Respiratory muscle weakness increases dead-space ventilation ratio aggravating ventilation-perfusion mismatch during exercise in patients with chronic heart failure

Abstract

Background and objective: Respiratory muscle weakness causes fatigue in these muscles during exercise and thereby increases dead-space ventilation ratio with decreased tidal volume. However, it remains unclear whether respiratory muscle weakness aggravates ventilation-perfusion mismatch through the increased dead-space ventilation ratio. In ventilation-perfusion mismatch during exercise, minute ventilation versus carbon dioxide production (VE/VCO₂ ) slope > 34 is an indicator of poor prognosis in patients with chronic heart failure (CHF). We examined the relationship of respiratory muscle weakness with dead-space ventilation ratio and ventilation-perfusion mismatch during exercise and clarified whether respiratory muscle weakness was a clinical predictor of VE/VCO₂ slope > 34 in patients with CHF.

Methods: Maximal inspiratory pressure (PI_max ) was measured as respiratory muscle strength 2 months after hospital discharge in 256 compensated patients with CHF. During cardiopulmonary exercise test, we assessed minute dead-space ventilation versus VE (VD/VE ratio) as dead-space ventilation ratio and VE/VCO₂ slope as ventilation-perfusion mismatch. Patients were divided into low, moderate and high PI_max groups based on the PI_max tertile. We investigated determinants of VE/VCO₂ slope > 34 among these groups.

Results: The low PI_max group showed significantly higher VD/VE ratios at 50% of peak workload and at peak workload and higher VE/VCO₂ slope than the other two groups (P < 0.001, respectively). PI_max was a significant independent determinant of VE/VCO₂ slope > 34 (odds ratio (OR): 0.67, 95% CI: 0.54-0.82) with area under the receiver operating characteristic curve of 0.812 (95% CI: 0.750-0.874).

Conclusion: Respiratory muscle weakness was associated with an increased dead-space ventilation ratio aggravating ventilation-perfusion mismatch during exercise in patients with CHF.

Keywords: chronic heart failure; dead-space ventilation; minute ventilation versus carbon dioxide production slope; respiratory muscle weakness; ventilation-perfusion mismatch.