JP6646296B2 - How the blood pump works - Google Patents
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- JP6646296B2 JP6646296B2 JP2015163030A JP2015163030A JP6646296B2 JP 6646296 B2 JP6646296 B2 JP 6646296B2 JP 2015163030 A JP2015163030 A JP 2015163030A JP 2015163030 A JP2015163030 A JP 2015163030A JP 6646296 B2 JP6646296 B2 JP 6646296B2
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- 210000004369 blood Anatomy 0.000 title claims description 47
- 239000008280 blood Substances 0.000 title claims description 47
- 210000003743 erythrocyte Anatomy 0.000 claims description 39
- 206010018910 Haemolysis Diseases 0.000 claims description 16
- 230000008588 hemolysis Effects 0.000 claims description 16
- 239000011347 resin Substances 0.000 claims description 14
- 229920005989 resin Polymers 0.000 claims description 14
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- 230000008878 coupling Effects 0.000 claims description 3
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- 238000000034 method Methods 0.000 claims 3
- 238000011017 operating method Methods 0.000 claims 1
- 210000002381 plasma Anatomy 0.000 description 24
- 238000005534 hematocrit Methods 0.000 description 13
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- 230000004087 circulation Effects 0.000 description 6
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- 241000283690 Bos taurus Species 0.000 description 2
- 210000004204 blood vessel Anatomy 0.000 description 2
- 238000007667 floating Methods 0.000 description 2
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- 206010019280 Heart failures Diseases 0.000 description 1
- 210000000601 blood cell Anatomy 0.000 description 1
- 238000007675 cardiac surgery Methods 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
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Description
本発明は、人工心臓用、補助循環用および心臓手術用の血液ポンプに関するものであって、特に、スラスト軸受として、動圧溝であるスパイラル溝を用いたものに関する。また、血液ポンプ以外にも、微小粒子を流す産業用ポンプとして使用することもでき、あるいは、培養や薬液の微小粒子を輸送する生物分野の輸送用ポンプとしても使用できるものである。 The present invention relates to a blood pump for an artificial heart, an auxiliary circulation, and a heart operation, and particularly to a blood pump using a spiral groove as a dynamic pressure groove as a thrust bearing. In addition to the blood pump, the pump can be used as an industrial pump for flowing microparticles, or can be used as a transport pump in the biological field for transporting microparticles of culture or a drug solution.
近年、医療技術等の進歩に伴い、人工心臓用、補助循環用及び心臓手術用のポンプとし
て遠心血液ポンプが用いられるようになってきた。
例えば、特許文献１では、流体力学的スラスト軸受を用いて、羽根車の非接触駆動を実現しているが、流体力学的スラスト軸受としての動圧溝は、いわゆるスパイラル溝を用いたものではない。
特許文献２〜４では、流体力学的スラスト軸受と吸引力を有する複数の永久磁石を用いて、羽根車の非接触駆動を実現しており、流体力学的スラスト軸受としての動圧溝にスパイラル溝を用いているが、溝深さに関する記載はあるものの、軸受隙間について記載されていない。
また、本出願人による特許文献５、６においても、スラスト動圧軸受としてスパイラル溝を用いたものを出願しているが、溝深さに関する記載は無く、特許文献５の羽根車下面の動圧溝はスパイラル溝ではない。
2. Description of the Related Art In recent years, centrifugal blood pumps have been used as pumps for artificial hearts, assisted circulation, and cardiac surgery with advances in medical technology and the like.
For example, in Patent Literature 1, non-contact driving of an impeller is realized by using a hydrodynamic thrust bearing. However, a dynamic pressure groove as a hydrodynamic thrust bearing does not use a so-called spiral groove. .
In Patent Documents 2 to 4, non-contact driving of an impeller is realized by using a hydrodynamic thrust bearing and a plurality of permanent magnets having an attractive force, and a spiral groove is formed in a dynamic pressure groove as a hydrodynamic thrust bearing. Although there is a description about the groove depth, there is no description about the bearing gap.
Patent Documents 5 and 6 by the present applicant also filed applications using spiral grooves as thrust dynamic pressure bearings. However, there is no description about the groove depth, and the dynamic pressure on the lower surface of the impeller disclosed in Patent Document 5 is not described. The groove is not a spiral groove.
