Long-term intermittent hypoxia in mice: protracted hypersomnolence with oxidative injury to sleep-wake brain regions

Pathophysiology of sleep apnea

Sleep-induced apnea and disordered breathing refers to intermittent, cyclical cessations or reductions of airflow, with or without obstructions of the upper airway (OSA). In the presence of an anatomically compromised, collapsible airway, the sleep-induced loss of compensatory tonic input to the upper airway dilator muscle motor neurons leads to collapse of the pharyngeal airway. In turn, the ability of the sleeping subject to compensate for this airway obstruction will determine the degree of cycling of these events. Several of the classic neurotransmitters and a growing list of neuromodulators have now been identified that contribute to neurochemical regulation of pharyngeal motor neuron activity and airway patency. Limited progress has been made in developing pharmacotherapies with acceptable specificity for the treatment of sleep-induced airway obstruction. We review three types of major long-term sequelae to severe OSA that have been assessed in humans through use of continuous positive airway pressure (CPAP) treatment and in animal models via long-term intermittent hypoxemia (IH): 1) cardiovascular. The evidence is strongest to support daytime systemic hypertension as a consequence of severe OSA, with less conclusive effects on pulmonary hypertension, stroke, coronary artery disease, and cardiac arrhythmias. The underlying mechanisms mediating hypertension include enhanced chemoreceptor sensitivity causing excessive daytime sympathetic vasoconstrictor activity, combined with overproduction of superoxide ion and inflammatory effects on resistance vessels. 2) Insulin sensitivity and homeostasis of glucose regulation are negatively impacted by both intermittent hypoxemia and sleep disruption, but whether these influences of OSA are sufficient, independent of obesity, to contribute significantly to the "metabolic syndrome" remains unsettled. 3) Neurocognitive effects include daytime sleepiness and impaired memory and concentration. These effects reflect hypoxic-induced "neural injury." We discuss future research into understanding the pathophysiology of sleep apnea as a basis for uncovering newer forms of treatment of both the ventilatory disorder and its multiple sequelae.

Mammillary body and fornix injury in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) is accompanied by reduced ventilatory sensitivity to CO2 and O2, respiratory drive failure during sleep, impaired autonomic, fluid, and food absorption regulation, and affective and cognitive deficits, including memory deficiencies. The deficits likely derive from neural injury, reflected as structural damage and impaired functional brain responses to ventilatory and autonomic challenges. Brain structures playing essential memory roles, including the hippocampus and anterior thalamus, are damaged in CCHS. Other memory formation circuitry, the fornix and mammillary bodies, have not been evaluated. We collected two high-resolution T1-weighted image series from 14 CCHS and 31 control subjects, using a 3.0-Tesla magnetic resonance imaging scanner. Image series were averaged and reoriented to a standard template; areas containing the mammillary bodies and fornices were over sampled, and body volumes and fornix cross-sectional areas were calculated and compared between groups. Both left and right mammillary body volumes and fornix cross-sectional areas were significantly reduced in CCHS over control subjects, controlling for age, gender, and intracranial volume. Damage to these structures may contribute to memory deficiencies found in CCHS. Hypoxic processes, together with diminished neuroprotection from micronutrient deficiencies secondary to fluid and dietary absorption issues, may contribute to the injury.

Pattern-specific sustained activation of tyrosine hydroxylase by intermittent hypoxia: role of reactive oxygen species-dependent downregulation of protein phosphatase 2A and upregulation of protein kinases

We investigated the role of protein phosphatases (PP) and protein kinases in tyrosine hydroxylase (TH) activation by two patterns of intermittent hypoxia (IH) in rat brainstem. Rats exposed to either IH(15s) (15 s, 5% O(2); 5 min, 21%O(2)) or IH(90s) (90 s each of 10% O(2) & 21%O(2)) for 10 days were used. IH(15s) but not IH(90s) caused a robust increase in TH activity, dopamine (DA) level, and TH phosphorylation at Ser-31 and Ser-40 in the medulla but not in the pons. Likewise, IH(15s) but not IH(90s) decreased activity and expression of protein phosphatase 2A (PP2A) and increased activity of multiple protein kinases. In vitro dephosphorylation with PP2A nearly abolished IH(15s)-induced increase in TH activity. IH(15s) increased generation of reactive oxygen species (ROS) in brainstem medullary regions which was nearly threefold higher than that evoked by IH(90s). Antioxidants prevented IH(15s)-induced downregulation of PP2A and increases in multiple protein kinase activity with subsequent reversal of serine phosphorylation of TH, TH activity, and DA to control levels. These findings demonstrate that IH in a pattern-specific manner activates TH involving ROS-mediated sustained increase in TH phosphorylation via downregulation of PP2A and upregulation of protein kinases.

Spatial learning and memory deficits following exposure to 24 h of sleep fragmentation or intermittent hypoxia in a rat model of obstructive sleep apnea

Obstructive sleep apnea is primarily characterized by hypoxemia due to frequent apneic episodes and fragmentation of sleep due to the brief arousals that terminate the apneic episodes. Though neurobehavioral deficits frequently accompany sleep apnea, the relative roles of hypoxia versus sleep fragmentation are difficult to separate in apneic patients. Here, we assessed cognitive function as measured by water maze in the Fischer/Brown Norway (FBN) rat, comparing 24 h of sleep interruption (SI) to 24 h of intermittent hypoxia (IH), in order to dissociate their relative contributions to cognitive impairment. For SI, automated treadmills were used to induce brief ambulation in rats every 2 min, either prior to, or after, initial water maze acquisition training. IH was simulated by cycling environmental oxygen levels between 6% and 19% every 2 min, again either prior to, or after, acquisition. Twenty-four hours of IH exposure had no significant effect on either acquisition or retention, irrespective of whether IH occurred prior to, or after, acquisition. To replicate previous work, another group of rats, exposed to 3 days of IH (10 h/day) prior to acquisition, had impaired performance during acquisition. A comparison of the 24 h IH and 3 day IH findings suggests that a minimum amount of IH exposure is necessary to produce detectable spatial memory impairments. Although SI before acquisition had no effect on acquisition or later retention of the hidden platform location, SI after acquisition robustly impaired retention, indicating that spatial memory consolidation is more susceptible to the effects of sleep disruption than is the acquisition (learning) of spatial information.

Reduced caudate nuclei volumes in patients with congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) children show cognitive and affective deficits, in addition to state-specific loss of respiratory drive. The caudate nuclei serve motor, cognitive, and affective roles, and show structural deficits in CCHS patients, based on gross voxel-based analytic procedures. However, the magnitude and regional sites of caudate injury in CCHS are unclear. We assessed global caudate nuclei volumes with manual volumetric procedures, and regional volume differences with three-dimensional surface morphometry in 14 CCHS (mean age+/-SD: 15.1+/-2.3 years; 8 male) and 31 control children (15.1+/-2.4 years; 17 male) using brain magnetic resonance imaging (MRI). Two high-resolution T1-weighted image series were collected using a 3.0 Tesla MRI scanner; images were averaged and reoriented (rigid-body transformation) to common space. Both left and right caudate nuclei were outlined in the reoriented images, and global volumes calculated; surface models were derived from manually-outlined caudate structures. Global caudate nuclei volume differences between groups were evaluated using a multivariate analysis of covariance (covariates: age, gender, and total intracranial volume). Both left and right caudate nuclei volumes were significantly reduced in CCHS over control subjects (left, 4293.45+/-549.05 vs. 4626.87+/-593.41 mm(3), P<0.006; right, 4376.29+/-565.42 vs. 4747.81+/-578.13 mm(3), P<0.004). Regional deficits in CCHS caudate volume appeared bilaterally, in the rostral head, ventrolateral mid, and caudal body. Damaged caudate nuclei may contribute to CCHS neuropsychological and motor deficits; hypoxic processes, or maldevelopment in the condition may underlie the injury.

