Which drug produces strong pulmonary arterial dilation with the least amount of systemic arterial dilation?

Which drug produces strong pulmonary arterial dilation with the least amount of systemic arterial dilation?

• A. Nitroprusside
• B. Prostaglandin E1
• C. Phentolamine
• D. Nitric oxide

Answer: (D)

Inhaled nitric oxide provides strong dilation of the pulmonary arteries with minimal systemic effects because it acts locally in the lungs. When NO is inhaled, it diffuses into pulmonary vascular smooth muscle and activates soluble guanylate cyclase, increasing cyclic GMP and causing relaxation of the smooth muscle. Since the gas is delivered directly to ventilated lung units, it preferentially reaches vessels where gas exchange is occurring, improving blood flow to well-ventilated areas and reducing ventilation–perfusion mismatch. Importantly, NO is rapidly scavenged by hemoglobin in the pulmonary capillaries, which limits its spread into the systemic circulation and keeps systemic vascular resistance largely unchanged. By contrast, nitroprusside dilates both systemic and pulmonary vessels, potentially causing systemic hypotension; prostaglandin E1 also causes systemic vasodilation and is not pulmonary-selective in this context; phentolamine, an alpha-blocker, lowers systemic vascular resistance as well and does not selectively target the pulmonary circulation. Therefore, inhaled nitric oxide best matches the goal of strong pulmonary arterial dilation with the least systemic arterial dilation.

Inhaled nitric oxide provides strong dilation of the pulmonary arteries with minimal systemic effects because it acts locally in the lungs. When NO is inhaled, it diffuses into pulmonary vascular smooth muscle and activates soluble guanylate cyclase, increasing cyclic GMP and causing relaxation of the smooth muscle. Since the gas is delivered directly to ventilated lung units, it preferentially reaches vessels where gas exchange is occurring, improving blood flow to well-ventilated areas and reducing ventilation–perfusion mismatch. Importantly, NO is rapidly scavenged by hemoglobin in the pulmonary capillaries, which limits its spread into the systemic circulation and keeps systemic vascular resistance largely unchanged.

By contrast, nitroprusside dilates both systemic and pulmonary vessels, potentially causing systemic hypotension; prostaglandin E1 also causes systemic vasodilation and is not pulmonary-selective in this context; phentolamine, an alpha-blocker, lowers systemic vascular resistance as well and does not selectively target the pulmonary circulation. Therefore, inhaled nitric oxide best matches the goal of strong pulmonary arterial dilation with the least systemic arterial dilation.