ABSTRACT
Definition of multisegment hemodynamic changes that take place in the body would provide a more complete understanding of the physiologic responses to various orthostatic stress techniques. A self-contained impedance device is described which may be used to measure the electrical transmission characteristics produced by blood flow and volume changes in six segments of the human body during head-up tilt, bed rest, and lower body negative pressure. The device consists of a module that contains the electronics for the impedance system, a separate controller/multiplexer, a personal computer interface/analog to digital conversion/power supply system, and the associated computer control software. The instrument is linear over a range of 0 to 200 ohms; provides analog outputs of base impedance, phase angle, pulsatile impedance change, and the first derivative of the pulsatile impedance changes; and can be used to automatically record basal impedance values into spread-sheet format with cycle times between 12 s and 1 h. Typical results are presented to illustrate its application in aerospace research.
Subject(s)
Hemodynamics/physiology , Hypotension, Orthostatic/physiopathology , Plethysmography, Impedance/instrumentation , Plethysmography, Whole Body/instrumentation , Equipment Design , Humans , Plethysmography, Impedance/methods , Plethysmography, Whole Body/methods , Software DesignABSTRACT
A specialized four-channel impedance plethysmograph is described that can be used to measure calf, thigh, and abdominal volume changes during rapid onset rate centrifuge acceleration. Typical results are presented to demonstrate its application to research and the design and assessment of countermeasures to enhance man's performance in the high-G environment.