Transcriptional responses to intermittent hypoxia

Recurrent apneas are characterized by transient repetitive cessations of breathing (two breaths duration or longer) resulting in periodic decreases in arterial blood PO2 or chronic intermittent hypoxia (IH). Patients with recurrent apneas and experimental animals exposed to chronic IH exhibit cardio-respiratory morbidities. The purpose of this article is to highlight the current information on the transcriptional mechanisms associated with chronic IH. Studies on rodents and cell cultures have shown that IH activates a variety of transcription factors including the hypoxia-inducible factor-1 (HIF-1), c-fos (immediate early gene), nuclear factor of activated T-cells (NFAT), and nuclear factor kB (NF-kB). The signaling pathways associated with transcriptional activation associated with IH differ from continuous hypoxia (CH). Compared to same duration and intensity of CH, IH is more potent in activating HIF-1 and c-fos and also results in long-lasting accumulation of HIF-1alpha and c-fos mRNA, a phenomenon that was not seen with CH. IH-evoked transcriptional activation by HIF-1, c-fos as well as the resulting activator protein-1 (AP-1) requires reactive oxygen species (ROS)-mediated signaling and involves complex feed forward interactions between HIF-1 and ROS. Chronic IH-evoked cardio-respiratory responses are absent in Hif-1alpha+/- mice, and hypertension elicited by chronic IH is absent in mice lacking NFAT3c. These studies indicate that cardiorespiratory responses to chronic IH depend on complex interactions between various transcription factors resulting in alterations in several down stream genes and their protein products.

Obstructive sleep apnea and cardiovascular disease: a perspective and future directions

Data from animal and human studies provide a biological plausibility to the notion that obstructive sleep apnea activates pathways that lead to insulin resistance, atherosclerosis and hypertension. Sleep apnea thus activates the same pathways as does obesity. That obstructive sleep apnea is a risk factor for cardiovascular disease is supported by epidemiological association studies. Longitudinal cohort studies also provide evidence that patients with untreated severe sleep apnea have an increased rate of cardiovascular events. But these studies, while highly suggestive, do not provide the evidence needed to convince the skeptic. This would only be obtained by randomized treatment trials with hard cardiovascular endpoints such as cardiac events and deaths. While such studies are in the planning stages, they will be challenging. There are issues about randomizing individuals with severe sleep apnea and excessive sleepiness into no therapy, since they are at known increased risk for car crashes. Thus, lack of therapy puts others on the road at risk as well as the subject with sleep apnea. There is, moreover, the concern that treating obstructive sleep apnea in very obese individuals will have little impact, since any effect of therapy for OSA will be overwhelmed by the effects of obesity itself. Data from randomized treatment trials for cardiovascular endpoints will likely not be available for many years. In the interim, physicians need to consider how to treat such patients. It is proposed that given that CPAP treatment for obstructive sleep apnea is highly effective and essentially totally safe, and that the evidence is suggestive that sleep apnea is a risk factor for cardiovascular disease, then we propose all patients with severe sleep apnea should be treated to reduce cardiovascular risk.

A pilot study of sleep, cognition, and respiration under 4 weeks of intermittent nocturnal hypoxia in adult humans

STUDY OBJECTIVES

A pilot study to examine the effects of intermittent nocturnal hypoxia on sleep, respiration and cognition in healthy adult humans.

METHODS

Participants were eight healthy, non-smoking subjects (four male, four female), mean age of 26.4+/-5.2 years, and BMI 22.3+/-2.6 kg/m(2), exposed to 9h of intermittent hypoxia between the hours of 10 P.M. and 7 A.M. for 28 consecutive nights. At a simulated altitude of 13,000 feet (FIO(2) 0.13), intermittent hypoxia was achieved by administering nasal nitrogen, alternating with brief (approximately 5s) boluses of nasal oxygen. Pre- and post-exposure assessments included polysomnography, attention (20-min Psychomotor Vigilance Test), working memory (10-min verbal 2 and 3-back), Multiple Sleep Latency Test, and the Rey Auditory Verbal Learning Test. Obstructive and non-obstructive respiratory events were scored.

RESULTS

Overall sleep quality showed worsening trends but no statistically significant change following exposure. There was no difference after hypoxia in sleepiness, encoding, attention or working memory. Hyperoxic central apneas and post-hyperoxic respiratory instability were noted as special features of disturbed respiratory control induced by intermittent nocturnal hypoxia.

CONCLUSIONS

In this model, exposure to nocturnal intermittent hypoxia for 4 weeks caused no significant deficits in subjective or objective alertness, vigilance, or working memory.

Can O2 dysregulation induce premature aging?

Chronic intermittent or episodic hypoxia, as occurs during a number of disease states, can have devastating effects, and prolonged exposure to this hypoxia can result in cell injury or cell death. Indeed, intermittent hypoxia activates a number of signaling pathways that are involved in oxygen sensing, oxidative stress, metabolism, catecholamine biosynthesis, and immune responsiveness. The cumulative effect of these processes over time can undermine cell integrity and lead to a decline in function. Furthermore, the ability to respond adequately to various stressors is hampered, and this is traditionally defined as premature aging or senescence. This review highlights recent advances in our understanding of the cellular and molecular mechanisms that are involved in the response to intermittent hypoxia and the potential interplay among various pathways that may accelerate the aging process.

Modafinil in the treatment of excessive sleepiness

The wake-promoting agent modafinil is approved for the treatment of excessive sleepiness associated with obstructive sleep apnea (OSA), shift work disorder (SWD), and narcolepsy. In OSA, modafinil is recommended for use as an adjunct to standard therapies that treat the underlying airway obstruction. This article reviews the literature on modafinil (pharmacology, pharmacokinetics, efficacy, tolerability, and abuse potential), with emphasis on use of modafinil in the treatment of excessive sleepiness in patients with OSA, SWD, and narcolepsy. In large-scale, double-blind, placebo-controlled studies, modafinil improved objectively determined sleep latency, improved overall clinical condition related to severity of sleepiness, and reduced patient-reported sleepiness. Improvements in wakefulness were accompanied by improvements in behavioral alertness, functional status, and health-related quality of life. In patients with SWD, diary data showed modafinil reduced the maximum level of sleepiness during night shift work, level of sleepiness during the commute home, and incidence of accidents or near-accidents during the commute home when compared with placebo. Modafinil was well tolerated, without adversely affecting cardiovascular parameters or scheduled sleep. These findings and those of extension studies which reported improvements were maintained suggest modafinil has a beneficial effect on daily life and well-being in patients with excessive sleepiness associated with OSA, SWD, or narcolepsy.

