How does resistance change as the diameter of a blood vessel changes?

Resistance in blood vessels is influenced significantly by the diameter of the vessel, following Poiseuille's law. According to this principle, resistance is not directly proportional to diameter, but rather is inversely proportional to the fourth power of the radius (or diameter, since radius is half of the diameter). This means that even small changes in the diameter of the vessel lead to significant changes in resistance.

When the diameter increases, the resistance decreases sharply, facilitating better blood flow. Conversely, when the diameter decreases, the resistance increases dramatically, which can impede blood flow. Therefore, the relationship between resistance and diameter highlights the importance of vascular health, as maintaining appropriate vessel diameter is crucial for ensuring adequate blood circulation throughout the body.

Understanding this relationship aids healthcare professionals in diagnosing and treating conditions that may affect blood flow, such as atherosclerosis or other vascular diseases.