Vascular Tonometry for Central Hemodynamics

A vascular tonometer (SPT301, Millar Inc., Houston, TX, USA) was used to obtain the radial artery pulse wave. The original pulse wave signal and electrocardiogram were integrated and sent to a physiological signal monitoring system (MP36, Biopac Systems, Inc., Goleta, CA, USA) for later analyses. A customized Matlab program was used to convert the radial artery waveform into a carotid artery waveform to obtain central systolic blood pressure (cSBP), diastolic pressure (cDBP), pulse pressure (cPP), augmented pressure, and augmentation index (AI%). By using the triangulation method, the carotid artery waveform was separated into the incident and reflected waves [28 (link),29 (link)], to determine the forward (Pf) and backward (Pb) pressure waves, aortic characteristic impedance (Zc), systolic time (ST; an index of cardiac sympathetic activity) [30 (link)], and the subendocardial viability ratio (SEVR) [28 (link)]. SEVR, also known as the Buckberg index, has been used as a surrogate measure of myocardial perfusion that correlates with the ratio of subendocardial to subepicardial blood flow, which is indicative of poorer perfusion if the SEVR value is lower than 1.0 [31 (link)].