Neural alterations associated with anxiety symptoms in obstructive sleep apnea syndrome

BACKGROUND

Neuropsychological comorbidities, including anxiety symptoms, accompany obstructive sleep apnea (OSA); structural and functional brain alterations also occur in the syndrome. The objective was to determine whether OSA patients expressing anxiety symptoms show injury in specific brain sites.

METHODS

Magnetic resonance T2-relaxometry was performed in 46 OSA and 66 control subjects. Anxiety symptoms were evaluated using the Beck Anxiety Inventory (BAI); subjects with BAI scores >9 were classified anxious. Whole brain T2-relaxation maps were compared between anxious and nonanxious groups using analysis of covariance (covariates, age and gender).

RESULTS

Sixteen OSA and seven control subjects showed anxiety symptoms, and 30 OSA and 59 controls were nonanxious. Significantly higher T2-relaxation values, indicating tissue injury, appeared in anxious OSA versus nonanxious OSA subjects in subgenu, anterior, and mid-cingulate, ventral medial prefrontal and bilateral insular cortices, hippocampus extending to amygdala and temporal, and bilateral parietal cortices. Brain injury emerged in anxious OSA versus nonanxious controls in bilateral insular cortices, caudate nuclei, anterior fornix, anterior thalamus, internal capsule, mid-hippocampus, dorsotemporal, dorsofrontal, ventral medial prefrontal, and parietal cortices.

CONCLUSIONS

Anxious OSA subjects showed injury in brain areas regulating emotion, with several regions lying outside structures affected by OSA alone, suggesting additional injurious processes in anxious OSA subjects.

Brain injury in autonomic, emotional, and cognitive regulatory areas in patients with heart failure

BACKGROUND

Heart failure (HF) is accompanied by autonomic, emotional, and cognitive deficits, indicating brain alterations. Reduced gray matter volume and isolated white matter infarcts occur in HF, but the extent of damage is unclear. Using magnetic resonance T2 relaxometry, we evaluated the extent of injury across the entire brain in HF.

METHODS AND RESULTS

Proton-density and T2-weighted images were acquired from 13 HF (age 54.6 +/- 8.3 years; 69% male, left ventricular ejection fraction 0.28 +/- 0.07) and 49 controls (50.6 +/- 7.3 years, 59% male). Whole brain maps of T2 relaxation times were compared at each voxel between groups using analysis of covariance (covariates: age and gender). Higher T2 relaxation values, indicating injured brain areas (P < .005), emerged in sites that control autonomic, analgesic, emotional, and cognitive functions (hypothalamus, raphé magnus, cerebellar cortex, deep nuclei and vermis; temporal, parietal, prefrontal, occipital, insular, cingulate, and ventral frontal cortices; corpus callosum; anterior thalamus; caudate nuclei; anterior fornix and hippocampus). No brain areas showed higher T2 values in control vs. HF subjects.

CONCLUSIONS

Brain structural injury emerged in areas involved in autonomic, pain, mood, language, and cognitive function in HF patients. Comorbid conditions accompanying HF may result from neural injury associated with the syndrome.

Dynamic arterial blood gas analysis in conscious, unrestrained C57BL/6J mice during exposure to intermittent hypoxia

Rodent models of chronic intermittent hypoxia (IH) are commonly used to investigate the pathophysiological sequelae that result from hypoxic exposure in patients experiencing obstructive sleep apnea (OSA). Despite the widespread use of IH models, little attention has been paid to carefully defining the degree of oxyhemoglobin desaturation that occurs during each hypoxic period. Therefore, we developed a rapid blood sampling technique to determine the arterial blood gas changes that occur in conscious unrestrained mice during a single IH event and hypothesized that the arterial Po(2) (Pa(O(2))) at the nadir level of the inspired oxygen profile causes oxyhemoglobin saturation to fall to between 80% and 90%. Mice were exposed to 120-180 cycles of IH at a rate of 60 cycles/h, and arterial blood samples were withdrawn (<3 s) at baseline and at 10-s time intervals over the course of a single IH cycle. The IH regimen caused a decline in the fraction of inspired oxygen from room air levels to a transient nadir of 6.0 +/- 0.2% over the 30-s hypoxic period. The Pa(O(2)) and arterial oxyhemoglobin saturation reached a nadir of 47 +/- 2 mmHg and 85 +/- 2% at 30 s, respectively. Arterial Pco(2) decreased to a nadir of 26 +/- 2 mmHg at 30 s, associated with a rise in arterial pH to 7.46 +/- 0.2. We conclude that the magnitude of oxyhemoglobin desaturation that is induced in our murine model of IH is consistent with the degree of hypoxic stress that occurs in moderate to severe clinical OSA.

Inflammation and sleep disordered breathing in children: a state-of-the-art review

Sleep disordered breathing (SDB) represents a spectrum of breathing disorders, ranging from snoring to obstructive sleep apnea syndrome (OSAS), that disrupt nocturnal respiration and sleep architecture. OSAS is a common disorder in children, with a prevalence of 2-3%. It is associated with neurobehavioral, cognitive, and cardiovascular morbidities. In children, adenotonsillectomy is the first choice for treatment and is reserved for moderate to severe OSAS, as defined by an overnight polysomnography. In adults, OSAS is the result of mechanical dysfunction of the upper airway, manifesting as severity-dependent nasal, oropharyngeal, and systemic inflammation that decrease after continuous positive airway pressure therapy. Inflammatory changes have been reported in upper airway samples from children with OSAS, and systemic inflammation, as indicated by high-sensitivity C-reactive protein (hsCRP) levels, has been shown to decrease in children with OSAS after adenotonsillectomy. Anti-inflammatory treatments for children with mild OSAS are associated with major improvements in symptoms, polysomnographic respiratory values, and radiologic measures of adenoid size. Inflammation is correlated to some extent with OSAS-related neurocognitive morbidity, but the role of inflammatory markers in the diagnosis and management of OSAS, and the role of anti-inflammatory treatments, remains to be clarified. This review examines the role of inflammation in the pathophysiology of sleep-disordered breathing in pediatric patients and the potential therapeutic implications.

Mammillary bodies and fornix fibers are injured in heart failure

Cognitive abnormalities, including memory deficits, are common in heart failure (HF). Brain structures, including the hippocampus, fornix, and thalamus participate in memory processing, and most show structural injury and functional deficits in HF. The mammillary bodies and fornix play essential roles in spatial and working memory processing, interact with other structures, and may also be injured in HF. We assessed mammillary body volumes and cross-sectional fornix areas in 17 HF and 50 control subjects using high-resolution T1-weighted magnetic resonance images. Mammillary body volumes and fornix cross-sectional areas were significantly reduced bilaterally in HF, and these differences remained after controlling age, gender, and intracranial volume. Mammillary body and fornix injury may contribute to the compromised spatial and working memory deficits in HF. Pathological processes eliciting the damage may include injury accompanying hypoxic/ischemic processes in pathologic HF perfusion and breathing, and thiamine deficiency accompanying diuretic use and nutritional mal-absorption in the condition.

