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The Laryngoscope Jul 2018Subglottic stenosis (SGS) is one of the most common airway disorders in pediatric patients. Currently, treatment decisions rely primarily on the Cotton-Myer scale, which...
OBJECTIVES
Subglottic stenosis (SGS) is one of the most common airway disorders in pediatric patients. Currently, treatment decisions rely primarily on the Cotton-Myer scale, which classifies SGS severity based on percentage reduction in airspace cross-sectional area (CSA). However, the precise relationship between upper airway resistance and subglottic CSA is unknown. We hypothesize that airway resistance can be described by the Bernoulli Obstruction Theory, which predicts that airway resistance is inversely proportional to airspace CSA ( R∝A-1) in cases of severe constriction.
METHODS
Computed tomography (CT) scans of six healthy subjects and five SGS patients were used to create three-dimensional models of the respiratory tract from nostrils to carina. Cylindrical segments of varying lengths and varying diameters were digitally inserted in the subglottis of the healthy subjects to create simulated SGS models. Computational fluid dynamics simulations were run, and airway resistance was computed in the simulated SGS models and actual SGS models.
RESULTS
Constriction diameter had a greater impact in airway resistance than constriction length. In agreement with the Bernoulli Obstruction Theory, airway resistance in the simulated SGS models was well represented by the power law R=aAb, where a is a constant and the exponent b ranged from -0.85 to -1.07. The percentage reduction in airflow (QOBSTRUCTIONQHEALTHY) at a constant pressure drop was found to be directly proportional to the percentage reduction in CSA (AOBSTRUCTIONAHEALTHY) in the limit of severe constrictions, namely QOBSTRUCTIONQHEALTHY=kAOBSTRUCTIONAHEALTHY, where k=2.25 ± 0.15. Airway resistances in the simulated SGS models were similar to resistances in models based on CT scans of actual SGS patients, suggesting that our simulated SGS models were representative of airway resistance in actual SGS patients.
CONCLUSION
Our computer simulations suggest that the degree of airflow limitation in SGS patients may be estimated based on anatomic measurements alone. Future studies are recommended to test these predictions in larger cohorts.
LEVEL OF EVIDENCE
4. Laryngoscope, 128:1551-1557, 2018.
Topics: Adult; Air Pressure; Airway Resistance; Case-Control Studies; Child; Child, Preschool; Glottis; Humans; Hydrodynamics; Infant; Laryngostenosis
PubMed: 29171660
DOI: 10.1002/lary.27006 -
Journal of Clinical Sleep Medicine :... Nov 2020To evaluate the long-term effects of a mandibular advancement device (MAD) on stress symptoms and cognitive function in patients with upper airway resistance syndrome... (Randomized Controlled Trial)
Randomized Controlled Trial
STUDY OBJECTIVES
To evaluate the long-term effects of a mandibular advancement device (MAD) on stress symptoms and cognitive function in patients with upper airway resistance syndrome (UARS) compared with placebo.
METHODS
This study was a randomized placebo-controlled clinical trial. Thirty UARS patients were randomized into 2 groups: placebo and MAD groups. UARS criteria were the presence of sleepiness (Epworth Sleepiness Scale ≥ 10) and/or fatigue (Modified Fatigue Impact Scale ≥ 38) associated with an apnea-hypopnea index ≤ 5 events/h and a respiratory disturbance index > 5 events/h of sleep, and/or flow limitation in more than 30% of total sleep time. All patients completed the Rey Auditory-Verbal Learning Test, the Logical Memory test, the Stroop Color Test, the Trail Making Test, the Digit Symbol Substitution Test, and Inventory of Stress Symptoms. Cognition protocol was defined based on the most used neuropsychological tests in the literature. Evaluations were performed before and after 1.5 years of treatment.
RESULTS
Mean adherence to placebo and to MAD was 6.6 ± 2.6 and 6.1 ± 2.4 h/night, respectively. Side effects reported by MAD group were minor and short-term. There was no statistically significant difference in Rey Auditory-Verbal Learning Test, Logical Memory test, Stroop Color Test, Trail Making Test, and Digit Symbol Substitution Test before and after 1.5 years of treatment in both groups. Inventory of Stress Symptoms score decreased at the alert phase and the resistance phase after 1.5 years of MAD treatment compared to the placebo.
