Blood flow 2 & 3

Introduction to Blood Flow

• Blood flow is the volume of blood that passes through a vessel in a specific time frame, often measured in milliliters per minute.

• Several factors influence blood flow, including pressure and resistance.

Understanding Fractions: The Relationship Between Numerator and Denominator

• Numerator: The number above the line in a fraction.

• Denominator: The number below the line in a fraction.

• Effect of Changing the Numerator:

  • Increasing the numerator leads to a higher value of the fraction (e.g., increasing from 1/2 to 2/2 results in 1).

  • Decreasing the numerator results in a lower value of the fraction.

• Effect of Changing the Denominator:

  • Increasing the denominator decreases the value of the fraction (e.g., changing 1/2 to 1/4 results in 1/4).

  • Decreasing the denominator results in a higher value.

Factors Affecting Blood Flow

• Pressure in: The pressure with which blood enters a vessel (e.g., left ventricle into the aorta).

• Pressure out: The pressure at which blood exits a vessel (e.g., into the right atrium).

• Flow Equation:

  • Flow (F) is influenced by the difference between pressure in and pressure out:

    • [ F = P_{in} - P_{out} ]

  • Greater pressure difference results in greater flow.

Examples of Pressure Differences

1. Example A: Pressure in = 100 mmHg, Pressure out = 0 mmHg

   • Difference = 100 (High flow)

2. Example B: Pressure in = 100 mmHg, Pressure out = 50 mmHg

   • Difference = 50 (Moderate flow)

3. Example C: Pressure in = 100 mmHg, Pressure out = 100 mmHg

   • Difference = 0 (No flow)

Resistance in Blood Flow

• Definition of Resistance: The opposition to blood flow within a vessel.

• Factors Influencing Resistance:

  • Viscosity of Blood:

    • Higher viscosity (thicker blood) increases resistance.

    • Lower viscosity (thinner blood) decreases resistance.

  • Length of Blood Vessel: Longer vessels create more resistance, but this is less variable in the body.

  • Radius of Blood Vessel: The most significant influence on resistance.

Understanding the Role of Radius in Resistance

• Vasoconstriction: Decreasing the radius increases resistance, making blood flow harder.

• Vasodilation: Increasing the radius decreases resistance, facilitating easier blood flow.

Combined Flow and Resistance Equation

• Total Flow (F) can also be understood through the relationship with resistance:

  • [ F = \frac{P_{in} - P_{out}}{R} ] where ( R ) represents resistance.

• Resistance Equation:

  • [ R = \text{Viscosity} \times \text{Length of Blood Vessel} / \text{Radius}^4 ]

Clinical Correlations

• Increased Viscosity: Seen in conditions like diabetes mellitus, which results in decreased blood flow due to increased resistance.

• Decreased Viscosity: Seen in anemia, making blood flow easier due to reduced resistance.

• Importance of Radius: A small reduction in radius (e.g., due to blockage) can greatly increase resistance and decrease blood flow significantly (e.g., 16 times less flow from 50% blockage).

Summary of Key Relationships

• Pressure Difference:

  • Increasing the difference => Increases flow.

  • Decreasing the difference => Decreases flow.

• Resistance:

  • Increasing resistance => Decreases flow.

  • Decreasing resistance => Increases flow.

• Critical Importance of Radius:

  • Vasoconstriction (decreasing radius) => More resistance and less flow.

  • Vasodilation (increasing radius) => Less resistance and more flow.

Conclusion

• Understanding how pressure, resistance, and other factors like blood viscosity and vessel radius influence blood flow is vital for examining cardiovascular health and diagnosing conditions related to blood circulation.