Effect of upper airway pressure pulses on breathing pattern

Importance of the time of application of upper airway pressure pulses on breathing pattern was investigated in 19 anesthetized, spontaneously breathing rabbits. The upper airway was functionally isolated into a closed system. A servo-respirator, triggered by the inspiratory activity of the diaphragm, was used to apply pressure pulses to the isolated upper airway. Negative pressure pulses of -5, -10, and -15 cm H2O when applied in early inspiration (within the first half) produced a reversible inhibition of inspiration in most trails (86.2%). This resulted in a prolongation of inspiratory duration (TI) and a decrease in mean inspiratory drive (P.Dia/TI) whereas peak diaphragm (P.Dia) activity and expiratory duration (TE) remained largely unaffected. In the remaining 13.8% of trials, an irreversible inhibition with short TI and reduced P.Dia activity was observed. In contrast, with late application of negative pressure pulses the only significant change was a shortening of TI. When positive pressure pulses were applied during expiration, no significant change in TE occurred with either early or late application. A significant prolongation of subsequent TI was seen irrespective of the time of positive pressure application. These results indicate that time of application during the respiratory cycle is an important variable in determining the response to upper airway pressure pulses.     

Total respiratory resistance and reactance in patients with upper airway obstruction

In 18 patients with upper airway obstruction, we measured dynamic lung volumes, maximal flows, airway resistance (Raw), and total respiratory resistance (Rrs) and reactance (Xrs) at various frequencies by means of a forced oscillation method. Patients were classified according to the site and the type of the obstruction. The values of Raw, Rrs and Xrs were tightly correlated and reflected the overall importance of the obstruction. In comparison with patients with chronic obstructive pulmonary disease the values of Rrs tend to be higher and to be influenced more by support of the cheeks during the measurement. These differences are not diagnostic, however.     

Hypersomnolent and nonhypersomnolent patients with upper airway obstruction during sleep.

When the syndrome consisting of sleep-induced apnea and hypersomnolence is due to upper airway obstruction, the hypersomnolence is believed to be the direct result of deprivation of sleep related to such obstructions. The purpose of this report is to describe a group of four asymptomatic subjects with upper airway obstruction during sleep. These subjects were matched with a group of patients with the syndrome of sleep-induced apnea and hypersomnolence. There were no significant differences between symptomatic and asymptomatic groups in terms of the absolute number of upper airway obstructions (252 vs 231), their mean duration (20.8 vs 25.9 seconds), the mean arterial carbon dioxide tension during sleep (39 vs 39 mm Hg), or the electroencephalographic patterns during sleep. The only variables that emerged as significantly different between the two groups were the weights (128 vs 90 kg; P less than 0.05), the low arterial oxygen pressure (PaO2) on waking (54 vs 80 mm Hg; P less than 0.002), and the lower PaO2 during sleep (47 vs 70 mm Hg; P less than 0.01) in the symptomatic patients. From these data, we conclude that the hypersomnolence in patients with sleep-induced apnea due to upper airway obstruction cannot be explained by deprivation of sleep, and other factors need to be carefully examined in future studies.     

New acoustic method for detecting upper airway obstruction in patients with sleep apnoea

Background and objective: OSA is a common disorder resulting in health and economic burdens. Currently identifying OSA in patients involves expensive techniques that require overnight studies in a laboratory setting with qualified staff. This paper tests a new acoustic device (AirwayClear (AC)) for assessing upper airway patency in human subjects with OSA. We hypothesize that obstructive apnoeas would be detected equally well with AC and polysomnography (PSG). Methods: Twenty‐three patients with severe OSA underwent an overnight CPAP titration study. We introduced pseudorandom noise (600–1200 Hz) using AC to the patient's nasal mask during 1 h of subtherapeutic CPAP. AC determined a measure of airway patency based on the level of pseudorandom noise reaching a sternal notch sensor. The ability of AC to detect obstructive respiratory events was compared with standard PSG. Results: Three hundred and twenty‐two obstructive events (obstructive and mixed apnoeas) were identified by PSG. AC scored 80% as complete obstructions and 16% as partial obstructions. Conversely, AC detected 281 complete obstructions. PSG recognized 84% as apnoeas and scored 11% as hypopnoeas. Of the 204 hypopnoeas identified with PSG, AC indicated the airway was partially or completely obstructed in 69% of patients. A Bland–Altman analysis for the apnoeas from the two measures showed a mean difference of 2.3 events/h and 95% confidence intervals of ±15.5 events/h. Conclusions: We conclude that AC is able to track airway patency and to identify airway closure in patients with OSA.     

