Physiological Responses and Perceived Comfort to High Flow Nasal Cannula Therapy in Awake Adults: Effects of Flow Magnitude and Temperature

Clinical use of heated, high flow nasal cannula (HFNC) for non-invasive respiratory support is increasing and may have a therapeutic role in stabilizing the upper airway in obstructive sleep apnea (OSA). However, physiological mechanisms by which HFNC therapy may improve upper-airway function and effects of different temperature modes are unclear. Accordingly, this study aimed to determine effects of incremental flows and temperature modes (heated and non-heated) of HFNC on upper airway muscle activity (genioglossus), pharyngeal airway pressure, breathing parameters and perceived comfort. Six participants (2 females, aged 35±14 years) were studied during wakefulness in supine position and received HFNC at variable flows (0-60 L/min) during heated (37ºC) and non-heated (21ºC) modes. Breathing parameters via calibrated Respitrace inductance bands (chest and abdomen), upper-airway pressures via airway transducers, and genioglossus muscle activity via intra-muscular bipolar fine wire electrodes were measured. Comfort levels during HFNC were quantified using a visual analogue scale. Increasing HFNC flows did not increase genioglossus muscle activation despite increased negative epiglottic pressure swings (p=0.009). HFNC provided ~7cmH2O positive airway pressure at 60 L/min in non-heated and heated modes. In addition, increasing the magnitude of HFNC flow reduced breathing frequency (p=0.045), increased expiratory time (p=0.040), increased peak inspiratory flow (p=0.002), and increased discomfort (p=0.004). Greater discomfort occurred at higher flows in non-heated versus heated mode (p=0.034). These findings provide novel insight into key physiological changes that occur with HFNC for respiratory support and indicate the primary mechanism for improved upper-airway stability is positive airway pressure, not increased pharyngeal muscle activity.

O037 Genioglossus motor control following the return to sleep after brief arousal

Rationale Arousal from sleep has been shown to elicit a prolonged increase in genioglossus muscle activity that persists following the return to sleep and may protect against airway collapse. We hypothesised that this increased genioglossal activity following return to sleep after an arousal is due to persistent firing of inspiratory single motor units (SMUs) recruited during the arousal. Methods 34 healthy participants were studied overnight while wearing a nasal mask/pneumotachograph to measure ventilation and with 4 intramuscular genioglossus SMU electrodes. During stable N2 and N3 sleep, auditory tones were played to induce brief (3-15s) AASM arousals. Ventilation and genioglossus SMUs were quantified for 5 breaths before the tone, during the arousal and for 10 breaths after the return to sleep. Results A total of 1089 tones were played and gave rise to 236 SMUs recorded across arousal and the return to sleep in 20 participants (age 23±4.2 years and BMI 22.5±2.2kg/m2). Ventilation was elevated above baseline during arousal and the first post-arousal breath (p<0.001). The peak firing frequency of expiratory and tonic SMUs was unchanged during arousal and return to sleep, whereas inspiratory modulated SMUs were increased during the arousal and for 4 breaths following the return to sleep (p<0.001). Conclusions The prolonged increase in genioglossus activity that occurs on return to sleep after arousal is a result of persistent activity of inspiratory SMUs. Strategies to elevate inspiratory genioglossus SMU activity may be beneficial in preventing/treating obstructive sleep apnea.

P005 The effect of alcohol on the motor control of the genioglossus muscle

Rationale Alcohol is recognised to worsen snoring and obstructive sleep apnea (OSA). This effect is thought to be due to alcohol’s depressant effect on upper airway dilator muscles such as the genioglossus, but how alcohol reduces genioglossus activity is unknown. The aim of this study was to investigate alcohol’s effect on genioglossus single motor units (SMUs). Methods Healthy individuals visited the lab on two days (Alcohol: breath alcohol concentration ~0.08% or Placebo). They were instrumented with a nasal mask, 4 intramuscular genioglossus SMU EMG wires and an ear oximeter. They were exposed to 8–12 hypoxia trials (45-60s of 10%O2 followed by one breath of 100%O2) while awake. The SMUs were sorted according to their firing patterns with respect to respiration and were quantified during baseline, hypoxia, hyperoxia and recovery. Results The total number of SMUs recorded at baseline (68 and 67 respectively) and their distribution (ET: 29 vs 22, IP: 5 vs 10, IT: 8 vs 20 and TT: 26 vs 15 respectively) was similar between conditions. The discharge frequency did not differ between conditions (21Hz vs 22.4Hz, p>0.08). There was no difference between placebo and alcohol in the number (101 vs 88 respectively) and distribution (ET: 35 vs 32, IP: 22 vs 16, IT: 14 vs 22 and TT: 30 vs 17 respectively, p<0.05) of SMUs during hypoxia. Afterdischarge following hypoxia was also not different between conditions. Conclusion Alcohol has little effect on genioglossus SMUs and afterdischarge. OSA following alcohol may be related to increased upper airway resistance/nasal congestion.

Mechanical Properties, Anatomy, and Control of the Upper Airway

The physiology of the upper airway is fundamental to current and trending therapy for obstructive sleep apnea and neurostimulation in particular. Proper functioning of the upper airway will promote sleep health by supporting the requisite airflow without snoring or significant flow limitation. Dysfunction produces snoring, obstructive hypopneas, and the metabolic sequelae of sleep disordered breathing. How a particular section of the upper airway (e.g., velopharynx, oropharynx, or hypopharynx) remains open while it is suspended from the skull base, maxilla, and mandible is the result of anatomy and neuromuscular control. The genioglossus muscle, originally designed for bringing food into the mouth and swallowing, along with multiple other muscles, participates in the maintenance of patency of the muscular pharynx during wakefulness and sleep. If the genioglossus were the only muscle important for airway stability, then hypoglossal nerve stimulation would likely be universally rather than selectively effective; instead, its effectiveness is predicted by velopharyngeal functions, which in terms of sleep health are poorly described. Literature clearly indicates a fundamental role for muscles other than the genioglossus in maintaining airway diameter, shape, and wall stiffness. Models that incorporate a more complete neuromechanical coupling of these components are necessary to understand a stable airway during sleep and helpful for decisions in management of obstructive sleep apnea.

What is and what is not an articulatory gesture in speech production

Articulatory data are provided showing that, in languages in which they have phonemic status, (alveolo)palatal consonants, dark /l/ and the trill /r/ are articulated with a single lingual gesture instead of two independent tongue front and tongue body gestures. They are therefore simple, not complex segments. It is argued that tongue body lowering and retraction for dark /l/ and the trill /r/ is associated with manner of articulation requirements and with requirements on the implementation of the darkness percept in the case of dark /l/, and that tongue body raising and fronting for (alveolo)palatals results naturally from the contraction of the genioglossus muscle. These consonant units resemble truly complex palatalized and velarized or pharyngealized dentoalveolars regarding lingual configuration and kinematics, as well as coarticulatory efects and phonological and sound change processes. Contrary to some views, the study also contends that clear /l/ and the tap /?/ are not complex segments but consonants articulated with a more or less neutral tongue body configuration which is subject to considerable vowel coarticulation.