We refer to the letters of Wilkinson and McEniery (1) and Avolio, Cockcroft, and O’Rourke (2). In our article, we make it abundantly clear that all results, including the transfer function utilized, were generated from data obtained in our laboratory (3). As the above correspondents note, we have previously reported at length in peer-reviewed literature how this is implemented by our group (4–9).
There is no published data to support the contention that any transfer function performs adequately in subjects with diabetes (10–13). This issue has not been addressed in the literature by enthusiasts of the technique, yet it is of crucial importance if the technique is to be used in clinical practice.
Wilkinson and McEniery (1) make the entirely unsupported suggestion that, on the basis of our results, “investigators may be better off using ‘commercial devices.’” We note that both groups of correspondents are prolific users of a particular commercial device and therefore presumably consider themselves “better off” (14–24). We would caution them and others against this leap of faith. While they may not consider our data to support the use of arterial transfer functions in general, there are no data from any source suggesting that any transfer function is able to perform better or that our data might not reflect the maximum achievable accuracy of a “generalized” arterial transfer function. We therefore strongly urge all potential users, especially the “nonspecialist readers” of such concern to Wilkinson and McEniery, to carefully evaluate the proven accuracy and validity of such techniques in the specific population and application of their interest (25).
Avolio, Cockcroft, and O’Rourke (2) opine that “an appropriately validated and approved generalized transfer function, however, is required.” The implication in this opinion, with which we agree, is that no such entity exists. Whether our results are indicative of the fundamental accuracy of a generalized arterial transfer function can only be disputed when appropriate and comparable data are available concerning other proposed transfer function techniques, commercially available or not. Unfortunately, such data can only be provided by those with access to and specific knowledge of the individual implementation, and we would strongly request that those groups, which presumably include the current correspondents, provide such data. Users could then move away from the “black-box” approach with some confidence regarding the likely accuracy for their application, whether it be simple central pulse pressure or more sophisticated waveform analysis. Until such data are available, we cannot share Avolio, Cockcroft, and O’Rourke’s optimistic belief (no evidence supplied) that “editorialists and readers of Diabetes Care can be reassured that no ‘diabetes-specific’ or ‘gender-specific’ transfer function, however, is required.”
As might be predicted, enthusiasts of the technique do not like our findings. However, the mature scientific response is to disprove a hypothesis rather than assign discredit (2). We therefore suggest that such enthusiasts provide robust data in support of oft-stated beliefs; in the absence of credible data we argue against an “ignorance is bliss” approach.
