Toothbrush efficacy for plaque removal.

OBJECTIVES: To determine the effectiveness of a novel sonic toothbrush in reducing plaque and in maintenance of gingival health when compared to a standard manual brush. METHODS: This study was a block-randomized, examiner-blind, two-treatment, parallel group, single centre clinical investigation. A total of 84 subjects were enrolled and randomly assigned to receive either the Panasonic EW-DL90 or an American Dental Association-endorsed manual toothbrush. Subjects were instructed to follow a twice-daily brushing regimen without flossing. Plaque levels and gingival health were assessed at baseline and after 1 and 3 weeks of treatment using the Turesky Modification of the Quigley-Hein Plaque Index and the Papillary Bleeding Score. RESULTS: Subjects assigned to the EW-DL90 group had significantly lower plaque levels after 1 and 3 weeks of treatment than those in the manual group (P = 0.003 and 0.0035, respectively). Both groups showed a reduction in plaque levels at Week 3 relative to baseline. The EW-DL90 group had significantly lower gingival inflammation scores after 1 week of treatment (P = 0.0293), but there was no difference between groups after 3 weeks of treatment. CONCLUSION: The EW-DL90 toothbrush safely and effectively removes more plaque than a standard manual toothbrush. Improvement in gingival inflammation was observed after 1 week of treatment. There was no difference in Papillary Bleeding Score between the two groups after 3 weeks of treatment. CLINICAL SIGNIFICANCE: The newly developed sonic brush (Panasonic EW-DL90) tested in this study was found to be more effective than a manual toothbrush at plaque removal. The papillary bleeding scores were significantly lower in the sonic brush group after 1 week of product use. After 3 weeks of product use, both treatment groups had similar papillary bleeding scores almost returning to baseline values.

HIV infection affects Streptococcus mutans levels, but not genotypes.

We report a clinical study that examines whether HIV infection affects Streptococcus mutans colonization in the oral cavity. Whole stimulated saliva samples were collected from 46 HIV-seropositive individuals and 69 HIV-seronegative control individuals. The level of S. mutans colonization was determined by conventional culture methods. The genotype of S. mutans was compared between 10 HIV-positive individuals before and after highly active antiretroviral therapy (HAART) and 10 non-HIV-infected control individuals. The results were analyzed against viral load, CD4+ and CD8+ T-cell counts, salivary flow rate, and caries status. We observed that S. mutans levels were higher in HIV-infected individuals than in the non-HIV-infected control individuals (p = 0.013). No significant differences in S. mutans genotypes were found between the two groups over the six-month study period, even after HAART. There was a bivariate linear relationship between S. mutans levels and CD8+ counts (r = 0.412; p = 0.007), but not between S. mutans levels and either CD4+ counts or viral load. Furthermore, compared with non-HIV-infected control individuals, HIV-infected individuals experienced lower salivary secretion (p = 0.009) and a positive trend toward more decayed tooth surfaces (p = 0.027). These findings suggest that HIV infection can have a significant effect on the level of S. mutans, but not genotypes.

Are procedures performed by dental auxiliaries safe and of comparable quality? A systematic review.

The objective of the current study was to systematically evaluate the existing evidence in relation to the safety, quality, productivity or cost-benefit, and patient satisfaction of the procedures performed by the different groups of dental providers. Due to the diversity of the procedures performed and the outcomes measured, it was not possible to create pooled estimates in a meaningful manner. Therefore, summary results of individual studies are presented and critically evaluated.

Periodontal pathogens and gestational diabetes mellitus.

In previous cross-sectional or case-control studies, clinical periodontal disease has been associated with gestational diabetes mellitus. To test the hypothesis that, in comparison with women who do not develop gestational diabetes mellitus, those who do develop it will have had a greater exposure to clinical and other periodontal parameters, we measured clinical, bacteriological (in plaque and cervico-vaginal samples), immunological, and inflammatory mediator parameters 7 weeks before the diagnosis of gestational diabetes mellitus in 265 predominantly Hispanic (83%) women in New York. Twenty-two cases of gestational diabetes mellitus emerged from the cohort (8.3%). When the cases were compared with healthy control individuals, higher pre-pregnancy body mass index (p=0.004), vaginal levels of Tannerella forsythia (p=0.01), serum C-reactive protein (p=0.01), and prior gestational diabetes mellitus (p=0.006) emerged as risk factors, even though the clinical periodontal disease failed to reach statistical significance (50% in those with gestational diabetes mellitus vs. 37.3% in the healthy group; p=0.38).

