Cerebral microvascular blood flow and CO2 reactivity in pulmonary arterial hypertension

Abstract Hypocapnia and endothelial dysfunction might impair microvascular cerebral blood flow (CBF micr ) and cerebrovascular reactivity to CO 2 (CVR CO2 ). Pulmonary arterial hypertension (PAH) is characteristically associated with chronic alveolar hyperventilation and microvascular endothelial dysfunction. We therefore determined CBF micr (pre-frontal blood flow index (BFI) by the indocyanine green-near infrared spectroscopy methodology) during hypocapnia and hypercapnia in 25 PAH patients and 10 gender- and age-matched controls. Cerebral BFI was lower in patients than controls at similar transcutaneous PCO 2 (P tc CO 2 ) levels in both testing conditions. In fact, while BFI increased from hypocapnia to hypercapnia in all controls, it failed to increase in 17/25 (68%) patients. Thus, BFI increased to a lesser extent from hypo to hypercapnia (“Δ”) in patients, i.e., they showed lower Δ BFI/Δ P tc CO 2 ratios than controls. In conclusion, CBF micr and CVR CO2 are lessened in clinically stable, mildly-impaired patients with PAH. These abnormalities might be associated with relevant clinical outcomes (hyperventilation and dyspnea, cognition, cerebrovascular disease) being potentially amenable to pharmacological treatment.