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.