An assessment of a non-invasive technique for measurement of stroke di
stance was made using a portable Doppler ultrasound machine. The aim w
as to determine the measurement error of repeated stroke distance meas
urements (within-observer variability) and to assess measurement agree
ment between two operators (between-observer variability), The measure
ment error (within-observer variability) for both operators was simila
r at approximately 2 cm. :However, the measurements of the two operato
rs (between-observer variability) did not agree well. Using the mean (
SD) of three readings by each operator, the mean difference between th
e operators was -0.21 cm (1.96) giving a 95% confidence interval for t
he differences of -4.0 to +3.6 cm. There were significant positive and
negative correlations between stroke distance and a variety of variab
les (age, height, weight, heart rate), but the relations were weak. Th
e results indicate that the Doppler ultrasound technique for measureme
nt of stroke distance would best be used to study trend changes in an
individual patient, or subject, by a single operator.