Accuracy of body mass index in diagnosing obesity in the adult general population

BACKGROUND

Body mass index (BMI) is the most widely used measure to diagnose obesity. However, the accuracy of BMI in detecting excess body adiposity in the adult general population is largely unknown.

METHODS

A cross-sectional design of 13 601 subjects (age 20-79.9 years; 49% men) from the Third National Health and Nutrition Examination Survey. Bioelectrical impedance analysis was used to estimate body fat percent (BF%). We assessed the diagnostic performance of BMI using the World Health Organization reference standard for obesity of BF%>25% in men and>35% in women. We tested the correlation between BMI and both BF% and lean mass by sex and age groups adjusted for race.

RESULTS

BMI-defined obesity (> or =30 kg m(-2)) was present in 19.1% of men and 24.7% of women, while BF%-defined obesity was present in 43.9% of men and 52.3% of women. A BMI> or =30 had a high specificity (men=95%, 95% confidence interval (CI), 94-96 and women=99%, 95% CI, 98-100), but a poor sensitivity (men=36%, 95% CI, 35-37 and women=49%, 95% CI, 48-50) to detect BF%-defined obesity. The diagnostic performance of BMI diminished as age increased. In men, BMI had a better correlation with lean mass than with BF%, while in women BMI correlated better with BF% than with lean mass. However, in the intermediate range of BMI (25-29.9 kg m(-2)), BMI failed to discriminate between BF% and lean mass in both sexes.

CONCLUSIONS

The accuracy of BMI in diagnosing obesity is limited, particularly for individuals in the intermediate BMI ranges, in men and in the elderly. A BMI cutoff of> or =30 kg m(-2) has good specificity but misses more than half of people with excess fat. These results may help to explain the unexpected better survival in overweight/mild obese patients.

Effect of pigmentation density upon 2.0 microm laser irradiation thermal response

Yucatan mini-pigs with predominantly dark skin have been used to determine skin safety standards for infrared (IR) wavelength irradiation due to its anatomical similarity to all human skin. It has generally been argued that water is the principle absorber in the IR-B band and melanin has relatively low absorbance. To accept dark pigmented damage thresholds for skin with various melanin densities, it is necessary to investigate the potential role of melanin in producing skin injury as characterized by an erythermal response. A Yucatan mini-pig covered with lightly pigmented pink and darkly pigmented brown skin was used in this study. The significance of skin pigmentation was investigated by comparing the transient thermal response, absorption coefficient, and the threshold damage of instant redness within 1 min and persistent redness at 48 h post exposure for dark and light skin areas at 2.0 microm wavelength. The density of melanin granules did not significantly alter the thermal and optical properties of in vivo skin exposed to 2.0 microm laser irradiation. For Gaussian shaped beam radiation at 1 s exposure duration and 4.83 mm 1/e spot diameter, the average radiant exposures at instant and persistent redness thresholds were 3.88 J cm and 5.08 J cm for dark skin, respectively, as well as 4.09 J cm and 4.09 J cm for light colored skin. Subjectively speaking, however, lightly pigmented mini-pig skin was more suitable for damage threshold estimation because of the increased contrast for visual determination of redness on light skin.

The correlation of regression in primary melanoma with sentinel lymph node status

BACKGROUND

The significance of regression in primary melanoma has been disputed for many years. Some have suggested regression as a marker for poor prognosis while others have reported a negligible or even a favourable effect, on prognosis.

AIM

To understand the significance of regression in melanoma and provide further information on whether patients should be subjected to sentinel lymph node biopsy (SLNB) on the basis of regression.

METHODS

146 melanoma cases who had undergone SLNB were included in the study. The histological criteria for offering SLNB were melanoma >1 mm in thickness, Clark's level IV or those with regression.

RESULTS

A statistically significant greater proportion of individuals without regression showed sentinel lymph node (SLN) positivity (p = 0.028) compared with those which do show regression. Metastatic disease correlated with growth phase of the primary lesion. All the node positive cases were in the vertical growth phase; none of the cases in radial growth phase and showing regression were associated with nodal metastasis (p = 0.029). 62 cases had melanomas with thickness <1 mm and were in radial growth phase, yet were offered SLNB because of regression. Of these, 44 showed features of regression and all were node negative. The remaining 16 cases of thin melanomas did not show regression; 2 of these had sentinel node metastasis.

