Differentiating obstructive and central sleep respiratory events through pulse transit time

Masked hypertension in obstructive sleep apnea syndrome

BACKGROUND

Ambulatory blood pressure (BP) monitoring (ABPM) detects subjects with normal clinic but high ambulatory 24-h BP, that is, masked hypertension.

METHODS

One hundred and thirty newly diagnosed obstructive sleep apnea syndrome (OSAS) patients, free of recognized cardiovascular disease were included (111 men, age = 48 +/- 1 years, BMI = 27.6 +/- 0.4 kg/m, respiratory disturbance index (RDI = 42 +/- 2/h). Clinic BP, 24-h ABPM, baroreflex sensitivity (BRS), echocardiography and carotid intima-media thickness (IMT) were assessed.

RESULTS

Forty-one patients (31.5%) were normotensive, 39 (30.0%) exhibited masked hypertension, four (3.1%) white-coat hypertension and 46 (35.4%) hypertension. Significant differences were found between normotensive, masked hypertensive and hypertensive patients in terms of BRS (10.5 +/- 0.8, 8.0 +/- 0.6 and 7.4 +/- 0.4 ms/mmHg, respectively, P < 0.001), carotid IMT (624 +/- 17, 650 +/- 20 and 705 +/- 23 microm, respectively, P = 0.04) and left ventricular mass index (37 +/- 1, 40 +/- 2 and 43 +/- 1 g/height2.7, respectively, P = 0.003). A clinic systolic BP more than 125 and a diastolic BP more than 83 mmHg led to a relative risk (RR) of 2.7 and a 90% positive predictive value for having masked hypertension.

CONCLUSION

Masked hypertension is frequently underestimated in OSAS and is nearly always present when clinic BP is above 125/83 mmHg.

How much influence does inspiration have on pulse transit time in sleep apnea?

Objectives

To study how much affect inspiration has on pulse transit time (PTT).

Study Design

Prospective study.

Subjects and Methods

Polysomnograms were performed in 51 consecutive patients (male 45, female 6; ages 49.2 π 14.7 years) with obstructive sleep apnea. PTT changes during normal breathing, obstructive apnea (OA), and central apnea (CA) were compared, and the correlations between simultaneous changes in PTT and intraesophageal pressure (Peso) were discussed.

Results

In comparison with normal breathing, increases in PTT were greater in OA but significantly less in CA. The mean continuous increases in PTT were significantly higher in OA (17.0 ± 4.9 ms) than those in CA (9.5 ± 2.7 ms). Simultaneous changes in Peso and PTT correlated significantly but with a lower correlation coefficient in a portion of patients.

Conclusions

Inspiration obviously affects PTT, and the linear relationship between simultaneous changes in PTT and Peso might be reflected to some extent.

Diagnostic issues in pediatric obstructive sleep apnea

Obstructive sleep apnea syndrome (OSAS) in children includes a spectrum of respiratory disorders with significant morbidities. Diagnosis of OSAS is based on clinical suspicion, history, and physical findings, and confirmation is made by polysomnography. There has been significant progress in recent years in technologies available for diagnosis of OSAS since the consensus statement of the American Thoracic Society in 1996. The current review describes methodologies that are available today for assessment and diagnosis of OSAS in children and summarizes the most recent recommendations of the American Academy of Sleep Medicine Task Force regarding scoring sleep-related respiratory events in children.

Theoretical study on the effect of sensor contact force on pulse transit time

Pulse transit time (PTT) has been widely used for noninvasive examination of the arterial viscoelastic properties, such as elasticity, compliance, and stiffness of the vessel walls. PTT is usually determined as the time interval between the peak of the electrocardiogram R wave and the foot of the photoplethysmogram (PPG). However, it was observed that the PPG is affected by the applied contact force between the photoplethysmographic sensor and the measurement site, e.g., finger. In this study, the nonlinear biomechanical properties of the finger arterial wall were considered when investigating the changes in PTT with varying contact force. Emphasis was placed on the changes in the shape of the arterial wall pressure-volume curve. The simulation results indicated that at positive transmural pressure, PTT increased with the applied contact force, reaching the maximum at zero transmural pressure and remaining at a constant level at negative transmural pressure. The theoretical analysis was further verified by the experiments carried out on thirty young subjects and six elderly subjects using twelve discrete levels of contact force.

Detection of central respiratory events using pulse transit time in infants

The prevalence of sudden infant death syndrome (SIDS) has been well studied and central sleep apnea is deemed as one of the possible causes. Current gold standard for its diagnosis is nocturnal polysomnography (PSG). However, this procedure is complex and generally needs to be performed in a sleep laboratory. Pulse transit time (PTT) shows its potential to indicate abrupt blood pressure (BP) changes during the occurrences of upper airway obstruction. The main objective of this study was to assess the capability of PTT to differentiate central respiratory events from tidal breathing in infants. This study involved 5 infants (4 male) with mean age of 7.8 months. 50 valid central respiratory events were randomly selected. These events were free from motion artifacts and pre-scored in the corresponding PSG studies by two blinded observers. PTT measurements from these events were then evaluated against the PSG scorings. Using a two-tailed F-test for variance, it was observed that central events differed from tidal breathing in a significant manner (p<0.05). Furthermore, PTT has showed its sensitivity to monitor marginal BP fluctuations during tidal breathing. Hence, the results herein suggest that PTT can be a valuable non-invasive technique to monitor central apneic events in sleeping infants.

