Exploring the Abnormal Modulation of the Autonomic Systems during Nasal Flow Limitation in Upper Airway Resistance Syndrome by Hilbert-Huang Transform.

Chen Lin,Christian Guilleminault,Men-Tzung Lo

doi:10.3389/fmed.2017.00161

Chen Lin, Christian Guilleminault + Show 1 more

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https://doi.org/10.3389/fmed.2017.00161

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Journal: Frontiers in medicine	Publication Date: Sep 28, 2017
Citations: 7	License type: cc-by

Affiliation: Stanford Medicine

Abstract

A breath-by-breath investigation based on the Hilbert-Huang transform was performed to explore autonomic nervous system changes observed during inspiratory flow limitation. Autonomic status was quantified from beat-to-beat heart rate analysis by high frequency (RRHF; 0.15-0.4 Hz), low frequency (RRLF; 0.04-0.15 Hz), and LF/HF ratio of each respiratory cycle. Based on respiratory-related mechanisms contained in the PPG signal, we further quantified the respiratory-related oscillations (PPGres). Based on esophageal pressure and nasal flow measurements, each respiratory cycle was identified and breathing patterns were classified into one of four groups: normal, inspiratory flow limitation cycles without increased effort [FL(-)], minimal inspiratory flow limitation with effort, and inspiratory flow limitation cycles with increased effort [FL(+)]. The resulting quantitative parameters of the identified cycles were calculated. 49 UARS patients (12 males; aged 26.8 ± 5.8 years) with apnea-hypopnea index (AHI) 3.1 ± 1.5 per hour and nine aged matched control subjects (3 males; aged 27.8 ± 4.0 years) with AHI 0.8 ± 1.1 per hour were retrospectively identified. Compared to the control group, hyperactivation of the parasympathetic system was noted during stage 2 NREM sleep by RRHF (27.8 ± 18.2 vs 22.5 ± 11.12, p < 0.05) in 49 UARS patients. Analysis of the different classifications of respiratory cycles indicated that during "high" (increased) respiratory efforts, the RRHF and PPGres were significantly higher compared to "normal cycle" and "FL(-)" groups. The RRLF/RRHF (an index of sympathetic activity) was significantly lower in the "FL(+)" group (1.66 ± 0.80) than in the "normal cycle" (1.93 ± 0.97, p < 0.05) and "FL(-)" groups (2.01 ± 1.01, p < 0.05). The proposed algorithm allows quantifying the temporal changes of specific mechanisms of the autonomic system on breath-by-breath basis. With no or very limited impact on oxygen saturation, the hyperactivation of parasympathetic system in associated with inspiratory flow limitation or increased respiratory efforts during stage 2 NREM sleep has been presented in this study.

Highlights

Flow limitation is a term used when analyzing polysomnography (PSG) and monitoring nasal flow with a nasal cannula/pressure transducer system [1, 2]
To address the question of the interaction between flow limitation and autonomic nervous system (ANS) changes during NREM sleep, we developed a new analytic technique rarely used in the field of sleep and breathing and based on Hilbert–Huang transform (HHT)
All subjects were seen successively at the Stanford Sleep Disorders Center during a 4-month period for complaints of poor sleep, tiredness, fatigue, some degree of daytime sleepiness, and other symptoms associated with sleep-related inspiratory flow limitation and “upper airway resistance syndrome (UARS).” The patients had no other clinical complaints indicating another sleep disorder and underwent a PSG confirming a normal obstructive sleep apnea–hypopnea-index (AHI) following the Academy of Sleep Medicine (AASM) guidelines [16], but presence of an abnormal amount of inspiratory flow limitation associated with EEG disturbances [3]

Summary

Introduction

Flow limitation is a term used when analyzing polysomnography (PSG) and monitoring nasal flow with a nasal cannula/pressure transducer system [1, 2]. Inspiratory flow limitation is the studied variable, and inspiratory flow decreases as upper airway resistance increases without clear drops of oxygen saturation and without association with the American Academy of Sleep Medicine (AASM)-defined “sleep-hypopnea”(3). Patients with such PSG-findings have clear clinical complaints involving poor sleep. This clinical syndrome has been previously well described as “upper airway resistance syndrome (UARS)” [3,4,5]. The authors indicate that patients with pathological amounts of flow limitation complain of their sleep but already have changes to lipid and glucose metabolisms as assessed by simple blood tests [6]

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