isoelectric period

isoelectric period

n.

The period in the electrocardiogram between the end of the S wave and the beginning of the T wave, during which electrical forces neutralize each other so that there is no difference in potential under the two electrodes.

---

isoelectric period,

a period in physiologic activity, such as nerve conduction or muscle contraction, when there is no variation in electric potential.

---

period [pēr´e-od]

an interval or division of time; the time for the regular recurrence of a phenomenon.

absolute refractory period the part of the refractory period from phase 0 to approximately −60 mV during phase 3; during this time it is impossible for the myocardium to respond with a propagated action potential, even with a strong stimulus. Called also effective refractory period.

blanking period a period of time during and after a pacemaker stimulus when the unstimulated chamber is insensitive to avoid sensing the electronic event in the stimulated chamber.

effective refractory period absolute refractory period.

ejection period the second phase of ventricular systole (0.21 to 0.30 sec), between the opening and closing of the semilunar valves, while the blood is discharged into the aorta and pulmonary artery. Called also sphygmic period.

gestation period see gestation period.

incubation period see incubation period.

isoelectric period the moment in muscular contraction when no deflection of the galvanometer is produced.

latency period

1. latent period.

2. latency stage.

latent period a seemingly inactive period, as that between exposure to an infection and the onset of illness (incubation period) or that between the instant of stimulation and the beginning of response (latency, def. 2).

refractory period the period of depolarization and repolarization of the cell membrane after excitation; during the first portion (absolute refractory period), the nerve or muscle fiber cannot respond to a second stimulus, whereas during the relative refractory period it can respond only to a strong stimulus.

relative refractory period the part of the refractory period from approximately −60 mV during phase 3 to the end of phase 3; during this time a depressed response to a strong stimulus is possible.

safe period the period during the menstrual cycle when conception is considered least likely to occur; it comprises approximately the ten days after menstruation begins and the ten days preceding menstruation. See the section on fertility awareness methods, under contraception.

sphygmic period ejection period.

supernormal period in electrocardiography, a period at the end of phase 3 of the action potential during which activation can be initiated with a milder stimulus than is required at maximal repolarization, because at this time the cell is excitable and closer to threshold than at maximal diastolic potential.

vulnerable period that time at the peak of the T wave during which serious arrhythmias are likely to result if a stimulus occurs.

Wenckebach's period a usually repetitive sequence seen in partial heart block, marked by progressive lengthening of the P–R interval; see also dropped beat.

---

isoelectric

showing no variation in electric potential.

---

isoelectric focusing

an electrophoretic method for separating proteins in gels which depends on the fact that the net charge on the protein varies with the pH of the surrounding medium. At the isoelectric point the protein has no net charge and will not therefore migrate further in an electric field. The polyacrylamide gel is cast in a narrow tube that provides a pH gradient from top to bottom.

isoelectric period

the moment in muscular contraction when no deflection of the galvanometer is produced.