Resting Heart Rate Variability Is Associated With Subsequent Orthostatic Hypotension: Comparison Between Healthy Older People and Patients With Rapid Eye Movement Sleep Behavior Disorder

Figures

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  Figure 1. Flowchart of subject enrollment. iRBD, idiopathic rapid eye movement sleep behavior disorder; OH, orthostatic hypotension; HRV, heart rate variability.

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  Figure 2. Smartphone Nexus 5X and wearable RR intervals sensor. The RRI data acquired by the wearable RRI sensor was sent to the smartphone application in real time. This figure shows the heart rate 66 calculated from the RRI at that time. In this experiment, the electrodes of the wearable RRI sensor were attached to the three poles of the trunk of the subject, just as in a normal electrocardiogram. The smartphone was in a running pouch attached to the back of the waist of the subject. RRI, RR intervals.

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  Figure 3. Orthostatic challenge protocol. Black circles (•) show when blood pressure and pulse rate were measured. The measurements were done every 3 min when in the supine position, and every 1 min when in the standing position. Ten min worth of RRI data in the supine position were analyzed for heart rate variability, which were divided into two segments (segment 1: 6–10 min and segment 2: 11–15 min).

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  Figure 4. Typical Poincaré plot of RRI. The Poincaré plot was based on a simple scatter of plots where the x value is nth RRI and its corresponding y value is the (n + 1)th RRI. Each plot is described in the (RRI n, RRI n + 1) space. This figure represents the Poincaré plot of a 5-min RRI. The Poincaré plot typically forms an ellipse with about a 45-degree tilt, and the diffusion range around the major axis and the minor axis of the ellipse are defined as SD2 and SD1, respectively. Their ratio is defined as SD1/SD2. RRI, RR intervals; SD1, standard deviation 1; SD2, standard deviation 2.

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  Figure 5. Comparison of orthostatic challenge test among healthy controls, OH (–) iRBD, and OH (+) iRBD groups. (A1–C1), absolute changes (mean ± standard error of the mean); (A2–C2), delta values compared to baseline supine position (mean ± standard error of the mean). BP, blood pressure; HR, heart rate; iRBD, idiopathic rapid eye movement sleep behavior disorder; OH, orthostatic hypotension. x-axis: base, mean baseline values in supine position; 1–15 min, after standing.

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  Figure 6. Poincaré plots during segment 2 in supine position of (A) a healthy control subject, (B) an OH (–) iRBD subject, and (C) an OH (+) iRBD subject. The Poincaré plot was based on a simple scatter of plots where the x value is the nth RRI and its corresponding y value is (n + 1)th RRI. (A) RRI plots were sparsely distributed between 900 and 1,050 ms. The distribution approximates a 45-degree tilted oval. (B) RRI plots were densely distributed between 840 and 920 ms. Both SD1 and SD2 were smaller than (A). (C) RRI plots were closely distributed between 890 and 940 ms. SD1 and SD2 were smaller than (A), in particular, SD2 was only ~40% of (A). OH, orthostatic hypotension; iRBD, idiopathic rapid eye movement sleep behavior disorder; RRI, R–R intervals; HR, heart rate; SD1, standard deviation 1; SD2, standard deviation 2.

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  Figure 7. Receiver operating characteristic curve of heart rate variability during segment 2 for the detection of orthostatic hypotension. The ROC curve with the AUC of 0.840 is shown (p = 0.012). The sensitivity to OH (+) is 1.000, and the specificity to OH (–) is 0.583. The optimal cutoff point is pNN50 of 0.69 and SD2 of 17.6. ROC, receiver operating characteristic; AUC, area under the curve; OH (+), orthostatic hypotension-positive; OH (–), orthostatic hypotension-negative; pNN50, percentage of successive RR intervals that differ by more than 50 ms; SD2, standard deviation 2.