CONCLUSIONS
Mandibular advancement devices were effective in decreasing stress symptoms in UARS patients after 1.5 years of treatment.
CLINICAL TRIAL REGISTRATION
Registry: ClinicalTrials.gov; Name: Efficacy of Oral Appliance for Upper Airway Resistance Syndrome; URL: https://clinicaltrials.gov/ct2/show/record/NCT02636621; Identifier: NTC02636621.
Topics: Airway Resistance; Continuous Positive Airway Pressure; Humans; Mandibular Advancement; Polysomnography; Sleep Apnea, Obstructive
PubMed: 32686643
DOI: 10.5664/jcsm.8698 -
Journal of Applied Physiology... Mar 2001The prevalence of irregular breathing during sleep is age and gender dependent, but the reason for this is unknown. This study tested the hypothesis that older men have... (Comparative Study)
Comparative Study
The prevalence of irregular breathing during sleep is age and gender dependent, but the reason for this is unknown. This study tested the hypothesis that older men have a greater sleep-related increase in respiratory resistance. In 48 healthy subjects, 12 in each of four groups of younger and older men and women, airway resistance was measured during wakefulness and sleep using a mask, pneumotachograph, and catheter-mounted pressure sensors. Total respiratory resistance and total "low-flow," and "high-flow" oropharyngeal resistance were analyzed from 170,000 breaths, high flow being at rates above 50% maximal inspiratory flow. High-flow oropharyngeal and total respiratory resistance increased during non-rapid eye movement (NREM) sleep in all groups but not low-flow resistance. Total respiratory resistance increased from 12 +/- 1.2 cmH(2)O. l(-1). s(-1) awake to 16.2 +/- 2.4 in NREM sleep in young men, from 22.8 +/- 3.6 to 33.6 +/- 5.4 in young women, from 18 +/- 3 to 34.8 +/- 4.8 in older men, and from 26.6. +/- 4.2 to 34.2 +/- 6 in older women. The percentage of change in total respiratory resistance from awake to NREM sleep was not different between age groups or genders. We conclude that there are no major age or gender differences in the changes in airway resistance with sleep in normal subjects.
Topics: Adolescent; Adult; Age Factors; Aged; Airway Resistance; Body Mass Index; Female; Humans; Male; Middle Aged; Oxygen; Respiratory Mechanics; Sex Characteristics; Sleep Apnea Syndromes; Sleep Stages; Sleep, REM; Wakefulness
PubMed: 11181609
DOI: 10.1152/jappl.2001.90.3.981 -
American Journal of Physiology. Lung... Oct 2021Deep inspiration (DI)-induced bronchodilation is the first line of defense against bronchoconstriction in healthy subjects. A hallmark of asthma is the lack of this...
Deep inspiration (DI)-induced bronchodilation is the first line of defense against bronchoconstriction in healthy subjects. A hallmark of asthma is the lack of this beneficial effect of DI. The mechanism underlying the bronchodilatory effect of DI is not clear. Understanding the mechanism will help us unravel the mystery of asthma pathophysiology. It has been postulated that straining airway smooth muscle (ASM) during a DI could lead to bronchodilation and bronchoprotection. The hypothesis is currently under debate, and a central question is whether ASM is sufficiently stretched during a DI for its contractility to be compromised. Besides bronchoconstriction, another contributor to lung resistance is airway heterogeneity. The present study examines changes in airway diameter and heterogeneity at different lung volumes. Freshly explanted sheep lungs were used in plethysmographic measurements of lung resistance and elastance at different lung volumes, whereas the airway dimensions were measured by computed tomography (CT). The change in airway diameter informed by CT measurements was applied to isolated airway ring preparations to determine the strain-induced loss of ASM contractility. We found that changing the transpulmonary pressure from 5 to 30 cmHO led to a 51% increase in lung volume, accompanied by a 46% increase in the airway diameter with no change in airway heterogeneity. When comparable airway strains measured in the whole lung were applied to isolated airway rings in either relaxed or contracted state, a significant loss of ASM contractility was observed, suggesting that DI-induced bronchodilation and bronchoprotection can result from strain-induced loss of ASM contractility.