Impaired Objective Daytime Vigilance in Obesity-Hypoventilation Syndrome

BACKGROUND

Obesity-hypoventilation syndrome (OHS) is efficiently treated by noninvasive ventilation (NIV). Sleep respiratory disturbances, reduced ventilatory drive, and excessive daytime sleepiness (EDS) are commonly reported, but their relationships remain unclear.

OBJECTIVES

To characterize sleep breathing disorders encountered in patients with OHS, to compare low and normal CO(2) responders in terms of sleep abnormalities, subjective and objective measures of EDS, and to measure the changes induced by NIV on these parameters.

METHODS

At baseline and after 5 nights of NIV, 15 consecutive patients (mean [+/- SD] age, 55 +/- 9 years; mean body mass index, 38.7 +/- 6.1 kg/m(2); Paco(2), 47.3 +/- 2.3 mm Hg) prospectively underwent polysomnography, CO(2) ventilatory response testing, Epworth sleepiness scale scoring, and the Oxford Sleep Resistance (OSLER) test, which is an objective vigilance test.

RESULTS

OHS patients exhibited obstructive sleep apnea syndrome (mean apnea-hypopnea index, 62 +/- 32 events per hour) and rapid eye movement (REM) sleep hypoventilation (mean REM sleep time, 35 +/- 33%). Baseline CO(2) sensitivity was significantly related to the proportion of hypoventilation during REM sleep (r = 0.54; p = 0.037). Six patients showed abnormal sleep latencies during the OSLER test (71% of the low CO(2) responders vs 14% of the normal CO(2) responders). Low CO(2) responders exhibited significantly shorter sleep latencies during the OSLER test (23 +/- 14 vs 37 +/- 8 min, respectively; p = 0.05). Using NIV, diurnal blood gas levels were improved and REM sleep hypoventilation were suppressed. Objective sleepiness was improved in low CO(2) responders (p = 0.04).

CONCLUSION

In OHS patients, the lower the daytime CO(2) response, the higher the proportion of REM sleep hypoventilation and daytime sleepiness. Short-term therapy with NIV improves all of these parameters.

[Anaesthetic management of adult patients with obstructive sleep apnea syndrome]

OBJECTIVE

The purpose of this review article is to update the anaesthetic management of adult patients with obstructive sleep apnoea syndrome (OSAS).

DATA SOURCES

All references obtained from the medical database Medline related to OSAS and anaesthesia from 1963 until May 2006 were reviewed. References included original articles, observations, clinical cases, and reviews published in English or in French.

DATA SYNTHESIS

The anaesthetic literature related to OSAS and anaesthesia is poor. Understanding anatomy and pathophysiology is important for an optimal anaesthetic management. Since the diagnosis is unknown in almost 80-90% of these patients, many undergo general or regional anaesthesia every day without recognition of the main dangers associated with the condition. Recognition of these patients, especially in the preanaesthetic assessment, is an essential step to prevent perioperative complications. Patients with OSAS are very sensitive to sedatives, hypnotics and opioids. The use of these drugs must be controlled and monitored. Anticipation of difficult intubation avoids complications during induction of general anaesthesia and the use of nasal CPAP decreases the incidence of respiratory complications in the perioperative period.

CONCLUSION

Further research is needed in this field of anesthesia. Intraoperative difficulties in the control of airway and postoperative cardiac and respiratory complications may happen. The use of nasal CPAP in the perioperative period makes the anaesthetic management easier and safer.

Non-arteritic anterior ischaemic optic neuropathy is nearly systematically associated with obstructive sleep apnoea

AIM

To evaluate newly diagnosed non-arteritic anterior ischaemic optic neuropathy (NAION) patients for the existence of an associated sleep apnoea syndrome.

METHODS

Newly identified NAION patient underwent polysomnography. The prevalence of sleep apnoea in NAION patients was compared to the prevalence previously found in the general population. Hypertension, diabetes, hyperlipidaemia, and atheromatous lesions of carotid vessels as classic risk factors associated with NAION were also identified.

RESULTS

27 consecutive newly diagnosed NAION patients (18 men and nine women, mean age 65 (SD 8) years, body mass index 27.2 (3.8) kg/m2) were included in the study. 24 of these 27 NAION patients (89%) exhibited a sleep apnoea syndrome (respiratory disturbance index: 37.2/h (SD 18.3/h). Risk ratio for a NAION patient to have sleep apnoea was 4.9 compared to the general population (p < 0.001). Sleep apnoea was 1.5-2-fold more frequent than the rate of the other identified risk factors typically associated with NAION (hypertension, diabetes).

