The autonomic burden in the Asthma-OSA Overlap syndrome

INTRODUCTION: The co-occurrence of Asthma and Obstructive Sleep Apnoea (OSA) results in a condition termed alternative Overlap Syndrome (aOVS), characterised by shared risk factors and pathophysiological mechanisms, that synergistically intensify each other. The aim of the study was to evaluate autonomic dysfunction in subjects with aOVS. METHODS: Fifty-one asthmatic patients diagnosed with OSA through standard polysomnography at the Sleep Disorders Centre of the University of Crete were consecutively included. Three polysomnographic autonomic markers indicative of Autonomic Burden (AB) were calculated for each patient: Arousal Index (AI), Pulse Wave Amplitude Drop (PWAD) index, and Pulse Transit Time (PTT) drop index. The Autonomic Burden z-score (AB_z), the normalised mean of the three markers, divided the cohort into High AB and Low AB. Subsequently, K-means clustering (k = 2) identified two different autonomic-respiratory phenotypes. RESULTS: Compared to Low AB group, High AB group had higher autonomic markers, respiratory burden, with fragmented sleep. In High AB group, oximetry-derived hypoxic load parameters correlated better with the PWAD index than with AHI. The PWAD index was the best predictor of hyperlipidaemia in the multivariate analysis. Clustering (k = 2) identified an autonomic-hypoxic phenotype (higher autonomic markers and respiratory burden with more fragmented sleep) and an autonomic-stable phenotype (preserved values). CONCLUSIONS: In aOVS, autonomic dysfunction may represent a pathophysiological core, closely related to hypoxic load, sleep quality, clinical presentation and cardiometabolic risk. The use of Autonomic Burden to stratify aOVS patients may represent the key to better management of this syndrome.