Wayne A. Gerth

A computer-based bioelectrical impedance spectroscopic system for noninvasive assessment of compartmental fluid redistribution

Bioimpedance methods using fixed frequency stimulation to measure volume changes and hemodynamic parameters in body segments of human subjects under various conditions of body position and orthostatic stress are discussed. An electrical impedance spectroscopic (EIS) system has been developed to allow extension of these studies to include examination of the redistribution of fluids between the intracellular and extracellular compartments of the monitored body segments. Evaluated in studies of the human calf and thigh during 90 min of 6 degrees or 10 degrees head-down bed rest, the system promises to enable tracking of segmental and compartmental fluid redistribution in response to various environmental and physiological stresses with both temporal and anatomic resolution greater than that attainable with other methods.<<ETX>>

The indigenous fisherman divers of Thailand: diving practices

Diving practices of a group of indigenous people living on Thailand’s west coast were investigated. Village chiefs were first interviewed using a questionnaire. Three hundred and forty-two active divers were then interviewed by health care workers using a second questionnaire. Field observation was used to further develop information and confirm diving practices. Divers in 6 villages, whose basic means of making a living is from diving for marine products such as fish and shellfish, have diving patterns that put them at substantial risk of decompression illness. Breathing air from a primitive compressor through approximately 100 m of air hose, these divers have long bottom times coupled with short surface intervals. Forty-six point two percent of the divers indicated that they would not make a stop during ascent from a long deep dive (40 m for 30 min). When comparing their previous day of diving to the U.S. Navy Standard Air Decompression Table (U.S. Navy, 1993), 72.1% exceeded the no-decompression limits set by the tables. Diving patterns point to a need for more in-depth research into the diving patterns of this indigenous group. Future research should include the use of dive logging devices to record depths and times. There is also a need to provide divers with information and training to reinforce positive practices and strengthen knowledge of the risks associated with their current diving practices.

The effect of interstitial air on the in vitro thrombogenicity of ePTFE vascular grafts

Gas trapped in the interstices of the biomaterials used for vascular prostheses causes thrombosis, and the process of eliminating this gas is known as denucleation. An apparatus was developed for testing the in vitro effects of denucleation on 4 mm I.D. expanded polytetrafluoroethylene (ePTFE) Vitagraft (Johnson and Johnson). The apparatus was designed to ensure that neither the blood nor the grafts came in contact with air. Blood from a single donor was incubated with control and denucleated grafts for 5, 10, 15, 20, and 30 minutes. The thrombus volume in the graft lumen was measured with a computer assisted videometric system. Little thrombus formed by 5 or 10 minutes, but there was less thrombus in the denucleated graft than in the con trol graft at all times. The differences were statistically significant at 15 and 20 minutes (p < 0.05). Denucleation nearly doubled the thrombus formation time. Thrombus was more adherent to denucleated grafts than to control grafts. These results are consistent with in vivo observations in the rat where denucleation decreased thrombus formation and increased patency duration.

Rheoencephalographic and electroencephalographic analysis of cognitive workload

Changes in brain blood flow and neural activity during mental work are investigated. Multichannel rheoencephalography (REG) and topographical electroencephalography (EEG) were used to measure subject responses to three levels of mathematical processing (MP), as administered by a modified version of the WPAFB criterion task set computer program. REG records were analyzed to provide indices of right and left hemisphere hemodynamic changes during MP. The EEG data were mathematically transformed to provide energy density distribution of the scalp electropotential which reflect the metabolic load required to perform each test sequence. The simultaneous use of these REG and EEG procedures may also be used in the study of a variety of disease states, such as brain injury and neurorehabilitation.<<ETX>>

Bioimpedance monitoring of cellular hydration during hemodialysis therapy

Introduction The aim of this paper is to describe and demonstrate how a new bioimpedance analytical procedure can be used to monitor cellular hydration of End Stage Renal Disease (ESRD) patients during hemodialysis (HD).

A system to monitor segmental intracellular, interstitial, and intravascular volume and circulatory changes during acute hemodialysis

Abstract This paper describes a new combined impedance plethysmographic (IPG) and electrical bioimpedance spectroscopic (BIS) instrument and software that allows noninvasive real-time measurement of segmental blood flow and changes in intracellular, interstitial, and intravascular volumes during various fluid management procedures. The impedance device can be operated either as a fixed frequency IPG for the quantification of segmental blood flow and hemodynamics or as a multi-frequency BIS for the recording of intracellular and extracellular resistances at 40 discrete input frequencies. The extracellular volume is then deconvoluted to obtain its intra-vascular and interstitial component volumes as functions of elapsed time. The purpose of this paper is to describe this instrumentation and to demonstrate the information that can be obtained by using it to monitor segmental compartment volumes and circulatory responses of end stage renal disease patients during acute hemodialysis. Such information may prove valuable in the diagnosis and management of rapid changes in the body fluid balance and various clinical treatments.