CONCLUSIONS

Sleep apnoea is the most frequent disorder associated with NAION and should be screened in this population. At least a questionnaire related to obstructive sleep apnoea symptoms and assessment of sleepiness should be systematically proposed to patients with NAION.

Pulse wave transit time for monitoring respiration rate

In this study, we investigate the beat-to-beat respiratory fluctuations in pulse wave transit time (PTT) and its subcomponents, the cardiac pre-ejection period (PEP) and the vessel transit time (VTT) in ten healthy subjects. The three transit times were found to fluctuate in pace with respiration. When applying a simple breath detecting algorithm, 88% of the breaths seen in a respiration air-flow reference could be detected correctly in PTT. Corresponding numbers for PEP and VTT were 76 and 81%, respectively. The performance during hypo- and hypertension was investigated by invoking blood pressure changes. In these situations, the error rates in breath detection were significantly higher. PTT can be derived from signals already present in most standard monitoring set-ups. The transit time technology thus has prospects to become an interesting alternative for respiration rate monitoring.

Pulse transit time in paediatric respiratory sleep studies

Pulse transit time (PTT) has emerged over the recent decades as a simple and non-invasive measure to quantify inspiratory effort changes in adults with sleep disordered breathing (SDB). Hence, this shows promise to be an effective screening tool for the paediatrics. However, little is known about its utility and suitability until recent studies has been provided quantitative knowledge about its relevance in clinical investigations. In this review, the origins, normative values, current uses and technical issues in its application to paediatric monitoring, particularly during sleep are discussed. Preliminary findings from these investigations suggest favourably its potential as an important element to screen SDB in the children population.

Cheyne–Stokes respiration with central sleep apnoea in chronic heart failure: Proposals for a diagnostic and therapeutic strategy

Central sleep apnoea (CSA) is highly prevalent in the evolutionary course of chronic heart failure. Such a ventilatory pattern during sleep is independently associated with poor prognosis in people with congestive heart failure. Chronic hyperventilation and daytime hypocapnia are the main mechanisms underlying the frequent association between CSA and cardiac failure. Simplified diagnostic strategies allowing easier recognition of CSA among people with severe heart failure are obviously needed but remain to be validated. Treatment of CSA is essentially aimed at improving cardiac function. When CSA persists, after appropriate adjustment of medication and resynchronisation therapy when indicated, specific ventilatory support during sleep should be considered. Continuous positive airway pressure (CPAP), oxygen, adaptive Servo-ventilation (ASV) and non-invasive ventilation have been proposed. Large randomised trials demonstrating survival and time free from heart transplantation are lacking.

The pulse transit time arousal index in obstructive sleep apnea before and after CPAP

BACKGROUND AND PURPOSE

Pulse transit time (PTT) is a non-invasive index which reflects changes in peripheral vascular resistance and intrathoracic pressure. PTT arousal index (PTT Ar/I) is defined as the frequency (number/hour) of a defined decrease in PTT which may serve as a marker for respiratory events, and associated arousals which occur in patients with obstructive sleep apnea (OSA). This study was designed to evaluate the PTT Ar/I before and after patients with OSA were treated with continuous positive airway pressure (CPAP).

PATIENTS AND METHODS

Individuals referred for evaluation of possible OSA underwent split-night polysomnography (PSG). The findings from 144 consecutive patients with a respiratory disturbance index (RDI)>/=20, who demonstrated at least a 50% drop in RDI with CPAP, provide the basis for this analysis. The PTT Ar/I measured before and after CPAP were compared to other measures of severity for OSA, including RDI and arousal index.

RESULTS

The PTT Ar/I correlates with the RDI (r=0.43, P</=0.0001) and with the arousal index (r=0.43, P<0.0001). Moreover, the decrease in RDI and arousal index that occurs with CPAP treatment correlates with a similar decrease in the PTT Ar/I (r=0.54, P<0.0001).

CONCLUSIONS

The PTT Ar/I correlates well with other standard measures of severity in patients with OSA and is potentially a non-invasive marker with which to measure the frequency of disruptive events that occur during sleep.

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.

Pulse transit time by R-wave-gated infrared photoplethysmography: review of the literature and personal experience

OBJECTIVE

Pulse transit time (PTT) is the time it takes a pulse wave to travel between two arterial sites. A rela tively short PTT is observed with high blood pressure (BP), aging, arteriosclerosis and diabetes mellitus. Most methods used for measuring the PTT are cumbersome and expensive. In contrast, the interval between the peak of the R-wave on the electrocardiogram and the onset of the corresponding pulse in the finger pad measured by photoplethysmography can be easily measured. We review herein the literature and impart the experience at our institution on clinical applications of R-wave-gated photo-plethysmography (RWPP) as measurement of PTT.

METHODS

The MEDLINE data base on clinical applications of RWPP was reviewed. In addition, studies performed in the author's institution are presented.