補助人工心臓に代表される補助循環用血液ポンプが重症心不全患者に適用されており、近年、血液ポンプには長期耐久性と高い血液適合性が求められるため、非接触軸受のひとつである動圧軸受が血液ポンプに応用されている（特許文献１〜５参照）。動圧軸受を有する血液ポンプの軸受隙間は、動圧軸受の原理上数十μｍと狭くなるため、狭い隙間に起因した赤血球破壊(溶血)が懸念される。一方、軸受隙間を溶血が改善される数百μｍまで広げると、動圧軸受の軸受剛性が低下し、インペラ（羽根車）の浮上が心拍の影響により不安定となってしまう。
したがって、本発明が解決しようとする課題は、軸受剛性を維持しながら、溶血の問題を改善させた血液ポンプを提供することにある。
Blood pumps for assisted circulation, represented by assisted artificial hearts, have been applied to patients with severe heart failure.In recent years, blood pumps have been required to have long-term durability and high blood compatibility. Bearings are applied to blood pumps (see Patent Documents 1 to 5). Since the bearing gap of a blood pump having a dynamic pressure bearing is narrowed to several tens of μm in principle of the dynamic pressure bearing, there is a concern about red blood cell destruction (hemolysis) due to the narrow gap. On the other hand, if the bearing gap is increased to several hundred μm at which the hemolysis is improved, the bearing rigidity of the dynamic pressure bearing decreases, and the floating of the impeller (impeller) becomes unstable due to the influence of the heartbeat.
Therefore, an object of the present invention is to provide a blood pump in which the problem of hemolysis is improved while maintaining the bearing rigidity.
そこで、軸受剛性を維持しながら、溶血の問題を改善させるため、赤血球と血漿が分離するプラズマスキミング現象に着目した。プラズマスキミングとは、生体内の血管において分岐した側の毛細管内の赤血球濃度（ヘマトクリット）が分岐前の血管のヘマトクリットよりも減少する現象である。動圧軸受を有する血液ポンプにおいて、十分な軸受剛性が得られる狭い軸受隙間でプラズマスキミングを生じさせ、高せん断となる軸受隙間で赤血球濃度を減少させることで、溶血の問題を改善させる。
すなわち、本発明は、流入口と流出口が設けられたケーシングと、前記ケーシング内で回転することによって前記流入口から流出口へ液体を送る羽根車と、前記羽根車内に内蔵された永久磁石と、前記永久磁石と隔壁越しに磁気カップリングを形成して前記羽根車を回転駆動する磁気発生装置と、前記羽根車と羽根車に対向する前記ケーシングのいずれかにスラスト動圧軸受を構成するスパイラル形状の動圧溝を備えた血液ポンプにおいて、前記羽根車と前記ケーシング間の前記スラスト動圧軸受の平均軸受隙間を２０μｍ以下とし、かつ、前記スラスト動圧軸受のスパイラル形状の動圧溝深さを５０μｍ以上とすることによりプラズマスキミング現象によってスパイラルグルーブ軸受の山側の狭い軸受隙間には血漿が入り、溝側のせん断応力が低い部分には赤血球が入るようにして溶血を防止したことを特徴とする。
また、本発明は、上記血液ポンプにおいて、前記羽根車のラジアル軸受として、前記ケーシングに設けた内筒と、前記内筒によりラジアル方向に支持される前記羽根車内側面と、のいずれかにヘリンボーン溝を設けてラジアル動圧軸受を構成し、前記羽根車とケーシング間のラジアル動圧軸受の平均軸受隙間を２０μｍ以下とし、ラジアル軸受の溝深さを５０μｍ以上としたことを特徴とする。
また、本発明は、上記血液ポンプにおいて、前記羽根車は樹脂にて構成され、該樹脂中に前記永久磁石が埋め込まれ、該永久磁石の外周面が樹脂により被覆され、前記ケーシングは樹脂にて構成され、前記駆動用の磁気発生装置の前記羽根車に内蔵された永久磁石に対向する内周面が樹脂により被覆されていることを特徴とする。
また、本発明は、上記血液ポンプにおいて、体内埋め込みの形式で使用するためのものである。
また、本発明は、上記血液ポンプにおいて、体外設置型の形式で使用するためのものである。
Therefore, in order to improve the problem of hemolysis while maintaining the bearing rigidity, attention was paid to a plasma skimming phenomenon in which red blood cells and plasma are separated. Plasma skimming is a phenomenon in which the concentration of red blood cells (hematocrit) in a capillary on a side of a blood vessel in a living body that branches off is lower than the hematocrit of a blood vessel before branching. In a blood pump having a dynamic pressure bearing, the problem of hemolysis is improved by causing plasma skimming in a narrow bearing gap where sufficient bearing rigidity can be obtained and reducing red blood cell concentration in a bearing gap where high shear occurs.
