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Biomedical subjects

Richard B Berry

Publications and source records attributed to Richard B Berry.

At least 19 recordsLinked to original sources
PubMed2006

Follow-up assessment of CPAP efficacy in patients with obstructive sleep apnea using an ambulatory device based on peripheral arterial tonometry.

This study aimed to assess the accuracy of a wrist-worn device based on peripheral arterial tonometry (Watch_PAT 100) to detect residual episodes of respiratory disturbance during continuous positive airway pressure (CPAP) therapy. Concurrent polysomnography was used as the reference standard to identify sleep disordered breathing (SDB) events. The study was conducted in three sleep laboratories affiliated with tertiary care academic medical centers. Seventy patients using CPAP to treat obstructive sleep apnea for at least 3 months, following an in-laboratory titration to determine the optimal therapeutic positive airway pressure, participated in this study. Symptoms indicating suboptimal therapy were not required for participation, but self-reported adherence to CPAP therapy was necessary for inclusion. Interventions are not applicable in this study. The accuracy of the PAT-derived respiratory disturbance index (PAT RDI scored by automated algorithm) to detect residual SDB on CPAP was assessed against polysomnography (PSG) using Bland-Altman analysis, receiver-operator characteristic (ROC) curves, and likelihood ratios for increasing (LR+) and decreasing (LR-) the probability of moderate-severe SDB in the study population. Respiratory events on the PSG were quantified using standard criteria for research investigations ("Chicago criteria") to yield a PSG RDI.C. Based on the PSG results, 19% of the participants had moderate-severe SDB (PSG RDI.C>15 events per hour) on their prescribed pressure. For PAT RDI >15 events per hour, the area under the ROC curve was 0.95 (SE 0.03, p < 0.0001, 95% CI 0.89 to 1.00), the LR+ was 8.04 (95% CI 3.64-17.7), and the LR- was 0.17 (95% CI 0.05-0.62). The mean difference between the PAT RDI and PSG RDI.C was three (2SD 14.5) events per hour. Therefore, residual moderate-severe SDB on CPAP was not uncommon in a multicenter population self-reporting adherence to CPAP therapy to treat obstructive sleep apnea. The Watch_PAT device accurately identified participants with moderate-severe SDB while using CPAP in the attended setting of a sleep laboratory.

Adult↗
PubMed2006

Effect of zolpidem on the efficacy of continuous positive airway pressure as treatment for obstructive sleep apnea.

STUDY OBJECTIVE: Assess the effect of the hypnotic zolpidem on the efficacy of nasal continuous positive airway pressure for treatment of Obstructive Sleep Apnea. DESIGN: Randomized double blind placebo controlled, cross-over study. SETTING: Veterans Administration Medical Center. PATIENTS: 16 patients with severe obstructive sleep apnea (apnea+ hypopnea index > 30/hr), on CPAP therapy for at least 6 months. INTERVENTION: Three sleep studies were performed over three consecutive weeks. On night one the pressure level required to prevent apnea, hypopnea, and snoring was determined. On the second and third study nights, either placebo (P) or 10 mg of zolpidem (Z) was given (random order) and subjects slept on the CPAP level determined on the first night. MEASUREMENTS: Sleep architecture, apnea + hypopnea index, arterial oxygen saturation. RESULTS: The sleep architecture was similar on the placebo and zolpidem nights except for a decrease in the sleep latency ( P: 23.5 +/- 4.7; Z: 13.1 +/- 3.3 minutes, P < 0.02) and a small decrease in the arousal index (P < 0.03) on zolpidem nights. The was no significant difference between placebo and zolpidem nights in the apnea + hypopnea index (P: 4.8 +/- 1.4 versus Z : 2.7 +/- 0.47 events/hour), oxygen desaturation index (1.46 +/- 0.53 versus 0.81 +/- 0.29 desaturations/hour), or the lowest SaO2 (91.4 +/- 0.6 versus 91.0 +/- 0.7%). CONCLUSIONS: Acute administration of zolpidem 10 mg does not impair the efficacy of an effective level of CPAP in patients with severe obstructive sleep apnea.

Adult↗
PubMed2005

Practice parameters for clinical use of the multiple sleep latency test and the maintenance of wakefulness test.

