CP1 1.7 blood flow

What is the normal oxygen concentration in arterial blood?

20 mL O2 / 100 mL of blood or 20% of blood volume

What is functional sympatholysis?

Activation of sympathetic nerves innervating the coronary vasculature causes only transient vasoconstriction mediated by alpha 1-adrenoreceptors. This brief (and small) vasoconstrictor response is followed by vasodilation caused by enhanced production of vasodilator metabolites (active hyperemia) due to increased mechanical and metabolic activity of the heart resulting from beta 1-adrenoreceptor activation of the myocardium. Therefore, sympathetic activation to the heart results in coronary vasodilation and increased coronary flow due to increased metabolic activity (increased heart rate and contractility) despite direct vasoconstrictor effects of sympathetic activation on the coronaries. This event is termed "functional sympatholysis".

What are some vasodilators?

Adenosine, CO2, Lactic acid, ADP compounds, Histamine, K ions, H ions

How does adenosine work with the heart?

An increased metabolic activity of the heart, a decrease in coronary blood flow, or a fall in myocardial O2 results in adenosine release from myocytes. Adenosine then diffuses to the vascular smooth muscle cells to induce vasodilation.

When?

During systole

Detail the compression of coronary arteries through systole and diastole

During systole, the left coronary blood flow drops to zero while the right coronary blood flow is about 20 mls/min. In early diastole, the left coronary greatly increases its blood flow compared to the right.

What is the kidney blood flow controlled by?

Feedback system between tubules and arterioles

What is more effective, long or short term control of blood flow?

long term

Coronary vascular control is mainly _____ and ______, and then _____

Metabolic & autoregulation Then sympathetic

Shear forces release what?

NO Cause vasodilation

What is an important stimulus for regulating tissue vascularity?

Oxygen

Diseased coronary arteries lead to what?

Oxygen deficit Myocardial hypoxia

What does parasympathetic stimulation do to the heart?

Parasympathetic stimulation of the heart (i.e. vagal nerve activation) elicits modest coronary vasodilation (due to the direct effects of released acetylcholine on the coronaries). However, if parasympathetic activation of the heart results in a significant decrease in myocardial oxygen demand due to a reduction in heart rate, then intrinsic metabolic mechanisms will increase coronary vascular resistance by constricting the vessels.

Which artery is the "widow maker"?

The left anterior descending artery

What does the right coronary artery branch into?

The marginal and posterior descending artery

What is the myogenic theory?

proposes that as arterial pressure falls the arterioles have an intrinsic property to dilate in response to decreases in wall tension.

What is the metabolic theory?

suggests that as arterial pressure is decreased, oxygen or nutrient delivery is decreased resulting in release of a vasodilator.

What is the brain blood flow controlled by?

Carbon dioxide, H+ concentration

What is autoregulation of blood flow?

Blood flow to an organ remains constant over a wide range of perfusion pressures

The delivery of oxygen to the myocardium is dependent on what 2 factors?

1. Coronary blood flow (CBF) 2. Oxygen content of arterial blood (CaO2)

Occlusion of the left anterior descending artery leads to what MI in what location?

Anterior wall MI

What is the force that drives the blood flow through the coronary arteries?

Aortic pressure

Where do the R and L coronary arteries originate?

At the root of the aorta behind the cusps of the aortic valve

What are the major factors that cause changes in coronary blood flow?

Changes in coronary vascular resistance. Physical changes causes by extravascular compression of the heart. Neural changes (sympathetic vs. parasympathetic nervous system) Metabolic changes (local mediators) Local (intrinsic) control of blood flow.

How does heart rate affect coronary blood flow?

Changes in heart rate, because they affect the duration of diastole more than that of systole, also affect coronary blood flow. During tachycardia, the fraction of the cardiac cycle spent in diastole decreases, minimizing the time available for maximal left coronary perfusion. If the heart is healthy, the coronary vessels can adequately dilate in response to the metabolic signals generated by increased cardiac work (active hyperemia), which offsets the negative effects of the shorter diastole. Patients with diseased coronary arteries could get into trouble at higher heart rates.

How does it work?

Changing the degree of vascularity of tissues (size and # of vessels)

How does collateralization work?

Collateralization increases myocardial blood supply by increasing the number of parallel vessels thereby reducing vascular resistance within the myocardium.

When is coronary blood flow lowest?

During isovolumetric contraction/ejection

Why?

During muscle contraction and shortening, the muscle cells increase in diameter. The increase in diameter results from an increase in intracellular pressure. The increased intracellular pressure counteracts the force generated by the contractile apparatus. The increase in muscle diameter takes place at the expense of the coronary vasculature. The ease of vascular deformation, and thus vascular emptying, determines the intracellular pressure. Purely fiber-isometric contractions do not affect the coronary vasculature, and force generation is not counteracted.

What is the Law of Laplace?

For a given blood pressure, increasing the radius of the cylinder leads to a linear increase in tension. This implies that large arteries must have thicker walls than small arteries in order to withstand the level of tension. Notice that as we increase the pressure (p) we increase the slope of the line. For a given radius (r), cyllinders carrying a higher pressure of flow also have higher tension. We can extend this idea to similar sized veins and arteries. Arteries must have thicker walls than veins because they carry much higher blood pressure. Capillaries also carry high blood pressure, but unlike arteries, capillary walls are thin. This is because their small size leads to a reduced level of tension so that thick walls are not necessary.

Progressive ischemic coronary artery disease results in what?

Growth of new vessels (angiogenesis) and collaterialization within myocardium

What organs exhibit this?

Heart Brain Kidneys

What is reactive hyperemia?

Is an increase in blood flow to an organ that occurs after a period of occlusion of flow The longer the period of occlusion is, the greater the increase in blood flow is above pre-occlusion levels

What does the left coronary artery branch into?

The circumflex and left anterior descending (interventricular) artery

What happens to coronary arterioles when cardiac perfusion pressure drops?

They vasodilate to keep coronary blood flow constant

Is blood flow through coronary vessels occluded under normal conditions?

YES

How does autoregulation work?

if perfusion pressure to the heart is suddenly decreased, compensatory vasodilation of the arterioles will occur to maintain a constant flow. On the flip side, if perfusion pressure to the heart is suddenly increased, compensatory vasoconstriction of the arterioles will occur to maintain a constant flow.