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Does fitness level modulate the cardiovascular hemodynamic response to exercise?

Faculties of ¹Physical Education and Recreation, ²Medicine and Dentistry, and ³Rehabilitation Medicine, University of Alberta, Edmonton, Alberta; ⁴Departments of Cardiac Sciences and Physiology/Biophysics, University of Calgary, Calgary, Alberta; and ⁵Department of Critical Care Medicine, Thunder Bay Regional Health Sciences Centre, Thunder Bay, Ontario, Canada

Submitted 23 November 2005 ; accepted in final form 21 February 2006

Subjects with greater aerobic fitness demonstrate better diastolic compliance at rest, but whether fitness modulates exercise cardiac compliance and cardiac filling pressures remains to be determined. On the basis of maximal oxygen consumption (O_2max), healthy male subjects were categorized into either low (LO: O_2max = 43 ± 6 ml·kg^–1·min^–1; n = 3) or high (HI: O_2max = 60 ± 3 ml·kg^–1·min^–1; n = 5) aerobic power. Subjects performed incremental cycle exercise to 90% O_2max. Right atrial (RAP) and pulmonary artery wedge (PAWP) pressures were measured, and left ventricular (LV) transmural filling pressure (TMFP = PAWP – RAP) was calculated. Cardiac output (CO) and stroke volume (SV) were determined by direct Fick, and LV end-diastolic volume (EDV) was estimated from echocardiographic fractional area change and Fick SV. There were no between-group differences for any measure at rest. At a submaximal workload of 150 W, PAWP and TMFP were higher (P < 0.05) in LO compared with HI (12 vs. 8 mmHg, and 9 vs. 4 mmHg, respectively). At peak exercise, CO, SV, and EDV were lower in LO (P < 0.05). RAP was not different at peak exercise, but PAWP (23 vs. 15 mmHg) and TMFP (12 vs. 6 mmHg) were higher in LO (P < 0.05). Compared with less fit subjects, subjects with greater aerobic fitness demonstrated lower LV filling pressures during exercise, whereas SV and EDV were either similar (submaximal exercise) or higher (peak exercise), suggesting superior diastolic function and compliance.

diastole; cardiac output; training; stroke volume; pericardium

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