In this model, increasing the left flow tube radius primarily affects which of the following?

In this model, increasing the left flow tube radius primarily affects which of the following?

• A. Flow rate
• B. Beaker pressure
• C. Left ventricular velocity
• D. Systemic arterial compliance

Answer: (B)

When you widen the left flow tube, you dramatically reduce its resistance (Poiseuille’s law says resistance scales roughly with 1/r^4). If the heart (the pressure source) keeps pushing with about the same upstream pressure, a smaller pressure drop along that tube means the downstream pressure at the beaker rises. That beaker pressure is the quantity that most directly reflects the change in the tube’s resistance, so it shifts the most when you adjust the radius. Flow rate will also change because the lower resistance allows more fluid to pass, and left ventricular velocity will adapt to the new pressure gradient, but the immediate, primary effect of increasing the radius is on the beaker pressure. Systemic arterial compliance, being a property of the vessel walls and the downstream load, doesn’t change chiefly due to this radius adjustment.

When you widen the left flow tube, you dramatically reduce its resistance (Poiseuille’s law says resistance scales roughly with 1/r^4). If the heart (the pressure source) keeps pushing with about the same upstream pressure, a smaller pressure drop along that tube means the downstream pressure at the beaker rises. That beaker pressure is the quantity that most directly reflects the change in the tube’s resistance, so it shifts the most when you adjust the radius. Flow rate will also change because the lower resistance allows more fluid to pass, and left ventricular velocity will adapt to the new pressure gradient, but the immediate, primary effect of increasing the radius is on the beaker pressure. Systemic arterial compliance, being a property of the vessel walls and the downstream load, doesn’t change chiefly due to this radius adjustment.