Dries Mahieu

Amplification of the Pressure Pulse in the Upper Limb in Healthy, Middle-Aged Men and Women

Central-to-peripheral amplification of the pressure pulse leads to discrepancies between central and brachial blood pressures. This amplification depends on an individuals hemodynamic and (patho)physiological characteristics. The aim of this study was to assess the magnitude and correlates of central-to-peripheral amplification in the upper limb in a healthy, middle-aged population (the Asklepios Study). Carotid, brachial, and radial pressure waveforms were acquired noninvasively using applanation tonometry in 1873 subjects (895 women) aged 35 to 55 years. Carotid, brachial, and radial pulse pressures were calculated, as well as the absolute and relative (with carotid pulse pressure as reference) amplifications. With subjects classified per semidecade of age, carotid-to-radial amplification varied from ≈25% in the youngest men to 8% in the oldest women. Amplification was higher in men (20±14%) than in women (13±12%; P<0.001) and decreased with age (P<0.001) in both. Amplification over the brachial-to-radial path contributed substantially to the total amplification. In univariate analysis, the strongest correlation was found with the carotid augmentation index (−0.51 in women; −0.47 in men; both P<0.001). In a multiple linear regression model with carotid-to-radial amplification as the dependent variable, carotid augmentation index, total arterial compliance, and heart rate were identified as the 3 major determinants of upper limb pressure amplification (R2=0.36). We conclude that, in healthy middle-aged subjects, the central-to-radial amplification of the pressure pulse is substantial. Amplification is higher in men than in women, decreases with age, and is primarily associated with the carotid augmentation index.

Carotid to femoral pulse wave velocity: a comparison of real travelled aortic path lengths determined by MRI and superficial measurements.

Objectives Carotid–femoral pulse wave velocity (PWV) is the gold standard method for determination of arterial stiffness. PWV is assessed by dividing travelled distance by travel time. Standardization and validation of the methodology for travelled distance measurement is of crucial importance. The aim of the current investigation was to standardize and validate the methodology for travelled distance measurement. Methods Real travelled carotid–femoral path lengths were measured with MRI in 98 healthy men/women (50% men, age 21–76 years) and are used as reference distance. This reference distance was compared with 11 estimates of aortic path length from body surface distances commonly used in PWV measurement, nine of them based on tape measures and two based on body height. Determinants of the difference between reference distance and the best body surface distance were determined. Additionally, the influence of body contours was identified. Results The tape measure distance from carotid to femoral artery (CA-FA), multiplied by 0.8, yielded the best agreement with the reference aortic path length [difference 0.26 cm (SD 3.8), not statistically significant]. Thirty percent of the variation in difference between the reference distance and tape measure distance (CA-FA × 0.8) was explained by age. Adding BMI increased this number to 34%. Conclusion The tape measure distance from CA-FA, multiplied by 0.8, corresponds best with the real travelled aortic path length. This distance is moderately (yet statistically significantly) influenced by age and minimally by BMI.

Noninvasive assessment of central and peripheral arterial pressure (waveforms): implications of calibration methods

Objectives Noninvasive estimation of central blood pressure (BP) from radial artery pressure waveforms is increasingly applied. We investigated the impact of radial artery waveform calibration on central BP assessment and calculated pressure amplification, with focus on the one-third rule used to estimate mean arterial BP (MAP). Methods Pressure waveforms were noninvasively measured at the radial and carotid arteries in 1873 individuals (age 45.8±6.1 years). Radial and carotid artery waveforms were calibrated using brachial artery DBP and SBP, MAP estimated with the one-third rule and MAP estimated as brachial DBP along with 40% of brachial artery pulse pressure. Results Central SBP obtained via a transfer function was 123.5 ± 15.7, 117.8 ± 14.2 and 126.0 ± 15.4 mmHg (mean ± SD) following above-mentioned three calibration schemes, respectively. Using the same calibration schemes, carotid artery SBP was 131.4 ± 15.2, 118.4 ± 14.4 and 126.8 ± 15.7 mmHg, respectively. Central-to-brachial amplification was 13.0 ± 3.6 mmHg using second method as compared with 4.6 ± 3.8 mmHg with third method. Brachial-to-radial amplification was actually negative (−6.3 ± 4.5 mmHg) using second method, whereas 3.4 ± 5.5 mmHg was found with third method. Conclusion Both carotid artery SBP and central SBP obtained via a transfer function are highly sensitive to the calibration of the respective carotid artery and radial artery pressure waveforms. Our data suggest that the one-third rule to calculate MAP from brachial cuff BP should be avoided, especially when used to calibrate radial artery pressure waveforms for subsequent application of a pressure transfer function. Until more precise estimation methods become available, it is advisable to use 40% of brachial pulse pressure instead of 33% to assess MAP.

