Increased hemodynamic pulsatility in the cerebral microcirculation during parabolic flight-induced microgravity: A computational investigation

Ground-based spaceflight analogs play a crucial role to understand and predict cardiovascular alterations during microgravity in a controlled and affordable way. Despite their extensive use in recent years, cerebral hemodynamics in microgravity remains poorly understood, multifaceted, and definitive data are still missing, due to the limited number and different duration of experiments, the individual variability, and the intrinsic difficulty in obtaining direct clinical measures. However, there is growing evidence that hemodynamic changes are among the underlying causes of neurological dysfunctions, such as the Spaceflight Associated Neuro-ocular Syndrome (SANS). We proposed to investigate the cerebral hemodynamics during supine posture parabolic flight by means of a validated computational approach, combining a 0D-1D central-systemic cardiovascular model together with a 0D cerebrovascular model. Present findings showed that, although with over- and under-shoots in the transition from one gravitational environment to the other, beat-averaged pressure and flow rate steady state values did not greatly vary between 0g and 1g due to the cerebral autoregulation. On the contrary, in microgravity there was an augmented hemodynamic pulsatility which increased towards the deep cerebral microcirculation. The greater pulsatility, inducing a higher variability of maximum and minimum values reached within each beat, was here observed for the first time also for important cerebral markers, such as the intracranial pressure, the cerebrospinal fluid circulation, and the cerebral blood flow. The proposed approach offers novel insights on how hemodynamic alterations, such as cerebral hypoperfusions and intracranial pressure fluctuations, can contribute to explain neurovestibular dysfunctions emerging during short-term exposure to 0g, including the onset of nausea, SANS and cognitive fatigue.