Supine awake oximetry as a screening tool for daytime hypercapnia in super-obese patients

BACKGROUND

Evidence-based screening tools are required for detection of daytime hypercapnia in high-risk patient populations.

AIMS

To determine the validity of supine awake oximetry as a test for daytime hypercapnia and severe sleep disordered breathing (SDB) in super-obese patients.

METHODS

This was a cross-sectional diagnostic test evaluation of super-obese adults (body mass index >50 kg/m² ) presenting to Liverpool Hospital, Australia, between 2009 and 2015 for diagnostic polysomnography (PSG) and arterial blood gas measurement. Supine awake oxygen saturation (SpO₂ ) was determined using oximetry measurements from the first three awake epochs of raw PSG data. Sensitivity and specificity of SpO₂ for detecting patients with daytime hypercapnia (PaCO₂ >45 mmHg) and severe SDB (respiratory disturbance index (RDI) >30 events/h) were assessed at various cut-off points and displayed using a receiver operating characteristic (ROC) curve. Area under the ROC curve and positive and negative predictive values (PPV and NPV) in the present patient population were derived.

RESULTS

Of 52 patients, 23 (44%) had daytime hypercapnia. SpO₂ measured awake in the supine position was associated with the presence of daytime hypercapnia but not with the presence of severe SDB. Overall, awake supine SpO₂ <91.2% had 34.8% sensitivity, 96.6% specificity and 88.8% PPV, and SpO₂ <96.7% had 87.0% sensitivity, 20.7% specificity and 66.7% NPV for the presence of daytime hypercapnia.

CONCLUSION

Awake supine oximetry is an easily performed test that may have novel use in identifying patients at high risk of respiratory failure. Future studies are required to evaluate prospectively its role in screening patients at risk of daytime hypercapnia.

Increased sexual desire with exogenous testosterone administration in men with obstructive sleep apnea: a randomized placebo-controlled study

Testosterone (T) deficiency, sexual dysfunction, obesity and obstructive sleep apnea (OSA) are common and often coexist. T prescriptions have increased worldwide during the last decade, including to those with undiagnosed or untreated OSA. The effect of T administration on sexual function, neurocognitive performance and quality of life in these men is poorly defined. The aim of this study was to examine the impact of T administration on sexual function, quality of life and neurocognitive performance in obese men with OSA. We also secondarily examined whether baseline T might modify the effects of T treatment by dichotomizing on baseline T levels pre-specified at 8, 11 and 13 nmol/L. This was a randomized placebo-controlled study in which 67 obese men with OSA (mean age 49 ± 1.3 years) were randomized to receive intramuscular injections of either 1000 mg T undecanoate or placebo at baseline, week 6 and week 12. All participants were concurrently enrolled in a weight loss program. General and sleep-related quality of life, neurocognitive performance and subjective sexual function were assessed before and 6, 12 and 18 weeks after therapy. T compared to placebo increased sexual desire (p = 0.004) in all men, irrespective of baseline T levels. There were no differences in erectile function, frequency of sexual attempts, orgasmic ability, general or sleep-related quality of life or neurocognitive function (all p = NS). In those with baseline T levels below 8 nmol/L, T increased vitality (p = 0.004), and reduced reports of feeling down (p = 0.002) and nervousness (p = 0.03). Our findings show that 18 weeks of T therapy increased sexual desire in obese men with OSA independently of baseline T levels whereas improvements in quality of life were evident only in those with T levels below 8 nmol/L. These small improvements would need to be balanced against potentially more serious adverse effects of T therapy on breathing.

The validity of wrist actimetry assessment of sleep with and without sleep apnea

INTRODUCTION

It is unclear whether actimetry can be reliably used to measure sleep in severe obstructive sleep apnea (OSA) patients. We compared polysomnography (PSG) with actimetric assessment of sleep on an epoch-by-epoch basis in subjects with and without OSA.

METHODS

21 subjects were recorded with simultaneous overnight standard PSG and actimetry.

