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

Mandibular Movements are a Reliable Noninvasive Alternative to Esophageal Pressure for Measuring Respiratory Effort in Patients with Sleep Apnea Syndrome

PURPOSE

Differentiation between obstructive and central apneas and hypopneas requires quantitative measurement of respiratory effort (RE) using esophageal pressure (PES), which is rarely implemented. This study investigated whether the sleep mandibular movements (MM) signal recorded with a tri-axial gyroscopic chin sensor (Sunrise, Namur, Belgium) is a reliable surrogate of PES in patients with suspected obstructive sleep apnea (OSA).

PATIENTS AND METHODS

In-laboratory polysomnography (PSG) with PES and concurrent MM monitoring was performed. PSGs were scored manually using AASM 2012 rules. Data blocks (n=8042) were randomly sampled during normal breathing (NB), obstructive or central apnea/hypopnea (OA/OH/CA/CH), respiratory effort-related arousal (RERA), and mixed apnea (MxA). Analyses were evaluation of the similarity and linear correlation between PES and MM using the longest common subsequence (LCSS) algorithm and Pearson's coefficient; description of signal amplitudes; estimation of the marginal effect for crossing from NB to a respiratory disturbance for a given change in MM signal using a mixed linear-regression.

RESULTS

Participants (n=38) had mild to severe OSA (median AH index 28.9/h; median arousal index 23.2/h). MM showed a high level of synchronization with concurrent PES signals. Distribution of MM amplitude differed significantly between event types: median (95% confidence interval) values of 0.60 (0.16-2.43) for CA, 0.83 (0.23-4.71) for CH, 1.93 (0.46-12.43) for MxA, 3.23 (0.72-18.09) for OH, and 6.42 (0.88-26.81) for OA. Mixed regression indicated that crossing from NB to central events would decrease MM signal amplitude by -1.23 (CH) and -2.04 (CA) units, while obstructive events would increase MM amplitude by +3.27 (OH) and +6.79 (OA) units (all p<10^-6).

CONCLUSION

In OSA patients, MM signals facilitated the measurement of specific levels of RE associated with obstructive, central or mixed apneas and/or hypopneas. A high degree of similarity was observed with the PES gold-standard signal.

Polysomnographic Plethysmography Excursions are Reduced in Obese Elderly Men

Sleep apnea is a widespread disorder and is defined by the complete or partial cessation of breathing. Obstructive sleep apnea (OSA) is caused by an obstruction in the upper airway while central sleep apnea (CSA) is characterized by a diminished or absent respiratory effort. It is crucial to differentiate between these respiratory subtypes as they require radically different treatments. Currently, diagnostic polysomnography (PSG) is used to determine respiratory thoracic and abdominal movement patterns using plethysmography belt signals, to distinguish between OSA and CSA. There is significant manual technician interrater variability between these classifications, especially in the evaluation of CSA. We hypothesize that an increased body mass index (BMI) will cause decreased belt signal excursions that increase false scorings of CSA. The hypothesis was investigated by calculating the envelope as a continuous signal of belt signals in 2833 subjects from the MrOS Sleep Study and extracting a mean value of each of the envelopes for each subject. Using linear regression, we found that an increased BMI was associated with lower excursions during REM sleep (-0.013 [mV] thoracic and -0.018 [mV] abdominal, per BMI) and non-REM (-0.014 [mV] thoracic and -0.012 [mV] abdominal, per BMI). We conclude that increased BMI leads to lower excursions in the belt signals during event-free sleep, and that OSA and CSA events are harder to distinguish in subjects with high BMI. This has a major implication for the correct identification of CSA/OSA and its treatment.

Endotyping Sleep Apnea One Breath at a Time: An Automated Approach for Separating Obstructive from Central Sleep Disordered Breathing

Rationale

Determining whether an individual has obstructive or central sleep apnea is fundamental to selecting the appropriate treatment.

Objectives

Here we derive an automated breath-by-breath probability of obstruction, as a surrogate of gold-standard upper airway resistance, using hallmarks of upper airway obstruction visible on clinical sleep studies.

