Normative cardiopulmonary exercise test responses at the ventilatory threshold in Canadian adults aged 40-80 years.
Physiological and symptom responses at the ventilatory threshold (Tvent) during incremental cardiopulmonary exercise testing (CPET) can provide important prognostic information.This study aimed to develop an updated normative reference set for physiological and symptom responses at Tvent during cycle CPET (primary aim) and evaluate previously recommended reference equations by Jones et al. (1985) for predicting Tvent responses (secondary aim).Participants were adults aged 40-80 years free of clinically relevant disease from the Canadian Cohort Obstructive Lung Disease. Rate of oxygen consumption (V’O2) at Tvent was identified by two independent raters; physiological and symptom responses corresponding to V’O2 at Tvent were identified by linear interpolation. Reference ranges (5th to 95th percentiles) for responses at Tvent were calculated according to participant sex and age for 29 and eight variables, respectively. Prediction models were developed for nine variables (oxygen pulse, V’O2, rate of carbon dioxide production, ventilation, tidal volume, inspiratory capacity and end-inspiratory [L] and -expiratory [L, % total lung capacity] lung volumes) using quantile regression, estimating the 5th (lower limit normal), 50th (normal), and 95th (upper limit normal) percentiles based on readily available participant characteristics. The two one-sided test of equivalence for paired samples evaluated the measured and Jones et al. (1985) predicted V’O2 at Tvent for equivalence.Reference ranges and equations were developed based on 96 (49% male) participants aged 63±9 (mean ± SD) years. Mean V’O2 at Tvent was 50% of measured V’O2 peak; the normal range was 33 to 66%. The Jones et al. (1985) reference equations overpredicted V’O2 at Tvent (mean difference: males=-0.17 L·min-1 [95%CI -0.25, -0.09]; females=-0.19 L·min-1 [95%CI -0.27, -0.12]).A contemporary reference set of CPET responses at Tvent from Canadian adults aged 40-80 years is presented, which differs from the previously recommended and often used reference set by Jones and coworkers.