Nasal Continuous Positive Airway Pressure Improves Quality of Life in Obesity Hypoventilation Syndrome

We studied the quality of life of obesity hypoventilation syndrome (OHS) by comparing it with age- and body mass index-matched patients without hypoventilation and age-matched obstructive sleep apnea (OSA) patients with body mass index (BMI) under 30, and the efficacy of nasal continuous positive airway pressure (CPAP) therapy for 3 to 6 months on the quality of life in these patients. Prospectively recruited patients from six sleep laboratories in Japan were administered assessments of the general health status by the Short-Form 36 Health Survey (SF-36) and subjective sleepiness by the Epworth Sleepiness Scale (ESS). Compared with matched healthy subjects, OHS and OSA patients not yet treated had worse results on the ESS scores and the SF-36 subscales for physical functioning, role limitations due to physical problems, general health perception, energy/vitality, role limitations due to emotional problems, and social functioning. The ESS scores of OHS patients were worse than those of the OSA groups including the age- and BMI-matched OSA patients. In the SF-36 subscales of OHS patients, only the subscale of social functioning showed worse results compared with that of BMI-matched OSA patients. After 3 to 6 months of treatment, ESS scores and these SF-36 subscales in all three patient groups improved to the normal level. These results suggested that the quality of life of OHS before nasal CPAP was significantly impaired and that nasal CPAP for OHS improved the quality of life associated with the improvement of daytime sleepiness to the level of the other OSA patients.     

Obesity hypoventilation syndrome: hypoxemia during continuous positive airway pressure

BACKGROUND: Polysomnography findings between matched groups with obstructive sleep apnea (OSA) and OSA plus obesity-hypoventilation syndrome (OHS) before and after continuous positive airway pressure (CPAP), particularly in the extremely severe obese (body mass index [BMI] >or= 50 kg/m2), are unclear. DESIGN: Prospective study of subjects (BMI >or= 50 kg/m2) undergoing diagnostic polysomnography. Subjects with an apnea-hypopnea index (AHI) >or= 15/h underwent a second polysomnography with CPAP. The effect of 1 night of CPAP on sleep architecture, AHI, arousal indexes, and nocturnal oxygenation was assessed. OHS was defined as those subjects with obesity, PaCo2 > 45 mm Hg, and PaO2 < 70 mm Hg in the absence of lung disease. RESULTS: Twenty-three subjects with moderate-to-severe OSA and 23 subjects with moderate-to-severe OSA plus OHS underwent a 1-night trial of CPAP. Both groups were matched for spirometry, BMI, and AHI, but oxygen desaturation was worse in the OSA-plus-OHS group. CPAP significantly improved rapid eye movement (REM) duration (p < 0.005), AHI (p < 0.005), arousal indexes (p < 0.005), and percentage of total sleep time (TST) with oxygen saturation (SpO2) < 90% (p < 0.005) in both groups. In subjects with OSA plus OHS, 43% continued to spend > 20% of TST with SpO2 < 90%, compared to 9% of the OSA group, despite the adequate relief of upper airway obstruction. CONCLUSIONS: Extremely severe obese subjects (BMI >or= 50 kg/m2) with moderate-to-severe OSA plus OHS exhibit severe oxygen desaturation but similar severities of AHI, arousal indexes, and sleep architecture abnormalities when compared to matched subjects without OHS. CPAP significantly improves AHI, REM duration, arousal indexes, and nocturnal oxygen desaturation. Some subjects with OHS continued to have nocturnal desaturation despite the control of upper airway obstruction; other mechanisms may contribute. Further long-term studies assessing the comparative role of CPAP and bilevel ventilatory support in such subjects with OHS is warranted.     