Methods

From five nocturnal polysomnography signals (airflow, thoracic and abdominal effort, oxygen saturation, and snore), nine features were extracted and weighted to derive the breath-by-breath probability of obstruction (P_obs). A development and initial test set of 29 subjects (development = 6, test = 23) (New York, NY) and a second test set of 39 subjects (Solingen, Germany), both with esophageal manometry, were used to develop P_obs and validate it against gold-standard upper airway resistance. A separate dataset of 114 subjects with 2 consecutive nocturnal polysomnographies (New York, NY) without esophageal manometry was used to assess the night-to-night variability of P_obs.

Measurements and Main Results

A total of 1,962,229 breaths were analyzed. On a breath-by-breath level, P_obs was strongly correlated with normalized upper airway resistance in both test sets (set 1: cubic adjusted [adj.] R² = 0.87, P < 0.001, area under the receiver operating characteristic curve = 0.74; set 2: cubic adj. R² = 0.83, P < 0.001, area under the receiver operating characteristic curve = 0.7). On a subject level, median P_obs was associated with the median normalized upper airway resistance (set 1: linear adj. R² = 0.59, P < 0.001; set 2: linear adj. R² = 0.45, P < 0.001). Median P_obs exhibited low night-to-night variability [intraclass correlation(2, 1) = 0.93].

Conclusions

Using nearly 2 million breaths from 182 subjects, we show that breath-by-breath probability of obstruction can reliably predict the overall burden of obstructed breaths in individual subjects and can aid in determining the type of sleep apnea.

Validity analysis of respiratory events of polysomnography using a plethysmography chest and abdominal belt

PURPOSE

Respiratory inductive plethysmography (RIP) is recommended as an alternative respiratory sensor for the identification of each apnea and hypopnea event in polysomnography. Using this sensor, the cumulative RIP results from the chest and abdomen (RIP sum) and time-derived results of the RIP sum (RIP flow) are calculated to track respiratory flow. However, the effectiveness of this sensor and the calculated respiratory results is still unclear, and validation studies for the scoring of respiratory events in polysomnography are rare.

METHODS

Two hundred subjects were selected according to the severity of obstructive sleep apnea. A sleep specialist re-evaluated the respiratory events based on RIP flow data in a single-blind study. Statistical analysis was conducted with paired respiratory events scored in each of the RIP flow and polysomnography datasets.

RESULTS

All respiratory events scored from the RIP flow were strongly correlated with those identified with standard sensors of polysomnography, regardless of disease severity. Most of the respiratory parameters from RIP flow trended toward underestimation. The RIP flow obtained from the alternative RIP sensor was appropriate for the diagnosis of obstructive sleep apnea based on a receiver operating characteristic curve.

CONCLUSIONS

Scored respiratory events from RIP flow data effectively reflected the respiratory flow and statistically correlated with the results from standard polysomnography sensors. Therefore, analyzing RIP flow utilizing an RIP sensor is considered a reliable method for respiratory event scoring.

Respiratory polygraphy in children with sleep-disordered breathing

At-home respiratory polygraphy has been shown to be a reliable substitute for in-laboratory polysomnography in adults for diagnosing obstructive sleep apnea, but this is less well studied in children. One aim of this study was to examine the quality of at-home respiratory polygraphy in children with sleep-disordered breathing and to evaluate the interrater reliability of the results. Another aim was to study whether calibrated respiratory inductance plethysmography (RIP) flow can be used for the scoring of respiratory events when the airflow measurements are unreliable. Children aged 4-10 years, with sleep-disordered breathing, underwent at-home respiratory polygraphy. Of 113 polygraphies, only 46% were of acceptable quality, with missing nasal airflow being the most common problem (40%). The median recorded time with artifact-free signal present in three traces simultaneously was 228 min (0-610 min). Seventeen polygraphy studies were selected for further study. Each study was scored by two independent scorers, with and without the nasal airflow signal present, the latter relying on RIP flow for the scoring of respiratory events. The apnea-hypopnea index (AHI) from the four different measurements was compared using intraclass correlation coefficients (ICC). Comparison of the two scorers showed moderate agreement, with (ICC = 0.66) and without (ICC = 0.53) nasal airflow. One scorer had good agreement between AHI with and without nasal airflow (ICC = 0.81), whereas the other had poor agreement (ICC = 0.12). In conclusion, the scoring of respiratory events based on RIP flow is scorer dependent even for experienced scorers. The nasal airflow signal is frequently missing in paediatric respiratory polygraphies, which limits the usefulness of the method.