Characterization of excessive sleepiness is an important task for the sleep clinician, and assessment requires a thorough history and in many cases, objective assessment in the sleep laboratory. These practice parameters were developed to guide the sleep clinician on appropriate clinical use of the Multiple Sleep Latency Test (MSLT), and the Maintenance of Wakefulness Test (MWT). These recommendations replace those published in 1992 in a position paper produced by the American Sleep Disorders Association. A Task Force of content experts was appointed by the American Academy of Sleep Medicine to perform a comprehensive review of the scientific literature and grade the evidence regarding the clinical use of the MSLT and the MWT. Practice parameters were developed based on this review and in most cases evidence based methods were used to support recommendations. When data were insufficient or inconclusive, the collective opinion of experts was used to support recommendations. These recommendations were developed by the Standards of Practice Committee and reviewed and approved by the Board of Directors of the American Academy of Sleep Medicine. The MSLT is indicated as part of the evaluation of patients with suspected narcolepsy and may be useful in the evaluation of patients with suspected idiopathic hypersomnia. The MSLT is not routinely indicated in the initial evaluation and diagnosis of obstructive sleep apnea syndrome, or in assessment of change following treatment with nasal continuous positive airway pressure (CPAP). The MSLT is not routinely indicated for evaluation of sleepiness in medical and neurological disorders (other than narcolepsy), insomnia, or circadian rhythm disorders. The MWT may be indicated in assessment of individuals in whom the inability to remain awake constitutes a safety issue, or in patients with narcolepsy or idiopathic hypersomnia to assess response to treatment with medications. There is little evidence linking mean sleep latency on the MWT with risk of accidents in real world circumstances. For this reason, the sleep clinician should not rely solely on mean sleep latency as a single indicator of impairment or risk for accidents, but should also rely on clinical judgment. Assessment should involve integration of findings from the clinical history, compliance with treatment, and, in some cases, objective testing using the MWT. These practice parameters also include recommendations for the MSLT and MWT protocols, a discussion of the normative data available for both tests, and a description of issues that need further study.

Continuous Positive Airway Pressure↗
PubMed2005

Low-dose mirtazapine increases genioglossus activity in the anesthetized rat.

STUDY OBJECTIVES: To examine the effects of mirtazapine on genioglossus and diaphragmatic electromyogram activity in the anesthetized rat. DESIGN: Parallel-group study. SUBJECTS: Sprague-Dawley adult male rats, 10 in each of 3 groups were studied. INTERVENTIONS: After anesthesia with 1.2 g/kg of urethane, a tracheostomy and bilateral vagotomy were performed. Femoral arterial and venous lines were placed, and fine wire hook electrodes were implanted into the genioglossus and diaphragm muscles. MEASUREMENTS: After a baseline period of measurement, either saline, 0.5 mg/kg of mirtazapine, or 5.0 mg/kg of mirtazapine was injected via the intraperitoneal route, and measurements were made for the next 3 hours. The average peak and tonic values of the moving time average of the genioglossus and diaphragm electromyogram for hours 1, 2, and 3 were determined and expressed as a percentage of the corresponding average value during the baseline (preinjection) monitoring period. RESULTS: At 0.5 mg/kg of mirtazapine, the peak genioglossus electromyogram was significantly higher than in control conditions over hours 2 and 3. At 5.0 mg/kg of mirtazapine, the genioglossus electromyogram was significantly lower than in control conditions for the first 2 hours of monitoring. The peak diaphragmatic electromyogram was slightly but significantly lower in the mirtazapine 5.0-mg/kg group than in controls. CONCLUSIONS: Mirtazapine, at a dose similar to one used clinically, increased genioglossus activity. We hypothesize that, at this dose, the ability of mirtazapine to increase serotonin and norepinephrine or block type-3 serotonin receptors predominated. At the higher dose of mirtazapine, the type-2 blockade effect predominated and genioglossus activity decreased.

Adrenergic alpha-Antagonists↗
PubMed2005

Comparison of respiratory event detection by a polyvinylidene fluoride film airflow sensor and a pneumotachograph in sleep apnea patients.

