Received August 4, 2006
Revised September 27, 2006
Accepted after revision December 4, 2006

Ellen Adele Dawson ^1*, Robert E Shave ², Gregory P Whyte ³, Derek Ball ⁴, C Selmer ⁵, Jans ⁵, Niels H Secher ⁵, Keith P George ⁶

¹ Manchester Metropolitan University
² Brunel University
³ English Institute of Sport
⁴ Defence Science and Technology Laboratory (MoD)
⁵ The Copenhagen Muscle Research Center
⁶ Research Institute for Sport and Exercise Science, Liverpool John Moores University

^* To whom correspondence should be addressed. E-mail: ellendawson{at}hotmail.com.

	Abstract

This study examined whether left ventricular function was reduced during 3 hr of semi-recumbent ergometer cycling at 70% of maximal oxygen uptake while preload to the heart was maintained via saline infusion. Indices of left ventricular systolic function (end-systolic blood pressure-volume relationship, SBP/ESV) and diastolic filling (ratio of early to late peak filling velocities into the left ventricle, E:A) were calculated during recovery and compared to baseline resting data. During exercise in 7 healthy, trained male subjects an arterial catheter allowed continuous assessment of arterial pressure, stroke volume (SV), cardiac output (Q) and an index of contractility (dP/dt max). A venous catheter assessed that central venous pressure (CVP) was maintained throughout rest, exercise and 10 min into recovery. Both systolic blood pressure and heart rate increased with the onset of exercise (66 ± 9 to 135 ± 23 beats^.min^-1 and 132 ± 5 to 185 ± 19 mmHg; increases from rest to the end of the first five minutes of exercise in HR and SBP, respectively) but systolic blood pressure did not change from 30-180 min of exercise (~150 mmHg), while heart rate only increased by 8 ± 9 beats^.min^-1 (mean ± SD; P>0.05). The attenuated increase in HR compared to other studies suggests that the maintained CVP (~5 mmHg) helped to prevent cardiovascular drift in this protocol. SV, and dP/dt max were all increased with the onset of exercise (85 ± 8 to 120 ± 18 ml, 5.4 ± 1.3 to 16.5 ± 3.3 L/min and 14.4 ± 4 to 28 ± 8 mmHg^.s^-1, values from rest to the end of the first five minutes of exercise for SV, Q and dP/dt max, respectively) and were maintained during exercise. There was no difference in the SBP/ESV ratio from pre to post exercise. Conversely, E:A was reduced from 2.0 ± 0.4 to 1.6 ± 0.5 post-race (P<0.05), to be normalised at a 24 hr post-exercise. This change in diastolic filling could not be fully explained (r² = 0.39) by an increased heart rate and with CVP unchanged, it likely represents some depression of intrinsic relaxation properties of left ventricular myocytes. Three hours of semi-supine cycling resulted in no evidence of a depression in LV systolic function, while LV diastolic function declined post-exercise.

Key Words: Cardiovascular, Exercise, Posture