24 hours of sleep deprivation in the rat increases sleepiness and decreases vigilance: introduction of the rat-psychomotor vigilance task

A novel animal-analog of the human psychomotor vigilance task (PVT) was validated by subjecting rats to 24 h of sleep deprivation (SD) and examining the effect on performance in the rat-PVT (rPVT), and a rat multiple sleep latency test (rMSLT). During a three-phase (separate cohorts) crossover design, vigilance performance in the rPVT was compared with 24 h SD-induced changes in sleepiness assessed by polysomnographic evaluation and the rMSLT. Twenty-four hours of SD was produced by brief rotation of activity wheels at regular intervals in which the animals resided throughout the experiment. In the rPVT experiment, exercise controls (EC) experienced the same overall amount of locomotor activity as during SD, but allowed long periods of undisturbed sleep. After 24 h SD response latencies slowed, and lapses increased significantly during rPVT performance when compared with baseline and EC conditions. During the first 3 h of the recovery period following 24 h SD, polysomnographic measures indicated sleepiness. Latency to fall asleep after 24 h SD was assessed six times during the first 3 h after SD. Rats fell asleep significantly faster immediately after SD, than after non-SD baseline sessions. In conclusion, 24 h of SD in rats increased sleepiness, as indicated by polysomnography and the rMSLT, and impaired vigilance as measured by the rPVT. The rPVT closely resembles the human PVT test widely used in human sleep research and will assist investigation of the neurobiologic mechanisms that produce vigilance impairments after sleep disruption.

Intermittent hypoxia activates peptidylglycine alpha-amidating monooxygenase in rat brain stem via reactive oxygen species-mediated proteolytic processing

Intermittent hypoxia (IH) associated with sleep apneas leads to cardiorespiratory abnormalities that may involve altered neuropeptide signaling. The effects of IH on neuropeptide synthesis have not been investigated. Peptidylglycine alpha-amidating monooxygenase (PAM; EC 1.14.17.3) catalyzes the alpha-amidation of neuropeptides, which confers biological activity to a large number of neuropeptides. PAM consists of O(2)-sensitive peptidylglycine alpha-hydroxylating monooxygenase (PHM) and peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL) activities. Here, we examined whether IH alters neuropeptide synthesis by affecting PAM activity and, if so, by what mechanisms. Experiments were performed on the brain stem of adult male rats exposed to IH (5% O(2) for 15 s followed by 21% O(2) for 5 min; 8 h/day for up to 10 days) or continuous hypoxia (0.4 atm for 10 days). Analysis of brain stem extracts showed that IH, but not continuous hypoxia, increased PHM, but not PAL, activity of PAM and that the increase of PHM activity was associated with a concomitant elevation in the levels of alpha-amidated forms of substance P and neuropeptide Y. IH increased the relative abundance of 42- and 35-kDa forms of PHM ( approximately 1.6- and 2.7-fold, respectively), suggesting enhanced proteolytic processing of PHM, which appears to be mediated by an IH-induced increase of endoprotease activity. Kinetic analysis showed that IH increases V(max) but has no effect on K(m). IH increased generation of reactive oxygen species in the brain stem, and systemic administration of antioxidant prevented IH-evoked increases of PHM activity, proteolytic processing of PHM, endoprotease activity, and elevations in substance P and neuropeptide Y amide levels. Taken together, these results demonstrate that IH activates PHM in rat brain stem via reactive oxygen species-dependent posttranslational proteolytic processing and further suggest that PAM activation may contribute to IH-mediated peptidergic neurotransmission in rat brain stem.

Obstructive sleep apnea: the new cardiovascular disease. Part I: Obstructive sleep apnea and the pathogenesis of vascular disease

Obstructive sleep apnea (OSA) is increasingly recognized as a novel cardiovascular risk factor. OSA is implicated in the pathogenesis of hypertension, left ventricular dysfunction, coronary artery disease and stroke. OSA exerts its negative cardiovascular consequences through its unique pattern of intermittent hypoxia. Endothelial dysfunction, oxidative stress, and inflammation are all consequences of OSA directly linked to intermittent hypoxia and critical pathways in the pathogenesis of cardiovascular disease in patients with OSA. This review will discuss the known mechanisms of vascular dysfunction in patients with OSA and their implications for cardiovascular disease.

Assessing sleepiness in the rat: a multiple sleep latencies test compared to polysomnographic measures of sleepiness

Sleepiness following 6 h of sleep deprivation (SD) was evaluated with a rat multiple sleep latencies test (rMSLT), and the findings were compared to conventional polysomnographic measures of sleepiness. The 6 h of SD was produced by automated activity wheels, and was terminated at either the end of the light period or at the beginning of the dark period. The rMSLT consisted of 5 min wakefulness induced by sensory stimulation followed by 25 min of freedom to sleep. This procedure was repeated every 30 min for 3 h and was designed to minimize the amount of sleep lost due to the testing procedure. In separate rats, 6 h SD was followed by undisturbed recovery, allowing evaluation of conventional polysomnographic measures of sleepiness. Sleep onset latencies were reduced following SD, with recovery in the light (baseline = 8 min, 3 s versus post-SD = 1 min, 17 s) and dark period (baseline = 14 min, 17 s versus 7 min, 7 s). Sleep onset latencies were not altered by varying the duration criterion for the first sleep bout (i.e., sleep bout length criteria of 10, 20, 30, or 60 s were compared). Polysomnographic variables (non-rapid eye movement sleep episode duration, delta power, and number of awakenings) also provided reliable indirect measures of sleepiness, regardless of whether the recovery sleep occurred in the light or dark period. Evaluation of effect size indicated that the rMSLT was a strong measure of sleepiness, and was influenced by homeostatic, circadian, and illumination factors. The rMSLT provided a simple, objective, robust and direct measure of sleepiness that was as effective as conventional polysomnographic measures of sleepiness.

Weight loss and brown adipose tissue reduction in rat model of sleep apnea

Background -

Obesity is related to obstructive sleep apnea-hypopnea syndrome (OSAHS), but its roles in OSAHS as cause or consequence are not fully clarified. Isocapnic intermittent hypoxia (IIH) is a model of OSAHS. We verified the effect of IIH on body weight and brown adipose tissue (BAT) of Wistar rats.

Methods

Nine-month-old male breeders Wistar rats of two groups were studied: 8 rats submitted to IIH and 5 control rats submitted to sham IIH. The rats were weighed at the baseline and at the end of three weeks, after being placed in the IIH apparatus seven days per week, eight hours a day, in the lights on period, simulating an apnea index of 30/hour. After experimental period, the animals were weighed and measured as well as the BAT, abdominal, perirenal, and epididymal fat, the heart, and the gastrocnemius muscle.

Results

Body weight of the hypoxia group decreased 17 ± 7 grams, significantly different from the variation observed in the control group (p = 0,001). The BAT was 15% lighter in the hypoxia group and reached marginally the alpha error probability (p = 0.054).