Topics: Airway Resistance; Animals; Asthma; Bronchi; Bronchoconstriction; Inhalation; Lung; Lung Volume Measurements; Muscle, Smooth; Respiratory Function Tests; Sheep; Tomography, X-Ray Computed
PubMed: 34287071
DOI: 10.1152/ajplung.00208.2021 -
British Journal of Anaesthesia Sep 2000We compared the airflow resistance of 7.5 and 8.5 mm internal diameter (i.d.) endotracheal tubes (ETTs) with that of a size 4 laryngeal mask airway (LMA). We thought... (Comparative Study)
Comparative Study
We compared the airflow resistance of 7.5 and 8.5 mm internal diameter (i.d.) endotracheal tubes (ETTs) with that of a size 4 laryngeal mask airway (LMA). We thought that any difference in the resistance of the devices alone might be offset by the resistance of the larynx. Sixteen adult ASA physical status I and II patients (14 males, two females) undergoing general anaesthesia were anaesthetized and paralysed with intravenous propofol, ketamine and vecuronium. After insertion of the LMA, controlled ventilation (tidal volume 10 ml kg-1, frequency 12 min-1) was established with three different settings for inspiratory flow (5.5, 7.5 and 12.5 ml kg-1 s-1). Ventilation with the same settings was used after orotracheal intubation with an ETT of i.d. 7.5 mm (females) or 8.5 mm (males). The position of the LMA mask and the tip of the ETT were checked through a fibrescope. The resistance of the devices and, in case of the LMA, of the larynx, was derived by relating proximal and distal pressures (measured via catheters) to inspiratory flow. Four patients--young, tall men--had to be excluded from further study because of a leak around the LMA. In the remaining 10 males and two females, resistance of the LMA (mean (SD) at high flow, 1.19 (0.22) mbar.s litre-1 in males) was less than that of the 8.5 mm i.d. ETT (3.34 (0.52) mbar.s litre-1) (P < 0.01). However, the structures between the LMA and the trachea added another, highly variable, resistance component, so that the mean resistance of the LMA and larynx together was similar (in males: 3.20 (2.71) mbar.s litre-1) to that of the 8.5 mm ETT. In eight patients the epiglottis projected on to one-tenth to two-thirds of the distal opening of the LMA; this was in no case associated with greater resistance. Greater resistance occurred in two patients with a central LMA position and unobstructed view of the glottis and in one patient with marked lateral deviation. In conclusion, there is no clinically relevant difference between the resistance of a size 4 LMA plus that of the larynx and that of an 8.5 mm i.d. ETT.
Topics: Adult; Aged; Airway Resistance; Anesthesia, General; Equipment Design; Female; Humans; Intubation, Intratracheal; Laryngeal Masks; Male; Middle Aged; Respiration, Artificial; Statistics, Nonparametric
PubMed: 11103183
DOI: 10.1093/bja/85.3.410 -
Journal of Applied Physiology... Oct 1997We present a dog lung model to predict the relation between inhomogeneous changes in airway morphometry and lung resistance (RL) and elastance (EL) for frequencies...
We present a dog lung model to predict the relation between inhomogeneous changes in airway morphometry and lung resistance (RL) and elastance (EL) for frequencies surrounding typical breathing rates. The RL and EL were sensitive in distinct ways to two forms of peripheral constriction. First, when there is a large and homogeneous constriction, the RL increases uniformly over the frequency range. The EL is rather unaffected below 1 Hz but then increases with frequencies up to 5 Hz. This increase is caused by central airway wall shunting. Second, the RL and EL are extremely sensitive to mild inhomogeneous constriction in which a few highly constricted or nearly closed airways occur randomly throughout the periphery. This results in extreme increases in the levels and frequency dependence of RL and EL but predominantly at typical breathing rates (<1 Hz). Conversely, the RL and EL are insensitive to highly inhomogeneous airway constriction that does not produce any nearly closed airways. Similarly, alterations in the RL and EL due to central airway wall shunting are not likely until the preponderance of the periphery constricts substantially. The RL and EL spectra are far more sensitive to these two forms of peripheral constriction than to constriction conditions known to occur in the central airways. On the basis of these simulations, we derived a set of qualitative criteria to infer airway constriction conditions from RL and EL spectra.