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.

Interobserver agreement among sleep scorers from different centers in a large dataset.

STUDY OBJECTIVES: To evaluate epoch by epoch agreement in sleep stage assignment between scorers from different laboratories. DESIGN: N/A. METHODS: 62 NPSGs were selected for analysis from 3 sleep centers (38 diagnostic studies for sleep disordered breathing [SDB], 10 studies during CPAP titration, and 14 studies in subjects with no sleep related complaints or sleep pathology). The sleep recording montage consisted of at least 2 EEG leads, left and right EOG and a submental EMG. Scoring was performed manually by 5 experienced sleep technologists. No scorer had knowledge of any other scorers' results. Agreement was tabulated both for sleep stage distribution and on an epoch by epoch basis for the entire data set and the normal and SDB subsets. MEASUREMENTS AND RESULTS: The mean epoch by epoch agreement between scorers for all records was 73% (range 67-82%). Agreements were higher in the normal subset (mean 76%, range 65-85%) than in the SDB subset (mean 71%, range 65-78%). There was significant variability in agreement between records and between pairs of scorers. Overall, 75% of epochs had at least 4 of the 5 scorers in agreement on the sleep stage and 96% of epochs had agreement of at least 3 of the 5 scorers. CONCLUSIONS: The level of agreement in sleep stage assignment varies between scorers, by diagnosis, and by record. The level of agreement between laboratories is lower than what can be maintained between scorers within the same laboratory. This warrants caution when comparing data scored in separate laboratories. The lower agreement in SDB patients supports the generally held view that sleep fragmentation makes application of the R&K rules less reliable.

Duration of asthma and physiologic outcomes in elderly nonsmokers.

Airway and alveolar inflammation have been described in asthma. Prolonged inflammation may lead to airway remodeling, which can result in physiologic abnormalities. Elderly lifetime nonsmokers are an ideal population in which to examine the consequences of longstanding asthma. To test the hypothesis that airflow limitation and hyperinflation are associated with the duration of asthma, we evaluated airflow and lung volumes in a cohort of elderly asthmatic individuals. All subjects were > 60 yr of age and were lifetime nonsmokers (n = 75). Patients with asthma of long duration (LDA; n = 38) had asthma for >/= 26 yr (median = 40.0 yr); patients with asthma of short duration (SDA; n = 37) had asthma for < 26 yr (median = 9 yr). Patients with LDA had a significantly lower FEV(1)% predicted than did those with SDA (59.5 +/- 2.6% versus 73.8 +/- 3.1% [mean +/- SEM], respectively; p < 0.007). Regression analysis demonstrated that duration of asthma was inversely associated with FEV(1)% predicted (r = 0.264, p < 0.03). After bronchodilator administration, the patients with LDA continued to show airflow obstruction (FEV(1)% predicted = 65.4 +/- 2.9). Only 18% of patients with LDA attained a normal postbronchodilator FEV(1), whereas 50% of those with SDA were able to do so (p < 0.003). The FRC% predicted was significantly higher in subjects with LDA than in those with SDA (142.9 +/- 5.6 versus 124.1 +/- 4.4, respectively, p < 0.01). Multiple regression analysis revealed an association between FRC and duration of asthma that was independent of the degree of airflow limitation. These data suggest that the duration of asthma is associated with the degree of airflow limitation and hyperinflation. Moreover, these abnormalities can become irreversible over time, and may reflect distal airway and/or parenchymal changes as well as proximal airway remodeling.

Non-Invasive detection of respiratory effort-related arousals (REras) by a nasal cannula/pressure transducer system.