[The syndrome of increased upper airways resistance: What are the clinical features and diagnostic procedures?]

The upper airway resistance syndrome "UARS" is a poorly defined entity, often described as a moderate variant of the obstructive sleep apnea syndrome. It is associated with respiratory effort-related arousal, absence of obstructive sleep apnea, and absence of significant desaturation. It is a relatively common condition that predominantly affects non-obese young adults, with no predominance in either sex. The degree of upper airway collapsibility during sleep of patients with UARS is intermediate between that of normal subjects and that of patients with mild-to-moderate sleep apnea syndrome. Craniofacial and palatal abnormalities are often noted. Patients frequently complain of a functional somatic syndrome, especially daytime sleepiness and chronic fatigue. Polysomnography with esophageal pressure measurements remains the gold standard diagnostic test. The absence of any neurological abnormality gives UARS a good prognosis and it is potentially reversible if treated early. However, some studies suggest that untreated UARS has an increased risk of arterial hypertension. It can also evolve into obstructive sleep apnea.

The role of flow limitation as an important diagnostic tool and clinical finding in mild sleep-disordered breathing

Obstructive sleep apnea (OSA) is defined by quantifying apneas and hypopneas along with symptoms suggesting sleep disruption. Subtler forms of sleep-disordered breathing can be missed when this criteria is used. Newer technologies allow for non-invasive detection of flow limitation, however consensus classification is needed. Subjects with flow limitation demonstrate electroencephalogram changes and clinical symptoms indicating sleep fragmentation. Flow limitation may be increased in special populations and treatment with nasal continuous positive airway pressure (CPAP) has been shown to improve outcomes. Titrating CPAP to eliminate flow limitation may be associated with improved clinical outcomes compared to treating apneas and hypopneas.

Rules for scoring respiratory events in sleep: update of the 2007 AASM Manual for the Scoring of Sleep and Associated Events. Deliberations of the Sleep Apnea Definitions Task Force of the American Academy of Sleep Medicine