CONCLUSION

Results suggest that regression is usually a favourable process, particularly in thin melanomas and that metastasis in "thin melanomas showing regression" is real but rare. Variant vertical growth phase, mitoses and other prognostically significant variables may be more important predictors of metastatic potential in thin melanomas.

Enhancement of sleep stability with Tai Chi exercise in chronic heart failure: preliminary findings using an ECG-based spectrogram method

OBJECTIVE

To assess the effects of a 12-week Tai Chi exercise program on sleep using the sleep spectrogram, a method based on a single channel electrocardiogram (ECG)-derived estimation of cardiopulmonary coupling, previously shown to identify stable and unstable sleep states.

METHODS

We retrospectively analyzed 24-h continuous ECG data obtained in a clinical trial of Tai Chi exercise in patients with heart failure. Eighteen patients with chronic stable heart failure, left ventricular ejection fraction <or= 40% (mean [+/-standard deviation] age, 59+/-14 years, mean baseline ejection fraction 24%+/-8%, mean) were randomly assigned to receive usual care (N=10), which included pharmacological therapy and dietary and exercise counseling, or 12 weeks of Tai Chi training (N=8) in addition to usual care. Using the ECG-based sleep spectrogram, we compared intervention and control groups by evaluating baseline and 12-week high (stable) and low (unstable) frequency coupling (HFC & LFC, respectively) as a percentage of estimated total sleep time (ETST).

RESULTS

At 12 weeks, those who participated in Tai Chi showed a significant increase in HFC (+0.05+/-0.10 vs. -0.06+/-0.09 % ETST, p=0.04) and significant reduction in LFC (-0.09+/-0.09 vs. +0.13+/-0.13 % ETST, p<0.01), compared to patients in the control group. Correlations were seen between improved sleep stability and better disease-specific quality of life.

CONCLUSIONS

Tai Chi exercise may enhance sleep stability in patients with chronic heart failure. This sleep effect may have a beneficial impact on blood pressure, arrhythmogenesis and quality of life.

Damage thresholds for cultured retinal pigment epithelial cells exposed to lasers at 532 nm and 458 nm

The determination of safe exposure levels for lasers has come from damage assessment experiments in live animals, which typically involve correlating visually identifiable damage with laser dosimetry. Studying basic mechanisms of laser damage in animal retinal systems often requires tissue sampling (animal sacrifice), making justification and animal availability problematic. We determined laser damage thresholds in cultured monolayers of a human retinal pigment epithelial (RPE) cell line. By varying exposure duration and laser wavelength, we identified conditions leading to damage by presumed photochemical or thermal mechanisms. A comparison with literature values for ocular damage thresholds validates the in vitro model. The in vitro system described will facilitate molecular and cellular approaches for understanding laser-tissue interaction.

Electrical activity during the 2006 Mount St. Augustine volcanic eruptions

By using a combination of radio frequency time-of-arrival and interferometer measurements, we observed a sequence of lightning and electrical activity during one of Mount St. Augustine's eruptions. The observations indicate that the electrical activity had two modes or phases. First, there was an explosive phase in which the ejecta from the explosion appeared to be highly charged upon exiting the volcano, resulting in numerous apparently disorganized discharges and some simple lightning. The net charge exiting the volcano appears to have been positive. The second phase, which followed the most energetic explosion, produced conventional-type discharges that occurred within plume. Although the plume cloud was undoubtedly charged as a result of the explosion itself, the fact that the lightning onset was delayed and continued after and well downwind of the eruption indicates that in situ charging of some kind was occurring, presumably similar in some respects to that which occurs in normal thunderstorms.

Optical properties of ocular tissues in the near infrared region

Near infrared characterization of optical properties of aqueous humor and vitreous humor of healthy human and bovine eyes has been performed. The indices of refraction (n) of these ocular tissues were determined using a Michelson interferometer. The total diffuse reflection (R (d)) and total transmission (T (t)) measurements had been taken for individual ocular tissue by using a double-integrating sphere setup and infrared laser diodes. The inverse adding doubling (IAD) computational method based on the diffusion approximation and radiative transport theory was applied to the measured values of n, R (d), and T (t) to calculate the optical absorption and scattering coefficients of the human and bovine ocular tissues. The scattering anisotropy value was determined by iteratively running the IAD method program and a Monte Carlo simulation of light-tissue interaction until the minimum difference in experimental and computed value for T (t) was realized. A comparison between the optical characterization of human and bovine ocular samples was also made.

