Key result
The new scaling index proposed by McLay et al. fails to remove dependency on baseline diameter, and the original allometric approach can indeed derive individually-adjusted values.
This response clarifies methodological misconceptions regarding allometric scaling of flow-mediated dilation, emphasizing the validity of the original approach for individual adjustments.
McLay et al. (Clin Physiol Funct Imaging (2017); DOI: 10.1111/cpf.12465) recently examined whether the allometric scaling of flow-mediated dilation influenced the mean difference between samples of young and older adults compared with the traditional percentage change approach. They also explored whether a new scaling calculation improved the ability to obtain individually scaled flow-mediated dilation. In our response to their study, we can demonstrate that McLay et al. (Clin Physiol Funct Imaging, 2017) have (i) managed to formulate a new scaling index which does nothing to remove the dependency of that index on baseline diameter and (ii) suggested, incorrectly, that the original allometric approach cannot be used to derive individually-adjusted values of flow-mediated dilation, which can be interpreted in a similar way to a percentage change.
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Lolli et al. (2017) conducted a letter in Flow-mediated dilation scaling. Allometric scaling of flow-mediated dilation vs. Traditional percentage change approach was evaluated on Dependency of scaling index on baseline diameter. The new scaling index proposed by McLay et al. fails to remove dependency on baseline diameter, and the original allometric approach can indeed derive individually-adjusted values.
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