Faculty Bibliography

OBJECTIVES: To examine the relative temporal appearance of flow limitation and snoring during continuous positive airway pressure (CPAP) titration, compare their sensitivity as indicators of airway obstruction, and assess their relative utility as feedback variables for automatic titration of CPAP. DESIGN: Retrospective review of data. SETTING: University teaching hospital. PATIENTS: Fifty-three patients diagnosed as having obstructive sleep apnea or upper airway resistance syndrome undergoing CPAP titration. MEASUREMENTS AND RESULTS: We used a prototype automatic CPAP device that adjusts pressure in response to apnea, snoring, and/or flow limitation. The present study takes advantage of the frequent automatic decreases in pressure from a therapeutic level, as well as any technician-initiated decreases in pressure. We tabulated, for each pressure decrease of >0.4 cm H2O, the occurrences of snoring alone, flow limitation alone, or simultaneous appearance of both. Of 2,177 automatic pressure decreases, 64% resulted in flow limitation alone, 8% in snoring alone, and 22% in the simultaneous occurrence of both. Overall, 86% of decreases resulted in flow limitation alone or were simultaneous with snoring, whereas 30% of decreases resulted in snoring alone or were simultaneous with flow limitation. In 10 of 35 patients, snoring alone occurred in > 10% of the pressure decreases. In all but 5 of 133 manual pressure decreases, flow limitation developed at or above the pressure at which snoring developed. CONCLUSIONS: While detection of snoring occasionally provided additional information, overall flow limitation was the earliest indicator of obstruction during decreases in CPAP

We previously showed that upper airway resistance can be inferred from the inspiratory flow contour during continuous positive airway pressure (CPAP) titration in obstructive sleep apnea syndrome (OSAS). The present study examines whether similar information can be obtained from inspiratory flow measured by a nasal cannula/pressure transducer. Ten symptomatic patients (snoring, upper airway resistance syndrome [UARS], or OSAS) and four asymptomatic subjects underwent nocturnal polysomnography (NPSG) with monitoring of flow (nasal cannula) and respiratory driving pressure (esophageal or supraglottic catheter). For each breath the inspiratory flow signal was classified as normal, flattened, or intermediate by custom software. 'Resistance' was calculated from peak inspiratory flow and pressure, and normalized to the resistance during quiet wakefulness. Resistance in all stages of sleep was increased for breaths with flattened (387 +/- 188%) or intermediate (292 +/- 163%) flow contour. In combination with apnea-hypopnea index (AHI), identification of 'respiratory events,' consisting of consecutive breaths with a flattened contour, allowed differentiation of symptomatic from asymptomatic subjects. Our data show that development of a plateau on the inspiratory flow signal from a nasal cannula identifies increased upper airway resistance and the presence of flow limitation. In patients with symptoms of excessive daytime somnolence and low AHI this may help diagnose the UARS and separate it from nonrespiratory causes of sleep fragmentation

Narcolepsy is a central nervous system disorder characterized by excessive daytime sleepiness and cataplexy. This placebo-controlled, double-blind, randomized, parallel-group, 18-center study assessed the efficacy and safety of modafinil, a new wake-promoting drug for treating sleepiness in narcolepsy. Subjects with narcolepsy (n = 283) received daily modafinil, 200 or 400 mg, or placebo, for 9 weeks, followed by an open-label treatment period. Subjective sleepiness was measured with the Epworth Sleepiness Scale. Objective sleepiness was assessed with the Multiple Sleep Latency Test and the Maintenance of Wakefulness Test. Level of illness was measured with the Clinical Global Impression of Change. Modafinil significantly reduced all measures of sleepiness and was associated with significant improvements in level of illness. Medication-related adverse experiences were few, dose-dependent, and mostly rated mild to moderate. Modafinil taken once daily was a very well tolerated and effective wake-promoting agent in the treatment of excessive daytime somnolence associated with narcolepsy. Modafinil demonstrated an excellent safety profile for up to 40 weeks of open-label treatment and efficacy was maintained, suggesting that tolerance will not develop with long-term use. Modafinil is a pharmacologically and clinically promising compound for the treatment of pathological daytime somnolence

