Single-institution experience and learning curve with upper airway stimulation

As upper airway stimulation (UAS) surgical implantation is a new procedure, the authors thought it would be instructive to describe a single-institution's experience with the inception of a UAS program. The description of our experience at the University of Pennsylvania may be useful for planning purposes when surgeons and sleep medicine physicians are considering program development. Laryngoscope, 126:S17-S19, 2016 Laryngoscope, 126:S17-S19, 2016.

An Examination of Methodological Paradigms for Calculating Upper Airway Critical Pressures during Sleep

STUDY OBJECTIVES

The goal of this study was to examine different paradigms for determining critical closing pressures (Pcrit). Methods of determining Pcrit were compared, including direct observation of occluded (no flow) breaths versus inferring Pcrit from extrapolated data, and Pcrit generated by aggregating pressure-flow data from multiple runs versus Pcrit averaged across individual pressure-flow runs. The relationship between Pcrit and obstructive sleep apnea (OSA) was examined.

METHODS

A total of 351 participants with and without OSA underwent overnight polysomnography with pressure-flow measurements to determine Pcrit. A series of filters were applied to raw data to provide consistent, objective criteria for determining which data to include in Pcrit calculations. Observed Pcrit values were computed as the mean nasal pressure level at which a subject had at least two breaths with peak inspiratory flow < 50 mL/sec. Extrapolated Pcrit was calculated in two ways: (1) separately for each individual run and then averaged; and (2) using all valid data from individual runs combined into one plot.

RESULTS

Observed Pcrit was calculated in 67% to 69% of participants, a similar or higher proportion of study subjects compared to extrapolated Pcrit values using a ± 3 cm H2O filter. Although raw (unfiltered) extrapolated Pcrit measures were able to be calculated among a greater proportion of participants than filtered, extrapolated Pcrit values, and thus had fewer missing values, they had larger variability. Both extrapolated and observed Pcrit were higher among individuals with OSA compared to those without OSA.

CONCLUSIONS

Observed Pcrit provides a reliable descriptor of hypotonic upper airway collapsibility. Different methods for determining Pcrit were able to distinguish subjects with and without OSA.

Cerebral metabolic rate of oxygen in obstructive sleep apnea at rest and in response to breath-hold challenge

Obstructive sleep apnea (OSA) is associated with extensive neurologic comorbidities. It is hypothesized that the repeated nocturnal apneas experienced in patients with OSA may inhibit the normal apneic response, resulting in hypoxic brain injury and subsequent neurologic dysfunction. In this study, we applied the recently developedOxFlowMRI method for rapid quantification of cerebral metabolic rate of oxygen (CMRO2) during a volitional apnea paradigm. MRI data were analyzed in 11 OSA subjects and 10 controls (mean ± SD apnea-hypopnea index (AHI): 43.9 ± 18.1 vs. 2.9 ± 1.6 events/hour,P < 0.0001; age: 53.8 ± 8.2 vs. 45.3 ± 8.5 years,P = 0.027; BMI: 36.6 ± 4.4 vs. 31.9 ± 2.2 kg/m(2),P = 0.0064). Although total cerebral blood flow and arteriovenous oxygen difference were not significantly different between apneics and controls (P > 0.05), apneics displayed reduced baseline CMRO2(117.4 ± 37.5 vs. 151.6 ± 29.4 µmol/100 g/min,P = 0.013). In response to apnea, CMRO2decreased more in apneics than controls (-10.9 ± 8.8 % vs. -4.0 ± 6.7 %,P = 0.036). In contrast, group differences in flow-based cerebrovascular reactivity were not significant. Results should be interpreted with caution given the small sample size, and future studies with larger independent samples should examine the observed associations, including potential independent effects of age or BMI. Overall, these data suggest that dysregulation of the apneic response may be a mechanism for OSA-associated neuropathology.

Understanding the anatomic basis for obstructive sleep apnea syndrome in adolescents

RATIONALE

Structural risk factors for obstructive sleep apnea syndrome (OSAS) in adolescents have not been well characterized. Because many adolescents with OSAS are obese, we hypothesized that the anatomic OSAS risk factors would be more similar to those in adults than those in children.

OBJECTIVES

To investigate the anatomic risk factors in adolescents with OSAS compared with obese and lean control subjects using magnetic resonance imaging (MRI).

METHODS

Three groups of adolescents (age range: 12-16 yr) underwent MRI: obese individuals with OSAS (n = 49), obese control subjects (n = 38), and lean control subjects (n = 50).

MEASUREMENTS AND MAIN RESULTS

We studied 137 subjects and found that (1) obese adolescents with OSAS had increased adenotonsillar tissue compared with obese and lean control subjects; (2) obese OSAS adolescents had a smaller nasopharyngeal airway than control subjects; (3) the size of other upper airway soft tissue structures (volume of the tongue, parapharyngeal fat pads, lateral walls, and soft palate) was similar between subjects with OSAS and obese control subjects; (4) although there were no major craniofacial abnormalities in most of the adolescents with OSAS, the ratio of soft tissue to craniofacial space surrounding the airway was increased; and (5) there were sex differences in the pattern of lymphoid proliferation.

CONCLUSIONS

Increased size of the pharyngeal lymphoid tissue, rather than enlargement of the upper airway soft tissue structures, is the primary anatomic risk factor for OSAS in obese adolescents. These results are important for clinical decision making and suggest that adenotonsillectomy should be considered as the initial treatment for OSAS in obese adolescents, a group that has poor continuous positive airway pressure adherence and difficulty in achieving weight loss.

Sleep in the intensive care unit

Sleep is an important physiologic process, and lack of sleep is associated with a host of adverse outcomes. Basic and clinical research has documented the important role circadian rhythm plays in biologic function. Critical illness is a time of extreme vulnerability for patients, and the important role sleep may play in recovery for intensive care unit (ICU) patients is just beginning to be explored. This concise clinical review focuses on the current state of research examining sleep in critical illness. We discuss sleep and circadian rhythm abnormalities that occur in ICU patients and the challenges to measuring alterations in circadian rhythm in critical illness and review methods to measure sleep in the ICU, including polysomnography, actigraphy, and questionnaires. We discuss data on the impact of potentially modifiable disruptors to patient sleep, such as noise, light, and patient care activities, and report on potential methods to improve sleep in the setting of critical illness. Finally, we review the latest literature on sleep disturbances that persist or develop after critical illness.

Volumetric MRI analysis pre- and post-Transoral robotic surgery for obstructive sleep apnea

OBJECTIVES/HYPOTHESIS

To quantitatively measure volumetric changes in upper airway soft tissue structures using magnetic resonance imaging (MRI) pre- and post transoral robotic surgery for obstructive sleep apnea (OSA-TORS).

STUDY DESIGN

Prospective, nonrandomized, institutional board-approved study.

METHODS

Apneics undergoing OSA-TORS, which included bilateral posterior hemiglossectomy with limited pharyngectomy and uvulopalatopharyngoplasty, had upper airway MRIs pre- and postoperatively. Changes (percent and absolute values) in upper airway and surrounding soft tissue volumes were calculated. We assessed whether there were significant volumetric changes and if changes correlated with apnea-hypopnea index (AHI) changes.

RESULTS

Nineteen MRIs and 18 polysomnograms were analyzed pre- and postoperation. Total airway volume increased by 19.4% (P = 0.030). Soft palate and tongue volumes decreased by 18.3% (P = 0.002) and 5.8% (P = 0.013), respectively. Retropalatal and total lateral wall volumes decreased by 49.8% (P = 0.0001) and 17.9% (P = 0.008), respectively. Changes in other structures were not significant. Eleven patients had surgical success, with a mean AHI decrease of 52.9; six were nonsuccesses with a mean AHI decrease of 4.5 (P =0.006). Decreased retropalatal lateral wall volume correlated with decreased AHI.

CONCLUSION

Airway, tongue, soft palate, and lateral wall volumes change significantly after OSA-TORS. Changes in the volume of the lateral walls correlated with changes in AHI. Volumetric upper airway MRI may be a helpful tool to better understand reasons for surgical success.

