BACKGROUND: Gas-exchange derived pulmonary capacitance (GXCAP) is a non-invasive index of pulmonary arterial capacitance obtainable from submaximal cardiopulmonary exercise testing (CPET), but reference intervals in older adults, a key target population, are lacking. METHODS: A secondary analysis of an open-label clinical device trial, including 207 adults ≥ 60 years undergoing elective non-cardiac surgery was performed. Submaximal CPET with the Shape II system provided peak GXCAP, GXCAP-time slope, and GXCAP-VO2 slope. Sex-specific empirical 95% reference intervals (2.5th-97.5th percentiles) and indirect reference intervals were calculated using the refineR algorithm, which models the latent healthy subpopulation within routine data. Associations with age and sex were examined using correlation and group comparisons. RESULTS: The analytic cohort comprised 207 nonsmoking participants (119 males, 88 females). Males demonstrated higher peak GXCAP and steeper GXCAP-time and GXCAP-VO2 slopes than females. Age was modestly and inversely associated with peak GXCAP and GXCAP-time slope. Empirical reference intervals were wide and right-skewed, whereas refineR produced narrower, physiologically plausible intervals, for example, peak GXCAP 144.9-810.0 mL.mmHg (overall), with higher upper limits in males. CONCLUSIONS: In older adults undergoing preoperative evaluation, GXCAP metrics show clear sex differences. Indirect, refineR-based, reference intervals provide stable, clinically interpretable ranges that may enhance the use of GXCAP for noninvasively assessing pulmonary arterial capacitance in submaximal CPET. GXCAP derivatives (GXCAP-time slope and GXCAP-VO2 slope were introduced and may offer distinct advantages in submaximal cardiopulmonary exercise testing. CLINICAL TRIAL REGISTRATION: NCT05743673, Principal Investigator: Zyad J. Carr, M.D.