A new method describing cross-sectional blood flow velocity profiles in the left ventricular outflow tract of patients with atrial fibrillation with the use of high-frame rate 2-dimensional color flow imaging.

A new Doppler method was developed to evaluate the instantaneous cross-sectional velocity profile variability in the left ventricular outlet tract in patients with atrial fibrillation. Blood flow velocities acquired at a high frame rate (>90 frames/s) from a single heart cycle were used to display the velocity profile. In 9 patients, 2 heart cycles with different R-R interval lengths were recorded in color flow mode in a transthoracic apical 5-chamber and long-axis view. Raw digital ultrasound data were analyzed with an external personal computer. The data indicated a variable skew in the profiles with the highest velocities and velocity-time integral (VTI) most often located in the center and toward the septum. The maximum VTI overestimated the mean VTI by approximately 40%. No significant difference existed between the two heartbeats. Thus the VTI can be averaged from heartbeats of different R-R lengths in atrial fibrillation.

Measurement of volumetric mitral and aortic blood flow based on a new freehand three-dimensional colour flow imaging method. An in vivo validation.

AIMS: To validate a new three-dimensional (3D) colour flow method used to calculate cardiac output (CO) in aortic and mitral blood flow. METHODS: The transducer was freely tilted transthoracically using a magnetic locating device recording its spatial position. Raw digital ultrasound data were recorded in healthy subjects during 10-20 heartbeats at a high frame rate ranging from 41 to 66 frames/s and analysed off-line with no loss in temporal resolution. Blood flow velocities aligned with the ultrasound beam were integrated across a moving spherical surface to calculate volumetric flow. RESULTS: The range of agreement between the 3D mitral and 3D aortic method was 0.04+/-1.32 l/min (mean+/-2 standard deviations). The range of agreement between 3D aortic flow and the two-dimensional (2D) pulsed wave Doppler method (2DPW) in the left ventricular outflow tract (LVOT) was 0.7+/-1.7 l/min, while the range of agreement between 3D mitral flow and the 2DPW method was 0.88+/-1.64 l/min. CONCLUSION: The 3D methods agreed well. The 3D volumetric flow overestimated the 2DPW method, as expected, and the range of agreement was wide. The common pitfalls in pulsed wave ultrasound methods to calculate CO were avoided, as the 3D method was angle-independent, no assumptions about the velocity profile were made, and a moving sample surface was applied. The acquisition of data was fast and easy and high temporal resolution was achieved.

Velocity profiles in mitral blood flow based on three-dimensional freehand colour flow imaging acquired at high frame rate.

AIMS: To describe the mitral blood flow velocity distribution, we applied a freehand dynamic three-dimensional (3D) colour flow method using a moving sample surface that followed the mitral apparatus during diastole. METHODS: Nineteen healthy volunteers were studied. The ultrasound data were captured from 10-20 heartbeats at high frame rate (mean 46 frames/s) while freely tilting the transducer in an apical position. A magnetic position sensor system recorded the spatial position and orientation of the probe. Blood flow velocities were integrated across a spherical surface. In volumetric blood flow measurements this would yield angle independence of the Doppler beam. Raw digital data were analysed off-line with no loss of temporal resolution. RESULTS: The ratio of the maximum velocity time integral (VTI) to the mean VTI was mean 1.3 (range 1.1-1.6). At the time of peak flow the ratio of the maximum to the mean velocity was mean 1.5 (range 1.2-2.6). CONCLUSION: The blood flow velocity profile was non-uniform. By using a single sample volume in Doppler measurements of the maximum VTI errors ranging from 10 to 60% may be introduced in calculations of stroke volumes.

Cross-sectional early mitral flow-velocity profiles from color Doppler in patients with mitral valve disease.