STUDY OBJECTIVES: The published AASM guidelines approve use of a nasal cannula/pressure transducer to detect apneas/hypopneas, but require esophageal manometry for Respiratory Effort-Related Arousals (RERAs). However, esophageal manometry may be poorly tolerated by many subjects. We have shown that the shape of the inspiratory flow signal from a nasal cannula identifies flow limitation and elevated upper-airway resistance. This study tests the hypothesis that detection of flow limitation events using the nasal cannula provides a non-invasive means to identify RERAs. DESIGN: N/A. SETTING: N/A. PATIENTS: 10 UARS/OSAS and 5 normal subjects INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: All subjects underwent full NPSG. Two scorers identified events from the nasal cannula signal as apneas, hypopneas, and flow limitation events. Two additional scorers identified events from esophageal manometry. Arousals were scored in a separate pass. Interscorer reliability and intersignal agreement were assessed both without and with regard to arousal. The total number of respiratory events identified by the two scorers of the nasal cannula was similar with an Intraclass Correlation (ICC) =0.96, and was essentially identical to the agreement for the two scorers of esophageal manometry (ICC=0.96). There was good agreement between the number of events detected by the two techniques with a slight bias towards the nasal cannula (4.5 events/hr). There was no statistically significant difference (bias 0.9/hr, 95%CI -0.3-2.0) between the number of nasal cannula flow limitation events terminated by arousal and manometry events terminated by arousal (RERAs). CONCLUSION: The nasal cannula/pressure transducer provides a non-invasive reproducible detector of all events in sleep disordered breathing; in particular, it detects the same events as esophageal manometry (RERAs).

CO(2) homeostasis during periodic breathing in obstructive sleep apnea.

The contribution of apnea to chronic hypercapnia in obstructive sleep apnea (OSA) has not been clarified. Using a model (D. M. Rapoport, R. G. Norman, and R. M. Goldring. J. Appl. Physiol. 75: 2302-2309, 1993), we previously illustrated failure of CO(2) homeostasis during periodic breathing resulting from temporal dissociation between ventilation and perfusion ("temporal V/Q mismatch"). This study measures acute kinetics of CO(2) during periodic breathing and addresses interapnea ventilatory compensation for maintenance of CO(2) homeostasis in 11 patients with OSA during daytime sleep (37-171 min). Ventilation and expiratory CO(2) and O(2) fractions were measured on a breath-by-breath basis by means of a tight-fitting full facemask. Calculations included CO(2) excretion, metabolic CO(2) production, and CO(2) balance (metabolic CO(2) production - exhaled CO(2)). CO(2) balance was tabulated for each apnea/hypopnea event-interevent cycle and as a cumulative value during sleep. Cumulative CO(2) balance varied (-3,570 to +1,388 ml). Positive cumulative CO(2) balance occurred in the absence of overall hypoventilation during sleep. For each cycle, positive CO(2) balance occurred despite increased interevent ventilation to rates as high as 45 l/min. This failure of CO(2) homeostasis was dependent on the event-to-interevent duration ratio. The results demonstrate that 1) periodic breathing provides a mechanism for acute hypercapnia in OSA, 2) acute hypercapnia during periodic breathing may occur without a decrease in average minute ventilation, supporting the presence of temporal V/Q mismatch, as predicted from our model, and 3) compensation for CO(2) accumulation during apnea/hypopnea may be limited by the duration of the interevent interval. The relationship of this acute hypercapnia to sustained chronic hypercapnia in OSA remains to be further explored.

Sleep habits of Long Island Rail Road commuters.

STUDY OBJECTIVES: We addressed the issue of how commuting affects sleep habits, and its association with general health and potential sleep disorders in individuals on a large, U.S. commuter rail system. DESIGN: Postage-paid mail back questionnaires were distributed to commuters over 6 consecutive weekdays. The questionnaire incorporated previously validated questions regarding sleep habits. SETTING: Questionnaires were dispensed at 15 different rail stations. PARTICIPANTS: 21,000 commuters accepted the questionnaire. MEASUREMENTS AND RESULTS: Data was analyzed by total group and length of commute. A total of 4715 (22%) questionnaires were returned. Over 50% of the sample reported difficulty with sleep and wakefulness while only 3% sought professional help. Sleep apnea was suspected in 4.2% of male and 1% of female respondents and was associated with increased reports of excessive daytime sleepiness, and history of hypertension, diabetes and obesity. Total nocturnal sleep time was significantly less in those subjects with long commutes. Seventy percent of respondents reported napping during the commute. Length of commute was associated with hypertension. CONCLUSION: Commuting long distances negatively impacts one's ability to capture adequate sleep. Data suggests that there may be significant numbers of respondents with unrecognized sleep disorders which further impact on general health.

