Optimizing respiratory function assessments to elucidate the impact of obesity on respiratory health.

There is an increasing prevalence of obesity worldwide and its impact on respiratory health is of significant concern. Obesity affects the respiratory system by several mechanisms, including by direct mechanical changes due to fat deposition in the chest wall, abdomen and upper airway, as well as via systemic inflammation. The increased mechanical load in obese individuals leads to reduced chest wall and lung compliance and increased work of breathing. While there is generally minimal effect on spirometric values, as body mass index increases, the expiratory reserve volume, and hence functional residual capacity, reduces, often approaching residual volume in more severe obesity. The majority of evidence however suggests that obese individuals free from lung disease have relatively normal gas exchange. The link between asthma and obesity, while initially unclear, is now recognized as being a distinct asthma phenotype. While studies investigating objective markers of asthma have shown that there is no association between obesity and airway hyper-responsiveness, a recent working group identified obesity as a major risk factor for the development of asthma in all demographic groups. Although the temptation may be to attribute obesity as the cause of dyspnoea in symptomatic obese patients, accurate respiratory assessment of these individuals is necessary. Lung function tests can confirm that any altered physiology are the known respiratory consequences of obesity. However, given that obesity causes minimal changes in lung function, significant abnormalities warrant further investigation. An important consideration is the knowledge that many of the respiratory physiology consequences of obesity are reversible by weight loss.

Surgical vs conventional therapy for weight loss treatment of obstructive sleep apnea: a randomized controlled trial.

CONTEXT: Obstructive sleep apnea (OSA) is strongly related to obesity. Weight loss is recommended as part of the overall management plan for obese patients diagnosed with OSA. OBJECTIVE: To determine whether surgically induced weight loss is more effective than conventional weight loss therapy in the management of OSA. DESIGN, SETTING, AND PATIENTS: A randomized controlled trial of 60 obese patients (body mass index: >35 and <55) with recently diagnosed (<6 months) OSA and an apnea-hypopnea index (AHI) of 20 events/hour or more. These patients had been prescribed continuous positive airway pressure (CPAP) therapy to manage OSA and were identified via accredited community sleep clinics. The trial was conducted between September 2006 and March 2009 by university- and teaching hospital-based clinical researchers in Melbourne, Australia. Patients with obesity hypoventilation syndrome, previous bariatric surgery, contraindications to bariatric surgery, or significant cardiopulmonary, neurological, vascular, gastrointestinal, or neoplastic disease were excluded. INTERVENTIONS: Patients were randomized to a conventional weight loss program that included regular consultations with a dietitian and physician, and the use of very low-calorie diets as necessary (n = 30) or to bariatric surgery (laparoscopic adjustable gastric banding; n = 30). MAIN OUTCOME MEASURES: The primary outcome was baseline to 2-year change in AHI on diagnostic polysomnography scored by staff blinded to randomization. Secondary outcomes were changes in weight, CPAP adherence, and functional status. RESULTS: Patients lost a mean of 5.1 kg (95% CI, 0.8 to 9.3 kg) in the conventional weight loss program compared with 27.8 kg (95% CI, 20.9 to 34.7 kg) in the bariatric surgery group (P < .001). The AHI decreased by 14.0 events/hour (95% CI, 3.3 to 24.6 events/hour) in the conventional weight loss group and by 25.5 events/hour (95% CI, 14.2 to 36.7 events/hour) in the bariatric surgery group. The between-group difference was -11.5 events/hour (95% CI, -28.3 to 5.3 events/hour; P = .18). CPAP adherence did not differ between the groups. The bariatric surgery group had greater improvement in the Short Form 36 physical component summary score (mean, 9.3 [95% CI, 0.5 to 18.0]; P = .04). CONCLUSION: Among a group of obese patients with OSA, the use of bariatric surgery compared with conventional weight loss therapy did not result in a statistically greater reduction in AHI despite major differences in weight loss. TRIAL REGISTRATION: anzctr.org Identifier: 12605000161628.

Adjustable gastric banding and conventional therapy for type 2 diabetes: a randomized controlled trial.

