Continuous blood pressure and augmentation index
stroke
STROKE
Hemodynamic data including continuous sBP and dBP, resting stroke volume (SV), resting heart rate (HR), pulse pressure (PP), and total peripheral resistance (TPR) was acquired using the Task Force® Monitor (TFM), which is a validated non‐invasive beat‐to‐beat monitoring system. Hemodynamic measures were acquired over a 5‐min period via impedance cardiography, with continuous beat‐to‐beat BP acquired via the vascular unloading technique at the proximal limb of the index or middle finger. These data was automatically corrected to oscilliometric BP values obtained at the brachial artery of the opposite arm. Raw data of the entire 5‐min continuous BP recording was analyzed for each participant using a bespoke analysis pipeline created in MATLAB R2021a. The pipeline was used to find the sBP and dBP troughs for each heartbeat, and discard any data that was too noisy to analyze, which comprised the following steps:
Using the MATLAB ‘findpeaks’ function from the signal processing toolbox, search for peaks with a sharp prominence. Take the mean distance between these and then rerun the search for peaks ensuring a minimum distance between peaks of 0.33 of the mean distance. This minimizes the chance of being distorted by sBP peaks that are too close to one another.Take the negative of the BP raw signal and run the ‘findpeaks’ function on these to find the dBP troughs.Loop through the indices for the sBP peaks and take each cycle to be defined as the recorded BP points between sBP peaks. Check that the second peak (which should be the second sBP1) is not significantly larger than the second peak—if it is, then skip to the next index.Check if there is a single peak between these, including the second point, which will correspond to sBP2.If a clear prominence is not found, then looking at the second derivatives of the raw BP signal in the heartbeat, find the index where this is at its minimum. This will provide the sBP2 peak.The AIx was then calculated as follows: (late peak sBP [sBP 2]—dBP)/(early peak of sBP [sBP 1]—dBP) × 100 (%) (Kohara et al., Example tracing of blood pressure waveforms and subsequent calculation of AIx.HR was acquired through a six‐channel ECG and SV was recorded via impedance cardiography through three electrode bands, two of which were adjacent to the thorax, in line with the xiphoid process, while the other was positioned on the nape of the neck. TPR was calculated in accordance with Ohm's law, while CO was automatically derived from HR and SV. Both TPR and CO were indexed to body surface area via the Du Bois method (Du Bois & Du Bois, 