Modeling thermal damage in skin from 2000-nm laser irradiation

An optical-thermal-damage model of the skin under laser irradiation is developed by using finite-element modeling software (FEMLAB 3.1, Comsol, Incorporated, Burlington, Massachusetts). The general model simulates light propagation, heat generation, transient temperature response, and thermal damage produced by a radically symmetric laser beam of normal incidence. Predictions from the model are made of transient surface temperatures and the thermal damage on a pigskin surface generated by 2000-nm laser irradiation, and these predictions are compared to experimental measurements. The comparisons validate the model predictions, boundary conditions, and optical, thermal, and rate process parameters. The model enables the authors to verify the suitability of the American National Standards Institute (ANSI) maximum permissible exposure (MPE) standard for a wavelength of 2000 nm with exposure duration from 0.1 to 1 s and 3.5-mm beam diameter. Compared with the ANSI MPE standard, however, the MPE values predicted by the model are higher for exposure durations less than 0.1 s. The model indicates that it may be necessary to modify the ANSI MPE standard for cases in which the laser-beam diameter is larger than 3.5 mm when a "safety factor" of ten is used. A histopathological analysis of the skin damage is performed to determine the mechanisms of laser-induced damage in the skin.

Damage Thresholds for Exposure to NIR and Blue Lasers in an In Vitro RPE Cell System

PURPOSE

Until reliable nonanimal systems of analysis are available, animal models will be necessary for ocular laser hazard analysis and for evaluating clinical applications. The purpose of this work was to demonstrate the utility of an in vitro system for laser bioeffects by identifying photothermal and photochemical cytotoxicity thresholds for continuous-wave (cw) and mode-locked (ml) laser exposures.

METHODS

Exogenous melanosomes were added to hTERT-RPE1 cells in exposure wells 1 day before laser exposure. Thermal or photochemical laser exposures were delivered to artificially pigmented retinal pigment epithelial (RPE) cultures, with subsequent assay for viability 1 hour after exposure. Beam delivery for the 1-hour photochemical exposures was via a modified culture incubator. The cytoprotective effect of pretreatment with two antioxidants was investigated.

RESULTS

Phagocytosis of melanosomes by the RPE cells was efficient, yielding cultures of uniform pigmentation. The damage threshold for the thermal exposure was consistent with published in vivo results. Thresholds for both blue exposures (cw and ml) were identical. Overnight treatment of cells with ascorbic acid (AA) minimized cell death from both cw and ml blue laser exposure, whereas similar treatment with N-acetyl-L-cysteine (NAC) was less effective.

CONCLUSIONS

The in vitro system described is suitable for measuring meaningful thermal and photochemical laser damage thresholds. The system is also useful in comparative laser bioeffects studies, such as comparisons between cw and ml laser exposures, cells with various degrees of pigmentation, and studies determining the efficacy and mechanisms of treatments altering the response of cells to lasers.

The effect of three-dimensional co-culture of hepatocytes and hepatic stellate cells on key hepatocyte functions in vitro

In this study, we demonstrate the ability of a three-dimensional co-culture model to preserve some key aspects of differentiated hepatocyte function in vitro. Freshly isolated rat hepatocytes in co-culture with activated stellate cells rapidly aggregate to form well-defined viable spheroids. After 5 days in culture, the spheroids have a complex extracellular matrix support and hepatic ultrastructure including bile canaliculi, tight junctions, desmosomes and lipid storage. Co-culture spheroids have superior cytochrome P450 (CYP450) 3A and 2B function, and increased inducibility of 2B function, relative to a range of hepatocyte monoculture techniques (high-performance liquid chromatography of testosterone metabolites). Increased function in co-culture is supported by greater expression of CYP450 3A23, 1A2, and 2E1 mRNA relative to monoculture (reverse transcriptase quantitative polymerase chain reaction). Also, high hepatocyte growth factor mRNA expression in co-culture suggests a post-traumatic, or possibly regenerative, environment. A preliminary study of human hepatocytes co-cultured with rat stellate cells demonstrated prolonged function of CYP450 3A4, 2C19 and 2C9. This study shows that stellate cells facilitate spheroid formation, influence spheroid architecture, and are an effective method of preserving some aspects of hepatocyte function in the early stage of culture.

