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

Effects of acute exposure to hypoxia on sleep structure in healthy adults: A systematic review

The sleep quality of lowlanders in hypoxic environments has become increasingly important with an increase in highland and alpine activities. This study aimed to identify the effects of acute exposure to hypoxia on the sleep structure of lowlanders and to analyze the changes in sleep indicators at varying levels of hypoxia. This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Twenty-three studies were screened and included in the quantitative analysis. The results showed that acute exposure to hypoxia reduced sleep quality in lowlanders. Post-sleep arousal events and the percentage of N1 were significantly increased, whereas total sleep time, sleep efficiency, and the percentage of N3 and rapid eye movement sleep were significantly decreased in hypoxic environments. Acute exposure to hypoxia had the greatest negative impact on wakefulness after sleep onset (WASO). In addition, a larger decrease in sleep efficiency and higher increase in the percentages of N1 and WASO were observed when lowlanders were exposed to higher levels of hypoxia. This study clarifies the quantitative effects of acute hypoxic exposure on sleep in lowlanders based on original studies and explains the sleep disorders faced by lowlanders in hypoxic environments.

Therapeutic acute intermittent hypoxia: A translational roadmap for spinal cord injury and neuromuscular disease

We review progress towards greater mechanistic understanding and clinical translation of a strategy to improve respiratory and non-respiratory motor function in people with neuromuscular disorders, therapeutic acute intermittent hypoxia (tAIH). In 2016 and 2020, workshops to create and update a "road map to clinical translation" were held to help guide future research and development of tAIH to restore movement in people living with chronic, incomplete spinal cord injuries. After briefly discussing the pioneering, non-targeted basic research inspiring this novel therapeutic approach, we then summarize workshop recommendations, emphasizing critical knowledge gaps, priorities for future research effort, and steps needed to accelerate progress as we evaluate the potential of tAIH for routine clinical use. Highlighted areas include: 1) greater mechanistic understanding, particularly in non-respiratory motor systems; 2) optimization of tAIH protocols to maximize benefits; 3) identification of combinatorial treatments that amplify plasticity or remove plasticity constraints, including task-specific training; 4) identification of biomarkers for individuals most/least likely to benefit from tAIH; 5) assessment of long-term tAIH safety; and 6) development of a simple, safe and effective device to administer tAIH in clinical and home settings. Finally, we update ongoing clinical trials and recent investigations of tAIH in SCI and other clinical disorders that compromise motor function, including ALS, multiple sclerosis, and stroke.

MAXIMUM EFFORT TRAINING PERFORMED IN HYPOXIA ALTERS THE MOOD PROFILE

ABSTRACT Introduction: Physical exercise at high altitude has become constant. However, the risks associated with this type of exercise represent a major concern, considering the influence of important stressors such as hypoxia and physical exercise on psychobiological and physiological responses. Objective: Analyze the mood state and behavior of physiological variables of volunteers subjected to a progressive loading protocol until they reached maximum volitional exhaustion, both at sea level and at a simulated altitude of 4500 meters. Method: For both conditions studied, the volunteers responded to two instruments that assess mood responses: The Brunel Mood Scale and the Visual Analogue Mood Scale. They also underwent blood sampling to measure blood lactate levels and to evaluate oxygen-hemoglobin saturation. These procedures were performed before, immediately after, and 30 and 60 minutes after the end of the protocol. Results: Hypoxia triggered negative effects on mood responses, especially when compared to sea level conditions. An increase in fatigue level (p=0.02) and mental confusion (p=0.04) was observed immediately after the exercise session, and reduction of vigor (p=0.03) was noted at 30 minutes, accompanied by a reduction in oxygen-hemoglobin saturation immediately after the session and at 30 minutes. There was also an increase in blood lactate levels immediately after the session (p=0.006). Conclusion: The particularities of the hypoxic environment associated with maximum exercise are able to cause a deterioration of mood and physiological responses, which can negatively modulate physical performance. This is a cross-sectional clinical study.

Why Is Working Memory Performance Unstable? A Review of 21 Factors

In this paper, we systematically reviewed twenty-one factors that have been shown to either vary with or influence performance on working memory (WM) tasks. Specifically, we review previous work on the influence of intelligence, gender, age, personality, mental illnesses/medical conditions, dieting, craving, stress/anxiety, emotion/motivation, stereotype threat, temperature, mindfulness training, practice, bilingualism, musical training, altitude/hypoxia, sleep, exercise, diet, psychoactive substances, and brain stimulation on WM performance. In addition to a review of the literature, we suggest several frameworks for classifying these factors, identify shared mechanisms between several variables, and suggest areas requiring further investigation. This review critically examines the breadth of research investigating WM while synthesizing the results across related subfields in psychology.