STUDY OBJECTIVES: Compare the ability of a polyvinylidene fluoride (PVDF) thermal sensor and a pneumotachograph to detect respiratory events in patients with obstructive sleep apnea. DESIGN: Single night of monitoring, single blinded scorer. SETTING: Veterans Affairs medical center. PATIENTS: Ten male subjects with obstructive sleep apnea. INTERVENTIONS: Nasal-oral airflow was simultaneously detected by a PVDF thermal sensor attached to the upper lip and a pneumotachograph in a mask over the nose and mouth. MEASUREMENTS: Events were scored from display views showing only the airflow tracings of the sensor in question and the events scored from that sensor. The apnea-hypopnea index was computed using two definitions for hypopnea. Hypopnea-1 was defined as a 50% reduction in flow for > or = 10 s in duration. Hypopnea-2 was defined as any reduction in airflow for > or = 10 s associated with a 3% drop in the arterial oxygen saturation or followed by an arousal. The level of agreement (kappa) for the sensors was determined by comparing whether or not they identified candidate events determined by a second blinded scorer. RESULTS: For the apnea-hypopnea-1 index (mean +/- SD), the event rate for the pneumotachograph (26.0 +/- 27.9 events/h) was slightly greater than that for the PVDF sensor (20.1 +/- 27.1 events/h; p < 0.05). For the apnea-hypopnea-2 index, the event rate for the pneumotachograph (29.4 +/- 26.8 events/h) and for that of the PVDF sensor (26.4 +/- 25.9 events/h) were similar (difference not significant). The mean +/- 2 SD difference was 3.0 +/- 8.5 events/h. The level of agreement between the sensors was in the "good range," whereby kappa = 0.69. For 20 randomly selected breaths per patient, the maximum deflections of the PVDF sensor varied linearly with pneumotachograph airflow deflections. CONCLUSION: The PVDF sensor compared favorably with a "gold standard" method of detecting respiratory events during sleep in patients with obstructive sleep apnea.

Adult↗
PubMed2004

Practice parameters for the dopaminergic treatment of restless legs syndrome and periodic limb movement disorder.

Dopaminergic agents, particularly dopamine agonists, have been used with increasing frequency in the treatment of restless legs syndrome and periodic limb movement disorder. These evidence-based practice parameters are complementary to the Practice Parameters for the Treatment of Restless Legs Syndrome and Periodic Limb Movement Disorder, published in 1999. These practice parameters were developed by the Standards of Practice Committee and reviewed and approved by the Board of Directors of the American Academy of Sleep Medicine. Recommendations are based on the accompanying comprehensive review of the medical literature regarding the dopaminergic treatment of restless legs syndrome (RLS) and periodic limb movement disorder (PLMD), which was developed by a task force commissioned by the American Academy of Sleep Medicine. The following recommendations serve as a guide to the appropriate use of dopaminergic agents in the treatment of RLS and PLMD. Levodopa with decarboxylase inhibitor, and the dopaminergic agonists pergolide, pramipexole, and ropinirole are effective in the treatment of RLS and PLMD. Other dopamine agonists (talipexole, cabergoline, piribidel, and alpha-dihydroergocryptine) and the dopaminergic agents amantadine and selegiline may be effective in the treatment of RLS and PLMD, but the level of effectiveness of these medications is not currently established. Lastly, no specific recommendations can be made regarding dopaminergic treatment of children or pregnant women with RLS or PLMD.

Dopamine Agonists↗
PubMed2003

Practice parameters for the use of portable monitoring devices in the investigation of suspected obstructive sleep apnea in adults.

BACKGROUND: A variety of devices are used to evaluate patients with a potential diagnosis of obstructive sleep apnea (OSA). A committee comprised of members of the American Academy of Sleep Medicine, American Thoracic Society, and American College of Chest Physicians systematically evaluated data on the use of these devices and developed practice parameters. DEVICES REVIEWED: Three categories of portable monitoring (PM) devices were reviewed with regard to assessing the probability of identifying an apnea-hypopnea index (AHI) of greater or less than 15 in attended and unattended settings. Type 2 (minimum of seven channels, including EEG, EOG, chin EMG, ECG or heart rate, airflow, respiratory effort, oxygen saturation), Type 3 (minimum of four channels, including ventilation or airflow (at least two channels of respiratory movement, or respiratory movement and airflow), heart rate or ECG and oxygen saturation) and Type 4 (most monitors of this type measure a single parameter or two parameters) devices were evaluated, and in-laboratory, attended polysomnography was used as a reference. SPECIFIC RECOMMENDATIONS: (1) Insufficient evidence is available to recommend the use of Type 2 PM devices in attended or unattended settings. (2) Type 3 PM devices appear to be capable of being used in an attended setting to increase or to decrease the probability that a patient has an apnea-hypopnea index greater than 15. (3) The use of Type 3 PM devices in an unattended setting is not recommended to rule in, rule out, or both rule in and rule out a diagnosis of OSA. (4) There is some evidence that the use of Type 3 PM devices in an attended in-laboratory setting may be acceptable to both rule in and rule out a diagnosis of OSA if certain limitations are in place. These limitations include manually scoring the records, using the devices only in patients without significant comorbid conditions, having an awareness that symptomatic patients with a negative study should have a Type 1 study, and not using these devices for titrating positive airway pressure or conducting split-night studies. (5) The use of Type 4 PM devices in attended or unattended settings is not recommended. GENERAL RECOMMENDATIONS: Type 3 and 4 PM devices cannot score sleep and, therefore, do not meet some current Medicare guidelines. The use of PM devices is not recommended for general-population screening or in the absence of a pretest probability of the patient having a diagnosis of OSA, for complaints other than those associated with OSA, without review of raw data during interpretation, by physicians without familiarity with their use and limitations, and without trained personnel to perform technical scoring. Future research should address the use of PM devices in patients with comorbid conditions; non-White patients and women; larger, better-controlled studies; studies focused on the use of Type 2 and 3 devices; studies focusing on decision making and outcomes rather than simple classification using arbitrary cutoffs; and studies that seek to elucidate cost-effectiveness data on the use of PM devices.

