【正文】 ation is reduced in hypokalemia, because the RMP is near the TMP. ③ The autorhythmicity is increased. ? In phase 4, the potassium permeability in hypokalemia is reduced, the outward potassium current is decreased and inward sodium current is relatively speed of spontaneous depolarization is increased. (Slope rise steeply) Summary of the effect of hypokalemia on the myocardiac cells The excitability is increased. Prolonged exaltation phase超常期延長 : Short absolute refractory period有效不應(yīng)期短 : The conductivity is reduced. The autorhythmcity is increased. All the alters make it easy to produce arrhythmia (increased heart rate, ectopic beats from Purkinje fiber and ventricular muscle). (Ectopic pacemaker) (nodus sinuatrialis) b) Abnormal contractibility, ? ? The contractibility of myocardiac cell is increased first, then reduced. K+ in ECF can inhibit the inward flow of calcium ions, this inhibiting effect is reduced in hypokalemia. ? More Ca 2+ within myocardiac cell will increase the contractibility. In severe hypokalemia , ATP production and ATPase activity are reduced which causes low myocardial contractibility. Electrocardiogram (ECG) ?The P wave reflects depolarization of atrial muscle and represents the original impulse passes through the atrium. ? The QRS plex represents depolarization of the ventricular muscle mass, and reflects the speed of conduction throughout the ventricle. ? The ST segment represents the period between the end of depolarization of ventricular muscle and the beginning of repolarization of ventricle. The ST segment corresponds to the plateau (phase 2) of AP. The T wave represents the major portion of repolarizatione after ventricular contraction. T wave corresponds to the phase 3 of AP. C) Abnormal ECG Broad and flat T wave appears because the potassium permeability in hypokalemia is reduced, the rate of repolarization is reduced. The phase 3 is prolonged. Prolonged QRS plex are caused by reduced conductivity. Suppressive ST segment is related to the short phase 2 due to accelerated inward flow of calcium. Prominent U wave can be often seen in hypokalemia, but it is hard to explain the mechanism. 3) Effect on the acidbase balance Hypokalemia leads to metabolic alkalosis. When [K+]e of ECF reduce, the K+ of ICF moves out of the cells, at the same time, H+ moves into the cells for electric neutrality. Then the [H+] in ECF will be reduced, which is called metabolic alkalosis. ? (Depending on the primary disease) There are two kinds of ion exchange in renal tu