LEVEL OF EVIDENCE

4.

Enhanced upper-airway muscle responsiveness is a distinct feature of overweight/obese individuals without sleep apnea

RATIONALE

Body habitus is a major determinant of obstructive sleep apnea (OSA). However, many individuals do not have OSA despite being overweight/obese (body mass index > 25 kg/m(2)) for reasons that are not fully elucidated.

OBJECTIVES

To determine the key physiologic traits (upper-airway anatomy/collapsibility, upper-airway muscle responsiveness, chemoreflex control of ventilation, arousability from sleep) responsible for the absence of OSA in overweight/obese individuals.

METHODS

We compared key physiologic traits in 18 overweight/obese subjects without apnea (apnea-hypopnea index < 15 events per hour) with 25 overweight/obese matched patients with OSA (apnea-hypopnea index ≥ 15 events per hour) and 11 normal-weight nonapneic control subjects. Traits were measured by repeatedly lowering continuous positive airway pressure to subtherapeutic levels for 3 minutes during non-REM sleep.

MEASUREMENTS AND MAIN RESULTS

Overweight/obese subjects without apnea exhibited a less collapsible airway than overweight/obese patients with apnea (critical closing pressure: -3.7 ± 1.9 vs. 0.6 ± 1.2 cm H2O; P = 0.003; mean ± 95% confidence interval), but a more collapsible airway relative to normal-weight control subjects (-8.8 ± 3.1 cm H2O; P < 0.001). Notably, overweight/obese subjects without apnea exhibited a threefold greater upper-airway muscle responsiveness than both overweight/obese patients with apnea (Δgenioglossus EMG/Δepiglottic pressure: -0.49 [-0.22 to -0.79] vs. -0.15 [-0.09 to -0.22] %max/cm H2O; P = 0.008; mean [95% confidence interval]) and normal-weight control subjects (-0.16 [-0.04 to -0.30] %max/cm H2O; P = 0.02). Loop gain was elevated (more negative) in both overweight/obese groups and normal-weight control subjects (P = 0.02). Model-based analysis demonstrated that overweight/obese individuals without apnea rely on both more favorable anatomy and collapsibility and enhanced upper-airway dilator muscle responses to avoid OSA.

CONCLUSIONS

Overweight/obese individuals without apnea have a moderately compromised upper-airway structure that is mitigated by highly responsive upper-airway dilator muscles to avoid OSA. Elucidating the mechanisms underlying enhanced muscle responses in this population may provide clues for novel OSA interventions.

Diagnosis and treatment of sleep disordered breathing in hospitalized cardiac patients: a reduction in 30-day hospital readmission rates

BACKGROUND

Sleep disordered breathing (SDB) is associated with significant cardiovascular sequelae and positive airway pressure (PAP) has been shown to improve heart failure and prevent the recurrence of atrial fibrillation in cardiac patients with sleep apnea. Patients who are hospitalized with cardiac conditions frequently have witnessed symptoms of SDB but often do not have a diagnosis of sleep apnea. We implemented a clinical paradigm to perform unattended sleep studies and initiate treatment with PAP in hospitalized cardiac patients with symptoms consistent with SDB. We hypothesized that PAP adherence in cardiac patients with SDB would reduce readmission rates 30 days after discharge.

METHODS

106 consecutive cardiac patients hospitalized for heart failure, arrhythmias, and myocardial infarction and who reported symptoms of SDB were evaluated. Patients underwent a type III portable sleep study and those patients diagnosed with sleep apnea were started on PAP. Demographic data, SDB type, PAP adherence, and data regarding 30-day hospital readmission/ED visits were collected.

RESULTS

Of 106 patients, 104 had conclusive diagnostic studies using portable monitoring systems. Seventy-eight percent of patients (81/104) had SDB (AHI ≥ 5 events/h). Eighty percent (65/81) had predominantly obstructive sleep apnea, and 20% (16/81) had predominantly central sleep apnea. None of 19 patients (0%) with adequate PAP adherence, 6 of 20 (30%) with partial PAP use, and 5 of 17 (29%) of patients who did not use PAP were readmitted to the hospital or visited the emergency department (ED) for a cardiac issue within 30 days from discharge (p = 0.025).

CONCLUSIONS

Performing diagnostic unattended sleep studies and initiating PAP treatment in hospitalized cardiac patients was feasible and provided important clinical information. Our data indicate that hospital readmission and ED visits 30 days after discharge were significantly lower in patients with cardiac disease and SDB who adhered to PAP treatment than those who were not adherent.

COMMENTARY

A commentary on this article appears in this issue on page 1067.

Tongue fat and its relationship to obstructive sleep apnea

STUDY OBJECTIVES

The objective of this study was to determine whether tongue fat is increased in obese sleep apneics compared to obese subjects without sleep apnea. We hypothesized that excess fat is deposited in the tongue in obese patients with sleep apnea.

DESIGN

Case-control design.

SETTING

Academic medical center.

PATIENTS

We examined tongue fat in 31 obese controls (apnea-hypopnea index, 4.1 ± 2.7 events/h) and 90 obese apneics (apnea-hypopnea index, 43.2 ± 27.3 events/h). Analyses were repeated in a subsample of 18 gender-, race-, age-, and BMI-matched case-control pairs.

INTERVENTIONS

All subjects underwent a MRI with three-point Dixon magnetic resonance imaging. We used sophisticated volumetric reconstruction algorithms to study the size and distribution of upper airway fat deposits in the tongue and masseter muscles within apneics and obese controls.

MEASUREMENTS AND RESULTS

The data supported our a priori hypotheses that after adjustment for age, BMI, gender, and race, the tongue in apneics was significantly larger (P = 0.001) and had an increased amount of fat (P = 0.002) compared to controls. Similar results were seen in our matched sample. Our data also demonstrate that within the apneic and normal tongue, there are regional differences in fat distribution, with larger fat deposits at the base of the tongue.

CONCLUSIONS

There is increased tongue volume and deposition of fat at the base of tongue in apneics compared to controls. Increased tongue fat may begin to explain the relationship between obesity and obstructive sleep apnea.

Heritability of craniofacial structures in normal subjects and patients with sleep apnea

OBJECTIVES

Accumulating evidence has shown that there is a genetic contribution to obstructive sleep apnea (OSA).The objectives were to use magnetic resonance imaging (MRI) cephalometry to (1) confirm heritability of craniofacial risk factors for OSA previously shown by cephalometrics; and (2) examine the heritability of new craniofacial structures that are measurable with MRI.

DESIGN

A sib pair "quad" design examining apneics, apneic siblings, controls, and control siblings. The study design used exact matching on ethnicity and sex, frequency matching on age, and statistical control for differences in age, sex, ethnicity, height, and weight.

SETTING

Academic medical center.

PATIENTS

We examined 55 apneic probands (apnea-hypopnea index [AHI]: 46.8 ± 33.5 events/h), 55 proband siblings (AHI: 11.1 ± 15.9 events/h), 55 controls (AHI: 2.2 ± 1.7 events/h), and 55 control siblings (AHI: 4.1 ± 4.0 events/h).

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Five independent domains reflecting different aspects of the craniofacial structure were examined. We confirmed heritability of sella-nasion-subspinale (38%, P = 0.002), saddle angle (55%, P < 0.0001), mandibular length (24%, P = 0.02) and lower facial height (33%, P = 0.006) previously measured by cephalometry. In addition, the current study added new insights by demonstrating significant heritability of mandibular width (30%, P = 0.005), maxillary width (47%, P < 0.0001), distance from the hyoid bone to the retropogonion (36%, P = 0.0018) and size of the oropharyngeal space (31%, P = 0.004). Finally, our data indicate that heritability of the craniofacial structures is similar in normal patients and those with apnea.

CONCLUSIONS

The data support our a priori hypothesis that the craniofacial structures that have been associated with obstructive sleep apnea (OSA) are heritable. We have demonstrated heritability for several intermediate craniofacial phenotypes for OSA. Thus, we believe that future studies should be able to identify genes associated with these intermediate craniofacial phenotypes.

