Effects of esophageal pressure monitoring on sleep architecture

Pediatric Sleep-Related Breathing Disorders and Restless Legs Syndrome

Sleep-related breathing disorders and restless legs syndrome have traditionally been felt to affect primarily adults. Recent research suggests that these conditions are surprisingly common in children as well, and that clinical manifestations may differ considerably from those seen in adults. This review summarizes the clinical characteristics, epidemiology, pathophysiology, and treatment of sleep-related breathing disorders and restless legs syndrome in children. Particular emphasis is placed on recent research and on how the presentation and treatment of these conditions are different in children compared with adults.

Use of Pulse Transit Time To Distinguish Respiratory Events From Tidal Breathing in Sleeping Children

STUDY OBJECTIVES

Currently, esophageal pressure monitoring is the "gold standard" measure for inspiratory efforts, but its invasive nature necessitates a better tolerated and noninvasive method to be used on children. Pulse transit time (PTT) has demonstrated its potential as a noninvasive surrogate marker for inspiratory efforts. The principle velocity determinant of PTT is the change in stiffness of the arterial wall and is inversely correlated to BP. Moreover, PTT has been shown to identify changes in inspiratory effort via the BP fluctuations induced by negative pleural pressure swings. In this study, the capability of PTT to classify respiratory events during sleep as either central or obstructive in nature was investigated.

SETTING AND PARTICIPANTS

PTT measure was used in adjunct to routine overnight polysomnographic studies performed on 33 children (26 boys and 7 girls; mean +/- SD age, 6.7 +/- 3.9 years). The accuracy of PTT measurements was then evaluated against scored corresponding respiratory events in the polysomnography recordings.

RESULTS

Three hundred thirty-four valid respiratory events occurred and were analyzed. One hundred twelve obstructive events (OEs) showed a decrease in mean PTT over a 10-sample window that had a probability of being correctly ranked below the baseline PTT during tidal breathing of 0.92 (p < 0.005); 222 central events (CEs) showed a decrease in the variance of PTT over a 10-sample window that had a probability of being ranked below the baseline PTT of 0.94 (p < 0.005). This indicates that, at a sensitivity of 0.90, OEs can be detected with a specificity of 0.82 and CEs can be detected with a specificity of 0.80.

CONCLUSIONS

PTT is able to categorize CEs and OEs accordingly in the absence of motion artifacts, including hypopneas. Hence, PTT shows promise to differentiate respiratory events accordingly and can be an important diagnostic tool in pediatric respiratory sleep studies.

Patient discomfort in polysomnography with esophageal pressure measurements

The reference method for measuring respiratory effort and for differentiating between obstructive and central apneas in the diagnosis of sleep-related breathing disorders is overnight monitoring of esophageal pressure. Despite this being the reference method, it is not widely used because it is considered invasive and uncomfortable for the patients. The aim of this study was to assess patient discomfort and insertion difficulty when using an esophageal catheter during polysomnography. We have performed a prospective questionnaire-based clinical study in 799 consecutive patients where polysomnography with an esophageal catheter was routinely performed in the diagnosis of sleep-related breathing disorders. The main outcome measures were the catheter-related discomfort experienced by the patient and difficulty of catheter insertion reported by the sleep technician. Ninety-six percent of the patients accepted the insertion of the catheter, and most of the patients considered it acceptable to sleep with the catheter. Correspondingly, in most of the patients, the catheter was easily inserted, and there were difficulties in only a few patients. Specifically, no complications or side effects were reported when using the catheter. To optimize the diagnosis of sleep-related breathing disorders, an esophageal sensor catheter can be used during polysomnography, without causing major patient discomfort.

Technical protocol for the use of esophageal manometry in the diagnosis of sleep-related breathing disorders

A time-tested protocol for intrathoracic pressure monitoring during sleep is described. This method of esophageal manometry uses a fluid-filled catheter to measure variations in transmitted intrathoracic pressure with respiration. Esophageal manometry is an invaluable tool for the sleep specialist in the diagnosis of sleep-related breathing disorders, especially for detecting cases of upper airway resistance syndrome and for distinguishing subtle central apneas from obstructive events. The methods for scoring esophageal pressure, the indications and contraindications for esophageal manometry, the use of esophageal manometry as the 'gold standard' for the measurement of respiratory effort, and directions for future research are also discussed.