The use of diameter distension waveforms as an alternative for tonometric pressure to assess carotid blood pressure

Proper non-invasive assessment of carotid artery pressure ideally uses waveforms recorded at two anatomical locations: the brachial and the carotid artery. Calibrated diameter distension waveforms could provide a more widely applicable alternative for local arterial pressure assessment than applanation tonometry. This approach might be of particular use at the brachial artery, where the feasibility of a reliable tonometric measurement has been questioned. The aim of this study was to evaluate an approach based on distension waveforms obtained at the brachial and carotid arteries. This approach will be compared to traditional pulse pressures obtained through tonometry at both the carotid and brachial arteries (used as a reference) and the more recently proposed approach of combining tonometric readings at the brachial artery with linearly or exponentially calibrated distension curves at the carotid artery. Local brachial and carotid diameter distension and tonometry waveforms were recorded in 148 subjects (119 women; aged 19-59 years). The morphology of the waveforms was compared by the form factor and the root-mean-squared error. The difference between the reference carotid PP and the PP obtained from brachial and carotid distension waveforms was smaller (0.9 (4.9) mmHg or 2.3%) than the difference between the reference carotid PP and the estimates obtained using a tonometric and a distension waveform (-4.8 (2.5) mmHg for the approach using brachial tonometry and linearly scaled carotid distension, and 2.7 (6.8) mmHg when using exponentially scaled carotid distension waves). We therefore recommend to stick to one technique on both the brachial and the carotid artery, either tonometry or distension, when assessing carotid blood pressure non-invasively.

Impact of Radial Artery Pressure Waveform Calibration on Estimated Central Pressure Using a Transfer Function Approach

To the Editor: It is with great interest that we have read the excellent work of McEniery et al1 on the variability of the relation between central and brachial pulse pressure (pressure amplification), assessed in >10 000 subjects. We were, however, a little surprised about the magnitude of the central-to-brachial pressure amplification, which is in the order of 1.38 for the entire population (estimated from their Table 1). We hypothesize that these high values arise from the use of central aortic pressure curves synthesized from radial pressure tracings, with the most important factor not being the generalized pressure transfer function …

Flawed Measurement of Brachial Tonometry for Calculating Aortic Pressure

We share O’Rourke and Takazawa’s1 interest in and pursuit of reliable, accurate noninvasive central blood pressure assessment. To that end, we use carotid applanation tonometry, calibrated with diastolic and mean blood pressures, for which we rely on brachial tonometry. In the Asklepios Study, all of the radial, brachial, and carotid artery data were measured by a single skilled, trained operator (a prerequisite for applanation tonometry in general) with a high-fidelity Millar pen-type tonometer, and 20-second sequences were processed automatically to an ensemble average after a procedure extensively described earlier.2 The relatively high dropout for the brachial measurements (virtually nonexistent for the other sites) is largely attributable …

Flawed Measurement of Brachial Tonometry for Calculating Aortic Pressure? Response

We share O’Rourke and Takazawa’s1 interest in and pursuit of reliable, accurate noninvasive central blood pressure assessment. To that end, we use carotid applanation tonometry, calibrated with diastolic and mean blood pressures, for which we rely on brachial tonometry. In the Asklepios Study, all of the radial, brachial, and carotid artery data were measured by a single skilled, trained operator (a prerequisite for applanation tonometry in general) with a high-fidelity Millar pen-type tonometer, and 20-second sequences were processed automatically to an ensemble average after a procedure extensively described earlier.2 The relatively high dropout for the brachial measurements (virtually nonexistent for the other sites) is largely attributable …