That is, the present invention provides a casing provided with an inlet and an outlet, an impeller that sends liquid from the inlet to the outlet by rotating in the casing, and a permanent magnet built in the impeller. A magnetic generator that forms a magnetic coupling over the partition wall with the permanent magnet and drives the impeller to rotate, and a spiral that forms a thrust dynamic pressure bearing in one of the impeller and the casing facing the impeller In the blood pump having a dynamic pressure groove having a shape, an average bearing gap of the thrust dynamic pressure bearing between the impeller and the casing is set to 20 μm or less, and a depth of a spiral dynamic pressure groove of the thrust dynamic pressure bearing is set. Is set to 50 μm or more, plasma enters the narrow bearing gap on the mountain side of the spiral groove bearing due to the plasma skimming phenomenon, and the shear stress on the groove side It is characterized in that erythrocytes are allowed to enter the lower part to prevent hemolysis.
Further, the present invention provides the blood pump, wherein, as a radial bearing of the impeller, an inner cylinder provided in the casing, or an inner surface of the impeller radially supported by the inner cylinder, the herringbone groove is provided on one of the inner cylinder and the inner cylinder. To provide a radial dynamic pressure bearing, wherein the average bearing clearance of the radial dynamic pressure bearing between the impeller and the casing is 20 μm or less, and the groove depth of the radial bearing is 50 μm or more.
Further, in the blood pump according to the present invention, the impeller is made of resin, the permanent magnet is embedded in the resin, an outer peripheral surface of the permanent magnet is coated with resin, and the casing is made of resin. Preferably, an inner peripheral surface of the driving magnetic generator facing the permanent magnet built in the impeller is coated with a resin.
Further, the present invention is for use in the above-described blood pump in a form of being implanted in a body.
In addition, the present invention is for use in the above-mentioned blood pump in a form of extracorporeal installation.
本発明では、インペラとケーシング間の平均軸受隙間を２０μｍ以下としつつ、スパイラル形状のスラスト軸受の動圧溝深さを５０μｍ以上としたことにより、スパイラルグルーブ軸受の山側と溝側とでプラズマスキミング現象を現出させて、スパイラルグルーブ軸受の山側から赤血球を排除し、溶血の原因となるせん断応力の高いスパイラルグルーブ軸受の山側の狭い軸受隙間には血漿が入り、溝側のせん断応力が低い部分には赤血球が入るため、軸受剛性を維持しながら、溶血を改善する血液ポンプが実現できるものである。
本発明の血液ポンプは、体内埋め込みの形式でも、体外設置型の形式でも使用することができる。
According to the present invention, the dynamic bearing groove depth of the spiral shaped thrust bearing is set to 50 μm or more while the average bearing gap between the impeller and the casing is set to 20 μm or less. To remove red blood cells from the ridge side of the spiral groove bearing, plasma enters the narrow bearing gap on the ridge side of the spiral groove bearing with high shear stress causing hemolysis, and into the part where the shear stress on the groove side is low. Since red blood cells enter, a blood pump that improves hemolysis while maintaining bearing rigidity can be realized.
The blood pump of the present invention can be used in a form implanted in the body or in a form installed outside the body.
