Summarize the relationship between Cardiac Output, Peripheral Resistance, Blood Volume, and Vessel Elasticity on blood pressure, including the key mechanisms involved.

Here is a summary of the factors affecting blood pressure from the image:

• Cardiac Output (CO)

  • Effect on Blood Pressure (BP): An increase in cardiac output leads to an increase in blood pressure. $$\uparrow \text{CO} \to \uparrow \text{BP}$$
  • Key Explanation/Mechanism: More blood pumped per minute results in higher pressure against vessel walls. Cardiac output is calculated as Heart Rate $\times$ Stroke Volume.

• Peripheral Resistance (TPR)

  • Effect on Blood Pressure (BP): An increase in resistance leads to an increase in blood pressure, and a decrease in resistance leads to a decrease in blood pressure. $$\uparrow \text{Resistance} \to \uparrow \text{BP}$$ $$\downarrow \text{Resistance} \to \downarrow \text{BP}$$
  • Key Explanation/Mechanism: Primarily controlled by arteriole diameter.
    • Vasoconstriction: Narrows blood vessels, increasing resistance and thus increasing blood pressure. $$\text{Vasoconstriction} \to \uparrow \text{Resistance} \to \uparrow \text{BP}$$
    • Vasodilation: Widens blood vessels, decreasing resistance and thus decreasing blood pressure. $$\text{Vasodilation} \to \downarrow \text{Resistance} \to \downarrow \text{BP}$$

• Blood Volume

  • Effect on Blood Pressure (BP): An increase in blood volume leads to an increase in blood pressure. $$\uparrow \text{Volume} \to \uparrow \text{BP}$$
  • Key Explanation/Mechanism: More circulating fluid (e.g., from fluid retention, high salt intake) increases pressure in the vessels.

• Vessel Elasticity

  • Effect on Blood Pressure (BP): A decrease in vessel elasticity leads to an increase in systolic blood pressure, especially. $$\downarrow \text{Elasticity} \to \uparrow \text{Systolic BP (especially)}$$
  • Key Explanation/Mechanism: Stiff arteries (due to aging or atherosclerosis) have a low ability to stretch, leading to higher peak pressure during systole.