Digitized echocardiographic measurements of left ventricular function: reproducibility and physiological factors influencing the method.

The variability of digitized M-mode echocardiographic measurements and the potential influence of physiological factors on these was studied in 28 relatively young (less than 50 years) healthy subjects. All had heart rates within the normal range. Echocardiographic recordings were standardized in the end-expiratory phase. The coefficients of variation for direct echocardiographic measurements were less than or equal to 6% and for most digitized time derived variables less than or equal to 15%. They were generally greater for inter- than for intracycle comparisons. In systole, the peak shortening rate and the time period from the start of systole to the point of peak shortening rate showed the best reproducibility, while in diastole the peak filling rate, the rapid filling period and the percentage filling during the same period. In multivariate analysis, age and heart rate were found to influence the digitized derived systolic but not the diastolic variables. Their influence, however, on digitized echocardiographic measurements may vary with study subjects selection and should be considered when interpreting results.