Validation of a new transit time ultrasound flowmeter in man

Objectives: To validate the new CardioMed CM 4000 transit time ultrasound apparatus for intraoperative measurement of volume blood flow in vivo in man. Design: Open, prospective series. Materials: Thirteen patients undergoing in situ saphenous vein grafting for chronic critical leg ischaemia and 12 patients subjected to myocardial revascularisation with the internal thoracic artery as coronary bypass. Methods: During operations, volume blood flows were measured simultaneously by exsanguination from the cut distal end of the in situ saphenous vein graft or the internal thoracic artery and by the transit time flowmeter equipment. In addition, the feasibility to detect arteriovenous fistula during in situ saphenous vein grafting was examined. Results: Within the examined blood flow range, the volume blood flow determined by the transit time method corresponded to the directly measured bloodflow. For in situ saphenous vein grafts: y = -2.4 + 0.95 x (r = 0.99; 35 measurements in 13 patients), and for internal thoracic artery grafts: y = -9.6 + 1.1 . x (r = 0.99; 21 measurements in 22 patients), where y is blood flow determined by transit time and x is directly measured blood flow by exsanguination (r = correlation coefficient) as calculated by the least squares regression method. Fistula detection was easy and swift. Conclusions: The transit time apparatus was simple to use during intraoperative settings and gave fast, precise measurements of volume blood flow.