Release date: 07/01
Human exposure to microgravity -- the unique low-gravity environment inside the International Space Station and other spacecraft -- results in a number of physiological changes to the human body. Among these changes are alterations in renal function, fluid redistribution, bone loss and muscle atrophy, all of which contribute to an altered urinary environment and the potential for renal stone formation during and immediately after flight.
Previous data have demonstrated that human exposure to microgravity increases the risk of renal (kidney) stone development during and immediately after space flight. In-flight changes previously observed include decreased urine volume and increased urinary excretion of calcium, phosphate, and sodium.
Calcium-containing stones are the most common type of kidney stones occurring in humans. Post-flight changes to the urinary chemical composition increase the risk of uric acid and calcium oxalate stone formation, while in-flight assessment has shown a greater risk of calcium oxalate, calcium phosphate and sodium urate stones.
Potassium citrate, a proven Earth-based therapy to minimize calcium-containing renal stone development, will be tested during Expedition Three as a countermeasure to reduce the risk of renal stone formation. This study will also assess the renal stone-forming potential in humans based on mission duration, and determine how long after space flight the increased risk exists.
Beginning three days before launch and continuing through 14 days after their return, International Space Station crewmembers will ingest two potassium citrate pills or placebos daily with the last meal of the day. Urine will be collected over 24-hour periods before, during and after flight. Food, fluid, exercise and medications will be monitored before and during the urine collection period in order to assess environmental influences other than microgravity.
The potassium citrate and placebo pills will be given to individual crewmembers in blister packs. Each crewmember will have a personal packet. However, pill composition - whether potassium citrate or placebo -- will not be identified to the crewmember or the investigators in what is called a double-blind study. The use of this type of study will help the investigators determine the effectiveness of this countermeasure.
Urine will be collected with the Urine Collection Kit (UCK) -- a Nomex pouch containing polyethylene Urine Collection Devices (UCDs), male or female adapters, Ziplock bags, and wet - dry wipes. Urine samples will be collected using the in-flight syringe sample tubes and syringe adapters and returned to Earth for analysis. The syringe adapters provide an interface to connect a sample syringe with Urine Collection Devices for sample removal. (Nomex is a fire-retardant, puncture-resistant fabric used in a variety of space equipment, including space suits and equipment pouches. It has a weight similar to denim.)
Filled Urine Collection Devices are placed in the Urine Containment Bag (UCB) -- a large Nomex container with absorbent material and a sealing zipper to prevent any possible leakage during storage.
The formation of kidney stones could have severe health consequences for Space Station crewmembers and negatively impact the success of a mission. This study will provide a better understanding of the risk factors associated with kidney stone development during and after flight, as well as test the effectiveness of potassium citrate as a countermeasure to reduce this risk. Understanding how the disease may form in otherwise healthy crewmembers under varying environmental conditions also may provide insight into stone-forming diseases on Earth.
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