Pulmonary Hypertension and Nitric Oxide

Pulmonary hypertension (PH) is characterized by high blood pressure in the pulmonary arteries. These vessels, which are responsible for transporting the blood from the right heart ventricle to the lungs, become narrowed and thickened as a result of the disease. As a result, the heart needs to work harder to pump the blood, which results in weakening and enlargement of the heart, and may cause right heart failure.

There is currently no cure for pulmonary hypertension, but there are treatments approved by the U.S. Food and Drug Administration (FDA) that help ease the symptoms and increase both life expectancy and quality of life. In addition to the drugs, there are life style alterations and other therapies that may be recommended to patients who suffer from the disease. Among them is nitric oxide, which is specifically formulated for pulmonary hypertension treatment, and has been shown as a viable option for patients in research.

What Is Nitric Oxide?

Nitric oxide, also known as nitrogen monoxide, is a gas discovered by the chemist and theologian Joseph Priestley in 1772, and recognized as an important endothelial-derived vasodilator molecule in 1987. The gas is produced by the human body and is composed of one atom of nitrogen and another of oxygen. It is included in the limited group of gaseous signaling molecules, which means that it enables communication between the cells and is involved in the regulation of physiological and pathological events like cell growth, differentiation or functioning.

Since learning that nitric oxide works as vasodilator, researchers have been focused on its applications and therapeutic potential. Nitric oxide is able to function as a selective pulmonary vasodilator, which means that it is able to improve oxygenation. Since the gas has a very reduced life, its effects are often limited to the lungs. However, studies have demonstrated its encouraging impact on numerous medical conditions, including pulmonary hypertension, congenital heart disease, mitrial valvular disease, and in orthotropic cardiac transplantation patients.

How Can Nitric Oxide Help PH Patients?

Nitric oxide has been used as a long-term therapeutic option for patients with pulmonary hypertension in the United States since 1999, when it was approved by the FDA. By inhaling the gas, it rapidly diffused through the alveolar-capillary membrane and pulmonary arteries muscles, causing an increase in the concentration level of intracellular cGMP and an activation of the soluble guanylate cyclase. Due to this effect, the muscles become more relaxed, enabling a more fluid blood flow from the heart to the lungs.

The study “Nitric oxide and pulmonary hypertension” published in 2010 reaffirmed nitric oxide’s ability to modulate vascular injury and interrupt the elevation of pulmonary vascular resistance selectively. For patients undergoing mechanical ventilation, the gas is administered through an artificial ventilation system with desired flow-rate after regulation of pressure, while patients without tracheal tubes are administered the gas through an oxygen mask or hood.

However, the research also notes the potential harmful effects of pulmonary hypertension treatment with nitric oxide. “It can also produce cytotoxic oxygen radicals and exert cytotoxic and antiplatelet effects. The balance between the protective and adverse effects of nitric oxide is determined by the relative amount of nitric oxide and reactive radicals,” as explained in the study. Therefore, during administration of nitric oxide, the levels of gas and expiratory gas flow should be monitored with an electrochemical analysis machine.

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