Correct Answer: A

Rationale: The correct answer is A: Chordae tendineae. Chordae tendineae are fibrous cords that connect the AV valves to the papillary muscles, preventing the valves from inverting during ventricular contraction. Papillary muscles (choice B) anchor the chordae tendineae to the ventricular wall but do not hold up the AV valves directly. Semilunar valves (choice C) are located between the ventricles and the major arteries and are not involved in holding up the AV valves. The aortic valve (choice D) is one of the semilunar valves and is not responsible for holding up the AV valves.

Correct Answer: A

Rationale: Emphysema is the correct answer. It is a chronic lung condition characterized by the permanent enlargement and damage of the alveoli, leading to shortness of breath and impaired oxygen exchange. Bronchitis is the inflammation of the bronchial tubes, not specifically related to alveolar damage. Atelectasis is the collapse of lung tissue, not enlargement. Pulmonary fibrosis involves scarring and thickening of lung tissue, different from the alveolar damage seen in emphysema.

Correct Answer: B

Rationale: The correct answer is B: Approximately 70 mL of blood per beat. The stroke volume of the heart is typically around 70 mL, indicating the volume of blood ejected from the left ventricle with each contraction. Choices A, C, and D are incorrect as they do not represent the standard approximate stroke volume of the heart, which is around 70 mL per beat.

Correct Answer: B

Rationale: The correct answer is to hold the digoxin and notify the healthcare provider. A potassium level of 3.0 mEq/L indicates hypokalemia, which can increase the risk of digoxin toxicity. Digoxin and low potassium levels can lead to serious cardiac arrhythmias. Administering a potassium supplement (choice A) without healthcare provider guidance can worsen the situation. Continuing the current digoxin dose (choice C) can further increase the risk of toxicity. Administering Digibind (choice D) is used in severe cases of digoxin toxicity, not for addressing low potassium levels.

Correct Answer: A

Rationale: The correct answer is Pneumothorax. Pneumothorax occurs when air or gas accumulates in the pleural space, causing the lung to collapse. This condition can result in symptoms such as chest pain and difficulty breathing. Pulmonary embolism (choice B) is a blockage in one of the pulmonary arteries in the lungs, usually caused by a blood clot. Pleural effusion (choice C) is the accumulation of excess fluid in the pleural space, not air or gas. Atelectasis (choice D) refers to the collapse or closure of a lung resulting in reduced or absent gas exchange.