Breath Taking. Michael J. Stephen
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Thomas Wright, William Harvey: A Life in Circulation (Oxford, UK: Oxford University Press, 2013), xvii–xxi.
33. David G. Ashbaugh, D. Boyd Bigelow, Thomas L. Petty, et al., “Acute Respiratory Distress in Adults,” Lancet 290, no. 7511 (August 12, 1967): 319–323.
34. Giacomo Bellani, John G. Laffey, Tai Pham, et al., “Epidemiology, Patterns of Care, and Mortality for Patients with Acute Respiratory Distress Syndrome in Intensive Care Units in 50 Countries,” JAMA 315, no. 8 (2016): 788–800.
35. Roy G. Brower, Michael A. Matthay, Alan Morris, et al., “Ventilation with Lower Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Lung Injury and the Acute Respiratory Distress Syndrome,” New England Journal of Medicine 342 (May 4, 2000): 1301–1308.
36. Michael A. Mathay, Carolyn S. Calfee, Hanjing Zhuo, et al., “Treatment with Allogeneic Mesenchymal Stromal Cells for Moderate to Severe Acute Respiratory Distress Syndrome (START Study): A Randomised Phase 2a Safety Trial,” Lancet Respiratory Medicine 7, no. 2 (February 2019): 154–162.
37. John B. West, “How Well Designed Is the Human Lung?” American Journal of Respiratory and Critical Care Medicine 173, no. 6 (2006): 583–584.
38. Adrian Bejan and Eden Mamut, Thermodynamic Optimization of Complex Energy Systems (Dordrecht, NL: Springer, 1999), 71.
Chapter 3
An Infant’s Drive to Breathe
The lungs not only facilitated the beginning of terrestrial life on this planet, they also facilitate the beginning of our individual lives. During the final trimester of pregnancy, the lungs are the only organ in the fetus that is not working. The heart is beating away at a fiery 160 beats per minute, the kidneys are making urine, with the baby peeing right into the amniotic fluid (which is then swallowed again by the baby in a repeating cycle). The brain and muscles are awake with kicks and backflips and rolls. But the lungs remain completely silent and nonfunctioning.
This all changes, and abruptly, when the baby emerges from the womb. The lungs must turn on in an instant in order to begin their job of oxygen extraction and carbon dioxide release. To measure the success of this change, all hospitals throughout the world use what is called the APGAR score, named after the distinguished professor of surgery from Columbia University, Virginia Apgar. The first woman to attain full professorial status at Columbia’s medical school, Dr. Apgar devised this beautifully simple and elegant way to assess the health of a newborn in 1953.
At one and five minutes after birth, the Appearance, Pulse, Grimace, Activity, and Respiration are assessed, and a score of 0, 1, or 2 is recorded for each, for a maximum of 10. The majority of babies easily achieve a score of 8 or 9. The purpose of the APGAR score is to identify babies at immediate risk and to take proactive measures to improve whatever deficiency is present. This could mean just agitating the baby until he or she wakes up, or it could mean giving more oxygen or inserting a breathing tube into the lungs. Sometimes in medicine inaction is preferable, along the lines of “First do no harm.” A low APGAR score is not one of these times. A newborn scored at 6 or 7 will usually improve on her or his own. A score under 5 is panic time.
The APGAR score reflects, on the most basic level, the ability of the lungs, heart, brain, and muscles of the chest to appropriately make the lightning jump from living in fluid to living in air. But of these four systems, the lungs have by far the most work to do, because in utero they are like a soaked sponge, filled with the mother’s amniotic fluid. The fetus’s source of oxygen is the placenta, that radiant red jellyfish-like structure that is expelled after birth. The placenta neatly takes oxygen-rich blood from vessels imbedded in the uterus and channels it to the fetus through the umbilical vein.
Once in the umbilical vein, the blood travels through a series of open ducts, one through the liver and another through the right to the left side of the heart, to ensure that the dormant lungs are bypassed. The blood then goes out the left side of the heart to the aorta, where it feeds the organs. The tissues expel the oxygen-depleted blood back into veins, where it ultimately travels back into the mother’s body through the umbilical artery.
The free oxygen ride must come to an end, and it does so dramatically at birth. In an instant, the ducts through the liver and heart close, shunting blood to the lungs to pick up oxygen. The brain must simultaneously start firing signals to the muscles of inspiration. The eyes must open and adjust to the harsh light of the world. Finally, the lungs, still filled with amniotic fluid, must inflate in an instant with the first breath of life. The alveoli pop open for the first time and, with that first deep breath, suck the fluid up and immediately begin extracting oxygen from the atmosphere. The lungs change from being water-filled to being air-filled, from being dormant to extracting oxygen, all in the first few seconds of life.
Unfortunately, for some babies this leap from in utero to living in the atmosphere is not without significant complications. I experienced this firsthand one day. On a brutally hot day in late spring, I drove frantically to the hospital in dense Philadelphia traffic with my very pregnant wife. Adding to the discomfort, my wife was intermittently squeezing the blood out of my arm in retaliation for the contractions in her belly.
We drove right up to the hospital and gave the attendant my key. A man instantly emerged with a wheelchair, and we were whisked up to the preadmission area for pregnant patients. A nurse in bright-green scrubs immediately and unceremoniously put a glove on her hand and inserted it into my wife. “You’re almost completed dilated,” the woman said. “We need to get you into the delivery room. Now!”
Our hearts started racing as we instinctively clutched each other’s hand. The nurse left, but not for long, and when she came back, she was accompanied by a horde of other hospital workers. With mechanical efficiency, one of them jabbed my wife’s arm for an IV line, another thrust a blood pressure cuff around her bicep, and a third strapped a monitor onto her belly to measure the baby’s heart rate. Then she was quickly moved to the delivery room, up onto the bed, and into position.
“What about my epidural?” my wife asked, squeezing my arm again as another harsh contraction pulsed through her. The doctor came in, young and fresh-faced, in blue scrubs and blue hat. She nodded at us and then studied the baby’s heart rate on the monitor. It had dipped down with the contraction, which was normal enough, but it was going too low, and staying too low for too long. After a long spell of slow, low-pitched, tortuous beeps, the pinging of the heart rate on the monitor resumed its brisk pace.
“Listen, there’s no time for an epidural. You need to get this baby out. He’s ready. Your body is ready. We need to do this.”
“You’re sure?” My wife looked anxiously around, stressed by the prospect of more pain.
“Yes, quite sure,” the doctor responded evenly. “We need to get this little guy out. There’s something irritating him in there. His heart rate is intermittently dropping too low. Way too low. He needs to come out now.”
Wild thoughts entered my head. He was a few days early, and now his heart rate was sporadically bottoming out. Questions about whether this would affect his brain, and whether his lungs would be ready to wake up and answer the call of terrestrial life, entered my head.
For the next fifteen minutes, my wife’s contractions came and went. With each one, the little guy’s heart rate dipped too low and for too long. But it always came back up, granting us some feeling that everything was okay.
Finally, in response to one long, very painful contraction and a lot of pushing, the baby’s head appeared in the canal, his hair all curly and slimy. “Okay, let’s do it on the next one,”