Metabolic activity of the tongue in obstructive sleep apnea. A novel application of FDG positron emission tomography imaging

RATIONALE

The metabolic activity of the tongue is unknown in patients with obstructive sleep apnea (OSA). Tongue electromyographic (EMG) activity is increased in patients with OSA. This increase in tongue EMG activity is thought to be related to either increased neuromuscular compensation or denervation with subsequent reinnervation of the muscle fibers. Increased glucose uptake in the tongue would support increased neuromuscular compensation, whereas decreased glucose uptake in the tongue would support denervation with subsequent reinnervation of the muscle fibers.

OBJECTIVES

To investigate the metabolic activity of the genioglossus and control upper airway muscles in obese patients with sleep apnea compared with obese control subjects.

METHODS

Obese subjects with and without OSA underwent a standard overnight sleep study to determine an apnea-hypopnea index. Each subject had a positron emission tomography with [(18)F]-2-fluoro-2-deoxy-D-glucose scan in addition to noncontrast computed tomography or magnetic resonance imaging. Glucose uptake was quantified within upper airway tissues with the standardized uptake value.

MEASUREMENTS AND MAIN RESULTS

We recruited 30 obese control subjects (apnea-hypopnea index, 4.7 ± 3.1 events per hour) and 72 obese patients with sleep apnea (apnea-hypopnea index, 43.5 ± 28.0 events per hour). Independent of age, body mass index, sex, and race, patients with OSA had significantly reduced glucose uptake in the genioglossus (P = 0.03) in comparison with obese normal subjects. No differences in standardized uptake value were found in the control muscles (masseter [P = 0.38] and pterygoid [P = 0.70]) and subcutaneous fat deposits (neck [P = 0.44] and submental [P = 0.95]) between patients with OSA and control subjects.

CONCLUSIONS

There was significantly reduced glucose uptake in the genioglossus of patients with sleep apnea in comparison with obese normal subjects with [(18)F]-2-fluoro-2-deoxy-D-glucose positron emission tomography imaging. The reduction in glucose uptake was likely secondary to alterations in tongue muscle fiber-type or secondary to chronic denervation. The reduced glucose uptake argues against the neuromuscular compensation hypothesis explaining the increase in tongue EMG activity in obese patients with OSA.

Examining the mechanism of action of a new device using oral pressure therapy for the treatment of obstructive sleep apnea

STUDY OBJECTIVES

The objective of this study was to explore the mechanism of action of the oral pressure therapy (OPT) device, a new treatment for sleep apnea.

DESIGN

Case series.

SETTING

Academic medical center.

PATIENTS

Fifteen subjects with sleep apnea who had been successfully treated (responders) with the OPT device and 4 subjects who were not successfully treated (non-responders) with the OPT device.

INTERVENTIONS

All subjects underwent a MRI (without the device, with the device in place without vacuum and with the device in place with vacuum) to examine the biomechanical changes associated with the OPT device.

MEASUREMENTS AND RESULTS

Oral pressure therapy significantly (P = 0.002) increased the size of the retropalatal airway in both the lateral and anterior-posterior dimensions by moving the soft palate anteriorly and superiorly and the anterior-superior segment of the tongue forward, toward the teeth. The percentage and absolute increase in the cross-sectional area of the retropalatal region, the superior movement of the soft palate, and the anterior displacement of the tongue were significantly greater in the responders than in the non-responders. In responders, there were significant increases in the mean (P = 0.002), maximum (P = 0.0002), and minimum (P = 0.04) cross-sectional areas of the retropalatal region with the OPT device. However, in the retroglossal region, airway caliber decreased with the OPT device.

CONCLUSIONS

In those who responded to oral pressure therapy, it increased airway caliber in the retropalatal region by moving the soft palate anteriorly and superiorly and the anterior-superior segment of the tongue forward.

CITATION

Schwab RJ, Kim C, Siegel L, Keenan BT, Black J, Farid-Moayer M, Podmore J, Vaska M. Examining the mechanism of action of a new device using oral pressure therapy for the treatment of obstructive sleep apnea.

Tongue fat infiltration in obese versus lean Zucker rats

STUDY OBJECTIVES

Obesity is the most important risk factor for obstructive sleep apnea (OSA), and the effects of obesity may be mediated by tongue fat. Our objective was to examine the effects of obesity on upper airway structures in obese (OBZ) and non-obese (NBZ) Zucker rats.

DESIGN

Animal study.

SETTING

Academic Medical Center.

PARTICIPANTS

OBZ (638.2 ± 39 g; 14.9 ± 1.1 w) and age-matched NBZ Zucker (442.6 ± 37 g, 15.1 ± 1.5 w) rats.

INTERVENTIONS

TONGUE FAT AND VOLUME AND WERE ASSESSED USING: in vivo magnetic resonance spectroscopy (MRS), magnetic resonance imaging including Dixon imaging for tongue fat volume, ex vivo biochemistry (fat quantification; triglyceride (mg)/tissue (g), and histology (Oil Red O stain).

MEASUREMENTS AND RESULTS

MRS: overall OBZ tongue fat/water ratio was 2.9 times greater than NBZ (P < 0.002) with the anterior OBZ tongue up to 3.3 times greater than NBZ (P < 0.002). Biochemistry: Triglyceride (TG) in the tongue was 4.4 times greater in OBZ versus NBZ (P < 0.0006). TG was greater in OBZ tongue (3.57 ± 1.7 mg/g) than OBZ masseter muscle (0.28 ± 0.1; P < 0.0001) but tongue and masseter TG were not different in NBZ rats (0.82 ± 0.3 versus 0.28 ± 0.1 mg/g, P = 0.67). Dixon fat volume was significantly increased in OBZ (56 ± 15 mm3) versus NBZ (34 ± 5 mm3, P < 0.004). Histology demonstrated a greater degree of intracellular muscle fat and extramuscular fat infiltration in OBZ versus NBZ rats.

CONCLUSIONS

Genetically obese rats had a large degree of fat infiltration in the tongue compared to both skeletal muscle and tongue tissues of the non-obese age-matched littermates. The significant fat increase and sequestration in the obese tongue may play a role in altered tongue neuromuscular function, tongue stiffness or metabolic function.

Obstructive sleep apnoea treatment and fasting lipids: a comparative effectiveness study

Obstructive sleep apnoea (OSA) is associated with cardiovascular disease. Dyslipidaemia has been implicated as a mechanism linking OSA with atherosclerosis, but no consistent associations with lipids exist for OSA or positive airway pressure treatment. We assessed the relationships between fasting lipid levels and obesity and OSA severity, and explored the impact of positive airway pressure treatment on 2-year fasting lipid level changes. Analyses included moderate-to-severe OSA patients from the Icelandic Sleep Apnoea Cohort. Fasting morning lipids were analysed in 613 untreated participants not on lipid-lowering medications at baseline. Patients were then initiated on positive airway pressure and followed for 2 years. Sub-classification using propensity score quintiles, which aimed to replicate covariate balance associated with randomised trials and, therefore, minimise selection bias and allow causal inference, was used to design the treatment group comparisons. 199 positive airway pressure adherent patients and 118 non-users were identified. At baseline, obesity was positively correlated with triglycerides and negatively correlated with total cholesterol, and low-density and high-density lipoprotein cholesterol. A small correlation was observed between the apnoea/hypopnoea index and high-density lipoprotein cholesterol. No effect of positive airway pressure adherence on 2-year fasting lipid changes was observed. Results do not support the concept of changes in fasting lipids as a primary mechanism for the increased risk of atherosclerotic cardiovascular disease in OSA.

Facial phenotyping by quantitative photography reflects craniofacial morphology measured on magnetic resonance imaging in Icelandic sleep apnea patients

STUDY OBJECTIVES

(1) To determine whether facial phenotype, measured by quantitative photography, relates to underlying craniofacial obstructive sleep apnea (OSA) risk factors, measured with magnetic resonance imaging (MRI); (2) To assess whether these associations are independent of body size and obesity.

DESIGN

Cross-sectional cohort.