CONTEXT: Observational studies suggest that surgically induced loss of weight may be effective therapy for type 2 diabetes. OBJECTIVE: To determine if surgically induced weight loss results in better glycemic control and less need for diabetes medications than conventional approaches to weight loss and diabetes control. DESIGN, SETTING, AND PARTICIPANTS: Unblinded randomized controlled trial conducted from December 2002 through December 2006 at the University Obesity Research Center in Australia, with general community recruitment to established treatment programs. Participants were 60 obese patients (BMI >30 and <40) with recently diagnosed (<2 years) type 2 diabetes. INTERVENTIONS: Conventional diabetes therapy with a focus on weight loss by lifestyle change vs laparoscopic adjustable gastric banding with conventional diabetes care. MAIN OUTCOME MEASURES: Remission of type 2 diabetes (fasting glucose level <126 mg/dL [7.0 mmol/L] and glycated hemoglobin [HbA1c] value <6.2% while taking no glycemic therapy). Secondary measures included weight and components of the metabolic syndrome. Analysis was by intention-to-treat. RESULTS: Of the 60 patients enrolled, 55 (92%) completed the 2-year follow-up. Remission of type 2 diabetes was achieved by 22 (73%) in the surgical group and 4 (13%) in the conventional-therapy group. Relative risk of remission for the surgical group was 5.5 (95% confidence interval, 2.2-14.0). Surgical and conventional-therapy groups lost a mean (SD) of 20.7% (8.6%) and 1.7% (5.2%) of weight, respectively, at 2 years (P < .001). Remission of type 2 diabetes was related to weight loss (R2 = 0.46, P < .001) and lower baseline HbA1c levels (combined R2 = 0.52, P < .001). There were no serious complications in either group. CONCLUSIONS: Participants randomized to surgical therapy were more likely to achieve remission of type 2 diabetes through greater weight loss. These results need to be confirmed in a larger, more diverse population and have long-term efficacy assessed. TRIAL REGISTRATION: actr.org Identifier: ACTRN012605000159651.

Polysomnography using abbreviated signal montages: impact on sleep and cortical arousal scoring.

OBJECTIVE: This study examined the impact of using two abbreviated signal montages on the accuracy, precision and inter-scorer reliability of polysomnography (PSG) sleep and arousal scoring, compared to a standard reference montage, in a cohort of patients investigated for obstructive sleep apnoea (OSA). One abbreviated montage incorporated two signals dedicated to sleep and arousal scoring, and the other incorporated a single signal. METHODS: Four scorers from two laboratories each scored 15 PSGS four times in random order: once using each abbreviated montage and twice using the reference montage. RESULTS: Use of the two-signal montage resulted in small changes in the distribution of sleep stages, a reduction in the arousal index and resultant reductions in sleep and arousal scoring agreement. For the one-signal montage, although similar magnitude sleep stage distribution changes were observed, there were larger reductions in the arousal index, and sleep and arousal scoring accuracy. Additionally, using the one-signal montage, there were statistically significant reductions in the precision of summary statistics including total sleep time (TST) and the amount of rapid eye movement (REM) sleep scored, and reductions in the inter-scorer reliability of REM sleep and arousal scoring. CONCLUSIONS: These findings demonstrate that abbreviated signal montages may result in underestimation of the arousal index and, depending on the montage, poorer precision in TST and REM sleep scoring, with potential consequences for apnoea-hypopnoea index (AHI) measures and OSA diagnosis. The results highlight the importance of careful evaluation of PSG results when using portable devices that have restricted signals, and they offer guidance for future PSG and portable monitoring standards.

Shorter Mandibular Length is Associated with a Greater Fall in AHI with Weight Loss.

