Respiratory muscle fatigue from functional upper airway obstruction

A case of functional upper airway obstruction is presented. The case is unusual because even though no identifiable organic cause could be found for dyspnea and stridor, the patient developed respiratory failure from respiratory muscle fatigue.     

Effect of nasal airway positive pressure on upper airway size and configuration

The effect of nasal airway positive pressure (NAPP) on upper airway size and configuration during wakefulness was studied by computerized tomography in 12 obese subjects with obstructive sleep apnea (OSA), seven weight- and age-matched subjects without OSA, and 12 normal subjects. NAPP of 10 to 12 cm H2O was associated with a significant increase in airway area throughout the upper airway in all three groups. The change in airway area per cm H2O NAPP increased from nasopharynx to hypopharynx. The change in airway area per cm H2O NAPP was significantly smaller in the OSA than in the normal subjects in the region of the soft palate. Electromyographic recordings of the genioglossus and alae nasi muscles with and without NAPP during wakefulness in five of the OSA and five of the normal subjects showed either a decrease or no change in phasic and tonic activity with NAPP. In a separate series of experiments in an additional five OSA and five normal subjects, NAPP of zero, 5, 10, and 15 cm H2O was associated with a linear increase in airway area at a given airway level. These results indicate that (1) the increase in pharyngeal cross-sectional area with application of NAPP during wakefulness is smaller in OSA than in normal subjects in the region of the soft palate and (2) changes in upper airway muscle activity may accompany changes in upper airway size and configuration.     

Moderate alcohol ingestion increases upper airway resistance in normal subjects

Apnea during sleep has been associated with both increased pharyngeal resistance and nasal obstruction. Alcohol can worsen obstructive sleep apnea, but its influence on pharyngeal resistance and nasal patency has not been evaluated. Accordingly, we determined the effects of alcohol on pharyngeal and nasal resistances in 11 normal awake subjects on 2 separate days. Baseline pharyngeal resistance prior to placebo and alcohol was not significantly different. After placebo, pharyngeal resistance did not change significantly. However, after alcohol, pharyngeal resistance increased from 1.9 +/- 0.5 (SEM) to 3.3 +/- 0.8 cm H2O/L/s at 45 min (p less than 0.05) and returned to near baseline level by 90 min. Baseline nasal resistance varied considerably within subjects on the 2 days, but the mean values for baseline nasal resistance on alcohol and placebo days were not significantly different. Nasal resistance did not change after placebo, but after alcohol, nasal resistance increased from 2.4 +/- 0.9 at baseline to 3.7 +/- 0.8 at 45 min (NS) and to 4.3 +/- 1.2 cm H2O/L/s at 90 min (p less than 0.05). We conclude that a decrease in pharyngeal airway size and an increase in nasal resistance may account for alcohol's ability to worsen obstructive sleep apnea.     

Lack of airway response to nasal irritation in normal and asthmatic subjects

Abstract Twenty two subjects (10 normals, nine asthmatics and three who had suggestive histories for asthma but normal bronchial histamine challenges) underwent nasal challenges with logarithmic incremental doses of histamine or saline on alternate days. Nasal resistance (measured by posterior rhinometry), and forced expiratory volume in one second (FEV₁) were assessed after each dose of nasal histamine or placebo. After each nasal challenge (maximum nasal dose of 250 μg of histamine or doubling of nasal resistance) bronchial responsiveness was measured with a bronchial histamine challenge. Despite significant changes in nasal resistance with nasal histamine (p < 0.01) there was no significant change in the forced expiratory volume in one second, or in bronchial responsiveness. We were unable to demonstrate nasobronchial reflexes initiated by acute irritation of the nasal mucosa with histamine in either normal subjects or in those with mild to moderate asthma.     

Respiratory and upper airway responses to nasal obstruction in awake lambs and ewes

The aims of this study were to compare the ability of awake newborn lambs and adult sheep to breathe orally when the nasal route was blocked and to determine the means by which it was accomplished. Chronic EMG electrodes (diaphragm, genioglossus, geniohyoid, posterior crico-arytenoid, digastric, thyroarytenoid) and fibre-optic catheters were implanted in 10 lambs and 4 ewes. Before each study soft tubes were fixed into the nostrils allowing rapid blockade of the nasal ventilatory pathway. During nasal blockade inspiratory upper airway dilator EMG activity increased. SaO2 fell until mouth opening occurred, then returned to near control values; oral breathing then ceased leading to desaturation again. In lambs and ewes there was significant hypoxia, hypercapnia and acidaemia. In lambs 2-14 days old, PO2 and pH fell to lower levels than in older lambs (15-30 days) or ewes and PCO2 rose more. In lambs PCO2 gradually increased during the period of obstruction. We conclude that maintenance of blood gas homeostasis in newborn lambs is more severely impaired by nasal obstruction than in older lambs or ewes, possibly due to an immaturity of neural mechanisms controlling the creation of an oral airway.     

