By Wendell Roelf

CAPE TOWN (Reuters) - Wheelchair-bound athletes could face tougher checks at next year's Rio Paralympics to stop them risking their health by sitting on their scrotums, or clamping off catheters to fill their bladders, in order to boost adrenaline and performance.

Officials said on Tuesday the International Paralympic Committee is reviewing guidelines against "boosting", a practice employed by some athletes with spinal cord injuries.

Banned for more than a decade, it does not use any artificial stimulants. Instead, it involves tricking the brain into triggering "autonomic dysreflexia" (AD), causing the body to flush with adrenaline to achieve more power and greater oxygen uptake during races.

Squeezing the scrotum or filling and then tapping the bladder are the most common external stimuli to induce AD, resulting in elevated heart rates and blood pressure.

Research shows deliberately induced AD can enhance athletic performance by as much as 10 percent, especially in endurance events such as long-distance wheelchair races.

But it can also raise blood pressure to dangerously high levels, leading to strokes and even death. Besides athletics, authorities are also monitoring hand-cycling, rowing and wheelchair rugby.

"The problem with the pathology of a spinal cord injury is that this response is deviated to the cardio-vascular system, including hypertension and increased heart rate," IPC medical and scientific director Peter Van de Vliet told Reuters.

"About 30 to 40 out of 4,300 athletes for Rio are vulnerable to this mechanism," he said in a telephone interview.

STRETCHING BOUNDARIES

The Paralympic movement has largely escaped the drugs scandals that have tainted able-bodied athletics. Revelations of state-backed doping among Russian athletes are the latest in a string of high-profile disclosures to hit the sport.

But with the Paralympic Games in Rio de Janeiro aiming to cement its position as a major global sporting event, the movement is strengthening its defenses against cheating.

"The profile of Paralympics sports has increased and that carries with it an intrinsic risk that people will try to stretch boundaries, by means of technology, by means of unauthorized substances and whatever is humanly possible," Van de Vliet said.

He said the IPC is considering plans to lower the 180 mm of mercury threshold it uses in a standard blood pressure test to detect boosting.

"We now have the data and it shows the majority of athletes are way below 180 mm," Van de Vliet said of a testing and education program in place since the Beijing Games of 2008.

If an athlete’s blood pressure is over 180, they are given 10 minutes to cool off before another pre-race test. The normal blood pressure during a rest period for high spinal cord-injured athletes is around 100 over 60 or 90 over 60.

Imposing a lower threshold could detect more boosters and have a deterrent effect, said Van de Vliet, adding that no athlete has so far ever been handed the minimum two-year sanction.

However, this could change should the new rules be adopted, he said. Most of the IPC’s doping sanctions, which include life bans, involve athletes competing in power-lifting.

“People think that the Paralympics is a more benign version of the Olympic Games and that it is not as pointed, as targeted and as fierce," said Wayne Derman, the IPC’s chief medical officer at October’s Doha championships.

"That is such a wrong misconception," he said.

(Reporting by Wendell Roelf; Editing by Ed Cropley and Mark Trevelyan)