The Intra Aortic Balloon Pump (IABP) is the most widely used form of temporary Cardiac Assist. The main benefits of IABP are listed below.
Increased
Decreased
Aortic diastolic pressure
systolic aortic pressure
Early trans-mitral flow
LVEDP
Ejection fraction
Myocardial O2 consumption
Cerebral & renal perfusion
Lactate production
Myocardial O2 supply
Afterload
Diastolic coronary flow
Click on the figure to watch a video clip of the modus operandi of the inflation and deflation of the balloon at the horizontal and vertical positions.
Whilst IABP has been extensively used clinically decades and its benefits demonstrated through numerous clinical trials for over 3 decades, the detailed scientific knowledge of its effects is not well understood.
We are interested in studying the solid mechanics of the balloon and also the associated fluid mechanics caused by the inflation and deflation of the balloon. An interesting point that is of our interest is the effect of patient’s posture on the performance of the balloon.
When the balloon is at an angle to the horizontal, such as when the patient is laying in the semi-recumbent position, there will be a hydrostatic pressure difference between the two ends of the balloon; bottom end falling under a higher pressure, Pbottom=Ptop + rgh where r is blood density, g is gravity acceleration (9.81 m/s2)and h is the latitude difference between the two ends of the balloon. This hydrostatic pressure difference between the two ends of the balloon forces the filling of the balloon to start from the top, and this pattern of inflation displaces more blood volume away from the ascending aorta, which is opposite to what is desired, and raises a wider question about the ratio between flow upstream and downstream from the balloon during inflation, which we term “balloon efficiency”. In order to force the filling of the balloon to start from the bottom to the top the possibility of changing the shape of the balloon requires to be explored. The cylindrical shape of the intra aortic balloon has not been changed for the past 25 years !
Clinical Importance: Most patients using IABP in intensive care units are usually laying in the semi-recumbent position for various clinical and social reasons. Thus, optimising the shape of the balloon to maintain – if not increase - patients’ benefit at various postures is certainly of clinical interest