Obesity hypoventilation syndrome: prevalence and predictors in patients with obstructive sleep apnea

Patients with obesity hypoventilation syndrome (OHS) have a lower quality of life, more healthcare expenses, a greater risk of pulmonary hypertension, and a higher mortality compared to eucapnic patients with obstructive sleep apnea (OSA). Despite significant morbidity and mortality associated with OHS, it is often unrecognized and treatment is frequently delayed. The objective of this observational study was to determine the prevalence of OHS in patients with OSA seen at the sleep disorders clinic of a large public urban hospital serving predominantly minority population and to identify clinical—not mechanistic—predictors that should prompt clinicians to measure arterial blood gases. In the first stage, we randomly selected 180 patients referred to our sleep disorders clinic between 2000 and 2004 for suspicion of OSA. From this retrospective random sample we calculated the prevalence of OHS in patients with OSA and identified independent clinical predictors using logistic regression. In the second stage, we prospectively validated these predictors in a sample of 410 consecutive patients referred to the sleep disorders clinic for suspicion of OSA between 2005 and 2006. The prevalence of OHS in patients with OSA was 30% in the retrospective random sample and 20% in the prospective sample. Three variables independently predicted OHS in both samples: serum bicarbonate level (p < 0.001), apnea–hypopnea index (p = 0.006), and lowest oxygen saturation during sleep (p < 0.001). Due to the serious morbidity associated with OHS, we selected a highly sensitive threshold of serum bicarbonate level. A threshold of 27 mEq/l had a sensitivity of 92% and a specificity of 50%. Only 3% of patients with a serum bicarbonate level <27 mEq/l had hypercapnia compared to 50% with a serum bicarbonate ≥27 mEq/l. In conclusion, OHS is common in severe OSA. A normal serum bicarbonate level excludes hypercapnia and an elevated serum bicarbonate level should prompt clinicians to measure arterial blood gases.     

Non-invasive Positive Airway Pressure in Obesity Hypoventilation Syndrome and Chronic Obstructive Pulmonary Disease: Present and Future Perspectives

Obesity hypoventilation syndrome (OHS) is a sleep disorder that has acquired great importance worldwide because of its prevalence and association with obesity leading to increased morbidity and mortality with reduced quality of life. The primary feature is insufficient sleep-related ventilation, resulting in abnormally elevated arterial carbon dioxide pressure (PaCO₂) during sleep and demonstration of daytime hypoventilation. There are three main mechanisms that can generate diurnal hypoventilation in obese patients: alteration of the respiratory mechanics secondary to obesity; central hypoventilation secondary to leptin resistance and sleep disorder with sleep hypoventilation and obstructive apnoeas, which can be potentially solved with the use of positive airway pressure: non-invasive ventilation (NIV) and continuous positive airway pressure (CPAP). There are no established guidelines for the treatment of OHS, and only a few randomised controlled trials have been published. In this review, we have gone over the role of positive airway pressure, in particular the mechanisms that produce improvement, ventilatory modes available, clinical applications, technical considerations and future research. In addition, we added a review on NIV efficacy in chronic obstructive pulmonary disease (COPD), both in acute respiratory failure due to exacerbation and mainly in stable setting where more controversy and scientific contributions are coming.     

Obesity hypoventilation syndrome as a spectrum of respiratory disturbances during sleep

