Critical closing pressure explains cerebral hemodynamics during the Valsalva maneuver

The Valsalva maneuver (VM), a voluntary increase in intrathoracic pressure of similar to 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 t he 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 mech anism 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 tho se in MABP, a pattern of events not explained by the physiological process of CA. Measurements of CBF velocity (transcranial Doppler) and MABP (Finapr es) 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 h ave found that this parameter suddenly drops at the start of phase TV, prov iding a coherent explanation for the large increase in CBF. If CCP is inclu ded in the estimation of cerebrovascular resistance, a temporal pattern mor e 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.