Mountain babies

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McGill Reporter
May 4, 2000 - Volume 32 Number 16
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Mountain babies

There are those who swear that mountain air is good for what ails you. But questions and concerns persist about the long-term effect mountain air has on some of us — most notably, on human fetuses.

| The effect on human fetuses of low oxygen, specifically that experienced at high altitudes, is the focus of a recent research effort led by physiology professor Jacopo Mortola.


As a species, we have evolved to process oxygen at a concentration of 20.9 per cent of the air around us. However, as we climb higher into mountainous terrain, the concentration and partial pressure of oxygen drop accordingly. A state of low oxygen intake, known as hypoxia, results.

How does this affect the fetus, and what are the long-term effects, if any?

For centuries, high-altitude peoples have been aware of the way hypoxia affects uterine development, noticing how their babies tended to be lighter than those born nearer sea level. It is said, notes Mortola, that it took more than 60 years before the Spanish conquistadors, who settled in the Andes, were able to have any full-term babies.

The Andeans themselves, though more accustomed to living high in the mountains, noticed the prevalence of their own low-weight babies and realized the best way around the problem. To this day, expectant mothers try to travel to lower elevations prior to giving birth, and stay there for as long as a year thereafter.

The whole notion of hypoxia intrigues Mortola. "[We want to know] how the body adapts to the situation [of hypoxia] and how it should adapt and why it doesn't adapt in many cases of people, [who are] hypoxic without going to high altitudes," said Mortola. These people include cardiac patients, smokers, and victims of respiratory distress.

Mortola was fortunate to come across a "natural lab" in an area of Peru. A series of villages dot a 300-km stretch of road, which snakes up from Lima at sea level to Cerro de Pasco, a town of 70,000 inhabitants, at an elevation of 4,330 m.

At each stop along the way, he made correlations between average birth weights and altitude. He found there was a threshold: up to the 2,000-m level, little variation occurred; above that, he observed a 63-gram drop in birth weight per 500 m rise in elevation.

Since natural populations (human as well as animal) vary a great deal, Mortola had to be sure that other factors, such as diet, were not influencing these discrepancies. He wanted to know if "hypoxia, per se, affects fetal growth and birth weight." Again, he found a ready-made laboratory set-up.

In Cerro de Pasco, a mining town, the inhabitants were served by two hospitals, one for the rich (mining executives and their families, for instance), the other for the poor miners and their families.

Although these two groups were obviously distinct in terms of medical care, diet, hygiene and so on, the average birth weight of their babies was "identical." Therefore, Mortola was able to draw a direct link between high-latitude hypoxia and low birth weight.

Why would hypoxia compromise development? The reason is that the body tries to adapt to oxygen restrictions by allocating resources preferentially. The major organs, such as the brain, heart and lungs, continue to benefit from adequate blood flow at the expense of other parts of the body — skin, muscles, bones — which receive less.

"The result is that the fetus is, first of all, small ... but also uneven," said Mortola.

Another adaptation to an oxygen-poor environment is to decrease body temperature. This "mini hibernation" resembles the way a mouse sleeping through the winter shuts down its metabolism. In the human infant, it's called "hypoxic hypometabolism."

The most encouraging aspect of this work on babies is the way even those with an initial disadvantage can catch up — as soon as the proper concentration of oxygen is resumed. Somehow, the body knows how to accelerate growth until some baseline has been reached. This phenomenon also has been seen in "blue babies," neonates that experience hypoxia due to heart defects or birth trauma; they, too, can catch up miraculously when their breathing returns to normal.

But, warns Mortola, children born with developmental and health problems as a result of hypoxia who remain at low-oxygen altitudes are at greater risk for a number of health woes, including blood disorders, heart and lung dysfunction, and, ultimately, a tendency toward shorter life spans.

For the record, Mortola believes the Andeans have the right idea when it comes to their children. Let Julie Andrews "climb every mountain" to her heart's delight. But if you can, bear your babies at lower altitudes.

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