Table 1 Overview of the carotid ultrasound-based and clinical features that were studied. Per feature, the source necessary for its computation is specified. A description or formula is added if appropriate. If a feature was extracted per beat, the values were averaged to obtain a single value for the measurement period
Source | Feature (units) | Description or formula, if appropriate |
|---|---|---|
Carotid ultrasound – velocity waveform | Peak systolic velocity (PSV) per beat (cm/s) | Maximal amplitude per beat |
Systolic foot velocity (SFV) per beat (cm/s) | Amplitude of the systolic foot per beat | |
Mean of the velocity waveform (cm/s) | Mean value of the entire velocity waveform | |
Velocity time integral (VTI) per beat (cm) | The area under the velocity waveform for a single beat | |
Interdecile range (cm/s) | \(90^{\mathrm{th}}-10^{\mathrm{th}}\;\mathrm{quantile}\) values of the velocity waveform | |
Signal stability index (no unit) | A heuristic measure of the quality of the signal based on the kernel density estimate, as described in (Joshi et al. 2018) | |
Signal instability index (no unit) | Bandwidth of the kernels from the kernel density estimate, as described in (Joshi et al. 2018) | |
Skewness of the velocity waveform (no unit) | A measure of the asymmetry of the distribution around the sample mean. A positive skewness implies that the data spreads out to the left of the sample mean | |
Kurtosis of the velocity waveform (no unit) | A measure that defines how heavily the tails of a distribution differ from the tails of a normal distribution, i.e., whether the tails contain extreme values. A positive kurtosis refers to a heavy-tailed distribution, indicating large outliers | |
Pulsatility index (no unit) | \(\frac{\mathrm{PSV}-\mathrm{SFV}}{\mathrm{mean}\;\mathrm{of}\;\mathrm{the}\;\mathrm{velocity}\;\mathrm{waveform}}\) | |
Resistive index (no unit) | \(\frac{\mathrm{PSV}-\mathrm{SFV}}{\mathrm{PSV}}\) | |
Corrected carotid flow time (ccFT) (ms) | \(\frac{\mathrm{systolic}\;\mathrm{flow}\;\mathrm{time}}{\sqrt{\mathrm{cycle}\;\mathrm{time}}}\) | |
Respirophasic peak velocity variation (ΔVpeak) (%) | \(\frac{PSV_{max}-PSV_{min}}{\frac12\left(PSV_{max}+PSV_{min}\right)}\times100\%\) | |
Carotid ultrasound – ensemble average of the velocity waveform | Acceleration (cm/s2) | \(\frac{\mathrm{PSV}-\mathrm{SFV}}{\mathrm{rise}\;\mathrm{time}}\) |
Relative acceleration time (no unit) | \(\frac{\mathrm{rise}\;\mathrm{time}}{\mathrm{length}\;\mathrm{of}\;\mathrm{the}\;\mathrm{cardiac}\;\mathrm{cycle}}\) | |
Deceleration (cm/s2) | \(\frac{\mathrm{PSV}-\mathrm{SFV}}{\mathrm{fall}\;\mathrm{time}}\) | |
Full-width half-maximum (FWHM) (s) | The width of the waveform shape at half (50%) of its maximum amplitude | |
Relative FWHM (no unit) | \(\frac{\mathrm{FWHM}}{\mathrm{length}\;\mathrm{of}\;\mathrm{the}\;\mathrm{cardiac}\;\mathrm{cycle}}\) | |
Ratio of the full-width at 75% of the peak to the full-width at 50% of the peak (FWQ3_to_FWHM) (no unit) | \(\frac{\mathrm{full}-\mathrm{width}\;\mathrm{at}\;75\%\;\mathrm{maximum}\;\mathrm{amplitute}}{\mathrm{FWHM}}\) | |
Velocity-based flow augmentation index (FAI) (no unit) | \(\frac{\mathrm{secondary}\;\mathrm{systolic}\;\mathrm{peak}-\mathrm{SFV}}{\mathrm{PSV}-\mathrm{SFV}}\) | |
Electronic health record | Age (years) | |
Sex | ||
Weight (kg) | ||
Height (m) | ||
American Society of Anesthesiologists (ASA) class (no unit) | ||
Fasting time (min) | ||
Baseline measurements | Baseline systolic blood pressure (SBP) (mmHg) | Noninvasively obtained with a brachial cuff |
Baseline mean arterial pressure (MAP) (mmHg) | Noninvasively obtained with a brachial cuff |