q were similar to the normal subjects. In CHF patients with increased slopem (n=5) however, the resting gravitational gradient of V/Q was lost, and there were no significant changes in relative perfusion distribution on exercise.

These findings suggest that the increased ventilatory cost of CO₂ elimination found in certain patients with CHF is related to inability to coordinate and optimise the relative distribution of lung perfusion with respect to ventilation during exercise.