RESULTS

10 subjects with apnea-hypopnea index (AHI) <10 (6.5 +/- 2.8/h) were classified as non-OSA subjects and 11 subjects with AHI >10 (42.0 +/- 27.3/h) were classified as OSA subjects. Overall sensitivity and specificity for actimetry to identify sleep was 94.6% and 40.6%, respectively, with an overall mean sleep/wake simple agreement of 84.6% and kappa of 0.38. There was no difference in agreement between non-OSA and OSA subjects (simple agreement: 83% vs. 86%, p = 0.73; kappa: 0.35 vs. 0.40, p = 0.73). The kappa agreement did not correlate with PSG arousal index (r = -0.21, p = 0.36) but declined with reduced sleep efficiency (r = 0.66, p = 0.001). There was no systematic difference (all p > 0.40) between actimetry and PSG in sleep latency, total sleep time and sleep efficiency, although correlations between the measurements using the two techniques were generally poor. However, while actimetry systematically underestimated wake after sleep onset (WASO) (35.5 +/- 18.8 vs. 59.4 +/- 35.1, p = 0.009), fragmentation index measured by actimetry only underestimated arousal index measured by PSG in OSA patients (23.9 +/- 17.8 vs. 33.1 +/- 18.5, p = 0.04).

CONCLUSIONS

Contrary to prior reports, epoch-by-epoch comparison of sleep/wake scoring showed similar fair agreement between actimetry and PSG in subjects with or without OSA. Fragmentation index by actimetry may underestimate arousals caused by respiratory events and offer misleading results in severe OSA patients.

Two randomized placebo-controlled trials to evaluate the efficacy and tolerability of mirtazapine for the treatment of obstructive sleep apnea

OBJECTIVE

Mirtazapine is an a2A antagonist and mixed 5-HT2/5-HT3 antagonist that has been proposed as a potential treatment for obstructive sleep apnea (OSA). A small, randomized, controlled trial has previously found an approximate halving in the severity of OSA with daily doses of 4.5 and 15 mg. We aimed to confirm and extend these findings in 2 randomized placebo-controlled, proof-of-concept trials.

METHODS

Two randomized, double-blind, placebo-controlled trials of mirtazapine for OSA (apnea-hypopnea index 10-40/h). Study 1: 3-way crossover, dose-finding study testing the self-administration of mirtazapine (7.5, 15, 30, and/or 45 mg) or placebo 30 minutes prior to bedtime for 2 weeks at each dose. Twenty patients were randomly assigned to 1 of 6 different dose-sequence groups, with each patient exposed to a maximum of 3 doses. Study 2: 3-arm, randomized, parallel-group trial of mirtazapine at 15 mg or mirtazapine 15 mg + Compound CD0012 or placebo for 4 weeks in 65 patients with OSA.

RESULTS

Two patients withdrew from Study 1 after complaints of unacceptable lethargy. Fifteen patients were withdrawn from study 2, 7 after complaints of unacceptable lethargy or other side-effects. No measurement of sleep apnea improved due to mirtazapine in either study. Weight gain was significantly greater on mirtazapine than on placebo in both trials.

CONCLUSIONS

Mirtazapine did not improve sleep apnea in either trial. Mirtazapine caused weight gain, which may further worsen OSA. Therefore, mirtazapine is not recommended for the treatment of OSA.

Assessment of sleep and breathing in adults with prader-willi syndrome: a case control series

OBJECTIVES

Prader-Willi syndrome (PWS) is a genetic disorder (linked to chromosome 15q11-13) characterized by hypotonia and developmental delay, hyperphagia and obesity, hypersomnia and abnormal sleep, and behavioral problems. Such patients may also be at increased risk of obstructive sleep apnea (OSA), although whether this risk is explained by known risk factors has not previously been directly tested. Our aim was to compare sleep and breathing in an older group of patients with Prader-Willi syndrome with a control group-matched on the basis of age, sex, and body mass index (BMI)-in order to determine which specific features are not explained by these known confounders.