Available techniques for objective assessment of upper airway narrowing in snoring and sleep apnea

A number of techniques are available to determine the level of obstructive predominance in snoring and in the obstructive sleep apnea hypopnea syndrome (OSAHS): lateral cephalography, awake endoscopy, awake endoscopy with the Müller maneuver, endoscopy during sleep, endoscopy with nasal continuous positive airway pressure during sleep, fluoroscopy, CT scanning, MR scanning, manometry, and acoustic reflections. Data from different studies using various methods suggest that different patients have different patterns of narrowing or collapse of the pharynx. No reference standard exists for the determination of the predominant obstructive level during obstructive events, so further investigations are necessary to improve and validate existing methods and develop new techniques. These would improve our understanding of the pathophysiology of OSAHS and snoring and help to select the correct treatment option for different patients. This article lists criteria that must be used to assess the available techniques for diagnosis of obstruction level in snoring and OSAHS. The advantages and limitations of each diagnostic technique are summarized, with emphasis on the acoustic reflectometry technique.

Is there a cost-effective way to diagnose mild sleep-disordered breathing?

QUESTION OF THE STUDY

To determine the utility and the cost-effectiveness of oesophageal pressure, respiratory flow and movement, and oximetry (ORO) as a diagnostic tool for mild sleep-disordered breathing (SDB), as compared with overnight polysomnography (PSG).

PATIENTS AND METHODS

Seventy-nine patients evaluated for mild SDB by PSG and simultaneously by oesophageal pressure (Pes) measurement, oximetry, respiratory flow and respiratory movement on a single night. An oesophageal event (OE) was defined as irregular respiration with crescendo in Pes and rapid return to baseline with a minimal increase in the negative Pes at the end of the OE of at least 5 cm H2O or more than 50% of the baseline level. SDB was defined by ORO when oesophageal events were > 5/h, and by PSG when the respiratory disturbance index was > 5/h. The diagnostic accuracy and cost-effectiveness of ORO were compared with PSG.

RESULTS

Although the ability of ORO to detect SDB was poor: sensitivity 64%, specificity 78%, use of ORO for screening prior to PSG would have saved 5000 EUR per 100 patients compared to initial PSG.

CONCLUSION

Using the combination of oesophageal pressure, respiratory flow and movement and oximetry for the diagnosis of mild SDB is not cost-effective, because of its poor diagnostic accuracy. New devices having alternative means to predict arousal and respiratory effort variation should be evaluated for cost-effectiveness.

Esophageal pressure monitoring in detection of sleep-disordered breathing

OBJECTIVE

The aim was to study the value of esophageal pressure monitoring combined with limited polygraphic recording (oxygen saturation, respiratory and leg movements, airflow, body position, and snoring sound) in diagnosis of sleep-disordered breathing.

STUDY DESIGN

A prospective study of consecutive patients with snoring was carried out.

METHODS

Sixty-seven patients underwent an overnight study on ward. Patients with normal oxygen desaturation index and any periodic breathing disturbances combined with elevated esophageal pressure were further studied with complete polysomnography.

RESULTS

The patient compliance with esophageal catheter was 87%. Esophageal pressure monitoring increased effectively the detection of sleep-disordered breathing with limited polygraphic recording. Sixty-seven percent of the patients with normal oxygen desaturation index and respiratory-related esophageal pressure variation had sleep-disordered breathing on complete polysomnography. Increased esophageal pressure variation was significantly related with oxygen desaturation index and obstructive sleep apnea diagnosis (P <.001). All together, 48% of the mainly nonobese snorers had objective findings of sleep-disordered breathing. Patients with upper airway resistance syndrome were few. Fifteen percent of the patients had periodic leg movements. Neither subjective or objective sleepiness nor snoring or obesity adequately exposed sleep-disordered breathing in this material.

CONCLUSION

Esophageal pressure monitoring increases markedly the diagnostic value of limited polygraphic recording as a screening study for sleep-disordered breathing.

Diagnosis of sleep apnea by automatic analysis of nasal pressure and forced oscillation impedance

Detecting and differentiating central and obstructive respiratory events is an important aspect of the diagnosis of sleep-related breathing disorders with respect to the choice of an appropriate treatment. The purpose of this study was to evaluate the performance of a new algorithm for automated detection and classification of apneas and hypopneas, compared with visual analysis of standard polysomnographic signals. The algorithm is based on time series analysis of nasal mask pressure and a forced oscillation signal related to mechanical respiratory input impedance, measured at a frequency of 20 Hz throughout the night. The method was applied to all-night measurements on 19 subjects. Two experts in sleep medicine independently scored the corresponding simultaneously recorded polysomnographic signals. Evaluating the agreement between two scorers by a weighted kappa statistic on a second-by-second basis, we found that inter-expert variability and the discrepancy between automatic analysis and visual analysis performed by an expert were not significantly different. Implementation of this algorithm in a device for home monitoring of breathing during sleep might aid in the differential diagnosis of sleep-related breathing disorders and/or as a means for follow-up and treatment control.

