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Objective: We examined sex‐specific microvascular reactivity and hemodynamic responses under conditions of augmented resting blood flow induced by passive heating compared to normal blood flow. Methods: Thirty‐eight adults (19 females) completed a vascular occlusion test (VOT) on two occasions preceded by rest with or without passive heating in a randomized, counterbalanced order. Skeletal muscle tissue oxygenation (StO2, %) was assessed with near‐infrared spectroscopy (NIRS), and the rate of desaturation and resaturation as well as maximal StO2 (StO2max) and prolonged hypersaturation (area under the curve, StO2AUC) were quantified. Before the VOT, brachial artery blood flow (BABF), vascular conductance, and relative BABF (BABF normalized to forearm lean mass) were determined. Sex × condition ANOVAs were used. A p‐value ≤.05 was considered statistically significant. Results: Twenty minutes of heating increased BABF compared to the control (102.9 ± 28.3 vs. 36.0 ± 20.9 mL min−1; p <.01). Males demonstrated greater BABF than females (91.9 ± 34.0 vs. 47.0 ± 19.1 mL min−1; p <.01). There was no sex difference in normalized BABF. There were no significant interactions for NIRS‐VOT outcomes, but heat did increase the rate of desaturation (−0.140 ± 0.02 vs. −0.119 ± 0.03% s−1; p <.01), whereas regardless of condition, males exhibited greater rates of resaturation and StO2max than females. Conclusions: These results suggest that blood flow is not the primary factor causing sex differences in NIRS‐VOT outcomes. [ABSTRACT FROM AUTHOR]

The function of micro- and macrovessels within the peripheral vasculature has been identified as a target for the investigation of potential cardiovascular-based promoters of cognitive decline. However, little remains known regarding the interaction of the microand macrovasculature as it relates to cognitive function, especially in cognitively healthy individuals. Therefore, our purpose was to unravel peripheral factors that contribute to the association between age and processing speed. Ninety-nine individuals (51 men, 48 women) across the adult life span (19-81 yr) were used for analysis. Arterial stiffness was quantified as carotid-femoral pulse-wave velocity (cfPWV) and near-infrared spectroscopy assessed maximal tissue oxygenation (StO2max) following a period of ischemia. Processing speed was evaluated with Trail Making Test (TMT) Parts A and B. Measures of central (cPP) and peripheral pulse pressure (pPP) were also collected. Moderated mediation analyses were conducted to determine contributions to the age and processing speed relation, and first-order partial correlations were used to assess associations while controlling for the linear effects of age. A P < 0.05 was considered statistically significant. At low levels of StO2max, there was a significant positive (b = 1.92; P = 0.005) effect of cfPWV on time to completion on TMT part A. In addition, cPP (P = 0.028) and pPP (P = 0.027) remained significantly related to part A when controlling for age. These results suggested that the peripheral microvasculature may be a valuable target for delaying cognitive decline, especially in currently cognitively healthy individuals. Furthermore, we reinforced current evidence that pulse pressure is a key endpoint for trials aimed at preventing or delaying the onset of cognitive decline. [ABSTRACT FROM AUTHOR]

This study investigated skeletal muscle tissue oxygenation (StO 2 ) desaturation in males and females across the adult lifespan. One hundred-two individuals (51 females) of 41 young, 34 midlife, and 27 older adults completed a vascular occlusion test with near-infrared spectroscopy (NIRS + VOT). This included five minutes of arterial occlusion, inducing transient ischemia in the forearm flexor muscle group while recording StO 2. The magnitude of desaturation (StO 2mag ) was quantified as the difference between baseline StO 2 and the minimum StO 2 value observed during ischemia. The rate of desaturation was also examined. Forearm adipose tissue thickness (ATT), forearm lean mass, and handgrip muscular strength were measured. A p  ≤ 0.05 was considered significant. Two-way between factor Analysis of variance (ANOVAs) indicated that males exhibited significantly ( p  < 0.001) less ATT than females (collapsed across age) and that forearm lean mass ( p  < 0.001) and muscular strength ( p  < 0.001) decreased across the lifespan independent of sex. Bivariate analyses revealed significant ( p  < 0.05) associations for sex, age, ATT, forearm lean mass, and muscular strength with the desaturation metrics. The ATT values demonstrated the strongest relations with StO 2mag and desaturation rate ( r = -0.620 and 0.618). Using a model comparison approach, ATT plus age offered the best predictive power for StO 2mag and desaturation rate ( R 2  = 0.456 and 0.438) such that the inclusion of sex did not improve the models. These findings suggested differences in desaturation were primarily explained by variations in ATT and, to a lesser extent, age, but biological sex had no meaningful effect. Future studies must determine what other factors influence desaturation during ischemia., Competing Interests: The authors declare there are no competing interests.

Objective. Peripheral Artery Disease (PAD) is a progressive cardiovascular condition affecting 8-10 million adults in the United States. PAD elevates the risk of cardiovascular events, but up to 50% of people with PAD are asymptomatic and undiagnosed. In this study, we tested the ability of a device, REFLO (Rapid Electromagnetic FLOw), to identify low blood flow using electromagnetic radiation and dynamic thermography toward a non-invasive PAD diagnostic. Approach. During REFLO radio frequency (RF) irradiation, the rate of temperature increase is a function of the rate of energy absorption and blood flow to the irradiated tissue. For a given rate of RF energy absorption, a slow rate of temperature increase implies a large blood flow rate to the tissue. This is due to the cooling effect of the blood. Post-irradiation, a slow rate of temperature decrease is associated with a low rate of blood flow to the tissue. Here, we performed two cohorts of controlled flow experiments on human calves during baseline, occluded, and post-occluded conditions. Nonlinear regression was used to fit temperature data and obtain the rate constant, which was used as a metric for blood flow. Main results. In the pilot study, ( N = 7) REFLO distinguished between baseline and post-occlusion during the irradiation phase, and between baseline and occlusion in the post-irradiation phase. In the reliability study, ( N = 5 with 3 visits each), two-way ANOVA revealed that flow and subject significantly affected skin heating and cooling rates, while visit did not. Significance. Results suggest that MMW irradiation can be used to distinguish between blood flow rates in humans. Utilizing the rate of skin cooling rather than heating is more consistent for distinguishing flow. Future modifications and clinical testing will aim to improve REFLO's ability to distinguish between flow rates and evaluate its ability to accurately identify PAD., (© 2024 Institute of Physics and Engineering in Medicine. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)