The American Academy of Sleep Medicine (AASM) Sleep Apnea Definitions Task Force reviewed the current rules for scoring respiratory events in the 2007 AASM Manual for the Scoring and Sleep and Associated Events to determine if revision was indicated. The goals of the task force were (1) to clarify and simplify the current scoring rules, (2) to review evidence for new monitoring technologies relevant to the scoring rules, and (3) to strive for greater concordance between adult and pediatric rules. The task force reviewed the evidence cited by the AASM systematic review of the reliability and validity of scoring respiratory events published in 2007 and relevant studies that have appeared in the literature since that publication. Given the limitations of the published evidence, a consensus process was used to formulate the majority of the task force recommendations concerning revisions.The task force made recommendations concerning recommended and alternative sensors for the detection of apnea and hypopnea to be used during diagnostic and positive airway pressure (PAP) titration polysomnography. An alternative sensor is used if the recommended sensor fails or the signal is inaccurate. The PAP device flow signal is the recommended sensor for the detection of apnea, hypopnea, and respiratory effort related arousals (RERAs) during PAP titration studies. Appropriate filter settings for recording (display) of the nasal pressure signal to facilitate visualization of inspiratory flattening are also specified. The respiratory inductance plethysmography (RIP) signals to be used as alternative sensors for apnea and hypopnea detection are specified. The task force reached consensus on use of the same sensors for adult and pediatric patients except for the following: (1) the end-tidal PCO(2) signal can be used as an alternative sensor for apnea detection in children only, and (2) polyvinylidene fluoride (PVDF) belts can be used to monitor respiratory effort (thoracoabdominal belts) and as an alternative sensor for detection of apnea and hypopnea (PVDFsum) only in adults.The task force recommends the following changes to the 2007 respiratory scoring rules. Apnea in adults is scored when there is a drop in the peak signal excursion by ≥ 90% of pre-event baseline using an oronasal thermal sensor (diagnostic study), PAP device flow (titration study), or an alternative apnea sensor, for ≥ 10 seconds. Hypopnea in adults is scored when the peak signal excursions drop by ≥ 30% of pre-event baseline using nasal pressure (diagnostic study), PAP device flow (titration study), or an alternative sensor, for ≥ 10 seconds in association with either ≥ 3% arterial oxygen desaturation or an arousal. Scoring a hypopnea as either obstructive or central is now listed as optional, and the recommended scoring rules are presented. In children an apnea is scored when peak signal excursions drop by ≥ 90% of pre-event baseline using an oronasal thermal sensor (diagnostic study), PAP device flow (titration study), or an alternative sensor; and the event meets duration and respiratory effort criteria for an obstructive, mixed, or central apnea. A central apnea is scored in children when the event meets criteria for an apnea, there is an absence of inspiratory effort throughout the event, and at least one of the following is met: (1) the event is ≥ 20 seconds in duration, (2) the event is associated with an arousal or ≥ 3% oxygen desaturation, (3) (infants under 1 year of age only) the event is associated with a decrease in heart rate to less than 50 beats per minute for at least 5 seconds or less than 60 beats per minute for 15 seconds. A hypopnea is scored in children when the peak signal excursions drop is ≥ 30% of pre-event baseline using nasal pressure (diagnostic study), PAP device flow (titration study), or an alternative sensor, for ≥ the duration of 2 breaths in association with either ≥ 3% oxygen desaturation or an arousal. In children and adults, surrogates of the arterial PCO(2) are the end-tidal PCO(2) or transcutaneous PCO(2) (diagnostic study) or transcutaneous PCO(2) (titration study). For adults, sleep hypoventilation is scored when the arterial PCO(2) (or surrogate) is > 55 mm Hg for ≥ 10 minutes or there is an increase in the arterial PCO(2) (or surrogate) ≥ 10 mm Hg (in comparison to an awake supine value) to a value exceeding 50 mm Hg for ≥ 10 minutes. For pediatric patients hypoventilation is scored when the arterial PCO(2) (or surrogate) is > 50 mm Hg for > 25% of total sleep time. In adults Cheyne-Stokes breathing is scored when both of the following are met: (1) there are episodes of ≥ 3 consecutive central apneas and/or central hypopneas separated by a crescendo and decrescendo change in breathing amplitude with a cycle length of at least 40 seconds (typically 45 to 90 seconds), and (2) there are five or more central apneas and/or central hypopneas per hour associated with the crescendo/decrescendo breathing pattern recorded over a minimum of 2 hours of monitoring.

[Diagnostic criteria and treatment for sleep-disordered breathing: RERA]

In polysomnography, RERA is defined as a respiratory parameter that indicates an arousal associated with a respiratory event and an increase in respiratory effort. Initially, RERA was described by means of esophageal manometry for the evaluation of respiratory effort. This greater respiratory effort occurs as a response to an increase in upper airway resistance, which is a factor present in the pathophysiology of sleep-disordered breathing, such as obstructive sleep apnea syndrome and upper airway resistance syndrome. Later, the use of a nasal pressure cannula was reported to be a reliable means of identifying airflow limitation and one that is more sensitive than is a thermistor. In addition, the nasal pressure cannula method has been used as a surrogate for esophageal manometry in the identification of periods in which upper airway resistance increases. Consequently, the American Academy of Sleep Medicine recommend the use of either method for the identification of RERA, which is defined by the flattening of the inspiratory curve, characteristic of airflow limitation. Although RERA has been identified and evaluated in current medical practice, it has yet to be standardized. Therefore, it is recommended that polysomnographic reports indicate which abnormal respiratory events were taken into consideration in the evaluation of the severity of sleep-disordered breathing.

Utility of split-night polysomnography in the diagnosis of upper airway resistance syndrome

PURPOSE

Split-night polysomnography can both establish the diagnosis and titrate continuous positive airway pressure (CPAP) during a single study in patients with sleep-disordered breathing. We sought to determine if split-night polysomnography could be effectively used in upper airway resistance syndrome (UARS) without diminishing diagnostic accuracy or success of CPAP titration.

METHODS

Consecutive patients diagnosed with UARS were included. Split-night studies were performed in patients meeting predefined criteria. We compared data between those undergoing traditional and split-night polysomnography.

