Letter to the Editor: In Response
We appreciate the opportunity to respond to the comments of Drs. Khorasani and Appavu. While we agree that the units of left ventricular stroke work used in our paper are not the strictly appropriate units of work (joules or newton-meters) , neither do the suggestions of Drs. Khorasani and Appavu completely represent total ventricular external work. In order to precisely represent left ventricular external work, two components of heart work must be considered. These are the sum of pressure-volume work represented by cardiac output times the pressure difference across the left ventricle plus acceleration work due to kinetic energy represented by [0.5(ejected volume)(mean aortic velocity of flow)2]. Clearly, under the conditions of our clinical study, except for cardiac output and stroke volume (ejected volume), these measurements were not obtainable. Furthermore, deviating from the clinical convention of g centered dot m centered dot beat-1 centered dot m-2 to the more correct units of joules or newton-meters would not enhance the clarity of the data for the clinical readers. More importantly, it would not change any conclusion of the paper.
John L. Fontana, MD
Rolf Bunger, PhD, MD
Departments of Anesthesiology and Physiology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
1. Dybkaer R. Approved recommendation (1978): quantities and units in clinical chemistry. Clin Chim Acta 1979;96:157.