Pitfalls in the measurement of the nocturnal blood pressure dip in adolescents with type 1 diabetes

Abstract

Objective: The purpose of this study was to screen adolescents with type 1 diabetes using ambulatory blood pressure monitoring (ABPM) to 1) test the hypothesis that using a preset sleep time results in an overdiagnosis of abnormal nocturnal dipping in systolic blood pressure and 2) assess the reproducibility of an abnormal nocturnal systolic blood pressure dip.

Research design and methods: For aim 1, ABPM from 53 adolescent patients with type 1 diabetes was reviewed. Nocturnal dips in systolic blood pressure calculated by actual sleep time were compared with those from a preset sleep time. For aim 2, blood pressure monitoring from 98 patients using actual reported sleep time was reviewed. Reproducibility of the nocturnal dip in systolic blood pressure was assessed in a subset of "nondippers."

Results: For aim 1, the actual mean +/- SE decline in nocturnal systolic blood pressure was 11.6 +/- 4.7%, whereas the mean decline in nocturnal systolic blood pressure calculated using the preset sleep time was 8.8 +/- 4.9% (P < 0.0001). For aim 2, 64% of patients had a normal nocturnal decline in systolic blood pressure (14.9 +/- 3.1% mmHg), whereas 36% had an abnormal dip (5.7 +/- 2.8% mmHg). Repeat ABPM performed in 22 of the 35 nondippers revealed that only 36% had abnormal systolic dipping confirmed on the repeat ABPM.

Conclusions: The use of actual reported sleep time is required to accurately determine the nocturnal dip in systolic blood pressure. Repeating ABPM in nondippers is essential to confirm this abnormality.

Figure 1

Comparison of the percent nocturnal dip in systolic blood pressure calculated from actual sleep time versus that from preset sleep time in 53 subjects with type 1 diabetes.

Figure 2

Bland and Altman plot. Solid line represents the mean of differences between percent decline in nocturnal systolic blood pressure (BP) calculated using actual versus preset sleep time. The average discrepancy between the different sleep times is 2.8%, with relative consistent variability.

Figure 3

ABPM from an individual patient. Shaded area indicates sleep time. A: Actual sleep time 2:00–7:00 a.m. Mean daytime systolic blood pressure (BP) 124 mmHg; mean nighttime systolic blood pressure 107 mmHg; percent dip 13.7%. B: Preset sleep time 10 p.m.–8 a.m. Mean daytime systolic blood pressure 122 mmHg; mean nighttime systolic blood pressure 117 mmHg; percent dip 4%.