Cardiogenic oscillations on the airflow signal during continuous positive airway pressure as a marker of central apnea.

UNLABELLED: Therapeutic decisions in patients with sleep apnea (eg, adjustment of continuous positive airway pressure [CPAP]) depend on differentiating central from obstructive apnea. Obstructive apnea is defined by cessation of airflow in the presence of continued respiratory effort, which is conventionally inferred from chest wall movement or intrathoracic pressure swings. Cardiogenic oscillations in the airflow have been observed during some central apneas, but there is controversy over whether they correlate with airway patency. The present study investigates whether these oscillations are markers of the absence of respiratory effort (central apnea) without regard to airway patency. METHODS: We examined 648 apneas in 52 patients undergoing nocturnal polysomnograms and CPAP titrations. Airflow was measured using the output of the CPAP generator, and apneas were identified from reduction of airflow to < 10% for > 10 s. We used only the presence or complete absence of thoracoabdominal motion to classify apneas: obstructive apnea when motion was present (297 apneas); and central apnea if motion was totally absent (351 apneas). Central apneas most often occurred at sleep onset or followed arousal with a big breath. Using only the flow signal, all apneas were examined for the presence of cardiogenic oscillation by an observer blinded to other signals and apnea types. RESULTS: No obstructive apnea showed definite cardiogenic oscillations. In four cases, there was a suggestion of oscillation that was not regular enough to be called cardiac. Sixty percent of central apneas showed clear, regular oscillations at cardiac frequency. Cardiogenic oscillations also were seen intermittently during quiet exhalation in apnea-free periods. CONCLUSION: The presence of cardiogenic oscillations on the CPAP flow signal is a specific indicator of central apnea and may have a role in self-titrating CPAP algorithms. We speculate that transmission of these cardiac-induced oscillations may relate to the relaxation of thoracic muscles during central apnea and is impeded by high muscle tone during obstructive apnea.

Relative occurrence of flow limitation and snoring during continuous positive airway pressure titration.

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.

Detection of flow limitation with a nasal cannula/pressure transducer system.

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.

Reliability of scoring respiratory disturbance indices and sleep staging.

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.

Respiratory psychophysiology of panic disorder: three respiratory challenges in 98 subjects.

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.

Detection of respiratory events during NPSG: nasal cannula/pressure sensor versus thermistor.

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.

Mechanism of relief of tachypnea during pressure support ventilation.

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.

Flow limitation as a noninvasive assessment of residual upper-airway resistance during continuous positive airway pressure therapy of obstructive sleep apnea.

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.

The utility of topographic EEG mapping in obstructive sleep apnea syndrome.

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.

CO2 homeostasis during periodic breathing: predictions from a computer model.

The Bohr/Riley model of CO2 homeostasis describes the relationship between CO2 production, ventilation, and arterial PCO2 and assumes that ventilation and CO2 delivery to the lung are both anatomically and temporally well matched. In contrast to normal breathing, periodic patterns of ventilation show temporal mismatch of ventilation to CO2 delivery. We developed a computer model of lung CO2 clearance that uses CO2 transfer equations to generate iterative solutions for PCO2 in multiple body compartments as a function of time. During continuous ventilatory patterns our model predicts steady-state arterial PCO2 identical to that of the Bohr model. During periodic ventilation, we predict mean PCO2 will be elevated unless mean ventilation is increased above that required by the Bohr model. Waxing and waning tidal volumes, low functional residual capacity, and low capillary blood volume potentiate the hypercapnia. However, if cardiac output oscillates in phase with breathing, hypercapnia is minimized. This analysis suggests a new mechanism for the development of sustained hypercapnia, separate from absolute hypoventilation or the presence of lung disease.