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Until now, right atrial (RA) volume calculation by means of two-dimensional echocardiography (2-DE) has only been attempted in a single plane: the apical four-chamber view. Our study reports a new method for RA volume calculation using two intersecting 2-DE views. For this purpose, silicone rubber casts of 19 human necropsy hearts were obtained and thin-walled natural rubber moulds of the RA casts were prepared. Totally filled with and immersed in water, the moulds could be visualized in the apical four-chamber view and an additional 2-DE plane, the latter corresponding to the subcostal view in vivo. In this view the vertical extension of RA could be estimated. Areas and lengths of RA were determined in the respective planes, and RA volume was calculated by applying the formula, area x length, to two intersecting planes. Finally, volume of the silicone casts was determined angiocardiographically (Angio) using a biplane method (30 degrees RAO, 40 degrees LAO-40 degrees hepatoclavicular). The true RA volume was 106 +/- 23 ml (mean +/- 1 SD) as determined by water displacement. Using Angio an excellent correlation was found: the calculated volume amounted to 106 +/- 23 ml; the difference was 5.5 +/- 4.8 ml (n.s.); Angio vol = 0.93 true vol + 7.77; r = 0.95; SEE = 7.4 ml. Volume determination from the apical four-chamber view of 2-DE using a monoplane disk method resulted in a mean volume of 62 +/- 17 ml. The mean difference to the true RA volume was 44 +/- 16 ml (p less than 0.001). When volume calculations were made using the biplane method, a value of 105 +/- 22 ml resulted. The mean difference to true volumes was 7.4 +/- 4.8 ml: y = 0.84x + 15.88; r = 0.91; SEE = 9.4 ml. In an in vivo study endsystolic RA volumes were calculated in a normal adult population (n = 40) from the same intersecting planes as in vitro. A normal value of 38 +/- 6 ml/m2 was found. In vivo validation using Angio showed a slightly higher normal value of 43 = 7 ml/m2. Thus, 2-DE is highly accurate in determining RA volume. In the in vitro as well as in the in vivo study the results of monoplane calculations are clearly inferior to a method which also takes account of the vertical extension of RA.

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For hydrodynamic comparison, 11 mechanical bileaflet valves have been perfused in a mock circulation system under pulsatile flow conditions. Six St. Jude Medical valves with different sizes from No. 21 to No. 31 and five Duromedics prostheses with corresponding sizes from No. 21 to No. 29 have been investigated. Flow, pressure, and orifice area were measured, while cardiac output was varied between 2 and 6 L/min. Insufficiency (I), maximal orifice area (Amax), mean orifice area (A), discharge coefficient (CD), performance index (PI), and efficiency index (EI) were determined. The St. Jude Medical valves show higher values of orifice area when compared with the Duromedics valves. For smaller valve sizes up to No. 25, the values of the orifice area are similar. The Duromedics valves show much lower values of insufficiency; thus, for small valve sizes, the Duromedics prosthesis seems to be superior. For larger valve sizes (No. 27, No. 29, and No. 31), a decision has to be made whether higher insufficiency and higher orifice area of the St. Jude Medical valve or lower insufficiency with lower orifice area is more acceptable.

In order to determine the effectiveness of mechanical heart valves two different types of mechanical heart valves, three tilting disc valves (BS-SD, BS-CCD, BS-M) and two bileaflet valves (St Jude Medical, Duromedics) with the same size of annulus diameter d, = 29 mm have been investigated in the mitral position of a mock circulation under pulsatile flow conditions. Flow, pressure and orifice area have been measured. Insufficiency, mean orifice area, discharge coefficient, performance index, and efficiency index have been calculated.The investigated tilting disc valves show smaller reflux volume and smaller insufficiency when comparing with the bileaflet valves. The bileaflet valves show higher values of orifice areas-that is to say smaller pressure drops-than the tilting disc valves. The St Jude Medical shows the biggest orifice areas, but also the highest reflux volume and insufficiency. Insufficiency of the Duromedics is slightly higher than that of the tilting disc valves. The orifice area of the Duromedics is bigger than that of the tilting disc valves and smaller than that of the St Jude Medical. The different pivot and the different profile of the disc of the BS-CCD and the BS-M are responsible for the more constant behaviour of the opening of these tilting disc valves when comparing with the BS-SD. Though the bileaflet valves show the better efficiency index, none of the valve types is superior in all hydrodynamic criteria. Both valve types, the bileaflet valves and the tilting disc valves, show different hydrodynamic advantages and disadvantages.

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