Conclusion

Our preliminary results justify a larger study for a longer time in order to confirm the effect of isocapnic intermittent hypoxia on body weight and BAT.

Reduced mammillary body volume in patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) patients show compromised emotional and cognitive functions, including anterograde memory deficits. While some memory inadequacies in OSA may result from earlier-described structural deficits in the hippocampus, mammillary body injury also could contribute, since these structures receive projections from the hippocampus via the fornix, project heavily to the anterior thalamus, and have been implicated in other conditions with memory deficiencies, such as Korsakoff's syndrome. However, volume loss in mammillary bodies has not been reported in OSA, likely a consequence of logistic difficulties in size assessment. We evaluated mammillary body volumes in 43 OSA (mean age+/-S.D., 46.9+/-9.2 years; mean apnea-hypopnea-index+/-S.D., 31.2+/-19.9 events/h) and 66 control subjects (age, 47.3+/-8.9 years). Two high-resolution T1-weighted image volumes were collected on a 3.0 T magnetic resonance scanner, averaged to improve signal-to-noise, and reoriented (without warping) into a common space. Brain sections containing both mammillary bodies were oversampled, and the bodies were manually traced and volumes calculated. OSA patients showed significantly reduced left, right, and combined mammillary body volumes compared with control subjects, after partitioning for age, gender, and head size (multivariate linear model, p<0.05). Left-side mammillary bodies showed greater volume reduction than the right side. Diminished mammillary body volume in OSA patients may be associated with memory and spatial orientation deficits found in the syndrome. The mechanisms contributing to the volume loss are unclear, but may relate to hypoxic/ischemic processes, possibly assisted by nutritional deficiencies in the syndrome.

Eif-2a protects brainstem motoneurons in a murine model of sleep apnea

Obstructive sleep apnea is associated with neural injury and dysfunction. Hypoxia/reoxygenation exposures, modeling sleep apnea, injure select populations of neurons, including hypoglossal motoneurons. The mechanisms underlying this motoneuron injury are not understood. We hypothesize that endoplasmic reticulum injury contributes to motoneuron demise. Hypoxia/reoxygenation exposures across 8 weeks in adult mice upregulated the unfolded protein response as evidenced by increased phosphorylation of PERK [PKR-like endoplasmic reticulum (ER) kinase] in facial and hypoglossal motoneurons and persistent upregulation of CCAAT/enhancer-binding protein-homologous protein (CHOP)/growth arrest and DNA damage-inducible protein (GADD153) with nuclear translocation. Long-term hypoxia/reoxygenation also resulted in cleavage and nuclear translocation of caspase-7 and caspase-3 in hypoglossal and facial motoneurons. In contrast, occulomotor and trigeminal motoneurons showed persistent phosphorylation of eIF-2a across hypoxia/reoxygenation, without activations of CHOP/GADD153 or either caspase. Ultrastructural analysis of rough ER in hypoglossal motoneurons revealed hypoxia/reoxygenation-induced luminal swelling and ribosomal detachment. Protection of eIF-2alpha phosphorylation with systemically administered salubrinal throughout hypoxia/reoxygenation exposure prevented CHOP/GADD153 activation in susceptible motoneurons. Collectively, this work provides evidence that long-term exposure to hypoxia/reoxygenation events, modeling sleep apnea, results in significant endoplasmic reticulum injury in select upper airway motoneurons. Augmentation of eIF-2a phosphorylation minimizes motoneuronal injury in this model. It is anticipated that obstructive sleep apnea results in endoplasmic reticulum injury involving motoneurons, whereas a critical balance of phosphorylated eIF-2a should minimize motoneuronal injury in obstructive sleep apnea.

Oxidative stress in obstructive sleep apnea: putative pathways to the cardiovascular complications

Obstructive sleep apnea (OSA) is a major public health problem because of its high prevalence in morbidity and mortality. A growing body of evidence suggests that OSA is an important risk factor for cardiovascular diseases. Although the mechanism for the initiation and aggravation of cardiovascular disease has not been fully elucidated, one theorized mechanism is intermittent hypoxia, which is produced by each sleep-disordered breathing event. This repeated hypoxia and reoxygenation cycle is similar to hypoxia-reperfusion injury, which initiates oxidative stress. Recent studies have suggested that OSA is associated with increased levels of oxidative stress or antioxidant deficiencies or both. Oxidative stress is involved in the activation of redox-sensitive transcription factors, which regulate downstream products such as inflammatory cytokines, chemokines, and adhesion molecules. This pathway may be able to explain the pathogenesis of atherosclerosis, a common pathologic factor underlying all types of cardiovascular disease. In addition, endothelial dysfunction derived from oxidative stress can contribute to cardiovascular diseases. This review summarizes current available evidence for and against the occurrence of oxidative stress in OSA and discusses the putative pathways initiating cardiovascular consequences associated with OSA.

Repeated inspiratory occlusions acutely impair myocardial function in rats

Repeated episodes of hypoxia and sympathetic activation during obstructive sleep apnoea are implicated in the initiation and progression of cardiovascular diseases, but the acute effects are unknown. We hypothesized that repeated inspiratory occlusions cause acute myocardial dysfunction and injury. In 22 spontaneously breathing pentobarbital-anaesthetized rats, inspiration was occluded for 30 s every 2 min for 3 h. After approximately 1.5 h, mean arterial pressure started to fall; heart rate between occlusions was stable throughout, consistent with only transient increases in sympathetic activity during each occlusion. Three hours of occlusions resulted in ventricular diastolic dysfunction (reduced peak rate of change of ventricular pressure and slower relaxation). Post-occlusions, the left ventricular contractile response to dobutamine was blunted. After 1 h of recovery, left ventricular pressure generation had returned to values no different from those in sham animals in 5 of 9 of the animals. Cardiac myofibrils from rats subjected to occlusions had depressed calcium-activated myosin ATPase activity, indicating myofilament contractile dysfunction that was not due to breakdown of contractile proteins. Haematoxylin and eosin-stained cross-sections revealed multifocal areas of necrosis within the septum and both ventricles. Repeated inspiratory occlusions, analogous to moderately severe obstructive sleep apnoea, acutely cause global cardiac dysfunction with multifocal myocardial infarcts.

