Cerebral blood flow velocity response induced by a 70-hPa Valsalva manoeuvre associated with normo-and hypergravity in humans

Abstract

Anti-G straining manoeuvres, derived from the Valsalva manoeuvre (VM), are physiological methods for protecting fighter pilots against positive accelerations (+G_z). The aim of this study was to investigate the effects of a standard VM on cerebral haemodynamics, in normo- and hypergravity. In six healthy male volunteers, we investigated the cerebral 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. Mean blood flow velocity ($\overline {{\text{BFV}}}$) in middle cerebral artery was monitored by transcranial Doppler velocimetry. In normogravity, no significant variation in $\overline {{\text{BFV}}}$ was observed at the onset of VM. After a maximal period of 1.2 s, while VM was sustained, $\overline {{\text{BFV}}}$ decreased significantly (P < 0.05). Following the end of the manoeuvre $\overline {{\text{BFV}}}$ did not change significantly. When the expiratory pressure had returned to the control value, $\overline {{\text{BFV}}}$ was transiently increased (P < 0.05) before returning to control values. During hypergravity, $\overline {{\text{BFV}}}$ 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 $\overline {{\text{BFV}}}$ (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, when VM is sustained for more than 1.2 s it results in a lasting decrease of cerebral perfusion which may lower + G_z tolerance.