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 pressure at night causes arousal from sleep and a change in the continuous blood pressure recorded simultaneously.
Design: Repeated measurement of blood pressure with two ambulatory blood pressure machines (Oxford Medical ABP and A&D TM2420) during continuous measurement of beat to beat blood pressure and continuous electroencephalography.
Setting: Sleep reseach laboratory. Subjects--Six normal subjects.
Main outcome measures: The duration of electroencephalographic arousal and the beat to beat changes in blood pressure produced by the measurement of ambulatory blood pressure; the size of any changes that this arousal and change in blood pressure produced in the blood pressure recorded by the ambulatory machine.
Results: Both ambulatory blood pressure machines caused arousal from 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. During non-rapid eye movement sleep, this rise led to the ABP machine overestimating the true systolic blood pressure during sleep by a mean of 10 (SD 14.8) mm Hg and the TM2420 by a mean of 6.3 (8.2) mm Hg. On average, diastolic pressure was not changed, but measurements in individual subjects changed by up to 23 mm Hg. These changes varied in size among subjects and stages of sleep and were seen after measurements that did not cause any electroencephalographic arousal.
Conclusions: Ambulatory blood pressure machines cause appreciable arousal from sleep and therefore alter the blood pressure that they are trying to record. This effect should be taken into account when recordings of blood pressure at night are interpreted in 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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BMJ 1994 308: 1634. [Extract] [Full Text]

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