Protective effect of melatonin against hippocampal injury of rats with intermittent hypoxia

Obstructive sleep apnea (OSA) patients suffer from intermittent hypoxia (IH) and neuropsychologic impairments. Oxidative stress is involved in the pathogenesis of OSA, so the application of an antioxidant may be useful. We evaluated the hypothesis that melatonin would reduce IH-induced hippocampal injury via an increased expression of antioxidant enzymes. Adult Sprague-Dawley rats that had received a daily injection of melatonin or vehicle were exposed to IH for 8 hr/day for 7 or 14 days. The serum and hippocampus were harvested for the measurement of malondialdehyde (MDA). Apoptotic cell death was studied histologically in hippocampal sections. The mRNA expression of inflammatory mediators including tumor necrosis factor-alpha, inducible nitric oxide synthase, cyclooxygenase-2 and antioxidant enzymes including glutathione peroxidase, catalase and copper/zinc superoxide dismutase were examined in the hippocampus by RT-PCR. The results show significant increases in levels of serum and hippocampal MDA, apoptotic cell death and mRNA levels of inflammatory mediators in hypoxic rats when compared with the normoxic controls. Also, mRNA levels of the antioxidant enzymes were decreased in hypoxic animals. In the melatonin-treated hypoxic rats, serum MDA levels were comparable with those in normoxic control rats. Also, melatonin treatment significantly reduced hippocampal MDA levels and totally prevented apoptosis. Moreover, there were a decreased expression of the inflammatory mediators and an elevated expression of antioxidant enzymes in the melatonin injected rats when compared with vehicle-treated animals. These results indicate that melatonin mitigates oxidative stress and the pathogenesis of IH-induced hippocampal injury via its antioxidant and anti-inflammatory properties which includes stimulation of transcriptional regulation of antioxidant enzymes.

Green tea catechin polyphenols attenuate behavioral and oxidative responses to intermittent hypoxia

RATIONALE

The intermittent hypoxia (IH) that characterizes sleep-disordered breathing impairs spatial learning and increases NADPH oxidase activity and oxidative stress in rodents. We hypothesized that green tea catechin polyphenols (GTPs) may attenuate IH-induced neurobehavioral deficits by reducing IH-induced NADPH oxidase expression, lipid peroxidation, and inflammation.

OBJECTIVES

To assess the effects of GTP administered in drinking water on the cognitive, inflammatory, and oxidative responses to long-term (>14 d) IH during sleep in male Sprague-Dawley rats.

METHODS

Cognitive assessments were conducted in the Morris water maze. We measured levels and expression of malondialdehyde (MDA), prostaglandin E(2), p47(phox) subunit of NADPH oxidase, receptor for advanced glycation end products (RAGE), and glial fibrillary acidic protein expression in rodent brain tissue.

MEASUREMENTS AND MAIN RESULTS

GTP treatment prevented IH-induced decreases in spatial bias for the hidden platform during the Morris water maze probe trails as well as IH-induced increases in p47phox expression within the hippocampal CA1 region. In untreated animals, IH exposure was associated with doubling of cortical MDA levels in comparison to room air control animals, and GTP-treated animals exposed to IH showed a 40% reduction in MDA levels. Increases in brain RAGE and glial fibrillary acidic protein expression were observed in IH-exposed animals, and these increases were attenuated in animals treated with GTP.

CONCLUSIONS

Oral GTP attenuates IH-induced spatial learning deficits and mitigates IH-induced oxidative stress through multiple beneficial effects on oxidant pathways. Because oxidative processes underlie neurocognitive deficits associated with IH, the potential therapeutic role of GTP in sleep-disordered breathing deserves further exploration.

Nocturnal hypoxia exposure with simulated altitude for 14 days does not significantly alter working memory or vigilance in humans

STUDY OBJECTIVES

To assess the effect of 2 weeks of nocturnal hypoxia exposure using simulated altitude on attention and working memory in healthy adult humans.

DESIGN

Prospective experimental physiological assessment.

SETTING

General Clinical Research Center.

PARTICIPANTS

Eleven healthy, nonsmoking, subjects (7 men, 4 women). The subjects had a mean age of 27 +/- 1.5 years and body mass index of 23 +/- 0.9 kg/m2.

INTERVENTIONS

Subjects were exposed to 9 hours of continuous hypoxia from 2200 to 0700 hours in an altitude tent. Acclimatization was accomplished by graded increases in "altitude" over 3 nights (7700, 10,000 and 13,000 feet), followed by 13,000 feet for 13 consecutive days (FIO2 0.13).

MEASUREMENTS AND RESULTS

Polysomnography that included airflow measurements with a nasal cannula were done at baseline and during 3 time points across the protocol (nights 3, 7, and 14). Attention (10-minute Psychomotor Vigilance Task) and working memory (10-minute verbal 2-back) were assessed at baseline and on day 4, 8, 9, and 15. Nocturnal hypoxia was documented using endpoints of minimum oxygen saturation, oxygen desaturation index, and percentage of total sleep time under 90% and 80%. Total sleep time was reduced, stage 1 sleep was increased, and both obstructive and nonobstructive respiratory events were induced by altitude exposure. There was no difference in subjective mood, attention, or working memory.

CONCLUSIONS

Two weeks of nocturnal continuous hypoxia in an altitude tent did not induce subjective sleepiness or impair objective vigilance and working memory. Caution is recommended in the extrapolation to humans the effects of hypoxia in animal models.

Distinct behavioral and neurochemical alterations induced by intermittent hypoxia or paradoxical sleep deprivation in rats

The current study investigated the effects of paradoxical sleep deprivation and intermittent hypoxia by examining whether a combination of the two would induce anxiety-like alterations in behavior. The neurochemical effects of these manipulations were investigated by measuring cortical, striatal and hippocampal monoamine concentrations. Wistar Hannover rats were submitted to subchronic (3 days) intermittent hypoxia exposure (alternating cycles of 2 min room air-2 min 10% O2 from 0700-1900 h) and paradoxical sleep deprivation using the single platform method. Rats were randomly assigned to four different protocols: 1) control, 2) intermittent hypoxia during the light period (12 h/day), 3) paradoxical sleep deprivation (24 h/day), and 4) intermittent hypoxia combined with paradoxical sleep deprivation. Rats subjected to intermittent hypoxia showed no modification in the behavioral or neurochemical parameters assessed. Although paradoxical sleep deprivation did not produce alterations in anxiety-like behavior, the rats did increase exploratory activity in the elevated plus-maze. Moreover, a significant increase in striatal epinephrine and hippocampal homovanilic acid (HVA) concentrations was found in the paradoxical sleep deprivation groups, but not in the intermittent hypoxia/paradoxical sleep deprivation group. Of note, both paradoxical sleep deprivation and intermittent hypoxia/paradoxical sleep deprivation groups showed an increase in plasma corticosterone concentration. These results suggest that paradoxical sleep deprivation induces behavioral alterations, and these abnormalities may reflect altered neurotransmission in the brain. When paradoxical sleep deprivation was combined with intermittent oxygen depletion, the behavioral and biochemical parameters were comparable to those of control rats.

Methionine sulfoxide reductase A and a dietary supplement S-methyl-L-cysteine prevent Parkinson's-like symptoms

Parkinson's disease (PD), a common neurodegenerative disease, is caused by loss of dopaminergic neurons in the substantia nigra. Although the underlying cause of the neuronal loss is unknown, oxidative stress is thought to play a major role in the pathogenesis of PD. The amino acid methionine is readily oxidized to methionine sulfoxide, and its reduction is catalyzed by a family of enzymes called methionine sulfoxide reductases (MSRs). The reversible oxidation-reduction cycle of methionine involving MSRs has been postulated to act as a catalytic antioxidant system protecting cells from oxidative damage. Here, we show that one member of the MSR family, MSRA, inhibits development of the locomotor and circadian rhythm defects caused by ectopic expression of human alpha-synuclein in the Drosophila nervous system. Furthermore, we demonstrate that one way to enhance the MSRA antioxidant system is dietary supplementation with S-methyl-L-cysteine (SMLC), found abundantly in garlic, cabbage, and turnips. SMLC, a substrate in the catalytic antioxidant system mediated by MSRA, prevents the alpha-synuclein-induced abnormalities. Therefore, interventions focusing on the enzymatic reduction of oxidized methionine catalyzed by MSRA represent a new prevention and therapeutic approach for PD and potentially for other neurodegenerative diseases involving oxidative stress.