RESULTS

We included 100 consecutive patients (41.2 +/- 7.4 years, 54% men). Forty-six underwent split-night polysomnography. Groups were similar at baseline. There were no differences in polysomnography or success rate of CPAP titration. Among those not undergoing split-night studies, the mean time between diagnostic polysomnography and CPAP titration was 71.9 +/- 49.0 days.

CONCLUSIONS

Split-night polysomnography can be effectively utilized to diagnose UARS and initiate CPAP therapy. This practice can reduce the number of studies needed and obviate the inherent delay in initiating CPAP therapy.

Diagnosis and Evaluation of Obstructive Sleep Apnoea in Children

Introduction: The aim of this article is to review the medical literature and describe clinical and laboratory findings in children with obstructive sleep apnoea (OSA) to differentiate children with OSA from those with primary snoring or other disorders, with a particular focus on Asian children. Methods: Medline search via Pub Med, search terms sleep apnoea and children; and sleep apnoea and children and Asian. Results and Conclusions: Children with OSA usually present with snoring, daytime sleepiness, and/or difficulties in school or behaviour. The prevalence of OSA in Asian children is less than that of other groups, but the severity of the disorder on presentation may be greater. Overnight polysomnography remains the diagnostic “gold standard”; limited studies, or studies in the home, are not sufficient to exclude OSA in a child with suggestive symptoms, nor can they reliably assess the severity of the disorder which is important in planning treatment. Limited studies may, however, be useful in large-scale research studies. Key words: Asian, Polysomnography, Sleep studies, Snoring

Childhood obstructive sleep-disordered breathing: a clinical update and discussion of technological innovations and challenges

Childhood sleep-disordered breathing (SDB) has been known to be associated with health and cognitive impacts for more than a century, and yet our understanding of this disorder is in its infancy. Neuropsychological consequences in children with snoring or subtle breathing disturbances not meeting the traditional definition of sleep apnea suggest that "benign, or primary snoring" may be clinically significant, and that the true prevalence of SDB might be underestimated. There is no standard definition of SDB in children. The polysomnographic technology used in many sleep laboratories may be inadequate to diagnose serious but subtle forms of clinically important airflow limitation. In the last several years, advances in digital technology as well as new observational studies of respiratory and arousal patterns in large populations of healthy children have led to alternative views of what constitutes sleep-related breathing and arousal abnormalities that may refine our diagnostic criteria. This article reviews our knowledge of childhood SDB, highlights recent advances in technology, and discusses diagnostic and treatment strategies that will advance the management of children with pediatric SDB.

Improved detection of obstructive events in childhood sleep apnoea with the use of the nasal cannula and the differentiated sum signal

The efficacy of the nasobuccal thermistor (NT) was compared with the nasal pressure cannula (NC) and the calibrated, time-differentiated respiratory inductance plethysmography sum signal (DS) in the detection of obstructive events in children during polysomnography (PSG). The overnight PSG of 20 consecutive referrals were selected for analysis. Obstructive events were scored in each study three times by one operator using a blinded procedure whereby either the NT, the NC or the DS was visible. The standard PSG channels were also visible. SPSS software was used for statistical analysis. Twenty patients aged 5 weeks to 16 years were studied. Agreement in obstructive apnoea-hypopnoea index (OAHI) was highest between the NT and NC, and the NC and DS. The NC signal was significantly more likely to be uninterpretable than the NT (P = 0.02) and this did not correlate with age. Event detection by the NT was significantly improved by the addition of either the NC (P = 0.01) or the DS (P = 0.001), while the NC stood alone unless the DS was added (P = 0.02). There was no significant difference in OAHI by the NC versus the DS. The NC detected significantly more OA than the NT or the DS (P = 0.04), while the DS trended towards detecting more OH. There was no significant difference in OAHI between any combination pair. The nasal cannula and differentiated sum signal perform better as measures of paediatric airflow than the NT. To optimize the detection of obstructive events in children we recommend using at least one, if not both these methods in paediatric sleep laboratories.

Alveolar recruitment in acute lung injury

Alveolar recruitment is one of the primary goals of respiratory care for acute lung injury. It is aimed at improving pulmonary gas exchange and, even more important, at protecting the lungs from ventilator-induced trauma. This review addresses the concept of alveolar recruitment for lung protection in acute lung injury. It provides reasons for why atelectasis and atelectrauma should be avoided; it analyses current and future approaches on how to achieve and preserve alveolar recruitment; and it discusses the possibilities of detecting alveolar recruitment and derecruitment. The latter is of particular clinical relevance because interventions aimed at lung recruitment are often undertaken without simultaneous verification of their effectiveness.

