support-information-section).

The arterial network in healthy young adults is thought to be structured to minimise wave reflection in conduit arteries, producing an ascending aortic pressure waveform with three key features: early systolic peak, negative systolic augmentation, and diastolic hump. One-dimensional computer models have provided significant insights into arterial haemodynamics, but no previous models of the young adult have exhibited these three features. Since the latter was likely to be related to unrepresentative or non-optimised impedance properties of the model arterial networks, we developed a new ‘YoungAdult’ model that incorporated 1) a novel and more accurate empirical equation for approximating wave speeds, based on area and relative distance to elastic-muscular arterial transition points, 2) optimally-matched arterial junctions, and 3) an improved arterial network geometry that eliminated ‘within-segment’ taper (which causes wave reflection in conduit arteries) whilst establishing ‘impedance-preserving’ taper. These model properties led to wave reflection occurring predominantly at distal vascular beds, rather than in conduit arteries. The model predicted all three typical characteristics of an ascending aortic pressure waveform observed in young adults. When compared with non-invasively acquired pressure and velocity measurements (obtained via tonometry and Doppler ultrasound in 7 young adults), the model was also shown to reproduce the typical waveform morphology observed in the radial, brachial, carotid, temporal, femoral, and tibial arteries. The YoungAdult model provides support for the concept that the arterial tree impedance in healthy young adults is exquisitely optimised, and it provides an important baseline model for investigating cardiovascular changes in ageing and disease states.

Background: An interarm difference (IAD) in blood pressure (BP) of 10 mmHg or more is a potential cardiovascular risk factor in adults, given its association with cardiovascular events/mortality. In children and adolescents, accurate BP assessment is critical for identifying risk of end organ damage. However, IAD has not been systematically studied in paediatric patients; if present and of significant magnitude, measuring BP in only one arm could lead to misclassification of hypertensive status.Method: In 95 children/adolescents with a normal aorta (including 15 with a history of tetralogy of Fallot) aged 7-18 years attending the Royal Children's Hospital, Melbourne, we aimed to determine the magnitude of IAD, frequency of IAD of at least 10 mmHg, difference in BP classification between arms, and influence of repeat measures on IAD in a single visit. After 5 min rest, simultaneous bilateral BP was measured in triplicate with an automated device.Results: Absolute systolic IAD was 5.0 mmHg (median, interquartile range 2-8 mmHg) and was 10 mmHg or more in 14%, with no change on repeat measures. In patients with a history of aortic surgery, IAD of 10 mmHg or more occurred in 27% (transposition of the great arteries, n ¼ 15) and 75% (aortic coarctation, n ¼ 8). Differences in BP classification, based on initial left vs. right arm measures, occurred in 25% (normal aorta) and 40%/63% (aortic surgery), or 17% and 33%/50%, respectively if second and third measurements were averaged.Conclusion: Substantial interarm BP differences were common, even in apparently healthy children and adolescents: evaluation of IAD may, therefore, be important for BP classification in the paediatric setting.

Objective: Central systolic blood pressure (cSBP) represents the load experienced by the heart and other central organs, and differs from brachial blood pressure due to pulse pressure amplification (PPA). Two widely-used automated devices (SphygmoCor XCEL and Mobil-O-Graph) incorporate algorithms to estimate cSBP and PPA, but in the recent KidCoreBP study, neither passed validation against invasively-measured cSBP in children and adolescents (J Hypertens 38:821–828, 2020). We investigated whether empirical correction equations, using information provided by these automated devices and basic demographics, could provide cSBP and PPA estimates with acceptable accuracy (error mean < 5 mmHg) and precision (error standard deviation < 8 mmHg). Design and method: Using data from the KidCoreBP study (n = 62, SphygmoCor; n = 52, Mobil-O-Graph), stepwise linear regression was used to identify empirical correction equations for predicting cSBP and PPA. Input variables included all blood pressures and pulse wave analysis indices provided by the device, as well as age, sex, height and weight. A leave-one-out cross-validation was then conducted to quantify accuracy and precision. Results: The empirical equations substantially improved estimation of cSBP (–0.1 ± 5.1 corrected vs 7.9 ± 6.8 mmHg uncorrected, SphygmoCor; and 0.03 ± 7.6 vs 5.7 ± 10.3 mmHg, Mobil-O-Graph) and PPA (0.0 ± 4.5 vs 4.2 ± 5.1 mmHg; and 0.0 ± 4.7 vs 6.8 ± 8.4 mmHg). Conclusions: This is the first study to demonstrate acceptable accuracy and precision of cSBP and PPA estimated using automated devices in children and adolescents, when compared to high fidelity invasive measurements. Device-specific empirical correction equations may overcome the present inaccuracy and/or imprecision of available devices.

Wave separation analysis (WSA) reveals the impact of forward- and backward-running waves on the arterial pressure pulse, but the calculations require a flow waveform. This study investigated (1) the variability of the ascending aortic flow waveform in children and adolescents with/without a childhood heart disease history (CHD); (2) the accuracy of WSA obtained with a representative flow waveform (RepFlow), compared with the triangulation method and published ultrasound-derived adult representative flow; (3) the impact of limitations in Doppler ultrasound on WSA; and (4) generalizability of results to adults with a history of CHD. Phase contrast MRI was performed in youth without (n = 45, Group 1, 10–19 years) and with CHD (n = 79, Group 2, 7–18 years), and adults with CHD history (n = 29, Group 3, 19–59 years). Segmented aortic cross-sectional area was used as a surrogate for the central pressure waveform in WSA. A subject-specific virtual Doppler ultrasound was performed on MRI data by extracting velocities from a sample volume. Time/amplitude-normalized ascending aortic flow waveforms were highly consistent amongst all groups. WSA with RepFlow therefore yielded errors < 10% in all groups for reflected wave magnitude and return time. Absolute errors were typically 1.5–3 times greater with other methods, including subject-specific (best-case/virtual) Doppler ultrasound, for which velocity profile skewing introduced waveform errors. Our data suggest that RepFlow is the optimal approach for pressure-only WSA in children and adolescents with/without CHD, as well as adults with CHD history, and may even be more accurate than subject-specific Doppler ultrasound in the ascending aorta.