One billion people are affected by high blood pressure. Photo / 123RF
One billion people are affected by high blood pressure. Photo / 123RF
Effective treatment for a condition affecting 1 billion people is in the sights of researchers at the University of Auckland. Chris Reed reports.
It's a silent killer that affects one in three adult Kiwis and creates huge healthcare bills.
But groundbreaking medicine to control high blood pressure is in the sights of researchers at Auckland University – and their focus is a little-known organ the size of a grain of rice.
Professor oftranslational physiology Julian Paton has been awarded almost $5 million to investigate the role of the carotid body.
Paton believes the "extremely powerful" organ serves as a sensor regulating the body's response to low blood oxygen by increasing nerve activity that raises blood pressure.
Yes, it's complex stuff – and the five-year project, funded by the Health Research Council, will involve genetics, molecular biology and human patients.
But the results could have a worldwide impact, which explains the close interest of major pharmaceutical company Merck.
"If we could only get a handle on better blood pressure management and then control it more effectively, I think [in New Zealand] we can save the district health boards huge amounts of money in hospitalisations and secondary events," said Paton.
"The hospitals are full of people with things that have occurred as a result of high blood pressure that wasn't detected or wasn't controlled properly."
Worldwide, 1 billion people are affected by high blood pressure – also known as hypertension – and that figure's forecast to hit 1.4b in six years.
Treatment is complicated by the fact it has no symptoms. Even when people are diagnosed - perhaps through a routine check-up at the GP – it's impossible to pinpoint the cause.
Yet hypertension, which disproportionately affects Maori and Pacific people, can have fatal consequences, including heart failure, chronic kidney disease and stroke.
Why? Think of blood flow like the movement of water through a garden hose. By putting your thumb over the end you increase the pressure within the hose but reduce the flow out of the tube.
That means blood flow is reduced and the body needs flow to deliver blood-borne oxygen and nutrients to your organs. With it being reduced, there's a risk of insufficient oxygen, causing organ damage.
Worse still, medicines for hypertension, such as beta blockers, don't always work, and aren't always popular because of side-effects. Even when they reduce blood pressure, they don't necessarily leave it at a safe level, Paton said.
"There are 750,000 people who are hypertensive in New Zealand. Scientific evidence is that 50 per cent of them, even though they are treated, are uncontrolled, so the problem is real and made worse by the law of halves – only 50 per cent of people are diagnosed, of those only 50 per cent are treated and of those only 50 per cent are controlled.
"So if we come up with a new way, even if it only affects 60 or 70 per cent of the population that's huge because the numbers we are dealing with are so massive."
Like stress – believed to be one of its causes – transient high blood pressure isn't always a bad thing. It's one way the body prepares itself for a fight or flight situation, ramping up pressure to feed blood to muscles as you prepare to run from a threat, for example. But in this case, blood pressure returns to safe levels after the event.
Paton's theory is that the carotid body is like a smoke alarm – detecting the threat posed by low oxygen levels and sending chemical signals to the brain and other organs that, in turn, boost flow by increasing pressure.
But sometimes there's a problem with regulation, so the carotid body - you'll find one at the top of each side of your neck - keeps cranking out signals and the pressure stays high.
Removing them altogether – like ripping out the battery when your smoke alarm goes off - isn't the answer; it's thought that would drive an increase in sleep disordered breathing.
So Paton's team, which will eventually number about 10, will seek results to allow the development of a treatment to disrupt the signals.
Professor Julian Paton. Photo / Chris Reed
There's not been a significant new hypertension medicine for almost 20 years. By the end of this programme, researchers will know whether the carotid body is over-active in patients with high blood pressure — a critical first step before testing any new treatment on humans.
With a commitment to racial equity, the work will also consider the role traditional Māori medicines could play in treatment.
The HRC manages government investment in medical research and assesses applications with rigour.
Acting chief executive Vernon Choy said Paton's programme provided a unique opportunity.
"High blood pressure is the biggest risk factor for cardiovascular disease — the leading cause of death globally — and it's clear we don't yet know everything about controlling it.
"This is research that could save lives, improve the quality of life in people with high blood pressure, and dramatically reduce hospital admissions."
Heart Foundation Medical Director Gerry Devlin said hypertension was an important cause of "cardiovascular mortality".
"It is underdiagnosed and poorly managed so any research exploring novel ways to manage high blood pressure, such as Julian's, is welcome."
Paton hopes the work will also influence policy about how blood pressure is measured. Many people are relaxed when tested by a GP but pressure fluctuates according to environment and emotional state, he said.
"I believe we should be measuring not just in the chair but also during exercise, just like the six-minute walk test to assess heart failure."
He's also helped create a hypertension network involving several North Island DHBs and hopes it will be extended to the South Island. The network, which meets quarterly, is the first national forum "talking about blood pressure as a problem in New Zealand".
There are plans for a national hypertension society and Paton hopes GPs will back a push for a specialist hypertension clinic in Auckland, one of the few cities in the world without one.
His funding was part of a $81 million HRC funding announcement.
Tall tale: How giraffes inform research
Giraffes have been around for about 1 million years, about five times longer than humans.
Professor Julian Paton from the University of Auckland believes they could illustrate how evolution has played a part in resistance to complications caused by high blood pressure.
Their long necks mean giraffes' hearts have to pump a heavy column of blood two metres up to their most important organ – their brain.
Yet the blood pressure at the base of their skull is comparable with humans when standing.
That's because arteries in their legs have narrowed to "almost-pinhole size", said Paton, while those in the neck are "wide open tubes", offering the path of least resistance to blood flowing from the heart.
Despite developing ways to generate high blood pressure, giraffes have also found ways to withstand fatal impacts – such as heart attack and stroke - common in humans with high blood pressure.
"I don't think humans have had time to evolve," said Paton. "This could be evolutionary."
