Comorbidity burden outweighs coronary heart disease diagnosis in impairing cardiopulmonary fitness: a cross-sectional study based on cardiopulmonary exercise testing.

BACKGROUND: Multimorbidity was highly prevalent in patients with coronary heart disease (CHD), yet its independent and cumulative impact on cardiorespiratory fitness (CRF) remains incompletely elucidated. This cross-sectional study analyzed the respective effects of comorbidity burden and CHD diagnosis on peak oxygen uptake (VO₂peak) and examined whether obesity modulated the comorbidity–CRF relationship. METHODS: A total of 335 adults undergoing symptom-limited cardiopulmonary exercise testing at Fuzhou University Affiliated Provincial Hospital were enrolled (CHD group: n = 156; non-CHD group: n = 179). Multiple linear regression models assessed the independent and interactive effects of CHD diagnosis, comorbidity count, and body mass index (BMI) on VO₂peak. RESULTS: Despite older age (63 vs. 53 years, P < 0.001) and a higher comorbidity burden (P < 0.001) in the CHD group, VO₂peak did not differ significantly between the two groups (20.33 vs. 20.88 mL/kg/min, P = 0.234). CHD diagnosis was not a statistically significant predictor of VO₂peak (β=−0.415, P = 0.386), whereas comorbidity count exhibited a dose–response relationship (β=−0.824, P < 0.001), with each additional comorbidity reducing VO₂peak by 0.82 mL/kg/min. As comorbidities increased from 0 to ≥ 3, VO₂peak declined from 21.19 to 19.58 mL/kg/min (P for trend = 0.004), accompanied by parallel deteriorations in oxygen uptake at the anaerobic threshold, oxygen uptake efficiency slope, and ventilatory efficiency. Although the linear interaction term between BMI and comorbidity was non-significant (P = 0.469), stratified analyses confirmed consistent negative trends across all groups, with the overweight group (BMI 24–28 kg/m²) exhibiting a numerically steeper downward trajectory. CONCLUSIONS: Comorbidity burden outweighed CHD diagnosis per se as the primary driver of CRF impairment, with cumulative effects exhibiting a dose–response relationship. Our findings suggest that the detrimental impact of multimorbidity is robust across different weight statuses. Although a steeper decline was visually observed in the overweight group, further large-scale studies are needed to verify whether specific BMI ranges confer heightened sensitivity.