Anatomy and mechanisms of vocal production in harvest mice

Characterizing mechanisms of vocal production provides important insight into the ecology of acoustic divergence. In this study, we characterized production mechanisms of two types of vocalizations emitted by western harvest mice (Reithrodontomys megalotis), a species uniquely positioned to inform trait evolution because it is a sister taxon to peromyscines (Peromyscus and Onychomys spp.), which use vocal fold vibrations to produce long-distance calls, but more ecologically and acoustically similar to baiomyines (Baiomys and Scotinomys spp.), which employ a whistle mechanism. We found that long-distance calls (∼10 kHz) were produced by airflow-induced vocal fold vibrations, whereas high-frequency quavers used in close-distance social interactions (∼80 kHz) were generated by a whistle mechanism. Both production mechanisms were facilitated by a characteristic laryngeal morphology. Our findings indicate that the use of vocal fold vibrations for long-distance communication is widespread in reithrodontomyines (Onychomys, Peromyscus, Reithrodontomys spp.) despite overlap in frequency content that characterizes baiomyine whistled vocalizations. The results illustrate how different production mechanisms shape acoustic variation in rodents and contribute to ecologically relevant communication distances.

Breathing a low-density gas reduces respiratory muscle force development and marginally improves exercise performance in master athletes

INTRODUCTION

We tested the hypothesis that breathing heliox, to attenuate the mechanical constraints accompanying the decline in pulmonary function with aging, improves exercise performance.

METHODS

Fourteen endurance-trained older men (67.9 ± 5.9 year, [Formula: see text]O2max: 50.8 ± 5.8 ml/kg/min; 151% predicted) completed two cycling 5-km time trials while breathing room air (i.e., 21% O2-79% N2) or heliox (i.e., 21% O2-79% He). Maximal flow-volume curves (MFVC) were determined pre-exercise to characterize expiratory flow limitation (EFL, % tidal volume intersecting the MFVC). Respiratory muscle force development was indirectly determined as the product of the time integral of inspiratory and expiratory mouth pressure (∫Pmouth) and breathing frequency. Maximal inspiratory and expiratory pressure maneuvers were performed pre-exercise and post-exercise to estimate respiratory muscle fatigue.

RESULTS

Exercise performance time improved (527.6 ± 38 vs. 531.3 ± 36.9 s; P = 0.017), and respiratory muscle force development decreased during inspiration (- 22.8 ± 11.6%, P < 0.001) and expiration (- 10.8 ± 11.4%, P = 0.003) with heliox compared with room air. EFL tended to be lower with heliox (22 ± 23 vs. 30 ± 23% tidal volume; P = 0.054). Minute ventilation normalized to CO2 production ([Formula: see text]E/[Formula: see text]CO2) increased with heliox (28.6 ± 2.7 vs. 25.1 ± 1.8; P < 0.001). A reduction in MIP and MEP was observed post-exercise vs. pre-exercise but was not different between conditions.

CONCLUSIONS

Breathing heliox has a limited effect on performance during a 5-km time trial in master athletes despite a reduction in respiratory muscle force development.

Heliox simulations for initial management of congenital laryngotracheal stenosis

OBJECTIVES

Congenital laryngotracheal stenosis is rare, potentially severe, and difficult to manage. Heliox is a medical gas effective in obstructive airway pathologies, given its physical properties. This study aims to model the interest of Heliox in reducing the respiratory work in congenital laryngotracheal stenosis, using numerical fluid flow simulations, before considering its clinical use.

DESIGN

This is a retrospective study, performing Computational Fluid Dynamics numerical simulations of the resistances to airflow and three types of Heliox, on 3D reconstructions from CT scans of children presenting with laryngotracheal stenosis.

PATIENTS

Infants and children who were managed in the Pediatric ENT department of a tertiary-care center and underwent CT scanning for laryngotracheal stenosis between 2008 and 2018 were included.

RESULTS

Fourteen models of congenital laryngotracheal stenosis were performed in children aged from 16 days to 5 years, and one model of the normal trachea in a 5-year-old child. Tightest stenosis obtained the highest airway resistances, ranging from 40 to 10 kPa/L/s (up to 800 times higher than in the normal case). Heliox enabled a decrease in pressure drops and airway resistances in all stenosis cases, correlated to increasing Helium concentration.

