Faculty Bibliography

STUDY OBJECTIVES: Unattended, home-based polysomnography (PSG) is increasingly used in both research and clinical settings as an alternative to traditional laboratory-based studies, although the reliability of the scoring of these studies has not been described. The purpose of this study is to describe the reliability of the PSG scoring in the Sleep Heart Health Study (SHHS), a multicenter study of the relation between sleep-disordered breathing measured by unattended, in-home PSG using a portable sleep monitor, and cardiovascular outcomes. DESIGN: The reliability of SHHS scorers was evaluated based on 20 randomly selected studies per scorer, assessing both interscorer and intrascorer reliability. RESULTS: Both inter- and intrascorer comparisons on epoch-by-epoch sleep staging showed excellent reliability (kappa statistics >0.80), with stage 1 having the greatest discrepancies in scoring and stage 3/4 being the most reliably discriminated. The arousal index (number of arousals per hour of sleep) was moderately reliable, with an intraclass correlation (ICC) of 0.54. The scorers were highly reliable on various respiratory disturbance indices (RDIs), which incorporate an associated oxygen desaturation in the definition of respiratory events (2% to 5%) with or without the additional use of associated EEG arousal in the definition of respiratory events (ICC>0.90). When RDI was defined without considering oxygen desaturation or arousals to define respiratory events, the RDI was moderately reliable (ICC=0.74). The additional use of associated EEG arousals, but not oxygen desaturation, in defining respiratory events did little to increase the reliability of the RDI measure (ICC=0.77). CONCLUSIONS: The SHHS achieved a high degree of intrascorer and interscorer reliability for the scoring of sleep stage and RDI in unattended in-home PSG studies.

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

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

OBJECTIVE: Respiratory abnormalities may play a central role in the pathophysiology of panic disorder. The current study was undertaken to examine the respiratory response in the largest series of subjects to date during three respiratory challenges that used improved methodology. METHOD: Fifty-nine patients with DSM-III-R panic disorder and 39 normal volunteers were challenged with 5% and 7% CO2 inhalation and room air hyperventilation separated by room air breathing with continuous spirometry. RESULTS: Patients with panic disorder were more sensitive to the anxiogenic effects of CO2 than were normal subjects, and CO2 was a more potent stimulus to panic than hyperventilation. Patients increased their respiratory rate more quickly during CO2 inhalation than did comparison subjects, and this increase preceded the panic attacks. Patients who panicked in response to 5% CO2 demonstrated continued rise in end-tidal CO2, while the end-tidal CO2 of the comparison groups stabilized. Low end-tidal CO2 and high variance in minute ventilation at baseline predicted panic attacks during CO2 inhalation. Following CO2 or hyperventilation challenges, respiratory rate dropped sharply, while tidal volume remained elevated longer in patients than in comparison subjects. CONCLUSIONS: The findings confirm the greater behavioral and physiological sensitivity of patients with panic disorder to CO2 inhalation and identify a series of respiratory abnormalities. Panic attacks in panic disorder may be explained by inefficient compensatory mechanisms, primarily of respiratory rate.

Pressure support ventilation (PSV) provides a range of ventilatory support from partial respiratory muscle unloading, where inspiratory work is shared between the patient and the mechanical ventilator, to total respiratory muscle unloading, where inspiratory work is performed solely by the ventilator. This study is designed to determine if minimizing work fully accounts for relief of tachypnea during PSV. We examined respiratory parameters over a range of PSV that includes the crossover from partial to total respiratory muscle unloading. Eight studies were obtained on seven intubated patients in respiratory failure. Ventilation, occlusion pressure (P0.1), and patient inspiratory work (WOBinsp) were measured while PSV was varied. In all patients, WOBinsp decreased as PSV increased. The level of PSV where WOBinsp was minimized was identified; this marked the crossover from partial to total respiratory muscle unloading. Frequency decreased with increasing PSV but remained elevated (range, 22 to 38 breaths/min) at the crossover. Frequency was normalized only at PSV levels 131 to 193% of the levels of pressure at the crossover. Tidal volume (VT) changed little during partial support and averaged 5.9 mL/kg at the crossover. VT increased only on PSV providing total unloading. Six of seven patients exhibited increasing static compliance with increasing VT suggesting alveolar recruitment. P0.1 tracked WOBinsp over the entire range of PSV (r = 0.95, p < 0.001). The normalization of frequency observed above the crossover coincided with increasing VT rather than decreasing work. These observations suggest that reflexes resulting from increased VT and/or alveolar recruitment may have contributed to the normalization of frequency

Many patients with obstructive sleep apnea syndrome (OSAS), despite therapy with nasal continuous positive airway pressure (CPAP), have persisting daytime somnolence that may be due to a persistently elevated upper-airway resistance associated with electroencephalographic (EEG) arousals. We tested the hypothesis that elevated upper-airway resistance can be inferred from the contour of the inspiratory flow tracing obtained from a conventional CPAP circuit. This may provide a noninvasive method for determining optimal CPAP. Data were collected during a CPAP titration of an upper-airway model and in eight patients with OSAS. Estimated inspiratory resistance was calculated from esophageal pressure, CPAP mask pressure, and inspiratory flow. At high CPAP, resistance was low and inspiratory flow contour was found to be rounded. At low CPAP, resistance was high and flow contour developed a plateau suggesting flow limitation. We also noted that the CPAP pressure at which high resistance developed, and at which flow limitation appeared, showed hysteresis. We conclude that when respiration is stable, the contour of inspiratory flow tracing from a CPAP system can be used to infer the presence of elevated upper-airway resistance and flow limitation. Optimizing flow contour may be an alternative to eliminating apneas in evaluation of the optimal therapeutic level of CPAP in OSAS

A study was undertaken to determine whether topographic brain mapping of standard EEG and cognitive evoked potentials would provide additional information for the detection of subtle brain abnormalities associated with obstructive sleep apnea. During nocturnal sleep, significant brain activity was detected in frontal regions not usually monitored with standard sleep recordings. Moreover, preliminary results suggest that total brain activity decreased in association with apneic events and depth of O2 desaturation. Also, component asymmetry in the P300 waveform observed in brain areas not typically recorded improved with treatment. We conclude that the use of topographic mapping adds important information to the study of brain function during sleep and sleep apnea