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Research Papers

In Vitro Measurement of the Coaptation Force Distribution in Normal and Functional Regurgitant Porcine Mitral Valves

[+] Author and Article Information
John Adams

School of Mechanical and Materials Engineering,
UCD Dublin,
Dublin 4, Ireland

Malachy J. O'Rourke

School of Mechanical and Materials Engineering,
UCD Engineering and Material Science Centre,
UCD Dublin,
Room 304, Belfield,
Dublin 4, Ireland
e-mail: malachy.orourke@ucd.ie

1Corresponding author.

Manuscript received March 22, 2013; final manuscript received January 28, 2015; published online June 3, 2015. Assoc. Editor: Jonathan Vande Geest.

J Biomech Eng 137(7), 071008 (Jul 01, 2015) (11 pages) Paper No: BIO-13-1151; doi: 10.1115/1.4029746 History: Received March 22, 2013; Revised January 28, 2015; Online June 03, 2015

Closure of the left atrioventricular orifice is achieved when the anterior and posterior leaflets of the mitral valve press together to form a coaptation zone along the free edge of the leaflets. This coaptation zone is critical to valve competency and is maintained by the support of the mitral annulus, chordae tendinae, and papillary muscles. Myocardial ischemia can lead to an altered performance of this mitral complex generating suboptimal mitral leaflet coaptation and a resultant regurgitant orifice. This paper reports on a two-part experiment undertaken to measure the dependence of coaptation force distribution on papillary muscle position in normal and functional regurgitant porcine mitral heart valves. Using a novel load sensor, the local coaptation force was measured in vitro at three locations (A1–P1, A2–P2, and A3–P3) along the coaptation zone. In part 1, the coaptation force was measured under static conditions in ten whole hearts. In part 2, the coaptation force was measured in four explanted mitral valves operating in a flow loop under physiological flow conditions. Here, two series of tests were undertaken corresponding to the normal and functional regurgitant state as determined by the position of the papillary muscles relative to the mitral valve annulus. The functional regurgitant state corresponded to grade 1. The static tests in part 1 revealed that the local force was directly proportional to the transmitral pressure and was nonuniformly distributed across the coaptation zone, been strongest at A1–P1. In part 2, tests of the valve in a normal state showed that the local force was again directly proportional to the transmitral pressure and was again nonuniform across the coaptation zone, been strongest at A1–P1 and weakest at A2–P2. Further tests performed on the same valves in a functional regurgitant state showed that the local force measured in the coaptation zone was directly proportional to the transmitral pressure. However, the force was now observed to be weakest at A1–P1 and strongest at A2–P2. Movement of the anterolateral papillary muscle (APM) away from both the annular and anterior–posterior (AP) planes was seen to contribute significantly to the altered force distribution in the coaptation zone. It was concluded that papillary muscle displacement typical of myocardial ischemia changes the coaptation force locally within the coaptation zone.

FIGURES IN THIS ARTICLE
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Copyright © 2015 by ASME
Topics: Valves , Muscle , Displacement
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Figures

Grahic Jump Location
Fig. 4

Coordinate system adapted for determination of papillary muscle position relative to the mitral valve. The origin is taken at the point of intersection of the annular, septolateral, and APP. Positions A1–P1, A2–P2, and A3–P3 indicated the points of coaptation where the coaptation force was measured.

Grahic Jump Location
Fig. 3

The coaptation measurement device was used to measure the coaptation force between the valve leaflets. (a) Exploded assembly: 1—sensor body upper, 2—load cell A, 3—ground stainless steel axle, 4—ground stainless steel lever arm A, 5—ground stainless steel lever arm B, 6—load cell B, 7—alignment pins, and 8—sensor body lower; (b) assembled device; and (c) schematic of a lever arm of the device showing the dynamic loading on the arm.

Grahic Jump Location
Fig. 2

A sample mitral valve mounted within the mitral chamber showing the annulus plate and papillary muscle force rods. The valve was sown to both the plate and the papillary muscle force rods. The location of the papillary muscles relative to the annulus plate was adjusted by moving the force rods.

Grahic Jump Location
Fig. 5

Measured static coaptation force against transmitral pressure for coaptation positions: (a) A1–P1, (b) A2–P2, and (c) A3–P3. The coaptation force is averaged across all ten hearts used in the sample, the error bars are indicative of the maximum and minimum values within the sample.

Grahic Jump Location
Fig. 6

The cardiac cycle was used in the left heart simulation as measured during testing on heart valve 4. Traces include the atrial pressure and the LV pressure within the mitral valve chamber. The volume flow rate through the mitral valve is also shown, flow into the ventricle is considered − ve. The flow in the return line to the pump is also shown, this was used to synchronize all the measurements made during testing.

Grahic Jump Location
Fig. 7

Normal mitral valve test results averaged over the four hearts tested. Results are shown for the transmitral pressure and mean coaptation force against time (left) and mean coaptation force against transmitral pressure (right). Error bars are indicative of the maximum and minimum values within the sample. (a) A1–P1, (b) A2–P2, and (c) A3–P3.

Grahic Jump Location
Fig. 8

Functional regurgitant mitral valve test results averaged over the four hearts tested. Results are shown for the transmitral pressure and mean coaptation force against time (left) and mean coaptation force against transmitral pressure (right). Coaptation force is observed to decrease at position A1–P1 and to increase at positions A2–P2 and A3–P3. Error bars are indicative of the maximum and minimum values within the sample. (a) A1–P1, (b) A2–P2, and (c) A3–P3.

Grahic Jump Location
Fig. 9

A regression analysis prediction of the coaptation force at a transmitral pressure of 100mmHg for normal and functional regurgitant mitral heart valve. The error bars are the standard error of the regression fit. A marked decrease in the coaptation force at position A1–P1 is observed whereas a marked increase in coaptation force at A2–P2 and A3–P3 is observed.

Grahic Jump Location
Fig. 10

Correlation of the change in coaptation force as a function of the change in papillary muscle position. The most significant correlations are selected at each position. (a) A1–P1, (b) A2–P2, and (c) A3–P3.

Grahic Jump Location
Fig. 1

Schematic of the UCD Dublin left heart simulator: 1—porcine mitral valve, 2—papillary muscle locator, 3—mechanical prosthetic aortic valve, 4—mitral valve chamber, 5—pressure sensor LV, 6—pressure sensor LV, 7—pressure sensor aortic, 8—pressure sensor left atrium, 9—compliance chamber, 10—characteristic aortic resistance, 11—peripheral resistance, 12—electromagnetic flow meter, 13—piston, 14—brushless AC servomotor, 15—FlexDrive II Motion Controller, 16—PC with MintDrive II Motion Control Software, 17—aortic head tank (vented), 18—left atrial head tank (vented), 19—temperature controlled reservoir, 20—cartridge filter, 21—sump pump, and 22—air bleed valve

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