Which of the following is associated with decrease in cardiac output ?

Options

A. Sympathetic nerves
B. Parasympathetic neural signals
C. Pneumotaxic centre
D. Adrenal medullary hormon

Answer

### Step-by-Step Solution:

1. **Understanding Cardiac Output**:
- Cardiac output (CO) is defined as the volume of blood the heart pumps per minute. It is calculated using the formula:
\[ \text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate} \]
- Stroke volume (SV) is the amount of blood pumped by each ventricle during one cardiac cycle, typically around 70 ml.

2. **Identifying Factors Affecting Cardiac Output**:
- Several factors can influence cardiac output, including neural signals, hormones, and physical conditions.

3. **Evaluating the Options**:
- **Option A: Sympathetic Nerves**: These nerves are responsible for increasing heart rate and cardiac output. Therefore, they are not associated with a decrease in cardiac output.
- **Option B: Parasympathetic Neural Signals**: These signals are known to decrease heart rate and, consequently, cardiac output. This option is likely correct.
- **Option C: Pneumotoxic Center**: This center primarily regulates respiration and does not directly influence cardiac output. Its role is more related to altering the rate of breathing rather than affecting cardiac output directly.

4. **Conclusion**:
- Based on the evaluation of the options, the correct answer is **Option B: Parasympathetic Neural Signals**, as they are associated with a decrease in cardiac output.