Effect of UPPP with respect to site of pharyngeal obstruction in sleep apnoea: follow-up at 18 months by overnight recording of airway pressure and flow

Continuous recording of upper airway pressure and airflow can identify the sites of obstructive events during sleep, and their relative distribution along the upper airway segments. A separation of transpalatal and subpalatal obstructive events has been used. The purpose of the present study was to investigate if uvulopalatopharyngoplasty (UPPP) had reduced transpalatal more than subpalatal obstructive events 18 months postoperatively, and to investigate any influence of age and obesity. Fourteen consecutive male patients were investigated by overnight recording of upper airway pressure and airflow before, and 18 months after, UPPP. The localization of obstructive events pre- and postoperatively revealed that the proportion of obstructive events located transpalatally were reduced from 65.1 to 30.5% of all (P < 0.05). Viewing the two sites separately, the reduction in number of transpalatal events (81%) was higher than the reduction in subpalatal events (42%) (P < 0.05). Age + Body Mass Index (BMI) correlated inversely with relative reduction in subpalatal events but did not correlate to any change in transpalatal events. Treatment response with regards to reduction in recorded Apnoea Hypopnoea Index (AHI) was achieved in 9 out of the 11 patients who had mainly transpalatal obstructive events preoperatively.

Assessment of sleepiness in children

Excessive sleepiness is a common but under-recognized problem in children. This article examines the clinical and laboratory evaluation of sleepiness in children, including the use of polysomnography, the multiple sleep latency test, and other varieties of neurophysiologic testing. Where applicable, technical aspects of laboratory testing are reviewed. Alternative laboratory and neurobehavioral techniques used to investigate daytime sleepiness are also briefly covered.

Clinical prediction of periodic leg movements during sleep in children

OBJECTIVE

To assess the utility of several symptoms and a questionnaire-based scale in the identification of children with periodic leg movements during sleep (PLMS).

BACKGROUND

PLMS may have important consequences in some children, but the extent to which a diagnosis can be established by clinical history is unknown.

METHODS

Subjects were patients aged 2-18 years who underwent polysomnography to assess for sleep-disordered breathing (SDB). Parents completed a Pediatric Sleep Questionnaire which contained items under consideration for inclusion in the desired scale.

RESULTS

Subjects (n=113) had a mean age of 9.8+/-4.0 (SD) and 73 (65%) were male; 59 (52%) had SDB and 29 (26%) had five or more PLMS per hour of sleep (PLMI> or =5). Severity of SDB was not different among those with and without PLMI> or =5. Yes/no responses to several question-items--about restless legs, growing pains, leaving the bed at night, waking more than twice per night, waking feeling unrefreshed, and morning headaches--showed some association with PLMI> or =5 and were combined into a composite PLMS score artificially weighted toward the first two items. The PLMS score averaged 0.40+/-0.31 and ranged from 0.0 to 1.0; a 1 SD increase was associated with PLMI> or =5 (odds ratio=1.87, 95% confidence interval (1.15, 3.13), P=0.014) after adjustment for age, sex, and SDB severity. Sensitivity of a PLMS score>0.33 for PLMI> or =5 was 0.79, specificity was 0.56, positive predictive value was 0.38, and negative predictive value was 0.89. Internal consistency was reasonable (Cronbach's alpha=0.71), as was test-retest reliability (rho=0.62, P=0.0026, n=21 separate subjects).

CONCLUSIONS

Restless legs, growing pains, sleep-maintenance insomnia, unrefreshing sleep, and morning headaches show moderate associations with polysomnographically-defined PLMS, but several other symptoms do not. These results require confirmation but suggest that clinical assessment and the PLMS score may be helpful but far from definitive.

The effect of esophageal pressure monitoring on nasal airway resistance

OBJECTIVE

Artificial obstruction of nasal airflow has been shown to increase the amount of apneas and arousals. An esophageal catheter inserted through the nasal cavity is used in sleep studies to show intrathoracic pressure variations as sign of obstructive apneas and increased respiratory resistance. This study evaluates the effect of transnasal esophageal catheter on nasal airflow.

STUDY DESIGN AND SETTING

Fifty patients with problem snoring referred to our ENT clinic underwent overnight limited sleep study with an esophageal catheter. Nasal airway resistance was measured the following morning with active anterior rhinomanometry. After exclusion of 17 measurements, the results of 33 patients were compared with same parameters obtained earlier without nasal manipulation.

RESULTS AND CONCLUSION

The ipsilateral nasal resistance was clearly elevated when measured with a catheter used overnight compared with the control measurement (P < 0.05). However, the combined nasal resistance was not significantly increased in this material with patent nasal airways. In patients with already compromised nasal airflow, the possibility of clinically relevant changes in nasal airflow during catheter use should be taken in account.

Flextube reflectometry for determination of sites of upper airway narrowing in sleeping obstructive sleep apnoea patients

The aim of this study was to examine a new technique based on sound reflections in a flexible tube for identifying obstructive sites of the upper airway during sleep. There was no significant difference between two nights in seven obstructive sleep apnoea (OSA) patients regarding the level distribution of pharyngeal narrowings, when the pharynx was divided into two segments (retropalatal and retrolingual). We also compared the level distribution determined by magnetic resonance imaging (MRI) with the level distribution found by flextube reflectometry in seven OSA patients. There was no significant difference between flextube and MRI level distributions during obstructive events, but due to few subjects the power of the test was limited. We found a statistically significant correlation between the number of flextube narrowings per hour of sleep and the number of obstructive apnoeas and hypopnoeas per hour of sleep determined by polysomnography (PSG) in 21 subjects (Spearman's correlation coefficient r = 0.79, P < 0.001). In conclusion, the flextube reflectometry system seems to be useful for level diagnosis in OSA before and after treatment.

Habitually sleepy drivers have a high frequency of automobile crashes associated with respiratory disorders during sleep

Sleepiness is a common cause of traffic crashes with a cost of billions of dollars per year. A recent study has found that 2 to 3% of drivers are habitually sleepy while driving. However, there has not been a controlled study to define the characteristics, driving performance, or automobile crash rate of habitually sleepy drivers. The prevalence of respiratory disorders during sleep, and whether these respiratory disorders contribute to the increased automobile crash frequency, is unknown in habitually sleepy drivers. We interviewed 4,002 randomly selected drivers to define the prevalence of drivers who are habitually sleepy while driving. We studied the habitually sleepy drivers and an age- and sex-matched control group of drivers. These studies included reporting of daytime sleepiness, automobile crashes, driving performance and sleep studies. Of the 4, 002 drivers interviewed, 145 (3.6%, confidence interval [CI] = 3.1 to 4.3) were habitually sleepy while driving. The habitually sleepy drivers reported a significantly higher frequency of auto crashes than control subjects (the adjusted odds ratio [OR] was 13.3, CI = 4. 1 to 43). The habitually sleepy drivers had a significantly higher prevalence of respiratory sleep disorders than control subjects. For a total respiratory events index (apneas, hypopneas, and other respiratory effort-related arousals) >/= 15 the adjusted OR was 6.0, CI = 1.1 to 32. In the habitually sleepy drivers group, the frequency of sleep apnea (apnea-hypopnea index) between subjects with or without auto crashes was not statistically different. However, if we consider total respiratory events index, this frequency of respiratory sleep disorders was significantly higher in subjects with automobile crashes (the adjusted OR for a total respiratory event index >/= 15 was 8.5, CI = 1.2 to 59). Habitually sleepy drivers are a large group of drivers (1 of 30 drivers) who are involved in several fold more automobile crashes than control subjects. As these excess auto crashes can be explained in part by the presence of respiratory disorders during sleep, which are treatable, many automobile crashes in these sleepy drivers may be preventable. Our findings suggest that asking about excessive sleepiness while driving may better predict which subjects with breathing disorders during sleep have crashes than asking about overall sleepiness.

Characterization of pharyngeal resistance during sleep in a spectrum of sleep-disordered breathing

Aims of the study were 1) to compare Hudgel's hyperbolic with Rohrer's polynomial model in describing the pressure-flow relationship, 2) to use this pressure-flow relationship to describe these resistances and to evaluate the effects of sleep stages on pharyngeal resistances, and 3) to compare these resistances to the pressure-to-flow ratio (DeltaP/V). We studied 12 patients: three with upper airway resistance syndrome (UARS), four with obstructive sleep hypopnea syndrome (OSHS), three with obstructive sleep apnea syndrome (OSAS), and two with simple snoring (SS). Transpharyngeal pressures were calculated between choanae and epiglottis. Flow was measured by use of a pneumotachometer. The pressure-flow relationship was established by using nonlinear regression and was appreciated by the Pearson's square (r(2)). Mean resistance at peak pressure (Rmax) was calculated according to the hyperbolic model during stable respiration. In 78% of the cases, the value of r(2) was greater when the hyperbolic model was used. We demonstrated that Rmax was in excellent agreement with P/V. UARS patients exhibited higher awake mean Rmax than normal subjects and other subgroups and a larger increase from wakefulness to slow-wave sleep than subjects with OSAS, OSHS, and SS. Analysis of breath-by-breath changes in Rmax was also a sensitive method to detect episodes of high resistance during sleep.

Comparison of esophageal pressure with pulse transit time as a measure of respiratory effort for scoring obstructive nonapneic respiratory events

Obstructive nonapneic respiratory events (ONAREs) are much more difficult to detect and classify than apneas unless sensitive measures of respiratory effort and airflow are employed. The aim of this study was to compare two measures of respiratory effort, esophageal pressure monitoring (Pes) and pulse transit time (PTT), for scoring of ONAREs by visual analysis. Nine men (age 49 +/- 10 yr) with mild to moderate sleep apnea syndrome (AHI of 25.1 +/- 10. 8/h) were studied and 340 ONAREs (hypopneas and upper airway resistance episodes) were randomly selected for scoring by two experienced observers. Each observer blindly scored each ONARE twice (once with Pes and once with PTT) with a concurrent pneumotachography trace available for airflow quantification. This permitted the respiratory events scored with PTT to be compared with those scored with Pes, and in addition interobserver variability could be assessed for each signal. Even though standard criteria were used for scoring, there was significant interobserver variability for both Pes (29.7%) and PTT (37.1%). Taking those events for which there was agreement between the observers, PTT had a sensitivity of 79.9% and a positive predictive value of 91.2% (using Pes as the gold standard). In those ONAREs for which there was agreement between the two observers there was a larger percentage reduction in airflow compared to ONAREs that did not concur (51 versus 30.3%, p < 0.001), a larger increase in respiratory effort as assessed by PTT (slope of PTT: 23.1 versus 14. 3 arbitrary units, p < 0.01), and a higher incidence in autonomic microarousals detected with PTT (90 versus 45% of ONAREs, p < 0.006). Subtle respiratory events are more difficult to detect than apneas or frank hypopneas. When comparing PTT with esophageal pressure in detecting those events the sensitivity of PTT is good but limited when the reduction in airflow, the increase in respiratory effort, or the arousal reaction is the less clear. However, PTT appears to be a good noninvasive alternative to Pes in the detection of nonapneic obstructive respiratory events, and its ability to detect autonomic arousal gives this physiological signal added clinical usefulness.

Sleep disordered breathing in patients with cluster headache

OBJECTIVE

To study subjects with active or inactive cluster headache (CH) for occult sleep disordered breathing (SDB).

BACKGROUND

CH frequently occurs during sleep. The authors previously found that symptoms of SDB predicted reported occurrence of CH in the first half of the night, which suggested that CH could be triggered in some cases by unrecognized SDB.

METHODS

The authors performed polysomnography in 25 adults (22 men) with CH. Subjects were not selected for any sleep-related complaint. In addition to standard measures, studies included monitoring of end-tidal carbon dioxide (n = 22), and esophageal pressure (n = 20).

RESULTS

The rate of apneas and hypopneas per hour of sleep was >5 in 20 subjects (80%; 95% CI, 64% to 96%), minimum oxygen saturation was <90% in 10 subjects, maximum negative esophageal pressure ranged from -13 to -65 cm H2O, and maximum end-tidal carbon dioxide was > or =50 mm Hg in eight subjects. The eight subjects with active (versus inactive) CH at the time of study had higher maximum end-tidal carbon dioxide levels (50 +/- 3 versus 44 +/- 5 mm Hg; p = 0.0007). More severe oxygen desaturation was associated with reports that CH typically occurred in the first half of the nocturnal sleep period (p = 0.008).

CONCLUSIONS

SDB occurred in the majority of patients with CH. Evaluation of a patient with CH should include consideration that SDB may be present.

Sleep onset REM periods during multiple sleep latency tests in patients evaluated for sleep apnea

Although 2 or more sleep onset rapid eye movement (REM) periods (2omSOREMPs) on a Multiple Sleep Latency Test (MSLT) raise the possibility of narcolepsy, patients with obstructive sleep apnea (OSA) also can have 2omSOREMPs, which may then cause diagnostic uncertainty. To explore what features among OSA patients predict 2omSOREMPs on an MSLT that follows nocturnal polysomnography, we reviewed data from 1,145 consecutively studied patients suspected or confirmed to have OSA rather than narcolepsy. Overall, 4.7% of the subjects had 2omSOREMPs. Variables that were independently predictive of 2omSOREMPs in logistic regression models included male gender (OR = 4.4, 95% CI = 1.9 to 12.7), a 5-min decrease in the MSLT-derived mean sleep latency (OR = 1.9, 95% CI = 1.3 to 2.8), a 90-min decrease in nocturnal latency to REM sleep (OR = 1.6, 95% CI = 1.1 to 2.5), and a 15-unit decrease in minimal recorded oxygen saturation (OR = 1.6, 95% CI = 1.3 to 2.0). We conclude that among patients suspected or confirmed to have OSA, one or more of these four variables-male sex, sleepiness, nocturnal REM sleep latency, and extent of oxygen desaturation-could reflect neurophysiological mechanisms responsible for 2omSOREMPs. Consideration of these variables, and especially gender, may be useful in clinical practice when 2omSOREMPs are found unexpectedly.

Pediatric sleep questionnaire (PSQ): validity and reliability of scales for sleep-disordered breathing, snoring, sleepiness, and behavioral problems

Objective: To develop and validate questionnaire scales that can be used in research to investigate the presence of childhood SRBDs and prominent symptom complexes, including snoring, daytime sleepiness, and related behavioral disturbances.Background: Obstructive sleep-related breathing disorders (SRBDs) are common but usually undiagnosed among children. Methods to help identify SRBDs without the expense of polysomnography could greatly facilitate clinical and epidemiological research.Methods: Subjects were children aged 2-18 years who had polysomnographically-confirmed SRBDs (n=54) or appointments at either of two general pediatrics clinics (n=108). Parents completed a Pediatric Sleep Questionnaire which contained items under consideration for inclusion in desired scales.Results: Item reduction, based on data from a randomly selected 50% of the subjects (group A), produced a 22-item SRBD score that was strongly associated with diagnosis of an SRBD (P<0.0001) in a logistic regression model that accounted for age and gender. Diagnosis was also strongly associated with subscores for snoring (four items, P<0.0001), sleepiness (four items, P=0.0003), and behavior (six items, P<0.0001) among group A subjects. The scales performed similarly well among group B subjects, and among subjects of different ages and gender. In group A and B subjects, respectively, a selected criterion SRBD score produced a sensitivity of 0.85 and 0.81; a specificity of 0.87 and 0.87; and a correct classification for 86 and 85% of subjects. The scales showed good internal consistency and, in a separate sample (n=21), good test-retest stability.Conclusions: These scales for childhood SRBDs, snoring, sleepiness, and behavior are valid and reliable instruments that can be used to identify SRBDs or associated symptom-constructs in clinical research when polysomnography is not feasible.

Accuracy of respiratory inductive plethysmography for the diagnosis of upper airway resistance syndrome

OBJECTIVE

To determine the sensitivity and specificity of quantitative respiratory inductive plethysmography (RIP) compared with the "gold standard," nocturnal esophageal pressure (Pes) measurement, in the diagnosis of upper airway resistance syndrome (UARS) in adults.

METHODS

Fourteen consecutive patients without obstructive sleep apnea and suspected of having UARS underwent simultaneous measurement of Pes with a catheter and standard nocturnal polysomnography along with RIP. UARS events (RERAs, respiratory effort-related arousals) were identified by observing crescendo changes in Pes with a Pes nadir < or = -12 cm H2O, followed by an arousal or microarousal. UARS was defined as > or = 10 RERAs per hour. For each patient, the ratio of peak inspiratory flow to mean inspiratory flow (PIFMF) measured by RIP was performed during quiet wakefulness and with 40 randomly selected breaths in the supine position for two conditions: stage 2 sleep, immediately prior to arousals in any sleep stage. The mean PIFMF (wake-sleep) was calculated for each condition.

RESULTS

The sensitivities and specificities, respectively, of RIP to distinguish UARS patients from non-UARS patients are from stage 2 sleep (67%, 80%), immediately prior to arousals (100%, 100%). For breaths occurring immediately prior to arousals, the mean PIFMF (wake-sleep) is > or = 0.13 for UARS patients and < 0.13 for non-UARS patients.

