Children born to mothers diagnosed with pregnancy-induced high blood pressure may face a higher risk of developing pulmonary hypertension later in life. So concludes research from Europe released at a medical conference in California early this month.1 These children may have a higher risk of being diagnosed with a form of the illness known as hypoxic pulmonary hypertension, in which blood is not being oxygenated even though it is circulating normally throughout the body.
PH at High Altitude
Hypoxic pulmonary hypertension can often occur at high altitudes when lower air pressure makes it harder for the lungs to absorb the lower amounts of oxygen. As a result, the pulmonary arteries tighten in their effort to direct blood to places in the body where there might be oxygen.2 In people living in high altitudes, a condition known as pulmonary edema (eh-DEE-muh) can occur, caused in part by dysfunction of the blood vessels in the lungs. Thus, PH can develop as affected individuals move to higher altitudes. But this form of PH can be reversed once a lower altitude is reached.
Pulmonary hypertension itself is a rare blood vessel disorder in which the blood pressure in the pulmonary artery leading from the heart to the lungs rises to abnormal levels. This resistance places an abnormal strain on the right side of the heart, and can potentially lead to right-heart failure. Common treatments include calcium channel blockers, prostacyclin, endothelin receptor antagonists (ETRAs), lung transplantation, or pulmonary thromboendarterectomy.3 It's estimated that primary pulmonary hypertension, occurring in the absence of a known cause, occurs in about 2 people for every 1 million each year.4
First Clues About Preeclampsia
According to the team of investigators who took part in the research, the study provides the first hints that high blood pressure that can occur in pregnancy known as preeclampsia (pree-eh-KLAMP-see-uh) can potentially create a physiologic change in the pulmonary circulation of a developing fetus.
"In preeclampsia, the diseased placenta releases circulating vasculotoxic factors that cause maternal endothelial [interior blood vessel lining] dysfunction," wrote Pierre-Yves Jayet, MD, a research fellow at University Hospital in Lausanne, France, who led the analysis. "These factors may pass the placental barrier and leave a persistent vascular imprint that may predispose to a pathological response in later life."
The study also involved doctors in La Paz, Bolivia, the highest major city in the Andes mountains at 12,000 to 13,000 feet. As a result, the research team was familiar with a form of high-altitude pulmonary edema that occurred in high-altitude natives when they returned from trips to lower altitudes.
While the exact cause of the "re-entry" pulmonary edema was not known, the researchers speculated that the natives who were susceptible to the condition when they returned to higher elevations had a type of pulmonary vessel dysfunction that is also seen in classical high-altitude pulmonary edema that leads to exaggerated pulmonary hypertension as affected individuals climb higher. When they compared the pulmonary blood pressures of those susceptible to the condition to those who were not, they found significantly higher pressures in the susceptible group. They also unexpectedly discovered that a significant percentage of the susceptible natives had been born to mothers diagnosed with preeclampsia during their pregnancies.
The latest study was an attempt to confirm the finding. Using echocardiography, the investigators measured systolic pulmonary artery pressure in a small group of 11 children from La Paz whose mothers had had preeclampsia. The test results were compared with those of children whose mothers had no preeclampsia during their pregnancies. The investigators found that the pulmonary artery pressures of the children born to mothers with preeclampsia were 33% higher compared to the other children.
Answers Remain Elusive
What causes this resulting pulmonary hypertension in the children? Jayet says that will be the focus of future research. He believes that determining the cause will likely lead to new ways to prevent and treat primary pulmonary hypertension, and perhaps other similar ailments.
The increased susceptibility to high-altitude PH of children born to mothers previously diagnosed with preeclampsia may have distinct implications for people at any altitude, explained Urs Scherrer, MD, a researcher in whose lab at University Hospital in Lausanne some of this study's work was conducted. Just as the low oxygen levels at high altitudes can trigger a response in these children, so may sustained lack of oxygen in the circulating bloodstream affect patients experiencing other forms of heart or lung disease, he said.
"These findings provide the very first evidence that preeclampsia leaves a persistent and potentially fatal imprint in the pulmonary circulation of the offspring, which predisposes them to exaggerated hypoxic pulmonary hypertension in later life," wrote Jayet and his team.
1. 1. Jayet PY, Thalmann S, Stuber S et al. Offspring of preeclamptic mothers are predisposed to hypoxic pulmonary hypertension. Experimental Biology 2005. 2005 Apr 2-6. San Diego, CA.
2. Boyer Hayes G. Living Too High: Altitude & PH. In: Pulmonary Hypertension. A Patient's Survival Guide. 3rd ed. Silver Spring, MD: Pulmonary Hypertension Association;2004:55-6.
3. PHCentral. What is Pulmonary Hypertension? Available at: http://www.phcentral.org/info/about.html. Accessed March 31, 2005.
4. Pulmonary Hypertension Association. What is PH? Available at: http://www.phassociation.org/Learn/What-is-PH/index.asp. Accessed March 31, 2005.
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.
