Cardiac power integral: a new method for monitoring cardiovascular performance

Abstract

Cardiac power (PWR) is the continuous product of flow and pressure in the proximal aorta. Our aim was to validate the PWR integral as a marker of left ventricular energy transfer to the aorta, by comparing it to stroke work (SW) under multiple different loading and contractility conditions in subjects without obstructions in the left ventricular outflow tract. Six pigs were under general anesthesia equipped with transit time flow probes on their proximal aortas and Millar micromanometer catheters in their descending aortas to measure PWR, and Leycom conductance catheters in their left ventricles to measure SW. The PWR integral was calculated as the time integral of PWR per cardiac cycle. SW was calculated as the area encompassed by the pressure–volume loop (PV loop). The relationship between the PWR integral and SW was tested during extensive mechanical and pharmacological interventions that affected the loading conditions and myocardial contractility. The PWR integral displayed a strong correlation with SW in all pigs (R2 > 0.95, P < 0.05) under all conditions, using a linear model. Regression analysis and Bland Altman plots also demonstrated a stable relationship. A mixed linear analysis indicated that the slope of the SW-to-PWR-integral relationship was similar among all six animals, whereas loading and contractility conditions tended to affect the slope. The PWR integral followed SW and appeared to be a promising parameter for monitoring the energy transferred from the left ventricle to the aorta. This conclusion motivates further studies to determine whether the PWR integral can be evaluated using less invasive methods, such as echocardiography combined with a radial artery catheter.

New insights into mitral heart valve prolapse after chordae rupture through fluid–structure interaction computational modeling

“…This variable represents the percentage of total energy expenditure by the myocardium that is converted into external stroke work ( SW ). LV efficiency was calculated as fSW / PLA , where fSW is the forward SW , and was defined as the time integral of the continuous product of flow across the AV and the aortic pressure during systole 23 . Figure 6 shows a representative pressure-volume loop for the isolated P2 model.…”

Cardiac power parameters during hypovolemia, induced by the lower body negative pressure technique, in healthy volunteers

“…As a consequence reductions in both pressure and flow due to hypovolemia will be incorporated in cardiac power, which theoretically should make cardiac power parameters able to track hypovolemia better than the two factors separately. We are developing a minimally invasive system for beat-by-beat measurement of cardiac power [ 8 ], soon ready for clinical research regarding possible applications including detection of hypovolemia. In this study we have analyzed previously recorded data from healthy volunteers using a laboratory system [ 9 ] with lower body negative pressure (LBNP) to simulate hypovolemia [ 10 ], to consider the potential use of cardiac power parameters in hemodynamically unstable patients.…”

Minimally invasive beat-by-beat monitoring of cardiac power in normal hearts and during acute ventricular dysfunction

“…Furthermore, since the PWR-integral is equivalent to stroke work (Rimehaug et al 2013) a suggestion is that it can be used to guide treatment, based on the theory that optimal stroke work is a result of optimized ventriculoarterial coupling (Borlaug and Kass 2009). In healthy individuals this coupling is optimized physiologically (De Tombe et al 1993), whereas individuals with acute ventricular dysfunction can be considered to have a coupling problem (Borlaug and Kass 2011).…”

“…To validate this minimally invasive system named ultrasound cardiac power (uPWR), we wish to compare it to a previously validated invasive version, transit time cardiac power (ttPWR) (Rimehaug et al. ).These systems may perform differently under different physiological and pathophysiological conditions; such as varying degrees of preload/afterload and ventricular dysfunction, motivating this validation study.…”

“…We have developed a laptop-based minimally invasive system with this capability, calculating cardiac power based on audio signals (Herr et al 2010) from Doppler ultrasound of aortic flow and blood pressure from the patient monitor. To validate this minimally invasive system named ultrasound cardiac power (uPWR), we wish to compare it to a previously validated invasive version, transit time cardiac power (ttPWR) (Rimehaug et al 2013). These systems may perform differently under different physiological and pathophysiological conditions; such as varying degrees of preload/afterload and ventricular dysfunction, motivating this validation study.…”