OBJECTIVE: To identify the spectrum of respiratory disturbances during sleep in patients with obesity hypoventilation syndrome (OHS) and to examine the response of hypercapnia to treatment of the specific ventilatory sleep disturbances. DESIGNS AND METHODS: Twenty-three patients with chronic awake hypercapnia (mean [+/- SD] PaCO(2), 55 +/- 6 mm Hg) and a respiratory sleep disorder were retrospectively identified. Nocturnal polysomnography testing was performed, and flow limitation (FL) was identified from the inspiratory flow-time contour. Obstructive hypoventilation was inferred from sustained FL coupled with O(2) desaturation that was corrected with treatment of the upper airway obstruction. Central hypoventilation was inferred from sustained O(2) desaturation that persisted after the correction of the upper airway obstruction. Treatment was initiated, and follow-up awake PaCO(2) measurements were obtained (follow-up range, 4 days to 7 years). RESULTS: A variable number of obstructive sleep apneas/hypopneas (ie, obstructive sleep apnea-hypopnea syndrome [OSAHS]) were noted (range, 9 to 167 events per hour of sleep). Of 23 patients, 11 demonstrated upper airway obstruction alone (apnea-hypopnea/FL) and 12 demonstrated central sleep hypoventilation syndrome (SHVS) in addition to a variable number of OSAHS. Treatment aimed at correcting the specific ventilatory abnormalities resulted in correction of the chronic hypercapnia in all compliant patients (compliant patients: pretreatment, 57 +/- 6 mm Hg vs post-treatment, 41 +/- 4 mm Hg [p < 0.001]; noncompliant patients: pretreatment, 52 +/- 6 mm Hg vs post-treatment, 51 +/- 3 mm Hg; [difference not significant]). CONCLUSIONS: This study demonstrates that OHS encompasses a variety of distinct pathophysiologic disturbances that cannot be distinguished clinically at presentation. Sustained obstructive hypoventilation due to partial upper airway obstruction was demonstrated as an additional mechanism for OHS that is not easily classified as SHVS or OSAHS.     

Sleep-related breathing disorders, loud snoring and excessive daytime sleepiness in obese subjects

OBJECTIVE: To investigate the prevalence of sleep breathing disorders, loud snoring and excessive daytime sleepiness in a group of obese subjects, and to identify the predictors of obstructive sleep apnea (OSA) severity in these patients. SUBJECTS: A total of 161 consecutive obese patients (body mass index (BMI)> or =30.0 kg/m(2)), ranging between 30.0 and 67.3, represented by 57 men and 104 women, aged 16-75 y. Forty (15 men and 25 women) age-matched (20-70 y) nonobese (BMI<27 kg/m(2)) volunteers were also recruited for the study. MEASUREMENTS: Respiratory function parameters, nocturnal sleep quality (evaluated by a specific questionnaire), nocturnal hypoventilation and OSA (evaluated by night polysomnography) were examined in all subjects. Anthropometric parameters (neck circumference, waist circumference, waist-to-hip ratio) were also investigated. RESULTS: Eighty-three obese patients (51.5% of the obese group) had a respiratory disturbance index (RDI)> or =10, corresponding to a moderate or severe sleep apnea. In particular, 24.8% (40/161), ie a quarter of all obese patients, were affected by severe OSA and this alteration was present in 42.1% of obese men (24/57) and in 15.4% (16/104) of obese women. When a stepwise multiple regression analysis was performed, neck circumference in men and BMI in women were shown to be the strongest predictors of sleep apnea. Twenty-nine percent of all obese subjects (40.3% of men and 23.1% of women) showed nocturnal hypoventilation; however, it was present as a unique breathing alteration in only 5% of the obese population. The percentage of patients having excessive daytime sleepiness was significantly higher than in nonobese subjects, even when only nonapneic obese patients were considered (P<0.001). CONCLUSION: This study shows that OSA is present in more than 50% of a population of obese patients with a mean BMI higher than 40.0, this percentage being much higher than that commonly reported in previous studies, particularly in women. Neck circumference in men and BMI in women seem to be the strongest predictors of the severity of OSA in obese patients. Nocturnal hypoventilation seems to be present in more than 29% of a severe obese population. Moreover, this study indicates that morbid obesity can be associated with excessive daytime sleepiness even in the absence of sleep apnea.     

