# resistance

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Related to Vascular resistance: Peripheral vascular resistance

## resistance,

property of an electric conductor by which it opposes a flow of electricity and dissipates electrical energy away from the circuit, usually as heat. Optimum resistance is provided by a conductor that is long, small in cross section, and of a material that conducts poorly. Resistance is basically the same for alternating and direct current circuits (see impedanceimpedance,
in electricity, measure in ohms of the degree to which an electric circuit resists the flow of electric current when a voltage is impressed across its terminals.
). However, an alternating current of high frequency tends to travel near the surface of a conductor. Since such a current uses less of the available cross section of the conductor than a direct current, it meets with more resistance than a direct current. In circuit analysis an ideal resistorresistor,
two-terminal electric circuit component that offers opposition to an electric current. Resistors are normally designed and operated so that, with varying levels of current, variations of their resistance values are negligible (see resistance).
, i.e., a circuit component whose only property is resistance, is called a resistance. The phenomenon of resistance arises from the interactions of electrons with ions in the conductor. The unit of resistance is the ohmohm
[for G. S. Ohm], symbol Ω, unit of electrical resistance, defined as the resistance in a circuit in which a potential difference of one volt creates a current of one ampere; hence, 1 ohm equals 1 volt/ampere. The megohm (1,000,000 ohms) and the milliohm (.
. See superconductivitysuperconductivity,
abnormally high electrical conductivity of certain substances. The phenomenon was discovered in 1911 by Heike Kamerlingh Onnes, who found that the resistance of mercury dropped suddenly to zero at a temperature of about 4.
; Ohm's lawOhm's law
[for G. S. Ohm], law stating that the electric current i flowing through a given resistance r is equal to the applied voltage v divided by the resistance, or i=v/r.
; conductionconduction,
transfer of heat or electricity through a substance, resulting from a difference in temperature between different parts of the substance, in the case of heat, or from a difference in electric potential, in the case of electricity.
.

## resistance,

in biology: see immunityimmunity,
ability of an organism to resist disease by identifying and destroying foreign substances or organisms. Although all animals have some immune capabilities, little is known about nonmammalian immunity.
.

## resistance,

in psychiatry: see psychoanalysispsychoanalysis,
name given by Sigmund Freud to a system of interpretation and therapeutic treatment of psychological disorders. Psychoanalysis began after Freud studied (1885–86) with the French neurologist J. M.
.

## Resistance

The physical property of a material to resist or impede the conduction of electrical current, measured in ohms. High resistance means poor conductivity and vice versa.

## resistance

[ri′zis·təns]
(acoustics)
(electricity)
The opposition that a device or material offers to the flow of direct current, equal to the voltage drop across the element divided by the current through the element. Also known as electrical resistance.
In an alternating-current circuit, the real part of the complex impedance.
(fluid mechanics)
(mechanics)
In damped harmonic motion, the ratio of the frictional resistive force to the speed. Also known as damping coefficient; damping constant; mechanical resistance.

## electrical resistance

The physical property of a device, conductor, element, branch, or system, by virtue of which power is lost as heat when current flows through it; the physical property which an electric conductor exhibits to the flow of current; measured in ohms.

## resistance

1.
a. the opposition to a flow of electric current through a circuit component, medium, or substance. It is the magnitude of the real part of the impedance and is measured in ohms.
b. (as modifier): resistance coupling
2. any force that tends to retard or oppose motion
3. (in psychoanalytical theory) the tendency of a person to prevent the translation of repressed thoughts and ideas from the unconscious to the conscious and esp to resist the analyst's attempt to bring this about
4. Physics the magnitude of the real part of the acoustic or mechanical impedance
References in periodicals archive ?
Espada, "Determination of renal vascular resistance in dogs with diabetes mellitus and hyperadrenocorticism," Veterinary Record, vol.
Probably this time is low and not sufficient to make significant differences in removal of metabolites and vascular resistance.
Current research includes developing non-invasive markers of pulmonary vascular resistance, numerical modeling of right-sided fluid dynamics, understanding pulmonary artery mechanics in vivo using intravascular ultrasound techniques, and developing new markers of pulmonary reactivity [2-5].
7] The positive inotropic effect of dobutamine hydrochloride results in an increase in cardiac output and subsequent reflex withdrawal of sympathetic tone and decrease in the total peripheral vascular resistance.
During exercise, recruitment of unopened vessels and distention of patent pulmonary blood vessels leads to increased blood flow and decreased pulmonary vascular resistance.
As a result, decreased amounts of insulin in the cells may lead directly to abnormal cellular metabolism and increased external vascular resistance, which can lead to hypertension.
Afterload can be estimated with a pulmonary artery catheter through calculation of the systemic vascular resistance index (SVRI).
When 14 patients stopped taking cyclosporine, their renal vascular resistance (a measure of pressure in the kidneys related to blood vessel size) dropped by about 36 percent, says Curtis.
The results show that a healthy diet supplemented with pistachios helps decrease systolic blood pressure, peripheral vascular resistance and heart rate during acute stress.
M2 PHARMA-July 12, 2017-Arena Pharmaceuticals Study of Ralinepag in Patients with Pulmonary Arterial Hypertension Shows Significant Improvement in Pulmonary Vascular Resistance
The clinical characteristic is that pulmonary vascular resistance progressively increases, which obstructs the right ventricular ejection, leading to right heart failure and even death.

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