BEYOND the wrinkles and the blemishes that come with advancing years, the invariable march of age will result in changes in the blood vessels that have served us so faithfully. Just as rubber becomes stiffer and less pliable over time, our arteries will also lose its elasticity and become less distensible. An effect of this is an increase in the upper or systolic blood pressure (SBP) value and labile fluctuation in SBP with varying levels of activities and emotional changes.
Hence, it is not uncommon to find in the elderly a blood pressure (BP) of 160/90 mm Hg at the doctor’s clinic, even though the preceding home BP recording showed 130/80 mm Hg.
“High” blood pressure that is normal
One elevated blood pressure reading does not mean that high blood pressure (hypertension) exists. While the pliable and elastic wall of the arteries in a young person allows the arteries to distend and “absorb” the increase pressure that is generated through an increase in heart rate or by stress, the loss in elasticity and stiffening of arteries with ageing means an elevation in the SBP will be more commonly seen with emotional stress, anxiety and physical exercise. Hence, in the elderly, the need to record blood pressure on multiple occasions at rest is necessary before a diagnosis of hypertension can be confirmed.
However, office and home blood pressure measurements may still be elevated in the situation of “pseudo-hypertension”, a condition where the SBP is falsely elevated because of significant stiffening and hardening of the walls of the arteries. In this situation, the cuff inflation during blood pressure recording may have to be inflated to very high pressures before the artery can be compressed, resulting in a highly elevated SBP value and a normal lower or diastolic blood pressure (DBP) value.
This may be more often seen in those who have diabetes mellitus where diffuse hardening of the arterial wall is more commonly seen. Furthermore, smaller arteries are more likely to be affected as compared to larger arteries.
Hence, in this situation, it may be better to use an arm BP measuring device rather than a wrist BP measuring device. This condition should be suspected if there are absolutely no symptoms and no evidence of any damage to any organs, despite the BP being persistently high and not responding to medication.
The three situations of labile SBP elevation, “white-coat hypertension” and “pseudo-hypertension” are more prevalent in the elderly and a correct diagnosis is important in avoiding overtreatment.
Impact of high blood pressure
Persistent elevation of high BP can manifest itself by the presence of damage to the brain (stroke, bleeding, dementia), the heart (chamber enlargement, abnormal heart rhythms), major blood vessels (aneurysm or enlargement of the aorta), kidneys (impairment of function) and eyes (degeneration of eyesight).
An objective way to assess the effect of persistent hypertension is to evaluate the impact of high BP on the heart. The left-side heart chambers are connected to the aorta, the main arterial channel which supplies blood to the entire body. In persistent poorly controlled hypertension, the thinned walled left upper heart chamber will be enlarged and the muscular left lower chamber will have thickened walls as the heart chamber has to pump harder against a higher BP for the blood to enter the aorta. This can be objectively confirmed by an ultrasound examination of the heart, which is also called echocardiography.
The absence of these changes on echocardiography in the presence of persistently high BP not responsive to medication and yet not accompanied by symptoms should lead one to suspect “pseudo-hypertension”.
How low should the blood pressure be?
The latest American College of Cardiology and the American Heart Association guidelines recommend that older adults with a BP of 130/80 mm Hg or higher should be treated. Under normal resting conditions, about 85 per cent of the blood perfusion of the muscle of the main heart pumping chamber, the left ventricle, occurs during diastole (relaxation phase of the heart chamber). Hence, the arterial diastolic BP (DBP) is the main force that “pushes” blood into the heart arteries to perfuse the left ventricle muscle.
Presently, we do not know what is the lowest limit of DBP where it is not able to maintain adequate perfusion to the left ventricle muscle. In patients with heart artery disease, if the cross-sectional area of the heart artery is reduced by more than 70 per cent , there will usually still be adequate perfusion due to compensatory dilatation of the microcirculation but the maximum heart artery blood flow will be reduced.
If the cross-sectional area reduction is at least 85 per cent to 90 per cent, there can be inadequate perfusion even at rest. Hence, in those with significant blockage of the heart arteries, the DBP should not be excessively low and should be individually titrated. Likewise, in those with significant narrowing of the brain arteries, a sudden drop in the SBP can precipitate a stroke. Hence, for the elderly diabetics who are at a higher risk of developing heart and brain artery disease, caution should be exercised.
In the ACCORD BP trial that looked at intensive BP lowering in diabetics, intensive BP control (SBP <120 mmHg) did not reduce the combined major cardiovascular complications (heart attack, stroke and death). However, when the outcomes were looked at individually, there was a reduction in stroke at the expense of increased serious adverse events. Hence, while achieving BP targets <140/90 mmHg may be suitable for some diabetics, not all will be better off with intensive BP lowering (SBP <120 mmHg).
In the International Database on Home Blood Pressure in Relation to Cardiovascular Outcome (IDHOCO) study published in Circulation journal in 2015, for those hypertensive octogenarians treated, a SBP of less than 127 mm Hg was associated with increased death and the lowest risk was at a systolic BP of about 149 mm Hg. Hence, for hypertensive octogenarians, as a result of age-related decreased circulation to the organs and a higher risk of a postural drop in BP on standing, maintaining the SBP between 150 mmHg and 140 mmHg is the sweet spot.