METHODS

Consecutive patients with PWS attending the PWS clinic at Royal Prince Alfred Hospital Sydney, Australia, were recruited. Age-, sex-, and BMI-matched controls were selected from the Sleep Investigation Unit at Royal Prince Alfred Hospital, and polysomnography-derived sleep and other parameters were compared across the groups.

RESULTS

Nineteen subjects with PWS (14 males) were included in the study. Eighteen (95%) had a total respiratory disturbance index (TRDI) of greater than 5 events per hour, with 4 (21%) having severe obstructive sleep apnea (TRDI > or = 30 events/hour) and 9 (47%) having evidence of obesity hypoventilation syndrome. Patients with PWS, as compared with the control group, had evidence of more nocturnal hypoxemia, with lower oxyhemoglobin saturations and percentages of sleep time at less than 80% oxyhemoglobin saturation (all p values < 0.05). There were no significant differences in sleep architecture; however, there was a reduction in rapid eye movement latency seen in the PWS group (p < 0.05). Serum leptin was higher than the reference range in the PWS group but was not measured in the control group.

CONCLUSION

Patients with PWS drawn from an adult and adolescent PWS clinic have a high rate of sleep-disordered breathing. There is evidence that patients with PWS may have more nocturnal hypoventilation than a well-matched control group. These data suggest that the chromosome region 15q11-13 may be involved in some aspects of the regulation of breathing, although whether putative molecular mechanisms act directly or indirectly will require further investigation.

Ethnicity and obstructive sleep apnoea

There is a scarcity of adult prevalence studies of OSA outside the Caucasian populations of North America, Europe and Australia, and comparisons have been complicated by methodological differences in sleep study settings, respiratory events definition, measured risk factors and clinical outcomes, and the lack of objective parameters for the measurement of ethnicity itself. Comparing studies with the same methodological design and respiratory events definition, recent large-scale prevalence studies from Hong Kong, Korea and India show similar OSA rates to populations of mainly Caucasian composition. OSA is a very complex disorder determined by several phenotypes such as obesity, craniofacial structure and abnormalities in neuromuscular and ventilatory control. Genetics may partially explain some of the ethnic clustering of these phenotypes, modulated by cultural and environmental factors. The exact contribution of these component phenotypes to overall OSA risk will be determined by their varying prevalence and relative risk conferred across ethnic groups. For lesser degrees of obesity, Asians are at risk for a more severe degree of illness compared with Caucasians. Inter-ethnic studies suggests that African-American ethnicity may also be a significant risk factor for OSA. The increased prevalences of OSA among American Indians and Hispanic adults, and increased severity among Pacific Islanders and Maoris, were mainly explained by increased obesity parameters. Most cephalometric studies have largely been conducted without specific regard to ethnicity and comparisons of findings across studies have been mainly limited by differences in sampling methods and the varying selection and definition of measured cephalometric variables. The limited number of studies with inter-ethnic comparative data suggest cephalometric variables and their degree of contribution to OSA vary across ethnic groups.

A multicentre comparison of the efficacy of terbutaline Turbuhaler and salbutamol pressurized metered dose inhaler in hot, humid regions

Twenty seven adults and 20 children with previously diagnosed stable asthma, using a salbutamol pressurized metered dose inhaler (P-MDI) and living in Cairns, Townsville and Southport, Queensland, Australia participated in a randomized, open-label cross-over comparison of terbutaline administered via Turbuhaler and salbutamol administered via P-MDI. The aim of the study was to compare the clinical effectiveness and patient acceptance of the two treatments in hot, humid regions. Terbutaline was administered via Turbuhaler and salbutamol via P-MDI on at least two occasions per day during each four week treatment period. Spirometry was performed at the start of the study, after the two week run-in and at the end of each treatment period. Patients used diary cards to record morning and evening peak expiratory flows, daily symptom scores and daily intake of beta 2 agonist medication. At the end of the study, patients answered a treatment preference question. Forty six patients completed the study. No statistically significant differences were observed between the two treatments in peak expiratory flow, change in morning peak expiratory flow pre- and post-beta-agonist, daily symptom scores, diurnal variability and spirometry. Forty four percent of patients preferred the terbutaline Turbuhaler and 39% preferred salbutamol P-MDI. Both agents were similarly tolerated. Terbutaline delivered by Turbuhaler is as clinically effective as salbutamol delivered by P-MDI in patients with asthma living in hot, humid regions.