本発明の血液ポンプは、赤血球と血漿が分離するプラズマスキミング現象に着目し、動圧軸受を有する血液ポンプにおいて、十分な軸受剛性が得られる狭い軸受隙間でプラズマスキミングを生じさせ、高せん断となる軸受隙間で赤血球濃度を減少させることで、溶血の問題を改善させたものであり、インペラ（羽根車）とケーシング間の平均軸受隙間を２０μｍ以下としつつ、動圧溝であるスパイラル形状のスラスト軸受の溝深さを５０μｍ以上とすることによりプラズマスキミング現象を発現させたものである。
The blood pump of the present invention focuses on the plasma skimming phenomenon in which red blood cells and plasma are separated, and in a blood pump having a dynamic pressure bearing, plasma skimming occurs in a narrow bearing gap where sufficient bearing rigidity is obtained, resulting in high shear. The present invention has improved the problem of hemolysis by reducing the red blood cell concentration in the bearing gap. The spiral shaped thrust bearing, which is a dynamic pressure groove, has an average bearing gap between the impeller (impeller) and the casing of 20 μm or less. By making the
図１に、本発明の血液ポンプの一実施例を示す。図１のごとく本発明の血液ポンプは、流入口（インレット）と流出口（アウトレット）が設けられたケーシングと、ケーシング内で回転することによって流入口から流出口へ血液を送る羽根車（インペラ）と、羽根車に内蔵された永久磁石と磁気カップリングを形成しケーシングに内蔵された羽根車駆動用の磁気発生装置（コイル）と、羽根車と対向するケーシングに設けられたスラスト動圧軸受を構成するスパイラル形状の動圧溝とを有し、羽根車とケーシング間のスラスト方向の平均軸受隙間を２０μｍ以下としつつ、スパイラル形状のスラスト軸受の溝深さを５０μｍ以上に構成したものである。本形状によりプラズマスキミング現象が発現し、溶血の原因となるせん断応力の高い動圧軸受の山側の狭い軸受隙間には血漿が入り、溝側のせん断応力が低い部分には赤血球が入るため、軸受剛性を維持しながら、溶血を改善する血液ポンプが実現できる。なお、図１ではスパイラル形状の動圧溝はケーシング側に設けてあるが、羽根車側に設けてもよい。
また、ケーシング内筒の固定軸と、羽根車内側面とでラジアル動圧軸受けを構成しており、図では、４円弧溝による動圧軸受（本出願人による、特開２０１３−２１２２１８号公報参照）を採用しているが、ケーシング内筒と、前記内筒によりラジアル方向に支持される前記羽根車内側面と、のいずれかにヘリンボーン溝を設けてラジアル動圧軸受を構成した場合には、前記羽根車とケーシング間のラジアル動圧軸受の平均軸受隙間を２０μｍ以下とし、ラジアル動圧軸受のヘリンボーン溝深さを５０μｍ以上とすれば前記スパイラル形状の動圧溝と同様にプラズマスキミング現象が発現し、溶血の原因となるせん断応力の高い動圧軸受の山側の狭い軸受隙間には血漿が入り、溝側のせん断応力が低い部分には赤血球が入るため、軸受剛性を維持しながら、溶血を改善することができる。
また、羽根車を樹脂で構成し、該樹脂中に前記永久磁石を埋め込み、該永久磁石の外周面が樹脂により被覆されるようにし、前記ケーシングを樹脂で構成し、前記駆動用の磁気発生装置の前記羽根車に内蔵された永久磁石に対向する内周面が樹脂により被覆されるように構成することが望ましい。
上記のごとく構成された血液ポンプにおいて、羽根車駆動用の磁気発生装置に通電すると磁気発生装置と永久磁石との相互作用により羽根車が回転し、流入口から入った血液は羽根車のベーン間流路に入り、回転する羽根車から遠心力を与えられた血液はベーン間流路を通って流出口から吐出される。羽根車が回転すると、スラスト動圧軸受により羽根車が浮上し非接触でスラスト方向に支持され、ラジアル動圧軸受によりラジアル方向にも非接触で軸支される。
FIG. 1 shows an embodiment of the blood pump of the present invention. As shown in FIG. 1, the blood pump according to the present invention includes a casing provided with an inlet (inlet) and an outlet (outlet), and an impeller that rotates the casing to send blood from the inlet to the outlet. And a magnetic generator (coil) for forming a magnetic coupling with a permanent magnet built in the impeller and driving the impeller and built in the casing, and a thrust dynamic pressure bearing provided in the casing facing the impeller. The spiral shaped dynamic pressure groove has a mean axial clearance between the impeller and the casing in the thrust direction of 20 μm or less, and the spiral thrust bearing has a groove depth of 50 μm or more. Due to the plasma skimming phenomenon caused by this shape, plasma enters into the narrow bearing gap on the mountain side of the dynamic pressure bearing with high shear stress causing hemolysis, and red blood cells enter into the part with low shear stress on the groove side. A blood pump that improves hemolysis while maintaining rigidity can be realized. In FIG. 1, the spiral dynamic pressure groove is provided on the casing side, but may be provided on the impeller side.