CONCLUSION

The PIFMF measured by RIP allows for the most accurate identification of UARS patients when breaths are selected for analysis immediately prior to arousals.

The upper airway resistance syndrome

The upper airway resistance syndrome (UARS) is a recently described form of sleep-disordered breathing in which repetitive increases in resistance to airflow within the upper airway lead to brief arousals and daytime somnolence. This review will first describe the chronological progression of our understanding of UARS within the broader context of sleep-disordered breathing. The primary symptom, daytime somnolence, appears to result directly from repetitive EEG arousals. The level of negative intrathoracic pressure is the most likely stimulus for arousal, possibly mediated by mechanoreceptors in the upper airway. A general consensus regarding the exact clinical definitions and the physiologic measurement techniques leading to a diagnosis does not exist, although esophageal manometry and pneumotachographic airflow measurements taken during polysomnography are the "gold standard." Less invasive diagnostic modalities have been proposed, but none of them have been well-validated. Aside from daytime somnolence, hypertension is an important sequela of this disorder, likely resulting from autonomic and cardiovascular changes induced by increased negative intrathoracic pressure. Nasal continuous positive airway pressure is the most efficacious form of therapy, although low patient compliance may limit its practical application. The safety and efficacy of surgical treatments are poorly documented in the literature. Palatal tissue reduction by radiofrequency ablation and the use of oral appliances hold promise as safe and effective modalities, but these treatments require further study.

[Measurement of respiratory effort (esophageal pressure) and estimation of resistance of the upper airway in polysomnography: indications, limitations and results]

During polysomnography, measurement of airflow and respiratory effort are essential for classifying the type of respiratory event and for evaluating the efficacy of treatment. There are various ways to measure respiratory effort, the reference technique being oesophageal manometry. This measures fluctuations in intrathoracic pressure which correspond to variations in upper airway resistance and therefore allows differentiation between central and obstructive respiratory events. Thus the simple snorer can be distinguished from an individual with the upper airway resistance syndrome (UARS). In the UARS abnormally high resistance develops in the upper airway in the absence of identifiable apnoeas and hypopnoeas. The characteristic cresendo-decresendo pattern of the oesophageal pressure signal, when associated with the micro-arousals which are responsible for the hypersomnolence, is pathognomonic of this condition. The clinical application of oesophageal manometry is limited by its poor tolerance in certain individuals and by the potential deleterious effect the catheter itself has on sleep quality and on the dynamics of the upper airway. Other less invasive techniques, such as nasal pressure and pulse transit time, are currently under evaluation.

Differentiating obstructive and central sleep respiratory events through pulse transit time

Noninvasive alternatives to esophageal pressure (Pes) are needed to evaluate respiratory effort during sleep. Pulse transit time (PTT) is the time taken for pulse pressure to travel from the aortic valve to the periphery. PTT has been shown to be inversely correlated with blood pressure, and can reveal acute changes generated by high pleural pressure swings during pulsus paradoxus. A close relationship has been demonstrated between the increase in Pes and a progressive rise in the amplitude of PTT oscillations. The aim of the present study was to assess the accuracy of PTT for the classification of sleep respiratory events as central or obstructive. Respiratory events occurring during sleep were randomly chosen from 13 unselected male patients (mean apnea-hypopnea index [AHI] = 25.1 per hour of sleep; age = 47.3 yr, body mass index [BMI] = 27.1 kg/m2). Two observers experienced in polysomnography classified 177 events on the basis of the "gold standard method": the measurement of Pes. For 167 events about which the observers agreed, the PTT signal was analyzed visually and independently by the two observers blinded to Pes, in order to reclassify the same sleep respiratory events. The two observers were in agreement for 94.6% of the events scored visually on PTT recordings. We evaluated sensitivity (Se) (Observer 1: 94%, Observer 2: 91%), specificity (Sp) (97% and 95%, respectively), negative predictive value (NPV) (95% and 92%, respectively), and positive predictive value (PPV) (96% and 94%, respectively), of PTT with Pes as the reference. Misclassifications of respiratory episodes were usually due to artifacts or baseline variations of the PTT signal (57%), and occurred during rapid eye movement (REM) sleep (42.8%). PTT has shown a high sensitivity and specificity in differentiating obstructive and central respiratory events, and may become the reference noninvasive tool for this purpose.

