The Association Between Contrast-Enhanced Ultrasound and Near-Infrared Spectroscopy-Derived Measures of Calf Muscle Microvascular Responsiveness in Older Adults

Clinical and Translational Imaging and Sensing of Diabetic Microangiopathy: A Narrative Review

Microvascular changes in diabetes affect the function of several critical organs, such as the kidneys, heart, brain, eye, and skin, among others. The possibility of detecting such changes early enough in order to take appropriate actions renders the development of appropriate tools and techniques an imperative need. To this end, several sensing and imaging techniques have been developed or employed in the assessment of microangiopathy in patients with diabetes. Herein, we present such techniques; we provide insights into their principles of operation while discussing the characteristics that make them appropriate for such use. Finally, apart from already established techniques, we present novel ones with great translational potential, such as optoacoustic technologies, which are expected to enter clinical practice in the foreseeable future.

Optoacoustic Imaging Offers New Insights into In Vivo Human Skin Vascular Physiology

Functional imaging with new photoacoustic tomography (PAT) offers improved spatial and temporal resolution quality in in vivo human skin vascular assessments. In the present study, we followed a suprasystolic reactive hyperemia (RH) maneuver with a multi-spectral optoacoustic tomography (MSOT) system. A convenience sample of ten participants, both sexes, mean age of 35.8 ± 13.3 years old, was selected. All procedures were in accordance with the principles of good clinical practice and approved by the institutional ethics committee. Images were obtained at baseline (resting), during occlusion, and immediately after pressure release. Observations of the RH by PAT identified superficial and deeper vascular structures parallel to the skin surface as part of the human skin vascular plexus. Furthermore, PAT revealed that the suprasystolic occlusion impacts both plexus differently, practically obliterating the superficial smaller vessels and evoking stasis at the deeper, larger structures in real-time (live) conditions. This dual effect of RH on the skin plexus has not been explored and is not considered in clinical settings. Thus, RH seems to represent much more than the local microvascular reperfusion as typically described, and PAT offers a vast potential for vascular clinical and preclinical research.

Fitness Level- and Sex-related Differences in Macro- and Microvascular Responses during Reactive Hyperemia

PURPOSE

Reactive hyperemia (RH) is widely used for the investigation of macrovascular (Flow-Mediated Dilation, FMD) and microvascular (Near Infrared Spectroscopy-Vascular Occlusion Test, NIRS-VOT) function. Mixed results have been reported on fitness level- and sex-related differences in FMD outcomes, and little is known about microvascular differences in untrained and chronically trained males and females.

METHODS

Fifteen chronically trained (CT: 8 MALES, 7 FEMALES) and sixteen untrained (UT: 8 MALES, 8 FEMALES) individuals participated in this study. Aerobic fitness (V[Combining Dot Above]O2max) was assessed during a cycling incremental exercise test to volitional exhaustion. FMD and NIRS-VOT were performed simultaneously on the lower limb investigating superficial femoral artery and vastus lateralis muscle, respectively.

RESULTS

%FMD was not different between groups (CT MALES, 4.62 ± 1.42; CT FEMALES, 4.15 ± 2.23; UT MALES, 5.10 ± 2.53; CT FEMALES, 3.20 ± 1.67). Peak blood flow showed greater values in CT vs UT (p ≤ 0.0001) and MALES vs FEMALES (p = 0.032). RH blood flow AUC was greater in CT vs UT (p = 0.001). At the microvascular level, desaturation and reperfusion rates were faster in CT vs UT (p = 0.018 and p = 0.013) and MALES vs FEMALES (p = 0.011 and p = 0.005). V[Combining Dot Above]O2max was significantly correlated with reperfusion rate (p = 0.0005) but not with %FMD.

CONCLUSION

Whereas NIRS-VOT outcomes identified fitness- and sex-related differences in vascular responses, %FMD did not. However, when reactive hyperemia-related outcomes from the FMD analysis were considered, fitness- and/or sex-related differences were detected. These data highlight the importance of integrating FMD and NIRS-VOT outcomes for a more comprehensive evaluation of vascular function.