Further, a radial dynamic pressure bearing is constituted by the fixed shaft of the casing inner cylinder and the inner surface of the impeller. In the figure, a dynamic pressure bearing with four arc grooves is used (see Japanese Patent Application Laid-Open No. 2013-212218 by the present applicant). However, if a radial dynamic pressure bearing is formed by providing a herringbone groove in one of the casing inner cylinder and the inner surface of the impeller radially supported by the inner cylinder, the blade If the average bearing gap of the radial dynamic pressure bearing between the car and the casing is set to 20 μm or less, and the herringbone groove depth of the radial dynamic pressure bearing is set to 50 μm or more, the plasma skimming phenomenon appears as in the case of the spiral dynamic pressure groove, Plasma enters the narrow bearing gap on the peak side of the dynamic pressure bearing with high shear stress that causes hemolysis, and red blood cells enter the low shear stress portion on the groove side. While maintaining hemolysis can be improved.
Further, the impeller is made of resin, the permanent magnet is embedded in the resin, the outer peripheral surface of the permanent magnet is covered with resin, the casing is made of resin, and the driving magnetic generator is provided. It is preferable that the inner peripheral surface facing the permanent magnet built in the impeller is coated with a resin.
In the blood pump configured as described above, when the magnetic generator for driving the impeller is energized, the impeller rotates due to the interaction between the magnetic generator and the permanent magnet, and blood entering from the inlet flows between the vanes of the impeller. The blood that has entered the flow path and given centrifugal force from the rotating impeller is discharged from the outlet through the inter-vane flow path. When the impeller rotates, the impeller floats by the thrust dynamic pressure bearing and is supported in the thrust direction without contact, and is axially supported by the radial dynamic pressure bearing in the radial direction without contact.
（作製例）
本発明の血液ポンプの作製例を以下に説明する。作成した動圧浮上遠心血液ポンプは、上面ケーシング、インペラ、および下面ケーシングから構成される。ポンプケーシングの直径は７３ｍｍで高さは５６ｍｍである。インペラ直径は３７ｍｍ、高さが２６ｍｍであり、６本のベーンを有するクローズドタイプである。インペラは、ラジアルおよびスラスト方向の動圧軸受によって支持される。上面ケーシング内側の円筒側面に４円弧形状のラジアル軸受を有する。上面および下面ケーシング表面には、スパイラルグルーブ形状のスラスト軸受を有する。スパイラルグルーブ軸受の溝数は１２本で、溝深さは１００μｍである。スラスト方向の上面隙間と下面隙間の合計は３００μｍである。インペラは、上面ケーシング内のステータコイルとインペラ内の永久磁石間の磁気力によって回転する。
(Production example)
A production example of the blood pump of the present invention will be described below. The created hydrodynamic levitation centrifugal blood pump includes an upper casing, an impeller, and a lower casing. The pump casing has a diameter of 73 mm and a height of 56 mm. The impeller has a diameter of 37 mm, a height of 26 mm, and is a closed type having six vanes. The impeller is supported by radial and thrust dynamic bearings. A radial bearing having a four-arc shape is provided on the cylindrical side surface inside the upper casing. Spiral groove-shaped thrust bearings are provided on the upper and lower casing surfaces. The spiral groove bearing has 12 grooves and a groove depth of 100 μm. The total of the upper gap and the lower gap in the thrust direction is 300 μm. The impeller is rotated by a magnetic force between a stator coil in the upper casing and a permanent magnet in the impeller.
（作製例のインペラ浮上特性試験）
インペラ浮上位置を評価するため、体循環系を模擬した模擬循環回路を使用したインペラ浮上特性試験を行った。図２に示すように、模擬循環回路は、リザーバ、チューブ、流路抵抗、および試験ポンプから構成される。作動流体には、ウシ保存血を使用した。ウシ血のヘマトクリット値は、自己血漿希釈により１.０％に調整した。リザーバは、３７℃の恒温槽につけた。インペラの浮上位置を計測するために、レーザ焦点変位計をポンプ下面側に設置した。駆動条件は、流路抵抗を用いて回転数２,８００ｒｐｍ時に揚程１００ｍｍＨｇ、流量５.０Ｌ／ｍｉｎとなるよう一定に保った。計測データはノートパソコンを用いてサンプリングした。サンプリング周波数は１ｋＨｚ、サンプリング時間は１０秒とした。１万個のデータから計測値の平均値を求めた。
(Impeller levitation characteristics test of production example)
In order to evaluate the impeller levitation position, an impeller levitation characteristic test using a simulated circulation circuit simulating a systemic circulation system was performed. As shown in FIG. 2, the simulated circulation circuit includes a reservoir, a tube, a flow path resistance, and a test pump. Bovine stored blood was used as a working fluid. The hematocrit of bovine blood was adjusted to 1.0% by autologous plasma dilution. The reservoir was placed in a 37 ° C. thermostat. In order to measure the floating position of the impeller, a laser focal displacement meter was installed on the lower surface of the pump. The driving conditions were kept constant using a flow path resistance so that the head was 100 mmHg and the flow rate was 5.0 L / min at a rotation speed of 2,800 rpm. The measurement data was sampled using a notebook computer. The sampling frequency was 1 kHz and the sampling time was 10 seconds. The average value of the measured values was determined from 10,000 data.
