Objective: We compared the accuracy with which central systolic aortic pressure (cSBP) can be estimated from the late systolic shoulder of the digital artery pressure waveform (SBP₂) when the digital waveform is calibrated using a validated non-invasive oscillometric device and when it is calibrated using mean (MAP) and diastolic (DBP) central blood pressure measurement.

Design: Subjects (n=25) were studied at the time of cardiac catheterisation for diagnostic angiography and/or angioplasty. The study was approved by the local research ethics committee and all subjects gave written informed consent.

Methods: cSBP was measured with a Millar SPC-454D (Millar instruments Houston, Texas) catheter with the tip of the catheter in the proximal aortic root. Peripheral pressure waveforms were acquired from the digital artery using a Finometer (Finapres medical systems, Netherlands) and were calibrated from aortic mean and diastolic pressures and from systolic and diastolic pressures measured using an Omron 750IT (Omron Healthcare). Measurements of digital artery and aortic pressures were obtained at baseline and after nitroglycerin (NTG, sublingual spray 500 μg).

Results: The overall mean (±SD) difference between cSBP and SBP₂ calibrated using the Omron 750IT was 1.4±11.8 mmHg. When SBP₂ was calibrated from aortic MAP and DBP the difference between cSBP and SBP₂ was −1.1±5.6 mmHg.

Conclusion: These results suggest non-invasive calibration does not produce a major systematic error in estimation of cSBP from SBP₂ but does introduce greater variability when compared to invasive calibration.