CONCLUSIONS

Heliox appears to reduce pressure drops and airway resistances in 3D models of laryngotracheal stenosis. It may represent a supportive treatment for laryngotracheal stenosis, while waiting for specialized care, thanks to the reduction of respiratory work.

Lung function changes in divers after a single deep helium-oxygen dive

INTRODUCTION

This study measured pulmonary function in divers after a single helium-oxygen (heliox) dive to 80, 100, or 120 metres of sea water (msw).

METHODS

A total of 26 divers participated, of whom 15, five, and six performed a 80, 100, or 120 msw dive, respectively. While immersed, the divers breathed heliox and air, then oxygen during surface decompression in a hyperbaric chamber. Pulmonary function was measured twice before diving, 30 min after diving, and 24 h after diving.

RESULTS

At 30 min after the 80 msw dive the forced expiratory volume in 1 s (FEV₁)/forced vital capacity (FVC) ratio and the maximum expiratory flow at 25% of vital capacity (MEF₂₅) values decreased (89.2% to 87.1% and 2.57 L·s⁻¹ to 2.35 L·s⁻¹, P = 0.04, P = 0.048 respectively) but FEV₁/FVC returned to the baseline values by 24 h post-dive. Other pulmonary indicators exhibited downward trends at 30 min after the dive, but statistical significance was lacking. Interestingly, though several parameters decreased after the 100 msw dive, statistical significance was not reached. After the 120 msw dive, the FEV₁/FVC and MEF₇₅ decreased (90.4% to 85.6% and 8.05 L·s⁻¹ to 7.46 L·s⁻¹, P = 0.01, P = 0.007). The relatively small numbers of subjects who dived to 100 and 120 msw depths may explain the inconsistent results. The subjects diving to 100 and 120 msw were more trained / skilled, but this would not explain the inconsistencies in results between these depths.

CONCLUSIONS

We conclude that single deep heliox dives cause a temporary decrease in FEV₁/FEV and MEF25 or MEF₇₅, but these changes can recover at 24 h after the dive.

[Chronic respiratory failure correction in cicatricial laryngeal and tracheal stenosis using helium-oxygen mixture]

The article provides a review of the literature on the development of chronic respiratory failure in patients with chronic cicatricial stenosis of the larynx and cervical trachea. The authors provide data on the etiology, pathogenetic features of the course of cicatricial stenosis of the larynx and trachea, the reasons for the development of chronic respiratory failure, the effect of hypoxemia on general metabolic processes in the body and on regeneration processes, as well as on methods of their correction and improvement of the postoperative period. The methods of respiratory impact on chronic respiratory failure in these patients are considered, based on the experience of a number of researchers and technical advances in recent years.

The influence of flowrate and gas density on positive airway pressure for high flow nasal cannula applied to infant airway replicas

High flow nasal cannula (HFNC) therapy has been previously shown to produce positive upper airway pressures in adult and child patients. This work aimed to evaluate and quantify the effects of HFNC flowrate and gas type on airway pressures measured in vitro in infant airway replicas. Ten realistic infant airway replicas, extending from nares to trachea, were connected in turn to a lung simulator and were supplied gas flows through HFNC. Air and heliox were each provided at two weight-indexed flowrates, 1 l/min/kg and 2 l/min/kg. Pressure and lung volume were continuously measured during simulated breathing. For constant simulated patient effort, no statistically significant change in tidal volume was measured between baseline and lower or higher HFNC flowrates, nor was there any significant difference in tidal volume between air and heliox. Tracheal pressure increased with increasing HFNC flow rate, and was highly variable between airway replicas. Higher pressures were measured for air versus heliox. For air supplied at 2 l/min/kg, average airway pressures in excess of 4 cm H₂O were generated, with positive end-expiratory pressure (PEEP) ranging from 2.5 to nearly 12 cm H₂O across the replicas. A predictive correlation for PEEP was proposed based on supplied gas density and flow velocities exiting the cannula and nares, and was able to account for a portion of variability between airway replicas (R² = 0.913). Additionally, PEEP was well correlated with, and predictive of, expiratory peak pressure (R² = 0.939) and average inspiratory pressure (R² = 0.944).

