Key result
Glyceryl trinitrate increases resting brachial artery diameter ~12% without altering forearm blood flow during exercise.
Why the study?
It was unknown whether separating forearm blood flow into diameter and blood velocity provides more useful information on muscle blood flow regulation downstream of the conduit artery.
Does prior vasodilation with glyceryl tri-nitrate affect the matching of forearm blood flow to oxygen demand during exercise in healthy males?
Does prior vasodilation with glyceryl tri-nitrate affect the matching of forearm blood flow to oxygen demand during exercise in healthy males?
Absolute Event Rate: 0.56% vs 0.5%
p-value: p=<0.05
Prior vasodilation with GTN does not affect the matching of forearm blood flow to oxygen demand during exercise, suggesting microvascular tone regulation is independent of conduit artery diameter.
GTN-induced conduit dilation leaves exercise hyperemia intact in healthy males; hypothesis-generating for microvascular independence from conduit diameter.
At the onset of exercise in humans, muscle blood flow (MBF) increases to a new steady-state that closely matches the metabolic demand of exercise. This increase has been attributed to “contraction-induced vasodilation,” comprised of the skeletal muscle pump and rapid vasodilatory mechanisms. While most research in this area has focused on forearm blood flow (FBF) and vascular conductance, it is possible that separating FBF into diameter and blood velocity can provide more useful information on MBF regulation downstream of the conduit artery. Therefore, we attempted to dissociate the matching of oxygen delivery and oxygen demand by administering glyceryl tri-nitrate (GTN) prior to handgrip exercise. Eight healthy males (29 ± 9 years) performed two trials consisting of two bouts of rhythmic handgrip exercise (30 contractions·min−1 at 5% of maximum) for 6 min, one for each control and GTN (0.4 mg sublingual) condition. Administration of GTN resulted in a 12% increase in resting brachial artery diameter that persisted throughout the duration of exercise (CON: 0.50 ± 0.01 cm; GTN: 0.56 ± 0.01 cm, p < 0.05). Resting FBF was greater following GTN administration compared to control (p < 0.05); however, differences in FBF disappeared following the onset of muscle contractions. Our results indicate that the matching of FBF to oxygen demand during exercise is not affected by prior vasodilation, so that any over-perfusion is corrected at the onset of exercise. Additionally, our findings provide further evidence that the regulation of vascular tone within the microvasculature is independent of the conduit artery diameter.
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Rotarius et al. (2021) studied Healthy males (n=8). Glyceryl tri-nitrate (GTN) vs. Control was evaluated on Resting brachial artery diameter (cm) (p=<0.05). Glyceryl tri-nitrate administration increased resting brachial artery diameter by 12% but did not alter forearm blood flow during light handgrip exercise compared to control.
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