Visible lesion thresholds with pulse duration, spot size dependency, and model predictions for 1.54-microm, near-infrared laser pulses penetrating porcine skin

Er:glass lasers have been in operation with both long pulses (hundreds of microseconds) and Q-switched pulses (50 to 100 ns) for more than 35 yr. The ocular hazards of this laser were reported early, and it was determined that damage to the eye from the 1.54-microm wavelength occurred mainly in the cornea where light from this wavelength is highly absorbed. Research on skin hazards has been reported only in the past few years because of limited pulse energies from these lasers. Currently, however, with pulse energies in the hundreds of joules, these lasers may be hazardous to the skin in addition to being eye hazards. We report our minimum visible lesion (MVL) threshold measurements for two different pulse durations and three different spot sizes for the 1.54-microm wavelength using porcine skin as an in vivo model. We also compare our measurements to results from our model, based on the heat transfer equation and the rate process equation. Our MVL-ED50 thresholds for the long pulse (600 micros) at 24 h postexposure were measured to be 20, 8.1, and 7.4 J cm(-2) for spot diameters of 0.7, 1.0, and 5 mm, respectively. Q-switched laser pulses of 31 ns had lower ED50 (estimated dose for a 50% probability of laser-induced damage) thresholds of 6.1 J cm(-2) for a 5-mm-diam, top-hat spatial profile laser pulse.

Adults with ADHD and sleep complaints: a pilot study identifying sleep-disordered breathing using polysomnography and sleep quality assessment

OBJECTIVE

ADHD and sleep-disordered breathing are both prevalent in adulthood. Because both conditions may be responsible for similar symptoms of cognitive impairment, the authors investigate whether their presentation may overlap in adults diagnosed with ADHD.

METHOD

Data are collected from six adults with sleep complaints who were diagnosed with ADHD using rigorous clinical criteria. All participants undergo overnight polysomnography and complete questionnaires about sleep quality, circadian sleep pattern, and daytime fatigue.

RESULTS

On standardized measures, all participants report poor sleep quality, two report daytime fatigue, and none report distinct deviation from normal sleep and wake cycle pattern. Polysomnography reveals evidence of sleep-disordered breathing and sleep fragmentation in all participants.

CONCLUSION

Objective evidence of breathing-related sleep disorders can be found in some adults with carefully diagnosed ADHD who report sleep complaints. This report highlights the importance of identifying treatable sleep disorder comorbidity in adults with ADHD.

Hepatic stellate cells on poly(DL-lactic acid) surfaces control the formation of 3D hepatocyte co-culture aggregates in vitro

Evidence for the functional superiority of cells cultured as 3D aggregates or on 3D scaffolds over conventional 2D monolayer cultures has created interest in material and cell based methods that influence the formation and structure of multicellular aggregates in vitro. We have created a co-culture of primary rat hepatocytes and hepatic stellate cells on a poly(DL-lactic acid) surface, a poor substrate for rat hepatocyte adhesion, to study the dynamics of multicellular spheroid formation and the resultant cell arrangement. The poly(DL-lactic acid) surface allows dynamic and rapid interaction of hepatocytes and stellate cells to form co-culture spheroids in a complex multistage process (shown by time lapse microscopy). This spheroid morphology supports enhanced cell viability relative to a mono-culture mono-layer system (measured by lactate dehydrogenase leakage). The distribution of the aggregating cell type in the final structure is related to the mechanics of formation i.e. mainly central and peripheral. This study provides a unique and generically applicable insight into the dynamics of multicellular spheroid formation where aggregation is induced by one cell type and imposed on another. This has implications for 3D cell culture models and a wide number of currently used stromal co-culture systems.

A preliminary study of sleep-disordered breathing in major depressive disorder

BACKGROUND AND PURPOSE

Individuals with obstructive sleep-disordered breathing (OSDB) commonly report symptoms of depression; however, the percentage of individuals with major depressive disorder (MDD) who experience OSDB is less clear. This study aimed to examine OSDB in a sample of individuals with MDD, unselected for sleep-related complaints, along a continuum of ventilatory and hypoxic abnormalities.

PATIENTS AND METHODS

The overnight sleep-related breathing of 19 individuals with MDD and 15 non-depressed controls was recorded using an unattended nasal pressure-based home sleep monitoring device. The device recorded nasal airflow, breathing effort, heart rate, oxygen saturation, and body position.

