At Hospital, Body Rhythms Often Broken
Years ago, it used to be standard practice for hospital nurses to leave bright lights on all the time in neonatal intensive care units because it helped the staff better attend to premature infants’ urgent medical needs. Over the years, though, researchers found that constant light was stressful for preemies, so many NICUs switched to near-darkness, aiming to mimic the darkness of the womb.
A provocative study published recently in the Journal of Pediatrics suggests a new approach: cycled light, or normal indoor lighting during the day and darkness at night, the better to replicate the day-night rhythms of the real world. Duke University researcher Debra Brandon monitored 62 babies born at least 10 weeks prematurely and weighing, on average, 2 pounds. Brandon, an assistant professor of nursing, randomly assigned the infants to three groups with different lighting conditions. She found that those exposed earlier to cycled light grew faster--at least 23 grams more per week--than those who got cycled light near the end of their hospital stay.
The Duke study is encouraging to scientists who study circadian medicine, a fledgling field of research that deals with the role that natural biological rhythms play in people’s health.
Dr. Charles Czeisler, chief of sleep medicine at Brigham and Women’s Hospital in Boston, says Brandon’s study is “exciting” because many hospitals still act as though “circadian rhythms don’t represent a biological need.”
“Hospitals aren’t organized to take into account the body’s time structure,” agrees Michael Smolensky, professor of environmental physiology at the University of Texas School of Public Health in Houston. “Studies like this are a wake-up call.”
Getting hospitals to respect the basic rhythms of the body is no easy task. Some patients still say that they are awakened in the wee hours for CT scans, not because of an emergency, but because that is when the busy machines are available. It’s also routine to wake patients before dawn to draw blood, not because that’s a good time for them but because it’s convenient for doctors to know the results early in the morning. Moreover, hospitals often try to wean patients from ventilators in the early morning, just when the biological rhythms that support respiratory drive are at their lowest.
Things can be even worse in intensive care units, where patients obviously need the most monitoring--but also need their sleep. Many hospitals do try to keep ICUs dark at night, says Maureen Harvey, a nurse who is president of the Society of Critical Care Medicine. Yet it’s at 5 a.m. “that everything happens: Patients get their EKGs, they get their labs drawn, X-rays, they get weighed, bathed.... It’s ridiculous.”
Basic Part of Biology
Scientists have known for years that circadian rhythms are a basic part of biology. Indeed, most creatures on Earth have an internal “clock” that governs circadian (literally, “about-daily”) rhythms. This suggests that since the early days of evolution, there has been a clear survival advantage to synchronizing an animal’s internal, chemical life to the light-dark rhythms of the outside world.
“You can live without a ‘clock,’ ” the structure in the brain that controls circadian rhythms, says Dr. Stephen Reppert, professor of neurobiology at the University of Massachusetts Medical Center. And some laboratory animals that have had this part of the brain destroyed do fine in the lab where food is plentiful and predators are not. In the wild, however, losing circadian rhythms could be fatal.
In people, at least those who work during the day and sleep at night, body temperature fluctuates according to circadian rhythms, rising in the morning, decreasing at night. Hormonal secretions follow daily rhythms, too.
Cortisol, a major stress hormone, kicks in dramatically at dawn to prepare the body for daytime activity and drops in the evening. Other hormones, such as melatonin and prolactin, kick in during sleep.
Medical conditions also show circadian patterns. Heart attacks and strokes are most common in the morning, when blood pressure and heart rate begin to rise. Asthma is often worse at night, when airways tend to constrict.
In humans and many other animals, the job of keeping the body’s natural rhythms in sync with night and day in the outside world falls to a small cluster of nerve cells called the suprachiasmatic nucleus, often called SCN, which lies in a part of the brain called the hypothalamus. The SCN functions as a master clock that, using chemical messengers and neural connections to other parts of the brain, keeps the body in harmony with night and day.
How It All Works
Details have been emerging rapidly in the last five years, and here’s how scientists now think it all works.
When light comes in through the eye and falls on the retina, a specialized pigment called melanopsin in photoreceptor cells is activated, says Fred Davis, a biologist at Northeastern University in Boston. This, in turn, causes nerves to fire, transmitting a signal to the SCN, which lies just at the point where optic nerves from the two eyes cross. The SCN then releases a chemical signal (glutamate), which acts on one or more “clock” genes in the nucleus of SCN cells.
So far, scientists have found at least eight such genes, giving them names like “clock” and “period.” Through a complicated feedback system, the “period” gene, for instance, turns itself on and off rhythmically all day, even in the absence of light, Davis notes. But when it’s in an “off” cycle, if light triggers the SCN, the cycle is speeded up.
Light, in essence, resets the SCN clock so that biological rhythms are in sync with the light-dark rhythms of the outside world. The fact that nature has gone to such trouble to keep the body’s cells and organs in sync with day and night strongly suggests that doctors and hospitals should, too.
For one thing, drugs can have different effects at different times of day and night, notes Smolensky, of the University of Texas. In studies of rodents and people, for instance, the antibiotic gentamicin has been shown to have more adverse effects on hearing and kidney function at night.
On the other hand, chemotherapy drugs for colon cancer such as 5-FU (fluorouracil) and leucovorin cause fewer side effects if given during the night. Some blood pressure-lowering drugs have different effects depending on whether they are taken in the morning or at night. Some cholesterol-lowering drugs must be taken in the evening for maximum effect.
Basic sleep-wake cycles can become disturbed, too, when hospital schedules disrupt circadian rhythms. It’s long been known, for instance, that ICU patients can become confused when they don’t get normal light-dark signals.
Even when it’s impossible to put a window in an ICU room, there are ways to increase patients’ awareness of day-night rhythms, says Donald Axon, an architect in Laguna Niguel who designs ICUs. Some hospitals, for instance, install special lighting on pictures for patients’ walls so that the light gets brighter during the day and dimmer at night.
Many routines in hospitals can’t easily be changed, especially in ICUs for adults and preemies, the sickest and most fragile of patients. But the more patients can be kept on normal day-night cycles, the better, says Duke University’s Brandon. Lighting, she says, is “the most practical time-of-day cue we can provide.”
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Judy Foreman is a lecturer at Harvard Medical School. She can be reached by e-mail at judyforeman@attbi.com.
