Both light and exercise are effective countermeasures for space and ground-based crews for circadian phase resetting, alertness levels, and fitness. We are testing the combined effects of these two countermeasures to determine whether adding exercise to light stimuli will further improve circadian phase resetting, objective performance, subjective alertness, and sleep. If there are increased positive responses to the addition of exercise to lighting countermeasures, then such schedules can be implemented on the ISS without additional equipment or devices. Recommendations can also be made for individuals on earth working night or rotating shifts or experiencing jet lag.
Ultra-Short Light Pulses as Efficient Countermeasures for Circadian Misalignment and Objective Performance and Subjective Alertness Decrements
Elizabeth B. Klerman, M.D., Ph.D.
Harvard Medical School/Brigham and Women's Hospital
We will be testing the hypotheses that addition of moderate-intensity exercise to short bright light stimuli will, relative to light exposure without exercise: increase the circadian phase shift, improve objective performance and subjective alertness during the stimuli, and improve objective and subjective sleep latency and total sleep time during the nights after the stimuli.
The one-year project will include an 8-day inpatient protocol with 8 healthy participants. The protocol will include a circadian phase delay, as occurs when traveling from Europe/ western Russia to the US.
Participants: Participants will be men and women (1:1 +/-1 ratio) who met the criteria for the first 3 years of this project: ages 26-55, healthy by history, physical exam, laboratory studies of blood and urine, and psychological screening. They must be using no prescription medications, except hormonal birth control in females. They must also report moderate-intensity exercise for at least 150 minutes per week.
Outpatient: Participants will maintain an 8-hour time-in-bed schedule of their own choosing for the 3 weeks prior to entry to the inpatient portion of the protocol. Compliance with this schedule will be verified with actigraphy, sleep/wake diaries, and call-ins to a time-stamped phone message center. During the last week before entry, no alcohol, tobacco, caffeine, health food supplements/remedies, or over-the-counter medications will be allowed. This will be verified using toxicology screening.
Inpatient: Admission to the BWH Center for Clinical Investigation (CCI) inpatient Intensive Physiological Monitoring Unit will be on day 1. The initial phase assessment using melatonin will be carried out on the day of admission under dim light conditions, starting 6 hours before habitual bedtime. That night, individuals will sleep at their habitual time for 8 hours. The first of four total cycles of combined exercise and light exposure intervention will start on the second study day, timed at a phase that is expected to induce maximal phase delay.
Intervention: During each of the four days of light exposure and exercise intervention the participants will be exposed to six bouts of 15-minute bright light pulses (750 Lux, 6500 K) starting 7 hours after wake using the SSLM-R LED lighting system, which is a ground based analogue of the LED lighting system that will be used on the ISS. When the participants are not receiving the bright light pulse, they will be exposed to standard background illumination (90 Lux, 4500 K) also using the same SSLM-R LED lighting system. The combined intervention is completed in 8 hours per each day of the intervention. Objective performance and subjective alertness testing will occur during the bright light when the individual is not actively exercising. During each exercise bout during the study, subjects will be required to maintain an intensity of 65-75% of their age-predicted maximal heart rate (208 - 0.7 x age).
Data Collected: Blood will be drawn hourly from an indwelling IV catheter and later assayed for melatonin. Objective performance will be measured using the Psychomotor Vigilance Test (PVT) every 2 hours. Subjective alertness will be measured using the Karolinska Sleepiness Scale every hour while the individual is awake except during exercise bouts. Sleep will be recorded and scored using standardized techniques and definitions for each scheduled sleep episode. Post-sleep questionnaires will be collected upon awakening; questions include (i) estimates of subjective sleep latency, total sleep time, and number of awakenings, and (ii) subjective assessment of how sound, good, and restful the prior night sleep was.
Expected outcomes: We expect a larger phase shift, improved objective performance, increased subjective alertness, and improved subjective and objective sleep when exercise is added to light as a countermeasure.
Individuals working night or rotating shifts and those experiencing jet lag seek countermeasures to improve realignment of the internal circadian rhythm timing to that of the external environment. Current recommendations are primarily based on light and pharmaceutical interventions. Exercise has been shown to affect circadian rhythms under indoor lighting conditions. Some individuals, however, exercise outside, during which light levels are high. Understanding the joint effects of light and exercise on the circadian system will be useful for designing and recommending countermeasures.