Effectiveness of CPAP vs. Noninvasive Ventilation Based on Disease Severity in Obesity Hypoventilation Syndrome and Concomitant Severe Obstructive Sleep Apnea

RationaleObesity hypoventilation syndrome (OHS) with concomitant severe obstructive sleep apnea (OSA) is treated with CPAP or noninvasive ventilation (NIV) during sleep. NIV is costlier, but may be advantageous because it provides ventilatory support. However, there are no long-term trials comparing these treatment modalities based on OHS severity.ObjectiveTo determine if CPAP have similar effectiveness when compared to NIV according to OHS severity subgroups.MethodsPost hoc analysis of the Pickwick randomized clinical trial in which 215 ambulatory patients with untreated OHS and concomitant severe OSA, defined as apnoea-hypopnea index (AHI) ≥ 30 events/h, were allocated to NIV or CPAP. In the present analysis, the Pickwick cohort was divided in severity subgroups based on the degree of baseline daytime hypercapnia (PaCO₂ of 45–49.9 or ≥50 mmHg). Repeated measures of PaCO₂ and PaO₂ during the subsequent 3 years were compared between CPAP and NIV in the two severity subgroups. Statistical analysis was performed using linear mixed-effects model.Results204 patients, 97 in the NIV group and 107 in the CPAP group were analyzed. The longitudinal improvements of PaCO₂ and PaO₂ were similar between CPAP and NIV based on the PaCO₂ severity subgroups.ConclusionIn ambulatory patients with OHS and concomitant severe OSA who were treated with NIV or CPAP, long-term NIV therapy was similar to CPAP in improving awake hypercapnia, regardless of the severity of baseline hypercapnia. Therefore, in this patient population, the decision to prescribe CPAP or NIV cannot be solely based on the presenting level of PaCO₂.     

Mass loading, sleep apnea, and the pathogenesis of obesity hypoventilation

To define the roles of mechanical loading, respiratory neuromuscular control, and sleep apnea in the pathogenesis of obesity hypoventilation, respiratory muscle drive and output, assessed by diaphragmatic electromyogram (EMGdi) and mouth occlusion pressure (P 0.15), respectively, were determined during CO2 chemostimulation in nonobese volunteers who were subjected to abdominal mass loading, and in three groups of markedly obese patients: eucapnic obese without sleep apnea (O), eucapnic obese with sleep apnea (OSA), and hypercapnic obese with sleep apnea (OH). The P0.15 responses were decreased in OSA and OH, but the EMGdi responses were not significantly different from those in control subjects. In O patients EMGdi responses were significantly greater than those in control subjects as well as those in OSA and OH patients. EMGdi and P0.15 responses increased in all nonobese subjects when they were subjected to mass loading. We conclude that both OSA and OH patients were equally unable to develop the expected increase in respiratory muscle drive and output. The presence of sleep apnea, possibly by causing nocturnal hypoxemia and/or sleep fragmentation, may result in impaired mass load compensation and predispose obese patients to develop hypercapnia.     

Rhinitis and sleep apnea

The nose and pharynx begin the upper airway system and represent a continuum. This is the biologic basis for the mutual influences of rhinitis and obstructive sleep apnea (OSA). Sleep-disordered breathing has a large differential diagnosis that includes snoring, upper airway resistance syndrome, and severe OSA. Nasal obstruction is an independent risk factor for OSA, but there is no correlation of daytime nasal resistance with the severity of OSA. However, nasal resistance was an independent predictor of apnea-hypopnea index in a recent study of nonobese OSA patients. Rhinitis alone is associated with mild OSA, but commonly causes microarousals and sleep fragmentation. Reduction of nasal inflammation with topical treatment improves sleep quality and subsequent daytime sleepiness and fatigue. Patient compliance with the nasal continuous positive airway pressure (nCPAP) device is relatively low, in part due to adverse nasal effects.     

Non‐invasive ventilation for obese patients with chronic respiratory failure: Are two pressures always better than one?