Upper airway resistance syndrome--one decade later

PURPOSE OF REVIEW

The term upper airway resistance syndrome (UARS) was coined to describe a group of patients who did not meet the criteria for diagnosis of obstructive apnea-hypopnea syndrome and thus were left untreated. Today, most of the patients with UARS remain undiagnosed and are left untreated.

RECENT FINDINGS

Today, the clinical picture of UARS is better defined. We have learned that patients usually seek treatment with a somatic functional syndrome rather than sleep-disordered breathing or even a disorder of excessive daytime sleepiness. Therefore, most of these patients are seen by psychiatrists. In addition, recent technologic advances have allowed a better recognition of the problem. We have learned that obstructive apnea-hypopnea syndrome is associated with a local neurologic impairment that is responsible for the occurrence of the hypopnea and apneas. In contrast, patients with UARS have an intact local neurologic system and have the ability to respond to minor changes in upper airway dimension and resistance to airflow. New treatment options including internal jaw distraction osteogenesis are used and are promising for treatment of patients with UARS.

SUMMARY

The clinical presentation of patients with UARS is similar to the presentation of subjects with functional somatic syndrome. To diagnose UARS, nocturnal polysomnography should include additional measurement channels.

Effects of Mechanical Insufflation-Exsufflation on Respiratory Parameters for Patients With Chronic Airway Secretion Encumbrance

STUDY OBJECTIVES

To analyze the physiologic effects and tolerance of mechanical insufflation-exsufflation (MI-E) for patients with chronic ventilatory failure of various etiologies.

DESIGN

Prospective clinical trial.

SETTING

Rehabilitation unit of a university hospital.

PATIENTS OR PARTICIPANTS

Thirteen patients with amyotrophic lateral sclerosis (ALS), 9 patients with severe COPD, and 7 patients with other neuromuscular disorders (oNMDs) with chronic airway secretion encumbrance and decreases in oxyhemoglobin saturation (Spo(2)).

INTERVENTIONS

Pressures of MI-E of 15 cm H(2)O, 30 cm H(2)O, and 40 cm H(2)O were cycled to each patient, with 3 s for insufflation and 4 s for exsufflation. One application was six cycles at each pressure for a total of three applications.

MEASUREMENTS AND RESULTS

We continuously evaluated respiratory inductance plethysmography (RIP) and Spo(2) during every application. Peak cough flow (PCF) and dyspnea (Borg Scale) were also measured before the first and after the last application. The technique was well tolerated in all patient groups. Median Spo(2) improved significantly (p < 0.005) in all patient groups. Median PCF improved significantly (p < 0.005) in the ALS and oNMD groups from 170 to 200 L/min and from 180 to 220 L/min, respectively, and dyspnea improved significantly in the patients with oNMDs and patients with COPD from 3 to 1 and from 2 to 0.75, respectively. Breathing pattern characteristics (RIP) did not deteriorate after MI-E in any patient groups. Inspiratory flow limitation significantly decreased at the highest MI-E pressures for the ALS group.

CONCLUSIONS

Our results confirm good tolerance and physiologic improvement in patients with restrictive disease and in patients with obstructive disease, suggesting that MI-E may be a potential complement to noninvasive ventilation for a wide variety of patient groups.

