Atrial systole: 0.1 seconds after global diastole (75% of ventricular filling)

ventricular systole

ventricular diastole

Atrial end-diastolic pressure is often used to reflect preload (end-diastolic pressure in the atria is almost equal to that of the ventricles)

Allometric autoregulation: the regulation of changes in myocardial contractility by changing the initial length of the myocardium.

The physiological significance of heterologous autoregulation: finely adjust small changes in stroke volume to maintain a balance between ventricular ejection volume and venous return blood volume.

Factors affecting preload

Aortic blood pressure is the afterload experienced by the ventricles during contraction

When aortic blood pressure increases, the isovolumic contraction period is prolonged and the ejection period is shortened, resulting in a decrease in stroke volume; conversely

Secondarily causes heterometric regulation: when stroke volume decreases, ventricular end-diastolic volume will increase, and the initial length of myocardium will increase, keeping stroke volume unchanged.

Refers to the intrinsic characteristics of the myocardium that can change its contraction strength and speed independent of pre/afterload.

Changes in isometric regulation by humoral and neural mechanisms

eg. The number of activated cross-bridges (Ca concentration in the cytoplasm, affinity of troponin for Ca), activity of myosin ATPase, etc.

Within a certain range "40~180", an increase in heart rate increases cardiac output.

If it exceeds 180, the diastolic period of the ventricles will be significantly shortened, and the filling volume during diastole will be reduced, resulting in a decrease in cardiac output.

Less than 40, the ventricular filling period is already close to the maximum, and the filling volume and stroke volume cannot be further increased, resulting in a reduction in cardiac output.

Increased sympathetic nervous activity increases the heart rate; increased parasympathetic nervous activity decreases the heart rate.

Increased adrenaline, norepinephrine, and thyroid hormones, increased heart rate

For every 1°C increase in body temperature, the heart rate can increase by 12 to 18 beats per minute.

ventricular myocyte action potential

sinoatrial node cell action potential

Purkinje cell action potential

Working cells: atrial and ventricular muscles; no self-discipline

Autonomic cells: special conduction system; non-contractile

Excitability

conductivity

automatic rhythmicity

Contractibility