Cerebral blood flow velocity response induced by a 70-hPa Valsalva manoeuvre associated with normo- and hypergravity in humans.
Eur J Appl Physiol Occup Physiol
; 72(5-6): 502-8, 1996.
Article
em En
| MEDLINE
| ID: mdl-8925823
ABSTRACT
Anti-G straining manoeuvres, derived from the Valsalva manoeuvre (VM), are physiological methods for protecting fighter pilots against positive accelerations (+Gz). 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 Gz acceleration plateaus. Mean blood flow velocity [formula see text] in middle cerebral artery was monitored by transcranial Doppler velocimetry. In normogravity, no significant variation in [formula see text] was observed at the onset of VM. After a maximal period of 1.2 s, while VM was sustained, [formula see text] decreased significantly (P < 0.05). Following the end of the manoeuvre [formula see text] did not change significantly. When the expiratory pressure had returned to the control value, [formula see text] was transiently increased (P < 0.05) before returning to control values. During hypergravity, [formula see text] was significantly decreased at +3 and +4 Gz (P < 0.05) before the onset of VM. While performing VM under +Gz, the main difference compared to the normogravity condition was a significant increase of [formula see text] (P < 0.05) at the onset of the manoeuvre. Our findings would suggest that when performed under +Gz 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 +Gz tolerance.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Velocidade do Fluxo Sanguíneo
/
Pressão Sanguínea
/
Circulação Cerebrovascular
/
Hipergravidade
Tipo de estudo:
Risk_factors_studies
Limite:
Adult
/
Humans
/
Male
Idioma:
En
Revista:
Eur J Appl Physiol Occup Physiol
Ano de publicação:
1996
Tipo de documento:
Article
País de afiliação:
França