Evaluation of Augmented Pressure and Wasted Pressure Work in Patients Undergoing CABG: An Observational Study

Background: Patients undergoing coronary artery bypass graft surgery (CABG) present with a loss in aortic compliance (C A ) and elevated systolic, diastolic and pulse pressures. The loss of C A leads to an increase in augmented pressure (AP) and wasted pressure work (WPW). It is unknown how these parameters changes in the pre-operative (pre-op) and post-anesthetic (post-A) state. Methods: The current observational prospective study evaluated CABG patients (n = 49, male: 41, female: 8, mean age= 65.0 ± 9.0 yrs). Pre-op and post-A data was collected in triplicate to create the mean of brachial and central blood pressures. Brachial pressure was processed (Sphygmocor Xcel, Cardiex Inc.) providing brachial systolic pressure (bSBP), central systolic blood pressure (cSBP), diastolic (dBP) and central pulse pressures (cPP). Augmentation pressure and WPW were calculated. The current WPW metric includes the ejection duration minus the timing of the reflected wave. We modified the WPW equation to include the timing for peak pressure (Tp) minus the timing for the arterial wave reflection (Tr) multiplied by AP and divided by two (WPWn), due to resemblance of this area to a triangle. This method provides a more physiological method for quantifying WPW. All pre-op and post-A hemodynamic data were compared using a paired t-test at p <0.05. Results: Both pre-op bSBP and cSPB met the HTN guidelines ≥ 130 mmHg in 40 and 31 out of 49 patients, respectively. Pre-op diastolic HTN was similar across both methods with 29/49 presenting with DBP ≥ 80. Pre-op AP (18.0 ± 8.4 mmHg) and cPP (52.1 ± 12.6) were greater than post-A AP (14.1 ± 7.4 mmHg) and cPP (37.6 ± 7.8 mmHg), p <0.05. WPWo and WPWn were highly correlated (r =0.99) with AP, suggesting that AP alone could be considered to replace the WPW metric. Conclusion: The results of this observational study provide several important findings. First, not all patients presenting for CABG who have bSBP HTN values may have cSBP HTN. In our sample, 19 patients had cSBPs < 130 mmHg while 40 patients presented bSBP ≥ 130 mmHg. With the correlation of AP with WPWo and WPWn, the AP metric may be useful in future studies to determine the metabolic cost of WPWn, in particular in patients presenting with limited myocardial reserve. Finally, cPP was lower than bPP pre-op with a PP >50 mmHg used as a threshold for risk of developing acute kidney injury. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.