Cerebral perfusion measured by 99mTc-HMPAO SPECT in a simulated microgravity model using a 5-day dry immersion
Résumé
Aim/Introduction: Regional cerebral perfusion (rCBF) may be modified during exposure to microgravity. Microgravity induces a rapid thoraco-cephalic fluid shift and generates a possible increase of intra-cranial pressure [1]. Dry immersion (DI) is a simulated microgravity model that reproduces the effects of microgravity on human fluids [2]. However, consequences on rCBF have never been directly assessed in real or simulated microgravity. Materials and Methods: Cerebral perfusion was measured 4 days before and at the end of a 5-day DI in 18 healthy male subjects (34.0 +/- 5.5 years old, 16 right dominant hand) using a single photon emission computed tomography (SPECT) with the radiopharmaceutical 99mTc-hexamethylpropylene amine oxime (HMPAO). SPECT-HMPAO were compared between the two groups using SPM 12, by paired t test statistical analysis with a threshold of p < 0.005. Results: DI induced a significant hypoperfusion in the cortex, mainly in the two temporal regions (right temporal peak level : Z = 3,61, p uncorr <0,001;left temporal peak level : Z = 3,40, puncorr <0,001))and induced an increase in perfusion in subcortical regions (including left thalamus (peak level: Z = 3,07, p uncorr <0,001)). Conclusion: After 5 days of DI, subjects presented significant hypoperfusion mainly in the bilateral temporal regions and hyperperfusion in the left thalamus region, measured by SPECT-HMPAO. Hyperperfusion in the left thalamus may be related to a muscular biopsy in the right vastus lateralis performedthe day before the SPECT the end of DI. Hypoperfusion in the cortical regions might be due to the thoraco-cephalic fluid shift and/or to the unloading support induced by the DI model. To test these assumptions, we need to conduct analysis of other parameters such as indirect assessment of intracranial pressure and psychological tests. References: [1] Heer M, et al. Space motion sickness: incidence, etiology, and countermeasures. Auton Neurosci 2006; 129(1-2):77-9.[2] Navasiolava et al. 2011). Long-term dry immersion: review and prospects. Eur J Appl Physiol 2011;111(7):1235-60.