Respiratory resistive impedance as an index of airway obstruction during nasal continuous positive airway pressure titration

Esophageal pressure amplitude (DeltaPes), inspiratory pulmonary resistance (RLI) and inspiratory flow limitation score (FS) are used as indices of upper airway obstruction for the titration of nasal continuous positive airway pressure (nCPAP) in patients with obstructive sleep apnea syndrome (OSAS). This study was designed to determine whether oscillatory respiratory resistive impedance at 16 Hz (RFO) might be proposed as an alternative index. Eleven OSAS patients were studied during a night of polysomnography-controlled nCPAP titration. Nasal flow (V) and airway opening and esophageal pressures (Pao and Pes, respectively) were continuously measured during nasal breathing, and forced-flow oscillations (FO) were applied for 5 min at each nCPAP level. RLI was calculated by linear regression analysis of resistive pressure versus V over inspiration. R FO was obtained by linear regression analysis of respiratory resistive impedance versus frequency. Application of FO affected neither sleep nor pulmonary mechanics. RFO correlated with RLI in all patients. RFO did not correlate with DeltaPes in two patients, and was not significantly related to FS in five patients. This study demonstrates the applicability of the FO technique in sleeping patients receiving nCPAP, and the reliability of RFO for assessing pulmonary resistance. RFO might therefore be proposed as a quantitative index of airway obstruction for nCPAP titration.

Within-night variation in respiratory effort preceding apnea termination and EEG delta power in sleep apnea

We studied the within-night variability of the maximum esophageal pressure deflection before apnea termination (DPmax) in nine patients with severe obstructive sleep apnea as an index of the arousal threshold and the mean electroencephalogram (EEG) delta power for each 30 s as an index of the timing of sleep cycles. Periodicity in the time variation of delta power and DPmax was analyzed by determining their power spectral density and their relationship determined by cross correlation. DPmax and delta power varied cyclically and in phase with a major periodicity (major peak in power spectral density) of 117.6 +/- 8.8 (SE) min. The correlation between the values of DPmax and delta power was significant (P < 0.001) in each subject (mean r = 0.47 +/- 0.03), and the coherence between DPmax and delta power at their dominant frequency was high. Within cycles of non-rapid-eye-movement sleep, DPmax and delta power increased, reaching peak values on average at or after midcycle. These findings suggest that the arousal threshold to airway occlusion in patients with obstructive sleep apnea varies cyclically during the night synchronous to the underlying cycles of sleep.

Radiofrequency volumetric tissue reduction of the palate in subjects with sleep-disordered breathing

STUDY OBJECTIVES

To evaluate pain, swallowing, speech, edematous response, tissue shrinkage, sleep, snoring, and safety (energy limits and adverse effects) following radiofrequency (RF) treatment to the palate in 22 subjects with sleep-disordered breathing.

DESIGN

This investigation is a prospective nonrandomized study. Polysomnography, radiographic imaging, and infrared thermography, along with questionnaires and visual analog scales, were used to evaluate the effects of RF treatment to the palate.

SETTING

Treatments were delivered on an outpatient basis at Stanford University Medical Center.

PATIENTS

Twenty-two healthy patients (18 men), with a mean age of 45.3+/-9.1 years, were enrolled. All were snorers seeking treatment and met predetermined criteria: a respiratory disturbance index < or = 15, oxygen saturation > or = 85%, and a complaint of daytime sleepiness.

INTERVENTION

RF was delivered to the submucosa of the palate with a custom-fabricated electrode for a mean duration of 141+/-30 s with a mean of 3.6+/-1.2 treatments per patient. Reduction of their snoring scores determined the end point of the study.

RESULTS

Neither speech nor swallowing was adversely affected. Pain was of short duration (0 to 48 h) and was controlled with acetaminophen. There were no infections. Although there was documented edema at 24 to 48 h, there were no clinical airway compromises. Polysomnographic data showed improvement in esophageal pressure measurements of the mean nadir and the 95th percentile nadir (p=0.031, p=0.001) respectively, as well as the mean sleep efficiency index (p=0.002). Radiographic imaging showed a mean shrinkage of 5.5+/-3.7 mm (p< or =0.0001). Subjective snoring scores fell by a mean of 77% (8.3+/-1.8 to 1.9+/-1.7, p=0.0001) accompanied by improved mean Epworth sleepiness scores (8.5+/-4.4 to 5.2+/-3.3, p=0.0001).

CONCLUSION

The results of this investigation allowed the formulation of safety parameters for RF in this defined population with mild sleep-disordered breathing. There was a documented tissue reduction and improvement in symptoms in all subjects. However, given the small sample size and short-term follow-up, these results should be confirmed by further investigation.