Development of Stroke Volume Response to Supine Aerobic Exercise as measured by Phase-Contrast Magnetic Resonance Angiography

G E Pieles, G Szantho, J C L Rodrigues, C B Lawton, A S Graham, C Bucciarelli-Ducci, M S Turner, R M R Tulloh, C Williams, M Hamilton

Abstract


Objectives Exercise induced oxygen delivery and tissue perfusion increase is facilitated by

lowering peripheral vascular resistance and increasing cardiac output (Q). The role of stroke volume (SV) response during supine exercise has been debated. We have assessed SV response to supine exercise by measuring aortic flow using phase-contrast Magnetic Resonance Angiography (PCMRA).

Materials and Methods Eight subjects performed supine exercise using a Magnetic Resonance Imaging (MRI) compatible cycle ergometer. At rest, two exercise stages (stage1 = 150% resting heart rate (HR), stage2 = 180% resting HR) and at 2 min recovery aortic blood flow was assessed using free breathing PCMRA. Flow sequence analysis was performed using offline software.

Results Exercise increased HR from 68±9 b∙min-1 at rest to 104±12 b∙min-1 (p<0.001, 95% CI=29/42) at stage1 and to 116±13 b∙min-1 (p<0.001, 95% CI=7/17) at stage2. Exercise resulted in Q increase from 6.3±1.4 L∙min-1 to 10.5±2.4 L∙min-1 (p<0.001) at stage1 and to 12.5±1.9 L∙min-1 (p=0.003) at stage2. SV increased from 88.8±15.6 ml at rest to 102.2±24.4 ml (p=0.03) at stage1and increased further to 114.2±28.6 ml (p=0.007) at stage2.

Conclusion Our data show that cardiac output is increased by equally significant changes in SV and HR during supine exercise. SV response to supine exercise is beyond that reported to adjust for changes in preload and central blood volume. This supports the concept of a multi-level adaptation of the cardio-vascular system to supine exercise with central and peripheral mechanisms of equal importance.


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