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Impedance and conductivity of bovine myocardium during freezing and thawing at slow rates - implications for cardiac cryo–ablation.

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Title: Impedance and conductivity of bovine myocardium during freezing and thawing at slow rates - implications for cardiac cryo–ablation.
Authors: Fischer, G.1,2 (AUTHOR) gerald.fischer@umit.at, Handler, M.1,3 (AUTHOR), Johnston, P.R.3 (AUTHOR), Baumgarten, D.1,4 (AUTHOR)
Source: Medical Engineering & Physics. Dec2019, Vol. 74, p89-98. 10p.
Subjects: Ice, Freezing points, Myocardium, Extracellular space, Magnitude (Mathematics), Water transfer, Osmotic pressure
Abstract: • The freezing point of tissue of isotonic osmolality is −0.6 ∘C. • At −5 ∘C impedance was increased by more than an order of magnitude. • We estimated that at −5 ∘C 89% of the water in the extracellular space was frozen. • Phase shifts at low temperatures reflect slower freezing in the intracellular space. Increasing impedance during freezing might be a valuable marker for guiding cardiac cryo-ablation. We provide model based insights on how decreasing temperature below the freezing point of tissue relates to the percentage of frozen water. Furthermore, we provide experimental data for comparing this percentage with the increase in impedance. Measurements were performed on a bovine tissue sample at frequencies between 5 and 80 kHz. Slow cooling and heating rates were applied to minimize temperature gradients in the myocardial sample and to allow accurate assessment of the freezing point. Computer simulation was applied to link impedance with temperature dependent conductivities. The osmotic virial equation was used to estimate the percentage of frozen water. Measurements identified the freezing point at −0.6 ∘C. At −5 ∘C, impedance rose by more than a factor of ten compared to that at the freezing point and the percentage of frozen water was estimated as being 89%. At −49 ∘C impedance had increased by up to three orders of magnitude and ice formation was most pronounced in the extracellular space. Progressive ice formation in tissue is reflected by a large increase in impedance, and impedance increases monotonically with the percentage of frozen water. Its analysis allows for experimental assessment of factors relevant to cell death. Solid ice contributes to the rupture of the micro-vasculature, while phase shifts reflect concentration differences between extra- and intracellular space driving osmotic water transfer across cell membranes. [ABSTRACT FROM AUTHOR]
Copyright of Medical Engineering & Physics is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
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Header DbId: egs
DbLabel: Engineering Source
An: 139769177
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PubType: Academic Journal
PubTypeId: academicJournal
PreciseRelevancyScore: 0
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  Data: Impedance and conductivity of bovine myocardium during freezing and thawing at slow rates - implications for cardiac cryo–ablation.
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  Data: <searchLink fieldCode="JN" term="%22Medical+Engineering+%26+Physics%22">Medical Engineering & Physics</searchLink>. Dec2019, Vol. 74, p89-98. 10p.
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  Data: <searchLink fieldCode="DE" term="%22Ice%22">Ice</searchLink><br /><searchLink fieldCode="DE" term="%22Freezing+points%22">Freezing points</searchLink><br /><searchLink fieldCode="DE" term="%22Myocardium%22">Myocardium</searchLink><br /><searchLink fieldCode="DE" term="%22Extracellular+space%22">Extracellular space</searchLink><br /><searchLink fieldCode="DE" term="%22Magnitude+%28Mathematics%29%22">Magnitude (Mathematics)</searchLink><br /><searchLink fieldCode="DE" term="%22Water+transfer%22">Water transfer</searchLink><br /><searchLink fieldCode="DE" term="%22Osmotic+pressure%22">Osmotic pressure</searchLink>
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  Data: • The freezing point of tissue of isotonic osmolality is −0.6 ∘C. • At −5 ∘C impedance was increased by more than an order of magnitude. • We estimated that at −5 ∘C 89% of the water in the extracellular space was frozen. • Phase shifts at low temperatures reflect slower freezing in the intracellular space. Increasing impedance during freezing might be a valuable marker for guiding cardiac cryo-ablation. We provide model based insights on how decreasing temperature below the freezing point of tissue relates to the percentage of frozen water. Furthermore, we provide experimental data for comparing this percentage with the increase in impedance. Measurements were performed on a bovine tissue sample at frequencies between 5 and 80 kHz. Slow cooling and heating rates were applied to minimize temperature gradients in the myocardial sample and to allow accurate assessment of the freezing point. Computer simulation was applied to link impedance with temperature dependent conductivities. The osmotic virial equation was used to estimate the percentage of frozen water. Measurements identified the freezing point at −0.6 ∘C. At −5 ∘C, impedance rose by more than a factor of ten compared to that at the freezing point and the percentage of frozen water was estimated as being 89%. At −49 ∘C impedance had increased by up to three orders of magnitude and ice formation was most pronounced in the extracellular space. Progressive ice formation in tissue is reflected by a large increase in impedance, and impedance increases monotonically with the percentage of frozen water. Its analysis allows for experimental assessment of factors relevant to cell death. Solid ice contributes to the rupture of the micro-vasculature, while phase shifts reflect concentration differences between extra- and intracellular space driving osmotic water transfer across cell membranes. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Medical Engineering & Physics is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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      – Type: doi
        Value: 10.1016/j.medengphy.2019.09.017
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      – Code: eng
        Text: English
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        PageCount: 10
        StartPage: 89
    Subjects:
      – SubjectFull: Ice
        Type: general
      – SubjectFull: Freezing points
        Type: general
      – SubjectFull: Myocardium
        Type: general
      – SubjectFull: Extracellular space
        Type: general
      – SubjectFull: Magnitude (Mathematics)
        Type: general
      – SubjectFull: Water transfer
        Type: general
      – SubjectFull: Osmotic pressure
        Type: general
    Titles:
      – TitleFull: Impedance and conductivity of bovine myocardium during freezing and thawing at slow rates - implications for cardiac cryo–ablation.
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            NameFull: Fischer, G.
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            NameFull: Handler, M.
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            NameFull: Johnston, P.R.
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            NameFull: Baumgarten, D.
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            – D: 01
              M: 12
              Text: Dec2019
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              Y: 2019
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