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An impedance index in normal subjects and in subarachnoid hemorrhage


, : An impedance index in normal subjects and in subarachnoid hemorrhage. Ultrasound In Medicine & Biology. 22(4): 373-382

The impedance of a hemodynamic system is defined as the ratio of each harmonic component of blood pressure to that of flow. Calculation of impedance curves has been extensively performed in the systemic circulation, leading to the recognition of reflected pressure and flow waves and clarifying the shape of ultrasound waveforms. Impedance in the human cerebral circulation has not been measured primarily because of the relative inaccessibility of simultaneous flow and pressure data in the human cerebral circulation. We defined an impedance index using the transcranial Doppler waveform for that of flow and a noninvasive applanation measure of the carotid artery pressure waveform. Middle cerebral artery velocities and carotid artery pressure waveforms were simultaneously recorded in 16 vessels from 10 normal volunteers, 42 vessels in 14 patients with aneurysmal subarachnoid hemorrhage, and 14 vessels in 7 subjects during conditions of hypocapnia, normocapnia and hypercapnia. Impedance was calculated by dividing the harmonic associated with pressure divided by that of flow, and averaging 10 to 20 such calculations. Relative impedance curves were calculated by dividing by the impedance at the first harmonic. Impedance was also studied in an electrical model consisting of a Windkessel element containing inductance in series with a second Windkessel to model the large vessel and vascular bed, respectively. Model parameters were taken from the literature for these calculations. For the normal subjects, the shape of the impedance index curve was similar to those found in the systemic circulation. The impedance index curves for patients in vasospasm (middle cerebral velocity greater than 180) showed a peak at the second or third harmonic, which appeared more frequently than the nonspasm group (p lt 0.01). Furthermore, the ratio of the second harmonic to the first harmonic was significantly gt 1.0 in the spasm group but significantly lt 1.0 in the normal group (p lt 0.05). Calculations from the electrical model replicated the appearance of these peaks at the second or third harmonic for vasospasm parameters. A statistically significant peak appeared at the second or third harmonic in the impedance index curves for patients in vasospasm, which was replicated quantitatively by our electrical model. Although such peaks can be explained in the systemic circulation by the presence of reflected waves, the distance to the reflection site is larger than expected for the cerebral circulation. This suggests the importance of the inertia of blood as a stenosis worsens and as the origin for the observed changes in the impedance index curves.

US$19.90

PMID: 8795163

DOI: 10.1016/0301-5629(96)00024-5


Other references

Park, S.H.; Kim, C.M.; Chang, Y.J.; Rhyu, I.J.; Chun, Y.H.; Kim, H., 1997: Cloning and localization of novel gene mapped on human chromosome 1q25. American Journal of Human Genetics 61(4 SUPPL ): A392, Oct

Suri, A.; Goel, R.Kumar.; Ahmad, F.Uddin.; Vellimana, A.Kesav.; Sharma, B.Shankar.; Mahapatra, A.Kumar., 2008: Transventricular, transaqueductal scope-in-scope endoscopic excision of fourth ventricular neurocysticercosis: a series of 13 cases and a review. Neurocysticercosis (NCC) is the most common parasitic infestation of the central nervous system worldwide. In patients presenting with acute hydrocephalus due to intraventricular NCC, surgery is the only option. Still, there is no consensus regard...

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Vandevenne, J.E.; Vanhoenacker, F.; Mahachie John, J.M.; Gelin, G.; Parizel, P.M., 2009: Fast MR arthrography using VIBE sequences to evaluate the rotator cuff. The purpose of this paper was to evaluate if short volumetric interpolated breath-hold examination (VIBE) sequences can be used as a substitute for T1-weighted with fat saturation (T1-FS) sequences when performing magnetic resonance (MR) arthrogra...

Bird, A.G.; Gore, S.M.; Jolliffe, D.W.; Burns, S.M., 1992: Anonymous HIV surveillance in Saughton Prison, Edinburgh. Objectives: To estimate the prevalence of HIV by anonymous saliva testing in Her Majesty's Prison, Saughton (Saughton Prison), Edinburgh, UK. To elicit linked anonymous risk factor information from which to estimate risk scores for those who...

Cameron, J.B., 1980: The role of agriculture and forestry. In: Forestry and farming in upland Britain. Selected papers presented at the British Association for the Advancement of Science, 1979. The paper draws attention to the damaging effects of some large scale blanket afforestation schemes on the environment, on farming and on long term employment in rural communities in the UK. While such large scale schemes can clearly be damaging i...

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