Obesity‐related respiratory failure is increasingly common but remains under‐diagnosed and under‐treated. There are several clinical phenotypes reported, including severe obstructive sleep apnoea (OSA), isolated nocturnal hypoventilation with or without severe OSA and OSA complicating chronic obstructive pulmonary disease (COPD). The presence of hypercapnic respiratory failure is associated with poor clinical outcomes in each of these groups. While weight loss is a core aim of management, this is often unachievable, and treatment of sleep‐disordered breathing with positive airway pressure (PAP) therapy is the mainstay of clinical practice. Although there are few long‐term clinical efficacy trials, the lack of equipoise would prevent the utilization of an untreated control group. The current data support the use of PAP therapy to improve respiratory failure and is associated with improvements in health‐related quality of life, reduced healthcare utilization and reduced mortality. Both continuous PAP (CPAP) and non‐invasive ventilation (NIV) appear safe and effective in patients with obesity‐related respiratory failure and OSA, with or without COPD, and the current evidence would not support a single therapy choice in all patients. There are no studies of CPAP in patients with isolated nocturnal hypoventilation, and NIV would be the current recommendation in this patient group. Whichever starting therapy is used, titration should be performed to correct sleep‐disordered breathing and reverse chronic respiratory failure, with consideration of step‐down of the treatment based on a clinical re‐evaluation. In contrast, failure to reach physiological and clinical treatment targets should lead to the consideration of treatment escalation.     

Endothelin-1 gene variant Lys198Asn and plasma endothelin level in obstructive sleep apnea

Obstructive sleep apnea (OSA) is a recognized risk factor for cardiovascular disorders. Thus, an association between endothelin-1 (EDN1) and OSA can be assumed. We investigated a cohort of 364 consecutive patients (age 57 +/- 10 years) with mild to severe OSA for the EDN1 variant Lys198Asn (G/T) and endothelin plasma levels and compared them with 57 controls. The Lys198Asn genotype was significantly associated with the apnea/hypopnea index (AHI) with a median of 30/h of sleep for GG, 27/h for GT and 59/h for TT genotype (p < 0.05). Further stratification of patients into 2 groups by body mass index (BMI) revealed a strong association between AHI and Lys198Asn polymorphism in 191 obese patients (p = 0.005), whereas in 173 nonobese patients, we observed no association. A substantial effect by BMI on OSA severity was seen with multiple linear regression (p < 0.001). However, this effect was modified by the Lys198Asn polymorphism and by gender: the AHI increase per unit of BMI was more pronounced in males than in females, and about 1.3 times greater in homozygous carriers of the mutant allele than in other carrier groups. EDN1 plasma levels of untreated OSA patients and of patients treated with nasal continuous positive airway pressure were not elevated compared with controls. Our results indicate that the Lys198Asn polymorphism is associated with the severity of OSA in obese subjects. The EDN1 plasma level cannot be used as a marker for OSA or its severity.     

The sleep supine position has a major effect on optimal nasal continuous positive airway pressure : relationship with rapid eye movements and non-rapid eye movements sleep, body mass index, respiratory disturbance index, and age.

STUDY OBJECTIVES: To evaluate the impact of sleep position on optimal nasal continuous positive airway pressure (nCPAP [op-nCPAP]) in obstructive sleep apnea (OSA) patients and to investigate how rapid eye movements (REM) and Non-REM (NREM) sleep, body mass index (BMI), respiratory disturbance index (RDI), and age are related to this effect. DESIGN: Retrospective analysis. Setting: Sleep Disorders Unit at Loewenstein Hospital Rehabilitation Center. PATIENTS: Eighty-three consecutive adult OSA patients who underwent a complete nCPAP titration. From this group, 60 patients who spent at least 30 min in both the supine (Sup) and lateral (Lat) positions and 46 patients who had data on both positions during REM and NREM sleep were included in the analysis. RESULTS: In most OSA patients (52; 86.7%), the recommended op-nCPAP was obtained when the patients slept in the Sup posture. The mean op-nCPAP was significantly higher in the Sup posture (10.00 +/- 2.20 cm H(2)O) than it was in the Lat posture (7.61 +/- 2.69 cm H(2)O). The op-nCPAP was significantly higher in the Sup position than it was in the Lat position in both REM and NREM sleep, as well as in the severe BMI group (BMI >/= 30) and in the less obese group (BMI < 30). Similarly, in the severe (RDI >/= 40) and less severe groups (RDI < 40), as well as in both age groups (< and > 60 years of age), the op-nCPAP was significantly higher in the Sup posture than it was in the Lat posture. Irrespective of the four parameters mentioned, the actual differences in op-nCPAP between the two body postures were almost identical, ranging between 2.31 and 2.66 cm H(2)O. CONCLUSIONS: For most OSA patients, the op-nCPAP level is significantly higher in the Sup position than it is in the Lat position. This is true for REM and NREM sleep, for obese and nonobese patients, for patients with different degrees of severity, and for young and old OSA patients. Since the op-nCPAP was highest in the Sup posture during REM sleep, no nCPAP titration should be considered complete without the patient having slept in the Sup posture during REM sleep.     

