hypokalemiaandpotassiumdeficit(參考版)
2024-10-22 02:02本頁面
【正文】 。治療：抗菌素，輸入生理鹽水1200ml。伴煩躁、煩渴。 Low [Ca2+] leads to the decrease of TMP. Ca2+ ← ———— → bining calcium H+ OH 2) Effect on heart (a)Effects on myocardiac cells a) Arrhythmia b) Abnormal contractibility c) Abnormal electrocardiogram (ECG) ① The excitability of myocardiac cell is increased. ? The potassium permeability of myocardiac cell is reduced in hypokalemia. ? Less K+ moves outside the cell, the RMP is less negative. ? The difference between RMP and TMP is reduced. Smaller stimulus may produce the AP. ? Prolonged exaltation phase超常期 caused by decreased K permeability and rate of phase 3 (repolarization) ? Short absolute refractory period caused by short phase 2. ② The conductivity of myocardiac cell is reduced. ? The rate of depolarization and repolarization 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
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