At the time of writing this (mid 2009), there is considerable debate over the mechanisms of left ventricular contraction. I became intrigued by the perceived conundrum that the systolic thickening of the left ventricular wall is greater than can be explained by the thickening of the individual myocytes. After reviewing some features of the anatomy of the wall (pages 1,2 & 3) and making some relevant observations on some images (pages 4-7) I apply some straightforward geometry to produce a model which illustrates the solution to the conundrum (pages 8-15).
Though the conundrum has been explained before, I think my model is a novel way of demonstrating the solution. Using the epicardial surface as a point of measurement has been done before (MacIver & Townsend 2008), but I think I use it in a slightly different way.
In the remaining pages I express some personal opinions on other aspects of ventricular function and movement, and raise a few questions. This section is not designed to be authoritative or comprehensive.(STOP PRESS Jan 2010: My appreciation of twist has improved and pages 20 to 24 need improving, hope to do it soon)
The layout of the section is summarised in the links to individual pages listed below. As you browse through it you can return to this page at any time by clicking on the main menu on the left. Each page (except 23 and 24) will load an image at the top and a scrolling text box below. You may have to scroll the box to see all the text on each page. There is a summary on page 26.
Page 4 - The Assertive Short Axis (part 1 - lessons from an ASD)
Page 5 - The Assertive Short Axis (part 2 - lessons from MRI tagging)
Page 6 - The Diastolic Shell - part 1
Page 7 - The Diastolic Shell - part 2
Page 8 - The Mathematic Model - initial assumptions
Page 9 - The Mathematic Model - concentric rings
Page 10 - The Mathematic Model - the initial model
Page 11 - The Mathematic Model - results from the spreadsheet for the initial model.
Page 12 - The Mathematic Model - the final model
Page 13 - The Mathematic Model - results from the final model
Page 14 - The wall/cavity ratio
Page 15 - Strengths and weaknesses of the mathematic model
Page 16 - The Elegance of the Outer Wall
Page 17 - The Problem of the Inner Wall
Page 18 - Long Axis contraction
Page 19 - Why is the apex static?
Page 20 - Twist: definitions and anatomic restrictions
Page 21 - Rotation of the base
Page 22 - Overall twist is a summation event?
Page 24 - Formative and Adaptive Growth
Page 25 - How we measure the axes
Page 26 - Summary and References
JP August 2009