The Skylab missions provided an opportunity to study the physiological responses of man to space flight, as well as the effects of space flight on basic biological systems. The Mercury, Gemini, and Apollo programs provided limited measurements of astronaut physiological responses. This was due to the fact that the operations on these missions were so complex that it left little time to make detailed physiological measurements. In addition, the interiors of these spacecraft were small, therefore not much medical equipment could be carried on board to make these measurements.
The Skylab payload was equipped to study the cardiovascular, musculoskeletal, hematological, vestibular, metabolic, and endocrine systems of the body. Analysis of the heart's electrical forces by vectorcardiography during the application of the lower body negative pressure was conducted on Skylab and used to study microgravity-induced orthostatic intolerance and hemodynamic changes in astronauts during and after flight. Vectorcardiographic parameters were measured before, during and after exercise on the bicycle ergometer to study cardiovascular deconditioning and cardiac arrhythmias that occurred during and after space flight. In addition, the metabolic analyzer, a device that measures oxygen consumption, was used on Skylab to study respiratory responses to bicycle exercise to determine how the capacity to do physical work in space differs from doing work on the ground.
The inflight blood collection system and urine collection system provided Skylab astronauts with a method to collect and store blood and urine samples. From these samples, scientists were able to study: 1) fluid and electrolyte balance, 2) regulation of calcium metabolism, 3) adrenal function, and 4) carbohydrate, fat, and protein utilization.
Early hematology studies done on Gemini and Apollo missions indicated decreased red blood cell mass in returning astronauts, which initiated investigation on Skylab into space flight induced anemia. Red blood cell mass, red blood cell life span, and plasma volume were measured to determine the mechanisms that caused the decrease in red blood cell mass on previous flights. Data on red blood cell metabolism as well as changes in cellular shape (morphology) supplemented the previous investigation into the altered red blood cell mass. Astronaut immunity was investigated by the measurement of the humoral factors and cellular parameters of the immune system. Cytogenetic studies on human peripheral leukocytes were performed to determine if radiation exposure affected the structure of chromosomes. The rotating chair imposed accelerative forces on the vestibular organ of the inner ear to establish astronauts? susceptibility to motion sickness and their neurosensory adaptation to microgravity, as well as the astronauts? subsequent readaptation back to Earth. Changes in posture, work performance, and sleep patterns were also studied on Skylab to understand the effects of space on the nervous system.
The effects of space flight on the musculoskeletal system were examined by taking measurements of muscle and bone mineral concentrations in the blood and urine. Nitrogen metabolic measurements were made to study protein loss in muscle tissue. Bone minerals such as calcium were measured to study bone demineralization. Muscle strength was measured preflight and postflight using a device called an isokinetic dynamometer.
Skylab 2 mission initiated a comprehensive medical research program that extended the knowledge gained in the Mercury, Gemini, and Apollo programs, and provided scientific data that could be used for future planning of longer duration flights.