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Changes in left ventricular dynamics during graded exercise
Author(s) -
HIRAGA A.,
HOBO S.,
BIRKS E. K.,
TAKAHASHI T.,
HADA T.,
SMITH B. L.,
CARR E. A.,
PASCOE J. R.,
JONES J. H.
Publication year - 1999
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/j.2042-3306.1999.tb05201.x
Subject(s) - ventricle , stroke volume , cardiology , end systolic volume , diastole , medicine , volume (thermodynamics) , end diastolic volume , ejection fraction , physics , blood pressure , heart failure , quantum mechanics
Summary 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 O 2 consumption [V̇ o 2max ]), 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 V̇ o 2max . 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.