RESULTS

When used as a surrogate for beat-to-beat BP monitoring, RWPP did not meet the level of accuracy required for medical practice (two studies). RWPP produced accurate and reproducible signals when utilized as a surrogate for intra-thoracic pressure changes in obstructive sleep apnea, as well as BP arousals which accompany central sleep apnea (five studies). In estimation of arterial stiffness, RWPP was unsatisfactory (one study). In assessment of cardiovascular reactivity, abnormal values of RWPP were noted in autonomic failure (one study), while disease-specific reactivity patterns were identified utilizing a method involving RWPP (two studies).

CONCLUSIONS

In clinical practice, sleep-apnea may be accurately monitored by RWPP. RWPP seems to reflect autonomic influences and may be particularly well-suited for the study of vascular reactivity. Thus, further descriptions of disease-specific cardiovascular reactivity patterns may be possible with techniques based on RWPP. Other clinical uses of RWPP are investigational.

Obstructive sleep apnea syndrome: effect of respiratory events and arousal on pulse wave amplitude measured by photoplethysmography in NREM sleep

The objective of the study is to evaluate changes in finger pulse wave amplitude (PWA), as measured by photoplethysmography, and heart rate (HR), related to obstructive respiratory events and associated arousals during sleep. We analyzed 1,431 respiratory events in NREM sleep from 12 patients according to (1) the type of event (apnea, hypopnea, upper airway resistance episode) and (2) the duration of the associated EEG arousal (>10, 3-10, <3 s). Obstructive respiratory events provoked a relative bradycardia and vasodilation followed by HR increase and vasoconstriction. Relative PWA changes were significantly greater than HR changes. These responses differed significantly according to EEG-arousal grades (time x arousal interaction, p<0.0001), with longer arousals producing greater responses, but not to the type of respiratory event (time x event interaction, p = ns). Obstructive respiratory events provoke HR and PWA changes, the magnitude seemingly related to the intensity of central nervous activation, with PWA changes greater than HR. PWA obtained from a simple pulse oxymeter might be a valuable method to evaluate sleep fragmentation in sleep breathing disorders.

Awake flow limitation with negative expiratory pressure in sleep disordered breathing

BACKGROUND AND PURPOSE

Although upper airway collapsibility (UAC) is theoretically useful to anticipate severity of sleep-disordered breathing (SDB), inspiratory UAC measurements are poorly correlated with obstructive sleep apnea (OSA) severity.

PATIENTS AND METHODS

We investigated in 15 healthy and 35 SDB awake subjects whether negative expiratory pressure (NEP) could be a technique which would allow us to anticipate SDB severity. We characterized in these subjects, both in supine and sitting position, at -5 and -10 cm H(2)O, the flow-volume curves and a new NEP quantitative index (ratio of the 'areas under the curve' of NEP flow-volume loop vs. spontaneous flow-volume loop).

RESULTS

Abnormal flow-volume curves were significantly more frequent in patients with SDB than in healthy subjects, for both negative pressures in sitting posture and -10 cm H(2)O in supine position. The quantitative index decreased with the severity of SDB, independently of confounding factors (age, body mass index (BMI) and expiratory reserve volume (ERV)). In the supine position, at -5 and -10 cm H(2)O, thresholds of less than 160 and 180% respectively identified in 96.6% of SDB, whereas thresholds of greater than 160 and 180% were adequately classified in 76.9% of controls.

CONCLUSIONS

NEP flow-volume curves and quantitative index during wakefulness are useful methods to detect UAC. These results, however, should be confirmed by a prospective study in the general population.

Pulse transit time improves detection of sleep respiratory events and microarousals in children

OBJECTIVES

To evaluate the additional information provided by pulse transit time (PTT), a noninvasive tool, when using during polysomnography for the diagnosis of sleep breathing disorders in a pediatric population.

MAIN FINDINGS

Respiratory and microarousals events were scored twice. The first scoring was performed using nasal pressure, thermistors, thoracic and abdominal movements, and oxygen saturation. The second scoring, blinded to the first scoring, was performed using PTT in combination with all the other signals. Microarousals were scored once visually on the EEG trace (cortical arousals [CAs]) and once using the PTT signal (autonomic arousals [AAs]) blinded to EEG. For the whole group of 16 children studied (mean age, 9.5 years), there was no significant difference between the respiratory disturbance index (RDI) with or without PTT analysis (22.4 +/- 13.5/h vs 20.4 +/- 14.3/h; not significant [mean +/- SD]). Among the children exhibiting a "without PTT" RDI < 30/h, 5 of 12 children (41.66%) showed a clinically significant >/= 5/h increase in RDI when using PTT. AAs detected by PTT were significantly more frequent than CAs during rapid eye movement (REM) sleep (7.4 +/- 3.9/h vs 3.2 +/- 2.3/h; p < 0.001) and slow wave sleep (SWS) [6.0 +/- 4.3/h vs 0.6 +/- 0.5/h; p < 0.0001].

