A six fold increase in blood flow through a major coronary artery is typically o
ID: 2079075 • Letter: A
Question
A six fold increase in blood flow through a major coronary artery is typically observed following an occlusion of about 10 seconds. This phenomenon is known as reactive hyperemia. It occurs without significant changes in pressure and is due to dilation of arteries distal to the occlusion. What fractional change in resistance is necessary to explain this result? If the relative increase in vessel diameters is uniform throughout this arterial tree, what is the r/ro where ro is the artery radius in the control state (before occlusion) and r is the radius during the reactive hyperemia? Assume Poiseuille flow. Assume that the resistance in the coronary artery equals the resitance in the distal arteries prior to occlusion.
Explanation / Answer
Vessel Diameter Analogy
• Vessel diameter affects peripheral resistance.
• As a the diameter of a tube gets smaller, a greater proportion of the fluid is in contact with the wall of
the tube. Therefore resistance to flow is increased and pressure rises.
• Larger diameter, same volume, less pressure.
• Smaller diameter, same volume, more pressure
Peripheral resistance is the resistance of the arteries to blood flow. As the arteries constrict, the resistance increases and as they dilate, resistance decreases.
Peripheral resistance is determined by three factors: