16 LISTENER SEPTEMBER 14 2019
blood pressure, although the threshold at
which it is described as such varies between
130/85 and 140/90, depending on which
expert you ask.
About 750,000 people in New Zealand
are estimated to have hypertension, but
only about half are treated. And of the
half who are treated, only about 50% are
well controlled. About 5-10% or more of
patients are like Bain, who has hypertension
that is resistant to treatment despite good
compliance and optimal medication. Over
time, high blood pressure damages blood
vessels, increasing the risk of heart attacks,
strokes, heart failure and kidney disease.
Julian Paton, a professor of translational
physiology at the University of Auckland
medical school, says in 95% of cases,
doctors don’t know the primary cause of
hypertension. But he believes a significant
contributor is the activity of our sympathetic
nervous system – the one we can’t control
that activates our fight-flight response.
“We know that in patients with high blood
pressure this sympathetic nerve activity
going to the heart, and to the blood vesselsto control their diameter, is extremely high
- much higher than it should be.”
But what about that Amazon tribe?
Wouldn’t their sympathetic nervous system
operate the same as ours? No, says Paton.
“This tribe is isolated from many of the
drivers of hypertension and sympathetic
activity, including continual stress, high
salt, high fat, smoking, alcohol and artificial
preservatives and sweeteners. Their crops are
free of artificial chemicals such as pesticides,
herbicides and fungicides. I’m not surprised
their blood pressure is normal.”
WHERE’S MY MOTIVATION?
Treatment of hypertension is poor,
partly because existing drugs don’t target
sympathetic activity, says Paton. Poor
control is also the result of treatment
resistance, as in Bain’s case, as well as drug
intolerance and poor compliance because
of the side effects of some medication. “It’s
a disaster,” says Paton. “When you take a
tablet for a condition that doesn’t hurt – it’s
not like arthritis, where every morning you
are reminded to take your pills because yourknees hurt – and you get side effects, and
you feel tired and lethargic, and it destroys
your sex life, and you felt better before, what
is the motivation? It’s a really big clinical
issue.”
Paton’s new $5 million Health Research
Council (HRC)-funded study targets two
tiny but powerful organs strategically
located at the base of the skull, known
as the carotid bodies, which control the
sympathetic nervous response. The size of
a grain of rice, they are the guardians of the
brain’s blood-oxygen status, acting as a kind
of smoke alarm telling the brain to increase
blood pressure to maintain oxygen supply.
They also force you to inhale again after
holding your breath for long periods.In an earlier study he did when based at
the University of Bristol, Paton’s research
team removed one of the carotid bodies
in 15 patients to find out if it would lower
blood pressure. “The answer was, ‘Bloody
hell, did it lower blood pressure!’ – by a
whopping 30mm of mercury.” Systolic
and diastolic blood-pressure readings – the
top and bottom figures – are measured
in millimetres of mercury, so a 30mm
reduction is dramatic indeed. In a 16th
patient in the Bristol study, blood pressure
did not change. It was later discovered that
the tissue removed from that patient was
fat and did not contain the carotid body.
Paton isn’t recommending carotid-body
surgery as a treatment, however. Studies
show it makes patients more vulnerable to
potentially life-threatening sleep apnoea,
and that blood pressure over time resets
to original levels as the body tries to
compensate for the change. However, a
novel drug, known as a purinergic receptor
antagonist, which Paton believes will dial
down the carotid bodies and sympathetic
activity and lower blood pressure, will be
used in animal studies as part of the HRC
research. He hopes that work will lead to
big-pharma collaboration in the first clinical
trial in hypertensive people in New Zealand.D The drug has been developed for people
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Over time, high blood
pressure damages bloodvessels, increasing the
risk of heart attacks,strokes, heart failure
and kidney disease.Resistant to treatment:
Ann Bain tests her blood
pressure at home.