It is one of the erectile dysfunction drugs that are used to treat right-heart hypertension. By Michael Lim

WHILE most of us are familiar with the kind of high blood pressure (hypertension) that imposes stress on the left heart chambers, there is another kind of hypertension which involves only the right heart chambers, termed pulmonary arterial hypertension or PAH.

PAH is usually seen in those with severe lung disease (often related to smoking), but may sometimes exist without any underlying disease.

Blue in the face

Last week, as Mr A, who is in his late 50s, walked into my clinic, he looked blue in the face. A smoker with chronic lung disease, he was huffing with the effort.

His long-standing lung disease had resulted in constriction of the vessels in his lungs, thereby increasing the resistance to the flow of blood being pumped from the right side of the heart through the lung artery (pulmonary artery) into the lung vessels, where oxygen is to be absorbed and carbon dioxide, removed.

This increased resistance to the flow raised the blood pressure in the right heart chambers, resulting in right-heart high blood pressure or PAH.

This week, Madam B , who was in her early 30s, came for a review of her heart condition as she was pregnant.

Four years ago, when she delivered her first child, she was diagnosed to have severe PAH, with a right heart pressure five times the upper limit of normal. With appropriate treatment, her severely swollen right heart chambers had returned to normal and her right heart pressure, to two times the upper limit of normal.

The difference between Madam B and Mr A was that Madam B had “primary” PAH, a primary lung arterial disease not due to other diseases; Mr A had “secondary” PAH from his underlying chronic lung disease.

They were both put on drugs primarily used for men with erectile dysfunction (ED), the condition under which a man is unable to maintain an adequate erection for sexual intercourse.

ED drugs for the heart

Currently, the ED drugs available include sildenafil citrate (also known as Viagra), tadalafil (Cialis) and vardenafil (Levitra).

They act by inhibiting the enzyme cGMP-specific phosphodiesterase type 5 (PDE5), which breaks down a chemical, c-GMP, which relaxes the walls of blood vessels.

With the PDE-5 enzyme blocked, c-GMP accumulates, increasing the size of the vessels and lowering resistance to blood flow, thus lowering right heart pressure.

Since PDE-5 is found mainly in the walls of the arteries in the lungs and penis, the effect of ED drugs are primarily in these two areas.

Studies have shown that the use of ED drugs in those with PAH is associated with an improvement in exercise tolerance and a reduction of pressure in the right heart chambers.

A few days after starting Mr A on ED drugs, his right heart pressure dropped from three times the upper limit of normal to two times the upper limit of normal. Some studies have also suggested that these drugs may also have a beneficial effect of reducing the likelihood of the progression of PAH.

Beyond the heart

Interestingly, ED drugs have also been found to be beneficial in other conditions.

For those who engage in climbing at high altitudes, a syndrome called high-altitude pulmonary oedema (HAPE) can occur shortly after ascent; this is an abnormal constriction of the lung arteries as a response to low oxygen levels at high altitudes in susceptible individuals.

It is a dreaded complication, accounting for most high-altitude deaths. Studies published by Richalet in 2004 and Fagenholz in 2007 have shown that ED drugs, in particular Viagra, were shown to protect against the development of HAPE and was beneficial for the treatment of HAPE.

Caution

Before smokers with damaged lungs and exertional breathlessness think that ED drugs are a panacea for their condition, they should be aware that ED drugs are not without their side effects.

These include headaches, flushing and nasal congestion. Users of Viagra may complain of a tinge of blue in their vision. Rare but serious adverse effects include visual impairment and sudden hearing loss.

Although Viagra consumption was reported by McGwin in 2006 to be associated with a rare visual impairment termed non-arteritic anterior ischemic optic neuropathy, this was not reported when used in PAH studies by Galiè and Machado in 2005.

Not all smokers with bad lungs may find relief in Viagra. While Madam B who had primary PAH showed significant improvement with Viagra, not all patients who develop PAH as a result of severe lung disease may benefit. For Mr A, who has had to curtail his daily activity significantly and requires oxygen daily, ED drugs present an opportunity to alleviate his symptoms and improve his quality of life.