| Background and Objective1. When the cardiac blood flow velocity is measured by using ultrasonic Doppler technology, the low- frequency, high-energy frequency shift signal generated by cardiac motion will also appear in the Doppler spectrum. However, for a long time, these Doppler signals generated by the cardiac motion are purposely ?ltered out and ignored. According to the Doppler effect, the velocity measured by ultrasonic Doppler technology represents the blood velocity relative to the probe. However, what people needs in clinical medicine is the velocity relative to cardiac valves, in order to reflect the functional state of the heart. Previous researches have shown that Doppler blood flow velocity measurement has underestimated the real speed, because of the movement of the heart itself. However, the underestimations of the cardiac blood flow velocities in different parts have not quantitatively determined and reported. In this study, in vitro and in vivo experiments were designed with the aim to quantitatively determine the underestimations of the flow velocity at aortic valve, pulmonary valve, mitral and tricuspid valve by a new technology, explore the mechanism of cardiac motion’s impact on Doppler blood flow measurement, and also put forward a correction method.2. The mechanism of the influence of intrathoracic pressure changes on cardiac hemodynamics has puzzled the scientific community for a long time. Even though the studies on this started one hundred years ago and a lot of data was accumulated. Meanwhile, many hypotheses have been proposed by scholars, but these hypotheses had internal contradiction, so there is no unified and widely accepted mechanism by now. We speculate that exploration of the mechanism has been hindered because the effects of intrathoracic pressure on left and right ventricular function were previously determined separately, not simultaneously, and the changes in each cardiac cycle during Valsalva maneuver were incompletely investigated in previous beat-by-beat studies. Based on our previous related study, we put forward a hypothesis that the cardiovascular system in the chest could be divided into the fully- intrathoracic and partially- intrathoracic enclosed fluid systems based on hydromechanic s and anatomy, and that their interactions may reflect and explain the underlying mechanism. The objective of this study was to use the PW/PW Doppler dual- mode technology for the first time to synchronously investigate the influence of Valsalva maneuver on left and right ventricular filling at a beat to beat basis in healthy adult male volunteers, and also to validate our proposed hypothesis.3. Heart- lung interactional issues such as pulsus paradoxus have been widely studied for more than 140 years, but the mechanical mechanism is still controversy. Researchers have agreed well with that the essence of the heart- lung interaction is that the cardiovascular function is influenced by the intrathoracic pressure generated by respiratory movement. In order to reveal the underlying mechanism of this problem, a fundamental and inevitable question, that is, how does the intrathoracic pressure transmit into the tissue in the chest. According to our study, we believe that the mechanism being not solved for a long time may be due to the lack of a unified basic law. In order to answer the concerning if the intrathoracic pressure may undiminished transmit into the tissue such as heart, we found that Pascal’s law can be extended to have a general meaning and as a more widely applicable new law. And we temporarily named the extended Pascal’s law the general Pascal’s law. Here we tried to prove it using mathematical and experimental approaches and explore its scientific significance. Methods1. Hitachi HI Vision Preirus ultrasound system and its dual PW/DTI mode were used, the transducer frequency was 1-5 MHz, sample volume was set as 3.0mm. In this in vitro study, we investigated the quantitative relationship of Doppler measurement and cardiac motion in two different conditions: when the transducer was separated from the slide bakelite board and stayed stationary, the simulative cardiac base had relative motion to the transducer; and when the transducer was fixed to the slide bakelite board and moved as a whole set, the simulative cardiac base had no relative motion to the transducer. In the in vivo study, 60 healthy volunteers(average age 30±7.7 years) were included, adopting a left lateral decubitus position with quiet breathing and simultaneous EC G. They were asked respiration held during recording, using dual PW/DTI mode, the aortic, mitral, tricuspid and pulmonary valvular blood flow velocity and the adjacent valvular annulus velocity were recorded, thus the underestimations of the flow velocities were calculated.2. Hitachi HI Vision Preirus ultrasound system and its dual PW/PW mode were used, the transducer frequency was 1-5 MHz, the sample volume was set as 3.5mm. Thirty healthy male volunteers(average age 31±7.7 years) were included, adopting a left lateral decubitus position, and the mitral, tricuspid blood flow velocity were simultaneously recorded by dual PW/PW mode at a clear display of an apical four-chamber view of the heart. After five stable cardiac cycles, the subject was asked to carry out a 40-mm Hg