The anxiety caused by the measurement itself or the environment in which it is taken can influence blood pressure by what is known as a defense reaction (Mancia et al., 1983, 1987). When the blood pressure of the patient is constantly higher when measured in the clinical environment than at home, it is known as white coat hypertension, i.e. patients who have white coat hypertension have a blood pressure that is within the normal range outside the clinic setting (Pickering et al., 2002). This phenomenon was first described more than 60 years ago (Ayman and Golshine, 1940).
The mechanism of white coat hypertension is still being investigated. It is thought that it may be due to an exaggerated learning or orientating response to stressful stimuli. However, studies have failed to demonstrate an increase in laboratory stressors when comparing individuals with white coat and sustained hypertension (Floras et al., 1981; Siegel et al., 1990). There is also no difference in the variability of blood pressure between hypertensive and normotensive adults (Siegel et al., 1990; White and Baker, 1986). It is possible that this defense reaction could be a learned or conditioned response, i.e. the patient associates the clinic with an unpleasant experience and the normal habituation does not occur. One study showed that in a group of young men, those who received a letter stating that they were hypertensive (prior to their appointment) had a significantly higher blood pressure (by 16/ 10 mmHg) than those who were sent a neutral letter. White coat hypertension may also be dependent on the interaction between subject and observer based on gender (Millar and Accioloy, 1996).
Its prevalence in a non-pregnant population is between 20 and 40% and there is some evidence that it is more commonly found in women (Hoegholm et al., 1992; Khoury et al., 1992; Krakoff et al., 1988). It is unlikely to be a benign condition in non-pregnant individuals, as the risk appears to fall somewhere in between those who are normotensive and those with sustained hypertension (Julius et al., 1990).
Its significance in an obstetric population has not been determined. Rayburn et al. (1984) showed that in the vast majority of cases where clinic blood pressures differed significantly from home readings, the readings taken at home were lower. More recent studies have shown that the presence of white coat hypertension may be more clinically significant in early pregnancy (Broughton Pipkin et al., 1998) rather than late pregnancy (Brown et al., 1999). There are no comparisons between pregnant and non-pregnant individuals as to the degree that this defense reaction causes blood pressure to change. It seems likely though that the influence of stress and anxiety is greater in the pregnant patient (e.g. admission to hospital, delivery, etc.).
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It seems like you hear it all the time from nearly every one you know I'm SO stressed out!? Pressures abound in this world today. Those pressures cause stress and anxiety, and often we are ill-equipped to deal with those stressors that trigger anxiety and other feelings that can make us sick. Literally, sick.