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  • Absolute atmosphere (ATA) The atmospheric pressure at sea level, equal to 1 ATA (760 mm Hg).

  • Acoustic impedance A material’s ability to transmit sound, related to the molecular density and structure of the material. Impedance is inversely related to transmission.

  • Acoustic streaming The forward movement of fluid created by acoustic oscillations of ultrasound energy.

  • Allodynia Pain produced by an otherwise non-noxious stimulus, such as light touch of the skin following sunburn; a form of hyperalgesia.

  • Alpha motoneuron The large, lower motor neurons of the brain and spinal cord that innervate skeletal muscle.

  • Alternating current (AC) The uninterrupted bidirectional flow of ions or electrons that must change direction at least one time per second.

  • Ampere (A; amp) The unit of electrical current reflecting the volume of current (electrons) passing a given point in a given time; 1 amp = 1 coulomb/sec.

  • Amplification The act of repeatedly bouncing light between two parallel reflectors arranged at opposite ends of a lasing chamber, causing the excitation of more photons.

  • Analgesia The decrease or absence of pain.

  • Analgesic tolerance A decline or loss in the analgesic effectiveness resulting from repeated use of a given therapeutic intervention.

  • Ankle-Brachial Index (ABI) A method used to determine the presence and severity of peripheral arterial disease, calculated as the ratio of ankle systolic blood pressure to the arm systolic blood pressure.

  • Anode A point or region of a circuit that has a deficiency of electrons; also referred to as the positive pole.

  • Antidromic Conduction along a nerve in the direction opposite of normal; for example, proximal to distal for sensory and distal to proximal for motor axons.

  • Aquatic therapy A therapeutic intervention, usually performed in a pool that uses water to facilitate physiological effects or exercise programs.

  • Asymmetrical Condition when the amplitude and duration characteristics between the two phases of the biphasic waveform differ in any manner.

  • Attenuation A measure of the decrease in sound energy either by absorption, reflection, or refraction.

  • Axonotmesis Axonal degeneration and myelin sheath disruption that occurs distal to and one node of Ranvier proximal to the nerve lesion.

  • Balanced When the area under the curve of the first phase (i.e., phase charge) of a biphasic pulse is equal to that of the second phase.

  • Beam nonuniformity ratio (BNR) The ratio between spatial peak intensity and spatial average intensity of an ultrasound beam.

  • Beat frequency The frequency at which peak constructive or destructive interference occurs for interferential current; calculated as the difference in frequency between the currents interfered.

  • Bipolar An electrode configuration in which all the electrodes of a single electrical circuit are placed over the treatment area.

  • Body mass index (BMI) A value that represents a measure of mass, calculated as body mass (in kg) divided by height (in meters) squared (kg/m2).

  • Buoyancy A force on a body immersed in a fluid that is equal to the weight of the fluid displaced by that object.

  • Burst A series of pulses or brief periods of alternating current delivered consecutively and ...

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