Math model to help plan sleep cycles

By Ivana Susic

According to the Better Sleep Council Web site, 32 percent of Americans are losing sleep at least once per week. This lack of sleep or failure to establish a set sleep pattern can throw the body out of order and affect many facets of health, such as alertness or disease susceptibility.

In early April, researchers funded by the National Space Biomedical Research Institute, or NSBRI,  developed mathematical software to help astronauts adjust to changing sleep and work schedules. These models can also be adapted to people who work rotating shifts, such as doctors and nurses, those who work night shifts or those who constantly travel and battle jet lag.

The body’s perception of time—its time clock or circadian rhythm—runs on a 24-hour system. The longer people are awake, the more tired they are likely to feel. When an individual must constantly try to adjust to different schedules, it is extremely difficult for the body to keep up and run smoothly, physically or mentally.

Dr. Elizabeth Klerman, associate team leader for NSBRI’s Human Factors and Performance Team, associate professor at Harvard Medical School and a physician in the Division of Sleep Medicine at Brigham and Women’s Hospital in Boston, said the model is used to show the discrepancy between how alert people think they are versus their actual expected performance.

“The model should be applicable toward truck drivers, [those who work] security jobs or anyone working long hours,” Klerman said. “One goal is to be able to use it anywhere.”

One reason it is important to make the software available to everyone is because people whose performance can suffer due to lack of sufficient sleep can affect others, Klerman said. Safety and productivity are issues that affect more than the tired individuals who may not even realize their performance ability has declined.

“These people are interacting with the rest of the world,” Klerman said. “I’m affected by your job.”

Klerman explained the model is based on decades of research on sleep and circadian rhythm, experimenting with how healthy individuals react to shifts in their sleep and wake times, and how this affects factors such as alertness and hormone levels. This data was used to create the software’s existing model.

According to Rachel Leproult, research associate for the Endocrinology, Diabetes and Metabolism Department of Medicine at the University of Chicago, physiological changes such as impairment in metabolism can occur from sleep deprivation. If the metabolism doesn’t operate normally, obesity or cardiovascular diseases may occur.

Kathryn Reid, a research assistant professor of neurology at Northwestern University’s Feinberg School of Medicine, said some people may be flexible in their sleep and wake cycles and suffer little harm. When people disrupt their sleeping cycle, the body does not know when it’s supposed to be awake or feel tired, Reid explained.

“[Our body] clock regulates bodily functions; how we feel, perform, reaction time, attention [and] memory,” she said.

This internal clock provides an “alerting signal” that is regulated by the circadian process, Reid said. When a schedule is shifted, the alerting signal is shifted as well.

“Your clock doesn’t shift instantaneously,” she said. “You shift [it] over time, an hour a day.”

This applies to those shifting to work schedules or traveling across time zones.

Controlling exposure to light can also help with time adjustment, Reid said. For people who work night shifts, the exposure to sunlight on the way home can cause the body to feel more alert when it should be prepping for sleep.  As a result, many people who primarily work nights tend to get less sleep than those that work during the day; usually two or three hours less, she said.

“Drowsy-driving accidents are common, especially with night-workers,” Reid said.

While adjusting to different work schedules can be difficult, jet lag is hard to deal with because of the added necessity to cope with changing time zones. This is where models such as the one Klerman is working on may be useful, Reid said. Prediction is also difficult with shift workers because their schedule constantly changes. Reid explained that this rotating schedule makes it hard to create any sort of rhythm for the body to get used to, referring to it as “desynchronization.”

“[With shift workers] it’s a little more tricky,” Leproult said. “Internally, they can never adapt.”

The best way to attempt adaptation is by looking at hormonal shifts. By doing a 24-hour hormone and body temperature profile, it is possible to estimate when the body is most productive.

Klerman said there is no evidence that people can train themselves to function on less sleep. Even those who feel they are operating well are often not performing their best.

“Humans are not very good at estimating when they’re not doing well,” Klerman said.

She cited studies in which individuals who were constantly sleep-deprived were found to be pre-diabetic and have a lower response to administered vaccines.

“The goal is to help people plan and realize self-assessment [alone] isn’t good,” Klerman said. “[The model is] an objective measure.”