Continuous positive airway pressure: new generations

Automatic positive airway pressure devices are the most technologically advanced positive airway pressure devices available for use in OSA. Although heterogeneous, they have in common the ability to detect and respond to changes in upper airway resistance. Data cannot necessarily be extrapolated from one device to another, and the field is rapidly advancing. Most studies of APAP have been performed in a supervised setting, or patients have been carefully selected to have a high likelihood of OSA uncomplicated by disorders such as alveolar hypoventilation or central apnea or technical problems such as mask leaks. Studies of APAP for the diagnosis of OSA have shown that APAP can diagnose severe OSA effectively, but the diagnosis of mild-moderate OSA is less reliable. APAP devices also can be effective therapy for selected patients with OSA, with overall similar results to conventional fixed CPAP in terms of respiratory disturbances, sleep quality, nocturnal oxygenation, and daytime sleepiness and performance, with less known or other long-term outcomes. In most studies, mean treatment pressures are lower, without change in side effect profile. Compliance and preference with APAP are similar to or somewhat better than CPAP in most studies. APAP also can be used in an attended setting to titrate an effective pressure for use in long-term conventional CPAP therapy, also with similar results to CPAP in many patients. APAP devices are more expensive than CPAP devices, but the cost may be outweighed if a group of patients who can be diagnosed, treated, or titrated safely in the unattended setting can be identified. Although diagnostic and therapeutic algorithms for APAP have been proposed, the best candidates for this modality must be defined better.     

持续气道正压通气治疗肥胖低通气综合征

目的探讨持续气道正压通气治疗肥胖低通气综合征（ＯＨＳ）的疗效。方法用ＣＰＡＰ（经鼻持续气道正压通气）及ＢｉＰＡＰ（双水平气道正压通气）呼吸机分别对２１例及１４例肥胖低通气综合征患者治疗２个月,比较治疗前后的呼吸紊乱指数（ＡＨＩ）、低通气指数（ＨＩ）、体块指数（ＢＭＩ）、４％的血氧饱和度降低次数（ＯＤＩ４）以及最低血氧饱和度（ｍｉｎＳａＯ２）,并将ＢＭＩ与ＡＨＩ、ＨＩ及ｍｉｎＳａＯ２作相关性分析。结果肥胖低通气患者治疗后ＡＨＩ、ＨＩ、ＢＭＩ、ＯＤＩ４、ｍｉｎＳａＯ２均有明显改善（Ｐ＜００５）;而ＢＭＩ与ＨＩ、及ｍｉｎＳａＯ２的相关性检验无显著性（相关系数分别为ｒ＝０．０３４６８和ｒ＝０．０５５８１,Ｐ＞００５）,提示单纯降低ＢＭＩ并不能有效地改善ＨＩ及ｍｉｎＳａＯ２。结论持续气道正压通气是治疗ＯＨＳ一种无创、有效的措施,且能在短期内明显改善临床症状,提高生活质量。     

Sleep-related breathing disorders in facioscapulohumeral dystrophy

Purpose

Severe manifestations of facioscapulohumeral dystrophy (FSHD) may be associated with sleep-disordered breathing (SDB), including obstructive sleep apnea (OSA) and nocturnal hypoventilation (NH), but prevalence data are scarce. In patients with respiratory muscle weakness, detection of NH can be facilitated by transcutaneous capnometry, but respective data derived from FSHD patients have not yet been published.

