Effect of measuring ambulatory blood pressure on sleep and on blood pressure during sleep

BMJ 1994;308:820-823 (26 March)

Papers

Effect of measuring ambulatory blood pressure on sleep and on blood pressure during sleep

R J O Davies, senior registrar,^a N E Jenkins, medical student,^a J R Stradling, consultant physician ^a

^a Osler Chest Unit, Churchill Hospital, Oxford OX3 7LJ

Correspondence to: Dr Davies.

Abstract

Objective: To assess whether recording of ambulatory blood pressureat night causes arousal from sleep and a change in the continuousblood pressure recorded simultaneously.
Design: Repeated measurement of blood pressure with two ambulatoryblood pressure machines (Oxford Medical ABP and A&D TM2420)during continuous measurement of beat to beat blood pressureand continuous electroencephalography.
Setting: Sleep reseach laboratory. Subjects--Six normal subjects.
Main outcome measures: The duration of electroencephalographicarousal and the beat to beat changes in blood pressure producedby the measurement of ambulatory blood pressure; the size ofany changes that this arousal and change in blood pressure producedin the blood pressure recorded by the ambulatory machine.
Results: Both ambulatory blood pressure machines caused arousalfrom sleep: the mean duration of arousal was 16 seconds (95%range 0-202) with the ABP and 8 seconds (0-73) with the TM2420.Both also caused a rise in beat to beat blood pressure. Duringnon-rapid eye movement sleep, this rise led to the ABP machineoverestimating the true systolic blood pressure during sleepby a mean of 10 (SD 14.8) mm Hg and the TM2420 by a mean of6.3 (8.2) mm Hg. On average, diastolic pressure was not changed,but measurements in individual subjects changed by up to 23mm Hg. These changes varied in size among subjects and stagesof sleep and were seen after measurements that did not causeany electroencephalographic arousal.
Conclusions: Ambulatory blood pressure machines cause appreciablearousal from sleep and therefore alter the blood pressure thatthey are trying to record. This effect should be taken intoaccount when recordings of blood pressure at night are interpretedin clinical work and epidemiological research.

Clinical implications

Clinical implications
Ambulatory blood pressure machines are widely used in the management of hypertension
Blood pressure at night during ambulatory recordings is assumed to represent blood pressure during sleep, but the noise and the pressure on the arm of a recording cycle may disturb sleep
This study shows that ambulatory blood pressure machines cause a variable rise in blood pressure and electroencephalographic arousal from sleep during measurements
The changes in blood pressure caused by this arousal lead to an overestimation of true systolic pressure during sleep and a variable change in diastolic pressure
The blood pressure recorded by ambulatory machines at night may underestimate to variable degrees the reduction in the blood pressure during sleep

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Nocturnal ambulatory blood pressure measurement: A Shennan, M De Swiet, and A Halligan
BMJ 1994 308: 1634. [Extract] [Full Text]

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