Abstract
BACKGROUND: Arterial CO(2) tension (PaCO(2)) and physiological dead space (V(D)) are not routinely measured during clinical cardiopulmonary exercise testing (CPET). Abnormal changes in PaCO(2) accompanied by increased V(D) directly contribute to impaired exercise ventilatory function in heart failure (HF). Because arterial catheterization is not standard practice during CPET, this study tested the construct validity of PaCO(2) and V(D) prediction models using 'ideal' alveolar air equations and basic ventilation and gas-exchangegas exchange measurements during CPET in HF. METHODS: Forty-seven NYHA class II/III HF (LVEF=21±7%; age=55±9years; male=89%; BMI=28±5kg/m(2)) performed step-wise cycle ergometry CPET to volitional fatigue. Breath-by-breath ventilation and gas exchange were measured continuously. Steady-state PaCO(2) was measured at rest and peak exercise via radial arterial catheterization. Criterion V(D) was calculated via 'ideal' alveolar equations, whereas PaCO(2) or V(D) models were based on end-tidal CO(2) tension (P(ET)CO(2)), tidal volume (V(T)), and/or weight. RESULTS: Criterion measurements of PaCO(2) (38±5 vs. 33±5mmHg, P<0.01) and V(D) (0.26±0.07 vs. 0.41±0.15L, P<0.01) differed at rest vs. peak exercise, respectively. The equation, 5.5+0.90×P(ET)CO(2)-0.0021×V(T), was the strongest predictor of PaCO(2) at rest and peak exercise (bias±95%LOA=-3.24±6.63 and -0.98±5.76mmHg; R(2)=0.57 and 0.75, P<0.001, respectively). This equation closely predicted V(D) at rest and peak exercise (bias±95%LOA=-0.03±0.06 and -0.02±0.13L; R(2)=0.86 and 0.83, P<0.001, respectively). CONCLUSIONS: These data suggest predicted PaCO(2) and V(D) based on breath-by-breath gas exchange and ventilatory responses demonstrate acceptable agreement with criterion measurements at peak exercise in HF patients. Routine assessment of PaCO(2) and V(D) can be used to improve interpretability of exercise ventilatory responses in HF.