What is the unit of measurement for normal vascular resistance?

Normal vascular resistance is typically measured in terms of pressure difference, flow, and volume, which leads to the correct choice being mmHg/L/min. This unit reflects the relationship between the pressure (in mmHg) required to drive blood through the circulation measured over time (in minutes) through a certain volume (in liters).

Understanding this measurement is essential because vascular resistance is a key factor in determining blood flow through the cardiovascular system. The resistance in a vessel correlates directly with the pressure difference and inversely with the flow rate. A higher resistance would require a greater pressure to maintain the same flow, which is why using mmHg (a measure of pressure) alongside flow (in liters per minute) properly captures the essence of vascular resistance.

The other units provided do not accurately reflect the relationship necessary for measuring normal vascular resistance. For instance, dynes/sec/cm^-3 is a unit of force per unit volume and does not apply to vascular resistance. Similarly, while dynes/sec/cm^-4 appears to be more related to resistance, it still doesn't represent the direct relationship of pressure to volume flow rate needed to assess vascular resistance. Finally, mmHg/L lacks the time component which makes it inadequate for representing resistance since resistance requires consideration of both pressure and flow