Methods

We collected sleep studies and capnometry recordings from 31 adult patients with genetically confirmed FSHD who were admitted to our sleep laboratory for first-ever evaluation of sleep-related breathing. Indications for admission included non-restorative sleep, morning headache, or excessive daytime sleepiness. In addition, sleep studies were initiated if symptoms or signs of respiratory muscle weakness were present. Thirty-one subjects with insomnia served as controls for comparison of respiratory measures during sleep.

Results

In the FSHD group, 17/31 (55%) patients showed OSA and 8 (26%) had NH. NH would have been missed in 7/8 patients if only oximetry criteria of hypoventilation had been applied. Capnography results were correlated with disease severity as reflected by the Clinical Severity Score (CSS). Non-invasive ventilation (NIV) was started in 6 patients with NH and 3 individuals with OSA. Nocturnal continuous positive airway pressure was administered to 2 patients, and positional therapy was sufficient in 4 individuals. In patients initiated on NIV, nocturnal gas exchange already improved in the first night of treatment.

Conclusions

SDB is common in adult patients with FSHD complaining of sleep-related symptoms. It may comprise OSA, NH, and most often, the combination of both. Sleep-related hypercapnia is associated with disease severity. Transcutaneous capnometry is superior to pulse oximetry for detection of NH.

     

Recent advances in understanding the pathogenesis of obstructive sleep apnea

PURPOSE OF REVIEW: The pathogenesis of obstructive sleep apnea (OSA) is incompletely understood. Historically it was believed that patients with OSA have a small upper airway (often due to obesity) that is kept patent during wakefulness by the activity of upper airway dilating muscles. With the reduction in muscle tone at sleep onset, the airway collapses and causes apnea. While this appears to be the case for many patients with OSA, other patients show no major airway anatomic defects or minimal obesity. RECENT FINDINGS: This has led to the concept that other factors such as unstable ventilatory control and changes in lung volume during sleep may be involved in the pathogenesis of OSA. Recently there have been several advances in our understanding of how these mechanisms are involved in OSA pathogenesis. SUMMARY: A more complete understanding of apnea pathogenesis may improve therapeutic techniques and reduce the consequences of OSA.     

Chemical control stability in patients with obstructive sleep apnea

The role of chemical control instability in the pathogenesis of obstructive sleep apnea (OSA) is not clear. We studied 32 patients with OSA during sleep while their upper airway was stabilized with continuous positive airway pressure. Twelve patients had repetitive OSA whenever they were asleep, regardless of body position or sleep stage, and were classified as having severe OSA (apnea-hypopnea index [AHI] = 88 +/- 19). The remaining 20 patients had sporadic OSA or repetitive OSA for only part of the time (mild/moderate OSA; AHI = 27 +/- 16). Susceptibility to periodic breathing (PB) was assessed by gradually increasing controller gain, using proportional assist ventilation. The increase in loop gain (LG) at each assist level was quantified from the ratio of assisted tidal volume (VT) to the VT obtained during single-breath reloading tests (VT amplification factor [VTAF]). Nine of 12 patients with severe OSA developed PB, with recurrent central apneas, whereas only six of 20 patients in the mild/moderate group developed PB (p < 0.02). This difference was observed despite the subjection of the mild/moderate group to greater amplification of LG; the highest values of VTAF in the mild/moderate and severe groups were 2.7 +/- 1.0 and 1.9 +/- 0.7, respectively (p < 0.01). We conclude that the chemical control system is more unstable in patients with severe OSA than in patients with milder OSA. We speculate that this may contribute to the severity of OSA, at least in some patients.     