SETTING

Landspitali, The National University Hospital, Iceland.

PARTICIPANTS

One hundred forty patients (87.1% male) from the Icelandic Sleep Apnea Cohort who had both calibrated frontal and profile craniofacial photographs and upper airway MRI. Mean ± standard deviation age 56.1 ± 10.4 y, body mass index 33.5 ± 5.05 kg/m(2), with on-average severe OSA (apnea-hypopnea index 45.4 ± 19.7 h(-1)).

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Relationships between surface facial dimensions (photos) and facial bony dimensions and upper airway soft-tissue volumes (MRI) was assessed using canonical correlation analysis. Photo and MRI craniofacial datasets related in four significant canonical correlations, primarily driven by measurements of (1) maxillary-mandibular relationship (r = 0.8, P < 0.0001), (2) lower face height (r = 0.76, P < 0.0001), (3) mandibular length (r = 0.67, P < 0.0001), and (4) tongue volume (r = 0.52, P = 0.01). Correlations 1, 2, and 3 were unchanged when controlled for weight and neck and waist circumference. However, tongue volume was no longer significant, suggesting facial dimensions relate to tongue volume as a result of obesity.

CONCLUSIONS

Significant associations were found between craniofacial variable sets from facial photography and MRI. This study confirms that facial photographic phenotype reflects underlying aspects of craniofacial skeletal abnormalities associated with OSA. Therefore, facial photographic phenotyping may be a useful tool to assess intermediate phenotypes for OSA, particularly in large-scale studies.

Altered circadian rhythmicity in patients in the ICU

BACKGROUND

Patients in the ICU are thought to have abnormal circadian rhythms, but quantitative data are lacking.

METHODS

To investigate circadian rhythms in the ICU, we studied core body temperatures over a 48-h period in 21 patients (59 ± 11 years of age; eight men and 13 women).

RESULTS

The circadian phase position for 17 of the 21 patients fell outside the published range associated with morningness/eveningness, which determines the normative range for variability among healthy normal subjects. In 10 patients, the circadian phase position fell earlier than the normative range; in seven patients, the circadian phase position fell later than the normative range. The mean ± SD of circadian displacement in either direction (advance or delay) was 4.44 ± 3.54 h. There was no significant day-to-day variation of the 24-h temperature profile within each patient. Stepwise linear regression was performed to determine if age, sex, APACHE (Acute Physiology and Chronic Health Evaluation) III score, or day in the ICU could predict the patient-specific magnitude of circadian displacement. The APACHE III score was found to be significantly predictive of circadian displacement.

CONCLUSIONS

The findings indicate that circadian rhythms are present but altered in patients in the ICU, with the degree of circadian abnormality correlating with severity of illness.

Risk factors for sleep-disordered breathing in pregnancy

RATIONALE

Symptoms of sleep-disordered breathing (SDB) are common among pregnant women, and several studies link SDB symptoms with gestational hypertension and preeclampsia. However, few prospective studies objectively measuring SDB during pregnancy have been performed.

OBJECTIVES

We performed a prospective cohort study examining risk factors for third trimester SDB in pregnant women.

MEASUREMENTS AND METHODS

105 pregnant women from the Hospital of the University of Pennsylvania obstetrics practices completed first and third trimester overnight polysomnography studies. We examined whether the number of SDB events per hour of sleep increased during pregnancy. We performed unadjusted and multivariable logistic regression analyses to estimate the effects of usual and pregnancy-specific characteristics on development of third trimester obstructive sleep apnoea (OSA). In secondary analyses, we examined the relationship between objectively measured SDB, hypertensive disorders of pregnancy, and other adverse maternal-fetal outcomes.

MAIN RESULTS

Mean Apnoea-Hypopnoea Index increased from 2.07 (SD 3.01) events/h at baseline (first trimester) to 3.74 (SD 5.97) in the third trimester (p=0.009). 10.5% of women had OSA in the first trimester. By the third trimester, 26.7% of women had OSA. In multivariable analyses, first trimester body mass index (BMI) and maternal age were significantly associated with third trimester OSA.

CONCLUSIONS

Third trimester OSA is common. Risk factors for third trimester OSA among women without baseline SDB include higher baseline BMI and maternal age.

An official American Thoracic Society statement: continuous positive airway pressure adherence tracking systems. The optimal monitoring strategies and outcome measures in adults

BACKGROUND

Continuous positive airway pressure (CPAP) is considered the treatment of choice for obstructive sleep apnea (OSA), and studies have shown that there is a correlation between patient adherence and treatment outcomes. Newer CPAP machines can track adherence, hours of use, mask leak, and residual apnea-hypopnea index (AHI). Such data provide a strong platform to examine OSA outcomes in a chronic disease management model. However, there are no standards for capturing CPAP adherence data, scoring flow signals, or measuring mask leak, or for how clinicians should use these data.

METHODS

American Thoracic Society (ATS) committee members were invited, based on their expertise in OSA and CPAP monitoring. Their conclusions were based on both empirical evidence identified by a comprehensive literature review and clinical experience.

RESULTS

CPAP usage can be reliably determined from CPAP tracking systems, but the residual events (apnea/hypopnea) and leak data are not as easy to interpret as CPAP usage and the definitions of these parameters differ among CPAP manufacturers. Nonetheless, ends of the spectrum (very high or low values for residual events or mask leak) appear to be clinically meaningful.

CONCLUSIONS

Providers need to understand how to interpret CPAP adherence tracking data. CPAP tracking systems are able to reliably track CPAP adherence. Nomenclature on the CPAP adherence tracking reports needs to be standardized between manufacturers and AHIFlow should be used to describe residual events. Studies should be performed examining the usefulness of the CPAP tracking systems and how these systems affect OSA outcomes.

Relationship between body fat distribution and upper airway dynamic function during sleep in adolescents

INTRODUCTION

The obstructive sleep apnea syndrome (OSAS) is associated with increased visceral adipose tissue (VAT) in adults; however, few studies have evaluated VAT in relation to upper airway function in adolescents. We hypothesized that increased neck circumference (NC) and VAT would be associated with increased upper airway collapsibility.

METHODS

Adolescents (24 obese patients with OSAS, 22 obese control patients, and 29 lean control patients) underwent abdominal magnetic resonance imaging, and measurement of upper airway pressure-flow relationships in the activated and hypotonic upper airway states.

RESULTS

Patients with OSAS had a greater activated slope of the pressure-flow relationship (SPF) than control groups (P < 0.001), whereas hypotonic SPF was greater in both obese groups compared with lean control patients (P = 0.01). NC and VAT were greater in obese control patients and those with OSAS than in lean control patients (P < 0.001), but did not differ between obese patients with OSAS and obese control patients. In lean control patients and those with OSAS, increased NC was associated with increased activated SPF, whereas in obese control patients it was associated with decreased activated SPF (P = 0.03). In contrast, increased NC was associated with increased hypotonic SPF in all groups (P < 0.001). There was no significant effect of VAT on either activated or hypotonic SPF for any of the three groups.

CONCLUSIONS

Increased neck circumference was associated with increased upper airway collapsibility in adolescents in the hypotonic but not activated state. These data suggest that obese adolescents without OSAS, despite a narrowed upper airway from adipose tissue, are protected from developing OSAS by upper airway neuromotor activation. Neither neck circumference nor visceral adipose tissue is useful in predicting upper airway collapsibility in obese adolescents.

