NO is an important mediator in vascular reactions especially in pulmonary circulation. Oral compounds can act by NO mediated pathways, but addressing the effect of pulsed inhaled NO (iNO) directly on the airways and pulmonary vasculature is worthwhile. Therefore a proof of concept study was performed using FRI to quantify blood vessel caliber directly from CT images.
During 20min pulsed iNO (30 mcg/kg IBW/hr) was administered via nasal cannula in 6 COPD patients with PAH. Patients underwent a HRCT scan with contrast before and after iNO. Using FRI, blood vessel and associated lobe volumes were quantified. Oxygen saturation and blood pressure were monitored and patients were requested about their subjective feelings.
Blood vessel volume increased by 7.06±5.37% after iNO. A strong correlation (W=0.57, p=0.002) was obtained between ventilation and vasodilation, suggesting that regions with better ventilation experience more vasodilation and that with a pulse system iNO is directed towards the ventilated zones. Patients did not develop oxygen desaturation, remained normotensive and perceived an improvement in their dyspnea sensation.
Pulsed iNO has a profound effect on the pulmonary vessels caliber and FRI can be used to detect these changes. Vasodilation is highly correlated with ventilation. The effect of upper airway resistance and of NO and oxygen inhalation will be subject of future studies.