CONCLUSIONS

The quantification of respiratory effort using PTT improves the detection of respiratory events in children. The detection of microarousals is improved particularly in REM and SWS.

Motion artefact reduction of the photoplethysmographic signal in pulse transit time measurement

Motion artefact is a common occurrence that contaminates photoplethysmographic (PPG) measurements. To extract timing information from signals during artefact is challenging. PPG signal is very sensitive to artefacts and can be used in applications like, pulse transit time (PTT) as part of the polysomnographic studies. A correlation cancellation or signal processing approach is implemented with the adaptive cancelling filter concept and a triaxial accelerometry. PPG signals obtained from a Masimo (Reference) pulse oximeter is used as reference to compare with the reconstructed PPG signals. Different hands are used for each PPG source, one stationary while the other involves typical movements during sleep. A second Masimo pulse oximeter is used to register intensity of timing errors on commercial PPG signals. 108 PTT measurements are recorded in three different movements with PTT estimates from unprocessed PPG signals showing 35.51+/-27.42%, Masimo 50.02+/-29.40% and reconstructed 4.32+/-3.59% difference against those from the Reference PPG. The triaxial accelerometry can be used to detect the presence of artefact on PPG signals. This is useful in PTT measurements when signal contaminated with artefacts are required for further analysis, especially after and during arousals in sleep. The suggested filtering model can then reconstruct these corrupted PPG signals.

Heart rate increment: an electrocardiological approach for the early detection of obstructive sleep apnoea/hypopnoea syndrome

The prevalence of OSAHS (obstructive sleep apnoea/hypopnoea syndrome) is high in developed countries and it is estimated that the vast majority of patients remain undiagnosed. On the basis of physiological evidence, we evaluated the frequency component of HRI (heart rate increment) as a simple and inexpensive screening tool for OSAHS detection in a first group of patients (group 1) and validated their discriminant capacity in a second group (group 2). The predictive accuracy of hourly %VLFI (frequency-domain HRI variable obtained from nocturnal ECG Holter monitoring) was analysed by comparison with an hour-by-hour respiratory disturbances index assessed by complete polysomnography in 28 consecutive clinically suspected OSAHS patients for group 1 and in 35 patients for group 2. OSAHS was present in 20 patients according to a mean hourly apnoea plus hypopnoea index >10 in group 1, and prevalence reached 77.1% in group 2. Sensitivity, specificity and positive and negative predictive accuracy were calculated and an ROC (receiver operating characteristic) curve was constructed for several polysomnographic threshold values. In group 1, hourly %VLFI appeared as an evident predictor of the apnoea/hypopnoea index (W=0.848, P<0.0001; where W is the area under the curve obtained using ROC curve analysis). Using an appropriate threshold (value ≥3.2%), %VLFI demonstrated a sensitivity of 78.1% and a specificity of 70.4%. These thresholds applied to group 2 yielded a sensitivity of 73.9% and a specificity of 76.6%. Frequency-domain analysis of the HRI appears to be a powerful tool for OSAHS prediction. The simplicity of its analysis and use makes of it a particularly well-suited variable for routine mass screening in high-risk populations undergoing ECG Holter monitoring.

Sleep . 3: Clinical presentation and diagnosis of the obstructive sleep apnoea hypopnoea syndrome

Patients with OSAHS may present to a sleep clinic or to other specialists with symptoms that are not immediately attributable to the condition. The diagnostic methods available are reviewed.

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.

Scoring arousals in the home environment

Arousals from sleep and consequent sleep disruption may be a causal link between sleep-disordered breathing and its sequellae in children. Quantification of arousals therefore makes an important contribution to the overall assessment of the sleep of a child with suspected obstructive sleep apnea (OSA) or other sleep disorders. Arousals are classically defined by changes in the electroencephalographic (EEG) channels, but most arousals in children involve body movement in addition to EEG changes. Several methods of quantifying arousals without the use of EEG have been proposed, with the aim of simplifying testing in children with suspected OSA so that it can be safely and efficiently performed in the child's home. The following paper gives a background to the assessment of arousals from sleep in children, and describes methods for detecting arousals and their potential application to recordings performed in a child's home.

Monitoring respiration during sleep

The sleep-related breathing disorders have been categorized in various ways. The most basic schema divides them into obstructive or central apneic events. An American Academy of Sleep Medicine (AASM) Task Force Report published in 1999 defined four separate syndromes associated with abnormal respiratory events during sleep among adults, namely, obstructive sleep apnea-hypopnea syndrome (OSAHS), central sleep apnea-hypopnea syndrome, Cheyne-Stokes breathing syndrome, and sleep hypoventilation syndrome. In this classification, the upper airway resistance syndrome was not regarded as a distinct syndrome; instead, respiratory event-related arousals (RERAs) were considered part of the syndrome of OSAHS.

