Noninvasive Monitoring of Cardiac Preload and Contractility by Heart Beat Derived Mechanical Vibration on the Chest Wall in Guinea Pigs
Background: Myocardial motion produces compression waves that are transmitted to the surface of the chest and vibrate the chest wall. Piezoelectric transducers, which detect mechanical vibrations, may be useful for evaluating cardiac and/or breathing movements when the sensor is placed under an animal's body. Methods: We assessed heartbeat related chest vibration signals (CVS) detected with a piezoelectric transducer in anesthetized guinea pigs while simultaneously monitoring the electrocardiogram, heart sounds, aortic pressure, and central venous pressure. Results: CVS displayed characteristic features as the ventricle and/or atrium contracted and relaxed during cardiac cycles. A transient positive wave, which occurred approximately at the onset of the R wave on the electrocardiogram, was followed by a profound negative wave during systole. The negative wave peaked early in systole and then gradually returned. A small notch was observed at the second heart sound. A dome shaped positive wave was observed during diastole that connected to the transient positive wave of the next cardiac cycle. In response to phlebotomy (blood volume, 15 ml/kg) the size of the dome shaped positive wave decreased, whereas saline transfusion (20 ml/kg) increased the positive wave during diastole. Administration of isoproterenol markedly increased the transient positive wave at the onset of systole, whereas phenylephrine affected the transient positive wave only slightly. Conclusions: Our findings suggest that CVS may be useful to identify cardiac cycles and to evaluate cardiovascular dynamics during changes in blood volume and/or cardiac contractility.