We have evaluated cerebral blood flow velocities (CBFV) using transcranial Doppler (TCD) during cardiovascular surgery under extracorporeal circulation. We attempted to determine cerebrovascular reactivity to CO₂ pressure by varying the concentration of inspired CO₂ and measuring CBFV with TCD under moderate hypothermia. In this study, 66 patients (mean age: 63.6±7.2 years) who underwent cardiac operations were assessed over a four-year period. Forty patients received aorto-coronary bypass grafts, 13 patients had valvular heart disease, and 12 had congenital septal defects. One patient had a left atrial myxoma. In all cases, cardiac surgery was performed with moderate hypothermia and non-pulsatile cardiopulmonary bypass. The pump flow was fixed at 2.6 L/min/m² in all patients.
Patients were divided into three groups according to age (cut-off value, 70 years) and type of surgery. Among the 41 patients under 70 years old, 15 patients underwent closure of septal defects or replacement of heart valves (non-CABG group), and 26 received coronary arterial bypass grafts (CABG group) . All of the 25 patients aged over 70 years received CABGs (elderly group) . As in the non-CABG group, there was a close correlation between PaCO₂ and mean CBFV (mean CBFV=-2.47+1.21×PaCO₂, R²=0.429) . The patients in the CABG group showed a mild linear correlation between PaCO₂ and mean CBFV (mean CBFV=1.64+0.89×PaCO₂, R²=0.216) . There were no significant correlations in the elderly group.
It is concluded that flow velocity is increased under moderate hypothermia in proportion to increased PaCO₂ in patients aged under 70 years. TCD is a practical non-invasive monitoring system and can provide an approximation of changes in cerebral circulation during moderate hypothermia.

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We measured end-diastolic flow velocities (EDFVs) of the internal carotid artery (ICA) bilaterally by duplex ultrasonography and calculated their side-to-side ratios in 14 healthy volunteers (normal group) and 29 patients with unilateral occlusion of the middle cerebral artery (MCA, n=5), distal internal carotid artery (distal ICA, n=7) or the origin of the ICA (ICA origin, n=17) . The site of arterial occlusion was confirmed by digital subtraction angiography, magnetic resonance angiography or transcranial color Doppler ultrasonography. The side-to-side ratio was 1.11±0.06 in the normal group. In the MCA occlusion group, it was 1.73±0.39 and exceeded 1.23 (the mean+2SD of the side-to-side ratio in the normal group) in four patients. In four patients with distal ICA occlusion, EDFVs were zero. However, in the other three patients with a flow to the posterior communicating artery or to moyamoya vessels, there was residual flow in the end-diastolic phase, and EDFV ratios were greater than 1.23. In the ICA origin occlusion group, no flow could be detected throughout the systolic and diastolic phases. In conclusion, measurement of EDFV and calculation of EDFV ratios of the ICA seem useful as screening measures to determine the site of occlusion of the ICA or MCA.

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Background and Purpose: With recent transcranial Doppler ultrasonography (TCD) techniques, high intensity transient signals (HITS) can be detected automatically. However, the significance of automatically detected HITS without associated sound is unclear. We attempted to determine whether HITS detected automatically during veno-arterial extracorporeal membrane oxygenation (V-A ECMO) reflect the state of blood coagulability. Methods : In an animal study, V-A ECMO was performed in 11 adult pigs by aortic and pulmonary cangulation using a roller pump and membrane oxygenator. HITS were counted automatically during bypass before and after administration of anticoagulants. In a clinical study of 6 patients with V-A ECMO after cardiac surgery, HITS were detected during and after removal of ECMO. Results: In the animal study, the majority of HITS recorded during V-A ECMO had no associated sound. The HITS count before and after ECMO was 0 and 49±35/10-min (n=11), respectively. The HITS count after administration of heparin was 4±4/10-min (n=5), and that after administration of argatroban was 7±7/10-min (n=6) . HITS counts were significantly reduced after administration of either anticoagulant (p<0.001) . In the clinical study, HITS were detected frequently during ECMO (158±99/15-min (n=6) ), but no HITS were detected after its removal. The HITS count rate was negatively correlated with activated clotting time. Conclusions: Automatically detected HITS without associated sound may reflect the degree of coagulation during V-A ECMO. Therefore, inaudible HITS may be a useful indicator of the level of anticoagulation during V-A ECMO.

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We evaluated the relationship between the grade of internal carotid artery (ICA) stenosis and the pulsatility index (PI) of the middle cerebral artery (MCA) . [Methods] PI and MCA mean velocity (Vm) values were obtained for 27 patients with ICA stenosis using transcranial Doppler sonography. The PI values were also obtained for 16 healthy volunteers (0.77±0.12) . The patients were divided into 3 groups (Group A (n=8) : PI<0.65; Group B (n=12) : 0.65≤PI<0.89; Group C (n=7) : 0.89≤PI) and the grades of ICA stenosis and the Vm values were compared among the three groups. [Results] There was a significant correlation between the grade of ICA stenosis and the PI (stenosis=112.5-39.3×PI, R=0.644, p=0.0003) . The grades of ICA stenosis in groups A (91.1±6.2%) and B (80.6±12.6%) were significantly greater than those in group C (67.9±9.1%) (p<0.05) . There was no significant correlation between Vm and PI. [Conclusions] There was a linear correlation between the grade of ICA stenosis and PI, suggesting that the grade of stenosis is greater in cases with lower PI.

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A velocity gradient is created by acoustic pressure in an ultrasonic wave travelling through an object (medium), and this will cause distortions in its wave form, generating harmonics as a result. Tissue Harmonic Imaging is a method for producing ultrasound images from harmonics (mainly second harmonics) .
Because of the sensitivity and directivity characteristics of harmonics, it has become possible to reduce acoustic noise, and to enhance and improve contrast resolution at organ boundaries, which will eventually lead to improved image quality in patients where imaging is difficult.
To realize this aim, it is most feasible to use a wide-band digital ultrasound scanner, whose basic performance has been dramatically improved in comparison with conventional analog scanners.

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