Near-infrared spectroscopy detects transient decrements and recovery of microvascular responsiveness following prolonged forearm ischemia

Background: Impairments at the microvascular level might lead to more overt cardiovascular complications, therefore, being able to early detect microvascular dysfunction would be beneficial. Thus, the present study investigated whether near-infrared spectroscopy (NIRS)assessment of microvascular responsiveness (reoxygenation slope, %.s⁻¹)would detect the detrimental effects on the forearm microvasculature following a period of arterial occlusion. Similarly, the effects of prolonged forearm ischemia on brachial artery function were also assessed by flow-mediated dilation (%FMD). Methods: Fourteen individuals were tested before (Pre), immediately after (Post_PI), 30 min after (Post₃₀), and 60 min after (Post₆₀)prolonged forearm ischemia. The Pre, Post₃₀, and Post₆₀ interventions consisted of 5 min of blood flow occlusion, whereas the post_PI involved a 20-min occlusion period. Results: The reoxygenation slope was reduced at Post_PI (1.33 ± 0.72%.s⁻¹ vs. 1.79 ± 0.68%.s⁻¹ Pre; p < 0.05), but not at Post₃₀ (1.93 ± 0.70%.s⁻¹)and Post₆₀ (1.87 ± 0.85%.s⁻¹)(both p > 0.05 vs. Pre). Similarly, the brachial FMD response was reduced at Post_PI (7.4 ± 3.9% vs. 10.9 ± 2.9% Pre; p < 0.05), but not at Post₃₀ (11.3 ± 4.1%)or Post₆₀ (11.8 ± 4.3%)(both p > 0.05 vs. Pre). Conclusion: These findings show that NIRS-derived reoxygenation slope detects the transient detrimental effects of prolonged ischemia within the forearm microvasculature. Additionally, this study found that the reduction in forearm microvascular responsiveness might have contributed to the decreased brachial artery FMD responsiveness.