Small airways' function in Obstructive Sleep Apnea-Hypopnea Syndrome

INTRODUCTION AND OBJECTIVES

Most of the studies of the pathophysiology of Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS) focus on the collapsibility and obstruction of the upper airways. The aim of our study was the investigation of small airways' function in patients with OSAHS.

MATERIALS AND METHODS

We studied 23 patients (mean age, 51.6 years) diagnosed with mild to severe OSAHS, without comorbidities and 8 controls (mean age, 45.9 years). All subjects underwent full polysomnography sleep study; spirometry and maximum flow/volume curves while breathing room air and a mixture of 80%He-20%O₂. The volume of equal flows (VisoV⋅) of the two curves and the difference of flows at 50% of FVC (ΔV˙max₅₀) were calculated, as indicates of small airways' function.

RESULTS

The results showed that VisoV⋅ was significantly increased in patients with OSAHS compared with controls (18.79±9.39 vs. 4.72±4.68, p=0.004). No statistically significantly difference was found in ΔV˙_max50% (p=0.551); or the maximum Expiratory flow at 25-75% of FVC (p=0.067) and the maximum expiratory flow at 50% of FVC (p=0.174) breathing air.

CONCLUSIONS

We conclude that at the time of the diagnosis of OSAHS, the function of the small airways is affected. This could be due to breathing at low lung volumes and the cyclic closure/opening of the small airways and may affect the natural history of OSAHS. The findings could lead to new therapeutic implications, targeting directly the small airways.

An explicitly multi-component arterial gas embolus dissolves much more slowly than its one-component approximation

We worked out the growth and dissolution rates of an arterial gas embolism (AGE), to illustrate the evolution over time of its size and composition, and the time required for its total dissolution. We did this for a variety of breathing gases including air, pure oxygen, Nitrox and Heliox (each over a range of oxygen mole fractions), in order to assess how the breathing gas influenced the evolution of the AGE. The calculations were done by numerically integrating the underlying rate equations for explicitly multi-component AGEs, that contained a minimum of three (water, carbon dioxide and oxygen) and a maximum of five components (water, carbon dioxide, oxygen, nitrogen and helium). The rate equations were straight-forward extensions of those for a one-component gas bubble. They were derived by using the Young-Laplace equation and Dalton's law for the pressure in the AGE, the Laplace equation for the dissolved solute concentration gradients in solution, Henry's law for gas solubilities, and Fick's law for diffusion rates across the AGE/arterial blood interface. We found that the 1-component approximation, under which the contents of the AGE are approximated by its dominant component, greatly overestimates the dissolution rate and underestimates the total dissolution time of an AGE. This is because the 1-component approximation manifestly precludes equilibration between the AGE and arterial blood of the inspired volatile solutes (O₂, N₂, He) in arterial blood. Our calculations uncovered an important practical result, namely that the administration of Heliox, as an adjunct to recompression therapy for treating a suspected N₂-rich AGE must be done with care. While Helium is useful for preventing nitrogen narcosis which can arise in aggressive recompression therapy wherein the N₂ partial pressure can be quite high (e.g.∼5 atm), it also temporarily expands the AGE, beyond the expansion arising from the use of Oxygen-rich Nitrox. For less aggressive recompression therapy wherein nitrogen narcosis is not a significant concern, Oxygen-rich Nitrox is to be preferred, both because it does not temporarily expand the AGE as much as Heliox, and because it is much cheaper and more conservation-minded.

High flow nasal cannula: Influence of gas type and flow rate on airway pressure and CO2 clearance in adult nasal airway replicas

BACKGROUND

High flow nasal cannula therapy is a form of respiratory support which delivers high flow rates of heated, humidified gas to the nares via specialized cannula. Two primary mechanisms of action attributed to the therapy are the provision of positive airway pressure as well as clearance of CO₂-rich exhaled gas from the upper airways.

