Sleep-Related Breathing Disorders: Hemodynamic Implications, Diagnosis and Mortality in Obstructive Sleep Apnea and Stroke

Sleep-related breathing disorder (SRBD) is an umbrella term for obstructive sleep apnea (OSA),
central sleep apnea (CSA) and Cheyne-Stoke respiration (CSR), among others. OSA is a known,
independent risk factor for stroke and other potentially fatal disorders. The purpose of this thesis is
to shed light on this association – both in OSA patients with and without stroke.
Study I addresses the diagnostic criteria for SRBD using polysomnographies of 63 patients with a
transient ischemic attack (TIA) or stroke. We compared the effect of the two previous hypopnea
criteria (A and B from 2007) and the new (2012) on diagnosis. We conclude that the B- and 2012-
criteria provide the same results regarding number of patients diagnosed with SRBD and patients
with moderate to severe SRBD, who are thus offered treatment. In contrast to these criteria,
significantly less stroke patients are diagnosed and treated if the A-criteria are applied (p = 0.0016
and 0.0001, respectively).
Study II is based on the same patients as study I. The aim was to determine polysomnographic
predictors of mortality of the stroke/TIA patients after a follow-up period of 19-37 months. 9
patients died during follow-up, and they all had moderate to severe SRBD. There was a higher
mortality in the group with an apnea hypopnea index (AHI) > 15 (p = 0.0427), a sleep efficiency <
75 % (p = 0.0404) and a total number of arousals > 200 (p = 0.0389). AHI is an established
predictor of mortality, but larger studies are needed in order to investigate the other two as
independent predictors.
In study III, we tried to find explanations as to the markedly increased risk of stroke in OSA
patients. Hypercapnia is one of the immediate effects of apneas and hypopneas. We therefore
conducted functional magnetic resonance imaging (fMRI) scans of OSA patients and controls in
order to investigate whether OSA patients have an impaired up-regulation of their cerebral blood
flow (CBF) as a reaction to hypercapnia. We found a significantly impaired autoregulation with
increasing OSA severity (p = 0.018). We also attempted to imitate apneas in the MRI scanner
(breath holding task), in order to evaluate changes in the cerebral blood flow caused by this.
However, this did not show any differences between OSA patients and controls or relations to OSA
severity.