Suitable hemolysis index for low-flow rotary blood pumps
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ORIGINAL ARTICLE Artificial Heart (Basic)
Suitable hemolysis index for low‑flow rotary blood pumps Takashi Yamane1,2 · Kazuki Adachi1 · Ryo Kosaka2 · Osamu Maruyama2 · Masahiro Nishida2 Received: 28 January 2020 / Accepted: 4 October 2020 © The Japanese Society for Artificial Organs 2020
Abstract A suitable index is needed for hemolysis tests that use low-flow pumps, such as pediatric blood pumps or blood purification pumps. To create such an index, the present study investigates the change of plasma-free hemoglobin in the pump circuit with time and the change of the hemolysis rate with flow rate and impeller rotational speed. The results show that the hemolysis rate or the increase rate of the total free hemoglobin are suitable measures for hemolysis evaluation for low-flow pumps. Keywords Hemolysis · Hemolysis rate · Centrifugal pump · Flow rate · Rotational speed
Introduction Mechanical trauma to blood cells, or hemolysis, is a severe problem for ventricular assist devices. Here, we consider mechanical trauma to blood cells caused by a device. Studies on such trauma initially used rheometers to apply a uniform stress to a small amount of blood. Nevaril et al. [1] showed that hemolysis starts at a threshold of shear stress, namely around 200 Pa. Leverett et al. [2] showed that two factors for hemolysis are exposure time and shear stress. Hashimoto [3] showed that hemolysis is almost constant on the line (exposure time) × (shear velocity)2 = constant. Schima et al. [4] showed that hemolysis exceeds a clinically allowable level when the shear stress is over 1000 Pa or when the exposure time is over 1 s. Based on these studies, Giersiepen et al. [5] derived the following empirical equation based on fresh animal blood:
ΔHb (%) = 3.62 × 10−5 t0.785 𝜏 2.416 Hb ΔHb : plasma-free hemoglobin concentration Hb : total blood hemoglobin concentration t: exposure time (ms)
* Takashi Yamane [email protected] 1
Kobe University, Kobe, Japan
National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
2
τ: shear stress (Pa) The mechanical trauma caused by a blood pump differs from that caused by a rheometer because high shear exposure occurs only near walls, such as the boundary layers of the impeller/casing, or at the offset jet near the outlet bifurcation, and thus the same blood is seldom exposed to the same high shear repeatedly. A flow visualization study of a centrifugal pump circuit by Nishida et al. [6] revealed at a wall shear stress of over 300 Pa a plasma-free hemoglobin level of 31.5 mg/dL/4 h, which is equivalent to a normalized index of hemolysis, NIH, of 0.009 g/100 L using animal blood. The study indicated that the shear stress was caused by the offset of the blood jet near the outlet bifurcation. Regarding the effect of flow rate on hemolysis in a blood pump, when the flow rate increases in the pump circuit, although the blood-passing frequency increases, the exposure time for each pass decreases and the total exposure time does not change. Regarding the effect of impeller s
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