Valsalva maneuver was carried out by each subject and the recording was maintained at the desired pressure for 15 cardiac cycles, after that, at the 16 t h cardiac cycle, the release began and the recording lasted to the 25 t h cardiac cycle. The peak velocity(PV) of each beat inflow(i.e., the E wave of inflow), the velocity–time integral(VTI) and the inflow volume(IV) through the mitral and tricuspid valves was measured on the PW/PW recording spectrum. The inflow volume(IV) of the left heart was calculated using the mitral inflow method, that is VTI multiplied by the cross-sectional area of the mitral annulus. Fifteen subjects were selected randomly to assess the intra-observer variability by the same observer as well as by another independent experienced observer to test the inter-observer variability.3. The mathematical method and experimental results of our previous study and another dynamics study of compression therapy were used to prove the general Pascal’s law. Results1. The results of the in vitro exp eriment for exploring the influence of cardiac motion on Doppler blood flow measurements showed that when the cardiac motion and the blood flow moved in opposite directions, the measured velocity was subtracted; when they were in the same directions, the measured velocity was added up. The in vivo study showed the conventional Doppler echocardiographic measurements significantly underestimated the true velocity(P<0.001). The true blood flow velocity relative to the valvular annulus could be obtained by dual PW/TDI technique. In healthy people, the actual aortic blood flow velocity had a significant underestimation of(8.5±1.2)%; the actual flow velocity of the pulmonary artery had a significant underestimation of(6.6±1.1)%; the underestimations of E and A wave of mitral valve’s were(13.4±1.8)% and(16.7±3.3)%; the underestimations of E and A wave of tricuspid valve’s were(18.3±2.4)% and(26.1±5.6)%.2. For the left heart, The values of the PV, VTI and IV were unchanged at the first beat after the onset of the Valsalva maneuver(compared with those at rest, p=0.13), began to decrease gradually, fell to the lowest value at the 11±1.2th beat(range, 9t h to 12 t h beat) and then kept at this stable level until the release phase(phase III, began at the 16 th beat). Simultaneously, for the right heart, the values of the PV, VTI and IV of the right heart decreased significantly compared with those at rest(60±6.7 vs 50±5.8 cm/s; 16±1.7 vs 12±1.1 cm; 78.9±8.4 vs 59.2±5.4 ml; p<0.05) at the first cycle, then decreased rapidly to the lowest at 6±0.8th beat(range, 4t h to 7th beat), and then increased gradually to the 9±1.3th beat(range, 8t h to 10 t h beat) and kept at this level until the release phase. After the release(from the 16 th beat), the values of the PV, VTI and IV of the right and left heart increased, and an overshoot was observed(the IV of the left heart increased by 15.8% and the right heart increased by 18.8%). The changes of IV in the right heart were before those of the left heart during and after 40- mm Hg Valsalva maneuver.3. General Pascal’s law states that pressure exerted anywhere in a confined incompressible fluid is transmitted undiminished throughout not only the fluid but also the incompressible solid inside the fluid. It can be seen from the gene ral Pascal’s law that Pascal’s law is only a special situation of general Pascal’s law when the solid inside the fluid is the fluid itself. The general Pascal’s law extends the Pascal’s law. The mathematical method and experimental results of our previous study and another dynamics study of compression therapy all could prove the general Pascal’s law. Conclusions1. Blood flow velocity measured by Doppler ultrasound could be influenced by the cardiac motion, the Doppler measurements are equal to the vector sum of the true blood flow velocity and the cardiac base velocity. The clinical used cardiac blood flow velocity measured by Doppler ultrasound has significantly underestimated the true velocity that relative to the valve annulus, its mechanism can be explained by the principle of motion relativity. Based on this, the underestimation can be quantified and corrected using dual PW/DTI technique so as to get the true blood flow velocity.2. The left heart and right heart have different physiological responses to cardiac filling during the increase of the intrathoracic pressure caused by 40 mm Hg Valsalva maneuver. The results of this study accord with our hypothesis of the interaction between the partially- intrathoracic system and the fully- intrathoracic system, and this hypothesis might help to explain the mechanism of intrathoracic pressure influencing the heart and circulatory system.3. The general Pascal’s law, based on the mathematical proof, experimental research and objective facts rational consideration, states that pressure exerted anywhere in a confined incompressible fluid is transmitted undiminished throughout not only the fluid but also the incompressible solid inside the fluid, may be maybe valid. It reveals a more widespread hydrostatic rule than Pascal’s law, may provide us theoretical basis for the heart- lung interaction mechanism. Of course, there should be a lot of work to be done for further study. |
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