Biomedical subjects

Irene Mendes

Publications and source records attributed to Irene Mendes.

3 recordsLinked to original sources

PubMed2002

A sudden arterial blood pressure decrease is compensated by an increase in intracranial blood volume.

BACKGROUND: A sudden decrease in arterial blood pressure (ABP) will cause the intracranial blood volume (IBV) to rise, despite the fact that arterial cerebral blood flow decreases. The aim of this study was to test the hypothesis that the increase in IBV is caused by a relative decrease of intracranial venous outflow. METHODS AND RESULTS: In 10 healthy volunteers we studied cerebral autoregulation (CA) by causing an ABP drop with bilaterally deflating leg cuffs. Blood flow velocities (BFV) in the middle cerebral artery and the straight sinus were monitored continuously with transcranial Doppler ultrasound, and the ABP with a non-invasive photoplethysmographic method. After transforming all variables in relative changes, the arterio-venous BFV difference was calculated. Allowing for diameter changes of the intracranial vessels of up to 10 %, and assuming a resting averaged cerebral blood flow of 55 to 60 ml per 100 g brain tissue per minute, an IBV increase of 9 to 10 ml could be calculated. CONCLUSIONS: In intact CA, a steep decrease of ABP results in an increase of intracranial blood volume. The transformation of our IBV data by means of the human intracranial pressure-volume relationship results in an excellent agreement with previously reported ICP increases of 10 mmHg. The increase in intracranial blood volume might be of clinical relevance in orthostatic dysregulation by increasing the ischemic tolerance of the brain before cerebral autoregulation becomes effective.

Adaptation, Physiological↗

PubMed2002

Assessment of intracranial collateral flow by transcranial color-coded duplex sonography using a temporal and frontal axial insonation plane.

BACKGROUND AND PURPOSE: The insonation of the posterior communicating artery (PcomA) is often hampered by the unfavorable insonation angle when the temporal acoustic bone window (TBW) is used. This problem may be ameliorated by a lateral frontal bone window (LFBW). This study evaluated the TBW and LFBW for the assessment of collateral intracranial flow conditions and aimed at defining diagnostic transcranial color-coded duplex sonography (TCCS) criteria that do not need compression maneuvers. METHODS: The A1 segment of the anterior cerebral artery (ACA), the PcomA, and the P1 segment of the posterior cerebral artery (PCA) were insonated by TCCS in 40 controls and 20 patients (16 internal carotid artery [ICA] occlusions or high grade stenoses, 3 middle cerebral artery stenoses or occlusions, 1 PCA stenosis). RESULTS: Detection rates for the A1 ACA and P1 PCA were higher for the TBW (94%, 98%) compared to the LFBW (86%, 81%) in controls. The PcomA was identified more frequently through the LFBW (86%) compared to the TBW (80%). Through the LFBW angle, corrected flow velocity (FV) measurements were possible for the PcomA with an average correction of 6.5 degrees. In controls, in > 80% of identified PcomAs, flow was directed towards the ICA. Side to side differences were below 7% for peak systolic FVs. In the patients with ICA disease, a flow reversal in the ipsilateral A1 ACA and a FV difference of > 30% seemed feasible for diagnosis of anterior communicating artery crossflow. Criteria for PcomA crossflow were side differences of FVs in the PcomA of > or = 30% and in the P1 PCA of > or = 20%. CONCLUSIONS: The LFBW proved useful as a complementary insonation plane to assess intracranial crossflow conditions, especially via the PcomA. We were able to define TCCS criteria for functional relevant collateralization without the need of compression maneuvers.

Adult↗

PubMedDate not supplied

Vertebrobasilar transcranial color-coded duplex ultrasonography: improvement with echo enhancement.

BACKGROUND AND PURPOSE: The diagnostic yield of vertebrobasilar transcranial color-coded duplex ultrasonography (US) is often hampered by insufficient acoustic penetration, anatomic variations, and vessel tortousity. The purpose of this study was to evaluate the effect of echo enhancement on vertebrobasilar transcranial color-coded duplex US. METHODS: In 23 consecutive patients (mean age, 61.0 +/- 11.1 years) with vertebrobasilar stroke, the vertebrobasilar system (P1 segment of the posterior cerebral artery [PCA], basilar head, V4 segment of the vertebral artery, and basilar artery) was examined with transcranial color-coded duplex US before and after injection of an echo-enhancer. The acoustic window was graded according to visibility of parenchymal structures, and vessel imaging was graded according to the appearance of the color mode signal. Maximum depth of the basilar color signal was recorded. All patients with an abnormal or inconclusive US finding underwent either digital subtraction angiography or MR angiography. RESULTS: In the P1 PCA, V4 vertebral artery, basilar artery, and basilar head, image quality was insufficient in 65%, 82%, 83%, and 38%, respectively, before echo enhancement, and in 15%, 30%, 35%, and 9%, respectively, after echo enhancement. In all graded vessels, the improved image quality with echo enhancement was statistically significant. Compared with the reference examinations in the 15 cases of occlusion or stenosis, definite diagnosis was possible in 60% (nine cases) with nonenhanced transcranial color-coded duplex US and in 93% of (14 cases) after echo enhancement. CONCLUSION: Echo enhancement resulted in improved image quality of the vertebrobasilar system and markedly increased diagnostic confidence.

Adult↗