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M Nassi

Publications and source records attributed to M Nassi.

10 recordsLinked to original sources
PubMed1992

Validation of a Doppler guide wire for intravascular measurement of coronary artery flow velocity.

BACKGROUND: An improved intravascular ultrasonic Doppler device could aid the clinical assessment of coronary hemodynamics. We evaluated a new device consisting of a 12-MHz piezoelectric transducer integrated onto the tip of a 0.018-in. flexible, steerable angioplasty guide wire. METHODS AND RESULTS: Doppler spectra were recorded in model tubes with pulsatile blood flow and in-line electromagnetic flowmeter. In four straight tubes (i.d., 0.79-4.76 mm), the time average of spectral peak velocity (APV) was linearly related to blood flow (QEMF) (r2 greater than or equal to 0.98 for each tube). A Doppler-derived quantitative flow estimate (QD) was calculated as the product of vessel cross-sectional area and mean velocity, with mean velocity estimated as 0.5 x APV. The slope of QD versus QEMF for the four tubes was near unity. APV was less accurate in a 7.94-mm straight tube and in tortuous segments. In four dogs, the left circumflex coronary artery (LCx) was perfused from the femoral artery via a cannula with in-line electromagnetic flowmeter. Good-quality signals were obtained in proximal and distal LCx vessels 3.3-1.2 mm in diameter. APV varied linearly with QEMF (r2 greater than or equal to 0.99 in the cannula, r2 = 0.93-0.99 in proximal LCx, and r2 = 0.86-0.99 in distal LCx). QD was calculated by quantitative angiography to determine proximal LCx diameter. For all dogs combined, the slope of QD versus QEMF was 0.95 in the cannula and 0.85 in the proximal LCx. CONCLUSIONS: The Doppler guide wire measures phasic flow velocity patterns and linearly tracks changes in flow rate in small, straight coronary arteries. It should facilitate measurement of phasic coronary flow velocity during coronary angiography and angioplasty.

Animals↗
PubMed1990

Instantaneous and continuous cardiac output in humans obtained with a Doppler pulmonary artery catheter.

A new Doppler pulmonary artery catheter was used to measure instantaneous and continuous cardiac output in both an in vitro model and in 44 patients undergoing cardiac catheterization. Cardiac output was calculated with use of the Doppler catheter-determined instantaneous space-average velocity and the ultrasonically determined instantaneous vessel area. Doppler flow and thermodilution were compared with electromagnetic flow in the in vitro model and with Fick cardiac output in patients. Doppler catheter-determined flow was highly predictive of electro-magnetic flow in the pulsatile flow model (r = 0.99, slope [m] = 1.01 and SEE = 0.05) and appeared comparable to thermodilution measurements (r = 1.00, m = 1.03 and SEE = 0.02). In patients undergoing cardiac catheterization, Doppler catheter-determined cardiac output appeared to modestly underestimate Fick cardiac output (r = 0.82, m = 0.80 and SEE = 0.09; mean error +/- SEM = -0.26 +/- 0.14 liters/min). However, predictive accuracy was comparable to simultaneously obtained thermodilution measurements (r = 0.85, m = 1.07 and SEE = 0.10; mean error +/- SEM = 0.61 +/- 0.16 liters/min). This new Doppler catheter system utilizes multiple ultrasound transducers to provide angle-independent measurements of vessel diameter and instantaneous velocity within the main pulmonary artery, resulting in a more accurate assessment of Doppler-derived cardiac output. In addition, useful information concerning hemodynamic variables such as peak flow, acceleration, deceleration, stroke work and pulmonary impedance may be derived.

Adult↗
PubMed1985

Flow determination using computed tomography: application to aortic dissection. Part I.

