Our main technique for recording arterial pressure waveforms and arterial function is via applanation tonometry (Figure 1).  This involves placement of a micromanometer-tipped probe (tonometer) on a superficial artery (e.g. radial, carotid, femoral). The artery is lightly flattened (applanated) and the tonometer records the pressure waveform from within the artery.

Figure 1: Example of radial artery pressure waveform recordings.

Using commercially available software (SphygmoCor 7.01) the central pressure (ascending aorta) waveform can be synthesized with a validated generalised mathematical transfer function (1). With this technology, recent large trials have shown the independent role of central blood pressure as a predictor of cardiovascular events (2,3).  Figure 2 illustrates how individuals with the same, or similar, brachial blood pressure can have significantly different central blood pressure, and this disparity is likely to have a major impact on cardiovascular risk between individuals.

Figure 2: Radial & central pressure waveforms from two middle aged men with similar brachial BP, but significantly different central BP. The top panels show low SBP amplification (3 mmHg) & high central SBP relative to brachial SBP. Whereas the bottom panels show high SBP amplification (28 mmHg) & low relative central SBP.

Other important clinical information relating to the interaction between the heart and the vascular system (e.g. augmentation index) can be determined from pressure waveform analysis. The augmentation index is a determinant of myocardial systolic loading and correlates with left ventricular hypertrophy (4). The augmentation index is regarded as a surrogate indicator of wave reflection and systemic arterial stiffness.

Our group is also interested in exercise haemodynamics and has the capacity to measure central pressure during aerobic activity using servo-controlled applanation tonometry (Figure 3) (5).  We have validated this technique against intra-arterial measures during exercise (6) and are now able to obtain a more “complete cardiovascular picture” with the integration of simultaneous echocardiography and tonometry.

Figure 3: Method for recording radial pressure waveforms during exercise using servo-controlled applanation tonometry.

Figure 4: Measurement of carotid-femoral pulse wave velocity by the foot to foot method.

Arterial Stiffness

In recent years, arterial stiffness has been recognised as playing a major role in the development of cardiovascular disease. The current “gold standard” measurement of large artery stiffness is carotid femoral pulse wave velocity (Figure 4) (7), which we record by ECG-gated sequential tonometry using the SphygmoCor system. This is a relatively simple, non-invasive and robust measurement which determines the speed of pulse transit time (m/s) along the aortic and aorto-iliac arterial pathway.

Personnel

• Dr James Sharman (Postdoctoral Fellow)
• David Holland (PhD student)

References

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2. The CAFE Investigators, for the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) Investigators, CAFE Steering Committee and Writing Committee, Williams B, Lacy PS, Thom SM, Cruickshank K, Stanton A, Collier D, Hughes AD, Thurston H, O'Rourke M. Differential Impact of Blood Pressure-Lowering Drugs on Central Aortic Pressure and Clinical Outcomes: Principal Results of the Conduit Artery Function Evaluation (CAFE) Study. Circulation. 2006;113:1213-1225.
3. Roman MJ, Kizer JR. Central blood pressure better predicts cardiovascular events than does peripheral blood pressure: The Strong Heart Study. Circulation. 2005;112:3362.
4. archais SJ, Guerin AP, Pannier BM, Levy BI, Safar ME, London GM. Wave reflections and cardiac hypertrophy in chronic uremia. Influence of body size. Hypertension. 1993;22:876-83.
5. Sharman JE, McEniery CM, Campbell R, Coombes JS, Wilkinson IB, Cockcroft JR. The Effect of Exercise on Large Artery Hemodynamics in Healthy Young Men. Eur J Clin Invest. 2005;Dec;35:738-44.
6. Sharman JE, Lim R, Qasem AM, Coombes JS, Burgess MI, Franco J, Garrahy P, Wilkinson IB, Marwick TH. Validation of a Generalized Transfer Function to Noninvasively Derive Central Blood Pressure During Exercise. Hypertension. 2006;47:1203-1208.
7. Laurent S, Cockcroft J, Van Bortel L, Boutouyrie P, Giannattasio C, Hayoz D, Pannier B, Vlachopoulos C, Wilkinson I, Struijker-Boudier H. Expert consensus document on arterial stiffness: methodological issues and clinical applications. Eur Heart J. 2006;27:2588-605.