Abstract 503: A Within-Subject Repeatability Coefficient Assessment of Snoring on Carotid Artery Velocities

Objectives: Vascular surgeons use duplex ultrasound (US) to evaluate carotid stenoses as a means to determine stroke risk. An under-appreciated risk factor is Obstructive Sleep Apnea (OSA). Although the mechanism is unknown, preliminary studies suggest snoring may play a role. The goals were to determine 1) daily carotid artery velocity variability within subjects and 2) the effect of simulated snoring on carotid artery velocities. Methods: 44 bilateral carotid artery US exams were performed on 11 subjects by 2 RVTs (4 exams/subject, 7 subjects/RVT A, 4 subjects/RVT B). Steps were taken to ensure measurements were made at identical sites under similar parameters for subsequent exams. PSV and EDV were measured at 8 locations at rest and during a simulated snore. For each location, limits of agreement was used to calculate PSV and EDV repeatability coefficients, which are the limits within which 95% of the differences will lie for two measurements made on the same subject. Repeatability coefficients were then used to determine significance for observed velocity changes in carotid arteries with and without stenosis during simulated snoring, at 3 locations. They were also used to assess velocity variability in CEA candidates. All US exams were performed in an IAC vascular testing accredited laboratory by RVTs. Results: Repeatability coefficients for RVT A ranged from 26 to 40cm/s for PSV and 11 to 20cm/s for EDV. For RVT B they ranged from 30 to 65 and 8 to 19cm/s for PSV and EDV, respectively. Maximum values occurred in the ICA ostia and ECA for RVT A, and in the ICA ostia and proximal for RVT B. In non-stenosed arteries, snoring most frequently caused a change in the PSV of the proximal ICA where it occurred in 17% of the arteries (4/24). However, the effect of snoring was greatest in stenosed arteries. In 75% of these arteries (6/8) there was a significant velocity change. 38% of proximal ICA PSVs and EDVs were affected. Conclusion: Repeatability coefficients can be used to determine significant changes in carotid artery velocities within diagnostic stenosis categories as measured by US. There is a possible connection between snoring, carotid velocities and stenosis which warrants further investigation to determine if it is part of the mechanism by which OSA increases stroke risk.

Pattern of simulated snoring is different through mouth and nose

Cineradiography of the pharynx during simulated snoring was done in 6 healthy volunteers, and supraglottic pressure and flow rate were recorded in 12 others. We observed, immediately before snoring, a decrease in the sagittal diameter of the oropharynx followed, during snoring, by high-frequency oscillations of soft palate and pharyngeal walls. The pattern of soft palate oscillations was different while snoring through the nose or mouth. During inspiratory snoring through the nose, the soft palate remained in close contact with the back of the tongue and only the uvula presented high-frequency oscillations. Snoring through the mouth resulted in ample high-frequency oscillations of the whole soft palate. Frequency of airflow and supraglottic pressure oscillations was less (P less than 0.05) during mouth (28.2 +/- 7.5 Hz) than during nasal snoring (77.8 +/- 36.7 Hz). This difference may be related to the smaller oscillating mass (i.e., uvula) during nasal snoring. At variance with our previous data, which showed that snoring during sleep, in both heavy (nonapneic) snorers and obstructive sleep apnea patients, was systematically preceded by flow limitation, this was not true during simulated snoring.