Cerebral haemodynamics during the Mueller manoeuvre in humans.

Voluntary negative intra-thoracic pressure (Mueller manoeuvre) is known to reduce arterial blood pressure (ABP). To investigate changes in cerebral blood flow velocity (CBFV) during 15 s Mueller manoeuvres at -30 mmHg intra-thoracic pressure, 27 young (aged 21-31 years, group A) and 11 older (52-64 years, group B) healthy adults were studied using transcranial Doppler and non-invasive ABP measurement (Finapres). After closely following the initial ABP drop, CBFV showed an overshoot during temporary recovery of ABP. Then ABP and CBFV decreased significantly to below baseline. While ABP declined further until the end of the manoeuvre, CBFV increased in group A 4.7 s (2.4-8.5) (median and range) and in group B 5.7 s (4. 1-7.2) after the onset of the CBFV decrease. Critical closing pressure (CCP), calculated for each cardiac cycle from the dynamic pressure-flow relationship (DPFR), indicated a reduction of intra-cranial pressure during the first half of the strain. DPFR-related estimation of cerebrovascular resistance provided a more physiological response than the conventional cerebrovascular resistance quotient ABP/CBFV, and decreased about 1.5 s before the observed CBFV increase. A modification of the previously described dynamic auto-regulation index ROR correlated significantly with CO2 reactivity values (r=0.61, P=0.001). In conclusion, changes in CBFV during Mueller manoeuvres are likely to reflect dynamic cerebral auto-regulation and may provide an estimate of dynamic cerebral auto-regulation capacity. In older adults, the maximal dynamic auto-regulatory response seems to be unchanged, but the onset of reaction is slightly delayed.