A new imaging technique to better understand the changes that occur in the pulmonary arteries of people with pulmonary hypertension (PH) may soon be available to doctors diagnosing the disease. It's described in a study paper in the December issue of the Journal of Applied Physiology.1
Peering Into the Lungs in a New Way
In their paper, Robert Molthen, PhD, an assistant professor of Medicine at the Medical College of Wisconsin and his colleagues describe the use of micro-computed tomography, a high-resolution form of computed tomography (CT) imaging to capture and document the three dimensional structure of the pulmonary vessels. It allows doctors to better understand the course of pulmonary hypertension.
"Our broad focus is on the structure/function relationship in the pulmonary circulation, with a goal of better understanding the causes, progression and impact of the vascular remodeling process," Molthen explained. Vascular remodeling is the medical term used to describe the pathological changes that occur in the pulmonary blood vessels as a consequence of pulmonary hypertension.
In their study, the researchers at the Medical College of Wisconsin, Marquette University and the VA medical Center-Milwaukee assessed the impact of animals kept in an environment with just 10% oxygen on the changes in the structure and function of their pulmonary arteries, and the role these changes play on the course of PH. (Oxygen is normally found at about 21% in the surrounding environment.)
This was done to mimic the decreased level of oxygen in the blood that is characteristic of pulmonary hypertension.
Reduced Oxygen and Vascular Changes
After 3 weeks of living in a oxygen-depleted environment, the rodents had reductions in the total length and branches detected in their pulmonary artery trees. These rats were compared to a second group of mice that had received normal oxygen, and the researchers found that those in the latter group had no reduction.
Additionally, the pulmonary arteries in the rats raised in a low-oxygen environment were much stiffer than in those receiving normal levels of oxygen, a change that usually results in a significant increase in pulmonary artery pressure.
Molthen's group used the high-resolution CT imaging successfully to view these changes.
The Pathology of PH
Pulmonary hypertension is a rare lung disorder in which the blood pressure in the pulmonary artery rises far above normal levels. The pulmonary artery is designed to carry oxygen-poor blood from the right ventricle of the heart to the lungs. That's where the blood picks up oxygen, and then flows to the left side of the heart, and finally, to the rest of the body.
Experts believe one of the ways PH begins is with injury to a layer of cells that lines the small blood vessels of the lung. This injury somehow changes the way the cells interact with smooth muscle cells. The smooth muscle cells, in turn, contract more than normal, and thus narrow the vessel. The process results in the development of extra amounts of tissue in the pulmonary arteries. The amount of muscle increases in some arteries, and muscle abnormally appears in the walls of arteries that usually have none. (The vascular remodeling mentioned earlier.) In time, the arteries become scarred (fibrotic), and eventually, stiff and thickened as a result.2
"In rats, various stimuli, such as exposure to lower-than-normal oxygen levels, as experienced when living at higher altitudes or with chronic obstructive pulmonary disorders [COPD], or exposure to certain toxins/drugs or blood-borne metabolic wastes, can lead to progressive pulmonary vascular remodeling, heart failure, and death," said Molthen.
1. Molthen RC, Karau KL, Dawson CA. Quantitative models of the rat pulmonary arterial tree morphometry applied to hypoxia-induced arterial remodeling. J Appl Physiol 2004 Dec;97(6):12372-84.
2. Parker JN, Parker PM. The Official Patient's Sourcebook on Primary Pulmonary Hypertension. San Diego:ICON Health Publications;2002.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include coverage of health news for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