Upper airway muscle activation is augmented in patients with obstructive sleep apnea compared with that in normal subjects

Although phasic electromyographic (EMG) activity of upper airway muscles in patients with obstructive sleep apnea (OSA) decreases at apnea onset, the presence of phasic activity in normal subjects has not been studied and compared with that in patients. We consequently compared the percentage of total sleep time in which phasic activity of the genioglossal EMG activity was present in 8 adult patients with OSA and 3 control groups without OSA, one consisting of 6 young, normal subjects, one matched for age, and one matched for age and obesity. From wakefulness to sleep, genioglossal EMG phasic activity time increased in patients but not in control subjects. Patients with OSA had more phasic genioglossal group EMG activity during non-REM sleep than did control subjects. At apnea onset, phasic EMG activity decreased in patients but remained greater than zero. In many control subjects, phasic activity was not detected, yet their pharyngeal airway remained patent. We conclude that phasic genioglossal group EMG activity occurs more frequently during sleep in patients with OSA than in control subjects, suggesting that it is a compensatory mechanism that occurs when patency of the pharyngeal airway is precarious.     

Upper airway obstruction during sleep in normal subjects after selective topical oropharyngeal anesthesia

Previous animal studies support the presence of an upper airway reflex mechanism that when blocked by topical anesthesia of the upper airway results in upper airway occlusion. We sought a similar reflex mechanism in humans. Nine normal male volunteers 20 to 28 yr of age underwent 3 successive overnight sleep studies: a control study (C); a study in which selective topical oropharyngeal anesthesia (OPA) was achieved prior to sleep using a 10% lidocaine spray and 0.25% bupivocaine solution; a study in which selective nasal anesthesia (NA) was achieved prior to sleep using a mixture of 2% lidocaine and 0.25% bupivocaine solutions instilled into the nose while the nasal airway was positioned as the most dependent part of the upper airway. Total sleep times were similar during the 3 study nights as were the amounts of slow-wave and rapid-eye-movement (REM) sleep. Obstructive apneas and hypopneas (OAH) differed significantly between the 3 study nights [13(3.8), mean (SEM), during OPA as compared to 3(1.8) during C and 7(2.5) during NA; p less than 0.01 by ANOVA] and were most frequent during REM sleep. Total apneas and hypopneas also differed significantly between the 3 study nights [19(3.9) during OPA as compared to 8(2.1) during C and 14(3.9) during NA; p less than 0.01 by ANOVA]. Movement arousals terminating periods of abnormal respiration also differed significantly [21(6.1) during OPA as compared to 12(3.6) during C and 14(4.6) during NA; p less than 0.05 by ANOVA]. No subject, however, developed clinically significant sleep apnea or significant oxygen desaturation during sleep.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tracheal sounds in upper airway obstruction.

A boy with subglottic narrowing secondary to laryngotracheitis presented with noisy breathing. Acoustic measurements of tracheal sounds at standardized air flows correlated well with the clinical course and with spirometric assessments. This indicates the potential value of respiratory sound characterization in patients with upper airway obstruction.     

The normal and abnormal pediatric upper airway. Recognition and management of obstruction

The pediatric airway is particularly vulnerable to obstruction because of its anatomy, size, and susceptibility to disease and trauma. This article concentrates on the differences between the pediatric and adult airway, congenital and acquired pathology affecting the airway, and the recognition and management of obstruction.     

Volume-pressure properties of the upper airway in normal subjects and patients with obstructive sleep apnoea

The aim of this study was to examine the volume-pressure (V-P) characteristics of isolated upper airways in normal subjects and patients with obstructive sleep apnoea (OSA) and to ascertain whether an increase in upper airway muscle activity affects these characteristics. We studied upper airway pressure changes during volume changes by inflation and deflation of air volumes of 5, 10, 15 and 20 mL without and with submental electrical stimulation, during voluntary closing of the glottis, in seven normal subjects and 13 OSA patients. Volume-pressure properties of the upper airway were assessed by elastance (Euaw) which was obtained from the slope of the regression line of the V-P relationships. Euaw in OSA patients was 0.52 +/- 0.08 cmH2O/mL, which was greater than in normal subjects (0.26 +/- 0.06 cmH2O/mL). Submental stimulation increased Euaw in both OSA patients and normal subjects (0.70 +/- 0.11 cmH2O/mL and 0.41 +/- 0.11 cmH2O/mL, respectively). These results suggest that upper airways of OSA patients during wakefulness are less collapsible than those of normal subjects, and that, in both groups, submental stimulation may stiffen the upper airway.     

