Cardiac output during exercise is related to plasma atrial natriuretic peptide but not to central venous pressure in humans

New Findings: What is the central question of this study? Is cardiac output during exercise dependent on central venous pressure? What is the main finding and its importance? The increase in cardiac output during both rowing and running is related to preload to the heart, as indicated by plasma atrial natriuretic peptide, but unrelated to central venous pressure. The results indicate that in upright humans, central venous pressure reflects the gravitational influence on central venous blood rather than preload to the heart. Abstract: We evaluated the increase in cardiac output (CO) during exercise in relationship to central venous pressure (CVP) and plasma arterial natriuretic peptide (ANP) as expressions of preload to the heart. Seven healthy subjects (four men; mean ± SD: age 26 ± 3 years, height 181± 8 cm and weight 76 ± 11 kg;) rested in sitting and standing positions (in randomized order) and then rowed and ran at submaximal workloads. The CVP was recorded, CO (Modelflow) calculated and arterial plasma ANP determined by radioimmunoassay. While sitting, (mean ± SD) CO was 6.2 ± 1.6 l min ⁻¹, plasma ANP 70 ± 10 pg ml ⁻¹ and CVP 1.8 ± 1.1 mmHg, and when standing decreased to 5.9 ± 1.0 l min ⁻¹, 63 ± 10 pg ml ⁻¹ and −3.8 ± 1.2 mmHg, respectively (P < 0.05). Ergometer rowing elicited an increase in CO to 22.5 ± 5.5 l min ⁻¹ as plasma ANP increased to 156 ± 11 pg ml ⁻¹ and CVP to 3.8 ± 0.9 mmHg (P < 0.05). Likewise, CO increased to 23.5 ± 6.0 l min ⁻¹ during running, albeit with a smaller (P < 0.05) increase in plasma ANP, but with little change in CVP (−0.9 ± 0.4 mmHg). The increase in CO in response to exercise is related to preload to the heart, as indicated by plasma ANP, but unrelated to CVP. The results indicate that in upright humans, CVP reflects the gravitational influence on central venous blood rather than preload to the heart.