Cardiovascular morbidity in obstructive sleep apnea: oxidative stress, inflammation, and much more

Sleep-disordered breathing and obstructive sleep apnea (OSA) are highly prevalent disorders throughout the lifespan, which may affect up to 2-10% of the population, and have now been firmly associated with an increased risk for cardiovascular and neurobehavioral complications. Nevertheless, the overall pathophysiologic mechanisms mediating end-organ injury in OSA remain undefined, particularly due to the very frequent coexistence of other disease states, such as obesity, that clearly complicate the potential cause-effect relationships. Two major, and to some extent overlapping, mechanisms have been proposed to explain the morbid consequences of OSA, namely increased generation and propagation of reactive oxygen species and initiation and amplification of inflammatory processes. The evidence supporting the validity of these concepts as well as that detracting from such mechanisms will be critically reviewed in the context of clinical and laboratory-based approaches. In addition, some of the contradictory issues raised by such evaluation of the literature will be interpreted in the context of putative modifications of the individual responses to OSA, as determined by genetic variants among susceptibility-related genes, and also by potential environmental modulators of the phenotypic expression of any particular end-organ morbidity associated with OSA.

Selective loss of catecholaminergic wake active neurons in a murine sleep apnea model

The presence of refractory wake impairments in many individuals with severe sleep apnea led us to hypothesize that the hypoxia/reoxygenation events in sleep apnea permanently damage wake-active neurons. We now confirm that long-term exposure to hypoxia/reoxygenation in adult mice results in irreversible wake impairments. Functionality and injury were next assessed in major wake-active neural groups. Hypoxia/reoxygenation exposure for 8 weeks resulted in vacuolization in the perikarya and dendrites and markedly impaired c-fos activation response to enforced wakefulness in both noradrenergic locus ceruleus and dopaminergic ventral periaqueductal gray wake neurons. In contrast, cholinergic, histaminergic, orexinergic, and serotonergic wake neurons appeared unperturbed. Six month exposure to hypoxia/reoxygenation resulted in a 40% loss of catecholaminergic wake neurons. Having previously identified NADPH oxidase as a major contributor to wake impairments in hypoxia/reoxygenation, the role of NADPH oxidase in catecholaminergic vulnerability was next addressed. NADPH oxidase catalytic and cytosolic subunits were evident in catecholaminergic wake neurons, where hypoxia/reoxygenation resulted in translocation of p67(phox) to mitochondria, endoplasmic reticulum, and membranes. Treatment with a NADPH oxidase inhibitor, apocynin, throughout hypoxia/reoxygenation exposures conferred protection of catecholaminergic neurons. Collectively, these data show that select wake neurons, specifically the two catecholaminergic groups, can be rendered persistently impaired after long-term exposure to hypoxia/reoxygenation, modeling sleep apnea; wake impairments are irreversible; catecholaminergic neurons are lost; and neuronal NADPH oxidase contributes to this injury. It is anticipated that severe obstructive sleep apnea in humans destroys catecholaminergic wake neurons.

ROS signaling in systemic and cellular responses to chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) is a common and life-threatening condition that occurs in many different diseases, including sleep-disordered breathing manifested as recurrent apneas. Reactive oxygen species (ROS) have been identified as one of the causative factors in a variety of morbidities. The purpose of this article is to present a brief overview of recent studies implicating a critical role of ROS in evoking phenotypic adverse effects in experimental models of CIH and in patients with recurrent apneas. In experimental models, CIH activates ROS signaling that contributes to several systemic and cellular responses that include (a) altered carotid body function, the primary chemoreceptor for sensing changes in arterial blood O2; (b) elevated blood pressures; (c) enhanced release of transmitters and neurotrophic factors; (d) altered sleep and cognitive behaviors; and (e) activation of second-messenger pathways and transcriptional factors. Considerable evidence indicates elevated ROS levels in patients experiencing CIH as a consequence of recurrent apneas. Antioxidants not only prevent many of the CIH-evoked physiologic and cellular responses in experimental settings, but more important, they also offer protection against certain phenotypic adverse effects in patients with recurrent apneas, suggesting their potential therapeutic value in alleviating certain morbidities associated with recurrent apneas.

Manganese superoxide dismutase protects mouse cortical neurons from chronic intermittent hypoxia-mediated oxidative damage

Obstructive sleep apnea (OSA) syndrome has been recognized as a highly prevalent public health problem and is associated with major neurobehavioral morbidity. Chronic intermittent hypoxia (CIH), a major pathological component of OSA, increases oxidative damage to the brain cortex and decreases neurocognitive function in rodent models resembling human OSA. We employed in vitro and in vivo approaches to identify the specific phases and subcellular compartments in which enhanced reactive oxygen species (ROS) are generated during CIH. In addition, we utilized the cell culture and animal models to analyze the consequences of enhanced production of ROS on cortical neuronal cell damage and neurocognitive dysfunction. In a primary cortical neuron culture system, we demonstrated that the transition phase from hypoxia to normoxia (NOX) during CIH generates more ROS than the transition phase from NOX to hypoxia or hypoxia alone, all of which generate more ROS than NOX. Using selective inhibitors of the major pathways underlying ROS generation in the cell membrane, cytosol, and mitochondria, we showed that the mitochondria are the predominant source of enhanced ROS generation during CIH in mouse cortical neuronal cells. Furthermore, in both cell culture and transgenic mice, we demonstrated that overexpression of MnSOD-decreased CIH-mediated cortical neuronal apoptosis, and reduced spatial learning deficits measured with the Morris water maze assay. Together, the data from the in vitro and in vivo experiments indicate that CIH-mediated mitochondrial oxidative stress may play a major role in the neuronal cell loss and neurocognitive dysfunction in OSA. Thus, therapeutic strategies aiming at reducing ROS generation from mitochondria may improve the neurobehavioral morbidity in OSA.

Relationship between hours of CPAP use and achieving normal levels of sleepiness and daily functioning

STUDY OBJECTIVES

Evidence suggests that, to maintain treatment effects, nasal continuous positive airway pressure (CPAP) therapy for obstructive sleep apnea (OSA) needs to be used every night. What remains unknown is the nightly duration of use required to normalize functioning. This study, employing probit analyses and piecewise regression to estimate dose-response functions, estimated likelihoods of return to normal levels of sleepiness and daily functioning relative to nightly duration of CPAP.

DESIGN

Multicenter, quasi-experimental study.

SETTING

Seven sleep centers in the United States and Canada.

PARTICIPANTS

Patients with severe OSA (total cohort n = 149; the numbers of included participants from 85 - 120, depending on outcome analyzed.)