（作製例のプラズマスキミング評価試験）
図３に示すように、血液ポンプのスパイラルグルーブ軸受内の赤血球流れを評価するため、微視的観察を行った。ズームレンズを接続したハイスピードマイクロスコープをポンプ下面側に設置し、赤血球の挙動を録画した。シャッタースピードとフレームレートは、それぞれ１／９０００００ｓと８０００ｆｐｓとした。撮影時間は、インペラ３周期分とした。
(Plasma skimming evaluation test of production example)
As shown in FIG. 3, microscopic observation was performed to evaluate the red blood cell flow in the spiral groove bearing of the blood pump. A high-speed microscope connected to a zoom lens was installed on the lower surface of the pump, and the behavior of red blood cells was recorded. The shutter speed and the frame rate were set to 1/900000 s and 8000 fps, respectively. The photographing time was three impeller cycles.
（プラズマスキミングの評価方法）
スパイラルグルーブ軸受の山側のヘマトクリットを評価するため、微視的観察結果から山側のヘマトクリットを推定した。撮影動画は連続静止画に変換し、画像処理を用いて解析した。これらの画像は二値化することで赤血球を黒で表現し、山側の黒のピクセル数の合計を求めた。画像上の赤血球占有率を下記の式（１）から求めた。
Ｑ＝ＡE／ＡRidgs （１）
ここで、Ｑは画像上の赤血球占有率、は山側の赤血球のピクセル数の合計、ＡRidgsは山側のピクセル数の合計である。画像上の赤血球占有率は、散乱係数の概念から次式（２）でも表すことができる。
Ｑ＝μS×ｄｘ （２）
ここで、μSは単位厚さ当たりの赤血球占有率、ｄｘは血液層の厚さである。単位厚さあたりの赤血球占有率は、生体光学における散乱係数として知られており、下記式（３）で表される。
ΜS＝（ＨＣＴ／ＭＣＶ）σS （３）
ここで、ＭＣＶは平均赤血球容積、σSは赤血球の幾何断面積である。式（３）より、スパイラル溝の山側の推定ヘマトクリットＨＣＴは次式（４）より求められる。
ＨＣＴ＝（１／σS）×（ＭＣＶ×（Ｑ／ｄｘ）） （４）
ここで、ＭＣＶには血球分析装置で計測した値を、Ｑには式（１）より求めた赤血球占有率を、ｄｘにはインペラ浮上特性試験において計測した軸受隙間をそれぞれ代入した。赤血球をバイコンケーブ形状（両面にくぼみを有する形状）と仮定すると、バイコンケーブ状の赤血球の方程式は、次式（５）で表される。
ｒ（θ）＝３ｓｉｎ4θ＋０.７５ （５）
ここで、ｒ（θ）は赤血球表面の関数であり、ｒは半径、θは長軸とＺ軸とのなす角である。赤血球の長軸が球の半径と等しいと仮定すると、赤血球と球の体積比は次式（６）で表される。
Ｃ＝ＭＣＶ／ＶS （６）
ここで、Ｃは赤血球と球の体積比、ＶSは赤血球の長軸半径が球の半径と等しい場合の球の体積である。式（６）より、赤血球のＭＣＶと長軸半径の関係は、次式（７）で表される。
ｒb＝（３ＭＣＶ／４πＣ）1/3 （７）
ここで、ｒbは赤血球の長軸半径である。赤血球の幾何断面積σSは赤血球の長軸半径を用いて、次式（８）から求めた。
ΣS＝πｒｂ 2 （８）
最終的に、式（４）を元に、スパイラルグルーブ軸受山側のプラズマスキミング効率は、次式（９）より求めた。
ＥS＝｛１−（ＨＣＴ／ＨＣＴW）｝×１００ （９）
ここで、ＥSはスパイラル溝の山側のプラズマスキミング効率であり、ＨＣＴWは作動流体のヘマトクリットである。
(Evaluation method of plasma skimming)
In order to evaluate the hematocrit on the mountain side of the spiral groove bearing, the hematocrit on the mountain side was estimated from microscopic observation results. The captured moving images were converted into continuous still images and analyzed using image processing. These images were binarized to represent red blood cells in black, and the sum of the number of black pixels on the mountain side was calculated. The red blood cell occupancy on the image was determined from the following equation (1).
