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Abstract Traditional indices such as the – slope describe ventilatory efficiency within the submaximal, near‐linear domain of exercise but underrepresent the nonlinear ventilatory behaviour emerging beyond the first ventilatory threshold (VT 1). We applied a semi‐logarithmic model that linearizes the post‐VT 1 response by relating CO 2 output to log‐transformed ventilation, extracting an empirical slope (bₑmp) and normalizing it to a theoretical upper limit of CO 2 clearance anchored to predicted maximal voluntary ventilation (MVVₚred), yielding the bounded ventilatory efficiency index. In 1150 rigorously screened healthy adults (52. 4% women; median age 49 years), exhibited minimal sex‐related variation (14. 3% vs. 14. 7%) and small positive associations with age (β = +0. 058 ± 0. 007, P 0. 20), indicating physiological, rather than geometric, determinants. By referencing ventilatory performance to a theoretical limit of CO 2 removal, provides a reproducible, scale‐independent descriptor that refines the physiological interpretation of ventilatory efficiency across health, ageing and contrasting ventilatory constraints. image Key points The – slope and nadir underestimate key ventilatory adjustments during the most decisive phase of the exercise response – from the first ventilatory threshold (VT 1) to peak exercise. This study introduces a semi‐logarithmic approach that linearizes the decisive post‐VT 1 segment of the ventilatory response, better capturing its underlying physiological behaviour. The resulting slope, when normalized to a theoretical physiological limit for gas exchange and scaled to the predicted maximal voluntary ventilation, yields a bounded efficiency index (, %). remained robustly stable and only weakly associated with age and lung function, while showing no meaningful dependence on sex or height in over 1000 healthy adults, from which valuable normative equations were derived. This framework integrates ventilatory drive, gas exchange and diffusion capacity, offering a unified and easily applicable tool for physiological and clinical evaluation of ventilatory efficiency.
Müller et al. (Wed,) studied this question.