Nitric oxide is a small molecule produced by vascular endothelium. Nitric oxide crosses into vascular smooth muscle and stimulates guanylate cyclase. Subsequently, cGMP produces smooth muscle relaxation and vasodilation. Nitric oxides administered by inhalation and cross the alveolar membrane to the vascular endothelium, producing smooth muscle relaxation. But when it crosses into the circulation, it is rapidly bound to haemoglobin (affinity 1500 times greater than carbon monoxide) and deactivated; thus it has no systemic vasodilation effect.
Since it is only delivered to ventilated alveoli. It increases blood to those areas and improves V/Q matching. Dosage ranges wide, but 20 to 40 parts per million is not an atypical dose. Deactivation on entering the circulation also limits the effectiveness of nitric oxide to the period in which it is administered by inhalation. Because storage in…
