Phase angle from bioelectrical impedance analysis remains an independent predictive marker in HIV-infected patients in the era of highly active antiretroviral treatment.

An adherent device is configured to adhere to the skin of the patient with an adherent patch, for example breathable tape, coupled to at least four electrodes. The device comprises impedance circuitry coupled to the at least four electrodes and configured to measure respiration of the patient to detect sleep apnea and/or hypopnea. The impedance circuitry may be used to measure hydration of the patient. An accelerometer can be mechanically coupled to the adherent patch such that the accelerometer can be coupled to and move with the skin of the patient. Electrocardiogram circuitry to generate an electrocardiogram signal may be coupled to at least two of the at least four electrodes to detect the sleep apnea and/or hypopnea.

Adherent Device for Sleep Disordered Breathing

Optimization of a free water elimination two-compartment model for diffusion tensor imaging.

The regulation of body fluid balance is a key concern in health and disease and comprises three concepts. The first concept pertains to the relationship between total body water (TBW) and total effective solute and is expressed in terms of the tonicity of the body fluids. Disturbances in tonicity are the main factor responsible for changes in cell volume, which can critically affect brain cell function and survival. Solutes distributed almost exclusively in the extracellular compartment (mainly sodium salts) and in the intracellular compartment (mainly potassium salts) contribute to tonicity, while solutes distributed in TBW have no effect on tonicity. The second body fluid balance concept relates to the regulation and measurement of abnormalities of sodium salt balance and extracellular volume. Estimation of extracellular volume is more complex and error prone than measurement of TBW. A key function of extracellular volume, which is defined as the effective arterial blood volume (EABV), is to ensure adequate perfusion of cells and organs. Other factors, including cardiac output, total and regional capacity of both arteries and veins, Starling forces in the capillaries, and gravity also affect the EABV. Collectively, these factors interact closely with extracellular volume and some of them undergo substantial changes in certain acute and chronic severe illnesses. Their changes result not only in extracellular volume expansion, but in the need for a larger extracellular volume compared with that of healthy individuals. Assessing extracellular volume in severe illness is challenging because the estimates of this volume by commonly used methods are prone to large errors in many illnesses. In addition, the optimal extracellular volume may vary from illness to illness, is only partially based on volume measurements by traditional methods, and has not been determined for each illness. Further research is needed to determine optimal extracellular volume levels in several illnesses. For these reasons, extracellular volume in severe illness merits a separate third concept of body fluid balance.

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Fluid balance concepts in medicine: Principles and practice

PURPOSE: To investigate the correlation between diffusion-weighted (DW) magnetic resonance (MR) image changes with alterations in extracellular volume and changes in cytochrome oxidase and Na+-K+–adenosine triphosphatase (ATPase) activity at various times during and after cerebral hypoxia-ischemia in neonatal and juvenile rats. MATERIALS AND METHODS: One– and 4-week-old rats were randomly assigned to control or transient cerebral hypoxia-ischemia (ie, right carotid artery occlusion plus exposure to 8% oxygen) groups. Hypoxic-ischemic changes compared with normal ipsilateral brain tissue on DW images and the apparent diffusion coefficient of water were measured during and at 1 and 24 hours after hypoxia-ischemia ended. Hypoxic-ischemic changes in extracellular space and ipsilateral versus contralateral differences in Na+-K+–ATPase and cytochrome oxidase activity were measured. RESULTS: Hyperintensities on DW images obtained during hypoxia-ischemia correlated well (P < .05) with extracellular space reductio...

Transient hypoxia-ischemia in rats: changes in diffusion-sensitive MR imaging findings, extracellular space, and Na+-K+ -adenosine triphosphatase and cytochrome oxidase activity.

In order to determine body fluid shifts between the intra- and extra-cellular spaces, multifrequency impedance measurement is performed. According to the Cole-Cole extrapolation, lumped values of intra- and extra-cellular conduction can be estimated which are commonly expressed in resistances and respectively. For this purpose the magnitude and phase of the impedance under study are determined at a number of frequencies in the range between 5 kHz and 1 MHz. An approach to determine intra- and extra-cellular conduction on the basis of Bode analysis is presented in this article. On this basis, estimation of the ratio between intra- and extra-cellular conduction could be performed by phase measurement only, midrange in the bandwidth of interest. An important feature is that the relation between intra- and extra-cellular conduction can be continuously monitored by phase measurement and no curve fitting whatsoever is required. Based on a two frequency measurement determining at 4 kHz and at 64 kHz it proved possible to estimate extra-cellular volume (ECV) more accurately compared with the estimation based on extrapolation according to the Cole-Cole model in 26 patients. Reference values of ECV were determined by sodium bromide. The results show a correlation of 0.90 with the reference method. The average error of ECV estimation was -3.6% (SD 8.4), whereas the Cole-Cole extrapolation showed an error of 13.2% (SD 9.5). An important feature of the proposed approach is that the relation between intra- and extra-cellular conduction can be continuously monitored by phase measurement and no curve fitting whatsoever is required. Keywords: electrical impedance plethysmography, electrical bio-impedance analysis, Cole-Cole modelling, extra-cellular volume

Extra-cellular volume estimation by electrical impedance--phase measurement or curve fitting: a comparative study.

An approach to determine intra- and extracellular conduction on the basis of Bode analysis is presented. Estimation of the ratio between intra- and extracellular conduction could be performed by phase measurement only, midrange in the bandwidth of interest. An important feature is that the relation between intra- and extracellular conduction can be continuously monitored by phase measurement and no curve fitting whatsoever is required. Based on a two-frequency measurement determining Re at 4 kHz and phi max at 64 kHz, it proved possible to estimate extracellular volume (ECV) in 23 patients. Reference values on ECV were determined by sodium bromide. The results show a good correlation (r = 0.90) with the reference method. The average error of ECV estimation was -3.6% (SD 8.4).

M. ten Bolscher

Papers

Extra-cellular volume estimation by electrical impedance--phase measurement or curve fitting: a comparative study.

Estimation of Extracellular Volume by a Two‐Frequency Measurement