METHODS

Physiologically accurate nose-throat airway replicas were connected at the trachea to a lung simulator, where CO₂ was supplied to mimic the CO₂ content in exhaled gas. Cannula delivered either air, oxygen or heliox (80/20%volume helium/oxygen) to the replicas at flow rates ranging from 0 to 60 l/min. Five replicas and three cannulas were compared. Tracheal pressure and CO₂ concentration were continuously measured. The lung simulator provided breaths with tidal volume of 500 ml and frequency of 18 breaths/min. Additional clearance measurements were conducted for tidal volume and breathing frequency of 750 ml and 27 breaths/min, respectively.

FINDINGS

Cannula flow rate was the dominant factor governing CO₂ concentration. Average CO₂ concentration decreased with increasing cannula flow rate, but above 30 L/min this effect was less pronounced. Tracheal positive end-expiratory pressure increased with flow rate and was lower for heliox than for air or oxygen. A predictive correlation was developed and used to predict positive end-expiratory pressure for a given cannula size as a function of supplied flow rate and occlusion of the nares.

INTERPRETATION

Compared with administration of air or oxygen, administration of heliox is expected to result in similar CO₂ clearance from the upper airway, but markedly lower airway pressure.

Heliox for inducible laryngeal obstruction (vocal cord dysfunction): A systematic literature review

OBJECTIVES

To perform a systematic literature review on the use of Heliox with patients with inducible laryngeal obstruction/vocal cord dysfunction to: i) identify current evidence base; and ii) establish the methodological quality of published research.

METHODS

Articles published up to March 2018 were searched for key words and terms using Cochrane Library, MEDLINE, PubMed, CINAHL, EMBASE and Dynamed. Studies were included if they presented original research into the use of Heliox for vocal cord dysfunction.

RESULTS

Only three studies met the inclusion criteria for review. All reported favorable results for the use of Heliox as an adjunctive therapy for vocal cord dysfunction but none had sufficient methodological quality to support their conclusions.

CONCLUSION

Despite review articles recommending the use of Heliox in vocal cord dysfunction, there is a lack of good quality research to support this conclusion. There is a need for further research to investigate the effectiveness of Heliox as an adjunctive therapy for vocal cord dysfunction.

LEVEL OF EVIDENCE

4.

[Does heliox administered by low-flow nasal cannula improve respiratory distress in infants with respiratory syncytial virus acute bronchiolitis? A randomized controlled trial]

OBJECTIVES

The aim of our study is to evaluate whether the use of heliox (79:21) delivered through a low flow nasal cannula would improve respiratory distress in infants with acute bronchiolitis caused by respiratory syncytial virus.

METHODS

We have conducted a prospective randomized controlled study. All patients fulfilled inclusion criteria were randomized to either heliox (79:21) or air via NC at 2 L/min for a continuous 24hours. Measurements were taken at baseline, after 2hours and at the end of the 24hours.

RESULTS

We have included 104 patients into our study. The MCA-S did not show any significant difference between the two groups after 2hours 4.3 vs. 4.1 (P =.78), or at 24hours after 4.2 vs. 4.3 (P =.89). No difference was found in the proportion of participants progressed to MV, n-CPAP or oxygen via nasal cannula (RR 1.0, 0.86 and 0.89) (P= 1.0, .77 and .73). There was no notable reduction in length of treatment in Heliox group 2.42 days vs. 2.79 days in air group P =.65. The in oxygen saturation, PaO₂, and PaCO₂ did not to have any statistical difference between the two studied groups after 2hours and 24hours of treatment.

CONCLUSION

Our data showed absence of any beneficial effect of heliox in a concentration (79:21) delivered through low flow nasal cannula in terms of respiratory distress improvement in infants with RSV acute bronchiolitis.

Heliox delivered by high flow nasal cannula improves oxygenation in infants with respiratory syncytial virus acute bronchiolitis

OBJECTIVE

The objective of this study is to evaluate the hypothesis that use of heliox would result in improvement of gas exchange when used with high flow nasal cannula in infants with RSV acute bronchiolitis.

METHODS

All patients that met the inclusion criteria were randomized to either heliox (70:30) or air-oxygen mixture 30% via high flow nasal cannula at 8L/min for a continuous 24h. Measurements were taken at baseline, after 2h, and at the end of the 24h.

