Noninvasive left ventricular pressure estimation using subharmonic emissions from microbubbles – an in vivo pilot study

The purpose of this study was to develop and investigate a new noninvasive approach to quantify left ventricular (LV) pressures using subharmonic emissions from microbubbles. A Sonix RP ultrasound scanner with PA4-2 phased array transducer was used in pulse inversion grayscale mode. Unprocessed radiofrequency data were obtained for 5 seconds (n=3) with pulsed wave Doppler from the aorta and/or LV of 4 canines during Sonazoid infusion. Simultaneous pressure measurements were obtained using Millar manometer. Subharmonic data (in dB) were extracted and processed. The resulting calibration factor (mmHg/dB), from the aorta, was used to estimate LV pressures. Errors ranged from 0.19 to 2.50 mmHg when estimating these pressures using the aortic calibration factor from the respective canines; but were considerably higher (0.64-8.98 mmHg) when a mean aortic calibration factor was used. In conclusion, subharmonic emissions from ultrasound contrast agents have the potential to noninvasively monitor LV pressures.