Changes in left ventricular dynamics during graded exercise.

A. Hiraga, S. Hobo, E. K. Birks, T. Takahashi, T. Hada, B. L. Smith, E. A. Carr, John Pascoe, James H Jones

Research output: Chapter in Book/Report/Conference proceedingChapter

4 Scopus citations


Three mature Thoroughbred horses were prepared surgically with ultrasonic sonomicrometer crystals affixed to their ventricular pericardia. Signals from crystals recorded dimensions of axes across the left ventricle. Cubic algorithms were fitted to dimensional data to generate volume estimates that matched stroke volumes simultaneously measured using the Fick principle. As horses stood at rest or exercised at various intensities (approx 7, 12, 24, 47 and 100% maximal rate of O2 consumption VO2max[), left ventricular dimensions were recorded and 20 consecutive diastolic and systolic volumes calculated. Although Fick estimates detected no difference in stroke volume at different exercise intensities, sonomicrometer measurements of stroke volume were significantly lower at rest and higher at VO2max. These differences mirrored changes in end-diastolic volume, although end-systolic volume did not change. At all exercise intensities, stroke volume was most variable and end-diastolic volume the least. The pattern conforms to the Frank-Starling mechanism, and indicates that at high exercise intensities ventricular myocytes generate high pressures with higher myocardial wall stress due to the increased size of the chamber.

Original languageEnglish (US)
Title of host publicationEquine veterinary journal. Supplement
Number of pages4
StatePublished - 1999
Externally publishedYes


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