Summary
To evaluate the accuracy of flow measurements in aortocoronary bypass grafts with
the ultrasound transit-time method, an in vitro and in vivo comparison was carried
out. The in vitro comparison with evaluation against both true flow and the ultrasound
Doppler method, was carried out with a fresh saphenous vein mounted in a pulsatile
flow rig. The two flow probes were placed on the graft 4-5 cm apart to avoid acoustic
interference, and blood was pumped through the System at different flow rates. The
comparison between the methods showed excellent agreement with a linear correlation
coefficient of 0.996, and a mean error of-2.9 ml/min with limits of agreement ± 13.1
ml/min (± 2 SD = 95% of measured differences between these limits). However, against
true flow, both methods overestimated flow slightly with mean error 4.4 and 7.3 ml/min
for the transit-time and Doppler, respectively. Both methods showed excellent correlation
with true flow (correlation coefficient 0.998 for the transit-time and 0.997 for the
Doppler mothod). The in vivo accuracy was evaluated by comparison of the two methods
in 9 patients. The two probes were placed on the same saphenous vein grafts 4-5 cm
apart, and a total of 34 measurements in 17 grafts were carried out including measurements
at baseline and after papaverine injection. The correlation coefficient was 0.990
and linear regression analysis gave the equation: Transit-time flow = 1.00 × Doppler
flow + 1.3. In terms of flow, tho mean error was 1.5 ml with limits of agreement ±
17.2 ml.
Conclusions: tho transit-time flow-meter showed excellent agreement with the Doppler
method for both in vitro and in vivo studies. Tho diameter-independence of the transit-time
flowmeter was an advantage in the clinical Situation. A disadvantage was the probe
design which made acoustic contact more difficult to obtain than for the Doppler method.
Zusammenfassung
Um die Genauigkeit der Flußmessungen im aortokoronaren Bypass zu bestimmen, wurden
In-vitro- und In-vivo-Untersuchungen vorgenommen. An einer montierten Vena saphena
wurden die beiden Meßköpfe im Abstand von 4-5 cm angebracht und dann wurde das Blut
in verschiedenen Flußgeschwindigkeiten gepumpt. Der Vergleich zeigte eine gute Übereinstimmung
der Methoden mit einem linearen Korrelations-koeffizienten von 0,996. Gegenüber dem
wahren Fluß überschätzten beide Methoden jedoch den Fluß leicht mit einem mittleren
Irrtum von 4,4 ml/min für die Transit-time und 7,3 ml/min für den Doppler. An 9 Patienten
wurden In-vivo-Messungen vorgenommen und zwar 34 Messungen an 17 Venenbrücken in einer
Ausgangslage und nach Papaverinanwendung. Auch hierbei fand sich eine gute Übereinstimmung
zwischen den beiden Meßmethoden.
Key words
Transit-time - Doppler shift - Ultrasound - Aortocoronary grafts - Blood flow
