Transesophageal Doppler echocardiographic assessment of pulmonary venous flow pattern in subjects without cardiovascular disease

Using a human cardiovascular-respiratory model to characterize cardiac tamponade and pulsus paradoxus

BACKGROUND

Cardiac tamponade is a condition whereby fluid accumulation in the pericardial sac surrounding the heart causes elevation and equilibration of pericardial and cardiac chamber pressures, reduced cardiac output, changes in hemodynamics, partial chamber collapse, pulsus paradoxus, and arterio-venous acid-base disparity. Our large-scale model of the human cardiovascular-respiratory system (H-CRS) is employed to study mechanisms underlying cardiac tamponade and pulsus paradoxus. The model integrates hemodynamics, whole-body gas exchange, and autonomic nervous system control to simulate pressure, volume, and blood flow.

METHODS

We integrate a new pericardial model into our previously developed H-CRS model based on a fit to patient pressure data. Virtual experiments are designed to simulate pericardial effusion and study mechanisms of pulsus paradoxus, focusing particularly on the role of the interventricular septum. Model differential equations programmed in C are solved using a 5th-order Runge-Kutta numerical integration scheme. MATLAB is employed for waveform analysis.

RESULTS

The H-CRS model simulates hemodynamic and respiratory changes associated with tamponade clinically. Our model predicts effects of effusion-generated pericardial constraint on chamber and septal mechanics, such as altered right atrial filling, delayed leftward septal motion, and prolonged left ventricular pre-ejection period, causing atrioventricular interaction and ventricular desynchronization. We demonstrate pericardial constraint to markedly accentuate normal ventricular interactions associated with respiratory effort, which we show to be the distinct mechanisms of pulsus paradoxus, namely, series and parallel ventricular interaction. Series ventricular interaction represents respiratory variation in right ventricular stroke volume carried over to the left ventricle via the pulmonary vasculature, whereas parallel interaction (via the septum and pericardium) is a result of competition for fixed filling space. We find that simulating active septal contraction is important in modeling ventricular interaction. The model predicts increased arterio-venous CO2 due to hypoperfusion, and we explore implications of respiratory pattern in tamponade.

CONCLUSION

Our modeling study of cardiac tamponade dissects the roles played by septal motion, atrioventricular and right-left ventricular interactions, pulmonary blood pooling, and the depth of respiration. The study fully describes the physiological basis of pulsus paradoxus. Our detailed analysis provides biophysically-based insights helpful for future experimental and clinical study of cardiac tamponade and related pericardial diseases.

Effects of respiration on pulmonary venous flow and its clinical applications by Doppler echocardiography

OBJECTIVES

This study was aimed to explore respiratory variations of pulmonary venous flow and its clinical applications and the potential mechanism.

METHODS

Pulsed-wave Doppler waveforms of right-upper pulmonary vein were recorded with Siemens Sequoia 512 in 20 healthy young subjects. Electrocardiogram and respiratory tracing were recorded simultaneously. The inspiratory and expiratory pulmonary venous peak flow velocities of S- and D-waves and their velocity-time integrals (VTIs) were acquired and averaged for five consecutive respiratory cycles, respectively. The ratios of velocities and the VTIs of S- to D-waves (S/D, VTIs/VTId) during inspiration and expiration were calculated.

RESULTS

The velocity and VTI of S-wave did not vary significantly between inspiration and expiration (58.31 cm/sec +/- 9.22 cm/sec, 58.96 cm/sec +/- 7.79 cm/sec, P = 0.221; 16.29 cm +/- 2.59 cm, 16.54 cm +/- 2.18 cm, P = 0.090), while the velocity and VTI of D-wave increased significantly from inspiration to expiration (48.23 cm/sec +/- 8.32 cm/sec, 51.82 cm/sec +/- 8.72 cm/sec, P < 0.0001; 10.84 cm +/- 1.65 cm, 11.66 cm +/- 1.53 cm, P < 0.0001), resulting in significantly decreased ratios of the velocity and the VTI of S- to D-waves from inspiration to expiration (1.23 +/- 0.22, 1.17 +/- 0.27, P < 0.0001; 1.53 +/- 0.31, 1.43 +/- 0.22, P < 0.0001).

CONCLUSIONS

Respiration has significant influence on pulmonary venous flow, which should be taken into account in evaluating left ventricular diastolic function when adopting pulmonary venous flow waveform, especially in diseased settings. The different anatomical positions of left and right heart relative to the thoracic cavity may account for the respiratory variations of pulmonary venous flow.

