health L15
THE BUSINESS TIMES WEEKEND SATURDAY/SUNDAY, MAY 26 - 27, 2012
D
O you really have high
blood pressure? High
blood pressure is an increasingly common condition, especially in a population with a higher proportion of elderly
people. Yet, many, especially the elderly,
do not understand what really constitutes
high blood pressure or hypertension.
Heart disease is
increased by up to
three times in those
with hypertension
and smoking
increases this risk
by an additional
two- to three-fold.
For those who
drink, the bad news
is that all alcoholic
drinks are
significantly
associated with high
blood pressure.
What is high blood pressure?
When the heart pumps blood out into the
aorta (the major artery that supplies blood
from the heart to the body) during contraction of the left lower heart chamber (LV),
the highest pressure generated is termed
as the systolic blood pressure (SBP). Subsequently, the LV relaxes and expands in
size, the pressure falls and the lowest recorded blood pressure is termed as the diastolic blood pressure (DBP). When the
SBP consistently exceeds 140 mm Hg ( millimetres mercury which is the unit of
measurement of blood pressure) and/or
the DBP exceeds 90 mm Hg, the person is
considered to have high blood pressure.
Age-related changes
In the young, the aorta is an elastic and
distensible vessel which is able to distend
when blood enters the vessel during contraction of the LV. As the blood flows from
the aorta to other organs during relaxation
of the LV, it recoils to its non-distended
resting state. An analogy will be to think of
the aorta as a large elastic rubber tubing.
As such, it is able to absorb part of the
pressure generated during LV contraction
and with its recoil, it will prevent the DBP
from dropping too low. The net effect is
that the difference between the SBP and
the DBP, also called pulse pressure, is usually kept about 40 mm Hg. Hence, it is
common in young individuals to record
blood pressure readings of 100/60, 110/70
or 120/80.
Just as a rubber tubing hardens and becomes less elastic over time, the aorta also
becomes stiffer with increasing age. As a
result, the aorta is less able to absorb the
blood pressure generated during LV contraction resulting in higher SBP values. An
interesting effect is that the aorta also has
less elastic recoil and hence, the DBP
tends to be lower during relaxation of the
heart chamber. Therefore, as age increases, elevation of the SBP becomes more
prevalent and the pulse pressure often increases beyond 140 mm Hg.
This SBP elevation is particularly more
pronounced in women. Data from the
Framingham heart study in the USA
showed that for older women 65 years or
more, the incidence of hypertension was
78 per cent. With increasing age, the prevalence increased markedly and was 85 per
cent for those 60 to 79 years, and 94 per
cent for those 80 years of age or more.
Is low blood pressure harmful?
One of the common findings in the elderly
is the presence of a high SBP associated
with a low DBP. While elevation of blood
pressure is harmful, the often asked question is whether a low DBP is harmful? For
the elderly, a DBP of less than 70 mm Hg
carries an increased risk of heart disease
similar to that associated with elevation of
the DBP of more than 90 mm Hg. A likely
FILE PHOTO
Under pressure
While our blood pressure inevitably increases as
we age, we can avoid aggravating it by adopting
healthy lifestyle habits. By Michael Lim
explanation is the decreased blood flow to
the heart muscles if the DBP drops too
low.
About 80 per cent of the blood flowing
into the heart muscle occurs during relaxation of the heart muscles. For an elderly individual with SBP elevation who exercises,
the heart has to work harder to pump
blood into the stiff aorta resulting in an increased demand for oxygen and yet the
faster heart rate means that there is less
time for the heart to relax, and hence less
time for blood to flow into the heart muscles. The lower DBP associated with a stiff
aorta also means that the pressure may
drop below the 60 mm Hg value which is
the minimal pressure required for adequate flow into the heart muscle. It is like
a tap with low pressure and the flow becomes slower and volume lower. The net
effect is insufficient oxygen supply to the
heart muscles and this is aggravated if the
individual also has a significant blockage
of the heart artery.
Underestimating and
overestimating blood pressure
Accurate measurement of the blood pressure in the elderly requires an understanding of the age-related changes in the regu-
latory mechanisms and the vessels. When
evaluating blood pressure, always use the
arm with the highest blood pressure measurement as the reference arm. A common
cause of underestimating SBP in the elderly is the failure to pump the pressure to a
sufficiently high level before starting to
auscultate or listen for sounds to detect
SBP. This may result in underestimating
SBP in the elderly where an “auscultatory
gap”, as defined by the period during
which sounds indicating true SBP fade
away and reappear at a lower pressure
point, is more commonly seen.
Blood pressure is often overestimated
in the elderly as the prevalence of the
“white-coat effect” ( transient elevation of
the blood pressure in a clinic or hospital
environment) may be as high as 25 per
cent. Home blood pressure monitoring is
increasingly seen as similar or better than
office blood pressure readings in being
able to reflect the true blood pressure readings. This is especially so in the elderly
where home monitoring will prevent over
diagnosis of hypertension resulting from
the “white-coat effect”.
Lifestyle effects
While there is little that can be done to pre-
vent age-related changes in the aorta, attention to lifestyle habits can make a difference. Heart disease is increased by up to
three times in those with hypertension
and smoking increases this risk by an additional two- to three-fold. For every additional 10 cigarettes smoked per day, mortality from heart disease increases by 18
per cent in men and 31 per cent in women. Contrary to common misconception,
It is never too late to benefit from smoking
cessation.
For those who drink, the bad news is
that it does not matter whether you drink
beer, wine or hard liquor; all alcoholic
drinks are significantly associated with
high blood pressure and this is especially
so if it is taken without meals.
Many elderly consume painkillers for
various ailments especially joint problems. Nonsteroidal anti-inflammatory
drugs (NSAIDs) are commonly prescribed
for elderly patients as painkillers. In the
elderly, use of NSAIDs may not only have
an adverse impact on blood pressure control but may be also be associated with deterioration of kidney function.
Hence, it is important to bear in mind
that hypertension in the elderly is not
quite the same as hypertension in the
younger population. The key points to remember are making sure it is truly hypertension, avoiding under or overtreatment,
and avoiding detrimental lifestyle habits
and drugs that aggravate the control of
high blood pressure.
✎ Dr Lim is medical director at the
Singapore Heart, Stroke & Cancer
Centre. He is also editor-in-chief, Heart
Asia; British Medical Journals
Publishing Group, chairman; Scientific
Advisory Board, Asia Pacific Heart
Association honorary professor and
senior medical adviser, Peking
University Heart Centre.
This series is brought to you
by the Heart, Stroke and
Cancer Centre. It is produced
on alternate Saturdays.