Mechanism Study Of Effects Of The Intrathoracic Pressure On The Velocity Of Tricuspid Regurgitation And Estimation Of Pulmonary Artery Pressure

ObjectiveTo study the mechanism of the effects of the intrathoracic pressure variation on the velocity of tricuspid regurgitation in quiet respiration, to accurately estimate the pulmonary artery systolic pressure, and to verify the new proposed mechanism of respiratory effects on hemodynamics using echocardiography.Methods1,Experiment subjects screened The patients with stable tricuspid regurgitation and clear Doppler spectral envelopes were selected for the study. Regurgitations were confirmed by continuous-wave Doppler method and apparent arrhythmia, moderate pericardial effusion, constrictive pericarditis, congenital heart disease were ruled out.2,Experimental data acquisition Together with Electro-cardiogram and respiratory curve recorded simultaneously, continuous-wave Doppler spectra of tricuspid regurgitation were recorded with the Siemens Sequoia 512 system using a 2.5-4.0MHz probe.Breathing thermal sensors (E99H450) were used to record respiratory curve in which the ascending branch represented the inspiratory phase and the decreasing branch represented the expiratory phase. The left lateral decubitus was adopted in all subjects with calm breathing. Followed with clear graphics got in parasternal four chamber view or apical four chamber view and focus area set under tricuspid valve, the tricuspid regurgitation velocity was detected by using color Doppler function. The probe position was adjusted to make the sound beam and the blood flow in the same direction as far as possible. The scan rate (sweep) set to 50mm/s (or 25mm/s) simultaneously. And the tricuspid regurgitation spectra recorded at the end-inspiration and end-expiration. According to tricuspid regurgitation velocity by using of simplified Bernoulli equation(△P = 4V2), the cross-tricuspid pressure gradients were acquired. The 5 continuous measurements were averaged in each phase.3,Statistical analysis Using SPSS 13.0 statistical software, all the ultrasound measurements were respectively compared between the inspiratory phase and expiratory phase of the regurgitation velocity and the pressure gradient. All the demographic data were expressed as mean±standard deviation. P values of <0.05 were considered as statistically significant.ResultsIn the calming-breath conditions, there was no significant difference between the inspiratory phase and expiratory phase of the tricuspid regurgitation velocity [(2.87±0.72) m / s of (2.84±0.75) m / s, p = 0.410] and the pressure gradients [(35.01±20.65) mmHg to (34.51±19.84) mmHg, p = 0.581].The tricuspid regurgitation velocity were affected by the respiration variation apparently, and showed three patterns:①The velocity increased in the inspiratory phase.②T he velocity decreased in the inspiratory phase.③The velocity changed randomly.ConclusionAccording to the new hypothesis by Chinese scholars, the thoracic pressure changes have a clear impact on the tricuspid regurgitation velocity, and the respiratory changes in pleural pressure has led to inter-tricuspid valve pressure changes, which results tricuspid regurgitation velocity varies with the respiratory changes. The former theory shows that the regurgitation velocity decreases followed the inter-tricuspid valve pressure decreases in inspiratory phase. And at the same time the peripheral blood return to right heart increases in right ventricular diastolic filling phase followed the increased contractility, which become the factors to lead to the regurgitation velocity increase. But there is no fixed relation between the normal respiratory and the cardiac cycle. So the heart contraction cycle can be occurred in any respiratory phase, which leads to the complex effects on the tricuspid regurgitation velocity. The regularity of the variations of the tricuspid regurgitation velocity affected by the respiratory pleural pressure shows two characteristics: complexity and non-regularity. So it is essential to keep respiratory movement in the medium-term during estimating pulmonary arterial pressure by using the tricuspid regurgitation velocity method, which can keep the intrathoracic pressure stability to improve the accuracy of the determination. This study provides more evidences for the new hypothesis that the cardiac function affected by the respiratory movement.