Respiratory muscle weakness elevates dead-space ventilation ratio during exercise in CHF patients
An association exists between respiratory muscle weakness and an increased dead-space ventilation ratio, which exacerbates ventilation–perfusion mismatch during exercise in patients with chronic heart failure (CHF), a study has found.
“Respiratory muscle weakness causes fatigue in these muscles during exercise and thereby increases dead‐space ventilation ratio with decreased tidal volume,” the authors said. “In ventilation–perfusion mismatch during exercise, minute ventilation vs carbon dioxide production (VE/VCO2) slope >34 is an indicator of poor prognosis in patients with CHF.”
This study 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.
The authors measured maximal inspiratory pressure (PImax) as respiratory muscle strength 2 months after hospital discharge in 256 compensated patients with CHF. Minute dead-space ventilation was assessed in comparison with VE (VD/VE ratio) as dead‐space ventilation ratio and VE/VCO2 slope as ventilation–perfusion mismatch.
The authors divided patients into low, moderate and high PImax groups based on the PImax tertile. They also examined the determinants of VE/VCO2 slope >34 among these cohorts.
Patients in the low PImax group had significantly greater VD/VE ratios at 50 percent of peak workload and at peak workload and higher VE/VCO2 slope compared with those in the other two groups (p<0.001). PImax was a significant independent determinant of VE/VCO2 slope >34 (odds ratio, 0.67; 95 percent CI, 0.54–0.82), with area under the receiver operating characteristic curve of 0.812 (0.750–0.874).