Role of surgical hyoid bone repositioning in modifying upper airway collapsibility

Background: Surgical hyoid bone repositioning procedures are being performed to treat obstructive sleep apnea (OSA), though outcomes are highly variable. This is likely due to lack of knowledge regarding the precise influence of hyoid bone position on upper airway patency. The aim of this study is to determine the effect of surgical hyoid bone repositioning on upper airway collapsibility.Methods: Seven anaesthetized, male, New Zealand White rabbits were positioned supine with head/neck position controlled. The rabbit’s upper airway was surgically isolated and hyoid bone exposed to allow manipulation of its position using a custom-made device. A sealed facemask was fitted over the rabbit’s snout, and mask/upper airway pressures were monitored. Collapsibility was quantified using upper airway closing pressure (Pclose). The hyoid bone was repositioned within the mid-sagittal plane from 0 to 5 mm (1 mm increments) in anterior, cranial, caudal, anterior-cranial (45°) and anterior-caudal (45°) directions.Results: Anterior displacement of the hyoid bone resulted in the greatest decrease in Pclose amongst all directions (p = 0.002). Pclose decreased progressively with each increment of anterior hyoid bone displacement, and down by −4.0 ± 1.3 cmH2O at 5 mm. Cranial and caudal hyoid bone displacement did not alter Pclose (p > 0.35). Anterior-cranial and anterior-caudal hyoid bone displacements decreased Pclose significantly (p < 0.004) and at similar magnitudes to the anterior direction (p > 0.68).Conclusion: Changes in upper airway collapsibility following hyoid bone repositioning are both direction and magnitude dependent. Anterior-based repositioning directions have the greatest impact on reducing upper airway collapsibility, with no effect on collapsibility by cranial and caudal directions. Findings may have implications for guiding and improving the outcomes of surgical hyoid interventions for the treatment of OSA

Proto Kranz-like leaf traits and cellular ionic regulation are associated with salinity tolerance in a halophytic wild rice

Species of wild rice (Oryza spp.) possess a wide range of stress tolerance traits that can be potentially utilized in breeding climate-resilient cultivated rice cultivars (Oryza sativa) thereby aiding global food security. In this study, we conducted a greenhouse trial to evaluate the salinity tolerance of six wild rice species, one cultivated rice cultivar (IR64) and one landrace (Pokkali) using a range of electrophysiological, imaging, and whole-plant physiological techniques. Three wild species (O. latifolia, O. officinalis and O. coarctata) were found to possess superior salinity stress tolerance. The underlying mechanisms, however, were strikingly different. Na+ accumulation in leaves of O. latifolia, O. officinalis and O. coarctata were significantly higher than the tolerant landrace, Pokkali. Na+ accumulation in mesophyll cells was only observed in O. coarctata, suggesting that O. officinalis and O. latifolia avoid Na+ accumulation in mesophyll by allocating Na+ to other parts of the leaf. The finding also suggests that O. coarctata might be able to employ Na+ as osmolyte without affecting its growth. Further study of Na+ allocation in leaves will be helpful to understand the mechanisms of Na+ accumulation in these species. In addition, O. coarctata showed Proto Kranz-like leaf anatomy (enlarged bundle sheath cells and lower numbers of mesophyll cells), and higher expression of C4-related genes (e.g., NADPME, PPDK) and was a clear outlier with respect to salinity tolerance among the studied wild and cultivated Oryza species. The unique phylogenetic relationship of O. coarctata with C4 grasses suggests the potential of this species for breeding rice with high photosynthetic rate under salinity stress in the future

Personalized Management Approach for OSA

OSA is a heterogeneous disorder. If left untreated, it has major health, safety, and economic consequences. In addition to varying levels of impairment in pharyngeal anatomy (narrow/collapsible airway), nonanatomical “phenotypic traits” are also important contributors to OSA for most patients. However, the majority of existing therapies (eg, CPAP, oral appliances, weight loss, positional therapy, upper airway surgery) target only the anatomical cause. These are typically administered as monotherapy according to a trial and error management approach in which the majority of patients are first prescribed CPAP. Despite its high efficacy, CPAP adherence remains unacceptably low, and second-line therapies have variable and unpredictable efficacies. Recent advances in knowledge regarding the multiple causes of OSA using respiratory phenotyping techniques have identified new targets or “treatable traits” to direct therapy. Identification of the traits and development of therapies that selectively target one or more of the treatable traits has the potential to personalize the management of this chronic health condition to optimize patient outcomes according to precision medicine principles. This brief review highlights the latest developments and emerging therapies for personalized management approaches for OSA