BACKGROUND: Cross-sectional flow-velocity profiles from early mitral flow in 20 patients (10 with mitral regurgitation and 10 with mitral stenosis) were constructed from the velocity data from each point in sequentially delayed two-dimensional digital Doppler ultrasound maps. METHODS AND RESULTS: The data suggested that the early mitral flow studied in an apical four-chamber view was variably skewed in both patient groups. The maximum flow velocity overestimated the cross-sectional mean velocity at the same time by a factor of 1.12-1.86. The maximum time-velocity integral was 1.13-1.77-fold greater than the cross-sectional mean time-velocity integral. In patients with mitral regurgitation, the cross-sectional flow-velocity profile appeared to be most skewed at the level of the mitral leaflet tips. The level of the mitral annulus appeared to give the most homogenous flow-velocity distribution in both patient groups. CONCLUSIONS: When calculations of volume flow are based on pulsed Doppler ultrasound recordings with a single sample volume, the possibility of a skewed flow-velocity profile must be taken into account.

Impact of changes in heart rate and stroke volume on the cross sectional flow velocity distribution of diastolic mitral blood flow. A study on 6 patients with pacemakers programmed at different heart rates.

The effect of changes in stroke volume on the cross sectional velocity distribution in the mitral orifice during passive mitral inflow was studied in six patients with total atrioventricular block, atrial fibrillation and VVI pacemakers during periods with different heart rates. The time velocity integrals recorded both in the left ventricular outflow tract and at the mitral orifice decreased significantly as the heart rate was increased from 60 to 80 and from 80 to 100 beats per minute. Instantaneous cross sectional flow velocity profiles were constructed by time interpolation of the velocity data from each point in sequentially delayed two dimensional digital ultrasound maps. Each patient had a characteristic cross sectional flow velocity profile in the mitral orifice recorded at the level of the leaflet tips in a four chamber view. The velocity profiles varied between the patients. With increase in heart rate only minimal changes in the flow profiles from individual patients were seen. The maximum velocity through the mitral orifice overestimated the cross sectional mean velocity at the same time by a factor of 1.4-1.9. The maximum time velocity integral overestimated the cross sectional mean by a factor of 1.4-1.8. The observed cross sectional skew varied between patients but did not change significantly with increasing heart rate and decrease in stroke volume.

Instantaneous cross-sectional flow velocity profiles: a comparative study of two ultrasound Doppler methods applied to an in vitro pulsatile flow model.

Two methods based on different techniques for construction of cross-sectional flow velocity profiles from Doppler ultrasound signals were compared: an intraluminal method using pulsed-wave Doppler echocardiography and an extraluminal method using two-dimensional (color) Doppler ultrasound. The methods were applied to an in vitro pulsatile flow model. With the intraluminal method, pulsed Doppler recordings obtained throughout several flow pulses at different positions across a tube were digitized, and cross-sectional flow velocity profiles were obtained by matching the onset of flow velocity at the various positions. With the extraluminal method, cross-sectional flow velocity profiles were obtained by time interpolation between the digital flow velocity data obtained from several flow velocity maps. The first flow velocity map was recorded at onset of flow and the following maps were incrementally delayed with 20 msec from one flow pulse to the next. The time lag caused by the time needed to update each of the flow velocity maps was compensated for by time interpolation between the sequentially recorded flow velocity maps. The cross-sectional flow velocity profiles obtained with the two methods were compared at identical positions within the tube model at equal flow settings and throughout the pulsatile flow periods. At three different flow settings with peak flow velocity of 0.3, 0.5, and 0.7 m/sec, the difference (mean +/- SD) between the obtained velocities were 0.01 +/- 0.04, -0.01 +/- 0.05, and -0.03 +/- 0.07 m/sec, respectively. The findings suggest that cross-sectional flow velocity profiles from pulsatile flow velocity recordings can be obtained equally well with both methods.

Estimation of regurgitant volume and orifice in aortic regurgitation combining CW Doppler and parameter estimation in a Windkessel-like model.

A method for noninvasive estimation of regurgitant orifice and volume in aortic regurgitation is proposed and tested in anesthetized open chested pigs. The method can be used with noninvasive measurement of regurgitant jet velocity with continuous wave ultrasound Doppler measurements together with cuff measurements of systolic and diastolic systemic pressure in the arm. These measurements are then used for parameter estimation in a Windkessel-like model which include the regurgitant orifice as a parameter. The aortic volume compliance and the peripheral resistance are also included as parameters measurements in the open chest pigs are used. Electromagnetic flow measurements in the ascending aorta and pulmonary artery are used for control, and a correlation between regurgitant volume obtained from parameter estimation and electromagnetic flow measurements of 0.95 over a range from 2.1 to 17.8 mL is obtained.

