This dissertation examined the effects of a chronic acidosis on vascular function during dynamic handgrip exercise and following post-occlusive reactive hyperemia. Seven males performed hand-grip exercise corresponding to 5% (moderate) and 10% (heavy) of maximal forearm strength during control (CON) and acidosis (acetazolamide 500 mg/d 3 d; AC) conditions. Flow-mediated dilation (FMD) was also measured on these subjects following a post-occlusive reactive hyperemia. Brachial artery diameters and velocities (MBV) were measured continuously during FMD and exercise using Doppler ultrasound. Muscle blood flow, shear rate, shear stress, mean arterial pressure, and vascular conductance were all computed. Muscle activity of the forearm flexors were measured using non-invasive electromyography. Arterialized venous blood was collected by catheter and analyzed for blood gases and ions.
Plasma [H+] were significantly higher during AC compared to CON for both moderate and heavy exercise as well as during FMD. Blood [HCO3-] and blood gas PCO2 were significantly decreased during AC compared to control for both moderate and heavy exercise as well as during FMD. Hematocrit was unchanged between rest and exercise for both conditions. As well, no differences in hematocrit were present between AC and CON conditions.
No difference in MBF or arterial diameters were detected between CON and AC conditions at rest or during moderate intensity exercise. As well, no significant difference was observed for MBF between CON and AC during heavy intensity exercise. However, heavy intensity exercise resulted in an increase in arterial diameter compared to rest for CON (p<0.05) but, no difference in arterial diameter was observed for AC. When expressed as a percent change from rest to heavy intensity exercise, the increase in diameter was greater (p<0.05) during CON compared to AC. FMD resulted in an increase in brachial artery diameter compared to rest (p<0.05). When expressed as %FMD, ACZ was significantly reduced compared to CON (p<0.05). In fact, the comparison resulted in a 48.5% difference in response between CON and ACZ conditions.
Shear rate (SR) and Shear stress (SS) values were well matched between conditions during both moderate and heavy exercise. Peak values for SR and SS were not significantly different between conditions during FMD. However, when FMD was normalized relative to shear rate (%FMD/SR), the ratio for ACZ was significantly lower (p<0.05) compared to CON.
Together these findings suggest that prior metabolic acidosis may alter vascular tone at rest and during heavy exercise but that MBF is unaltered between conditions during moderate and heavy exercise. As well, these results indicate that the endothelial-dependent FMD response is attenuated following chronic AC even after normalizing for changes in shear stress.