Reference ranges for Doppler-assessed pulmonary venous blood flow velocities and pulsatility indices in normal human fetuses

OBJECTIVES

To establish reference ranges with gestation for Doppler parameters of fetal pulmonary venous blood flow during the second half of pregnancy, including not only peak velocities, but also relative indices reflecting left atrial pressure changes.

METHODS

In this cross-sectional study, 114 normal singleton pregnancies between 19 and 37 weeks' gestation were examined by Doppler echocardiography. In 98 fetuses, peak systolic velocity (S), peak diastolic velocity (D), end-diastolic velocity (A), and time velocity integral (TVI) were measured, and S/D ratio, pulsatility index for veins (PIV), as well as peak velocity index for veins (PVIV), were calculated. Regression analysis was used to determine reference ranges with gestation.

RESULTS

With advancing gestation, a significant increase in S, D and A velocities as well as in TVI, was observed. Whereas the S/D ratio remained constant, PVIV and PIV decreased significantly during the second half of pregnancy.

CONCLUSIONS

During the second half of pregnancy the increase in left atrial and ventricular compliance is reflected by the observed decrease in PIV and PVIV, which could be mainly due to the increased flow during atrial contraction. Such relative Doppler indices are better comparable than absolute values and are independent from the insonation angle. Potential clinical applications for such Doppler indices are conditions with possibly impaired left atrial function, like heart defects with left atrial obstruction or late stages of severe intrauterine growth retardation.

Fetal pulmonary venous flow pattern is determined by left atrial pressure: report of two cases of left heart hypoplasia, one with patent and the other with closed interatrial communication

We report two cases of fetal left heart hypoplasia with extremes of size of interatrial communication, i.e. a closed foramen ovale and an atrial septal defect. Doppler examinations of the pulmonary veins showed almost to and fro flow in the fetus with the closed foramen ovale and, in contrast, a normal flow velocity waveform in the fetus with the atrial septal defect, despite mitral atresia. Our observations support the importance of left atrial pressure in the creation of a pulmonary venous flow pattern in the fetus.

Transesophageal echocardiography

This article presents an overview of the benefits and efficacy of transesophageal echocardiography (TEE) in the critically ill patient. The echocardiographic evaluation of ventricular function both regional and global, is discussed with special emphasis on ischemic heart disease; assessment of preload, interrogation of valvular heart disease (prosthetic and native) and its complications; endocarditis and its complications; intracardiac and extracardiac masses, including pulmonary embolism; aortic diseases (e.g., aneurysan, dissection, and traumatic tears); evaluation of patent foramen ovale and its association with central and peripheral embolic events; advancements in computer technology; and finally, the effect of TEE on critical care.

Assessment of left ventricular function and hemodynamics with transesophageal echocardiography

Transesophageal echocardiography (TEE) plays an important role in the evaluation of left ventricular function and hemodynamics in the critical care setting. The technique provides immediate data regarding regional myocardial ischemia, global ventricular function, volume, and the presence of cardiac tamponade. This article outlines the role of TEE in the evaluation of left ventricular function in the intensive care unit and presents practical information for the use of TEE in evaluating systolic function, diastolic function, and cardiac tamponade.

An introduction to transoesophageal echocardiography: I. Basic principles

PURPOSE

The purpose of this review is to introduce the uninitiated to transoesophageal echocardiography (TEE): how it works, and what it can do. Sufficient detail is provided to serve as a reference guide to anaesthetists already using TEE in clinical practice.

SOURCE

A Medline search of English language literature up to and including August 1995 was conducted using the key words echocardiography and TEE. Reference echocardiography textbooks were also utilized in the preparation of this review.

PRINCIPLE FINDINGS

All information available from TEE is derived from either cardiac imaging or analysis of blood flow velocity using various Doppler modes. To understand the diagnostic capabilities of TEE we review clinically useful views of the heart as well as modes of cardiac imaging. Sufficient basic physics is presented to allow proper use of adjustment features on the echocardiography machine so that cardiac imaging can be optimized. Available Doppler modes are explained along with an overview of their clinical applications. Figures illustrating clinically useful views obtainable with omniplane TEE are included along with colour prints demonstrating clinical applications of colour flow Doppler.

CONCLUSION

TEE is becoming increasingly important in the management of cardiac patients for cardiac and non-cardiac surgery. An understanding of the capabilities of the technology as well as the underlying physics allows the anaesthetist to glean the most information from this valuable technique, both quantitatively and qualitatively.