Obstructive sleep apnoea (OSA) is a condition that is defined by episodes of upper airway obstruction during sleep with continued respiratory effort, which leads to a cessation in airflow, a decrease in blood oxygen saturations and transient arousal from sleep to lighter sleep or wakefulness. Sufferers of OSA are often unaware that these apnoeic episodes are occurring; it is often reported by others or due to the negative effects of sleep disturbance on the person, such as excessive daytime sleepiness. Causes of OSA include anything that prevent the airway from remaining potent during sleep such as old age, brain injury, decreased muscle tone, abnormal structure, and obesity.
Diagnosis of OSA is made by performing overnight sleep studies either in a clinic or at home. Testing in clinics often combines the results of electroencephalography (EEG), electromyography (EMG), chest and abdomen movements, airflow, pulse oximetry and electrocardiography (ECG). Sometimes sound and video recording equipment is also used. The severity of OSA is measured using the apnoea-hypopnoea index (AHI), which measures the number of apnoea-hypopnoea events that occur in one hour of sleep. Apnoea is a complete blockage of air intake, hypopnoea is a partial blockage of air intake. Each event must last for at least 10 seconds and be associated with oxygen desaturation. Severity of OSA can then be separated into mild (5-14 episodes per hour), moderate (15-30 episodes per hour) and severe (>30 episodes per hour).
Review of current literature
Reports have shown that the prevalence of OSA is approximately 4% in adult males and 2% in adult females [1]. The effects of OSA are detrimental, impacting on cognition, work performance, daytime sleepiness, relationships and mood. Studies have shown that there are significant complications associated with OSA, particularly regarding cardiovascular health, with an increased risk of stroke [2, 3] and developing hypertension [4, 5]. As well as increased risk of developing certain medical conditions, Pagel found that there is a 6-15 fold increased risk of being involved in a road traffic accident in untreated OSA sufferers, due to their excessive daytime sleepiness and poor concentration [6].
As discussed, the negative effect of OSA on physiological systems such as an increased risk of stroke and hypertension have been studied in depth and are well-known among healthcare professionals. Studies have explored the link between primary insomnia and the development of depression, with Riemann and Voderholzer concluding that insomnia symptoms are predictive for an increased risk of depression [7]. Other studies have also shown that people with insomnia have at least twice the risk of developing depression compared to healthy controls [8, 9]. It has also been shown that people with both insomnia and depression are more resistant to standard treatment for depression, which could be due to lack of quality sleep perpetuating the depression [10]. The effect that poor sleep in OSA has on mental health however, is less reported. The proposed study will investigate the impact of OSA on mood disorders such as depression and anxiety. It is well-known by both healthcare professionals and the general public, the impact that poor sleep can have on your life, but how much of an impact do conditions such as OSA have on our mental health? One study acknowledged that psychological symptoms such as depression and anxiety are commonly reported in people with OSA but wanted to investigate whether the prevalence was different to the
It is important to note the similarity between symptoms of depression and OSA. The ICD-10 criteria for depression includes two out of three core symptoms: anergia (lack of energy), low mood for two weeks, and anhedonia (lack of interest in previously enjoyed activities) as well as combination of other symptoms including loss of self-esteem, suicidal thoughts, self-harm, poor concentration, sleep disturbance, excessive guild, and changes in appetite. Many of these symptoms overlap with those of OSA: fatigue, anergia, daytime sleepiness, poor concentration. This can make diagnosis challenging but could also mean that many people are being diagnosed with depression, when the symptoms could be due to the presence of undiagnosed OSA. As mentioned previously with regards to insomnia, perhaps problems with sleep such as OSA could be responsible for treatment failure in depression. When looking at the prevalence of depression, it is higher in populations of people diagnosed with OSA which lends two questions: which came first, depression or OSA, and is there a relationship between the two?
Proposed study
The proposed study has two overarching objectives: (1) to explore whether the prevalence of affective disorders is increased in adults with OSAS when compared with healthy controls matched for age and IQ, and (2) to determine whether patients undergoing CPAP treatment experience acute positive changes in mood (as compared to patients on a CPAP waiting list).
Participant recruitment
Fifty adults diagnosed with OSAS (30-60 years old) will be recruited through the out-patient sleep apnoea clinic at York Teaching Hospital. Diagnoses will be confirmed with a respiratory sleep study with electroencephalography (EEG). Participants will be screened using the PHQ-9 mood questionnaire, allowing us to quickly rate mood and assess severity of depression if present.
Project details
There will be two cohorts of participants; those who are about to start CPAP treatment, and matched participants who are on a waiting list. They will complete three computerised tasks to assess declarative and procedural memory consolidation. Attention will be measured using the Attention Networking Test (ANT) and the Psychomotor Vigilance Test (PVT).
Attention Network Test (ANT)
The ANT focuses on the model of attention devised by Posner that separates attention into alerting, orienting and executive attention. The test is a measure of attention and requires the subject to respond as rapidly and as accurately as possible. The test used in this study lasts approximately 15 minutes with three 5 minute breaks. The subject responds to the stimulus by pressing either the right mouse key with their right index finger, or the left mouse key with their left index finger, depending on the direction of the central arrow. The test has six possible stimuli and four different cues as shown in figure 1. The outcomes of the task are mean RT for each of the four cues and mean RT for the three different stimuli possibilities.
Figure 1 Examples of the cues and stimuli that participants are presented with a) the four different cue conditions that appear before stimuli b) the six different stimuli
Psychomotor Vigilance Test (PVT)
Sustained attention (vigilant attention) is the ability to maintain concentration and produce consistent results on a specific task over time. Neuroimaging studies using positron emission tomography (PET) scanning have found that the areas of the brain involved in sustained attention are the prefrontal and superior parietal cortices in the right hemisphere (30, 31). Currently the most common way of measuring sustained attention is the Psychomotor Vigilance Test (PVT) (32) and in recent years studies have been using the PVT to measure how sleep deprivation affects sustained attention. The task usually lasts for 10 minutes and measures a person’s response time (RT) to a stimulus that appears randomly 2-10 seconds after the previous stimulus. The subject responds to each stimulus by pressing a button with their chosen index finger. The outcomes of the task are the response times (RTs) to the stimulus, how many lapses (RT > 500ms) and how many false starts a person makes. Dorrian et al. found that a 10 minute PVT provides data that is reliable and shows intra-class correlations (33). Balkin et al. found that the PVT was highly sensitive to sleep restriction with a sensitivity index of 0.954 (effect size (0.208) divided by confidence interval size (0.218)), and was also not subject to learning which meant the test could be repeated multiple times (34, 35). It is for these reasons that the PVT was chosen for this study.
Half of participants will have an overnight sleep EEG and oximetry. Remaining participants will sleep at home with oximetry recording equipment but not EEG. Those beginning CPAP therapy will start. They will then all be retested again the following morning. There is potential for follow up to review any long terms changes in mood and cognition in those that have remained on CPAP compared to those still on the waiting list.
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