If heart rate increases, initially, what must happen to keep the cardiac output the
same?
End systolic volume must decrease
Stroke volume must increase
Breathing rate must decrease
Stroke volume must decrease
End diastolic volume must be cut in half
Question 22 (1 point)
usten
The Frank-Starling Mechanism states that:
ventricular muscle walls) will result in increased contractility.
negative inotropic factors result in decreased contractility
positive chronotropic factors result in increased heart rate
a decreased preload will result in an increased contractility

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UpStudy AI · Accepted Answer

**Step 1. Cardiac Output Question**

The cardiac output ($$CO$$) is given by

$$
CO = HR \times SV,
$$

where $$HR$$ is the heart rate and $$SV$$ is the stroke volume.

If the heart rate increases and the cardiac output is to remain constant, then the stroke volume must decrease because

$$
HR \uparrow \quad\text{and}\quad CO \text{ constant} \quad\Longrightarrow\quad SV \downarrow.
$$

Among the given options, the correct answer is:

- **Stroke volume must decrease**

---

**Step 2. Frank-Starling Mechanism Question**

The Frank-Starling Mechanism states that an increase in the pre-load (which is reflected by the end-diastolic volume) increases the stretch of the ventricular muscle fibers. This increased stretch enhances the contractility of the heart muscle, allowing it to eject a larger volume of blood during systole.

This concept can be summarized as:

$$
\text{Increased pre-load} \quad\Longrightarrow\quad \text{Increased fiber stretch} \quad\Longrightarrow\quad \text{Increased contractility}.
$$

Thus, the appropriate statement is:

- **Ventricular muscle walls (when stretched) will result in increased contractility.**
**Cardiac Output Question:** To keep cardiac output the same when heart rate increases, stroke volume must decrease. **Frank-Starling Mechanism Question:** Ventricular muscle walls, when stretched, result in increased contractility.

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