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New Finding: What is the central question of this study? Transition to supine posture induces an inspiratory load associated with cortical activation in awake healthy subjects. Some obstructive sleep apnoea patients exhibit this cortical activity in the sitting position contributing to the arousal-dependent compensation of their upper airway abnormalities. Does a transition to the supine posture in awake obstructive sleep apnoea patients increase this cortical activity? What is the main finding and its importance? The transition to supine posture induces a reduction in the cortical activity despite evidence of an increase in genioglossus activity, suggesting that genioglossus activation is not driven by cortical activity., Abstract: The anatomy and mechanical properties of the upper airway (UA) depend on posture. Lying in a supine position causes cephalad fluid shift to the neck, thus narrowing the UA and predisposing the individual to obstructive sleep apnoea (OSA). Increased UA dilator muscle activity during wakefulness prevents the UA collapse but the underlying mechanism has not yet been elucidated. In the sitting position during wakefulness, some OSA patients exhibit preinspiratory cortical activity (preinspiratory potential, PIP) probably related to UA abnormalities. The aim of this study was to investigate changes in the preinspiratory cortical activity and UA dilator muscle in OSA patients during postural challenge. An electroencephalogram was used to detect PIP, and the genioglossus electromyographic activity and ventilation were analysed in 17 awake, male OSA patients while they were sitting, just after lying down, and then in response to leg positive pressure to enhance cephalad fluid shift. The prevalence of PIP decreased from 53% (sitting) to 12% (supine) (P = 0.002) in association with increased genioglossus activity (tonic from median (25th, 75th centiles) 2.3 (1.8, 2.8)% to 3.6 (1.7, 5.0)% of voluntary deglutition, P = 0.019; phasic from 2.3 (1.9, 2.8)% to 3.7 (2.0, 6.1)%, P = 0.024), and with increased transcutaneous carbon dioxide pressure (from 43.0 (42.4, 44.2) to 44.6 (43.5, 45.2) mmHg). No change was observed during leg-positive-pressure application. Moving from the sitting position to the supine position reduces respiratory-related premotor cortical activity in awake OSA patients. The concomitant increase in genioglossus activity, therefore, is not driven by cortical respiratory activity., (© 2019 The Authors. Experimental Physiology © 2019 The Physiological Society.)

New Findings: What is the central question of this study? Moving to supine induces upper airway modifications and a fluid shift to the neck, which represent inspiratory load that predisposes to upper airway collapse. Is there cortical participation in the response to the load induced by transition to a supine posture in awake healthy subjects? What is the main finding and its importance? Moving to supine induces transient cortical activation in awake healthy subjects, with greater fluid shift, supporting possible cortical participation in the response to upper airway load induced by transition to a supine posture. Our findings open new perspectives in the understanding of the pathogenesis of obstructive sleep apnoea., Abstract: Moving from sitting upright to lying supine causes anatomical modifications and a fluid shift to the neck, which represent inspiratory loads that predispose to upper airway collapse. The pre-inspiratory potential (PIP) corresponds to the cortical activity observed during inspiratory load. In the sitting position during wakefulness, some obstructive sleep apnoea patients exhibit PIP, probably in relationship to upper airway abnormalities. The aim of this study was to investigate whether moving to the supine position induces respiratory-related cortical activation (PIP) in awake healthy subjects. The ECG was analysed to detect PIP, and EMG activity of the genioglossus muscle and ventilation were measured in the sitting position, immediately after moving to the supine position, and during application of leg positive pressure in the supine position to promote fluid shift, which was measured by bioelectrical impedance. Twenty-four subjects were included. From sitting to lying, PIP prevalence increased from 1/24 to 11/24 (P = 0.002), and ventilation decreased with no change in genioglossus activity. The fluid shift from sitting to supine was higher in the subjects exhibiting PIP while supine compared with the subjects without PIP [median (25th; 75th centiles) 440 (430; 520) versus 320 (275; 385) ml, P = 0.018], without any other differences. From before to during leg positive pressure, PIP disappeared (P = 0.006). These results indicate that moving from sitting to lying induces transient respiratory-related cortical activity in awake healthy subjects with greater fluid shift, supporting possible cortical participation in the response to upper airway loading induced by moving from sitting upright to lying supine. This study offers new perspectives in the understanding of obstructive sleep apnoea pathogenesis., (© 2019 The Authors. Experimental Physiology © 2019 The Physiological Society.)

Thoracoabdominal breathing movements are a complex source of postural disturbance, but there are contradictory reports in the literature with inspiration described as having either a backward or a forward disturbing effect. To elucidate the mechanisms underlying this phenomenon, the present study studied the postural disturbance caused by isolated contractions of the diaphragm. Eight male and four female healthy subjects followed an original paradigm of phrenic nerve stimulation (bilateral and unilateral) and "diaphragmatic" voluntary sniff maneuvers in the seated and standing postures. Center of gravity (CG) acceleration was calculated from force plate recordings, and respiratory kinematics were assessed with thoracic and abdominal sensor belts. CG and respiratory signals revealed that, while seated, bilateral phrenic stimulation and sniff maneuvers consistently produced expansion of the abdomen associated with a forward peak of CG acceleration. In the standing posture, the direction of the CG peak was reversed and always directed backward. Unilateral phrenic stimulation induced an additional medial-lateral acceleration of the CG, directed toward the nonactive side while seated, but in the opposite direction while standing. These results suggest that isolated diaphragmatic contractions produce a constant disturbing pattern for a given posture, but with opposite effects between standing and seated postures. This could be related to the different biomechanical configuration of the body in each posture, corresponding to distinct kinematic patterns of the osteoarticular chain. In addition, the lateral component of the CG acceleration induced by unilateral diaphragm contractions could be clinically relevant in patients with hemidiaphragm paralysis., (Copyright © 2014 the American Physiological Society.)

Patients with central respiratory paralysis can benefit from diaphragm pacing to restore respiratory function. However, it would be important to develop a continuous respiratory monitoring method to alert on apnea occurrence, in order to improve the efficiency and safety of the pacing system. In this study, we present a preliminary validation of an acoustic apnea detection method on healthy subjects data. Thirteen healthy participants performed one session of two 2-min recordings, including a voluntary respiratory pause. The recordings were post-processed by combining temporal and frequency detection domains, and a new method was proposed—Phonocardiogram-Derived Respiration (PDR). The detection results were compared to synchronized pneumotachograph, electrocardiogram (ECG), and abdominal strap (plethysmograph) signals. The proposed method reached an apnea detection rate of 92.3%, with 99.36% specificity, 85.27% sensitivity, and 91.49% accuracy. PDR method showed a good correlation of 0.77 with ECG-Derived Respiration (EDR). The comparison of R-R intervals and S-S intervals also indicated a good correlation of 0.89. The performance of this respiratory detection algorithm meets the minimal requirements to make it usable in a real situation. Noises from the participant by speaking or from the environment had little influence on the detection result, as well as body position. The high correlation between PDR and EDR indicates the feasibility of monitoring respiration with PDR. [ABSTRACT FROM AUTHOR]