Effect of Acute Hyperglycemia on Microvascular Hemodynamics and Tissue Oxygenation during Handgrip Exercise

Abstract

Acute hyperglycemia elicits endothelial dysfunction at rest through reactive oxygen species-mediated damage to the endothelial surface layer (ESL). The ESL is associated with many of the mechanisms responsible for appropriate microvascular adjustments to exercise. PURPOSE: We tested the hypotheses that acute hyperglycemia would lead to 1) an ‘overshoot’ in deoxygenated heme concentration (deoxy-[heme]) at exercise onset reflecting greater fractional oxygen extraction and 2) less increase in total heme concentration (total-[heme]) during exercise reflecting less increase in microvascular hematocrit. METHODS: Three healthy young men (26 ± 4 yr) completed a 10-minute constant-load handgrip exercise test at 40% of peak power (9.6 ± 0.7 W) under control conditions (CON) and during acute hyperglycemia (HGL), i.e., 90-minutes after oral consumption of a 10 ounce solution containing 75g of dextrose. Near-infrared spectroscopy was used to measure deoxy-[heme] and total-[heme] of the flexor digitorum superficialis (FDS) continuously at rest and during exercise. RESULTS: Deoxy-[heme]CON and total-[heme]CON were significantly greater during exercise (189 ± 28 μM and 341 ± 34 μM, respectively) compared to rest (164 ± 13 μM and 302 ± 17 μM, respectively) (p < 0.01). Deoxy-[heme]HGL and total-[heme]HGL were significantly greater during exercise (181 ± 14 μM and 322 ± 27 μM, respectively) compared to rest (168 ± 26 μM and 313 ± 16 μM, respectively) (p < 0.01). As a percent of steady-state (SS) values, deoxy-[heme]CON was greater than deoxy-[heme]HGL from 35s until 75s of exercise (p<0.05). Deoxy-[heme]CON and deoxy-[heme]HGL were not different at SS. Total-[heme]HGL was significantly lower than total-[heme]CON at SS (p < 0.01). CONCLUSION: These data suggest that acute hyperglycemia leads to 1) increased fractional oxygen extraction at the onset of moderate-intensity handgrip exercise reflecting impaired perfusive oxygen delivery and 2) less of an increase in microvascular hematocrit reflecting impaired diffusive oxygen conductance during exercise steady state.