Noninvasive determination of upper airway resistance and flow limitation

We have shown that a polynomial equation, FP = AP3 + BP2 + CP + D, where F is flow and P is pressure, can accurately determine the presence of inspiratory flow limitation (IFL). This equation requires the invasive measurement of supraglottic pressure. We hypothesized that a modification of the equation that substitutes time for pressure would be accurate for the detection of IFL and allow for the noninvasive measurement of upper airway resistance. The modified equation is Ft = At3 + Bt2 + Ct + D, where F is flow and t is time from the onset of inspiration. To test our hypotheses, data analysis was performed as follows on 440 randomly chosen breaths from 18 subjects. First, we performed linear regression and determined that there is a linear relationship between pressure and time in the upper airway (R2 0.96 +/- 0.05, slope 0.96 +/- 0.06), indicating that time can be a surrogate for pressure. Second, we performed curve fitting and found that polynomial equation accurately predicts the relationship between flow and time in the upper airway (R2 0.93 +/- 0.12, error fit 0.02 +/- 0.08). Third, we performed a sensitivity-specificity analysis comparing the mathematical determination of IFL to manual determination using a pressure-flow loop. Mathematical determination had both high sensitivity (96%) and specificity (99%). Fourth, we calculated the upper airway resistance using the polynomial equation and compared the measurement to the manually determined upper airway resistance (also from a pressure-flow loop) using Bland-Altman analysis. Mean difference between calculated and measured upper airway resistance was 0.0 cmH2O x l(-1) x s(-1) (95% confidence interval -0.2, 0.2) with upper and lower limits of agreement of 2.8 cmH2O x l(-1) x s(-1) and -2.8 cmH2O x l(-1) x s(-1). We conclude that a polynomial equation can be used to model the flow-time relationship, allowing for the objective and accurate determination of upper airway resistance and the presence of IFL.

[Sleepy drivers have a high frequency of traffic accidents related to respiratory effort-related arousals]

INTRODUCTION

Respiratory effort-related arousals (RERA) are secondary to subtle obstructions of the upper airway during sleep and can appear in the absence of a predominance of apneas and hypopneas, causing excessive daytime sleepiness. Analyzing the possible consequences of these new respiratory events is of increasing interest. Habitually sleepy drivers are at high risk of having traffic accidents related to sleep disorders (apneas, hypopneas and RERA).

OBJECTIVE

The aim of this study was to determine whether excess RERA alone is an independent risk factor among sleepy drivers.

METHOD

We studied 40 habitually sleepy drivers and 23 age- and sex-matched controls selected from a sample of 4,002 automobile drivers. We surveyed sleep habits, daytime sleepiness and traffic accidents. Sleep studies of esophageal pressure were performed.

RESULTS

The sleepy drivers with apneas (apnea/hypopnea index > 10) had a higher 5-year accident rate (0.33 0.50) than did control drivers (0.004 0.21; p < 0.05). However, a high RERA index, but not sleep apnea, was an independent risk factor among the habitually sleepy drivers. The adjusted odds ratio (OR) for a RERA index > or = 10 was 7.6 (confidence interval [CI], 1.2 to 48); for a RERA index > or = 15, the OR was 17 (CI 1.5 to 91).

CONCLUSIONS

The high risk of traffic accidents among sleepy drivers is mainly determined by the presence of RERA rather than the presence of apneas and hypopneas. These findings verify the importance of identifying RERA in routine sleep laboratory studies.

The upper airway in sleep: physiology of the pharynx

The upper airway is the primary conduit for passage of air into the lungs. Its physiology has been the subject of intensive study: both passive mechanical and active neural influences contribute to its patency and collapsibility. Different models can be used to explain behavior of the upper airway, including the "balance of forces" (airway suction pressure during inspiration versus upper airway dilator tone) and the Starling resistor mechanical model. As sleep is the primary state change responsible for sleep disordered breathing (SDB) and the obstructive apnea/hypopnea syndrome (OSAHS), understanding its effects on the upper airway is critical. These include changes in upper airway muscle dilator activity and associated changes in mechanics and reflex activity of the muscles. Currently SDB is thought to result from a combination of anatomical upper airway predisposition and changes in neural activation mechanisms intrinsic to sleep. Detection of SDB is based on identifying abnormal (high resistance) breaths and events, but the clinical tools used to detect these events and an understanding of their impact on symptoms is still evolving. Outcomes research to define which events are most important, and a better understanding of how events lead to physiologic consequences of the syndrome, including excessive daytime somnolence (EDS), will allow physiologic testing to objectively differentiate between "normal" subjects and those with disease.

