The importance of ventilatory thresholds to define aerobic exercise intensity in cardiac patients and healthy subjects

Abstract

Background: Although structured exercise training is strongly recommended in cardiac patients, uncertainties exist about the methods for determining exercise intensity (EI) and their correspondence with effective EI obtained by ventilatory thresholds. We aimed to determine the first (VT₁ ) and second ventilatory thresholds (VT₂ ) in cardiac patients, sedentary subjects, and athletes comparing VT₁ and VT₂ with EI defined by recommendations.

Methods: We prospectively enrolled 350 subjects (mean age: 50.7±12.9 years; 167 cardiac patients, 150 healthy sedentary subjects, and 33 competitive endurance athletes). Each subject underwent ECG, echocardiography, and cardiopulmonary exercise testing. The percentages of peak VO₂ , peak heart rate (HR), and HR reserve were obtained at VT₁ and VT₂ and compared with the EI definition proposed by the recommendations.

Results: VO₂ at VT₁ corresponded to high rather than moderate EI in 67.1% and 79.6% of cardiac patients, applying the definition of moderate exercise by the previous recommendations and the 2020 guidelines, respectively. Most cardiac patients had VO₂ values at VT₂ corresponding to very-high rather than high EI (59.9% and 50.3%, by previous recommendations and 2020 guidelines, respectively). A better correspondence between ventilatory thresholds and recommended EI domains was observed in healthy subjects and athletes (90% and 93.9%, respectively).

Conclusions: EI definition based on percentages of peak HR and peak VO₂ may misclassify the effective EI, and the discrepancy between the individually determined and the recommended EI is particularly relevant in cardiac patients. A ventilatory threshold-based rather than a range-based approach is advisable to define an appropriate level of EI.

Keywords: cardiopulmonary exercise testing; exercise intensity; exercise prescription; lactate; ventilatory threshold.