Assessment of Central Blood Pressure in Patients With Type 2 Diabetes: A Comparison Between Sphygmocor and Invasively Measured Values

BACKGROUND The SphygmoCor is used for noninvasive assessment of ascending aortic blood pressure (BP). However, the validity of the SphygmoCor transfer function has not been tested in an exclusively type 2 diabetic patient sample. Calibration with systolic (SBP) and diastolic (DBP) brachial BP has previously been associated with substantial imprecision of central BP estimates. We hypothesized that different noninvasive calibration strategies might improve the accuracy of the estimated ascending aortic BPs. METHODS In 34 patients with type 2 diabetes we estimated ascending aortic SBP and DBP using the SphygmoCor device and compared these data with invasively recorded data. The validity of the transfer function was assessed by calibrating with invasively recorded DBP and mean BP (MBP). The influence of noninvasive calibration strategies was assessed by calibrating with brachial oscillometric SBP+DBP vs. DBP+MBP using a form factor (ff) of 0.33 and 0.40, respectively. RESULTS When calibrating with invasive BP, the difference between estimated and invasively measured ascending aortic SBP and DBP was −2.3±5.6/1.0±0.9mm Hg. When calibrating with oscillometric brachial BPs, the differences were −9.6±8.1/14.1±6.2mm Hg (calibration with SBP and DBP), −8.3±11.7/13.9±6.1mm Hg (DBP and MBP; ff = 0.33), and 1.9±12.2/14.1±6.2mm Hg (DBP and MBP; ff = 0.40), respectively. Calibration with the average of 3 brachial BPs did not improve accuracy. CONCLUSIONS The SphygmoCor transfer function seems valid in patients with type 2 diabetes. Noninvasive calibration with DBP and MBP (ff = 0.40) enables accurate estimation of mean ascending aortic SBP at the group level. However, the wide limits of agreement indicate limited accuracy in the individual patient. CLINICAL TRIALS REGISTRATION Clinical Trials No. NCT01538290.