Obstructive sleep apnoea

Obstructive sleep apnoea is a disease of increasing importance because of its neurocognitive and cardiovascular sequelae. Abnormalities in the anatomy of the pharynx, the physiology of the upper airway muscle dilator, and the stability of ventilatory control are important causes of repetitive pharyngeal collapse during sleep. Obstructive sleep apnoea can be diagnosed on the basis of characteristic history (snoring, daytime sleepiness) and physical examination (increased neck circumference), but overnight polysomnography is needed to confirm presence of the disorder. Repetitive pharyngeal collapse causes recurrent arousals from sleep, leading to sleepiness and increased risk of motor vehicle and occupational accidents. The surges in hypoxaemia, hypercapnia, and catecholamine associated with this disorder have now been implicated in development of hypertension, but the association between obstructive sleep apnoea and myocardial infarction, stroke, and congestive heart failure is not proven. Continuous positive airway pressure, the treatment of choice for obstructive sleep apnoea, reduces sleepiness and improves hypertension.

Classification of sleep-disordered breathing

Increasing recognition of sleep-disordered breathing (SDB) and its morbidity have prompted reevaluation of techniques to identify respiratory events during sleep. The present study was designed to evaluate the utility of various metrics of SDB and to identify the optimal respiratory metric that objectively correlates to symptoms of excessive daytime somnolence (EDS). Metrics were derived from combinations of conventional apnea/hypopnea, flow limitation events (transient elevated upper airway resistance identified by characteristic flattening on the flow/time tracing, using a noninvasive nasal cannula technique), desaturation, and arousal. A total of 137 subjects underwent clinical evaluation and nocturnal polysomnogram. In 34 randomly selected subjects, the best metrics for discriminating between 13 subjects with no EDS/snoring and 21 patients with EDS and snoring were identified by receiver operator curve analysis. Of the metrics and cut points tested, a total respiratory disturbance index (RDI(Total), sum of apneas, hypopnea, and flow limitation events) of 18 events/h was found to have the best discriminant ability (100% sensitivity and 96% specificity). Prospective testing of this metric was then performed with the remaining 103 subjects (14 nonsnoring non-EDS, 21 snoring non-EDS, 68 snoring with EDS). Using this cutoff of 18 events/h, we obtained 71% sensitivity and 60% specificity for identifying subjects with EDS. We conclude that, in subjects with upper airway dysfunction, an index that incorporates all respiratory events provides the best quantitative physiological correlate to EDS.

Follow-up of primary snoring in children

We reevaluated 13 children with primary snoring 3 years after their original polysomnograms were performed and compared them with healthy control subjects. As a group, the patients' snoring and polysomnographic findings did not change. There was no difference in any sleep-disordered breathing of the patients and control subjects. Only the youngest individual in the study developed frank obstructive sleep apnea. Children with primary snoring are not likely to develop polysomnography-confirmed obstructive sleep apnea, and it is safe to defer treatment.

Comparison of respiratory polysomnographic parameters in matched cohorts of upper airway resistance and obstructive sleep apnea syndrome patients

OBJECTIVE

To compare respiratory nocturnal polysomnography (NPSG) characteristics between matched cohorts of upper airway resistance syndrome (UARS) and obstructive sleep apnea syndrome (OSAS) patients.

METHODS

All patients received 13-channel NPSG, including esophageal pressure (Pes) manometry. By definition, OSAS patients had an apnea-hypopnea index (AHI, number of apneas/hypopneas per hour total sleep time) > or = 15, and UARS patients had an AHI < 5. Respiratory effort-related arousal (RERA) was defined as the absence of apnea/hypopnea with > or = 10 s duration of progressive negative Pes, culminating in an arousal or microarousal. UARS patients, by definition, had > or = 15 RERAs per hour. Fifteen consecutively diagnosed UARS patients were matched with OSAS patients on the basis of body mass index (BMI) and gender.

RESULTS

Respiratory disturbance index (sum of the AHI and RERA per hour) was the same for both cohorts: UARS, 36+/-4; OSAS, 42+/-6 (p = 0.34). There were no differences between cohorts for mean inspiratory Pes nadirs for each 30-s epoch of sleep compared for each sleep stage over an entire night. For randomly selected breaths from supine stage 2 sleep, the mean inspiratory Pes nadir was the same for the cohorts: UARS, -16.6+/-2 cm H2O; OSAS, -16.1+/-3 cm H2O (p = 0.30). Differences between cohorts for each parameter fell within respective 95% confidence intervals.

CONCLUSION

With the exception of AHI, respiratory NPSG parameters were the same for UARS and OSAS patients when BMI and gender were controlled for.