Thymoma

A 40-year-old woman begins complaining of dyspnea while recovering in the post-anesthesia care unit. Earlier in the day, the patient underwent a laparoscopic cholecystectomy for treatment of symptomatic gallstones. Past medical history is unremarkable. Her temperature is 37.7°C (99.9°F), pulse is 93/min, respiratory rate is 24/min and blood pressure is 125/72 mmHg. Physical examination shows the patient in distress with shallow breaths, using accessory muscles. In addition, the patient is observed to have drooping of the eyelids and corners of the mouth bilaterally. Pupils are 3 cm bilaterally and reactive to light. An arterial blood gas measurement reveals the following findings:  

Laboratory Value	Result	Reference Range
pH	7.31	7.35-7.45
PaCO2	56 mmHg	33-45 mmHg
PaO2	71 mmHg	75-105 mmHg
Bicarbonate	25 mmol/L	22-28 mmol/L

   
The patient’s condition improves with administration of edrophonium chloride. Which of the following best describes the cause of this patient’s condition?