Non-invasive ambulatory BP monitoring during the night: randomised comparison of different reading intervals.

Frequent measurements of BP during noninvasive monitoring could interfere with sleep, with consequent possible overestimation of nocturnal BP. We performed 24h noninvasive ambulatory BP monitoring (Space-Labs 90207) in 24 patients with essential hypertension twice, 1 week apart. Subjects were instructed to follow, as far as possible, a similar pattern of daily activity during the two sessions. The frequency of daytime readings (from 06.00 to 22.00 h) was kept constant in the two sessions (one every 15 minutes), while that of nocturnal readings (from 22.00 to 06.00 h) varied in random order: every 15 minutes in session A and every 60 minutes in session B. Mean sleep BP did not differ between session A (138/83 mmHg (SD 15/10 mmHg)) and session B (138/83 mmHg (SD 14/10 mmHg)). The percentage reduction of ambulatory SBP and DBP from wake to sleep was 9.7% and 10.0%, respectively, in session A, and 14.0% and 14.1%, respectively, in session B (all P = NS). The duration of sleep was 6.1 hours (SD 2 hours) in session A and 6.0 hours (SD 2 hours) in session B (P = NS). On average, 6.8% of nocturnal readings in session A and 7.6% of nocturnal readings in session B failed to pass the automatic editing criteria, but no hourly interval was lacking in valid measurements on both sessions.(ABSTRACT TRUNCATED AT 250 WORDS)