Static and dynamic upper airway obstruction in sleep apnea: role of the breathing gas properties

Increased upper airway collapsibility in the sleep apnea/hypopnea syndrome (SAHS) is usually interpreted by a collapsible resistor model characterized by a critical pressure (Pcrit) and an upstream resistance (Rup). To investigate the role played by the upstream segment of the upper airway, we tested the hypothesis that breathing different gases would modify Rup but not Pcrit. The study was performed on 10 patients with severe SAHS (apnea-hypopnea index: 59 +/- 14 events/hour) when breathing air and helium-oxygen (He-O2) during non-REM sleep. The continuous positive airway pressure that normalized flow (CPAPopt) was measured. Rup and Pcrit were determined from the linear relationship between maximal inspiratory flow VImax and nasal pressure (PN):VImax = (PN - Pcrit)/Rup. Changing the breathing gas selectively modified the severity of dynamic (CPAPopt, Rup) and static (Pcrit) obstructions. CPAPopt was significantly (p = 0.0013) lower when breathing He-O2 (8.44 +/- 1.66 cm H2O; mean +/- SD) than air (10.18 +/- 2.34 cm H2O). Rup was markedly lower (p = 0.0001) when breathing He-O2 (9.21 +/- 3.93 cm H2O x s/L) than air (15.92 +/- 6.27 cm H2O x s/L). Pcrit was similar (p = 0.039) when breathing He-O2 (4.89 +/- 2.37 cm H2O) and air (4.19 +/- 2.93 cm H2O). The data demonstrate the role played by the upstream segment of the upper airway and suggest that different mechanisms determine static (Pcrit) and dynamic (Rup) upper airway obstructions in SAHS.     

Pulmonary function and resting breathing pattern in myotonic dystrophy

In 17 patients with myotonic dystrophy, spirometric, flow-volume, and maximal mouth occlusion variables were obtained and compared with 8 normal subjects. Ventilatory CO₂, response was measured by the estimation of the steady-state effect of a sufficiently large serial dead space. Variability of resting breathing pattern was expressed by the variation coefficients of respiratory cycle time and tidal volume.The group means of the total lung capacity (TLC), vital capacity (VC), forced expiratory volume in 1 sec (FEV)₁, and forced inspiratory volume in 1 sec (FIV)₁, showed a restrictive pattern. Only maximal static mouth pressure (Pi,max), measured at residual volume (RV) level, showed a significant positive correlation with both VC (p = 0.03) and FIV₁, (p = 0.02), suggesting inspiratory muscle weakness as a determinant of the restriction.Although the differences were just not significant, both variation coefficients of the respiratory cycle time and tidal volume were larger in the group with a CO, sensitivity below the lower limit of normal compared to those with a normal ventilatory response to CO₂. In 3 patients, fluctuations in FRC were also present. We hypothesize that, in addition to the already documented FRC fluctuations by uncoordinated spontaneous intercostal muscle action, a defect of integration of afferent neural input and chemical drive in the medullary region may also be present in these patients.     

Cervical lung herniation associated with upper airway obstruction

We present the case of a 6-year-old boy with reactive airway disease who developed cervical lung herniation resulting in compression of the trachea and audible stridor. This association has never been reported in the pediatric age group, and a review of the literature revealed that lung herniation is a rare condition in the pediatric population. Most patients are asymptomatic. Herniation occurs in the cervical area in approximately one fourth of patients. The diagnosis is usually made by physical examination and confirmed by radiographic studies. Treatment is seldom necessary; most patients require only education and reassurance. Surgical intervention is indicated when respiratory distress, cosmetic concerns, or progressive increase in size occur.     