Estimation of arterial compliance in aortic regurgitation: three methods evaluated in pigs.

Three methods for measuring arterial compliance when aortic regurgitation is present are examined. The first two methods are based on a Windkessel model composed of two elements, compliance C and resistance R. Arterial compliance was estimated from diastolic pressure waveforms and diastolic regurgitant flow for one method, and from systolic aortic pressure waveforms and systolic flow for the other method. The third method was based on a three-element Windkessel model, composed of characteristic resistance r, compliance C and resistance R. In this method arterial compliance was calculated by adjusting the model to the modulus and phase of the first harmonic term of the aortic input impedance. The three methods were compared and validated in six anaesthetised pigs over a broad range of aortic pressures. The three methods were found to give quantitatively similar estimates of arterial compliance at mean aortic pressures above 60 mm Hg. Below 60 mm Hg, estimates of arterial compliance varied widely, probably because of poor validity of the Windkessel models in the low pressure range.

Quantification of aortic regurgitation by Doppler echocardiography: a new method evaluated in pigs.

We have developed a method to quantify aortic regurgitant orifice and volume, based on measurements of the velocity of the regurgitant jet, aortic systolic flow, the systolic and diastolic arterial pressures, a Windkessel arterial model, and a parameter estimation technique. In six pigs we produced aortic regurgitant flows between 2.1 and 17.8 ml per beat, i.e. regurgitant fractions from 0.06 to 0.58. Pulmonary and aortic flows were measured with electromagnetic flow probes, aortic pressure was measured invasively, and the regurgitant jet velocity was obtained with continuous-wave Doppler. The parameter estimation procedure was based on the Kalman filter principle, resulting primarily in an estimate of the regurgitant orifice area. The area was multiplied by the velocity integral of the regurgitant jet to estimate regurgitant volume. A strong correlation was found between the regurgitant volumes obtained by parameter estimation and the electromagnetic flow measurement. These results from our study in pigs suggest that it may be possible to quantify regurgitant orifice and volume in patients completely noninvasively from Doppler and blood pressure measurements.

Cross sectional early mitral flow velocity profiles from colour Doppler.

Instantaneous cross sectional flow velocity profiles from early mitral flow in 10 healthy men were constructed by time interpolation of the velocity data from each point in sequentially delayed two dimensional digital Doppler ultrasound maps. This interpolation allows correction of the artificially produced skewness of velocities across the flow sector caused by the time taken to scan the flow sector for velocity recording of pulsatile blood flow. These results suggested that early mitral flow studied in an apical four chamber view is variably skewed both at the leaflet tips and at the annulus. The maximum flow velocity overestimated the cross sectional mean velocity at the same time by a factor of 1.2-2.2. Also the maximum time velocity integral overestimated the cross sectional mean time velocity integral to the same extent. This cross sectional skew must be taken into account when calculation of blood flow is based on recordings with pulsed wave Doppler ultrasound from a single sample volume.

Half time of the diastolic aortoventricular pressure difference by continuous wave Doppler ultrasound: a measure of the severity of aortic regurgitation?

Thirty four patients with aortic regurgitation were studied by continuous wave Doppler ultrasound. In 30 of these the regurgitation was graded by cineangiography as mild, moderate, or severe and in four severe regurgitation was confirmed at operation. The half times of the aortoventricular pressure differences obtained with Doppler compared well with those obtained from pressure recordings at catheterisation. The relation between pressure half times and cineangiographic gradings of severity was not consistent. Similarly, a control group of patients without aortic regurgitation showed a wide range of the invasively recorded pressure half times which overlapped with those in patients with aortic regurgitation. This suggests that factors such as systemic vascular resistance, and aortic and left ventricular compliance can have an appreciable effect on the pressure half time. If these factors are not included the method will be of limited value, except in patients with pressure half times of less than 300 ms, when regurgitation invariably is severe. These results suggest that at present the method is of value only in recognising the patients with the most severe aortic regurgitation who need early operation.