Differential effects of external ventilatory constraint on submaximal and peak exercise responses

Background

Exercise intolerance is a hallmark of heart failure and is closely linked to limited ventilatory reserve rather than overt hemodynamic instability. Whether external ventilatory constraint uniformly impairs exercise performance or selectively affects specific intensity domains has not been fully characterized. Clarifying intensity-dependent physiological responses may provide mechanistic insight relevant to functional limitation commonly observed in heart failure.

Objectives

To investigate whether external ventilatory constraint differentially affects submaximal versus peak exercise responses during incremental cardiopulmonary exercise testing.

Methods

Forty healthy adults (mean age 33 ± 7 years; 50% female) underwent symptom-limited cardiopulmonary exercise testing using a randomized crossover design under three conditions: no mask, a moderate-filtration respirator (~80% filtration efficiency), and a high-filtration respirator (~94% filtration efficiency, functionally comparable to N95/FFP2). Tests were separated by ≥48 hours and performed using a modified Bruce protocol. Oxygen uptake (VO₂), minute ventilation (VE), tidal volume (VT), respiratory rate (RR), heart rate (HR), oxygen saturation (SpO₂), and systolic blood pressure (SBP) were continuously measured. Physiological responses were analyzed across incremental stages and peak exertion, with condition × stage interactions assessed using repeated-measures analysis of variance.

Results

Across incremental stages, VO₂ and METs were progressively reduced with increasing ventilatory constraint, with a significant condition × stage interaction for VO₂ and METs (both p < 0.001), indicating intensity-dependent amplification of the effect. Similar interaction patterns were observed for VE and VT (both p < 0.001), whereas RR, HR, and SpO₂ did not demonstrate significant interaction effects. Differences between conditions were modest at lower intensities but became most pronounced at AT and peak exercise. Absolute reductions in VO₂ and METs between no mask and high-filtration conditions increased progressively with exercise intensity.

Conclusion

External ventilatory constraint selectively limits maximal exercise performance, supporting ventilatory reserve as a central physiological determinant of exercise intolerance.

[Figure 1]

Stage-wise cardiopulmonary exercise responses under increasing external ventilatory constraint.

[Figure 2]

Intensity-dependent amplification of performance differences under external ventilatory constraint.For image description, please refer to the figure legend and surrounding text.For image description, please refer to the figure legend and surrounding text.