Acetazolamide vasoreactivity in persistent vegetative state and vascular dementia evaluated by transcranial harmonic perfusion imaging and Doppler sonography

TCD Diastolic Velocity Decay and Pulsatility Index Increment in PVS Cases

Background:

Functional neuroimaging has provided new insights for assessing cerebral function in persistent vegetative state patients (PVS). Compared to controls, positron emission tomography and single photon emission tomography have shown a substantial reduction of global brain cerebral glucose metabolism and perfusion in PVS. Doppler ultrasonography (TCD) assesses local blood flow velocity and direction in the proximal portions of large intracranial arteries; it is a noninvasive technique, and it can be carried out at the bedside. To date, few studies have applied TCD to study PVS.

Methods:

We assessed intracranial circulation by TCD in five PVS patients. The cause of brain insult was hypoxic encephalopathy in four cases, and the other suffered an embolic cerebral infarct causing a top of the basilar artery syndrome. The sample volume was set at 12 mm; power output and gain settings were maximized as needed. The temporal bone acoustic window was not suitable for intracranial vessel insonation in all patients. As an alternative, the internal carotid artery siphon was assessed by orbital insonation between 55-70 mm.

Results:

Systolic velocity was within a normal range, between 44 and 62 cm/second in all cases. However, the diastolic amplitude was reduced, as well as the end diastolic velocity, and the pulsatility index was increased in all patients.

Conclusions:

We conclude that TCD diastolic velocity decrement and PI augmentation in our cases might be related to uncoupling of cerebral blood flow and cerebral metabolic rate, arising from reduced cerebral glucose consumption and oxygen uptake, after extensive brain injury.

Vasoreactivity induced by acetazolamide in patients with vascular dementia versus Alzheimer's disease

Acetazolamide vasoreactive test measures the increment of cerebral blood flow caused by compensatory vasodilatation ability of cerebral vessels which can be detected by transcranial Doppler ultrasound (TCD). This study aimed to compare the vascular reactivity in patients with vascular dementia (VaD) and Alzheimer's disease (AD).

PATIENTS AND METHODS

AD and VaD patients were recruited from the King Chulalongkorn Hospital Dementia Clinic. Thai Mini-mental State Examination was used for dementia detection. AD and possible VaD were defined by NINCDS/ADRDA and NINDS-AIREN criteria. Patients with extracranial carotid artery stenosis >50% and intracranial artery stenosis were excluded. TCD examination was performed using DWL Multi Dop-T. TCD was performed on MCA with insonation depth between 45 and 60 mm. Baseline end diastolic velocity (EDV), mid systolic velocity (MSV) and peak systolic velocity (PSV) were recorded. The velocities were obtained at 2, 5, 10 and 20 min after acetazolamide (1000 mg) injection. Mean baseline velocities (Vo) and velocities after acetazolamide injection (Va) were compared. Percentage of mean increment velocities was calculated {[(Va-Vo)/Vo]x100%}. Percentage differences of mean velocity change from Vo to Va at each recorded minute were compared. SPSS for Windows version 11.5.0. was used.

RESULT

Nine AD (5 males) and 9 VaD (6 males) were selected. Average ages of VaD and AD groups were 66.11 years-old and 75.22 years-old respectively. Mini-mental State Examination (MMSE) score in VaD and AD were 21.13 and 19.00. Mean baseline EDV and MSV in VaD were higher than AD but mean PSV was lower. The percentage of velocity change after acetazolamide in AD was higher than VaD at 5, 10 and 20 min. However the differences were not statistically significant.

CONCLUSION

Acetazolamide vasoreactive test using TCD may be the additional criterion to differentiate VaD from AD. Further study with more number of subjects for the study or higher dose of acetazolamide may be needed to reveal the significant difference of vasoreactive response between VaD and AD patients.

Effects of poor bone window on the assessment of cerebral autoregulation with transcranial Doppler sonography - a source of systematic bias and strategies to avoid it

BACKGROUND

The consequences of poor insonation conditions on autoregulation parameters assessed with transcranial Doppler (TCD) are unclear.

METHODS

We present two new complementary methods to assess the quality of a TCD signal. Inserting a thin aluminium foil between TCD probe and skin makes a simple model to artificially worsen a good insonation window. Validation studies are presented. We assessed insonation quality and cerebral autoregulation parameters with transfer function analysis and cross correlation in 46 healthy volunteers with and without the aluminium foil model. The same studies were operated on 45 patients with good insonation windows, naïve, after worsening the bone window and during constant infusion of an ultrasound contrast agent. For studying reproducibility, we assessed autoregulation twice in 30 patients with poor bone windows, with and without constant contrast infusion.

RESULTS

Both methods to measure insonation quality are valid and reproducible. The aluminium foil model realistically simulates a natural poor bone window, reducing the signal quality (e.g. energy of the signal spectrum from 33.4+/-3.5 to 26.2+/-2.5 dB, p<0.001). Thereby, the autoregulation parameters are systematically biased (e.g. phase difference from 37.3+/-10.1 degrees to 25.9+/-15.1 degrees , p<0.001); while with the use of an ultrasound contrast agent this can be largely compensated (phase difference 35.7+/-10.7 degrees , p<0.001). The reproducibility is significantly improved (ICC from 0.76 to 0.90, p<0.05).

CONCLUSIONS

Poor bone windows can cause considerable bias in TCD autoregulation parameters. This bias might be avoided by the use of ultrasound contrast agents, which may greatly improve the credibility of TCD autoregulation assessment in elderly patients.