Electrocardiography↗
PubMed2003

Practice parameters for the role of actigraphy in the study of sleep and circadian rhythms: an update for 2002.

Actigraphy is a method used to study sleep-wake patterns and circadian rhythms by assessing movement, most commonly of the wrist. These evidence-based practice parameters are an update to the Practice Parameters for the Use of Actigraphy in the Clinical Assessment of Sleep Disorders, published in 1995. These practice parameters were developed by the Standards of Practice Committee and reviewed and approved by the Board of Directors of the American Academy of Sleep Medicine. Recommendations are based on the accompanying comprehensive review of the medical literature regarding the role of actigraphy, which was developed by a task force commissioned by the American Academy of Sleep Medicine. The following recommendations serve as a guide to the appropriate use of actigraphy. Actigraphy is reliable and valid for detecting sleep in normal, healthy populations, but less reliable for detecting disturbed sleep. Although actigraphy is not indicated for the routine diagnosis, assessment, or management of any of the sleep disorders, it may serve as a useful adjunct to routine clinical evaluation of insomnia, circadian-rhythm disorders, and excessive sleepiness, and may be helpful in the assessment of specific aspects of some disorders, such as insomnia and restless legs syndrome/periodic limb movement disorder. The assessment of daytime sleepiness, the demonstration of multiday human-rest activity patterns, and the estimation of sleep-wake patterns are potential uses of actigraphy in clinical situations where other techniques cannot provide similar information (e.g., psychiatric ward patients). Superiority of actigraphy placement on different parts of the body is not currently established. Actigraphy may be useful in characterizing and monitoring circadian rhythm patterns or disturbances in certain special populations (e.g., children, demented individuals), and appears useful as an outcome measure in certain applications and populations. Although actigraphy may be a useful adjunct to portable sleep apnea testing, the use of actigraphy alone in the detection of sleep apnea is not currently established. Specific technical recommendations are discussed, such as using concomitant completion of a sleep log for artifact rejection and timing of lights out and on; conducting actigraphy studies for a minimum of three consecutive 24-hour periods; requiring raw data inspection; permitting some preprocessing of movement counts; stating that epoch lengths up to 1 minute are usually sufficient, except for circadian rhythm assessment; requiring interpretation to be performed manually by visual inspection; and allowing automatic scoring in addition to manual scoring methods.

Circadian Rhythm↗
PubMed2003

Model-based assessment of autonomic control in obstructive sleep apnea syndrome.

STUDY OBJECTIVES: To quantitatively assess autonomic cardiovascular control in patients with obstructive sleep apnea syndrome (OSAS) using a mathematical model that relates changes in R-R interval (RRI) to respiration and changes in systolic blood pressure (SBP), and to compare the results obtained with conventional techniques. DESIGN: Respiration, RRI, and arterial blood pressure were monitored noninvasively in awake subjects in the supine and standing postures. A mathematical model was used to partition the fluctuations in RRI into a component ("RSA") correlated with respiration and a component ("baroreflex") correlated with fluctuations in SBP. SETTING: Sleep disorders laboratory in a hospital setting. PATIENTS OR PARTICIPANTS: 11 middle-aged male patients with untreated OSAS (apnea-hypopnea index = 75.9 +/- 11.1 (SE) events h-1) and 11 age-matched normal controls (10 males + 1 female). INTERVENTIONS: The subjects were monitored while breathing spontaneously in both supine and standing postures. Each subject also had to perform a battery of 5 standard autonomic stress tests (AST). MEASUREMENTS AND RESULTS: Four of the 5 ASTs did not indicate any difference between controls and OSAS subjects. There were also no differences in the indices derived from power spectral analysis of RRI and blood pressure variability; however, these spectral indices were sensitive to postural changes (orthostatic stress). Both RSA and baroreflex gains estimated from the model were substantially depressed in OSAS (P < 0.02) Changes in posture affected RSA gain but not baroreflex gain. The time-courses of the dynamics of these model components were not significantly different between subject groups. CONCLUSIONS: OSAS leads to abnormal parasympathetic and sympathetic control of heart rate, as reflected in depressed RSA and baroreflex gains. Model-based assessment was more sensitive in detecting abnormal autonomic function, compared to standard autonomic testing and power spectral analysis. The model-based approach represents a relatively simple and nonintrusive means of quantifying the key aspects of autonomic control in spontaneously breathing OSAS patients during wakefulness.