The effect of nasal polyposis related nasal obstruction on cognitive functions

Chronic rhinosinusitis with nasal polyposis is a chronic inflammatory disease of the respiratory mucosa of the nasal cavity and paranasal sinuses. The aim of this study was investigate the effect of nasal obstruction related to chronic rhinosinusitis with nasal polyposis on cognitive functions. Patients with chronic rhinosinusitis with nasal polyposis causing bilateral total or near total nasal obstruction were enrolled in the study. Symptoms of nasal congestion, loss of smell, postnasal drip, headaches, snoring, concentration difficulties and blunted affect were evaluated by Visual Analog Scale. Brief symptom inventory test, Stroop test, visual aural digit span, serial digit learning test and P300 test were used to evaluate cognitive functions. Three months after treatment, the tests done before surgery were repeated and the results were compared. A total of 30 patients were included in the study. On the Visual Analog Scale, all symptoms showed significant postoperative improvement in all patients (p < 0.001 for all symptoms). Preoperative nasal congestion accompanied with impaired concentration were detected in 27 patients (90%), and these symptoms recovered in all these patients after treatment (p = 0.035) (correlation coefficient 0.4). Only 22 patients completed the neuropsychological tests. The mean preoperative Stroop test (23.16 ± 5.30), visual aural digit span test (24.68 ± 3.52), and serial digit learning test (16.18 ± 5.35) scores were showed significant improvement compared with mean postoperative Stroop test (21.12 ± 5.69), visual aural digit span test (26.45 ± 2.98), and serial digit learning test (19.31 ± 4.47) scores (p = 0.047, p = 0.022, p = 0.005 respectively). The postoperative P300 latency values improved in 19 (63%) patients. The preoperative and postoperative latency values for P300 showed a significant difference (p = 0.029), whereas the preoperative and postoperative amplitude values for P300 did not differ (p = 0.096). In conclusion, the results of this study indicate that chronic rhinosinusitis with nasal polyposis (CRSwNP) has negative effects on cognitive functions, such as the ability to focus and maintain concentration. These cognitive functions improve after the patients undergo endoscopic sinus surgery to treat their CRSwNP.

Temporal trajectories of novel object recognition performance in mice exposed to intermittent hypoxia

Intermittent hypoxia is one of the major perturbations of sleep-disordered breathing and has been causally implicated in neurocognitive deficits. However, the reversibility of such deficits is unclear.

Male C57BL/6J mice were exposed to either intermittent hypoxia or room air for 3–240 days, and then half were randomly selected and allowed to recover in normoxic conditions for the same duration of the previous exposure. A novel object recognition (NOR) test was performed.

NOR performance was stable over time in room air. Intermittent hypoxia induced significant reductions in recognition index that progressed over the first 45 days and stabilised thereafter. Normoxic recovery of recognition index was essentially complete and indistinguishable from room air in mice exposed to shorter intermittent hypoxia times (<90 days). However, significant residual deficits emerged after normoxic recovery following prolonged intermittent hypoxia exposures (p<0.01). In addition, gradual attenuation of the magnitude of recovery in recognition index occurred with increasingly longer intermittent hypoxia exposures (MANOVA p<0.0001).

Intermittent hypoxia during the resting period reduces NOR performance in a time-dependent fashion. Reversal of NOR performance deficits is unlikely after prolonged intermittent hypoxia duration. These findings suggest that early recognition of sleep apnoea and effective treatment are critical for restoration of the adverse cognitive effects of the disease.

Clostridium difficile contamination of health care workers' hands and its potential contribution to the spread of infection: Review of the literature

BACKGROUND

Clostridium difficile infection (CDI) can be transmitted from patient to patient by the hands of health care workers (HCWs); however, the relative importance of this route in the spread of C difficile in the hospital is currently unknown. Our aim was to review studies examining HCWs' hand carriage and its potential role in CDI transmission.

METHODS

First, English-speaking references addressing HCWs' hand sampling obtained from the PubMed database were reviewed. Second, C difficile outbreaks definitely or probably implicating HCWs were retrieved from the Outbreak Database Web site (www.outbreak-database.com). Finally, cases of C difficile occurring in HCWs after contact with an infected patient were retrieved from PubMed.

RESULTS

A total of 11 studies dealing with HCWs' hand carriage were selected and reviewed. Between 0% and 59% of HCWs' hands were found contaminated with C difficile after caring for a patient with CDI. There were several differences between studies regarding site of hands sampling, timing after contact, and bacteriologic methods. Only 2 C difficile outbreaks implicating HCWs and 6 series of cases of transmission from patients to HCWs have been reported.

