Shear rate normalization is not essential for removing the dependency of flow-mediated dilation on baseline artery diameter: past research revisited.

Hdl Handle:
http://hdl.handle.net/10149/337377
Title:
Shear rate normalization is not essential for removing the dependency of flow-mediated dilation on baseline artery diameter: past research revisited.
Authors:
Atkinson, G. (Greg)
Affiliation:
Teesside University. Health and Social Care Institute.
Citation:
Atkinson, G. (2014) 'Shear rate normalization is not essential for removing the dependency of flow-mediated dilation on baseline artery diameter: past research revisited.' Physiological measurement; 35 (9):1825-35
Publisher:
IOP Science
Journal:
Physiological measurement
Issue Date:
Sep-2014
URI:
http://hdl.handle.net/10149/337377
DOI:
10.1088/0967-3334/35/9/1825
PubMed ID:
25139144
Additional Links:
http://iopscience.iop.org/0967-3334/35/9/1825/
Abstract:
A ratio index (FMD%) is used ubiquitously to scale (by simple division) brachial artery flow-mediated dilation (Ddiff) in direct proportion to baseline diameter (Dbase). It is now known that Ddiff is inversely proportional to Dbase rendering FMD% wholly inappropriate. Consequently, FMD% is still substantially dependent on Dbase. Although this problem is grounded in statistics, normalization of FMD% for the change in arterial shear rate (ΔSR) has been proposed to remove this Dbase-dependency. It was hypothesized that, if the flow-mediated response is scaled properly to Dbase in the first place, shear rate normalization would not be needed to remove Dbase-dependency. Dedicated software (Digitizelt) was employed to extract the data from a seminal study on FMD% normalization. The underlying allometric relationship between Dbase and peak diameter (Dpeak) was described. The re-analyses revealed that the absolute change in arterial diameter was strongly inversely proportional to Dbase (r= - 0.7, P < 0.0005). The allometric exponent for the Dbase-Dpeak relationship was 0.82 (95% CI: 0.78-0.86) rather than the value of 1 needed for appropriate use of FMD%. The allometric approach completely eliminated the originally reported dependency on Dbase without any need for ΔSR normalization (r=0.0, P=0.96). The correlation between ΔSR and FMD% reduced from 0.69 to 0.37, when adjusted for Dbase. In conclusion, this new re-analysis of data from an influential study demonstrates that the FMD%-Dbase correlation is caused by the inappropriate size-scaling properties of FMD% itself. Removal of Dbase-dependency via FMD%/ΔSR normalization is not essential at all if allometric scaling is applied to isolate the flow-mediated response in the first place. Consequently, the influence of ΔSR on this properly scaled response can also be isolated and quantified accurately without the confounding influence of Dbase.
Type:
Article
Language:
en
Keywords:
allometric scaling; normalisation; endothelial function; Spurious correlation
ISSN:
1361-6579
Rights:
Following 12 month embargo author can archive post-print (ie final draft post-refereeing). For full details see http://www.sherpa.ac.uk/romeo [Accessed: 18/12/2014]

Full metadata record

DC FieldValue Language
dc.contributor.authorAtkinson, G. (Greg)en
dc.date.accessioned2014-12-18T16:02:06Zen
dc.date.available2014-12-18T16:02:06Zen
dc.date.issued2014-09en
dc.identifier.citationPhysiological measurement; 35 (9):1825-35en
dc.identifier.issn1361-6579en
dc.identifier.pmid25139144en
dc.identifier.doi10.1088/0967-3334/35/9/1825en
dc.identifier.urihttp://hdl.handle.net/10149/337377en
dc.description.abstractA ratio index (FMD%) is used ubiquitously to scale (by simple division) brachial artery flow-mediated dilation (Ddiff) in direct proportion to baseline diameter (Dbase). It is now known that Ddiff is inversely proportional to Dbase rendering FMD% wholly inappropriate. Consequently, FMD% is still substantially dependent on Dbase. Although this problem is grounded in statistics, normalization of FMD% for the change in arterial shear rate (ΔSR) has been proposed to remove this Dbase-dependency. It was hypothesized that, if the flow-mediated response is scaled properly to Dbase in the first place, shear rate normalization would not be needed to remove Dbase-dependency. Dedicated software (Digitizelt) was employed to extract the data from a seminal study on FMD% normalization. The underlying allometric relationship between Dbase and peak diameter (Dpeak) was described. The re-analyses revealed that the absolute change in arterial diameter was strongly inversely proportional to Dbase (r= - 0.7, P < 0.0005). The allometric exponent for the Dbase-Dpeak relationship was 0.82 (95% CI: 0.78-0.86) rather than the value of 1 needed for appropriate use of FMD%. The allometric approach completely eliminated the originally reported dependency on Dbase without any need for ΔSR normalization (r=0.0, P=0.96). The correlation between ΔSR and FMD% reduced from 0.69 to 0.37, when adjusted for Dbase. In conclusion, this new re-analysis of data from an influential study demonstrates that the FMD%-Dbase correlation is caused by the inappropriate size-scaling properties of FMD% itself. Removal of Dbase-dependency via FMD%/ΔSR normalization is not essential at all if allometric scaling is applied to isolate the flow-mediated response in the first place. Consequently, the influence of ΔSR on this properly scaled response can also be isolated and quantified accurately without the confounding influence of Dbase.en
dc.language.isoenen
dc.publisherIOP Scienceen
dc.relation.urlhttp://iopscience.iop.org/0967-3334/35/9/1825/en
dc.rightsFollowing 12 month embargo author can archive post-print (ie final draft post-refereeing). For full details see http://www.sherpa.ac.uk/romeo [Accessed: 18/12/2014]en
dc.subjectallometric scalingen
dc.subjectnormalisationen
dc.subjectendothelial functionen
dc.subjectSpurious correlationen
dc.titleShear rate normalization is not essential for removing the dependency of flow-mediated dilation on baseline artery diameter: past research revisited.en
dc.typeArticleen
dc.contributor.departmentTeesside University. Health and Social Care Institute.en
dc.identifier.journalPhysiological measurementen
or.citation.harvardAtkinson, G. (2014) 'Shear rate normalization is not essential for removing the dependency of flow-mediated dilation on baseline artery diameter: past research revisited.' Physiological measurement; 35 (9):1825-35en

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