The fast flush test--is the clinical comparison equivalent to its in vitro simulation?

Abstract

An in vitro simulation of the fast flush (FL) test has previously been used to prove that the FL test-measures the dynamic response of entire the blood pressure monitoring system. This simulation has also been used to confirm that the FL test is equivalent to the "gold standard" test for determining dynamic response, namely the square wave (SW) test. The conditions of the in vitro simulation can be reproduced in vivo during cardiopulmonary bypass (CPB) and circulatory arrest. Therefore the present objective was to verify that the previous conclusions about the validity of the FL test, obtained from an in vitro model, are equally valid when applied to in vivo clinical conditions. A secondary objective was to determine whether the patient's arterial tree has any affect on the dynamic characteristics of fluid-filled manometers. Fourteen patients were studied during surgery that required CPB. We measured the dynamic response of the fluid filled arterial manometer during pulsatile conditions prior to the initiation of CPB, and then repeated the measurements during non-pulsatile CPB. In four of the fourteen patients we measured the dynamic response during circulatory arrest. A manometer, consisting of a fluid-filled tubing component, measured the patient's arterial blood pressure as well as the damped sinusoidal wave form created by the fast flush tests. The fluid-filled tubing was connected to a transducer (Utah Medical Products, Inc., Midvale, UT). The arterial pressures and the results of flush testing were recorded and displayed by a monitor (Marquette 7010, Marquette Electronics Inc., Milwaukee, WI). In an additional three patients we measured the dynamic response of the manometer in vitro and then in vivo. The dynamic response of the arterial pressure measuring system was the same during normal pulsatile flow, CPB and circulatory arrest. In addition, the dynamic response of the fluid-filled manometer was the same in vivo as in vitro. The clinical conditions during CPB and particularly during circulatory arrest duplicate the in vitro FL test simulation model. These results confirm the validity of the FL test in vivo as well as proving that the dynamic characteristics of a fluid-filled manometer are independent of the patient's vasculature.