Q = A E / A Ridgs (1)
Here, Q is the occupancy rate of red blood cells on the image, is the total number of pixels of red blood cells on the mountain side, and A Ridgs is the total number of pixels on the mountain side. The red blood cell occupancy on the image can also be expressed by the following equation (2) from the concept of the scattering coefficient.
Q = μ S × dx (2)
Here, μ S is the occupancy of red blood cells per unit thickness, and dx is the thickness of the blood layer. The occupancy rate of red blood cells per unit thickness is known as a scattering coefficient in bio-optics and is represented by the following equation (3).
Μ S = (HCT / MCV) σ S (3)
Here, MCV is the average red blood cell volume, and σ s is the geometric cross-sectional area of the red blood cells. From the equation (3), the estimated hematocrit HCT on the mountain side of the spiral groove is obtained from the following equation (4).
HCT = (1 / σ S ) × (MCV × (Q / dx)) (4)
Here, the value measured by the blood cell analyzer was substituted for MCV, the red blood cell occupancy determined by equation (1) was substituted for Q, and the bearing gap measured in the impeller levitation characteristic test was substituted for dx. Assuming that the red blood cells have a biconcave shape (a shape having depressions on both sides), the equation of the biconcave-shaped red blood cells is expressed by the following equation (5).
r (θ) = 3 sin 4 θ + 0.75 (5)
Here, r (θ) is a function of the surface of the red blood cell, r is the radius, and θ is the angle between the long axis and the Z axis. Assuming that the major axis of the red blood cell is equal to the radius of the sphere, the volume ratio between the red blood cell and the sphere is expressed by the following equation (6).
C = MCV / V S (6)
Here, C is the volume ratio of red blood cells and the sphere, V S is the volume of a sphere when the major axis radius of the red blood cells is equal to the radius of the sphere. From Equation (6), the relationship between the MCV of red blood cells and the major axis radius is expressed by the following Equation (7).
r b = (3MCV / 4πC) 1/3 (7)
Here, r b is the major axis radius of the red blood cells. The geometric cross-sectional area σ S of red blood cells was determined from the following equation (8) using the major axis radius of red blood cells.
Σ S = πr b 2 (8)
Finally, the plasma skimming efficiency on the spiral groove bearing peak side was obtained from the following equation (9) based on the equation (4).
E S = {1- (HCT / HCT W )} × 100 (9)
Here, E S is the plasma skimming efficiency mountain side of the spiral groove, HCT W is hematocrit of the working fluid.
