Noninvasive Pump Flow Estimation of a Centrifugal Blood Pump

Abstract

A flow rate estimating method was investigated for a centrifugal blood pump developed in our institute. The estimated flow rate was determined by the power consumption, the rotating speed of the motor, and the hematocrit value. The power consumption and the rotating speed of the motor were measured with a wattmeter. The examinations were performed in a closed mock loop filled with goat blood with hematocrit values of 21.5%, 28%, 34%, and 42%. Measured values of blood viscosity were 2.47, 3.09, 3.71, and 5.07 mPa.s at a share rate of 37.5/s, respectively. A linear correlation between the power consumption and the pump flow rate was observed in all hematocrit values. But variations in hematocrit caused a difference in the flow rate up to 1.1 L/min at the same power consumption and rotating speed. Effects of blood viscosity on the flow estimation were corrected by the hematocrit value. The value of the coefficient of determination, R2, between the estimated flow rate and the measured flow rate was 0.988. These results may indicate that the flow estimating method calculated by the power consumption of the motor, the rotating speed, and the hematocrit value is useful in the clinical situation.

Noninvasive Average Flow Estimation for an Implantable Rotary Blood Pump: A New Algorithm Incorporating the Role of Blood Viscosity

“…As Bertram (2) reports, the study by Wakisaka et al (8) represented the first successful attempt at estimation. Using a NCVC-2 (National Cardiovascular Center, …”

“…A noticeable drawback of this study is also that the effects of blood viscosity were investigated at only a single target speed (2800 rpm). Due to the similarity in experimental procedures, the algorithm by Wakisaka et al (8) was tested on the flow maps collected using the VentrAssist; however, results were unsatisfactory, as the constant offset term accounting for HCT failed to describe the difference in flow rates between flow maps. Yoshizawa et al (4), analyzing data collected in a mock loop using water and a 37% aqueous glycerol solution, proposed a new algorithm for a Kyocera C1E3 pump (Kyocera Corporation, Kyoto, Japan).…”

“…Working on data from static and pulsatile mock loops containing ovine blood or aqueous glycerol solutions, as well as chronic and acute sheep experiments, Ayre and coworkers (5,6) proposed a flow estimate given by 3 , which performed well, with high R 2 values both in vitro and in vivo. However, this flow estimate made no attempt to compensate for variations in blood viscosity.…”

“…As Wakisaka et al (8) note, the rheological properties of blood as a shear thinning fluid are such that its viscosity is not purely dependent on HCT, but it also varies according to shear rate, temperature, plasma viscosity, and fibrinogen content. However, in the clinical setting, except for cases of anomalous fibrinogen concentration, such as during thrombus formation (10), most …”

“…Many research groups claim to have developed satisfactory algorithms for sensorless flow estimation (for a review, see [2]). However, it is evident upon closer inspection of the reported equations that the design characteristics of different pumps cause the proposed algorithms, which have been obtained through an empiric process of pump flow mapping, to be substantially different from each other, and possibly unique to every individual pump design (3)(4)(5). A clear example of the extreme variability of algorithms is also outlined by Ayre et al (6), where it is evident that, even when using the same pump, a small change in impeller shape can introduce significant modifications in the relationship between power, speed, and flow.…”