Ventilación mecánica no invasiva en pacientes con síndrome de obesidad-hipoventilación. Evolución a largo plazo y factores pronósticos

IntroductionObesity is associated with 2 closely related respiratory diseases: obesity hypoventilation syndrome (OHS) and obstructive sleep apnea-hypopnea syndrome (OSAHS). It has been shown that noninvasive ventilation during sleep produces clinical and functional improvement in these patients. The long-term survival rate with this treatment, and the difference in clinical progress in OHS patients with and without OSAHS are analyzed.MethodologyLongitudinal, observational study with a cohort of patients diagnosed with OHS, included in a home ventilation program over a period of 12 years, divided into 2 groups: pure OHS and OSAHS-associated OHS. Bi-level positive airway pressure ventilation was administered. During the follow-up period, symptoms, exacerbations and hospitalizations, blood gas tests and pulmonary function tests, and survival rates were monitored and compared.ResultsEighty-three patients were eligible for analysis, 60 women (72.3%) and 23 men (27.7%), with a mean survival time of 8.47 years. Fifty patients (60.2%) were included in the group without OSAHS (OHS) and 33 (39.8%) in the OSAHS-associated OHS group (OHS-OSAHS). PaCO₂ in the OHS group was significantly higher than in the OHS-OSAHS group (P < .01). OHS patients also had a higher hospitalization rate (P < .05). There was a significant improvement in both groups in FEV₁ and FVC, and no differences between groups in PaCO₂ and PaO₂ values. There were no differences in mortality between the 2 groups, but low FVC values were predictive of mortality.ConclusionsThe use of mechanical ventilation in patients with OHS, with or without OSAHS, is an effective treatment for the correction of blood gases and functional alterations and can achieve prolonged survival rates.     

Impaired objective daytime vigilance in obesity-hypoventilation syndrome: impact of noninvasive ventilation

BACKGROUND: Obesity-hypoventilation syndrome (OHS) is efficiently treated by noninvasive ventilation (NIV). Sleep respiratory disturbances, reduced ventilatory drive, and excessive daytime sleepiness (EDS) are commonly reported, but their relationships remain unclear. OBJECTIVES: To characterize sleep breathing disorders encountered in patients with OHS, to compare low and normal CO(2) responders in terms of sleep abnormalities, subjective and objective measures of EDS, and to measure the changes induced by NIV on these parameters. METHODS: At baseline and after 5 nights of NIV, 15 consecutive patients (mean [+/- SD] age, 55 +/- 9 years; mean body mass index, 38.7 +/- 6.1 kg/m(2); Paco(2), 47.3 +/- 2.3 mm Hg) prospectively underwent polysomnography, CO(2) ventilatory response testing, Epworth sleepiness scale scoring, and the Oxford Sleep Resistance (OSLER) test, which is an objective vigilance test. RESULTS: OHS patients exhibited obstructive sleep apnea syndrome (mean apnea-hypopnea index, 62 +/- 32 events per hour) and rapid eye movement (REM) sleep hypoventilation (mean REM sleep time, 35 +/- 33%). Baseline CO(2) sensitivity was significantly related to the proportion of hypoventilation during REM sleep (r = 0.54; p = 0.037). Six patients showed abnormal sleep latencies during the OSLER test (71% of the low CO(2) responders vs 14% of the normal CO(2) responders). Low CO(2) responders exhibited significantly shorter sleep latencies during the OSLER test (23 +/- 14 vs 37 +/- 8 min, respectively; p = 0.05). Using NIV, diurnal blood gas levels were improved and REM sleep hypoventilation were suppressed. Objective sleepiness was improved in low CO(2) responders (p = 0.04). CONCLUSION: In OHS patients, the lower the daytime CO(2) response, the higher the proportion of REM sleep hypoventilation and daytime sleepiness. Short-term therapy with NIV improves all of these parameters.