The CT method of flow determination evaluated in this study was based on the application of contrast enhancement dynamics. In order to characterize flow, such parameters as mean transit time, rise time, peak CT value, curve width and variance, and others were derived from the venoarterial indicator dilution curves using a perfect mixers-in-series model of curve fitting analysis and a bolus injection of contrast medium. The technique was first validated in a steady state phantom model that simulated in vivo conditions of right-sided mixing closely by the introduction of a number of mixers. A series of flows through small tubes was measured. Good correlation was obtained (r = .85). For a fixed number of mixers, the central second moment of the primary peak of the indicator dilution curve or variance decreased with increasing flow and peak CT value increased. Applied to the clinical situation, this method would allow characterization of blood flow using an intravenous bolus of contrast.

Aortic Dissection↗
PubMed1985

Flow determination using computed tomography: application to aortic dissection. Part II.

Dynamic CT is not only useful in imaging an aortic dissection but may provide additional information concerning the hemodynamic significance of differing flow patterns in the false channel compared with the true channel. Once validated, the computed tomographic (CT) method of flow determination (See Part I) was applied to an experimental animal model with a surgically created aortic dissection. Good correlation was obtained for the flow estimates of cardiac output derived for the true and false channel (r = .82). The shapes of the curves, however, were distinct, reflecting different flow patterns for the true and false channels. Curve parameters, such as peak CT number (P = .0001), variance (P = .006), and, in particular, the number of mixers (a parameter used to quantify the degree of mixing) (P = .0001), demonstrated significant differences between the two channels of the dissection. The curve parameters derived can therefore be used to differentiate the true and false channels and may then predict the long-term outcome of the false channel, and the aortic branches derived from it.

Aortic Dissection↗
PubMedDate not supplied

The critical importance of convolution function (algorithm) selection in the measurement of blood flow in small blood vessels by computed tomography scanning.

In order to assess the capability for measuring blood flow in small vessels, the cardiac output was measured directly by either the microsphere reference sample technique or by obtaining blood samples simultaneously with the CT scan. The cardiac output was also measured in vivo by dynamic CT scanning and intravenous contrast as the indicator in an indicator dilution curve. Cardiac output was then calculated by two convolution back projection algorithms which optimized for either contrast or spatial resolution. The results of this study suggest that CT scanners are capable of accurately averaging intravascular changes in contrast density. Although it is good to optimize contrast resolution, the convolution back projection algorithm selected must have a pixel matrix which is much smaller than the vessel being analyzed.

Animals↗
PubMedDate not supplied

Variability of myocardial CT measurements in vivo.

Variability of myocardial CT measurements, as indicated by standard deviations of mean CT numbers from four myocardial regions, was compared in 12-second scans, 3-second scans, and gated end-diastolic and end-systolic images, all from the same 12 seconds of scan data, both without and with radiographic contrast enhancement in experimental animals. There were statistically significant differences (P less than 0.05) in standard deviations of myocardial CT measurements when comparing 3-second and 12-second scans without contrast (10.4 vs. 7.7 CT#s), and 12-second scans without and with contrast (7.7 vs. 11.2 CT#s). Standard deviations of mean myocardial CT measurements were significantly greater (P less than 0.01) in gated images (end-diastolic) when compared with 12-second scans, both without contrast (22.2 vs. 7.7 CT#s) and with contrast (20.2 vs. 11.2 CT#s). In this study variability of myocardial CT measurements increased as scan time decreased, with radiographic contrast enhancement and with gating cardiac images.

Animals↗
PubMedDate not supplied

Quantitative evaluation of left ventricular function using computed tomography.

Computed tomography (CT) provides a noninvasive technique with high resolution cross-sectional tomographic images which allow volume measurements of an object, independent of its geometric configuration. A phantom of known volume with controllable periodic motion was used to validate the CT method of volume determination. A good correlation (P less than 0.05) was achieved. Missing angle reconstruction algorithms for gating were applied to estimate left ventricular volumes and ejection fraction in an experimental animal, and the results compared with a standard angiographic method. Left ventricular volumes correlated poorly, whereas the ejection fraction obtained correlated well (r = 0.9). The discrepancies may be attributed in part to the CT method in which difficulties were recognized in defining the left ventricular borders at the base of the heart and partial volume effect, and in part to inaccuracies in the standard angiographic method. Once validated, this method has been applied to the animal model in the form of a pilot study.

Animals↗