Volume blood flow measurements with a transit time flowmeter: an <i>in vivo</i> and <i>in vitro</i> variability and validation study

<jats:p><jats:bold>Summary. </jats:bold> A transit time flowmeter, Transonic TC101 (Transonic Inc., USA) has been evaluated to study volume flow. Two flow probes, 4 and 6 mm, were used. The experiments were carried out <jats:italic>in vivo</jats:italic> on the carotid arteries (<jats:italic>n</jats:italic>= 16) in sheep and <jats:italic>in vitro</jats:italic> against a pre calibrated rotational pump. Exsanguination measurements, <jats:italic>n</jats:italic>= 32, were used for the calculation of the error of measurement <jats:italic>in vivo.</jats:italic> The error of measurement <jats:italic>in vitro</jats:italic> was calculated on 11 different flow rates from 0 to 150 ml min<jats:sup>‐1</jats:sup>.</jats:p><jats:p>The variability <jats:italic>in vivo</jats:italic> was evaluated using data from 10, 30 s measurement periods with a 30 s pause between measurements. The variability <jats:italic>in vitro</jats:italic> was evaluated at three flow rates (46, 78, and 113 ml min<jats:sup>‐1</jats:sup>). Five 1‐min measurements with a 1‐min pause between measurements were made.</jats:p><jats:p>The error of measurement <jats:italic>in vivo</jats:italic> was 12.05% and <jats:italic>in vitro</jats:italic> 5.50% (4 mm probe) and 14.90% (6 mm probe). <jats:italic>In vivo</jats:italic> the variability was between 1.1 and 4.4% and <jats:italic>in vitro</jats:italic> between 1.5 and 11.2%. The correlation coefficients between the flowmeter on the one hand and exsanguination and the rotational pump on the other were 0.99, 0.99 (4 mm probe) and 0.98 (6 mm probe).</jats:p><jats:p>It is concluded that the flowmeter has a small variability and error of measurement both <jats:italic>in vivo</jats:italic> and <jats:italic>in vitro.</jats:italic>,</jats:p>