RATIONALE: Obesity is a major risk factor towards the development of obstructive sleep apnea, while significant weight loss (both conservatively managed and surgically assisted) has a variable effect upon its severity. Differences in the effect of weight loss on obstructive sleep apnea may be due to underlying craniofacial characteristics. OBJECTIVES: To determine whether craniofacial characteristics can predict OSA treatment response to significant weight loss. METHODS: We analyzed craniofacial measurements from lateral cephalograms performed at baseline on 57 patients enrolled in a previously reported 2-year randomized clinical weight loss trial (laparoscopic adjustable gastric band surgery versus conservatively [dietician and very low calorie diet] treated). Group mean weight loss was ∼ 13% (mean weight loss 131 to 114 kg), with corresponding reduction in mean apnea-hypopnea index (AHI) from 61 to 41 events/h. Computer assisted lateral cephalogram analysis was undertaken by three trained staff blinded to treatment. We analyzed lateral cephalogram and demographic data at baseline (cross-sectional) and change over two years (interventional) in 54 patients. MEASUREMENTS AND MAIN RESULTS: Baseline cross-sectional analysis indicated no cephalometric measurement correlated significantly with baseline AHI when corrected for neck circumference. The percentage change in AHI over 2 years correlated with a shorter menton-gonion distance (i.e., mandibular body length). The % change in AHI correlated with the % weight change (R(2) = 0.25, p < 0.001) and mandibular body length (R(2) = 0.19, p = 0.002). The % change in AHI correlated with combined weight change and mandibular body length (combined R(2) = 0.31, p < 0.001). CONCLUSIONS: Weight loss as a therapeutic option for severe OSA with severe obesity may be predicted by shorter mandibular body length as measured by lateral cephalometry.

Predicting sleep apnea and excessive day sleepiness in the severely obese: indicators for polysomnography.

BACKGROUND: Obstructive sleep apnea (OSA) is common in severely obese subjects (body mass index [BMI] > 35). Overnight polysomnography (OPS) is the "gold standard" method of evaluating this condition; however, it is time-consuming, inconvenient, and expensive. Selection of patients for OPS would be enhanced if we could better predict those likely to have clinically significant OSA. STUDY OBJECTIVE: To look for clinical and biochemical predictors of OSA in symptomatic patients presenting for obesity surgery. DESIGN AND PATIENTS: Symptoms suggestive of OSA were sought in a structured interview. We report OPS results of 99 consecutive subjects in whom OSA was clinically suspected. Predictors of apnea-hypopnea index (AHI) were sought from an extensive preoperative data collection. Multivariate linear and logistic analysis was used to identify independent predictors of AHI. RESULTS: Symptoms were poor predictors of AHI, with observed sleep apnea the only positive predictor. Four clinical and two biochemical factors independently predicted AHI: observed sleep apnea, male sex, higher BMI, age, fasting insulin, and glycosylated hemoglobin A(Ic) (r(2) = 0.42). Neck circumference (the best single measure) could replace BMI and sex in the analysis (r(2) = 0.43). With cutoffs selected, a simple scoring system using these six factors provides a method of predicting those with moderate or severe OSA. A score > or = 3 provides a sensitivity and specificity of 89% and 81%, and 96% and 71% for AHIs of > or = 15 and > or = 30, respectively. None of the 31 subjects with scores of 0 or 1 were found to have an AHI > or = 15. CONCLUSION: We explore sleep disturbance and report a simple method of predicting OSA in severely obese symptomatic subjects. This should assist in limiting the use of OPS to those with greater risk and provide a method of assessing risk in those not presenting primarily with a sleep problem.

Severe gastroesophageal reflux is associated with reduced carbon monoxide diffusing capacity.

OBJECTIVE: To assess whether severe gastroesophageal reflux (GER) is associated with abnormalities in lung function including measures of lung volume and gas diffusion. METHODS: Data from 147 patients with obesity (body mass index [BMI] range, 31.7 to 70 kg/m(2)) who presented for obesity surgery was analyzed retrospectively. A questionnaire was completed preoperatively that included a history of GER, frequency and severity of symptoms, investigations, and medications used. A history of lung disease, sleep-disordered breathing, and smoking also was obtained. A physician who was blinded to lung function graded GER severity prospectively by the results of pH monitoring and/or gastroscopy, and medication use. Spirometry, lung volumes, and gas transfer were measured preoperatively. RESULTS: Patients with severe GER had reduced levels of the diffusing capacity of the lung for carbon monoxide (DLCO) [21.1 mL/min/mm Hg; 95% confidence interval (CI), 18.9 to 23.2], as measured by CO transfer, compared with those patients without GER (26.3 mL/min/mm Hg; 95% CI, 24.4 to 28.2; p = 0.001). This remained significant after adjusting for age, gender, BMI, and smoking history. Gas transfer corrected for lung volume also was reduced in the group with severe GER (4.6 mL/min/mm Hg per L; 95% CI, 4.3 to 4.9) compared to the group without GER (5.3 mL/min/mm Hg per L; 95% CI, 5.1 to 5.5; p = 0.001). There was no significant difference in other measures of lung function. CONCLUSIONS: Severe GER is associated with an impairment of gas exchange. This may be due to microaspiration of gastric acid or fluid into the airways.

