How is coronary blood flow regulated?

How is coronary blood flow regulated?

• A. By blood pressure alone
• B. By heart contraction; vessels open during relaxation and are impeded during contraction
• C. By neural reflexes independent of the cardiac cycle
• D. By external compression during respiration

Answer: (B)

Coronary blood flow follows the heart’s pumping cycle because the contracting myocardium itself compresses the coronary vessels, especially the intramyocardial arterioles. During systole the heart’s muscle and surrounding tissue generate high pressure, squeezing the vessels and markedly reducing blood entry. When the heart relaxes in diastole, the compression eases and the vessels are relieved, allowing a surge of blood to perfuse the myocardium. This diastolic phase is the main window for coronary flow, particularly in the left ventricle with its thick muscle. Metabolic signals and autonomic inputs also tune flow by adjusting vessel tone to match oxygen demand, but they do not override the basic pattern imposed by the cardiac cycle's mechanical compression. The other options don’t fit because blood pressure alone doesn’t explain the cyclical restriction of flow, neural reflexes are not acting completely independently of the cardiac cycle, and external compression from respiration isn’t the primary determinant of coronary perfusion.

Coronary blood flow follows the heart’s pumping cycle because the contracting myocardium itself compresses the coronary vessels, especially the intramyocardial arterioles. During systole the heart’s muscle and surrounding tissue generate high pressure, squeezing the vessels and markedly reducing blood entry. When the heart relaxes in diastole, the compression eases and the vessels are relieved, allowing a surge of blood to perfuse the myocardium. This diastolic phase is the main window for coronary flow, particularly in the left ventricle with its thick muscle.

Metabolic signals and autonomic inputs also tune flow by adjusting vessel tone to match oxygen demand, but they do not override the basic pattern imposed by the cardiac cycle's mechanical compression. The other options don’t fit because blood pressure alone doesn’t explain the cyclical restriction of flow, neural reflexes are not acting completely independently of the cardiac cycle, and external compression from respiration isn’t the primary determinant of coronary perfusion.