CONCLUSIONS

This review shows that HCWs' hands could play an important role in the transmission of C difficile. Hand hygiene and reduction of environmental contamination are essential to control C difficile transmission.

Quantitative electroencephalogram measures in adult obstructive sleep apnea - Potential biomarkers of neurobehavioural functioning

Obstructive sleep apnea (OSA) results in significantly impaired cognitive functioning and increased daytime sleepiness in some patients leading to increased risk of motor vehicle and workplace accidents and reduced productivity. Clinicians often face difficulty in identifying which patients are at risk of neurobehavioural dysfunction due to wide inter-individual variability, and disparity between symptoms and conventional metrics of disease severity such as the apnea hypopnea index. Quantitative electroencephalogram (EEG) measures are determinants of awake neurobehavioural function in healthy subjects. However, the potential value of quantitative EEG (qEEG) measurements as biomarkers of neurobehavioural function in patients with OSA has not been examined. This review summarises the existing literature examining qEEG in OSA patients including changes in brain activity during wake and sleep states, in relation to daytime sleepiness, cognitive impairment and OSA treatment. It will speculate on the mechanisms which may underlie changes in EEG activity and discuss the potential utility of qEEG as a clinically useful predictor of neurobehavioural function in OSA.

Intermittent Hypoxia Does not Elicit Memory Impairment in Spinal Cord Injury Patients

There is a critical need for new therapeutic strategies to restore motor function in patients with spinal cord injuries (SCIs), without unwanted effects. Intermittent hypoxia (IH) induces plasticity in spared synaptic pathways to motor neurons below the level of injury, which can be harnessed to elicit motor recovery in incomplete SCI patients. However, there is conflicting evidence regarding the effects of IH on memory function. The aim of this study was to assess episodic verbal and visual memory function with the Complutense verbal learning test (TAVEC) and the Rey-Osterrieth Complex Figure Test (ROCF), respectively, before and after a 4-week protocol of repetitive IH combined with body weight-supported treadmill training (BWSTT) in incomplete ASIA C and D SCI subjects. Subjects received either IH (cycling 9%/21% FiO2 every 1.5 min, 15 cycles per day) or continued normoxia (Nx, 21% FiO2) combined with 45 min of BWSTT for 5 consecutive days, followed by 3 times per week IH and BWSTT for 3 additional weeks. ROCF Z scores between IH plus BWSTT and Nx plus BWSTT were not significantly different (p = .43). Compared with baseline, IH and BWSTT group showed a significantly greater (p < .05) verbal memory performance for immediate, short-term, and long-term recall; however, it was not different from Nx plus BWSTT group in all verbal memory components (p > .05). Our results suggest that a 4-week protocol of moderate IH does not elicit visual or verbal memory impairment. Thus, repetitive IH may be a safe therapeutic approach to incomplete spinal cord injury patients, without deleterious cognitive effects.

Intermittent hypoxia: a low-risk research tool with therapeutic value in humans

Intermittent hypoxia has generally been perceived as a high-risk stimulus, particularly in the field of sleep medicine, because it is thought to initiate detrimental cardiovascular, respiratory, cognitive, and metabolic outcomes. In contrast, the link between intermittent hypoxia and beneficial outcomes has received less attention, perhaps because it is not universally understood that outcome measures following exposure to intermittent hypoxia may be linked to the administered dose. The present review is designed to emphasize the less recognized beneficial outcomes associated with intermittent hypoxia. The review will consider the role intermittent hypoxia has in cardiovascular and autonomic adaptations, respiratory motor plasticity, and cognitive function. Each section will highlight the literature that contributed to the belief that intermittent hypoxia leads primarily to detrimental outcomes. The second segment of each section will consider the possible risks associated with experimentally rather than naturally induced intermittent hypoxia. Finally, the body of literature indicating that intermittent hypoxia initiates primarily beneficial outcomes will be considered. The overarching theme of the review is that the use of intermittent hypoxia in research investigations, coupled with reasonable safeguards, should be encouraged because of the potential benefits linked to the administration of a variety of low-risk intermittent hypoxia protocols.

Sleep-disordered breathing, hypoxia, and risk of mild cognitive impairment and dementia in older women

CONTEXT

Sleep-disordered breathing (characterized by recurrent arousals from sleep and intermittent hypoxemia) is common among older adults. Cross-sectional studies have linked sleep-disordered breathing to poor cognition; however, it remains unclear whether sleep-disordered breathing precedes cognitive impairment in older adults.

OBJECTIVES

To determine the prospective relationship between sleep-disordered breathing and cognitive impairment and to investigate potential mechanisms of this association.

DESIGN, SETTING, AND PARTICIPANTS

Prospective sleep and cognition study of 298 women without dementia (mean [SD] age: 82.3 [3.2] years) who had overnight polysomnography measured between January 2002 and April 2004 in a substudy of the Study of Osteoporotic Fractures. Sleep-disordered breathing was defined as an apnea-hypopnea index of 15 or more events per hour of sleep. Multivariate logistic regression was used to determine the independent association of sleep-disordered breathing with risk of mild cognitive impairment or dementia, adjusting for age, race, body mass index, education level, smoking status, presence of diabetes, presence of hypertension, medication use (antidepressants, benzodiazepines, or nonbenzodiazepine anxiolytics), and baseline cognitive scores. Measures of hypoxia, sleep fragmentation, and sleep duration were investigated as underlying mechanisms for this relationship.

MAIN OUTCOME MEASURES

Adjudicated cognitive status (normal, dementia, or mild cognitive impairment) based on data collected between November 2006 and September 2008.

RESULTS

Compared with the 193 women without sleep-disordered breathing, the 105 women (35.2%) with sleep-disordered breathing were more likely to develop mild cognitive impairment or dementia (31.1% [n = 60] vs 44.8% [n = 47]; adjusted odds ratio [AOR], 1.85; 95% confidence interval [CI], 1.11-3.08). Elevated oxygen desaturation index (≥15 events/hour) and high percentage of sleep time (>7%) in apnea or hypopnea (both measures of disordered breathing) were associated with risk of developing mild cognitive impairment or dementia (AOR, 1.71 [95% CI, 1.04-2.83] and AOR, 2.04 [95% CI, 1.10-3.78], respectively). Measures of sleep fragmentation (arousal index and wake after sleep onset) or sleep duration (total sleep time) were not associated with risk of cognitive impairment.

CONCLUSION

Among older women, those with sleep-disordered breathing compared with those without sleep-disordered breathing had an increased risk of developing cognitive impairment.

Chronic intermittent hypoxia in humans during 28 nights results in blood pressure elevation and increased muscle sympathetic nerve activity

Chronic intermittent hypoxia (CIH) is thought to be responsible for the cardiovascular disease associated with obstructive sleep apnea (OSA). Increased sympathetic activation, altered vascular function, and inflammation are all putative mechanisms. We recently reported (Tamisier R, Gilmartin GS, Launois SH, Pepin JL, Nespoulet H, Thomas RJ, Levy P, Weiss JW. J Appl Physiol 107: 17-24, 2009) a new model of CIH in healthy humans that is associated with both increases in blood pressure and augmented peripheral chemosensitivity. We tested the hypothesis that exposure to CIH would also result in augmented muscle sympathetic nerve activity (MSNA) and altered vascular reactivity contributing to blood pressure elevation. We therefore exposed healthy subjects between the ages of 20 and 34 yr (n = 7) to 9 h of nocturnal intermittent hypoxia for 28 consecutive nights. Cardiovascular and hemodynamic variables were recorded at three time points; MSNA was collected before and after exposure. Diastolic blood pressure (71 +/- 1.3 vs. 74 +/- 1.7 mmHg, P < 0.01), MSNA [9.94 +/- 2.0 to 14.63 +/- 1.5 bursts/min (P < 0.05); 16.89 +/- 3.2 to 26.97 +/- 3.3 bursts/100 heartbeats (hb) (P = 0.01)], and forearm vascular resistance (FVR) (35.3 +/- 5.8 vs. 55.3 +/- 6.5 mmHg x ml(-1) x min x 100 g tissue, P = 0.01) all increased significantly after 4 wk of exposure. Forearm blood flow response following ischemia of 15 min (reactive hyperemia) fell below baseline values after 4 wk, following an initial increase after 2 wk of exposure. From these results we conclude that the increased blood pressure following prolonged exposure to CIH in healthy humans is associated with sympathetic activation and augmented FVR.

One week of exposure to intermittent hypoxia impairs attentional set-shifting in rats

Intermittent hypoxia (IH), a characteristic of sleep apnea, was modeled in Fischer Brown Norway rats (10h/day for 7 days) followed by cognitive testing in an attentional set-shifting task. The ability to shift attention from one sensory modality (e.g., odor) to another (e.g., digging medium) was impaired, a finding that could not be attributed to deficits in attention, discrimination, learning, or motor performance. Instead, the deficit is likely to reflect impaired allocation of attentional resources of the working memory system.