Energy Medicine: Focus on Nonthermal Electromagnetic Therapies
Len Wisneski in The Scientific Basis of Integrative Health, 2017
Popular acupuncture diagnostic machines often use low-voltage DC with microampere currents that are induced by potentials applied in the range of 1–12 V. Therapeutic electroacupuncture routinely uses much higher current levels (e.g., perhaps several milliamperes, at 2–100 Hz, versus 200 μA for the most intense diagnostic device, the Ryodoraku Neurometer). Many diagnostic devices compute impedance during current flow. Impedance is the total opposition to current flow, including both resistance and reactance. In biological tissue, an applied electrical potential induces two major effects: (1) charged particles are mobilized in response to the field potentials and (2) stationary particles become polarized. Both of these effects contribute to impedance. Moving particles encounter resistance, and stationary materials experience reactance, with components, such as membranes and proteins, becoming polarized in a manner similar to dielectric material between plates of a capacitor. Reactance is composed of both inductance and capacitance, but inductance is usually assumed not to play a significant role in biological systems.
Vascular Impedance
Wilmer W Nichols, Michael F O'Rourke, Elazer R Edelman, Charalambos Vlachopoulos in McDonald's Blood Flow in Arteries, 2022
When the general term “impedance” is applied to the vascular system, it is usually in reference to input impedance, this being the relationship between pulsatile pressure and pulsatile flow (Figure 11.1) recorded in an artery feeding a particular vascular bed. However, four types of impedance need to be defined: Longitudinal impedance: ZL = (P1− P2)/Q.Input impedance: Zi = P/Q (where P and Q are influenced by wave reflection).Characteristic impedance: Z0 = P/Q (where P and Q are not influenced by wave reflection).Terminal impedance: (where P and Q are measured at the termination of the system immediately upstream from the reflecting site).
ABCs of Ultrasound Imaging
Armin Ernst, David J. Feller–Kopman in Ultrasound–Guided Procedures and Investigations, 2005
The transducer materials must be efficient electromechanical energy converters. This means that their electromechanical coupling coefficient for the thickness mode (Kt) must be as large as possible. However, because transducers are placed directly on the tissue, they must have the appropriate acoustic impedance to couple energy efficiently into the tissue. The impedance of tissue is approximately 1.5 Mrayl, but the impedance of typical transducers is approximately 33 MRayl. Impedance coupling is accomplished with electronic matching circuits and with physical matching layers on the front or back of the transducer. Transducers also must couple their energy efficiently into the transmission line that attaches them to the scanning machine. This requires that the dielectric coefficient (ϵS) be adjustable to fit the requirements of the specific array geometry. Of course the electrical and mechanical losses must be low, requiring tan δ < 10% (9).
Should we overcome the resistance to bioelectrical impedance in heart failure?
Published in Expert Review of Medical Devices, 2020
Stephen J. Hankinson, Charles H. Williams, Van-Khue Ton, Stephen S. Gottlieb, Charles C. Hong
Heart failure (HF) is associated with alterations in autonomic control that causes increased neurohormonal activation and the progressive retention of salt and water, resulting in volume overload [1]. It is important to have methods to assess body composition and fluid changes in patients with HF [2]. Bioelectrical impedance (BI) is a method that measures body composition based on conduction of electrical current through body fluids [3,4]. In whole-body BI an electrical current is passed through both hands and feet to calculate impedance. In contrast, during segmental BI an electrical current is passed through various parts of the body to calculate arm, leg, and trunk impedance. Impedance (units Ohms or Ω) is proportional to the length of the conductor and inversely related to the cross-sectional area of the conductor [5]. BI is a combination of resistance (R) and reactance (Xc), defined as the opposition to flow of alternating current through intra- and extracellular ionic solutions and the opposition to flow of alternating current based on the capacitance of cell membranes, respectively [6]. In principle, as salt and water retention worsens, the BI decreases, and vice versa. In this review, we discuss BI as a method to guide the diagnosis, prognostication, and treatment of HF. Our methodology involved searching the PubMed and Scopus databases using the terms ‘bioelectrical impedance’, ‘bioimpedance’, ‘intrathoracic impedance’, ‘bioelectrical impedance vector analysis’, ‘bioreactance’, and ‘heart failure’ up to the third week of June 2020.
Reliability and precision of single frequency bioelectrical impedance assessment of lower extremity swelling following total knee arthroplasty
Published in Physiotherapy Theory and Practice, 2021
Brian J. Loyd, Kristine Burrows, Jeri E. Forster, Scott K. Stackhouse, Craig Hogan, Jennifer E. Stevens-Lapsley
SF-BIA was used to quantify lower extremity swelling at each assessment time point. Testing was performed using the RJL Systems Quantum® (Clinton Township, MI) bioelectrical impedance device, which delivers a 2.5 µA alternating current at a frequency of 50 kHz. The impedance to this current is displayed in Ohms (Ω) and is recorded at a precision of 1 Ω. Using SF-BIA with a frequency of 50 kHz meant that the level of impedance detected reflected composition of the tissue and the presence of both intra and extracellular fluid. This differs from the use of BIS, which allows for measurements at much lower frequencies (nearing 0 Hz, i.e. direct current). At lower frequencies, bioelectrical impedance values are believed to represent only extracellular fluid levels (Altay et al., 2012; Ellis, Shypailo, and Wong, 1999; Ertürk et al., 2015; Kyle et al., 2004a; Pichonnaz et al., 2015). However, BIS devices are highly expensive and the authors believe that both intra- and extracellular fluid fluctuations represent important values when assessing whole limb swelling following TKA and therefore, SF-BIA provides an acceptable alternative to BIS.
“Reactance inversion” at low frequencies during lung function measurement by impulse oscillometry in children with persistent asthma#
Published in Journal of Asthma, 2022
Ramiro González Vera, Alberto Vidal Grell, Alejandra Mendez Yarur, Constanza Olivares Meneses, Jose A. Castro-Rodriguez
Impulse oscillometry (IOS) has become relevant for lung function evaluation. IOS has been shown to be useful for detecting and evaluating small-airway dysfunction in patients even when spirometry is normal (9–12). IOS measures the impedance of the respiratory system (Z), which is the net force to be overcome to move the gas in and out of the respiratory system. Impedance involves the resistance (R) and the reactance (X). The R of the airway includes the resistance of the central and peripheral airway, which is the energy required to propagate the pressure wave through bronchi and bronchioles and distend the lung. R is measured when the pressure wave in phase with the air flow and does not have the opposition of the recoil of the airway and the lung. The X represents the reactive component of respiratory impedance and includes the inertial forces of the movement of the air column in the airways, called the inertance, with a positive sign, and the elastic properties of the lung, called capacitance, with a negative sign.
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