（評価結果）
図４は、ポンプの回転数を２,５００ｒｐｍ、２,８００ｒｐｍ、および３,０００ｒｐｍに変えて試験を行ったときの、インペラ浮上特性試験とプラズマスキミング評価試験の結果を示した図であり、図４の左側がポンプの回転数２５００ｒｐｍ、中央が回転数２８００ｒｐｍ、右側が回転数３０００ｒｐｍにおける結果である。図４の上側のグラフの左縦軸はヘマトクリット率を示し、右縦軸は軸受隙間を示す。ヘマトクリット率は、初期のヘマトクリットを１００％としたときのヘマトクリットの変化を示す。横軸はインペラの回転角度を示す。図４の下側の写真は、各回転数におけるスパイラルグルーブ軸受の溝側の軸受隙間と山側の軸受隙間を高速度カメラで撮影した写真であり、黒丸状に写っているのが赤血球である。
ポンプの回転数を２,５００ｒｐｍ、２,８００ｒｐｍ、および３,０００ｒｐｍに変えたとき、インペラとスパイラルグルーブ軸受山側間の距離である下面隙間は、それぞれ３０μｍ、２４μｍ、２０μｍとなった。このとき、下面隙間３０μｍ、２４μｍ、２０μｍに対して、スパイラルグルーブ軸受山側の推定ヘマトクリット率は、それぞれ７２％、２２％、３％となった。つまり、隙間を２０μｍとすることで、山側の赤血球は９７％減少し、スパイラルグルーブ軸受の山側から赤血球を排除することが出来た。本形状により、隙間を２０μｍ以下とすれば、溶血の原因となるせん断応力の高い動圧軸受の山側の狭い軸受隙間には血漿が入り、溝側のせん断応力が低い部分には赤血球が入るため、軸受剛性を維持しながら、溶血を改善する血液ポンプが実現できることが確認された。
(Evaluation results)
FIG. 4 is a diagram showing the results of an impeller levitation characteristic test and a plasma skimming evaluation test when the tests were performed while changing the rotation speed of the pump to 2,500 rpm, 2,800 rpm, and 3,000 rpm. The left side of FIG. 4 shows the result at a pump rotation speed of 2500 rpm, the center shows the result at a rotation speed of 2800 rpm, and the right side shows the result at a rotation speed of 3000 rpm. The left vertical axis of the upper graph in FIG. 4 indicates the hematocrit ratio, and the right vertical axis indicates the bearing clearance. The hematocrit ratio indicates a change in hematocrit when the initial hematocrit is set to 100%. The horizontal axis indicates the rotation angle of the impeller. The photograph on the lower side of FIG. 4 is a photograph taken by a high-speed camera of the bearing gap on the groove side and the bearing gap on the mountain side of the spiral groove bearing at each rotation speed, and red blood cells are shown in black circles.
When the rotation speed of the pump was changed to 2,500 rpm, 2,800 rpm, and 3,000 rpm, the lower surface gaps, which are the distances between the impeller and the spiral groove bearing ridge side, were 30 μm, 24 μm, and 20 μm, respectively. At this time, the estimated hematocrit on the spiral groove bearing ridge side was 72%, 22%, and 3%, respectively, for the lower surface gaps of 30 μm, 24 μm, and 20 μm. That is, by setting the gap to 20 μm, the red blood cells on the mountain side were reduced by 97%, and the red blood cells could be eliminated from the mountain side of the spiral groove bearing. With this shape, if the gap is set to 20 μm or less, plasma enters into the narrow bearing gap on the mountain side of the hydrodynamic bearing with high shear stress causing hemolysis, and red blood cells enter into the part with low shear stress on the groove side. It has been confirmed that a blood pump that improves hemolysis while maintaining bearing rigidity can be realized.
本発明の血液ポンプは、医療機器である左心補助ポンプや体外循環用ポンプとして利用される。また、生物分野や産業機器分野において、微小粒子の入った溶液を送るための培養や薬液の輸送用ポンプや産業用ポンプとしても利用される。 The blood pump of the present invention is used as a left heart auxiliary pump or a pump for extracorporeal circulation, which is a medical device. In the biological field and industrial equipment field, it is also used as a pump for transporting a solution containing microparticles, a chemical solution, and an industrial pump.
Claims (4)
前記スラスト動圧軸受において、前記羽根車と前記ケーシング間の平均軸受隙間を２０μｍ以下とし、かつ、前記動圧溝深さを５０μｍ以上とすることで、前記動圧溝の山側と溝側との間のせん断応力差でプラズマスキミング現象を生じさせ、前記溝側のせん断応力が低い部分に赤血球を分離して通過させて溶血を防止するように前記血液ポンプが作動することを特徴とする血液ポンプの作動方法。 A casing provided with an inflow port and an outflow port, an impeller that sends liquid from the inflow port to the outflow port by rotating in the casing, a permanent magnet built in the impeller, and the permanent magnet A magnetic generation device that forms a magnetic coupling over the partition wall to rotationally drive the impeller, and a spiral dynamic pressure groove that forms a thrust dynamic pressure bearing in one of the impeller and the casing facing the impeller. A method of operating the blood pump provided,
In the thrust dynamic pressure bearing, the average bearing gap between the impeller and the casing is set to 20 μm or less, and the dynamic pressure groove depth is set to 50 μm or more, so that the peak side and the groove side of the dynamic pressure groove The blood pump operates to cause a plasma skimming phenomenon due to a difference in shear stress between the blood pump and the blood pump to separate and pass red blood cells through a portion having a low shear stress on the groove side to prevent hemolysis. How it works .
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