Evaluation of impaired dynamic cerebral autoregulation by the Mueller manoeuvre

Arterial blood pressure (ABP) shows polyphasic changes during the Mueller m anoeuvre (voluntary negative intrathoracic pressure). The aim of the presen t study was to investigate (1) whether these changes could be applied to de tect impaired dynamic cerebral autoregulation (dCA) in carotid stenosis and (2) whether the degree of indicated impairment correlates with transfer fu nction phase as another current measure for dCA (deep breaching method) and CO2-reactivity. We examined 13 patients with severe unilateral carotid art ery stenosis and 16 age-matched controls during 15-s Mueller manoeuvres (MM ) at -30 mmHg using bilateral transcranial Doppler sonography and non-invas ive ABP recordings (Finapres, 2300, Ohmeda, Englewood, CO, USA). After an i nitial biphasic oscillation, cerebral blood flow velocity (CBFV) and ABP de creased to below baseline. CBFV reincreased in controls and on contralatera l sides in patients 6.0 s (3.8-9.5 s, median and range) after the onset of the decrease, despite a further fall in ABP. CBFV over the affected side re vealed a significantly delayed reincrease (8.0 (5.6-10.3) s; P<0.01) combin ed with a relatively flat and inertial amplitude behaviour. An applied auto regulation index derived from the MM (mROR), phase shift and CO2-reactivity were severely reduced on the affected side in patients (P<0.01). Reduction of the mROR correlated significantly with reduction of phase shift (r=0.69 ; P = 0.002) and CO2-reactivity (r = 0.78; P = 0.002). In conclusion, the d ifferent cerebral haemodynamic pattern during the MM in patients is likely to reflect impaired dCA. The degree of indicated impairment correlates with that of transfer function phase and CO2-reactivity. Therefore, the MM repr esents a convenient method for grading of compromised cerebral haemodynamic s in patients with carotid artery stenosis.