Single slice vs. volumetric MR assessment of visceral adipose tissue: reliability and validity among the overweight and obese

Visceral adipose tissue (VAT) is associated with abnormal cardiovascular and metabolic profiles. Total VAT volume of the abdominal compartment by magnetic resonance imaging (MRI) is the gold-standard measurement for VAT but is costly and time consuming. Prior studies suggest VAT area on a single slice MR image may serve as a surrogate for total VAT volume but it is unknown if this relationship is maintained in overweight and obese men and women. Untreated sleep apnea subjects enrolled into the Icelandic Sleep Apnea Cohort (ISAC) underwent abdominal MRI. VAT area and subcutaneous adipose tissue (SAT) area at the L2-L3 and L4-L5 interspaces and total VAT and SAT volumes were determined by manual examination using image analysis software; 539 men and 129 women with mean ages of 54.1 and 58.8 years and mean BMI of 32.2 kg/m(2) and 33.7 kg/m(2), respectively, were studied. Mean total VAT volume was 40% smaller and mean total SAT was 25% larger among females compared with males. The correlation with VAT volume was significantly larger for L2-L3 VAT area (r = 0.96) compared to L4-L5 VAT area (r = 0.83). The difference in correlation coefficients was statistically significant (nonparametric bootstrap P < 0.001 with 95% confidence interval (CI) for the difference from 0.11 to 0.15. VAT area at L2-L3 was also significantly better correlated with VAT volume than traditional anthropometric variables. Linear regression analyses demonstrated that L2-L3 area alone was sufficient for predicting total VAT volume and that the nature of the linear association was maintained across all levels of obesity and in both genders.

The interaction of obstructive sleep apnea and obesity on the inflammatory markers C-reactive protein and interleukin-6: the Icelandic Sleep Apnea Cohort

STUDY OBJECTIVES

To assess the relative roles and interaction of obstructive sleep apnea (OSA) severity and obesity on interleukin-6 (IL-6) and C-reactive protein (CRP) levels.

DESIGN

Cross-sectional cohort.

SETTING

The Icelandic Sleep Apnea Cohort.

PARTICIPANTS

454 untreated OSA patients (380 males and 74 females), mean ± standard deviation age 54.4 ± 10.6 yr.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Participants underwent a sleep study, abdominal magnetic resonance imaging to measure total abdominal and visceral fat volume, and had fasting morning IL-6 and CRP levels measured in serum. A significantly higher correlation was found for BMI than visceral fat volume with CRP and IL-6 levels. Oxygen desaturation index, hypoxia time, and minimum oxygen saturation (SaO₂) significantly correlated with IL-6 and CRP levels, but apnea-hypopnea index did not. When stratified by body mass index (BMI) category, OSA severity was associated with IL-6 levels in obese participants only (BMI > 30 kg/m²). A multiple linear regression model with interaction terms showed an independent association of OSA severity with IL-6 levels and an interaction between OSA severity and BMI, i.e., degree of obesity altered the relationship between OSA and IL-6 levels. An independent association of OSA severity with CRP levels was found for minimum SaO₂ only. A similar interaction of OSA severity and BMI on CRP levels was found for males and postmenopausal women.

CONCLUSIONS

OSA severity is an independent predictor of levels of IL-6 and CRP but interacts with obesity such that this association is found only in obese patients.

Identification of craniofacial risk factors for obstructive sleep apnoea using three-dimensional MRI

The alteration of craniofacial structures has been associated with obstructive sleep apnoea (OSA). We hypothesised that: 1) a smaller mandible is a risk factor for OSA; and 2) the previously observed inferiorly positioned hyoid bone in apnoeics is associated with enlarged tongue volume. This is a case-control study using three-dimensional magnetic resonance imaging cephalometry. 55 apneics and 55 controls were matched for age, sex and race. The analysis was stratified by sex and controlled for age, race, height, neck visceral fat, skeletal type and tongue volume. We found that a 1-sd increase in mandibular length and depth were associated with decreased risk of sleep apnoea (OR 0.52, 95% CI 0.28-0.99 and OR 0.46, 95% CI 0.23-0.91, respectively) in males but not in females. Greater hyoid-to-nasion (OR 2.64, 95% CI 1.19-5.89 in males and OR 5.01, 95% CI 2.00-12.52 in females) and supramentale-to-hyoid (OR 2.39, 95% CI 1.12-5.14) in males and OR 3.38, 95% CI 1.49-7.68 in females) distances were associated with increased risk of OSA. The difference for hyoid position between apnoeics and controls was lost after controlling for tongue volume. Enlargement of tongue is likely to be the pathogenic factor for inferior-posterior positioning of hyoid. A small and shallow mandible is an independent risk factor for OSA in males but not in females.

Comparative effects of two oral appliances on upper airway structure in obstructive sleep apnea

STUDY OBJECTIVES

Oral appliances are increasingly being used for treatment of obstructive sleep apnea (OSA). Mandibular advancement splint (MAS) mechanically protrudes the mandible, while the tongue stabilizing device (TSD) protrudes and holds the tongue using suction. Although both appliances can significantly improve or ameliorate OSA, their comparative effects on upper airway structure have not been investigated.

DESIGN

Cohort study.

SETTING

Sleep Investigation Unit.

PATIENTS

39 patients undergoing oral appliance treatment for OSA.

INTERVENTIONS

OSA patients underwent magnetic resonance imaging (MRI) of the upper airway during wakefulness at baseline and with MAS and TSD in randomized order. Treatment efficacy was determined by polysomnography in a subset of 18 patients.

MEASUREMENTS AND RESULTS

Upper airway lumen and surrounding soft tissue structures were segmented using image analysis software. Upper airway dimensions and soft tissue centroid movements were determined. Both appliances altered upper airway geometry, associated with movement of the parapharyngeal fat pads away from the airway. TSD increased velopharyngeal lateral diameter to a greater extent (+0.35 ± 0.07 vs. +0.18 ± 0.05 cm; P<0.001) and also increased antero-posterior diameter with anterior displacement of the tongue (0.68 ± 0.04 cm; P<0.001) and soft palate (0.12 ± 0.03 cm; P<0.001). MAS resulted in significant anterior displacement of the tongue base muscles (0.35 ± 0.04 cm). TSD responders (AHI reduction ≥50%) increased velopharyngeal volume more than non-responders (+2.65 ± 0.9 vs. -0.44 ± 0.8 cm(3); P < 0.05). Airway structures did not differ between MAS responders and non-responders.

CONCLUSIONS

These results indicate that the patterns and magnitude of changes in upper airway structure differ between appliances. Further studies are warranted to evaluate the clinical relevance of these changes, and whether they can be used to predict treatment outcome.

Pharmacokinetics and safety of multiple doses of daptomycin 6 mg/kg in noninfected adults undergoing hemodialysis or continuous ambulatory peritoneal dialysis

AIMS

The purpose of this study was to characterize the pharmacokinetics and tolerability of daptomycin in subjects undergoing hemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD).

METHOD

16 noninfected adults on stable dialysis regimens were enrolled. Daptomycin 6 mg/kg was administered after HD during a 48 h - 48 h - 72 h dialysis week or before a CAPD dwell time over a 48 h - 48 h - 48 h dialysis week. Pharmacokinetic parameters were described, and adverse events were monitored.

RESULTS

Daptomycin had mean half-lives in HD subjects of 28.0 and 35.9 h on Days 1 and 5, with corresponding values of 25.8 and 26.7 h in CAPD subjects. Steady state was reached by Day 5 in both groups. At steady state, HD subjects had a mean peak plasma concentration (Cmax) of 81.6 µg/ml and a mean trough concentration of 15.3 µg/ml (on Day 8). In CAPD subjects, Cmax was 93.9 µg/ml and the trough was 20.7 µg/ml (on Day 7). Adverse events were experienced by 71.4% and 66.7% of HD and CAPD subjects, respectively. Most of these were mild or moderate in intensity; however, 2 subjects experienced muscle spasms and mild creatine phosphokinase elevations although neither event was considered to be related to study drug.

CONCLUSIONS

The pharmacokinetics of daptomycin 6 mg/kg support a dosing regimen of every 48 h in CAPD and thrice-weekly dosing in HD.

Respiratory modulation of the pharyngeal airway in lean and obese mice

Obesity is an important risk factor for pharyngeal airway collapse in obstructive sleep apnea (OSA). To examine the effect of obesity on pharyngeal airway size on inspiration and expiration, respiratory-gated MRI of the pharynx was compared in New Zealand obese (NZO) and New Zealand white (NZW) mice (weights: 50.4g vs. 34.7g, p<0.0001).

