There is increasing evidence that heart performance directly influences cerebral perfusion. We hypothesised that increased inspiratory resistance would affect the cardiac contribution to the relationship between blood pressure and pial artery pulsation oscillations.Design and method:
Experiments were performed in a group of 20 healthy volunteers undergoing controlled intermittent Mueller Manoeuvers. Blood pressure and heart rate were measured using continuous finger-pulse photoplethysmography; oxyhaemoglobin saturation with an ear-clip sensor; end-tidal CO2 with a gas analyser; cerebral blood flow velocity, pulsatility and resistive indices with Doppler ultrasound. Changes in the pial artery pulsation and in the width of subarachnoid space were recorded with a new method called near-infrared transillumination/backscattering sounding. Wavelet transform analysis was used to assess the relationship between blood pressure and pial artery pulsation oscillations.Results:
Initiating Mueller manoeuvers evoked pial artery pulsation decline (by 18% vs. baseline; P < 0.001), blood pressure and heart rate increase (by 6% P < 0.001, and 3% P < 0.05, respectively). By the end of Mueller manoeuvers, pial artery pulsation and heart rate did not change, but blood pressure was elevated (by 12% vs. baseline; P < 0.001). A decrease in wavelet coherence between blood pressure and pial artery pulsation oscillations at cardiac frequency found in the first half of the Mueller manoeuvers was followed by recovery by the end of Mueller manoeuvers (Tab.). Wavelet phase coherence was high at baseline and did not change throughout the Mueller manoeuvers (Tab.).Results:
Tab.: Effects of a 60 s Mueller manoeuvres series on WCO and WPCO between BP and cc-TQpial artery pulsation.Results:
Caption: *P < 0.05; **P < 0.01; ***P < 0.001; WCO – wavelet coherence; WPCO – wavelet phase coherence; cc-TQ – cardiac component of transillumination quotient (pial artery pulsation); left – left hemisphere; right – right hemisphere; SD – standard deviation.Conclusions:
Increased inspiratory resistance is associated with swings in the cardiac contribution to the dynamic relationship between blood pressure and pial artery pulsation oscillations. Impaired cardiac performance seen during Mueller manoeuvers may be transmitted to the cerebral microcirculation.