RESULTS

The two groups varied significantly on three sleep-related breathing variables: major flow-limitation events, major flow-limitation events accompanied by a desaturation, and average saturation throughout the evening; and these groups approached significance on minor flow-limitation events accompanied by a desaturation and average number of desaturations throughout the evening. Sleep-related breathing variables predicted accurate grouping in 81.3% of those with MDD and 80.6% of the non-depressed participants.

CONCLUSIONS

These results suggest that OSDB may play a more important role in MDD than previously recognized. OSDB may contribute to or exacerbate the condition of someone predisposed to MDD, and the treatment of OSDB may ameliorate or possibly prevent depressive symptoms.

Recognition and management of complex sleep-disordered breathing

PURPOSE OF REVIEW

The recent rapid evolution of our understanding of the mechanisms involved in control of respiration during sleep has yielded new insights to guide our care of difficult-to-treat sleep apnea patients with complex sleep-disordered breathing. This review will describe these recent advances in the literature and suggest a model for their incorporation into clinical practice.

RECENT FINDINGS

Control of respiration during sleep shows amplified instability relative to that seen during wake in these difficult patients. Baseline (eupneic) carbon dioxide levels as well as the responsiveness of the ventilatory system to changes in carbon dioxide are all-important in this relative instability. Furthermore, the instability seen during sleep varies widely across sleep states. A further refinement of our definition of stable and unstable sleep has been developed that directly informs our understanding of the control of respiration across a night of sleep.

SUMMARY

Complex sleep-disordered breathing is a distinct form of sleep apnea. It has recognizable characteristics that are present without, and often worsened during, positive airway pressure treatment. Both sleep state stability and the behavior of the respiratory control system contribute to this complexity. It is only with a clear understanding of the factors contributing to complex sleep-disordered breathing that implementation of truly effective clinical therapy can be achieved for this disorder, which to date is poorly controlled.

Fatigue in the executive cortical network demonstrated in narcoleptics using functional magnetic resonance imaging—a preliminary study

BACKGROUND AND PURPOSE

To demonstrate dynamic changes in cerebral functional activation during a working memory task in a state of severe excessive daytime sleepiness.

PATIENTS AND METHODS

Omitting the usual morning dose of stimulants in three narcoleptics induced sleepiness. Functional magnetic resonance imaging (fMRI) was used to map cerebral activation during the performance of a 2-back verbal working memory task. Repeated 9.5 min scans were performed, until the subjects felt they could not continue. This was the functional imaging equivalent of the maintenance of wakefulness test.

RESULTS

Bilateral and widespread activation in known nodes of the executive network were seen during the first scan in all subjects, including the lateral prefrontal, posterior parietal and anterior cingulate cortex. There was a reduction in cerebral activation, especially but not exclusively in the prefrontal cortex, associated with slowing of performance from the first to the last tolerated scan. On stimulants, subjective alertness, activation and objective performance were readily maintained.

CONCLUSION

This preliminary study suggests that fatigue in the executive cortical network may be demonstrated by a progressive reduction in regional cerebral activation across scans, which may be prevented by stimulant use. Averaging multiple scan runs, a typical practice in fMRI, could blur important dynamic components of activation.

Reorganization of sleep patterns in severe OSAS under prolonged CPAP treatment

OBJECTIVE

To evaluate the immediate and long-term recovery processes of sleep and daytime vigilance in patients with sleep apnea syndrome (OSAS) after continuous CPAP treatment.

METHODS

Five consecutive polysomnographic (PSG) studies were carried out on 10 male patients with severe OSAS. The first recording (baseline) was accomplished without ventilatory support (N0). The other 4 recordings were carried out during the CPAP titration night (N1), during the second night of treatment (N2), during the third night of treatment (N3), and after 30 days of regular CPAP use (N30). Ten age-balanced healthy male subjects were selected from the Parma Sleep Center database as controls. Respiratory variables, conventional PSG variables, arousals, CAP (cyclic alternating pattern) variables, and daytime function (including MSLT) were quantified. ANOVA followed by post-hoc tests explored the differences between controls and OSAS patients in the different recording conditions (N0, N1, N2, N3, N30). The PSG measures that showed significant ANOVA values were correlated with the MSLT scores.

