Cerebrovascular reactivity in acute hyperoxia in patients with acute ischaemic stroke

This study aimed to assess the effect of acute hyperoxia on cerebral and systemic heamodynamics and the plasma concentration of prostacyclin and thromboxane in patients with stroke.

Mean blood flow velocity (MBFV), pulsatility and resistance indices of the middle cerebral artery using transcranial Doppler ultrasound before and during acute hyperoxia (4 L of 100%O₂/15' over facial mask) in 92 participants - 25 patients with acute ischaemic stroke (AIS) that occurred within 72 hours and diabetes mellitus (SPDM), 26 AIS patients without DM (SP) and in 41 healthy controls (HS), were measured. Partial pressure of O₂ (pO₂), blood pressure and heart rate were measured using pulse oxymeter and pressure gauge, respectively. All the above measurements, as well as cerebral vasoreactivity assessments were performed, before, at the end of the 15 minute period of hyperoxia, and 15 minutes after hyperoxia. The plasma concentration of thromboxane and prostacyclin were determined by ELISA assays.

MBFV increased in both SP and SPDM, while MBFV decreased in HS in response to hyperoxia. Thromboxane correlated negatively and prostacyclin positively with MBVF in the SPDM, although their concentrations did not differ significantly after hyperoxia among groups.

Results suggest impaired vascular reactivity to acute hyperoxia in patients with stroke and the possible role of thromboxane A2/prostacycline in mediating cerebrovascular reactivity in SPDM.

ANG, II angiotensin II; ASA, acetylsalicylic acid; ATP, Adenosine triphosphate; BP, blood pressure; CBF, cerebral blood flow; CDI, colour Doppler imaging; COX, cyclooxigenase; COVR, cerebrovascular oxygen vasoreactivity; CVR, cerebrovascular reactivity; HR, heart rate; HS, healthy subjects; MBFV, mean blood flow velocity; MCA, middle cerebral artery; PG, 6-keto-PGF1alfa; PGI2, prostacycline; PI, pulsatility index; pO₂ partial pressure of O₂; RI, resistance index; ROS, reactive oxygen species; SP, stroke patients; TCD, transcranial doppler; TXA₂, thromboxane A2; TXB, thromboxane B2; VSMC, vascular smooth muscle cell; 20-HETE, 20-hydroxieicosatetraenoic acid.