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.     

Influence of the upper airway on breathing pattern and expiratory time constant in unanesthetized dog pups

Unanesthetized dog pups (2 to 31 days old) respond to sudden opening of a tracheal cannula to atmospheric pressure with a marked increase in breathing frequency. This response is achieved with a 25% decrease in inspiratory and 40% decrease in expiratory times. Expiratory thyroarytenoid muscle activity increased concomitantly, while inspiratory diaphragmatic and posterior cricoarytenoid muscle activities were reduced. These responses are interpreted as a compensatory mechanism for maintenance of an elevated end-expiratory lung volume with functional loss of the upper airway. The changes in expiratory time and thyroarytenoid muscle activity were not observed when positive pressure was applied at the trachea. The expiratory time constant was assessed during spontaneous breathing. The mean value was twice as long during nasal breathing than during tracheal breathing. The nasal value was substantially increased when the thyroarytenoid muscle was active during expiration.     

76例上气道阻塞临床分析

目的探讨上气道阻塞的认识和早期诊断。方法回顾分析2004年1月-2007年4月确诊为上气道阻塞的76例病例的临床及病理学特点。结果本组患者呼吸道淀粉样变19例；复发性多软骨炎23例；肿瘤25例，结核8例；临床表现为咳嗽46例；呼吸困难36例；声嘶43例、略痰29例；肺功能检查56例，其中27例（48．21％）表现为阻塞性通气功能障碍，14例（25％）表现为混合性通气功能障碍；有70例纤维支气管镜或喉镜检查，有明显阳性发现者67例，约占95．71％，其中气管、支气管壁增厚和／或狭窄者35例，占50％；异常气管内结节或新生物32例，占45．71％；76例中60例进行病理学检查：刚果红染色阳性者16例；符合复发性多软骨炎5例；肿瘤25例；支气管黏膜慢性炎10例。讨论肺功能测定、纤支镜检查可用于诊断和评估上气道阻塞。肺功能与纤支镜检查，有助于上气道阻塞的诊断与评估，并可用于病情的随访。     

Post-extubation pulmonary function tests in detection of upper airway obstruction in drug-overdosed patients

A relatively high percentage of hypnotic-sedative drug-overdosed (HSDO) patients suffer post-extubation upper airway obstruction. Since early detection and treatment of these lesions is desirable, we studied 20 recently extubated (within 24 hours) as well as 11 non-intubated HSDO patients employing flow-volume loops and spirometry. Abnormalities in tests for upper airway obstruction were common in both groups but only in the four post-extubation patients with clinically suspected upper airway obstruction was an inspiratory plateau by flow volume loops found. In addition, three of these four patients had mid-VC ratios greater than 1.25. We conclude that the Inspiratory flow volume loop and the mid-VC ratio may help in detecting post-extubation upper airway obstruction in lethargic, HSDO patients.     

Influence of negative pressure applied to the upper airway on the breathing pattern in unanesthetized awake dogs

We examined the influence of changes in upper airway pressure on the breathing pattern in 5 unanesthetized awake dogs. The dogs breathed through an endotracheal tube or through a comfortably fitting fiberglass snout mask. With matched resistances and volume of the dead space, the inspiratory duration, tidal volume, and minute ventilation were higher during nasal breathing compared to tracheal breathing. Nasal and tracheal occlusion produced prolongation of inspiration in the first occluded breathing attempt, but the prolongation was more marked in nasal occlusion tests. Augmentation of genioglossus muscle activity occurred on the first occluded breath in nasal but not tracheal occlusion. In another series of experiments, negative pressure was applied to the isolated upper airway while the dog breathed through a tracheostomy tube. Negative pressure caused a prolongation of inspiratory duration which was proportional to the level of the applied pressure. However, the prolongation of inspiratory duration was significantly more marked when application of negative pressure was timed simultaneously with tracheal occlusion. Our results demonstrate that the upper airway has a powerful effect on the control of breathing, which becomes more evident during tracheal occlusion.