磁場對凝血之作用

1. Aggregation of blood platelets in static magnetic fields
Iwasaka, M.; Takeuchi, M.; Ueno, S.
Magnetics, IEEE Transactions
Volume 36, Issue 5, Sep 2000 Page(s):3721 - 3723
Digital Object Identifier   10.1109/20.908952
Summary:We investigated the effects of intense magnetic fields on the blood platelet aggregation process with and without static magnetic fields of up to 14 T. A rabbit plasma and collagen mixture was used as the model system for a wounded blood vessel. Platelet aggregation was activated by the stimulation of acid soluble collagen. The platelet aggregates in strong magnetic fields were larger than the aggregates in an ambient field. An optical transmission of blood plasma during platelet aggregation also indicated that strong magnetic fields enhanced blood platelet aggregation in plasma.

 

2. Magnetic relaxation in blood and blood clots.

Bryant RG, Marill K, Blackmore C, Francis C.

Department of Biophysics, University of Rochester, School of Medicine and Dentistry, New York 14642.

Magn Reson Med. 1990 Jan;13(1):133-44.

Summary:Nuclear magnetic relaxation rates are measured for whole blood, blood plasma, whole blood clots, and plasma clots in vitro. Relaxation rates are linear in the hematocrit and transverse relaxation rates are significantly greater than longitudinal relaxation rates. Longitudinal relaxation rates measured from 0.01 to 42 MHz for proton Larmor frequencies are found to decline monotonically with increasing magnetic field strength; however, the dispersion curves do not follow a simple Lorentzian behavior, which is anticipated in a suspension of particles in a solution of proteins having a distribution of molecular weights. The transverse relaxation rate is a function of the acquisition parameters, in particular, the choice of TE in either Hahn echo experiments or in echo-train experiments. The origin of this dependence of T2 on TE or the interpulse spacing in an echo train is identified with the exchange of water from inside the red blood cell to the outside and is only an important relaxation mechanism in the case where the blood cell membrane is intact and the cell contains deoxygenated hemoglobin. The dependence of the apparent transverse relaxation rate on the interpulse spacing in a Meiboom-Gill-Carr-Purcell pulse sequence provides the estimate that the mean residence time of water inside the blood cell is about 10 ms. These data provide a sound basis for understanding the dependence of magnetic images on magnetic field strength and the choices of the image acquisition parameters, TE and TR.

 

3. The Mechanics of Blood Clots：How Biophysics can Investigate One Aspect of Hemostasis

Robert Harrand

   When a person is cut, there is an immediate cascade of reactions resulting in the formation of a blood clot. Molecules called fibrinogen are altered, with small sections being snipped off, allowing them to join together in long chains. These chains then line up and form thick, rigid fibres called fibrin. The final clot is made up of a fibrous network which traps platelets (fragments of cells) and red blood cells, stemming the flow of blood from the damaged area. This process of preventing blood loss is known as hemostasis.

Summary:

Disorders in the Blood Clotting System

Throughout the evolution of this highly sophisticated system, genetic faults and diseases have emerged that circumvent the clotting mechanism. Haemophiliacs, for example, lack one type of molecule involved in the clotting reaction, and tricks by other animals can disrupt our clotting ability, such as the hindrance of clot formation by the saliva of both snakes and mosquitos.

Blood Clots Have Different Characteristics

Not all blood clots are the same - some are tight and compact, others are sparse and flexible, and forming the right one in the right circumstances can be a matter of life and death. If a clot is too stiff, the body will have trouble breaking it down when the wound has healed. A clot that is too compliant will not stop the flow of blood from the wound.

Mechanical Measurements of Clots Using Magnets

How is the stiffness of a blood clot measured? What can test whether or not a patient can form a healthy clot, or if a certain type of treatment can help to turn a poor clotting response into something healthier? This is where a simple trick with magnets steps in to lend a hand.

A magnet can be moved, from a distance, by inducing an external magnetic field. Sliding a magnet across a desk using a second magnet held underneath is a classic example.

Now imagine the first magnet stuck in the middle of a sponge, which bends and distorts when a second magnet is moved around. Picture the sponge as a blood clot, around ten thousand times smaller than an actual sponge.

Forming and Testing Blood Clots

In the experimental procedure, fibrinogen molecules extracted from blood samples are mixed with a second type of molecule that initiates the clotting reaction. In addition, small magnetic particles (acting like tiny magnets) are added, and nature left to run its course. The clot forms and traps the magnetic particles. Next, the clot is placed under a microscope, one of the magnetic particles is located, and a nearby, much larger electromagnet is activated.

The result is that the tiny magnets inside the clot move towards the larger one, and this distorts the fibrin network. By knowing how strong the magnets are, and how far they move, the mechanical properties of the clot can be worked out. If this is repeated with different samples, from, say, one patient with diabetes and one without, the differences in the various types of clot can be measured.

The Merging of Scientific Disciplines

Today, at the edges of the traditional scientific disciplines, there is a merging of ideas and techniques. Physics on the scale of between millionths and billionths of a metre is precisely where biology happens, whether it be a living cell, a single molecule of DNA, or a blood clot. And in this case, it took no more than the principle behind a classroom trick to further increase our understanding of nature.

References:

Ramzi Ajjan, Bernard C. B. Lim, Kristina F. Standeven, Robert Harrand, Sarah Dolling, Fladia Phoenix, Richard Greaves, Radwa H. Abou-Saleh, Simon Connell, D. Alastair M. Smith, John W. Weisel, Peter J. Grant, and Robert A. S. Ariëns. Common variation in the C-terminal region of the fibrinogen β-chain: effects on fibrin structure, fibrinolysis and clot rigidity. Blood, Jan 2008; 111: 643 - 650