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BABY'S BREATH New treatment guidelines may save lives Dr. Man Yi examines smooth cells from a lung as part of her research. IT'S EVERY PARENT'S NIGHTMARE. A baby is born with persistent pulmonary hypertension, a condition that makes it difficult for the infant to breathe properly. Every year, as many as three per cent of babies in Canada are born with this condition. About a third of these infants will die. "It's not common, but when it happens it is severe," says Dr. Man Yi, a researcher at the Department of Pediatrics and Child Health at the University of Manitoba's Faculty of Medicine. Persistent pulmonary hypertension, or PPHN, usually occurs when a newborn's lungs remain full of fluid, making it difficult for them to breathe. As Yi explains, when babies are still in the womb, their lungs are filled with fluid, and the blood pressure on the right side of the heart, which pumps blood to the lungs, is very high. In the hours right before birth and immediately afterward, the fluid is absorbed by the baby's body and the blood pressure on the right side of the heart normally drops. But due to infection or reasons still unknown, some babies are born with fluid still in the lungs. As a result, the heart struggles to push the blood into the lungs, where it is oxygenated before flowing to the rest of the body. It's not unlike trying to pump air into an already inflated ball. When this happens, the baby's skin turns blue because not enough blood is able to get into the lungs to be oxygenated and then returned to the heart to be pumped out to feed the rest of the body. "If the condition lasts a long time, it can have an effect not only on the lungs and the heart, but also on other organs like the brain." The most common treatment for babies with this condition is to provide oxygen, but no guidelines exist on how much oxygen should be given. Too little can starve the baby's organs of oxygen, but too much can be equally damaging. "There are really no guidelines for how much oxygen we should supply to the baby and how fast we should increase oxygen requirements," she says. "If we're using too much, it may…worsen the baby's condition." Yi's goal is to establish guidelines to ensure babies receive the best treatment. Currently, she is focusing on the role played by smooth muscle cells in the pulmonary artery. When these cells are stressed and constrict, they reduce the blood supply to the lungs. As part of her research, Yi has been working with smooth muscle cells from the lungs of piglets, treating them with different levels of oxygen and measuring the effects. One of the concerns of doctors has been that too much oxygen might actually harm the cells, but her research so far has found that doesn't happen. She has found, however, that high levels of oxygen cause the smooth muscle cells to proliferate – a condition unique to newborns because their bodies are already growing rapidly at a cellular level. This is a normal condition for growth in early life as long as cells proliferate in the right areas. When smooth muscle cells proliferate along the arterial walls, it can lead to potential long-term problems for babies who survive PPHN because the build-up creates an unnatural condition called "remodelling," in which the pulmonary artery's smooth muscle lining thickens and become less elastic. As a result, the child's main artery feeding the lungs is narrowed permanently. Blood flow to the lungs is reduced, increasing blood pressure and potentially leading to lifelong heart problems, she says. If Yi's research can find the right balance of oxygen – not too much or too little – she says they can develop enhanced treatment guidelines that will improve outcomes for the babies who survive PPHN. The guidelines might also help save the lives of the one-third of newborns with the PPHN for whom the condition would have otherwise proven fatal. November/December 2011 25

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