Engineering topics

Bhagat, P. K.

Publications and source records attributed to Bhagat, P. K..

7 records

NASA NTRS1983

Development of limb volume measuring system

The mechanisms underlying the reductions in orthostatic tolerance associated with weightlessness are not well established. Contradictory results from measurements of leg volume changes suggest that altered venomotor tone and reduced blood flow may not be the only contributors to orthostatic intolerance. It is felt that a more accurate limb volume system which is insensitive to environmental factors will aid in better quantification of the hemodynamics of the leg. Of the varous limb volume techniques presently available, the ultrasonic limb volume system has proven to be the best choice. The system as described herein is free from environmental effects, safe, simple to operate and causes negligible radio frequency interference problems. The segmental ultrasonic ultrasonic plethysmograph is expected to provide a better measurement of limb volume change since it is based on cross-sectional area measurements.

Bhagat, P. K.↗

NASA NTRS1983

Transducers for ultrasonic limb plethysmography

The design, construction, and performance characteristics of ultasonic transducers suitable for limb plethysmography are presented. Both 3-mm-diameter flat-plate and 12-mm-diameter hemispheric ceramic transducers operating at 2 MHz were fitted in 1-mm thick epoxy-resin lens/acoustic-coupling structures and mounted in exercie-EKG electrode housings for placement on the calf using adhesive collars. The effects of transducer directional characteristics on performance under off-axis rotation and the electrical impedances of the transducers were measured: The flat transducer was found to be sensitive to rotation and have an impedance of 800 ohms; the hemispheric transducer, to be unaffected by rotation and have an impedance of 80 ohms. The use of hemispheric transducers as both transmitter and receiver, or of a flat transducer as transmitter and a hemispheric transducer as receiver, was found to produce adequate dimensional measurements, with minimum care in transducer placement, in short-term physiological experiments and long-term (up to 7-day) attachment tests.

Nickell, W. T.↗

NASA NTRS1983

A comparison of limb plethysmograph systems proposed for use on the Space Shuttle

Comparisons of a Whitney mercury-filled double-stranded strain gauge with two plethysmographs proposed for Shuttle use - an ultrasound and an impedance plethysmograph - were performed on 20 subjects. An occlusive thigh pressure cuff, inflated to 50 mm Hg, caused partial venous occlusion and subsequent blood pooling distal to the cuff. The average maximum volume changes observed in the Whitney/ultrasound test were 2.07% and 3.35%, respectively, and 2.12% and 2.53% for the Whitney/Impedance comparison. Applying the ratio of the maximum volume changes to the gain of each test system caused the impedance and ultrasound volume change determinations to be essentially identical to the Whitney gauge. The three different limb parameters measured result in significant magnitude differences but the three systems track their respective changes identically.

Levitan, B. M.↗

NASA NTRS1982

A practical ultrasonic plethysmograph

An ultrasonic plethysmograph, which gives improved performance over the standard Whitney Strain Gauge, is described. This instrument monitors dimension changes in human limbs by measuring the transit times of acoustic pulses across two chords of the limb. In the case of a small uniform expansion, the percentage change in limb volume is shown to be proportional to twice the percentage change in either of the measured chords. Measurement of two chords allows correction for possible non-uniform expansion. In addition, measurement of two chords allows an estimate of the absolute cross-sectional area of the limb. The developed instrument incorporates a microprocessor, which performs necessary calculation and control functions. Use of the microprocessor allows the instrument to be self-calibrating. In addition, the device can be easily reprogrammed to incorporate improvements in operating features or computational schemes.

Wu, V. C.↗

NASA NTRS1981

Microprocessor-controlled ultrasonic plethysmograph

Safe, nonintrusive microprocessor system times ultrasonic pulses to measure limb cross-sectional area. Simple instrument requires no calibration and does not confine leg movement, making tests relating limb volume to activity level possible. Program considers more realistic geometries of human limb than circular cross-sections and monitors changes in area with great accuracy. Errors due to body temperature changes and timing roundoff are insignificant.

Bhagat, P. K.↗

NASA NTRS1981

Apparatus for determining changes in limb volume

Measuring apparatus for determining changes in the volume of limbs or other boty extremities by determining the cross-sectional area of such limbs many comprise a transmitter including first and second transducers for positioning on the surface of the limb at a predetermined distance there between, and a receiver including a receiver crystal for positioning on the surface of the limb. The distance between the receiver crystal and the first and second transducers are represented by respective first and second chords of the cross-section of the limb and the predetermined distance between the first and second transducers is represented by a third chord of the limb cross section.

Bhagat, P. K.↗

NASA NTRS1980

An ultrasonic plethysmograph for space flight applications

The development of an ultrasonic plethysmograph based on the transit time measurement principle is reported, which meets the space-imposed requirements for evaluating cardiovascular deconditioning. It consists of a pulse generator, pulse receiver amplifier, voltage comparator, synchronous pulse generator, elapsed time counter, and transmit and receive piezoelectric crystals resonant at 2 MHz and of 3 mm diameter. The transit time for an ultrasonic pulse to propagate across a limb cross section is computed in a digital fashion using a 32 MHz clock, and resolution is 0.049 mm with the range being approximately 200 mm. Experimental results regarding dynamic system response were found comparable in both accuracy and sensitivity to those of a Whitney strain gage using a 50 torr venous occlusion.

Bhagat, P. K.↗