RESULTS

(1) pharyngeal airway cross-sectional area was greater during inspiration than expiration in NZO mice, but in NZW mice airway area was greater in expiration than inspiration; (2) inspiratory-to-expiratory changes in both mouse strains were largest in the caudal pharynx; and (3) during expiration, airway size tended to be larger, though non-significantly, in NZW than NZO mice. The respiratory pattern differences are likely attributable to obesity that is the main difference between NZO and NZW mice. The data support an hypothesis that pharyngeal airway patency in obesity is dependent on inspiratory dilation and may be vulnerable to loss of neuromuscular pharyngeal activation.

Relationship between surface facial dimensions and upper airway structures in obstructive sleep apnea

STUDY OBJECTIVES

We hypothesized that the facial phenotype is closely linked to upper airway anatomy. The aim of this study was to investigate the relationship between surface facial dimensions and upper airway structures using magnetic resonance imaging (MRI) in subjects with obstructive sleep apnea (OSA).

DESIGN

Cohort study.

SETTING

Sleep investigation unit.

PATIENTS

Sixty-nine patients (apnea-hypopnea index > or = 10/h) underwent MRI as part of a study of upper airway anatomy in oral appliance therapy.

INTERVENTIONS

Measurements of a range of surface facial dimensions and upper airway soft tissue volumes were performed on the MR images using image-analysis software. Pearson correlation analyses were performed.

MEASUREMENTS AND RESULTS

Significant correlations were identified between a number of surface facial dimensions and neck circumference. Significant positive correlations were demonstrated between surface facial dimensions (including facial widths, facial heights, nose width, interocular and intercanthal widths) and upper airway structures. The strongest associations were between the tongue volume and the midface width (r = 0.70, P < 0.001), and lower-face width (r = 0.60, P <0.001). Surface facial dimensions in combination were also strong determinants for tongue volume (r2 = 0.69). Correlations between surface soft tissue thickness and upper airway soft tissue volumes occurred at the level of the midface but not at the level of the lower face.

CONCLUSIONS

This study demonstrates that there is a relationship between surface facial dimensions and upper airway structures in subjects with OSA. These findings support the potential role of surface facial measurements in anatomic phenotyping for OSA.

The effect of mandibular advancement on upper airway structure in obstructive sleep apnoea

BACKGROUND

The mechanisms by which mandibular advancement splints (MAS) improve obstructive sleep apnoea (OSA) are not well understood. This study aimed to evaluate the mechanism of action of MAS by assessing their effect on upper airway structure in patients with OSA.

METHODS

Patients were recruited from a sleep disorders clinic for treatment with a custom-made MAS. MRI of the upper airway was performed during wakefulness in the supine position, with and without the MAS.

RESULTS

Sixty-nine patients with OSA were recruited. Treatment with the MAS reduced the apnoea-hypopnoea index (AHI) from 27.0+/-14.7 events/h to 12.2+/-12.5 events/h (p<0.001). There was an increase in the total airway volume with mandibular advancement (16.5+/-0.7 cm(3) vs 18.1+/-0.8 cm(3); p<0.01) that occurred predominantly because of an increase in the volume of the velopharynx (5.7+/-0.3 cm(3) vs 6.5+/-0.3 cm(3); p<0.001). This increase in airway calibre was associated with an increase in the lower anterior facial height (6.8+/-0.1 cm vs 7.5+/-0.1 cm; p<0.001), reduction in the distance between the hyoid and posterior nasal spine (7.4+/-0.1 cm vs 7.2+/-0.1 cm; p<0.001), lateral displacement of the parapharyngeal fat pads away from the airway (right parapharyngeal fat pad 0.17+/-0.02 cm; left parapharyngeal fat pad 0.22+/-0.02 cm) and anterior movement of the tongue base muscles (0.33+/-0.03 cm). Subanalyses in responders and non-responders to MAS treatment showed that the increase in upper airway calibre with mandibular advancement occurred only in responders.

CONCLUSION

These results suggest that the mechanism of action of MAS is to increase the volume of the upper airway, predominantly by increasing the volume of the velopharynx, and this increased volume is associated with changes in the surrounding bony and soft tissue structures.

Bench-to-bedside review: delirium in ICU patients - importance of sleep deprivation

Delirium occurs frequently in critically ill patients and has been associated with both short-term and long-term consequences. Efforts to decrease delirium prevalence have been directed at identifying and modifying its risk factors. One potentially modifiable risk factor is sleep deprivation. Critically ill patients are known to experience poor sleep quality with severe sleep fragmentation and disruption of sleep architecture. Poor sleep while in the intensive care unit is one of the most common complaints of patients who survive critical illness. The relationship between delirium and sleep deprivation remains controversial. However, studies have demonstrated many similarities between the clinical and physiologic profiles of patients with delirium and sleep deprivation. This article aims to review the literature, the clinical and neurobiologic consequences of sleep deprivation, and the potential relationship between sleep deprivation and delirium in intensive care unit patients. Sleep deprivation may prove to be a modifiable risk factor for the development of delirium with important implications for the acute and long-term outcome of critically ill patients.

Obstructive sleep apnea in patients undergoing bariatric surgery--a tertiary center experience

BACKGROUND

The patient population that is evaluated for bariatric surgery is characterized by a very high body mass index (BMI). Since obesity is the most important risk factor for obstructive sleep apnea (OSA), sleep disordered breathing is highly prevalent in this population. If undiagnosed before bariatric surgery, untreated OSA can lead to perioperative and postoperative complications. Debate exists whether all patients that are considered for bariatric surgery should undergo polysomnography (PSG) evaluation and screening for OSA as opposed to only those patients with clinical history or examination concerning sleep disordered breathing. We examined the prevalence and severity of OSA in all patients that were considered for bariatric surgery. We hypothesized that, by utilizing preoperative questionnaires (regarding sleepiness and OSA respiratory symptoms) in combination with menopausal status and BMI data, we would be able to predict which subjects did not have sleep apnea without the use of polysomnography. In addition, we hypothesized that we would be able to predict which subjects had severe OSA (apnea-hypopnea index (AHI) > 30).

METHODS

Three hundred forty-two consecutive subjects, evaluated for bariatric surgery from November 1, 2005 to January 31, 2007 underwent overnight polysomnography and completed questionnaires regarding sleepiness, menopausal status, and respiratory symptoms related to OSA. Apneas and hypopneas were classified as follows: mild apnea 5 ≤ AHI ≤ 15, moderate apnea 15 < AHI ≤ 30, and severe apnea AHI > 30.

RESULTS

The overall sample prevalence of OSA was 77.2%. Of these, 30.7% had mild OSA; 19.3% had moderate OSA, and 27.2% had severe OSA. Among men, the prevalence of OSA was 93.6% and 73.5% among women. The mean AHI (events per hour) for men with OSA was 49.2 ± 35.5 and 26.3 ± 28.3 for women with OSA. Separate logistic regression models were developed for the following three outcomes: AHI ≥ 5 events per hour, AHI > 15 events per hour, and AHI > 30 events per hour. When predicting these three levels of OSA severity, the area under the curve (AUC) values were: 0.8, 0.72, and 0.8, respectively. The negative predictive value for the presence of sleep apnea (AHI ≥ 5) was 75% when using the most stringent possible cutoff for the prediction model.

CONCLUSIONS

The prevalence of OSA in all patients considered for bariatric surgery was greater than 77%, irrespective of OSA symptoms, gender, menopausal status, age, or BMI. The prediction model that we developed for the presence of OSA (AHI ≥ 5 events per hour) has excellent discriminative ability (evidenced by an AUC value of 0.8). However, the negative prediction values for the presence of OSA were too low to be clinically useful due to the high prevalence of OSA in this high-risk group. We demonstrated that, by utilizing even the most stringent possible cutoff values for the prediction model, OSA cannot be predicted with enough certainty. Therefore, we advocate routine PSG testing for all patients that are considered for bariatric surgery.

Clinical guideline for the evaluation, management and long-term care of obstructive sleep apnea in adults

BACKGROUND

Obstructive sleep apnea (OSA) is a common chronic disorder that often requires lifelong care. Available practice parameters provide evidence-based recommendations for addressing aspects of care.