Recording of respiratory airflow is an integral part of polysomnography (NPSG). It is conventionally monitored with a thermistor that measures temperature as a surrogate of flow. The subjectivity of interpreting hypopnea from this signal has prompted us to measure nasal airflow directly with a simple pneumotachograph consisting of a standard nasal cannula connected to a 2-cm H2O pressure transducer. We manually analyzed respiratory events using simultaneous thermistor and nasal cannula in 11 patients with obstructive sleep apnea syndrome (OSAS) and 9 with upper airway resistance syndrome (UARS). Definite events were scored separately for each signal when amplitude was <50% for >10 seconds. Events were also scored on the nasal cannula signal when the flattened shape of the signal suggested flow limitation, and these were tabulated separately. Definite events in one signal were tabulated by whether the other signal showed a definite event or not. In addition, nasal cannula events were compared to a more liberal thermistor criterion (any change in the signal for > or = 2 breaths). Visually, events were more easily recognized on the nasal cannula signal than on the thermistor signal. In OSAS, 1,873 definite thermistor events were detected. Of these, 99.1% were detected by nasal cannula, and 0.9% were missed. Of 3,541 definite nasal cannula events, 51.9% were detected by definite thermistor criteria; 75.0% were detected by liberal thermistor criteria; 25.0% were missed. In UARS, 123 definite thermistor events were detected. Of these, 89.4% were detected by nasal cannula and 10.6% were missed. Nine hundred and three nasal cannula events were detected. However, only 17.2% of these were detected by definite thermistor criteria; 38.6% were detected by liberal thermistor criteria; 61.4% were completely undetected by thermistor. When events identified on the nasal cannula by flow limitation alone were excluded, the thermistor detected 30.1% of events by definite criteria and 78.6% by liberal criteria, still leaving 21.4% completely undetected by the thermistor. We conclude that the nasal cannula reliably detects respiratory events seen by thermistor. Additional events (including some characterized only by flow limitation) that help define the UARS, were recognized by nasal cannula but often completely missed by thermistor. We propose that respiratory monitoring during NPSG with nasal cannula significantly improves event detection and classification over that with thermistor

The comparability among epidemiological surveys of sleep disorders has been encumbered because of the array of methodologies used from study to study. The present international initiative addresses this limitation. Many such studies using the exact same methodology are being completed in six European countries (France, the United Kingdom, Germany, Italy, Portugal, and Spain), two Canadian cities (metropolitan areas of Montreal and Toronto), New York State, and the city of San Francisco. These surveys have been undertaken with the aim of documenting the prevalence of sleep disorders in the general population according to criteria of the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) and the International Classification of Sleep Disorders (ICSD-90). Data are gathered over the telephone by lay interviewers using the Sleep-EVAL expert system. This paper describes the methodology involved in the realization of these studies. Sample design and selection procedures are discussed

The Sleep Heart Health Study (SHHS) is a prospective cohort study designed to investigate obstructive sleep apnea (OSA) and other sleep-disordered breathing (SDB) as risk factors for the development of cardiovascular disease. The study is designed to enroll 6,600 adult participants aged 40 years and older who will undergo a home polysomnogram to assess the presence of OSA and other SDB. Participants in SHHS have been recruited from cohort studies in progress. Therefore, SHHS adds the assessment of OSA to the protocols of these studies and will use already collected data on the principal risk factors for cardiovascular disease as well as follow-up and outcome information pertaining to cardiovascular disease. Parent cohort studies and recruitment targets for these cohorts are the following: Atherosclerosis Risk in Communities Study (1,750 participants), Cardiovascular Health Study (1,350 participants), Framingham Heart Study (1,000 participants), Strong Heart Study (600 participants), New York Hypertension Cohorts (1,000 participants), and Tucson Epidemiologic Study of Airways Obstructive Diseases and the Health and Environment Study (900 participants). As part of the parent study follow-up procedures, participants will be surveyed at periodic intervals for the incidence and recurrence of cardiovascular disease events. The study provides sufficient statistical power for assessing OSA and other SDB as risk factors for major cardiovascular events, including myocardial infarction and stroke