Topics: Airway Resistance; Animals; Bronchi; Dogs; Elasticity; Functional Residual Capacity; Lung; Models, Anatomic; Respiratory Physiological Phenomena; Respiratory System; Total Lung Capacity; Trachea
PubMed: 9338428
DOI: 10.1152/jappl.1997.83.4.1192 -
American Journal of Physiology. Lung... Feb 2017Taking a big breath is known to reverse bronchoconstriction induced by bronchochallenge in healthy subjects; this bronchodilatory effect of deep inspiration (DI) is...
Taking a big breath is known to reverse bronchoconstriction induced by bronchochallenge in healthy subjects; this bronchodilatory effect of deep inspiration (DI) is diminished in asthmatics. The mechanism underlying the DI effect is not clear. Observations from experiments using isolated airway smooth muscle (ASM) preparations and airway segments suggest that straining of ASM due to DI could lead to bronchodilation, possibly due to strain-induced reduction in ASM contractility. However, factors external to the lung cannot be excluded as potential causes for the DI effect. Neural reflex initiated by stretch receptors in the lung are known to inhibit the broncho-motor tone and enhance vasodilatation; the former directly reduces airway resistance, and the latter facilitates removal of contractile agonists through the bronchial circulation. If the DI effect is solely mediated by factors extrinsic to the lung, the DI effect would be absent in isolated, nonperfused lungs. Here we examined the DI effect in freshly isolated, nonperfused sheep lungs. We found that imposition of DI on isolated lungs resulted in significant bronchodilation, that this DI effect was present only after the lungs were challenged with a contractile agonist (acetylcholine or histamine), and that the effect was independent of the difference in lung volume observed pre- and post-DI. We conclude that a significant portion of the bronchodilatory DI effect stems from factors internal to the lung related to the activation of ASM.
Topics: Airway Resistance; Animals; Bronchi; Bronchodilator Agents; Calibration; Inhalation; Organ Size; Plethysmography; Pressure; Rheology; Sheep
PubMed: 27913423
DOI: 10.1152/ajplung.00321.2016 -
Journal of Applied Physiology... Mar 2000Reported values of lung resistance (RL) and elastance (EL) in spontaneously breathing preterm neonates vary widely. We hypothesized that this variability in lung...
Reported values of lung resistance (RL) and elastance (EL) in spontaneously breathing preterm neonates vary widely. We hypothesized that this variability in lung properties can be largely explained by both inter- and intrasubject variability in breathing pattern and demographics. Thirty-three neonates receiving nasal continuous positive airway pressure [weight 606-1,792 g, gestational age (GA) of 25-33 wk, 2-49 days old] were studied. Transpulmonary pressure was measured by esophageal manometry and airway flow by face mask pneumotachography. Breath-to-breath changes in RL and EL in each infant were estimated by Fourier analysis of impedance (Z) and by multiple linear regression (MLR). RL(MLR) (RL(MLR) = 0.85 x RL(Z) -0.43; r(2) = 0.95) and EL(MLR) (EL(MLR) = 0.97 x EL(Z) + 8.4; r(2) = 0.98) were highly correlated to RL(Z) and EL(Z), respectively. Both RL (mean +/- SD; RL(Z) = 70 +/- 38, RL(MLR) = 59 +/- 36 cm H(2)O x s x l(-1)) and EL (EL(Z) = 434 +/- 212, EL(MLR) = 436 +/- 210 cm H(2)O/l) exhibited wide intra- and intersubject variability. Regardless of computation method, RL was found to decrease as a function of weight, age, respiratory rate (RR), and tidal volume (VT) whereas it increased as a function of RR. VT and inspiratory-to-expiratory time ratio (TI/TE). EL decreased with increasing weight, age, VT and female gender and increased as RR and TI/TE increased. We conclude that accounting for the effects of breathing pattern variability and demographic parameters on estimates of RL and EL is essential if they are to be of clinical value. Multivariate statistical models of RL and EL may facilitate the interpretation of lung mechanics measurements in spontaneously breathing infants.
Topics: Airway Resistance; Elasticity; Female; Humans; Infant, Newborn; Infant, Premature; Lung Compliance; Male; Models, Biological; Multivariate Analysis; Respiratory Mechanics
PubMed: 10710396
DOI: 10.1152/jappl.2000.88.3.997 -
Experimental Physiology Oct 2020What is the central question of this study? What is the impact of airway cholinergic history on the properties of airway mucus secretion in a cystic fibrosis-like...