Adult↗
PubMed2003

Awake negative pressure reflex response of the genioglossus in OSA patients and normal subjects.

We hypothesized that the response of the genioglossus to negative pressure during wakefulness should be intact in obstructive sleep apnea (OSA) patients despite published evidence showing impairment of the response of palatal muscles (Mortimore IL and Douglas NJ. Am J Respir Crit Care Med 156: 867-873, 1997). Thus the response of the genioglossus to brief nasal negative pressure applications (NPAs) in early inspiration was compared between OSA patients and an age-matched group of normal subjects at two study sites (n = 11 per group in Long Beach, n = 14 per group in Boston). Subjects were studied in the sitting (Long Beach) or supine (Boston) posture, and the genioglossus electromyogram (EMGgg) was measured with an intraoral surface electrode (Long Beach) or intramuscular electrode (Boston). The response of the EMGgg was expressed as the percent change from baseline where the baseline EMGgg was the value at the onset of the NPA. In Long Beach, the EMGgg response was significantly higher in the OSA patients at a lower suction pressure of approximately 10 cmH(2)O (75.2 +/- 8.4 vs. 37.4 +/- 4.0% increase; P < 0.001) but not at a higher suction pressure of approximately 20 cmH(2)O. In Boston, the response in the OSA patients was also greater (107.2 +/- 25.9 vs. 46.3 +/- 8.3%; P < 0.05) at a suction pressure of approximately 13 cmH(2)O. We conclude that the response of the genioglossus to NPA during wakefulness is not impaired in OSA patients compared with normal subjects and is greater at low suction pressures.

Adult↗
PubMed2003

Selective augmentation of genioglossus electromyographic activity by L-5-hydroxytryptophan in the rat.

The present study was undertaken to determine the effects of intravenous L-5 hydroxytryptophan (5HTP), the immediate precursor of serotonin, on the electromyographic (EMG) activity of the genioglossus (gEMG) and diaphragm (dEMG) in the spontaneously breathing, vagotomized anesthetized male Sprague-Dawley rats (urethane 1.2-1.4 g/kg). Sequential administration of saline and 0.05-, 0.1-, 0.2-, 1-, and 5-mg/kg doses of 5HTP were given intravenously every 15 min. There was a significant increase (percent change from predrug) in both gEMG and dEMG amplitude at 1.0 and 5.0 mg/kg of 5HTP compared to saline. The percent increase in gEMG induced by 1.0 and 5.0 mg/kg 5HTP however was significantly greater than the increase in dEMG. There was no significant change in heart rate (HR), mean arterial blood pressure (MAP), or respiratory rate at any of the doses of 5HTP tested. These results suggest that intravenous 5HTP at doses of 1 and 5 mg/kg preferentially increased the gEMG in the anesthetized rat compared to the dEMG. We hypothesize that at appropriate doses serotonin precursors could increase genioglossus activity in humans during sleep and help maintain upper-airway patency.

5-Hydroxytryptophan↗
PubMed2003

Practice parameters for using polysomnography to evaluate insomnia: an update.

Insomnia is a common and clinically important problem. It may arise directly from a sleep-wake regulatory dysfunction and/or indirectly result from comorbid psychiatric, behavioral, medical, or neurological conditions. As an important public-health problem, insomnia requires accurate diagnosis and effective treatment. Insomnia is primarily diagnosed clinically with a detailed medical, psychiatric, and sleep history. Polysomnography is indicated when a sleep-related breathing disorder or periodic limb movement disorder is suspected, initial diagnosis is uncertain, treatment fails, or precipitous arousals occur with violent or injurious behavior. However, polysomnography is not indicated for the routine evaluation of transient insomnia, chronic insomnia, or insomnia associated with psychiatric disorders.