Proceedings of Meetings on Acoustics

Acoustic impedance spectrometry using the three-microphone, three-calibration technique has recently been applied to the vocal tract during phonation (Hanna et al., 2016. JASA, 139, 2924– 2936). The qualitative and quantitative similarity of the impedance spectrum of the vocal tract with a simple cylindrical duct prompts the question: How well do geometric parameters derived from the measured impedance correspond to the vocal tract morphology? The main aim of this study is to compare, in one male subject (age 34, height 184 cm), the effective acoustic length of the vocal tract derived from impedance spectrometry with the anatomical length measured from a separate magnetic resonance imaging (MRI) scan. Three conditions were studied: 1) acoustic impedance measurements while the subject performed a neutral /ɜ/ vowel gesture with the lips sealed around the impedance measurement head, 2) MRI scan acquired while the subject performed the same gesture with a section of pipe between his lips of the same dimensions as the impedance head, and 3) MRI scan during closed- mouth nasal breathing. Even for the neutral vowel, the effective acoustic length is a (weak) function of frequency. Consequently, each of the acoustic tract resonances gives a slightly different effective length, with a range from 155 to 195 mm with glottis closed. Compared with the 1:3:5:7 ratios expected for cylindrical geometry, the higher resonances have slightly lower frequencies. This is perhaps because the cross-section in the region of the tract closer to the lips is on average greater than that of the region from the palate to glottis. However there is agreement between the length derived from the first acoustic resonance and the smoothed airway centroid length in the MRI of the mid-sagittal plane

Sleep and respiratory physiology in adults

Respiration during sleep is determined by metabolic demand; respiratory drive is determined by a central respiratory generator. Changes in pharyngeal dilator muscle tone resulting in increased upper airway resistance and collapsibility contribute to hypoventilation. Relative hypotonia of respiratory muscles, body posture changes, and altered ventilatory control result in additional physiologic changes contributing to hypoventilation. This article reviews mechanisms of central control of respiration and normal upper and lower airway physiology. Understanding sleep-related changes in respiratory physiology will help in developing new therapies to prevent hypoventilation in susceptible populations. © 2014 Elsevier Inc

Snoring-related energy transmission to the carotid artery in rabbits

Epidemiological studies link habitual snoring and stroke, but mechanisms involved are poorly understood. One previously advanced hypothesis is that transmitted snoring vibration energy may promote carotid atheromatous plaque formation or rupture. To test whether vibration energy is present in carotid artery walls during snoring we developed an animal model in which we examined induced snoring (IS)-associated tissue energy levels. In six male, supine, anesthetized, spontaneously breathing New Zealand White rabbits, we surgically inserted pressure transducer-tipped catheters (Millar) to monitor tissue pressure at the carotid artery bifurcation (PCT) and within the carotid sinus lumen (PCS; artery ligated). Snoring was induced via external compression (sandbag) over the pharyngeal region. Data were analyzed using power spectral analysis for frequency bands above and below 50 Hz. For frequencies below 50 Hz, PCT energy was 2.2 (1.1–12.3) cmH₂O² [median (interquartile range)] during tidal breathing (TB) increasing to 39.0 (2.5–95.0) cmH₂O² during IS (P = 0.05, Wilcoxon's signed-rank test). For frequencies >50 Hz, PCT energy increased from 9.2 (8.3–10.4) x 10⁻⁴ cmH₂O² during TB to 172.0 (118.0–569.0) x 10⁻⁴ cmH₂O² during IS (P = 0.03). Concurrently, PCS energy was 13.4 (8.5–18.0) x 10⁻⁴ cmH₂O² during TB and 151.0 (78.2–278.8) x 10⁻⁴ cmH₂O² during IS (P < 0.03). The PCS energy was greater than PCT energy for the 100–275 Hz bandwidth. In conclusion, during IS there is increased energy around and within the carotid artery, including lower frequency amplification for PCS. These findings may have implications for carotid atherogenesis and/or plaque rupture.7 page(s

Snoring effects on the baroreflex: An animal model

Baroreflex sensitivity (BRS) is reduced in humans during snoring, however the mechanisms are unknown. We used an anaesthetised rabbit induced snoring (IS) model, to test: (1) whether IS was associated with reduced BRS; and (2) if snoring related vibration transmission to peri-carotid tissues influenced BRS levels. BRS was quantified using the spontaneous sequence technique. During IS, BRS fell by 40%, without any associated change in blood pressure (BP) but accompanied by an increase in heart rate (HR). Direct application of a snore frequency and intensity matched vibratory stimulus to the peri-carotid tissues of non-snoring tracheostomised rabbits had no effect on BRS, HR or BP. In conclusion, IS induced depression of BRS is likely mediated via a HR driven change in BRS operating point that is unrelated to snoring-related vibration transmission to carotid baroreceptors. The anaesthetised IS rabbit provides a model in which mechanistic interactions between snoring and BRS can be further explored. © 2012

Resetting the baroreflex during snoring: Role of resistive loading and intra-thoracic pressure

Baroreflex sensitivity (BRS) is reduced during snoring in humans and animal models. We utilised our rabbit model to examine the contribution of increased upper airway resistance to baroreflex resetting during snoring, by comparing BRS and baroreflex operating point (OP) values during IS to those obtained during tracheostomised breathing through an external resistive load (RL) titrated to match IS levels of peak inspiratory pleural pressure (Ppl). During both IS and RL, BRS decreased by 45% and 49%. There was a linear relationship between the change in Ppl and the decrease in BRS, which was similar for IS and RL. During both RL and IS, there was a shift in OP driven by ∼16% increase in HR and no change in arterial pressure. Snoring related depression of BRS is likely mediated via a HR driven change in OP, which itself may be the outcome of negative intra-thoracic pressure mediated effects on right atrial wall stretch reflex control of heart rate. © 2012 Elsevier B.V