Spectral Analysis of Resting Near‐Infrared Spectroscopy Shows Preserved Endothelial Function after Aerobic Training Exercise in Chronic Kidney Disease
Authors: Yao Jingting , Sprick Justin D. , Mammino Kevin , Nocera Joe R. , DaCosta Dana R. , Park Jeanie , Reiter David A. 
Published: May 2022

This study aims to evaluate the effectiveness of aerobic exercise training on microcirculatory function among individuals with chronic kidney disease (CKD). Microcirculatory dysfunction is a prevalent complication in CKD that progresses as CKD evolves. Endothelial dysfunction is an early manifestation of microvascular disease and contributes to increased cardiovascular‐related mortality in CKD. Evidence indicates that endothelial dysfunction might be linked to deficits in blood perfusion and oxygen delivery. Aerobic exercise has been shown to improve cardiorespiratory function and blood pressure control for adults with CKD. Previous work has validated correspondence of specific frequency intervals in resting microvascular blood flow fluctuations with physiological events. Specifically, the spectrum amplitude from three frequency intervals (0.0095 – 0.02 Hz, 0.02 – 0.06 Hz, 0.06 – 0.15 Hz) have been attributed to microvascular regulation by endothelial, neurogenic, and myogenic origins, respectively. We hypothesized that 12 weeks of aerobic exercise would improve endothelial function in CKD.Ten CKD participants (Table 1) were randomized into treatment and control groups that performed progressive aerobic cycling exercise (N = 5) for 20‐45 min up to 80% of heart rate reserve and non‐aerobic, stretching exercise (N = 5). Each group performed activities 3 days/week for 12 weeks. Resting microvascular blood flow was measured in the forearm for 5 minutes using total hemoglobin (tHb) signal from near‐infrared spectroscopy. Reactive hyperemic index (RHI) was measured using peripheral artery tonometry at the upper arm, providing an accepted, single‐value index of endothelial function. Both measures were obtained at the beginning (baseline) and end of the 12‐week intervention (EOS), respectively. The resting tHb signal was analyzed using wavelet transform to obtain time‐frequency information on microcirculation regulated by endothelial, neurogenic, and myogenic functions. Differences at baseline and EOS were assessed using pairwise Student’s t‐test (statistical significance: p < 0.05). The Pearson correlation coefficient between RHI and individual mean spectral amplitude was also obtained.Endothelial spectral amplitudes significantly decreased (p = 0.007) in the stretching group over the 12‐week intervention, suggesting decreased endothelial function (Fig.1). There was no significant change in the endothelial spectral amplitude (p = 0.16) in the cycling group. Changes in individual endothelial spectral amplitude and RHI were moderately correlated (r = 0.57 and p = 0.02).In conclusion, spectral analysis of resting microvascular blood flow in CKD suggests preserved endothelial function over 12 weeks of progressive aerobic cycling exercise, compared with a decline in those who performed a non‐aerobic stretching exercise. Ongoing work focuses on adapting and applying this wavelet methodology to MRI‐derived signals that provide temporo‐spatially resolved information on tissue oxygenation and perfusion. Resting microcirculatory properties yielded from this work may be useful for monitoring disease progression and guiding targeted therapeutic strategies to improve microvascular function in CKD.