NEW FINDINGS
What is the central question of this study? What is the impact of airway cholinergic history on the properties of airway mucus secretion in a cystic fibrosis-like environment? What is the main finding and its importance? Prior cholinergic challenge slightly modifies the characteristics of mucus secretion in response to a second cholinergic challenge in a diminished bicarbonate and chloride transport environment. Such modifications might lead to retention of mucus on the airway surface, thereby potentiating exacerbations of airway disease.
ABSTRACT
Viral infections precipitate exacerbations in many airway diseases, including asthma and cystic fibrosis. Although viral infections increase cholinergic transmission, few studies have examined how cholinergic history modifies subsequent cholinergic responses in the airway. In our previous work, we found that airway resistance in response to a second cholinergic challenge was increased in young pigs with a history of airway cholinergic stimulation. Given that mucus secretion is regulated by the cholinergic nervous system and that abnormal airway mucus contributes to exacerbations of airway disease, we hypothesized that prior cholinergic challenge would also modify subsequent mucus responses to a secondary cholinergic challenge. Using our established cholinergic challenge-rechallenge model in pigs, we atomized the cholinergic agonist bethanechol or saline control to pig airways. Forty-eight hours later, we removed tracheas and measured mucus secretion properties in response to a second cholinergic stimulation. The second cholinergic stimulation was conducted in conditions of diminished chloride and bicarbonate transport to mimic a cystic fibrosis-like environment. In pigs previously challenged with bethanechol, a second cholinergic stimulation produced a mild increase in sheet-like mucus films; these films were scarcely observed in animals originally challenged with saline control. The subtle increase in mucus films was not associated with changes in mucociliary transport. These data suggest that prior cholinergic history might modify mucus secretion characteristics with subsequent stimulation in certain environmental conditions or disease states. Such modifications and/or more repetitive stimulation might lead to retention of mucus on the airway surface, thereby potentiating exacerbations of airway disease.
Topics: Airway Resistance; Animals; Bethanechol; Bicarbonates; Biological Transport; Chlorides; Cholinergic Agents; Cystic Fibrosis; Female; Male; Mucociliary Clearance; Respiratory Mucosa; Respiratory Tract Diseases; Swine; Trachea
PubMed: 32735372
DOI: 10.1113/EP088900 -
Ultrasonics Mar 2017With every breath, the airways within the lungs are strained. This periodic stretching is thought to play an important role in determining airway caliber in health and...
With every breath, the airways within the lungs are strained. This periodic stretching is thought to play an important role in determining airway caliber in health and disease. Particularly, deep breaths can mitigate excessive airway narrowing in healthy subjects, but this beneficial effect is absent in asthmatics, perhaps due to an inability to stretch the airway smooth muscle (ASM) embedded within an airway wall. The heterogeneous composition throughout an airway wall likely modulates the strain felt by the ASM but the magnitude of ASM strain is difficult to measure directly. In this study, we optimized a finite element image registration method to measure the spatial distribution of displacements and strains throughout an airway wall during pressure inflation within the physiological breathing range before and after induced narrowing with acetylcholine (ACh). The method was shown to be repeatable, and displacements estimated from different image sequences of the same deformation agreed to within 5.3μm (0.77%). We found the magnitude and spatial distribution of displacements were radially and longitudinally heterogeneous. The region in the middle layer of the airway experienced the largest radial strain due to a transmural pressure (Ptm) increase simulating tidal breathing and a deep inspiration (DI), while the region containing the ASM (i.e., closest to the lumen) strained least. During induced narrowing with ACh, we observed temporal longitudinal heterogeneity of the airway wall. After constriction, the displacements and strain are much smaller than the relaxed airway and the pattern of strains changed, suggesting the airway stiffened heterogeneously.
Topics: Airway Resistance; Animals; Bronchoconstriction; Cattle; Elasticity Imaging Techniques; Finite Element Analysis; In Vitro Techniques; Muscle, Smooth; Pressure; Respiration
PubMed: 27988462
DOI: 10.1016/j.ultras.2016.11.023