The Story of Surfactant

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Clement Smith's lab group at the Boston Lying-in Hospital, 1959

In the late 1950s, Mary Ellen Avery was a research fellow in Jeremiah (“Jere”) Mead’s lab at Harvard School of Public Health, with Clement Smith as her clinical supervisor. She was working nights in the delivery room at the Boston Lying-In, where she saw many premature babies with hyaline membrane disease (now called respiratory distress syndrome, or RDS) struggle to breathe. She had access to the lungs of babies who died of RDS, and noticed that these babies had no residual air in their lungs at autopsy – as though they’d been unable to keep the air spaces in their lungs open. Having read in her studies that lungs are able to retain air due to low surface tension, she wondered if the surface tension in the lungs had something to do with it.

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Letter to John Clements, 1958

Avery was inspired by a 1957 article by John Clements which examined the effects of nerve gases on the lungs by measuring surface tension. Clements used a modified Wilhelmy balance, a device that has been around since the late 1800s, to measure surface tension in the lungs.  Avery soon visited Clements at the U.S. Army Chemical Center in Edgewood, Maryland, to learn how to build her own version of the device.

In a letter to Clements in 1958 (pictured at right), Avery said:

"As I expect you have heard, I have been pecking away at surfaces this summer. The results are fun (Jere's word is spurious), but at any rate, I would like to talk with you about them."

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Letter from Avery with sketch of Wilhelmy balance, 1959

Using their handmade balance, Avery and Mead measured surface tension in the lungs of babies that had died of RDS, and found that surface tension was low due to the lack of a foamy fluid – surfactant - found in the lungs of healthy babies. Essentially, premature infants suffering from RDS could take their first breath and exhale, but because their underdeveloped lungs lacked surfactant, their alveoli would collapse entirely, making it much more difficult to inhale again. Avery and Mead published their findings in American Journal of Diseases of Childhood in 1959, though it took some time for these findings to fully catch on. There were many competing theories as to the cause of RDS, for instance, many thought it had to do with pulmonary circulation.

The Story of Surfactant