Human alveolar gas-mixing efficiency for gases of differing diffusivity in health and airflow limitation

1. Incomplete mixing of alveolar gas may be expressed as an equivalent alveolar dead space serving a remaining alveolar space in which mixing is regarded as complete. Calculation of this dead space during multiple-breath, inert gas wash-in or wash-out leads to an estimate of 'multiple-breath alveolar mixing efficiency' (MBME). 2. We measured MBME in 25 healthy subjects and six patients with chronic airflow limitation (CAL), and in three asthmatic patients before and after bronchial provocation with histamine aerosol, from successive breaths during open-circuit, multiple-breath wash-in of a mixture containing helium (He) and sulphur hexafluoride (SF6). The simultaneous use of a light and a heavy gas helps to identify diffusive mechanisms. 3. MBME fell almost linearly with log Z, the proportion of total wash-in remaining uncompleted. For a given Z, MBME was always lower for SF6 than for He in the same subject. In health the lowest MBME (52.2%) was seen for SF6 in a man aged 21 years. The same wash-in yielded a ventilation distribution with an extreme range of specific ventilation of less than 1 decade. MBME of this order is thus consistent with estimates of ventilation distribution in health. 4. Patients with CAL showed a big increase in the volume of the conducting airways or 'series dead space' (VDS) for both gases, and VDS was always bigger for SF6 than for He. This very large VDS appears to be the main reason for wash-in delay in these patients, followed by impaired diffusive mixing in the peripheral air spaces. Ventilation maldistribution may play little part in the mixing defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Recovery of ventilation distributions by gas wash-out of a mechanical pump

A method for deriving virtually continuous distributions of ventilation in the lungs from multiple-breath wash-out of inert, insoluble gases has been tested using a mechanical pump in which two parallel compartments, simulating lung regions, could be differentially ventilated to any desired, and known, extent. With more than moderate non-uniformity, bimodal distributions were always recovered from wash-out data, and with high reproducibility. In a substantial proportion of wash-out experiments ventilation was recovered in regions of very low and very high turnover in addition to the expected modes. These spurious modes may be abolished by various computational devices, none entirely satisfactory. Simultaneous wash-out and wash-in of two or three gases of similar diffusivity give essentially identical solutions. When the pump is operated with the two cylinders out of phase, emptying patterns derived from gas wash-out correspond quite well with those expected from the pump setting. These results help to identify and clarify some of the errors which affect physiological wash-out studies.

Data acquisition from a multiplex, quadrupole mass spectrometer

Although various methods have been used to correct the output of a respiratory mass spectrometer for the delay and rise time in its response, thereby reducing the error in measured gas concentrations, there are additional considerations in the case of a multiplex mass spectrometer. The measured signal from the detector is a series of discrete samples of the concentration of several different gases rather than a continuous monitor of a single gas concentration as generated by other types of mass spectrometer. If the time constant of the mass spectrometer is of the same order as the interval between samples of a gas in the multiplex mode, correction techniques based on continuous-time analysis would not be as valid as those based on discrete-time analysis. Such correction techniques were compared to the use of a simple time shift. For multibreath gas washout analysis with simulated worst-case 'square wave breathing' it was found that, because of the complex nature of the response of the mass spectrometer, a simple time shift provided a reduction in error nearly equal to that of an additional first order response correction, and that such further corrections may be unnecessary or even invalid under some circumstances.