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After studying sweat metabolic changes, investigators noted significant effects in the metabolism of carbohydrates, amino acids, energy metabolism, the urea cycle, and metabolic pathways connected to oxidative stress due to OSA and the severity stage.
Measuring night sweats, specifically sweat metabolomes, can help determine the severity of obstructive sleep apnea (OSA), according to a new study.1
“By analyzing sweat metabolome and its alterations, mainly at night, we were able to see what stage of the disease the patients were in,” said lead investigator Laura Castillo, PhD candidate, from the department of analytical chemistry at the University of Córdoba and the Maimonides Institute for Biomedical Research in Córdoba, in a press release. “It is a non-invasive and clean sample since, unlike the case with blood, we don’t have to remove proteins, and it’s much easier to analyze and detect metabolites.”
The current way to diagnose OSA is through Apnea-Hypopnea Index (AHI) levels, measuring sleep apnea based on the episodes of shortness of breath occurring per hour. According to an International Consensus Document about OSA, individuals are considered not to have OSA when their AHI is < 15 events per hour, non-severe OSA when their AHI is between 15 and <30 events per, and severe OSA when AHI is ≥ 30 events per hour.2 The investigators note the issue with the index is that it does not provide enough information about the disease since it does not account for episode severity—simply the number of episodes.
To determine the severity of a disease, alterations in metabolism need to be studied—and they are usually studied through blood or urine samples. For Castillo’s team, they wanted to study sleep apnea severity in a “less invasive” and “more accessible alternative.”1
In their observational and prospective study, the team measured sweat samples from before and after sleep of 72 individuals. Participants were recruited from the Sleep Unit of Reina Sofía University Hospital in Córdoba, Spain between October 2018 – June 2019 if they were suspected to have breathing sleep disorders and experienced snoring, unrefreshing sleep, and excessive daytime sleepiness. In total, 61 individuals were identified for inclusion in the study. Among these, 14 had nonsevere sleep apnea, 17 had severe sleep apnea, and 20 were included as controls.
The team used the gas chromatography technique with high-resolution mass spectrometry to detect chemical components. Investigators identified 78 metabolites and studied their changes concerning energy production and oxidative stress.
“We could see how the sweat metabolism itself indicates those alterations during sleep as a result of which the person’s energy production worsens and their oxidative stress increases,” Castillo said in the press release.
The pre-sleeping samples showed 4 biomolecules with significant differences in sweat samples. For instance, pyruvate (P = .046) and lactose (P = .028) demonstrated a significant increase in sweat from patients with OSA. In contrast, serine (P = .016) and hydroxybutyrate (P = .049) showed a significant reduction in sweat from patients with OSA. Additionally, when considering the AHI and ODI classifications of OSA severity, the investigators noted significant differences in metabolites such as lactose, succinate, urea, and oxoproline.
The investigators tracked the disease and potential effects such as cardiovascular issues. With the metabolomic profile, they were able to tell apart who had sleep apnea and who did not and therefore were in the control group.
“This study reveals that metabolic changes induced by OSA overnight could be a mirror of the long-term further metabolic repercussions (permanent changes) caused by this disease, which could represent intermediate physiopathological mechanisms that may influence cardiovascular complications risk,” investigators wrote.
Castillo and colleagues highlighted the importance of using the oxygen desaturation index when diagnosing sleep apnea. Rather than using the Apnea-Hypopnea Index, the oxygen desaturation index can show how serious episodes are by calculating the number of events where oxygen saturation has reduced by > 3%.
“Analysis of sweat metabolic changes before sleep and overnight revealed significant effects in the metabolism on carbohydrates and amino acids, energy metabolism, the urea cycle, and metabolic pathways related to oxidative stress due to OSA and severity stages,” investigators wrote. “Overall, the results indicate that OSA is a disease that mainly alters energy production processes in cells, as reported in previous studies.”