OBJECTIVE

This guideline is designed to assist primary care providers as well as sleep medicine specialists, surgeons, and dentists who care for patients with OSA by providing a comprehensive strategy for the evaluation, management and long-term care of adult patients with OSA.

METHODS

The Adult OSA Task Force of the American Academy of Sleep Medicine (AASM) was assembled to produce a clinical guideline from a review of existing practice parameters and available literature. All existing evidence-based AASM practice parameters relevant to the evaluation and management of OSA in adults were incorporated into this guideline. For areas not covered by the practice parameters, the task force performed a literature review and made consensus recommendations using a modified nominal group technique.

RECOMMENDATIONS

Questions regarding OSA should be incorporated into routine health evaluations. Suspicion of OSA should trigger a comprehensive sleep evaluation. The diagnostic strategy includes a sleep-oriented history and physical examination, objective testing, and education of the patient. The presence or absence and severity of OSA must be determined before initiating treatment in order to identify those patients at risk of developing the complications of sleep apnea, guide selection of appropriate treatment, and to provide a baseline to establish the effectiveness of subsequent treatment. Once the diagnosis is established, the patient should be included in deciding an appropriate treatment strategy that may include positive airway pressure devices, oral appliances, behavioral treatments, surgery, and/or adjunctive treatments. OSA should be approached as a chronic disease requiring long-term, multidisciplinary management. For each treatment option, appropriate outcome measures and long-term follow-up are described.

Altered upper airway and soft tissue structures in the New Zealand Obese mouse

RATIONALE

The effect of obesity on upper airway soft tissue structure and size was examined in the New Zealand Obese (NZO) mouse and in a control lean mouse, the New Zealand White (NZW).

OBJECTIVES

We hypothesized that the NZO mouse has increased volume of neck fat and upper airway soft tissues and decreased pharyngeal airway caliber.

METHODS

Pharyngeal airway size, volume of the upper airway soft tissue structures, and distribution of fat in the neck and body were measured using magnetic resonance imaging (MRI). Dynamic MRI was used to examine the differences in upper airway caliber between inspiration and expiration in NZO versus NZW mice.

MEASUREMENTS AND MAIN RESULTS

The data support the hypothesis that, in obese NZO versus lean NZW mice, airway caliber was significantly smaller (P < 0.03), with greater parapharyngeal fat pad volumes (P < 0.0001) and a greater volume of other upper airway soft tissue structures (tongue, P = 0.003; lateral pharyngeal walls, P = 0.01; soft palate, P = 0.02). Dynamic MRI showed that the airway of the obese NZO mouse dilated during inspiration, whereas in the lean NZW mouse, the upper airway was reduced in size during inspiration.

CONCLUSIONS

In addition to the increased volume of pharyngeal soft tissue structures, direct fat deposits within the tongue may contribute to airway compromise in obesity. Pharyngeal airway dilation during inspiration in NZO mice compared with narrowing in NZW mice suggests that airway compromise in obese mice may lead to muscle activation to defend upper airway patency during inspiration.

Upper airway imaging in obstructive sleep apnea

PURPOSE OF REVIEW

Obstructive sleep apnea continues to be a significant public health problem. A variety of imaging modalities have been used recently to gain insight into the pathogenesis of this disease, as well as to identify therapeutic options.

RECENT FINDINGS

Data from more recent imaging studies have highlighted key findings regarding the anatomic sites of collapse and local tissue factors promoting upper airway compromise. The role of genetics, aging, gender and ethnicity in the development of sleep apnea and the identification of predictors for successful treatment outcomes for sleep-disordered breathing are also reviewed.

SUMMARY

As our understanding of obstructive sleep apnea evolves, newer imaging techniques and computerized models may be able to further enhance our understanding of the pathogenesis and treatment of this disease.

Sleep in the critically ill patient

Critically ill patients are known to suffer from severely fragmented sleep with a predominance of stage I sleep and a paucity of slow wave and REM sleep. The causes of this sleep disruption include the intensive care unit (ICU) environment, medical illness, psychological stress, and many of the medications and other treatments used to help those who are critically ill. The clinical importance of this type of sleep disruption in critically ill patients, however, is not known. This article reviews the literature on sleep disruption in the ICU, the effects of sepsis on sleep, the effects of commonly used ICU medications on sleep, the relationship between sleep and sedation, and the literature on the biological and psychological consequences of sleep deprivation specifically as it relates to the critically ill. Finally, an integrative approach to improving sleep in the ICU is described.

Family aggregation of upper airway soft tissue structures in normal subjects and patients with sleep apnea

RATIONALE

Sleep apnea is believed to be a genetic disorder. Thus, we hypothesized that anatomic risk factors for sleep apnea would demonstrate family aggregation.

OBJECTIVES

We used volumetric magnetic resonance imaging in a sib pair "quad" design to study the family aggregation of the size of upper airway soft tissue structures that are associated with increased risk for obstructive sleep apnea.

METHODS

We examined 55 sleep apnea probands (apnea-hypopnea index [AHI]: 43.2 +/- 26.3 events/h), 55 proband siblings (AHI: 11.8 +/- 16.6 events/h), 55 control subjects (AHI: 2.1 +/- 1.7 events/h), and 55 control siblings (AHI: 4.2 +/- 4.0 events/h). The study design used exact matching on ethnicity and sex, frequency matching on age, and statistical control for visceral neck fat and craniofacial dimensions.

MEASUREMENTS AND MAIN RESULTS

The data support our a priori hypothesis that the volume of the important upper airway soft tissue structures is heritable. The volume of the lateral pharyngeal walls (h(2) = 36.8%; p = 0.001), tongue (h(2) = 36.5%; p = 0.0001), and total soft tissue (h(2) = 37.5%; p = 0.0001) demonstrated significant levels of heritability after adjusting for sex, ethnicity, age, visceral neck fat, and craniofacial dimensions. In addition, our data indicate that heritability of the upper airway soft tissue structures is found in normal subjects and patients with apnea. Thus, it is not simply a consequence of the prevalence of apnea.

CONCLUSIONS

This is the first time family aggregation of size of the upper airway soft tissue structures has been demonstrated.

Changes in Symptoms of Sleep-Disordered Breathing During Pregnancy

BACKGROUND

Although incident snoring is common in pregnant women and has been proposed as a potential risk factor for adverse maternal-fetal outcomes, the development of sleep-disordered breathing during pregnancy has not been prospectively described.

METHODS

Using the Apnea Symptom Score from the Multivariable Apnea Prediction Index and the Epworth Sleepiness Scale, we prospectively assessed symptoms of sleep-disordered breathing and daytime somnolence in 155 women to determine whether symptoms increased during pregnancy and the characteristics associated with increasing symptoms.

RESULTS

We found that sleep-disordered breathing symptoms (Apnea Symptom Score, 0.44 (SEM 0.58) vs 0.95 (0.09, P < .001) and the degree of daytime somnolence (Epworth Sleepiness Scale, 8.6 (0.3) vs 10.2 (0.4), P = .0003) increased significantly during pregnancy. Women with higher baseline body mass indexes and greater increases in neck circumference during pregnancy reported higher apnea symptom scores. Of the 155 subjects, 11.4% reported an increase in Apnea Symptom Score of 2 units or more, consistent with a clinically significant increase in symptoms; these women experienced a significantly greater increase in subjective sleepiness than other subjects (P = .03). Excessive daytime somnolence (Epworth Sleepiness Scale > 10) was prevalent throughout pregnancy (31.0%-45.5%).

CONCLUSIONS

Our data demonstrate that symptoms of sleep-disordered breathing increase during pregnancy and that more than 10% of our subjects may be at risk for developing sleep apnea during pregnancy. Excessive daytime somnolence was highly prevalent even early in pregnancy and became increasingly common as pregnancy progressed.

