Chapter 6 /Hz 1500 pCO = 30 mmHg 2 2 PSD ABP mmHg pCO = 40 mmHg 1000 2 pCO = 50 mmHg 2 500 0 0 0.1 0.2 0.3 0.4 0.5 /Hz PSD CBFV (cm/s) 2 600 400 200 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Frequency Hz Figure 2 Group averaged power spectral densities of ABP and CBFV during cardiopul- monary bypass at three different paCO2 levels. Error bars represent ± 1 standard deviation at 0.1 Hz. Since no significant differences are found between left and right MCA CBFV only left-right averaged results are presented for CO2R and dCA. In the left and right MCA mean CBFV is significantly lower (p<0.01) for hypocapnia compared to both normocapnia and hypercapnia. Although ABP standard deviation was equal for all three paCO2 levels, CBFV standard deviation is significantly lower for hypocapnia compared to both normocapnia (p<0.05) and hypercapnia (p<0.01). No significant differences were found for CBFV power spectral density at 0.1 Hz. Figure 3 shows group averaged dCA plots. Coherence is significantly higher (p<0.05) for hypercapnia compared to both hypocapnia and normocapnia. dCA parameters gain, phase and ARI are significantly higher (p<0.01) for hypocapnia compared to both normo- and hypercapnia. Moreover, normocapnia values are significantly lower (p<0.01) than hypercapnia values. Figure 4 shows group averaged dCA step responses for the three paCO2 levels. The initial step response rise decreases from hypocapnia to normocapnia and hypercapnia whereas the end level is highest for hypercapnia indicating impaired autoregulation. 110
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