VE/VCO₂ Slope and Functional Capacity in Patients Post-Heart Transplantation

The ventilatory efficiency represented cardiovascular, pulmonary, and musculoskeletal performance into an integrate index has been used as long-term and short-term prognostic variables in congestive heart failure. The heart failure patients post heart transplantation, whether the ventilatory efficiency was also normalized is still unknown.

This was a cross-sectional study. We measured ventilation to carbon dioxide production slope and oxygen consumption in peak exercise (peak VO₂) by cardiopulmonary exercise test, which represented ventilatory efficiency and functional capacity respectively. Strength of hand grip, the 30-second chair stand test, and 6-minute walking test were also evaluated. Patients with ventilation to carbon dioxide production slope <30 were defined as the normal group; others were defined as the abnormal group. Independent t tests and paired t tests were used when appropriate. The level of statistical significance was set at .05.

There were 51 clinically stable post-heart transplantation patients (age 53 ± 12.4 years; 86.3% were male) at 65.14 ± 41.17 months after transplantation. The ventilation to carbon dioxide production slope was 29.2 ± 5.6, which significantly improved compared to that recorded 1 month after heart transplantation (32.6 ± 6.4). There were 20 patients in the abnormal group, characterized by lower 6-minute walking test distance (normal vs abnormal, 422.5 ± 97.8 vs 532.6 ± 87.6 m) and peak VO₂ (normal vs abnormal, 14.9 ± 5.3 vs 18.8 ± 5.1 mL/kg/min). The abnormal ventilation to carbon dioxide production slope was significantly correlated with 6-minute walking test distances in multivariate analyses.

Our findings indicate that the ventilation to carbon dioxide production slope is partially abnormal among patients post-heart transplantation. A ventilation to carbon dioxide production slope above the normal range is characterized by a lower peak VO₂ during cardiopulmonary exercise test and lower 6-minute walking test distance. The ventilation to carbon dioxide production slope is also significantly negatively correlated with peak VO₂, peak work rate, and 6-minute walking test distance. The prognostic utility of the ventilation to carbon dioxide production slope for patients post-heart transplantation requires further investigation.