Genetic determinants of upper airway structures that predispose to obstructive sleep apnea

Genetic factors are thought to play an important role in human development. Recent data indicate that obstructive sleep apnea may have a genetic basis. Sleep apnea is a very common disorder with significant cardiovascular and neurophysiologic morbidity. The pathogenesis of sleep apnea is related to a reduction in the size of the upper airway. The reduction in airway size is secondary to increased adipose tissue (enlargement of the parapharyngeal fat pads), alterations in craniofacial structure (reduction in mandibular size) and enlargement of the surrounding soft tissue structures (tongue, lateral pharyngeal walls). Genetic factors are one of the factors that have been proposed to mediate the size of each of these anatomic risk factors for sleep apnea. Recent evidence is accumulating about the genetic loci for these structural risk factors that predispose to the development of obstructive sleep apnea.

Sleep disorders during pregnancy

This paper reviews the topic of sleep disorders in pregnant women. We describe changes in sleep architecture and sleep pattern during pregnancy, discuss the impact of the physical and biochemical changes of pregnancy on sleep in pregnant women and examine whether maternal-fetal outcomes may be adversely affected in women with disordered sleep. The literature on common sleep disorders affecting pregnant women, including insomnia, sleep-disordered breathing and restless legs syndrome, is reviewed and recommendations are made for the management of these disorders during pregnancy.

Mandibular Dimensions in Children with Obstructive Sleep Apnea Syndrome

OBJECTIVE

We hypothesized that mandibular size may play a role in the etiology of obstructive sleep apnea syndrome (OSAS) in children, since a smaller mandible may reduce airway size. We used magnetic resonance imaging to determine the mandible dimensions of children with OSAS.

DESIGN

Case control study.

SETTING

Tertiary-care pediatric hospital.

PARTICIPANTS

Twenty-four subjects (mean age 4.9 +/- 1.7 years) with mild to moderate OSAS (Apnea Index 3.5 +/- 5.1), and 24 matched controls (mean age 4.9 +/- 1.8 years).

INTERVENTION

Magnetic resonance imaging of the upper airway under sedation.

MEASUREMENTS

Eight measurements were obtained from a 3-dimensional segmentation of the mandible using 3DVIEWNIX software. Measurements included length, height, width, midsymphysis menti angle, angle of mandible, enclosure area, surface area, and volume. Descriptive comparisons using Student t test and multivariate analyses of variance were performed.

RESULTS

Individual measurement comparisons revealed no significant differences between groups. Multivariate analysis showed a lower bound of a 95% confidence interval for an effect size measure for "general mandibular size," including all 6 linear, the area, and the volume measurements, to be -0.25.

CONCLUSION

Our study shows that a smaller mandible is not a feature in children with OSAS who do not have apparent craniofacial abnormalities.

Identification of upper airway anatomic risk factors for obstructive sleep apnea with volumetric magnetic resonance imaging

We used sophisticated volumetric analysis techniques with magnetic resonance imaging in a case-control design to study the upper airway soft tissue structures in 48 control subjects (apnea-hypopnea index, 2.0 +/- 1.6 events/hour) and 48 patients with sleep apnea (apnea-hypopnea index, 43.8 +/- 25.4 events/hour). Our design used exact matching on sex and ethnicity, frequency matching on age, and statistical control for craniofacial size and visceral neck fat. The data support our a priori hypotheses that the volume of the soft tissue structures surrounding the upper airway is enlarged in patients with sleep apnea and that this enlargement is a significant risk factor for sleep apnea. After covariate adjustments the volume of the lateral pharyngeal walls (p < 0.0001), tongue (p < 0.0001), and total soft tissue (p < 0.0001) was significantly larger in subjects with sleep apnea than in normal subjects. These data also demonstrated, after covariate adjustments, significantly increased risk of sleep apnea the larger the volume of the tongue, lateral pharyngeal walls, and total soft tissue: (1) total lateral pharyngeal wall (odds ratio [OR], 6.01; 95% confidence interval [CI], 2.62-17.14); (2) total tongue (OR, 4.66; 95% CI, 2.31-10.95); and (3) total soft tissue (OR, 6.95; 95% CI, 3.08-19.11). In a multivariable logistic regression analysis the volume of the tongue and lateral walls was shown to independently increase the risk of sleep apnea.

A novel volumetric magnetic resonance imaging paradigm to study upper airway anatomy

STUDY OBJECTIVES

We utilized novel three-dimensional volumetric analysis techniques with magnetic resonance imaging (MRI) to study the upper airway and surrounding soft-tissue structures. These MRI techniques allowed us to objectively quantify the volume of the tongue, soft palate, parapharyngeal fat pads, and lateral pharyngeal walls.

DESIGN

We first validated our volumetric imaging techniques on a phantom and then demonstrated that our results were reliable and reproducible in normal subjects who did not lose weight. Finally, we studied 12 obese, nonapneic women during wakefulness before and after weight loss. We hypothesized that our novel magnetic-resonance computer-reconstruction techniques would allow us to detect small reductions in the volume of the tongue, soft palate, lateral pharyngeal walls, and parapharyngeal fat pads and increases in the volume of the upper airway with weight loss.

SETTING

University medical center.

PARTICIPANTS

Normal controls and 12 obese nonapneic women.

INTERVENTIONS

Weight loss.

MEASUREMENTS AND RESULTS

Following a mean 17.1+/-8.62 kg (17.3%) reduction in weight, upper airway volume increased (p = 0.06) in both the retropalatal and retroglossal regions. This increase in upper airway volume was mediated by significant reductions in the volume of the lateral pharyngeal wall (p = 0.0001) and parapharyngeal fat pads (p = 0.001). However, the volume of the tongue (p = 0.35) and soft palate (p = 0.39) were not reduced significantly with weight loss.

CONCLUSIONS

These data indicate that volumetric MRI is a powerful tool to study anatomic changes in the upper airway and surrounding soft-tissue structures and is sensitive enough to detect changes in these structures.

Linear dimensions of the upper airway structure during development: assessment by magnetic resonance imaging

The upper airway undergoes progressive changes during childhood. Using magnetic resonance imaging (MRI), we studied the growth relationships of the tissues surrounding the upper airway (bone and soft tissues) in 92 normal children (47% males; range, 1 to 11 yr) who underwent brain MRI. None had symptoms of sleep-disordered breathing or conditions that impacted on their upper airway. MRI was performed under sedation. Sequential T1-weighted spin echo sagittal and axial sections were obtained and analyzed on a computer. We measured lower face skeletal growth along the midsagittal and axial oropharyngeal planes. In the midsagittal plane the mental spine-clivus distance related linearly to age (r = 0.86, p < 0.001). Along this axis, the dimensions of tongue, soft palate, nasopharyngeal airway, and adenoid increased with age and maintained constant proportion to the mental spine-clivus distance. Similarly, a linear relationship was noted for mandibular growth measured along the intermandibular line on the axial plane and age (r = 0.78, p < 0.001). In addition, the intertonsillar, tonsils, parapharyngeal fat pads, and pterygoids widths maintained constant proportion to intermandibular width with age. We conclude that the lower face skeleton grows linearly along the sagittal and axial planes from the first to the eleventh year. Our data indicate that soft tissues, including tonsils and adenoid, surrounding the upper airway grow proportionally to the skeletal structures during the same time period.

Imaging for the snoring and sleep apnea patient

Upper airway imaging techniques have significantly advanced the understanding of the pathogenesis of obstructive sleep apnea and the biomechanical mechanisms by which therapeutic interventions for this disorder exert their effects. Both static and dynamic imaging studies have been used to examine the structure and function of the upper airway during wakefulness and sleep. These studies have highlighted the importance of the lateral pharyngeal walls in addition to the tongue and soft palate in modulating changes in upper airway caliber. Upper airway imaging has also been used to understand the changes in upper airway anatomy associated with weight loss, mandibular repositioning devices, and upper airway surgery. At present, upper airway imaging should be considered in patients undergoing upper airway surgery and possibly in patients being evaluated for oral appliances. MR imaging and nasopharyngoscopy are the imaging modalities of choice in patients undergoing a UPPP. Cephalometrics should be considered in patients being treated with mandibular repositioning devices. Upper airway imaging has provided an important framework to examine the pathogenesis of airway closure, and these investigations may, in time, lead to more effective treatment options for patients with sleep apnea.