Diastolic blood pressure influences cerebrovascular reactivity measured by means of123I-iodoamphetamine brain single photon emission computed tomography in medically treated patients with occlusive carotid or middle cerebral artery disease

Carotid endarterectomy improves cerebrovascular reserve capacity preferentially in patients with preoperative impairment as indicated by asymmetric BOLD response to hypercapnia

PURPOSE

In patients with symptomatic carotid artery disease the predominant mechanism causing ischaemic injury is considered to be thromboembolic, however compromise of cerebral haemodynamics is considered to be a significant factor. Removal of the embolic source is accepted as the major benefit from carotid endarterectomy (CEA), however improvement in cerebral haemodynamics may be another beneficial outcome as suggested by transcranial doppler (TCD). Blood oxygen level-dependent (BOLD) hypercapnia functional magnetic resonance imaging (fMRI) can be used to map the cerebrovascular reserve (CVR). The aim of this study was to assess the effects of carotid surgery on cerebral haemodynamics in patients with carotid artery disease using a hypercapnia BOLD fMRI and assessment of hemispheric asymmetry.

MATERIALS AND METHODS

Seventeen patients with symptomatic internal carotid artery stenosis were scanned using a clinical 1.5T MR scanner. Scanning was done immediately prior to and between 4 and 8 weeks after CEA. 10% carbon dioxide was administered to achieve transient episodes of hypercapnia. The data was analyzed using FMRIB Software Library (FSL) software to derive percentage signal change (PSC) for the grey matter of the middle cerebral artery (MCA-GM) territory for both hemispheres. MCA-GM PSC was furthermore normalized to the contralateral hemisphere to derive an Hemispheric Asymmetry Index (hAI) for all patients pre- and postoperatively.

RESULTS

Ipsilateral GM CVR improved significantly following CEA (2.47% preoperatively vs. 2.73% postoperatively, p=0.038). There was no change in CVR in the contralateral grey and white matter MCA territories (p=0.27, p=0.1). Also, the hAI was significantly more shifted to the ipsilateral hemisphere after CEA (preoperative hAI -0.56, vs. -3.90 postoperatively, p=0.02). Patients with an impaired hAI preoperatively were found to show the greatest improvement in PSC and hAI following CEA (p=0.007).

CONCLUSIONS

CEA resulted in improved CVR in patients with carotid artery disease as shown by the absolute and hemispheric asymmetry of BOLD response to hypercapnia.. These findings show that benefits from recanalisation may go beyond removal of the embolic source, by improving the cerebrovascular reserve. Moreover, hypercapnia BOLD fMRI may be a useful clinical tool in predicting this therapeutic potential in patients with severe carotid artery disease.

Measurement of hemodynamics during postural changes using a new wearable cephalic laser blood flowmeter

BACKGROUND

Patients with orthostatic hypotension have pathologic hemodynamics related to changes in body posture. A new cephalic laser blood flowmeter that can be worn on the tragus to investigate the hemodynamics upon rising from a sitting or squatting posture was developed.

METHODS AND RESULTS

The relationship between cephalic hemodynamics and cerebral ischemic symptoms in 63 subjects in a sitting, squatting, and standing positions using the new device was evaluated. Transient decrease in blood pressure within 15 s after rising to an erect position possibly causes dizziness, syncope, and fall. Subjects exhibiting dizziness upon standing showed a significant decrease in the cephalic blood flow (CBF) and indirect beat-to-beat systolic blood pressure, as monitored by the Finometer, and a significant correlation was observed between the drop ratio (drop value on rising/mean value in the squatting position) of CBF and that of systolic blood pressure.

CONCLUSIONS

This new wearable CBF-meter is potentially useful for estimating cephalic hemodynamics and objectively diagnosing cerebral ischemic symptoms of subjects in a standing posture.

N-isopropyl-4-[123I]iodoamphetamine (123I-IMP) products: a difference in radiochemical purity, unmetabolized fraction, and octanol extraction fraction in arterial blood and regional brain uptake in rats

N-isopropyl-4-[123I]iodoamphetamine (123I-IMP) is a lipophilic compound utilized for cerebral blood flow (CBF) measurement with single photon emission computed tomography (SPECT). Two different 123I-IMP products (IMP(A) and IMP(B)) are commercially available. We examined the radiochemical purity, unmetabolized fraction, and octanol extraction fraction in arterial blood, and the regional brain uptake of IMP(A) and IMP(B) in a rat model. IMP(B) (96.4% +/- 0.08%, P < 0.05) showed significantly higher radiochemical purity than IMP(A) (95.5% +/- 0.20%). The mean unmetabolized fraction in arterial blood taken at 10 min after intravenous administration of IMP(B) (69.5% +/- 4.4%, P < 0.01) was significantly higher than that of IMP(A) (59.6% +/- 2.6%). The mean octanol extraction fraction of IMP(B) (75.0% +/- 1.3%, P < 0.01) was also significantly higher than that of IMP(A) (67.2% +/- 0.8%). The mean levels of radioactivity in arterial blood sampled at 10 min after injection and mean regional brain radioactivity (cerebral cortices, basal ganglia, brain stem, and cerebellum) at 10-12 min after injection were not significantly different between IMP(A) and IMP(B). The present study indicates differences in the radiochemical purity and the unmetabolized and octanol extraction fraction in arterial blood between the two commercially available 123I-IMP products. The appropriate octanol extraction fractions for IMP(A) and IMP(B) should be determined in humans and employed for quantitative CBF measurement in clinical SPECT.