INTERVENTIONS

CPAP.

MEASUREMENTS AND RESULTS

Before treatment and again after 3 months of therapy, participants completed a day of testing that included measures of objective and subjective daytime sleepiness and functional status. There were significant differences in mean nightly CPAP duration between treatment responders and nonresponders across outcomes. Thresholds above which further improvements were less likely relative to nightly duration of CPAP were identified for Epworth Sleepiness Scale score (4 hours), Multiple Sleep Latency Test (6 hours), and Functional Outcomes associated with Sleepiness Questionnaire (7.5 hours). A linear dose-response relationship (P < 0.01) between increased use and achieving normal levels was shown for objective and subjective daytime sleepiness, but only up to 7 hours use for functional status.

CONCLUSIONS

Our analyses suggest that a greater percentage of patients will achieve normal functioning with longer nightly CPAP durations, but what constitutes adequate use varies between different outcomes.

Persistent sleepiness in CPAP treated obstructive sleep apnea patients: evaluation and treatment

Nasal continuous positive airway pressure (CPAP) is an effective treatment for most patients with obstructive sleep apnea syndrome (OSAS), improving sleepiness, cognitive function and mood. A number of patients, however, complain about persistent sleepiness after CPAP. In these cases another clinical history should be carried out to confirm the diagnosis of OSAS, to check CPAP compliance and to exclude associated conditions such as poor sleep hygiene, depression, narcolepsy or idiopathic hypersomnia. If necessary, a full polysomnography (PSG) followed by a multiple sleep latency test or even a full PSG with CPAP titration should be performed. Experimental data in animals suggest that long-term intermittent hypoxia related to the apneic events could deteriorate the brain structures that regulate alertness. This impairment, if present in humans, could be another reason for residual sleepiness after CPAP. Modafinil has been shown to reduce subjective sleepiness after CPAP in OSAS patients. Further studies are warranted to clarify the way in which CPAP modifies sleepiness.

Impaired spatial working memory and altered choline acetyltransferase (CHAT) immunoreactivity and nicotinic receptor binding in rats exposed to intermittent hypoxia during sleep

Exposure to intermittent hypoxia (IH), such as occurs in sleep-disordered breathing (SDB), is associated with cognitive impairment, neurodegeneration, oxidative stress, and inflammatory responses within rodent brain regions such as the basal forebrain. In this region, damage to cholinergic neurons correlates with working memory deficits in a number of neurodegenerative disorders, suggesting that degeneration of cholinergic systems may also contribute to the working memory impairments observed after IH exposures. We therefore examined basal forebrain choline acetyltransferase (CHAT) immunohistochemistry, nicotinic receptor binding in the prefrontal cortex (PFC), and working memory, in male rats tested on a delayed matching to place (DMP) task in the water maze following exposure to either room air (RA) or intermittent hypoxia (IH; alternating 90s epochs of 21% and 10% O(2) during sleep). IH-treated animals displayed impaired working memory with respect to controls, along with significant reductions in CHAT-stained neurons in the medial septal nucleus, in both the vertical and horizontal limbs of the diagonal band, and the substantia inominata after 14 days of IH exposure. In addition, increases in nicotinic binding and receptor affinity in the PFC were observed after 14 days of IH exposure. Thus, a loss of cholinergic neuronal phenotype in the basal forebrain may contribute to the cognitive impairments associated with CIH exposure. However, compensatory mechanisms may also be activated in other brain regions, and may provide potential therapeutic targets for the cognitive impairments associated with SDB.

Consequences of subchronic and chronic exposure to intermittent hypoxia and sleep deprivation on cardiovascular risk factors in rats

Since studies suggest that both hypoxia and sleep fragmentation are related to cardiovascular alterations induced by obstructive sleep apnea, the present study was designed to evaluate the effects of hypoxia, sleep deprivation, and their combination on biochemical blood parameters in rats. In subchronic experiments (4 days), rats were exposed to intermittent hypoxia (IH) during the light period (2min room air-2min 10% O(2) for 12h/day) and/or paradoxical sleep deprivation (PSD, 24h/day). Consequences of chronic intermittent hypoxia (CIH) exposure were examined after 21 consecutive days of hypoxia protocol from 10:00 to 16:00 followed by a sleep restriction (SR) period of 18h (16:00-10:00). Rats were randomly assigned to seven treatment groups: (1) control (2) IH (3) PSD (4) IH-PSD (5) SR (6) CIH and (7) CIH-SR. PSD reduced triglycerides and very low-density lipoprotein (VLDL) cholesterol concentrations and increased total cholesterol and high-density lipoprotein (HDL) cholesterol. IH did not alter any of these parameters. The combination of IH-PSD did not modify the values of total cholesterol and HDL compared to control group. In the chronic experiment, the animals exposed to CIH displayed a reduction of Vitamin B(6) and an increase of triglycerides and VLDL. Our findings show a duration-dependent effect of hypoxia on triglycerides. Rats in the SR and CIH-SR groups showed a diminished concentration of triglycerides and VLDL. SR rats showed a reduction in the concentration of homocysteine but the animals in the CIH-SR treatment condition did not display any alterations in this parameter. In this latter group, an augmentation of cysteine concentration was observed. These results suggest that sleep deprivation and hypoxia modify biochemical blood parameters in distinct ways.

[Effects of nasal positive airway pressure treatment on oxidative stress in patients with sleep apnea-hypopnea syndrome]

OBJECTIVE

To analyze whether nasal continuous positive airway pressure (CPAP) reduces oxidative stress in patients with sleep apnea-hypopnea syndrome (SAHS).

PATIENTS AND METHODS

Thirty-six patients with SAHS requiring nasal CPAP treatment and 10 controls in whom SAHS was ruled out were enrolled. Oxidative stress was evaluated by measuring plasma malondialdehyde (MDA) concentrations to assess lipid peroxidation at the beginning of the study and then again after a mean (SD) of 2.9 (0.6) months of nasal CPAP. Plasma MDA concentrations were determined by measuring thiobarbituric acid reactive substances. We controlled for the following factors known to influence oxidative stress: age, sex, use of vitamin supplements, smoking habit, body mass index (kg/m2), ischemic cardiopathy, hypertension, diabetes, and hypercholesterolemia.

RESULTS

The mean age of patients with SAHS was 51.4 (9.9) years and the mean body mass index was 32.9 (5.3) kg/m2. Nasal CPAP was titrated to a mean pressure of 8.9 (3.4) cm H2O. The mean score on the Epworth sleepiness scale was 10.2 (4.3) before treatment and 4.2 (2.8) after treatment (P<.001). The apnea-hypopnea index decreased from 43.7 (22.6) before treatment to 4 (3.5) after treatment (P<.001). Mean MDA concentrations in patients with SAHS were 2.0 (1.1) micromol/mL before treatment and decreased significantly to 1.6 (.07) micromol/mL after treatment, whereas MDA concentrations remained unchanged in control subjects.

CONCLUSIONS

Nasal CPAP treatment significantly reduced oxidative stress in patients with SAHS in our study.