RESULTS

This prospective study included 48 patients. After 2h of treatment with heliox, the oxygen saturation and PaO₂ significantly improved when compared with the air-oxygen group, 98.3% vs. 92.9%, 62.0mmHg vs. 43.6mmHg (p=0.04 and 0.01), respectively. Furthermore, PaO₂/FiO₂ ratio was significantly higher in the heliox group when compared with the air-oxygen group, 206.7 vs. 145.3. Nevertheless, CO₂ showed better elimination when heliox was used, without significance. MWCA score dropped significantly in the heliox group, 2.2 points vs. 4.0 points in air-oxygen (p=0.04), 2h after starting the therapy.

CONCLUSION

Transient improvement of oxygenation in infants with RSV acute bronchiolitis during the initial phase of the therapy is associated with heliox when provided with HFNC, may provide a precious time for other therapeutic agents to work or for the disease to resolve naturally, avoiding other aggressive interventions.

Acute management of croup in the emergency department

Croup is one of the most common causes of upper airway obstruction in young children. It is characterized by sudden onset of barky cough, hoarse voice, inspiratory stridor and respiratory distress caused by upper airway inflammation secondary to a viral infection. Published guidelines for the diagnosis and treatment of croup advise using steroids as the mainstay treatment for all children who present to emergency department (ED) with croup symptoms. Dexamethasone, given orally as a single dose at 0.6 mg/kg, is highly efficacious in treating croup symptoms. Despite the evidence supporting the use of steroids as the cornerstone of croup treatment, there is significant practice variation among physicians treating croup in the ED. This practice point discusses evidence-based management of typical croup in the ED.

Total and regional deposition of inhaled aerosols in supine healthy subjects and subjects with mild-to-moderate COPD

Despite substantial development of sophisticated subject-specific computational models of aerosol transport and deposition in human lungs, experimental validation of predictions from these new models is sparse. We collected aerosol retention and exhalation profiles in seven healthy volunteers and six subjects with mild-to-moderate COPD (FEV1 = 50-80%predicted) in the supine posture. Total deposition was measured during continuous breathing of 1 and 2.9 μm-diameter particles (tidal volume of 1 L, flow rate of 0.3 L/s and 0.75 L/s). Bolus inhalations of 1 μm particles were performed to penetration volumes of 200, 500 and 800 mL (flow rate of 0.5 L/s). Aerosol bolus dispersion (H), deposition, and mode shift (MS) were calculated from these data. There was no significant difference in total deposition between healthy subjects and those with COPD. Total deposition increased with increasing particle size and also with increasing flow rate. Similarly, there was no significant difference in aerosol bolus deposition between subject groups. Yet, the rate of increase in dispersion and of decrease in MS with increasing penetration volume was higher in subjects with COPD than in healthy volunteers (H: 0.798 ± 0.205 vs. 0.527 ± 0.122 mL/mL, p=0.01; MS: -0.271±0.129 vs. -0.145 ± 0.076 mL/mL, p=0.05) indicating larger ventilation inhomogeneities (based on H) and increased flow sequencing (based on MS) in the COPD than in the healthy group. In conclusion, in the supine posture, deposition appears to lack sensitivity for assessing the effect of lung morphology and/or ventilation distribution alteration induced by mild-to-moderate lung disease on the fate of inhaled aerosols. However, other parameters such as aerosol bolus dispersion and mode shift may be more sensitive parameters for evaluating models of lungs with moderate disease.

Strategies to enhance the benefits of exercise training in the respiratory patient

Despite the well-established benefits of exercise training in people with chronic respiratory disease, there are a group of people in whom it confers minimal gains. Furthermore, there is increasing recognition of the prevalence of comorbid conditions among people with chronic obstructive pulmonary disease and other respiratory diseases, such as musculoskeletal disorders, which make participation in traditional exercise training programs challenging. This article focuses on several adjuncts or strategies that may be implemented by clinicians during exercise training, with the goal of optimizing the proportion of pulmonary rehabilitation participants who achieve significant and meaningful gains on program completion.