CEREBRAL BLOOD-FLOW VELOCITY RESPONSE INDUCED BY A 70-HPA VALSALVA MANEUVER ASSOCIATED WITH NORMOGRAVITY AND HYPERGRAVITY IN HUMANS

Anti-G straining manoeuvres, derived from the Valsalva manoeuvre (VM), are physiological methods for protecting fighter pilots against posit ive accelerations (+G(z)). The aim of this study was to investigate th e effects of a standard VM on cerebral haemodynamics, in normo- and hy pergravity. In six healthy male volunteers, we investigated the cerebr al blood flow velocity response induced by a 10-s, 70-hPa (52.5 mmHg) VM, under normogravity, + 2, + 3 and + 4 G(z) acceleration plateaus. M ean blood flow velocity (BFV) in middle cerebral artery was monitored by transcranial Doppler velocimetry. In normogravity, no significant v ariation in BFV was observed at the onset of VM. After a maximal perio d of 1.2 s, while VM was sustained, BFV decreased significantly(P < 0. 05). Following the end of the manoeuvre BFV did not change significant ly. When the expiratory pressure had returned to the control value, BF V was transiently increased (P < 0.05) before returning to control val ues. During hypergravity, BFV was significantly decreased at + 3 and 4 G(z) (P < 0.05) before the onset of VM. While performing VM under G(z), the main difference compared to the normogravity condition was a significant increase of BFV (P < 0.05) at the onset of the manoeuvre . Our findings would suggest that when performed under + G(z) stress, a 70-hPa VM can transiently improve cerebral haemodynamics. However, w hen VM is sustained for more than 1.2 s it results in a lasting decrea se of cerebral perfusion which may lower + G(z) tolerance.