Continuous recording of pulmonary artery diastolic pressure and cardiac output using a novel ultrasound transducer

Background: The feasibility of hands-free transthoracic continuous determination of pulmonary artery (PA) diastolic pressure (PAD) and cardiac output (CO) by Doppler ultrasound has not been previously demonstrated. We developed a 2.5-MHz spherical transducer mounted in an external housing to permit steering in 360 degrees (Contison). The external housing was attached to the chest wall using an adhesive patch. Methods and Results: Fifty patients in the coronary care department who had PA catheters had Doppler ultrasound studies. The 2.5-MHz spherical transducer was placed at the left sternal border to permit imaging of the pulmonic valve and was attached to a commercial ultrasound machine. The PA was imaged and its diameter measured. The pulmonary flow velocity signal was recorded and the time velocity integral obtained. The CO was calculated as: CO = time velocity integral of the PA systolic flow velocity signal x pi diameter(2) divided by 4 x heart rate. The pulmonary regurgitation signal was then recorded and the end-diastolic velocity of the regurgitant signal was measured. Right atrial pressure was assessed from the jugular venous pressure or from the size and pulsatility of the inferior vena cava. The PADP was calculated as: PADP = 4 end-diastolic velocity of the regurgitant signal(2) + right atrial pressure. The CO, PADP, and pulmonary wedge pressure were recorded from the PA catheter immediately after the ultrasound studies. Serial data were obtained every half hour or 1 hour up to a maximum of 5 hours. Adequate Doppler signals were obtained in 43 patients. Results. There was a good correlation between the PADP by Doppler versus PA catheter (r = 0.90, standard error of the estimate = 3.3 nun Hg); PADP by Doppler versus PA wedge pressure (r = 0.88, standard error of the estimate = 3.7 mm Hg); and CO by Doppler versus PA catheter (r = 0.92, standard error of the estimate = 0.7 L/min). Conclusion: The 2.5-MHz spherical transducer permitted accurate assessment of CO and PAD. This transducer could be of potential value in monitoring patients in the intensive care setting.