The residence time of a drug within the human body, described using pharmacokinetics, is governed by its absorption from the site of administration and clearance. Clearance is directly related to the dose of a drug, and inversely related to the systemic exposure of the drug. Important parameters affecting the pharmacokinetics of many drugs include blood flow (potentially affecting absorption, systemic distribution and/or clearance), and hepatic and renal function, the two primary organs of metabolism and excretion, respectively. Not surprisingly, the pharmacokinetics of many drugs is altered in patients who have hepatic dysfunction. Hepatic clearance is governed by two key physiological factors: hepatic arterial and portal vein blood flow and the liver’s intrinsic metabolizing enzyme activity.
Negative nutrient balance directly affects the energy level of an individual which in turn decreases motivation and cognitive ability. Actigraphy has been used to study activity levels of individuals during light and dark cycles. The investigators have used and validated in a related investigation, the methods proposed to collect sleep and performance variables in this study. The investigators examined the sleep quality by measuring sleep-related variables in astronauts working on altered work-sleep schedules aboard the space shuttle. Sleep variables were measured using wrist actigraphy before flight, during preflight light treatment period, and after flight. The data generated by the actigraph were analyzed for the sleep-wake cycle, the quality of rest (number of minutes awake after sleep onset), and sleep to wake ratio. Results of this study suggested that actigraphy could successfully detect changes in activity associated with an alteration in sleep dynamics.
This experiment has concluded in ground-based studies sponsored by the National Aeronautics and Space Administration's Human Adaptation and Countermeasures Division. This experiment was performed during Bed Rest Campaigns 1 and 3A. LSDA doesn't expect to receive results from this study.