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ALTERATIONS IN BREATHING PATTERNS BY USE OF THE INSPIRATORY IMPEDANCE THRESHOLD VALVE (ITV).   V.A. Convertino¹, D.A. Ratliff², S.D. Clah³. ¹Research Physiologist, U.S. Army Institute of Surgical Research, ²Research Physiologist, Environmental Health, ³SLSTP trainee, Dine College, Shiprock.

   Approximately 50% of astronauts returning to Earth experience orthostatic hypotension.  Before spaceflight an astronaut’s blood is evenly distributed throughout his body due to adequate blood pressure regulation and the pressure of a 1-G environment.   As the astronaut enters into space, the blood is re-directed to the chest and upper body due to lack of gravity.   This shift causes excess fluid loss over time due to barorecptors signaling apparent increased blood pressure in the carotid bodies.  When the astronauts reenter the earth’s gravitational pull, the blood and the fluids are again distributed throughout the body however, there is not enough blood.  Therefore, astronauts could possibly faint due to lack of circulating fluids. 

   In our experiment, we are testing a way to increase the blood pressure upon reentry to the Earth to prevent fainting, by using a device called an Inspiratory Impedance Threshold Valve (ITV).  We hypothesized that the ITV will increase venous return and lead to an increase in stroke volume.  More importantly, we hypothesize  breathing with the ITV will increase respiratory rate to maintain a steady state minute volume of airflow.  This effect will be increased with increasing resistance of the ITV. 

   Our hypothesis was tested with this protocol:  Subjects were sensored for bioimpedance measurement of stroke volume.  Subjects respiratory rate was measured by counting the number of baseline excursions of end tidal C0₂ in 1 minute.  A minute volume of air inspired was also measured.  After 3 minutes of breathing on the ITV respiration measurements were recorded.  At minute 4, Stroke volume was sampled for 20 seconds.

   We looked at the difference between the recorded measurements of the volume and rate using the 00 cm, 07 cm, or 12 cm valve.  There has not been an experiment on how the ITV will affect respiration using the different size valves on the same subject.  Another factor is that this will be the first time using the ITV on healthy human subjects.  The results for breaths are given in bar graphs showing the increase of respiratory rate and  minute volume of inspiration from breathing in three different size valves.