Characteristics of patients with a relatively greater minimum VE/VCO₂ against peak VO₂% and impaired exercise tolerance

Cardiopulmonary exercise testing (CPX) is used to evaluate functional capacity and assess prognosis in cardiac patients. Ventilatory efficiency (VE/VCO₂) reflects ventilation-perfusion mismatch; the minimum VE/VCO₂ value (minVE/VCO₂) is representative of pulmonary arterial blood flow in individuals without pulmonary disease. Usually, minVE/VCO₂ has a strong relationship with the peak oxygen uptake (VO₂), but dissociation can occur. Therefore, we investigated the relationship between minVE/VCO₂ and predicted peak VO₂ (peak VO₂%) and evaluated the parameters associated with a discrepancy between these two parameters.

A total of 289 Japanese patients underwent CPX using a cycle ergometer with ramp protocols between 2013 and 2014. Among these, 174 patients with a peak VO₂% lower than 70% were enrolled. Patients were divided into groups based on their minVE/VCO₂ [Low group: minVE/VCO₂ < mean - SD (38.8-5.6); High group: minVE/VCO₂ > mean + SD (38.8 + 5.6)]. The characteristics and cardiac function at rest, evaluated using echocardiography, were compared between groups.

The High group had a significantly lower ejection fraction, stroke volume, and cardiac output, and higher brain natriuretic peptide, tricuspid regurgitation pressure gradient, right ventricular systolic pressure, and peak early diastolic LV filling velocity/peak atrial filling velocity ratio compared with the Low group (p's < 0.01). In addition, the Low group had a significantly higher prevalence of pleural effusion than did the High group (26 vs 11%, p < 0.01).

Patients with a relatively greater minVE/VCO₂ in comparison with peak VO₂ had impaired cardiac output as well as restricted pulmonary blood flow increase during exercise, partly due to accumulated pleural effusion.