Background: When considering a possible Obstructive Sleep Apnea (OSA) diagnosis, clinicians often need to rely on subjective,
patient reported symptoms such as excessive daytime sleepiness, snoring and witnessed apnea. Measuring impaired brain function caused by sleep deprivation and hypoxia could provide needed objectivity to potentially aid case finding and risk stratification and potentially demonstrate treatment effect. Over 50% of brain pathways are utilized in vision and reading. K-D Test measures speed and accuracy during a rapid number naming task in which a series of single-digit numbers is read aloud. The King-Devick Test (KDT) is a rapid number naming test used in baseline assessments and remove from play decisions for concussion. KDT is an objective physical measure of neurologic function. Abnormalities in saccadic eye movements are associated with issues frequently found in OSA patients (i.e. sleep deprivation, hypoxia and cognitive impairment).
Specific Aims: 1. Test for association of subject KDT time with OSA severity, based on Apnea Hypopnea Index (AHI); 2. Evaluate for improvement in brain function after treatment with Continuous Positive Airway Pressure (CPAP) by way of KDT time.
Hypothesis: OSA patients who adhere to CPAP therapy will demonstrate a statistically significant improvement in their KDT time compared to baseline.
Methods: Design: Pilot study of a prospective cohort; Subjects: Patients referred to Sleep lab for initial evaluation of Sleep Disordered Breathing concerns; Sample size: 60 subjects provide adequate power to detect a 0.36 correlation coefficient between AHI and KDT time. Assuming half will have OSA which requires CPAP treatment, there would be adequate power to detect a 0.55 SD difference in KDT pre- and post-treatment. Subjects read aloud from left to right as fast as possible for 3 screens. Total time and errors are recorded.
Data Collection: Collect KDT in sleep lab prior to scheduled polysomnography. Collect demographic information and data necessary for Sleep Apnea Clinical Score. Collect medical histories from Electronic Health Record. Collect sleep testing outcomes from sleep lab database. Repeat KDT for those treated with CPAP at compliance visit with Sleep Medicine provider. Descriptive analysis about demographic and clinical characteristics of the cohort are summarized by severity of OSA. Estimate correlation coefficient between KDT and AHI. Compare mean KDT between patient subgroups with the two-sample t-test with or without moderate OSA (AHI < & ‑ 15), with normal and abnormal AHI (< 5 & ‑ 5). For the OSA subgroup, measure the improvement in KDT and AHI pre and post CPAP treatment by paired t-test.
Results: Recruitment 1/30/2018-3/27/2018: 126 patients presented to Sleep Lab; 11 declined 60 enrolled 55 screen failures
37 with CPAP recommendation, 23 with no CPAP recommendation; 35 with AHI ≥ 15 2 with AHI < 15; 22 with repeat KDT for comparison; 14 lost to follow up; 1 excluded from analysis due to dementia. OSA patients with moderate OSA (AHI score greater than or equal to 15) had worse KDT scores compared to OSA patients without moderate OSA (AHI scores less than 15) (64.9s (3.16) vs 61.0 (3.74)). OSA patients with abnormal AHI scores (greater than or equal to 5) had worse KDT scores compared to OSA patients with normal AHI scores (less than 5) (63.9 (2.92) vs. 59.6 (6.24)). There was not a statistically significant association of KDT with AHI as a continuous variable (Pearson correlation coefficient 0.10 (-0.16, 0.35). CPAP treatment was associated with significantly improved KDT time (mean difference -6.6s (12.2), p=0.02).
Conclusions: The neurologic function of patients with moderately severe OSA differs from those with mild or no OSA, as determined by the King Devick Test. KDT time ranges between normal and abnormal patients, however, overlap. Clinically, patients with established neurologic illness such as MCI, Dementia and Parkinson’s have slower baseline KDT times. This may decrease the utility of OSA prediction by KDT in these patients. Larger studies are needed to assess if KDT time thresholds exist to aid OSA screening. KDT has the potential to optimize OSA risk stratification processes through demonstrating patient neurologic impairment. OSA patients treated with CPAP demonstrate improved brain function as measured by significantly faster times on KDT. Assessment with KDT has the potential to be a paradigm shifting tool in OSA patient management.