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Many healthcare professionals suspect that
tension surrounding a visit to the doctor could cause an increased blood
pressure reading in the office. This so-called "white coat hypertension"
(WCH) may lead to an incorrect diagnosis. Two recent studies appearing
in The American Journal of Hypertension confirm this suspicion.
Paola Verdecchia and colleagues in Italy studied
white coat hypertension and how it related to heart damage.
"The standard measurement of blood pressure
(BP) in the clinical environment may trigger an alerting reaction and a
pressor rise in the patient," said Dr. Verdecchia. "The transient pressor
rise during clinical visits is usually referred to as 'white coat effect',
while the coexistence of persistently high office BP (OBP) with normal
BP outside the medical setting is often referred to as ' white coat' hypertension.
The effect is defined as the difference between clinical BP and average
daytime ambulatory BP(ABP)."
Their study population included 1,333 people
in a local hypertension registry. All involved underwent an extensive health
and cardiac workup that included Doppler echocardiography.
A cohort of 178 healthy and normotensive subjects
composed mostly of staff, students, fellows or people undergoing echo studies
for other reasons were given the same battery of tests and used as controls.
In both groups, blood pressures were taken
during clinic visits. ABPs were obtained over 24-hours.
White coat hypertension was diagnosed in those
who had elevated BPs during office or clinic visits but average ambulatory
findings of less than 131/86 mmHg for women or 136/87 mmHg for men. The
white coat effect was calculated for both diastolic and systolic BP as
the difference between clinic BP and average daytime ABP.
"The prevalence of white coat hypertension
was 18.9 percent in the overall hypertensive population," stated Dr. Verdecchia.
"White coat hypertension decreased with increased severity of disease as
measured by the Joint National Committee V classification system. Office
BP, cuff BP following echocardiographic study, ambulatory BP and longer
duration of hypertension were all higher in the group with ambulatory hypertension
then with white coat hypertension."
Left ventricular mass during echocardiography
was used to assess damage to the heart secondary to elevated blood pressures.
They found that white coat hypertension was associated with a normal LV
mass.
"The normalcy of ambulatory BP and LV mass
in our subjects with white coat hypertension suggests that their risk for
future cardiovascular complications might be low," stated Dr. Verdecchia.
"The actual levels of ambulatory BP should be used to identify the subjects
with normal BP outside the clinic and potentially low cardiovascular risk."
A group from Denmark studied age-related concerns
about white coat hypertension. A total of 954 subjects were randomly selected
from a community register in an age and gender stratified manner. Between
25 and 30 persons of each sex in all decades of life from 20 to 79 were
recruited. After exclusions and refusals to participate, 352 patients were
enrolled in the study.
The participants first had five readings taken
with a standard sphygmomanometer to establish the accuracy of monitoring
equipment and obtain an OBP reading. They were then fitted with ABP monitoring
equipment for a 24 hour period.
Ambulatory BP during the day was an average
of 5 mmHg lower than OBP. The mean difference between the two increased
with age. The variability of the difference also increased as the population
got older.
"In contrast to studies using OBP, we found
diastolic daytime ambulatory blood pressure increased only slightly in
both sexes until the fifth and six decades and then declined," said Niels
Wiinberg an investigator who participated in the study. "As expected, systolic
daytime ambulatory readings increased steadily through the age groups,
but the rise with age was more modest then expected from studies of OBP.
This could at least partly be explained by the white coat effect, which
in this and other studies, seems to be more pronounced in higher age groups."
Wiinberg noted that office BP of normal persons
is a poor predictor of daytime ambulatory measurements. In the elderly,
and in particular for systolic pressures in women, office measurements
were consistently higher that daytime ambulatory blood pressures.
"In the youngest age groups, the tendency
was reversed, with all findings suggesting that that the previously observed
increase in blood pressure with aging at least partly might reflect the
greater impact of white coat hypertension in older people," according to
Dr. Wiinberg. "The variation between OBP and ambulatory BP increases with
age, making the 24-hour AMBP measurements more relevant in the older age
group."
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