The laparoscopic adjustable gastric band (Lap-Band): a prospective study of medium-term effects on weight, health and quality of life.

BACKGROUND: Obesity is now one of our major public health problems. Effective and acceptable treatment options are needed. The Lap-Band system is placed laparoscopically and allows adjustment of the level of gastric restriction. METHODS: A prospective study of 709 severely obese patients was conducted over a 6-year period at a university-based multidisciplinary referral center. After extensive preoperative evaluation, patients with a body mass index > 35 were treated by Lap-Band placement. Close follow-up with progressive adjustment of gastric restriction continued permanently. Medical co-morbidities were monitored as part of comprehensive prospective data collection. RESULTS: There have been no deaths perioperatively or during follow-up. Significant perioperative adverse events occurred in 1.2% only. Reoperation has been needed for prolapse (slippage) in 12.5%, erosion of the band into the stomach in 2.8% and for tubing breaks in 3.6%. A steady progression of weight loss has occurred through the duration of the study with 52 +/- 19% EWL at 24 months (n = 333), 53 +/- 22% EWL at 36 months (n = 264), 52 +/- 24% EWL at 48 months (n = 108), 54 +/- 24% EWL at 60 months (n = 30), and 57 +/- 15% EWL at 72 months (n = 10). Major improvements have occurred in diabetes, asthma, gastroesophageal reflux, dyslipidemia, sleep apnea and depression. Quality of life as measured by Rand SF-36 shows highly significant improvement. CONCLUSIONS: Placement of the Lap-Band system provides safe and effective control of severe obesity. The effect on weight loss is durable and is associated with major improvement in health and quality of life. It has the potential to provide a broadly acceptable option for this common and serious disease.

Preoxygenation is more effective in the 25 degrees head-up position than in the supine position in severely obese patients: a randomized controlled study.

BACKGROUND: Class III obese patients have altered respiratory mechanics, which are further impaired in the supine position. The authors explored the hypothesis that preoxygenation in the 25 degrees head-up position allows a greater safety margin for induction of anesthesia than the supine position. METHODS: A randomized controlled trial measured oxygen saturation and the desaturation safety period after 3 min of preoxygenation in 42 consecutive (male:female 13:29) severely obese (body mass index > 40 kg/m) patients who were undergoing laparoscopic adjustable gastric band surgery and were randomly assigned to the supine position or the 25 degrees head-up position. Serial arterial blood gases were taken before and after preoxygenation and 90 s after induction. After induction, ventilation was delayed until blood oxygen saturation reached 92%, and this desaturation safety period was recorded. RESULTS: The mean body mass indexes for the supine and 25 degrees head-up groups were 47.3 and 44.9 kg/m, respectively (P = 0.18). The group randomly assigned to the 25 degrees head-up position achieved higher preinduction oxygen tensions (442 +/- 104 vs. 360 +/- 99 mmHg; P = 0.012) and took longer to reach an oxygen saturation of 92% (201 +/- 55 vs. 155 +/- 69 s; P = 0.023). There was a strong positive correlation between the induction oxygen tension achieved and the time to reach an oxygen saturation of 92% (r = 0.51, P = 0.001). There were no adverse events associated with the study. CONCLUSION: Preoxygenation in the 25 degrees head-up position achieves 23% higher oxygen tensions, allowing a clinically significant increase in the desaturation safety period--greater time for intubation and airway control. Induction in the 25 degrees head-up position may provide a greater safety margin for airway control.