Impact of Arterial Stiffness on WatchPAT Variables in Patients With Obstructive Sleep Apnea

Abstract

Study objectives: The WatchPAT is a wrist-worn portable device that creates integration data regarding peripheral arterial tone (PAT), oxyhemoglobin saturation, heart rate, and actigraphy to diagnose or screen for obstructive sleep apnea (OSA). Previous studies have demonstrated the efficacy and validity of respiratory variables measured by the WatchPAT compared to those using polysomnography (PSG). However, the effects of arterial stiffness or atherosclerosis on WatchPAT parameters remain to be elucidated.

Methods: Sixty-one consecutive patients with suspected OSA who underwent home-based testing with the WatchPAT 200, standard in-laboratory overnight polysomnography (PSG), and pulse wave velocity (PWV) as an index of arterial stiffness were studied. All PSG recordings were scored manually using the American Academy of Sleep Medicine criteria, whereas WatchPAT data were analyzed by an automatic algorithm. We evaluated how arterial stiffness affected respiratory event index data in WatchPAT (WP-AHI), because WP-AHI could be partly influenced by PAT, comparing WP-AHI and the apneahypopnea index measured by PSG (PSG-AHI) in consideration of PWV result.

Results: Overall, WP-AHI was moderately correlated to PSG-AHI, but WP-AHI was significantly lower than PSG-AHI (28.4 ± 19.2 versus 53.6 ± 30.2 events/h, P < .0001). For the lower PWV group, there was a significant correlation and good agreement between the WP-AHI and PSG-AHI, but as the PWV increased, there was low correlation between the WP-AHI and PSG-AHI.

Conclusions: Arterial stiffness may affect the respiratory variables measured by WatchPAT in patients with OSA.

Commentary: A commentary on this article appears in this issue on page 301.

Keywords: WatchPAT; apnea-hypopnea index; arterial stiffness; obstructive sleep apnea; pulse wave velocity.

Figure 1. Bland-Altman plot of respiratory event indices.

Differences were calculated as the PSG-AHI minus WP-AHI. Means for the PSG and WatchPAT findings are on the x-axis, and differences are on the y-axis. Solid lines on the y-axis are drawn from 0, mean difference. Dotted lines on the y-axis are drawn from mean ± 1.96 × standard deviation of the differences. PSG = polysomnography, PSGAHI = apnea-hypopnea index as measured by PSG, WP-AHI = respiratory event index as measured by WatchPAT.

Figure 2. ROC curve identifying pathologic apnea and hypopnea events from sleep for the WatchPAT and PSG.

The comparison threshold was set at PSG-AHI ≥ 30 events/h on PSG. PSG = polysomnography, PSG-AHI = apnea-hypopnea index as measured by PSG, ROC = receiver operating characteristic.

Figure 3. Scatterplot of PSG-AHI by WP-AHI.

A moderate correlation was found (r = .69, P < .0001, n = 61) between PSG-AHI and WP-AHI. PSG-AHI = apnea-hypopnea index as measured by polysomnography, WP-AHI = respiratory event index as measured by WatchPAT.

Figure 4. Scatterplots of PSG-AHI by WP-AHI based on the PWV threshold of 1500 cm/s.

Data are shown for patients with a PWV under 1500 cm/s (A) and a PWV over 1500cm/s (B). The Pearson correlation coefficients were .78 (P < .0001) and .40 (P < .04), respectively. PSG-AHI = apnea-hypopnea index as measured by polysomnography, PWV = pulse wave velocity, WP-AHI = respiratory event index as measured by WatchPAT.