Posture matters: how body position shapes cardiopulmonary response to maximal exercise testing

Aims: Body posture influences cardiovascular and respiratory responses during exercise, yet in clinical setting differences in body positions are not considered when comparing different methodologies analyzing physical effort such has cardiopulmonary exercise test (CPET), stress echo or invasive hemodynamic. We aimed to investigate how upright (UP), semi-recumbent (SR), and supine (SP) positions affect key CPET variables and cardiac output (CO), in healthy adults. Methods: Twelve healthy volunteers (30.9 ± 4.4 years; 50% female) performed 3 randomized CPETs in UP, SR, and SP positions. Breath-by-breath gas exchange data (Oxygen uptake [VO2], Carbon dioxide production [VCO2], minute ventilation [VE], tidal volume [TV], respiratory rate [RR]) and hemodynamic parameters (CO by thoracic bioimpedance, stroke volume [SV], heart rate [HR]) were continuously monitored. Data were analyzed at rest, anaerobic threshold, iso-watt stages, and peak exercise. Results: At rest and submaximal workloads, HR decreased and SV increased with more reclined positions, maintaining CO. VE and TV were lower in SR and SP positions, while RR and SpO2 were unchanged. At peak exercise, VO2, VCO2, workload, and exercise duration declined progressively from UP to SP (VO2: 2587 ± 1009, 2520 ± 982, 2269 ± 847 mL·min-1; p<0.001), with lower VE driven by reduced TV. Despite reduced metabolic and ventilatory demands, CO was unchanged via increased SV. Dyspnea perception was lower in reclined postures. Conclusion: Body posture modulates cardiopulmonary responses during exercise. Semi-recumbent and supine positions reduce VO2 and VE preserving CO. These findings highlight the importance of posture-specific reference values for accurate interpretation in clinical practice.