A 72-year-old woman with systolic heart failure and newly diagnosed atrial fibrillation presents with dizziness and two episodes of syncope upon standing over the past week. Two weeks ago, metoprolol succinate 50 mg daily was initiated for rate control. She also takes furosemide 40 mg daily and recently completed a course of trimethoprim-sulfamethoxazole for a urinary tract infection. On examination, supine blood pressure is 138/82 mmHg and heart rate is 58 bpm; upon standing, blood pressure drops to 110/68 mmHg with heart rate remaining at 58 bpm. Physical examination reveals dry mucous membranes. Laboratory studies show: sodium 138 mEq/L, potassium 3.8 mEq/L, creatinine 1.1 mg/dL. Which of the following best explains the mechanism of her orthostatic hypotension?

1. A)Beta-adrenergic blockade impairing the reflex tachycardia needed to maintain blood pressure during positional changesGABARITO
2. B)Hypokalemia-induced impairment of vascular smooth muscle contractility
3. C)Trimethoprim-sulfamethoxazole-mediated inhibition of norepinephrine reuptake in sympathetic neurons
4. D)Furosemide-induced depletion of intravascular volume reducing venous return
5. E)Parasympathomimetic effects of metoprolol causing unopposed vagal tone