Use of Arterial Transfer Functions for the Derivation of Central Aortic Waveform Characteristics in Subjects With Type 2 Diabetes and Cardiovascular Disease

Abstract

OBJECTIVE -Optimal blood pressure control in subjects with diabetes reduces cardiovascular complications. There is theoretical benefit in the assessment of central aortic waveforms including the augmentation index, which is taken as a putative index of stiffness. Transfer functions may be used to reconstruct aortic from radial pressure waveforms; however, a single generalized transfer function may not be appropriate for all patients. We aimed to evaluate the technique in subjects with diabetes.RESEARCH DESIGN AND METHODS -Simultaneous invasive central aortic and noninvasive radial waveforms were acquired in 19 subjects with type 2 diabetes, and a diabetesspecific transfer function was derived. Similar data were acquired from 38 age-and sex-matched subjects without diabetes. Central waveforms were reconstructed using a generalized transfer function in all patients and the diabetes-specific transfer function in individuals with diabetes.RESULTS -There was no difference between groups in measured central pressures. The error in generalized transfer function-derived systolic pressure was greater in individuals with diabetes (6 Ϯ 7 mmHg) (mean Ϯ SD) than without diabetes (2 Ϯ 8 mmHg) (P Ͻ 0.05). Errors in other parameters were no different. The diabetes-specific transfer function reduced the error in derived systolic pressure to 0 Ϯ 7 mmHg in individuals with diabetes-no different than that with the generalized transfer function in individuals without diabetes. The central augmentation index reconstructed by either transfer function was unrelated to that directly measured.CONCLUSIONS -A generalized transfer function is inappropriate for the derivation of central waveforms in subjects with type 2 diabetes. Errors in subjects with diabetes might be reduced with a diabetes-specific transfer function. Diabetes Care 27:746 -751, 2004C ardiovascular disease is the major cause of mortality and morbidity in western societies (1). Diabetes, reaching epidemic proportions in some populations, is an important risk factor for cardiovascular disease, augmenting the effects of coexistent risk factors such as hypertension (1). Optimal blood pressure control in subjects with diabetes and hypertension significantly reduces risk of cardiovascular complications and death (2). Thus, potential benefit from improvements in the recognition and treatment of hypertension may be even greater for patients with diabetes than without.The central aortic pressure waveform is thought to represent the sum of a forward traveling wave, the product of cardiac contraction, and a backward traveling wave, due to wave reflection from the periphery (3). The timing, and potentially the magnitude, of wave reflection in the ascending aorta is influenced by arterial mechanical properties that change early in the course of diabetes (4,5) and may adversely affect the relationship between cardiac workload and myocardial blood supply (3). With increasing appreciation of the potential contribution of wave reflections to central aortic blood pressure and cardiovascula...

Brachial Blood Pressure–Independent Relations Between Radial Late Systolic Shoulder-Derived Aortic Pressures and Target Organ Changes

“…Regression coefficients were compared with z statistics. To ensure that comparisons of P2-versus GTF-derived aortic BP-target organ relations were not confounded by possible inaccuracies in the use of a GTF in diabetics (and, thus, the need for a diabetes-specific transfer function) 17 or because of inaccuracies in the use of a transfer function that is sex inappropriate (and, hence, a possible need for sex-specific transfer functions), 18 sensitivity analysis was conducted in nondiabetics (and those with an HbA 1C Յ6.1%) and in men separate from women.…”

“…In contrast to tonometry performed at alternative sites, which often cannot be reliably applied (eg, in obesity), radial tonometry, together with a GTF, provides an easy and reproducible method of deriving aortic BP. However, the GTF may be limited in certain circumstances, [15][16][17][18] and the actual GTF in the SphygmoCor device, although validated, has not been described and is, therefore, not available for careful scrutiny by the general scientific community. In the present study we show that using the SphygmoCor device, P2-derived BPc, which does not require complex transformations using a GTF, is associated with target organ changes independent of brachial BP, that these relationships are as strong as brachial BP-independent GTF-derived BPc-target organ changes, and that P2-derived BPc-target organ relations survive adjustments for nursederived brachial BP measurement, whereas gold-standard 24-hour, day, or night brachial BP-target organ relations do not.…”

“…However, there is uncertainty as to the validity of the GTF to derive central pressures, 15,16 and concerns regarding inaccuracies in GTF-derived aortic BP when assessed in patients with diabetes mellitus and the possibility that diabetes mellitus-and/or sex-specific GTFs may be required have been raised previously. [15][16][17][18] As a consequence of the uncertainties that surround the use of the GTF, [15][16][17][18] complementary approaches to deriving aortic BP from radial tonometry have been sought. One such approach, as first described by Takazawa et al, 19 is to estimate the pressure at the peak of the second systolic shoulder of the radial pulse (P2), a method that does not require the use of a GTF.…”

“…One potential limitation of the use of the GTF is a potential need for sex-and diabetes mellitusspecific transfer functions. 17,18 To address this limitation, in sensitivity analysis we compared P2-derived BPc-with GTFderived BPc-target organ relations in sex-specific groups and in nondiabetics (including participants with an HbA 1C Յ6.1%). In this regard, similar results were noted in these subgroups as noted in all of the participants.…”

Renal Dysfunction Does Not Affect the Peripheral-to-Central Arterial Pressure Transfer Function

“…13,[23][24][25] However, the invasive nature of these validation studies limits them to individuals undergoing clinically indicated cardiac catheterization and is not suited to examining the transfer function in at-risk subjects in whom such investigations are not justified. Differences have been described previously in the peripheral-to-central transfer function between men and women, 26 diabetic and nondiabetic populations, 27 individuals with and without coronary disease, 28 and before and after exercise, 16 and the effects of CKD on vascular function might, therefore, be expected to also impact on the transfer function in this population. There is no single agreed method of validation, and so we have attempted to study the effect of renal function on a range of factors, both in the time domain and frequency domain.…”