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1 University Department of
Medicine for the Elderly,
The Valsalva
maneuver (VM), a voluntary increase in intrathoracic pressure of ~40
mmHg, has been used to examine cerebral autoregulation (CA). During
phase IV of the VM there are pronounced changes in mean arterial blood
pressure (MABP), pulse interval, and cerebral blood flow (CBF), but the
changes in CBF are of a much greater magnitude than those seen in MABP,
a finding to date attributed to either a delay in activation of the CA
mechanism or the inability of this mechanism to cope with the size and
speed of the blood pressure changes involved. These changes in CBF also precede those in MABP, a pattern of events not explained by the physiological process of CA. Measurements of CBF velocity (transcranial Doppler) and MABP (Finapres) were performed in 53 healthy volunteers (aged 31-80 yr). By calculating beat-to-beat values of critical closing pressure (CCP) during the VM, we have found that this parameter
suddenly drops at the start of phase IV, providing a coherent
explanation for the large increase in CBF. If CCP is included in the
estimation of cerebrovascular resistance, a temporal pattern more
consistent with an autoregulatory response to the MABP overshoot is
also found. CCP is intricately involved in the control of CBF during
the VM and should be considered in the assessment of CA.
cerebral blood flow; cerebral autoregulation; cerebrovascular resistance
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