Pulse transit time as a measure of arousal and respiratory effort in children with sleep-disordered breathing

The upper airway resistance syndrome (UARS) is associated with neurobehavioral morbidity in children. The diagnostic gold standard for UARS is esophageal manometry. However, this is invasive. Furthermore, upper airway obstructive events in sleeping children frequently terminate without visible electrocortical (EEG) arousal. The pulse transit time (PTT) is a noninvasive marker of blood pressure and, therefore, subcortical arousal. Blood pressure elevation, associated with respiratory arousal from sleep, results in a drop in the PTT. We hypothesized that: 1) the PTT is a more sensitive measure of respiratory arousal than EEG; and 2) the PTT arousal index can distinguish children with UARS from those with primary snoring. Polysomnography, including esophageal manometry and PTT, was measured prospectively in 24 symptomatic children and 10 normal controls. Apnea, hypopnea, and respiratory effort-related arousal events terminated in a PTT arousal 91%, 83%, and 80% of the time, and in an EEG arousal in 55%, 51%, and 43% (all p < 0.05), respectively. The PTT arousal index was significantly greater in children with UARS (6.8 events/h) than primary snoring (2.2 events/h) (p < 0.05). We conclude that, in children, PTT arousals are a more sensitive measure of obstructive events than visible EEG arousals.

Sleep studies for sleep apnoea

Sleep studies have grown to encompass a broad range of technologies employed to study and diagnose a variety of sleep disorders. From their inception in neurophysiology laboratories interested in investigating primary disorders of sleep architecture from psychiatric illness, their remit has widened such that their most common role is currently to diagnose secondary sleep disruption from respiratory, cardiovascular or other systemic causes. This review outlines the pathophysiology of obstructive sleep apnoea in particular and how sleep studies have improved our understanding of the complex dynamic changes in blood gas tensions, cardiovascular control and cerebral arousal that occur with these repetitive events. We review the historical development of standard laboratory-based sleep studies and discuss their limitations in staging sleep, reflecting the episodes of increased upper airway resistance that underlie these disorders and their ability to predict individuals' symptoms or response to medical or surgical therapies. We then describe some alternative signals that have been employed to monitor the physiological changes in upper airway resistance and arousal with a discussion of some of the evidence that these 'limited' studies may provide diagnostic information that can guide clinical decision making and may predict the outcome without the need, in some cases, for more complex and costly laboratory-based studies.

Can mandibular advancement devices be a satisfactory substitute for short term use in patients on nasal continuous positive airway pressure?

BACKGROUND

Mandibular advancement devices (MADs) can successfully control both snoring and obstructive sleep apnoea (OSA). Many patients on nasal continuous positive airway pressure (NCPAP) for OSA would like a more portable alternative, even if only temporarily. This study assesses what proportion of patients with OSA already on NCPAP can successfully use a MAD for short periods (up to 1 month) as a temporary alternative to NCPAP.

METHODS

Fifty patients with OSA, already on NCPAP for at least 3 months, were recruited by invitation. They were provided with a simple fixed MAD estimated to provide 75% of maximum mandibular protrusion. Sleep studies using a portable home recorder were performed on and after three nights without NCPAP to provide control data. Following acclimatisation to the MAD, sleep studies were also planned after 3, 7, and 28 days while using the MAD. If their overnight >4% SaO(2) dips per hour deteriorated to >20 or the Epworth sleepiness score (ESS) rose to >9 (or increased by >4 over baseline) on nights 3 or 7, they were then deemed to have failed the trial and were withdrawn.

RESULTS

Of the 50 patients entered, one had inadequate teeth for a MAD and 31 gave up trying to use the device during the acclimatisation period because of side effects. Of the 18 prepared to use the device, two patients failed at night 3, five at night 7, and two at night 28. Thus, nine patients remained controlled by our criteria at night 28. On average, sleep study indices while using the MAD were poor compared with the night on NCPAP.

CONCLUSIONS

Simple MADs are poorly tolerated by patients with OSA already on NCPAP. OSA was adequately controlled by our criteria in 32% of those recruited for the equivalent of a weekend, in 22% for 1 week, and in 18% for up to 1 month. Better tolerated devices would be likely to improve on these figures.

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.

Ambulatory blood pressure after therapeutic and subtherapeutic nasal continuous positive airway pressure for obstructive sleep apnoea: a randomised parallel trial

BACKGROUND

Obstructive sleep apnoea is associated with raised blood pressure. If blood pressure can be reduced by nasal continuous positive airway pressure (nCPAP), such treatment could reduce risk of cardiovascular disease in patients with obstructive sleep apnoea. Our aim was to see whether nCPAP for sleep apnoea reduces blood pressure compared with the most robust control intervention subtherapeutic nCPAP.

METHODS

We did a randomised parallel trial to compare change in blood pressure in 118 men with obstructive sleep apnoea (Epworth score > 9, and a > 4% oxygen desaturation index of > 10 per h) who were assigned to either therapeutic (n=59) or subtherapeutic (59) nCPAP (about 1 cm H(2)O pressure) for 1 month. The primary outcome was the change in 24-h mean blood pressure. Secondary outcomes were changes in systolic, diastolic, sleep, and wake blood pressure, and relations between blood pressure changes, baseline blood pressure, and severity of sleep apnoea.

