You are caring for a patient admitted with chronic obstructive pulmonary disease. During your shift assessment, you find that your patient is experiencing a change in his respiratory and mental status.
You are aware that the most accurate measurement of the concentration of oxygen in the patient's blood is what?

Choice A rationale

A ventricular pacemaker is designed to pace the ventricles, not the atria. Therefore, a pacemaker spike appearing before each P wave would indicate atrial pacing, which is not the primary function of a ventricular pacemaker. P waves represent atrial depolarization, and a ventricular pacemaker's stimulus is delivered to the ventricles to initiate a QRS complex.

Choice B rationale

A pacemaker spike appearing after each QRS complex suggests either oversensing, undersensing with competitive rhythms, or a malfunction. The purpose of a pacemaker spike is to *initiate* depolarization, not to follow it. If the spike occurs after the QRS, it indicates that the ventricle has already depolarized, and the spike is not contributing to ventricular contraction.

Choice C rationale

A pacemaker spike appearing with each T wave would be inappropriate and potentially dangerous. The T wave represents ventricular repolarization, a vulnerable period during which an electrical stimulus can induce life-threatening arrhythmias like ventricular fibrillation (R-on-T phenomenon). Pacing should occur before ventricular depolarization, not during repolarization.

Choice D rationale

A ventricular pacemaker functions by delivering an electrical impulse to the ventricle when its intrinsic rate falls below a programmed threshold. This impulse, seen as a pacemaker spike on the ECG, should precede ventricular depolarization, thus initiating a QRS complex. This indicates that the pacemaker is effectively stimulating ventricular contraction at the appropriate time.

Choice A rationale

Idiopathic Parkinsonism is characterized by the degeneration of dopaminergic neurons in the substantia nigra, leading to a deficiency of dopamine in the basal ganglia. This creates an imbalance with acetylcholine, an excitatory neurotransmitter. Benztropine, an anticholinergic, helps restore this balance by blocking acetylcholine receptors, reducing tremors and rigidity.

Choice B rationale

While some forms of Parkinson's disease have genetic links, idiopathic Parkinsonism is not primarily defined by an autosomal dominant genetic defect. It is multifactorial, involving a complex interplay of genetic predispositions and environmental factors, with no single dominant gene responsible for the vast majority of cases.

Choice C rationale

Atherosclerosis and lack of blood supply are associated with vascular Parkinsonism, which is distinct from idiopathic Parkinsonism. Vascular Parkinsonism results from cerebrovascular disease leading to neuronal damage, while idiopathic Parkinsonism involves neurodegeneration of dopamine-producing neurons, not primarily ischemic injury.

Choice D rationale

Estrogen and progesterone are sex hormones and are not directly involved in the primary pathophysiological imbalance of neurotransmitters in idiopathic Parkinsonism. While hormonal fluctuations can influence neurological conditions, the core defect in Parkinsonism involves dopamine and acetylcholine dysregulation in the basal ganglia.