Infectious mononucleosis presenting as upper airway obstruction

Upper airway obstruction though a common complication of infectious mononucleosis is rarely considered in differential diagnosis of stridor. We report a three-year-old child who had upper airway obstruction due to infectious mononucleosis, managed conservatively with oxygen, intravenous fluids and steroids.     

Effect of nasal or oral breathing route on upper airway resistance during sleep.

Healthy subjects with normal nasal resistance breathe almost exclusively through the nose during sleep. This study tested the hypothesis that a mechanical advantage might explain this preponderance of nasal over oral breathing during sleep. A randomised, single-blind, crossover design was used to compare upper airway resistance during sleep in the nasal and oral breathing conditions in 12 (seven male) healthy subjects with normal nasal resistance, aged 30+/-4 (mean+/-SEM) yrs, and with a body mass index of 23+/-1 kg x m2. During wakefulness, upper airway resistance was similar between the oral and nasal breathing routes. However, during sleep (supine, stage two) upper airway resistance was much higher while breathing orally (median 12.4 cmH2O x L(-1) x s(-1), range 4.5-40.2) than nasally (5.2 cmH2O x L(-1) x s(-1), 1.7-10.8). In addition, obstructive (but not central) apnoeas and hypopnoeas were profoundly more frequent when breathing orally (apnoea-hypopnoea index 43+/-6) than nasally (1.5+/-0.5). Upper airway resistance during sleep and the propensity to obstructive sleep apnoea are significantly lower while breathing nasally rather than orally. This mechanical advantage may explain the preponderance of nasal breathing during sleep in normal subjects.     

Isoflow-volume curves in the diagnosis of upper airway obstruction

We evaluated the ability of air and helium-O2 maximal expiratory flow-volume curves to distinguish upper airway obstruction from the diffuse, peripheral airway obstruction of chronic obstructive pulmonary disease. The increase in expiratory flows at peak, 75, 50, and 25 per cent of the vital capacity during helium-O2 breathing compared to air breathing was determined in 5 normal subjects and 3 patients with chronic obstructive pulmonary disease while breathing through fixed resistances, and in 6 patients with documented tracheal obstruction. In the normal subjects, the helium response at all 4 points remained normal and was unchanged from baseline until the simulated obstruction was severe (6-mm orifice), at which point all ofthe helium responses increased by 50 per cent. The patients with chronic obstructive pulmonary disease maintained their low baseline helium responses until the obstruction was severe (6-mm orifice), when only the expiratory flows at peak, 75, and 50 per cent of the vital capacity increased by at least 50 per cent. Five of the 6 patients with upper airway obstruction had helium responses very similar to those of the normal subjects with similar degrees of simulated obstruction, but the one patient with concomitant airway obstruction extending well below the carina had very small helium responses at each point. We conclude that upper airway obstruction can usually be identified by high helium responses and that upper airway obstruction, if severe, can be identified even in the presence of more peripheral airway obstruction by a normal helium response at high lung volumes.     

Pulmonary edema following relief of upper airway obstruction

In six pediatric patients, pulmonary edema (PE) appeared on chest x-ray film following intubation for upper airway obstruction (UAO). In spite of the x-ray appearance of PE, there was generally no concomitant physiologic or clinical decline. Only one of the patients required positive airway pressure following intubation. We conclude that PE on chest x-ray film following intubation for UAO is not uncommon, and may not be a harbinger of clinical and/or physiologic deterioration.     

Lung sound analysis of upper airway obstruction]

The frequency spectrum of stridor was studied by the computer program in the patients with upper airway obstruction. The results showed that the peak frequency of respiratory sound increased significantly, the frequency spectrum got wider and removed to the high frequency area above 200Hz, the E ratio was smaller than 1. These changes were more apparent during inspiration than those during expiration. It is concluded that the stridorous sound could be determined exactly and quantitatively, and differentiated from wheezing by the spectral analysis.