FINDINGS

Therapeutic nCPAP reduced mean arterial ambulatory blood pressure by 2.5 mm Hg (SE 0.8), whereas subtherapeutic nCPAP increased blood pressure by 0.8 mm Hg (0.7) (difference -3.3 [95% CI -5.3 to -1.3]; p=0.0013, unpaired t test). This benefit was seen in both systolic and diastolic blood pressure, and during both sleep and wake. The benefit was larger in patients with more severe sleep apnoea than those who had less severe apnoea, but was independent of the baseline blood pressure. The benefit was especially large in patients taking drug treatment for blood pressure.

INTERPRETATION

In patients with most severe sleep apnoea, nCPAP reduces blood pressure, providing significant vascular risk benefits, and substantially improving excessive daytime sleepiness and quality of life.

Evidence for persistence of upper airway narrowing during sleep, 12 years after adenotonsillectomy

AIMS

To establish whether subjects with previous evidence of sleep apnoea prior to adenotonsillectomy continue to have evidence of narrower upper airways during sleep, 12 years later.

METHODS

Twenty subjects (median age 16 years) underwent repeat sleep studies at home, 12 years after such studies had shown significant sleep apnoea in many of them prior to an adenotonsillectomy. Twenty control subjects, also studied 12 years ago, underwent repeat home sleep studies as well. The sleep studies provided information on snoring, hypoxia, and inspiratory effort (from measures of pulse transit time). A questionnaire was also administered, the subjects were weighed, and their heights measured.

RESULTS

There was more reported snoring in the previous adenotonsillectomy group (50% versus 20%) and also during the sleep study (80 versus 31 snores per hour). The measure of inspiratory effort overnight was higher in the previous adenotonsillectomy group (15.6 versus 12.3 ms). Allowance for potentially confounding variables (obesity and nasal congestion) partially reduced the statistical significance of the difference in snoring, but not that of the measure of inspiratory effort.

CONCLUSION

Results suggest that a narrower upper airway during sleep, to the point of snoring, persists 12 years after adenotonsillectomy, and may partly account for the occurrence earlier of preoperative sleep apnoea while adenotonsillar hypertrophy was present. It is not known if this narrowing is one of the risk factors for later development of adult sleep apnoea.

Comparison of the effects of sleep deprivation, alcohol and obstructive sleep apnoea (OSA) on simulated steering performance

Patients with obstructive sleep apnoea (OSA) are reported to have an increased risk of road traffic accidents. This study examines the nature of the impairment during simulated steering in patients with OSA, compared to normal subjects following either sleep deprivation or alcohol ingestion. Twenty-six patients with OSA and 12 normal subjects, either deprived of one night's sleep or following alcohol ingestion [mean (SD) alcohol blood level 71.6 mg dl(-1) (19.6)], performed a simulated steering task for a total of 90 min. Performance was measured using the tendency to wander (SD), deterioration across the task, number of 'off-road' events and the reaction time to peripheral events. Control data for OSA, sleep deprivation and alcohol were obtained following treatment with nasal continuous positive airway pressure (nCPAP), after a normal night of sleep, and following no alcohol, respectively. Patients with untreated OSA, and sleep-deprived or alcohol-intoxicated normal subjects performed significantly less well, compared to their respective controls (P<0.01 for all tests), with untreated OSA lying between that of alcohol intoxication and sleep deprivation. Alcohol impaired steering error equally throughout the whole drive, whilst sleep deprivation caused progressive deterioration through the drive, but not initially. Untreated OSA was more like sleep deprivation than alcohol, although there was a wide spread of data. This suggests that the driving impairment in patients with OSA is more compatible with sleep deprivation or fragmentation as the cause, rather than abnormal cognitive or motor skills.

Sleep fragmentation: comparison of two definitions of short arousals during sleep in OSAS patients

The measurement of arousals during sleep is useful to quantify sleep fragmentation. The criteria for electroencephalography (EEG) arousals defined by the American Sleep Disorders Association (ASDA) have recently been criticized because of lack of interobserver agreement. The authors have adopted a scoring method that associates the increase in chin electromyography (EMG) with the occurrence of an alpha-rhythm in all sleep stages (Université Catholique de Louvain (UCL) definition of arousals). The aim of the present study was to compare the two scoring definitions in terms of agreement and repeatability and the time taken for scoring in patients with obstructive sleep apnoea syndrome (OSAS) of varying severity. Two readers using both ASDA and UCL definitions scored twenty polysomnographies (PSGs) each on two occasions. The PSGs were chosen retrospectively to represent a wide range of arousal index (from 6-82) in OSAS patients. There was no difference in the arousal indices between readers and between scoring methods. The mean+/-SD difference between the two definitions (the bias) was 1.1+/-3.76 (95% confidence interval: -0.66-2.86). There was a strong linear relationship between the arousal index scored with the two definitions (r=0.981, p<0.001). Mean+/-SD scoring duration was significantly shorter for UCL than for ASDA definitions (18.5+/-5.4 versus 25.3+/-6.6 min, p<0.001). In conclusion, it has been found that in obstructive sleep apnoea syndrome patients, the American Sleep Disorders Association and Université Catholique de Louvain definitions were comparable in terms of agreement and repeatability.