Chronic Disease↗
PubMed2002

The use of auto-titrating continuous positive airway pressure for treatment of adult obstructive sleep apnea. An American Academy of Sleep Medicine review.

This paper reviews the efficacy of auto-titrating continuous positive airway pressure (APAP) for treatment of obstructive sleep apnea. It is based on a review of 30 articles published in peer review journals conducted by a task force appointed by the American Academy of Sleep Medicine to develop practice parameters for use of APAP devices for treatment of obstructive sleep apnea (OSA). The data indicate that APAP can be used to treat many patients with OSA (auto-adjusting) or to identify an effective optimal fixed level of continuous positive airway pressure (CPAP) for treatment (auto-titration). Patients with significant congestive heart failure, chronic obstructive pulmonary disease (COPD), or significant amounts of central apnea were excluded from many treatment trials and there is insufficient evidence that APAP can be used to treat these patients. Many clinical trials have been performed in patients already on CPAP or with the initial APAP night in a laboratory setting. At this time only a few studies have evaluated initial titration with APAP in CPAP-naïve patients in an unattended setting. Further studies of APAP in this circumstance are needed. No studies have systematically compared the efficacy of one APAP technology with another. Devices using different technology may not give the same results in a given patient. Devices solely dependent on vibration may not work in non-snorers or patient who have undergone upper-airway surgery. High mask or mouth leaks may prevent adequate titration in devices monitoring snoring, flow, or impedance (forced oscillation technique). Review of the raw data to identify periods of high leak was performed in several of the APAP titration studies, to identify a pressure for fixed CPAP treatment or to determine if the titration was adequate. There is conflicting evidence for and against the premise that treatment with APAP increases acceptance and adherence compared to fixed CPAP. In studies demonstrating an increase in adherence with APAP, there was similar improvement in measures of daytime sleepiness as with fixed CPAP treatment. Further studies are needed to determine if APAP can increase acceptance or adherence with positive pressure treatment in patients with OSA.

Adult↗
PubMed2002

The characteristics of five patients with obstructive sleep apnea whose apnea-hypopnea index deteriorated after uvulopalatopharyngoplasty.

The objective of this retrospective, consecutive, case series design study was to determine the number of unselected patients with obstructive sleep apnea (OSA) who deteriorated after uvulopalatopharyngoplasty (UPPP). Sixteen of 27 patients at the Sleep Clinic at Veterans Affairs Medical Center who underwent UPPP for OSA and who completed both a pre- and postpolysomnogram were studied. After comparing the apnea-hypopnea index (AHI) before and after UPPP, three groups of patients were identified: deteriorators, unchanged, and improvers. In five patients (31%), the AHI increased by more than 10% after UPPP (deteriorators); in four (25%), the AHI showed a change in either direction of less than 10% (unchanged); and in the remaining seven (44%), the AHI decreased by more than 10% after UPPP (improvers). The AHI deteriorated in five of 16 (31%) unselected patients with OSA in our clinic population who underwent UPPP. The mean pre-UPPP AHI was lower in the patients who deteriorated relative to all other patients (P = 0.02). We suggest that patients who undergo UPPP should have a post-UPPP polysomnogram to determine whether they have improved or deteriorated after the procedure and that alternative forms of treatment may be needed in some patients.

Aged↗
PubMed2002

Assessment of closed-loop ventilatory stability in obstructive sleep apnea.

Previous studies on ventilatory control in obstructive sleep apnea (OSA) have generally indicated depressed chemosensitivity, implying greater stability of the chemical control of breathing in these subjects. However, these results were based on tests involving steady-state or quasi-steady measurements obtained in wakefulness. We have developed a method for assessing the dynamic stability characteristics of chemoreflex control in OSA patients during sleep. While continuous positive airway pressure was applied to stabilize the upper airways, acoustically stimulated arousals were used to perturb the respiratory system during sleep. The fluctuations in esophageal pressure that ensued were analyzed, using a closed-loop minimal model, to estimate the chemoreflex loop impulse response (CLIR). Tests using simulated data confirmed the validity of our estimation algorithm. Application of the method to arousal responses measured in six OSA and five normal subjects revealed no statistically significant differences in gain margins and loop gain magnitudes between the two groups. However, the CLIR in the OSA subjects exhibited faster and more oscillatory dynamics. This result implies that, in addition to unstable upper airway mechanics, an underdamped chemoreflex control system may be another important factor that promotes the occurrence of periodic obstructive apneas during sleep.

Arousal↗