Cerebrovascular pulsatility following long duration spaceflight is associated with changes in pulse pressure and carotid artery stiffness

Central artery stiffening increases the haemodynamic pulsations transmitted downstream towards target organs, including the brain. While recent evidence suggests that long duration spaceflight is associated with reduced common carotid artery (CCA) distensibility, cerebrovascular pulsatility has not been extensively characterized in astronauts. This study investigated changes in pulsatility from pre-flight to after 6 months in space, using a secondary analysis of data from four separate experiments. Middle cerebral artery blood velocity (MCAv) was measured during supine rest in 27 astronauts (20 men, 7 women). In subsets of this cohort, we measured CCA distensibility and β stiffness (n = 20), and CCA wave intensity (n = 12). The overall increase in MCAv pulsatility index (PI_mca) from pre-flight to post-flight was not significant (0.73 ± 0.12 vs. 0.77 ± 0.11, P = 0.060, partial η² = 0.13). However, individual changes in PI_mca were directly associated with changes in estimated aortic pulse pressure (r = 0.51, P = 0.007) and β stiffness (r = 0.54, P = 0.015), and inversely associated with changes in distensibility (r = -0.62, P = 0.003), in separate bivariate analyses. Wave intensity analysis suggested a reduction in normalized wave reflection (P = 0.07), and that forward compression wave amplitude was directly related to PI_mca (r = 0.64, P = 0.025). These findings suggest that PI_mca in the days immediately following spaceflight is a function of lower carotid distensibility, highlighting the interplay between arterial stiffness and cerebrovascular pulsatility.