Charcot-Marie-Tooth disease and sleep apnoea syndrome: a family study

BACKGROUND

Charcot-Marie-Tooth (CMT) disease is a genetically heterogeneous group of hereditary motor and sensory polyneuropathies in which sleep apnoea has rarely been reported and no causal relation shown. We looked for an association between the most common subtype of CMT disease (CMT1A) and sleep apnoea syndrome.

METHODS

Having diagnosed sleep apnoea and CMT in one family member (index case), we prospectively investigated 13 further members not previously suspected of having neuropathy or apnoeas. All had a neurological examination, electroneuromyography, polysomnography, and genetic testing for CMT disease.

FINDINGS

11 of the 14 family members had the autosomal dominant demyelinating form of CMT disease with PMP22 gene duplication on chromosome 17. Whatever their neurological disability, all 11 individuals had sleep apnoea syndrome with a mean (SD) apnoea-hypopnoea index of 46.6/h (28.5) of sleep (normal value <15/h). The remaining three family members were free from neuropathy and sleep apnoea syndrome. Sleep apnoea and neuropathy severity were highly correlated; the compound muscle action potential (CMAP) amplitude of the median nerve was inversely correlated with the apnoea-hypopnoea index (r=-0.69, p=0.029). The severity of neuropathy and sleep apnoea were higher in male CMT individuals and were correlated with age and body mass index. No wake or sleep diaphragmatic dysfunction was shown.

INTERPRETATION

We think that sleep apnoea syndrome is related to a pharyngeal neuropathy. Upper airway dysfunction, previously described in the CMT2C subtype, might be a clinical expression of the CMT1A subtype, to which familial susceptibility could predispose.

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.

Which aspects of breathing during sleep influence the overnight fall of blood pressure in a community population?

BACKGROUND

Obstructive sleep apnoea (OSA) causes recurrent rises in blood pressure during sleep, and recent community surveys have suggested a link between mild OSA and diurnal hypertension. The fact that OSA and hypertension share some risk factors, as well as problems accurately quantifying OSA severity, have diluted the power of such studies. This study tries to circumvent some of these problems by measuring the overnight change in blood pressure and relating it to relevant measures of the severity of upper airway obstruction on the same night.

METHODS

Men born between 1930 and 1960 and their wives living in a market town north of Oxford were identified from a GP practice register. Enough couples were recruited to provide approximately 10 (20 individuals) per year of birth. Subjects were visited at home where a questionnaire was administered, anthropometric measurements made, blood pressures taken (including by the subject), and sensors applied for a subsequent overnight sleep study. The sleep study measured indices of hypoxia, snoring, autonomic arousal, degree of respiratory effort; the last two of these derived from measurements of pulse transit time (indirect beat to beat blood pressure). After waking the following morning, the subjects took their own blood pressures again.

RESULTS

Data were available from 224 couples (448 subjects). On average, systolic BP fell 8 mm Hg from evening to morning. Only hypoxic dips (>4% SaO(2) dips/h) and the measure of degree of respiratory effort were significant independent predictors of this overnight change in systolic BP, together accounting for 7-10% of the variation (p<0.0001). Dividing the subjects into quartiles according to the respiratory effort overnight showed a progressive reduction in the fall of systolic BP overnight: 13.6, 10.8, 7.3, and 5.6 mm Hg, lowest to highest quartiles.

CONCLUSIONS

This study suggests that increased respiratory effort during sleep (seen in OSA and related syndromes of increased upper airway resistance during sleep) offsets the normal fall in BP that occurs overnight, even within this community population. This may be one of the mechanisms by which hypertension is carried over into the waking hours in patients with OSA.

Sleep-related breathing disorders and cardiovascular disease

Sleep-related breathing disorders, ranging from habitual snoring to the increased upper airway resistance syndrome to sleep apnea, are now recognized as major health problems. The majority of patients have excessive daytime sleepiness and tiredness. Neuropsychological dysfunction results in poor work performance, memory impairment, and even depression. Until recently, the coexistence of cardiovascular and cerebrovascular diseases with sleep-related breathing disorders was thought to be the result of shared risk factors, such as age, sex, and obesity. However, in the past 5 years several epidemiologic studies have demonstrated that sleep-related breathing disorders are an independent risk factor for hypertension, probably resulting from a combination of intermittent hypoxia and hypercapnia, arousals, increased sympathetic tone, and altered baroreflex control during sleep. Sleep apnea may lead to the development of cardiomyopathy and pulmonary hypertension. Early recognition and treatment of sleep-related breathing disorders may improve cardiovascular function.