Assessing microvascular function in adults with type II diabetes using near-infrared spectroscopy: Implications for exercise capacity
Authors: Michielsen M , Chatzinikolaoi P , Claes J , Decorte E , Bekhuis Y , Goetschalckx K , Hansen D , De Craemer M , Cornelissen V 
Published: June 2024

Abstract

Introduction
Adults with type 2 diabetes mellitus (T2DM) commonly present with a worse exercise capacity compared to their healthy peers. The underlying mechanisms of this exercise intolerance, such as impaired microcirculation and altered tissue oxygenation, remain to be elucidated.

Purpose
To evaluate the role of muscle oxygenation during exercise using near-infrared spectroscopy (NIRS) in adults with T2DM.

Methods and analyses
Data were collected from 60 adults with T2DM (36 men, 59 ± 10.21 years old) participating in the PROTECTION trial. A graded maximal cardiopulmonary exercise test was performed on a cycle ergometer (Vyntus CPX, Duomed) to assess exercise capacity, by means of V02peak. Concurrently, muscle oxygenation was measured in the vastus lateralis muscle, using NIRS (Portamon, Artinis).
Changes in deoxyhemoglobin (HHb), reflecting oxygen utilization, and the tissue saturation index (TSI), reflecting the balance between oxygen delivery and utilization, were analysed, during both exercise and recovery. During exercise, changes in HHb were calculated from start to termination, whereas changes in TSI were computed from maximum to minimum value. During recovery, changes in HHb and TSI were calculated between the cessation of the exercise to the following 30 seconds. Adults with T2DM were then divided into four subgroups based on quartiles of exercise capacity. One-way ANOVA and chi-squared tests were used to evaluate differences between groups. Two-tailed p-values ≤0.05 were considered statistically significant.

Results
34 adults with T2DM (57%) had poor-quality NIRS measurements. Poor quality measurements were more frequent among females (21 poor quality vs 3 good quality, p=0.002) and those with higher fat mass (poor quality 39.58 ± 8.04 % vs high quality 30.63 ± 6.23, p&lt;0.001), despite similar body mass index (poor quality 30.86 ± 5.61 kg/m² vs high quality 30.08 ± 6.27 kg/m², p=0.612). 26 adults with T2DM (43%) had high-quality NIRS measurements which could be used in the final analysis. During exercise, no significant differences in changes in HHb and TSI could be observed among the four quartiles (p&gt;0.05 for all) (Fig 1A and 1C). During recovery, adults with T2DM with the worst exercise capacity (Q1) showed significant smaller changes in HHb, compared to those with best exercise capacity (Q4) (p&lt;0.05) (Fig 1B). Additionally, a trend towards a smaller increase of TSI in adults with T2DM with a poorer exercise capacity was found (Fig 1D).

Conclusion
These findings suggest a relationship between worsened reoxygenation after exercise and low V02peak, indicating that muscle oxygenation may affect exercise capacity. This highlights the need for further exploration into the use of NIRS in adults with T2DM. However, the high proportion of low quality measurements warrants further exploration on how the use of NIRS can be optimized in more obese clinical populations.