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Chronotropic effects (from chrono-, meaning time, and tropos, "a turn") are those that change the heart rate. Chronotropic drugs may change the heart rate and rhythm by affecting the electrical conduction system of the heart and the nerves that influence it , such as by changing the rhythm produced by the sinoatrial node .
Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction. The term inotropic state is most commonly used in reference to various drugs that affect the strength of contraction of heart muscle. However, it can also refer to pathological conditions.
Epinephrine (adrenaline). Activation of β 1 receptors induces positive inotropic, chronotropic output of the cardiac muscle, leading to increased heart rate and blood pressure, secretion of ghrelin from the stomach, and renin release from the kidneys.
The primary antihypertensive mechanism of beta blockers is unclear, but may involve reduction in cardiac output (due to negative chronotropic and inotropic effects). [73] It may also be due to reduction in renin release from the kidneys, and a central nervous system effect to reduce sympathetic activity (for those beta blockers that do cross ...
As various drugs and other factors act on the resting potential and bring it closer to the threshold potential, an action potential is more easily and rapidly obtained. Likewise, when the sodium channels are in a state of greater activation, then the influx of sodium ions that allows the membrane to reach threshold potential occurs more readily.
The class of CCBs known as dihydropyridines mainly affect arterial vascular smooth muscle and lower blood pressure by causing vasodilation. The phenylalkylamine class of CCBs mainly affect the cells of the heart and have negative inotropic and negative chronotropic effects. The benzothiazepine class of CCBs combine effects of the other two classes.
Isoprenaline has positive inotropic and chronotropic effects on the heart. β 2-Adrenergic receptor stimulation in arteriolar smooth muscle induces vasodilation. Its inotropic and chronotropic effects elevate systolic blood pressure, while its vasodilatory effects tend to lower diastolic blood pressure.
Non-dihydropyridine calcium channel blockers such as verapamil block the slow inward calcium current in cardiac tissues, thereby having a negatively dromotropic, chronotropic and inotropic effect. [5] This (and other) pharmacological effect makes these drugs useful in the treatment of angina pectoris.