RESULTS

Values of control subjects were recovered by REM sleep, REM latency, subtypes A3 and arousal index during N1, by CAP rate and total arousals during N2, by deep sleep (stages 3 + 4) during N3, by light sleep (stages 1 + 2) during N30. The only measures which remained below control values even after 1 month of sustained treatment were the amount of CAP cycles and A1 subtypes. MSLT scores correlated significantly with CAP rate, deep sleep and arousals.

CONCLUSIONS

The changes induced by CPAP treatment do not restore immediately a normal sleep structure, which is re-established with different time scales

SIGNIFICANCE

The modifications of sleep patterns and the different adjustments of phase A subtypes allow us to monitor the reorganization of sleep in OSAS patients treated with CPAP and the hierarchy of the mechanisms involved in sleep regulation.

Perspective: the evolution of warning coloration is not paradoxical

Animals that are brightly colored have intrigued scientists since the time of Darwin, because it seems surprising that prey should have evolved to be clearly visible to predators. Often this self-advertisement is explained by the prey being unprofitable in some way, with the conspicuous warning coloration helping to protect the prey because it signals to potential predators that the prey is unprofitable. However, such signals only work in this way once predators have learned to associate the conspicuous color with the unprofitability of the prey. The evolution of warning coloration is still widely considered to be a paradox, because it has traditionally been assumed that the very first brightly colored individuals would be at an immediate selective disadvantage because of their greater conspicuousness to predators that are naive to the meaning of the signal. As a result, it has been difficult to understand how a novel conspicuous color morph could ever avoid extinction for long enough for predators to become educated about the signal. Thus, the traditional view that the evolution of warning coloration is difficult to explain rests entirely on assumptions about the foraging behavior of predators. However, we review recent evidence from a range of studies of predator foraging decisions, which refute these established assumptions. These studies show that: (1) Many predators are so conservative in their food preferences that even very conspicuous novel prey morphs are not necessarily at a selective disadvantage. (2) The survival and spread of novel color morphs can be simulated in field and aviary experiments using real predators (birds) foraging on successive generations of artificial prey populations. This work demonstrates that the foraging preferences of predators can regularly (though not always) result in the increase to fixation of a novel morph appearing in a population of familiar-colored prey. Such fixation events occur even if both novel and familiar prey are fully palatable and despite the novel food being much more conspicuous than the familiar prey. These studies therefore provide strong empirical evidence that conspicuous coloration can evolve readily, and repeatedly, as a result of the conservative foraging decisions of predators.

Cardiac rehabilitation after myocardial infarction: a review to understand barriers to participation and potential solutions

As survival after myocardial infarction (MI) improves, secondary prevention is becoming increasingly important. Cardiac rehabilitation (CR) is one modality for delivery of secondary prevention, whose ultimate goal is to help patients receive appropriate preventive therapies that will help them optimize health and reduce the risk of future cardiac diseases. However, participation rates in CR are less than optimal: in the United States, only 29.5% of MI survivors participated, in Japan 21% of those with acute MI, and in Australia 29% of those eligible were referred, and only 1/3 of those referred acutally attended CR; moreover, there does not appear to be a trend towards increasing participation over time. After reviewing the components of CR and the benefits of participation, this paper will focus on the barriers to participation in CR: from a theoretical framework to consider barriers at patient, provider, health system, and societal levels. We then explore the possible solutions to overcome them and finally propose recommendation for future research.

Functional imaging of working memory in obstructive sleep-disordered breathing

Functional magnetic resonance imaging was used to map cerebral activation in 16 patients with obstructive sleep-disordered breathing (OSDB) and 16 healthy subjects, during the performance of a 2-back verbal working memory task. Six patients with OSDB were reimaged after a minimum period of 8 wk of treatment with positive airway pressure. Working memory speed in OSDB was significantly slower than in healthy subjects, and a group average map showed absence of dorsolateral prefrontal activation, regardless of nocturnal hypoxia. After treatment, resolution of subjective sleepiness contrasted with no significant change in behavioral performance, persistent lack of prefrontal activation, and partial recovery of posterior parietal activation. These findings suggest that working memory may be impaired in OSDB and that this impairment is associated with disproportionate impairment of function in the dorsolateral prefrontal cortex. Nocturnal hypoxia may not be a necessary determinant of cognitive dysfunction, and sleep fragmentation may be sufficient. There may be dissociations between respiratory vs. cortical recovery and objective vs. subjective recovery. Hypofrontality may provide a plausible biological mechanism for a clinical overlap with disorders of mood and attention.