Rachel Forman, MD
The importance of sleep is becoming increasingly evident as it pertains to stroke. The article “Sleep and Stroke” in the June issue of Stroke by Drs. Khot and Morgenstern highlights the importance of post-stroke sleep disturbance and sleep disordered breathing as a vascular risk factor.
Over 50% of stroke patients experience sleep disorders; however, as little as 6% undergo any formal sleep testing (with only 3% in the 3-month post-stroke period). This is likely because of the lack of provider awareness. This article reviews types of sleep-disordered breathing (SDB): central sleep apnea (CSA) and obstructive sleep apnea (OSA). Central apneas are typically seen in heart failure and opioid use and occur in stroke patients due to distinct brainstem lesions, although this is rare. More commonly, patients have OSA, and this appears to be more significant in post-stroke patients.
When a patient undergoes a sleep study, they are given an apnea-hypopnea index (AHI), which is the number of respiratory events per hour of sleep. Based on the number, they are classified as having mild (5-14 per hour), moderate (15-29 per hour), or severe (>30 per hour) obstructive sleep apnea. In a meta-analysis of SDB after stroke or TIA, 72% of patients had an AHI of at least 5. The reason for such high rates is not entirely clear, but it is thought to be related to positional sleep apnea, stroke-related upper airway tone changes, and untreated OSA preceding the stroke.
OSA is a known independent stroke risk factor. In one prospective study, an AHI >20 per hour was associated with an increased 4-year stroke risk (p=0.02). This article goes on to list other significant studies showing this correlation. OSA can also have an effect on other stroke risk factors (i.e., hypertension) with the presumed mechanism that apnea periods will cause high levels of sympathetic activity and blood pressure surges.
The gold standard treatment for OSA is CPAP; however, not all patients are compliant for a variety of reasons. Patients in the peri-stroke period may have their own set of barriers. Another study mentioned refers to patients having a 3-fold increased risk of nonfatal cardiovascular events (including stroke) in those who were not able to tolerate CPAP. Secondary prevention with CPAP trials has been limited with low sample sizes or poor CPAP usage. For example, in the SAVE (Sleep Apnea Cardiovascular Endpoints) study, the patients did not adhere to the study’s criteria of >4 hours per night.
As far as functional recovery following stroke in patients with OSA, the benefit from CPAP is unknown. Some observational studies have found no difference, while others have shown improvement in depressive symptoms, sleepiness, and motor recovery. A pooled analysis of 5 studies with~400 stroke patients with OSA showed greater short-term neurological improvement with CPAP than without.
There are no randomized clinical trials of CPAP after stroke; however, the upcoming phase 3 Sleep for SMART (Stroke Management and Recovery Trial) will evaluate the treatment of OSA with CPAP on secondary stroke prevention and recovery within the NIH StrokeNet.
This article ends with highlighting that sleep disturbances in stroke patients extend beyond SDB and include sleep-wake cycle disorders with half of stroke survivors reporting insomnia. Particularly, they mention how sleep disturbances may account for some of the increased stroke risk in patients who live in the inner city as they get reduced sleep from loud noises. This is an interesting point as looking at the actual living conditions/location itself of patients is often not considered when it comes to assessing stroke risk. In clinical practice, we often focus the majority of our attention on the main stroke risk factors: hypertension, hyperlipidemia, etc. We put our patients through intensive thorough workups such as looking for arrhythmias; however, the discussion about sleep apnea rarely makes its way into the conversation. It is also rare to have patients evaluated for OSA during the inpatient stay, but clearly this should be revisited. By bringing this into the spotlight, providers can become more aware of this issue and hopefully start providing more routine sleep evaluations for our at-risk patients.