**Core Concept**
The patient's temporary cessation of breathing is due to a phenomenon where the diaphragm becomes inactivated and fatigued due to prolonged and repetitive activation, leading to a temporary loss of respiratory function.

**Why the Correct Answer is Right**
When the patient is ventilated at twice her normal frequency, the diaphragm experiences repetitive and prolonged activation, leading to muscle fatigue. This fatigue causes a decrease in the diaphragm's ability to contract and relax, resulting in a temporary cessation of breathing when mechanical ventilation is stopped. This phenomenon is known as **diaphragmatic fatigue**.

**Why Each Wrong Option is Incorrect**

* **Option A:** This option is incorrect because diaphragmatic fatigue is not related to the patient's blood gas levels. The patient's temporary cessation of breathing is not due to a lack of oxygen or an excess of carbon dioxide.
* **Option B:** This option is incorrect because the patient's temporary cessation of breathing is not due to a neurological cause, such as a brainstem lesion. The patient's diaphragm is functioning normally, but it is simply fatigued from prolonged activation.
* **Option C:** This option is incorrect because the patient's temporary cessation of breathing is not due to a mechanical obstruction, such as a bronchospasm or a foreign body. The patient's airways are clear, and the problem lies with the diaphragm's ability to contract and relax.

**Clinical Pearl / High-Yield Fact**
Diaphragmatic fatigue can occur in patients who are mechanically ventilated for an extended period, especially if they are ventilated at high frequencies. This phenomenon highlights the importance of monitoring patients for signs of diaphragmatic fatigue and adjusting their ventilation settings accordingly.

**Correct Answer: B.** Diaphragmatic fatigue.