title: Potentially spurious correlations between arterial size, flow-mediated dilation, and shear rate.
abstract: The use of indices formed from the ratio of 2 variables often generates spurious correlations with other variables that are mathematically coupled. In this context, we examined the correlations between percent flow-mediated dilation, baseline diameter, and shear rate. In a sample of 315 participants, with and without substantial vascular risk factors, the observed correlation coefficients between the variables were of a similar magnitude to those reported in the literature. We then applied a Monte Carlo procedure based on random permutations to remove any physical or physiological explanation for these correlations. We found that the median residual correlation coefficients were comparable with those observed in our original sample. When the confounding influence of artery size was adjusted for, the mean difference in percent flow-mediated dilation between high-risk and low-risk samples was halved. These findings indicate that the widely reported correlations between flow-mediated dilation, basal artery diameter, and shear rate have a substantial spurious component. This is because percent flow-mediated dilation and shear rate are mathematically coupled to artery size.
authors.affiliation: From Centro Cardiologico Monzino IRCCS, Milan, Italy (F.V., M.A., M.G., A.R., C.C.T., B.F., E.T., D.B.); and Dipartimento di Scienze Farmacologiche e Biomolecolari, Università di Milano, Milan, Italy (E.T., D.B.). fabrizio.veglia@ccfm.it.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Veglia
authors.affiliation: From Centro Cardiologico Monzino IRCCS, Milan, Italy (F.V., M.A., M.G., A.R., C.C.T., B.F., E.T., D.B.); and Dipartimento di Scienze Farmacologiche e Biomolecolari, Università di Milano, Milan, Italy (E.T., D.B.).
authors.forename: Mauro
authors.initials: M
authors.lastname: Amato
authors.affiliation: From Centro Cardiologico Monzino IRCCS, Milan, Italy (F.V., M.A., M.G., A.R., C.C.T., B.F., E.T., D.B.); and Dipartimento di Scienze Farmacologiche e Biomolecolari, Università di Milano, Milan, Italy (E.T., D.B.).
authors.forename: Marta
authors.initials: M
authors.lastname: Giovannardi
authors.affiliation: From Centro Cardiologico Monzino IRCCS, Milan, Italy (F.V., M.A., M.G., A.R., C.C.T., B.F., E.T., D.B.); and Dipartimento di Scienze Farmacologiche e Biomolecolari, Università di Milano, Milan, Italy (E.T., D.B.).
authors.forename: Alessio
authors.initials: A
authors.lastname: Ravani
authors.affiliation: From Centro Cardiologico Monzino IRCCS, Milan, Italy (F.V., M.A., M.G., A.R., C.C.T., B.F., E.T., D.B.); and Dipartimento di Scienze Farmacologiche e Biomolecolari, Università di Milano, Milan, Italy (E.T., D.B.).
authors.forename: Calogero C
authors.initials: CC
authors.lastname: Tedesco
authors.affiliation: From Centro Cardiologico Monzino IRCCS, Milan, Italy (F.V., M.A., M.G., A.R., C.C.T., B.F., E.T., D.B.); and Dipartimento di Scienze Farmacologiche e Biomolecolari, Università di Milano, Milan, Italy (E.T., D.B.).
authors.forename: Beatrice
authors.initials: B
authors.lastname: Frigerio
authors.affiliation: From Centro Cardiologico Monzino IRCCS, Milan, Italy (F.V., M.A., M.G., A.R., C.C.T., B.F., E.T., D.B.); and Dipartimento di Scienze Farmacologiche e Biomolecolari, Università di Milano, Milan, Italy (E.T., D.B.).
authors.forename: Daniela
authors.initials: D
authors.lastname: Sansaro
authors.affiliation: From Centro Cardiologico Monzino IRCCS, Milan, Italy (F.V., M.A., M.G., A.R., C.C.T., B.F., E.T., D.B.); and Dipartimento di Scienze Farmacologiche e Biomolecolari, Università di Milano, Milan, Italy (E.T., D.B.).
authors.forename: Elena
authors.initials: E
authors.lastname: Tremoli
authors.affiliation: From Centro Cardiologico Monzino IRCCS, Milan, Italy (F.V., M.A., M.G., A.R., C.C.T., B.F., E.T., D.B.); and Dipartimento di Scienze Farmacologiche e Biomolecolari, Università di Milano, Milan, Italy (E.T., D.B.).
authors.forename: Damiano
authors.initials: D
authors.lastname: Baldassarre
mesh_terms: D000328:Adult; D001916:Brachial Artery / Q000000981:diagnostic imaging* / Q000503:physiopathology; D002318:Cardiovascular Diseases / Q000503:physiopathology*; D004730:Endothelium, Vascular / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D012039:Regional Blood Flow / Q000502:physiology*; D013314:Stress, Mechanical; D014463:Ultrasonography; D014664:Vasodilation / Q000502:physiology*
keywords: Monte Carlo methods; cardiovascular risk factors; flow-mediated dilation; mathematical artifacts; ratio variables; shear stress