Identification of Blood

Properties of Blood

Properties & Identification

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Blood is a serological fluid that consists of several kinds of cells suspended in a salty aqueous solution called plasma. (If one considers that living organisms such as humans have evolved from species originally living and breathing in seawater, then one might surmise that the saline solution of blood plasma is the body’s way of internalizing the seawater and living on dry land).

The color of blood comes from the red blood cells (RBC's) or erythrocytes (disk-shaped particles shown above). Red blood cells make up about 40% of blood (by volume). This is readily apparent in a simple centrifuge test. Each red blood cell is filled with hemoglobin, the protein which carries oxygen to tissues and carries carbon dioxide away from tissues.

Hemoglobin carries oxygen by using heme, a large ring-like molecule which has at its center a single atom of iron (Fe), which is what actually binds to the oxygen to form an iron (hydr)oxide complex. The chemical property of heme that gives it these abilities is in the many double covalent bonds that form the ring. These double bonds can be shifted into many different “resonant” configurations. This allows for much more oxygen to be carried than if it were simply dissolved in the blood.

There are a variety of cells found within the blood. White blood cells ('hairy' spherical particles shown above) for example, are instrumental in the body’s immune system by producing antibodies to defend against harmful disease-carrying bacteria, viruses, or fungi. Platelets are white blood cell fragments (also shown above) which assist in blood clotting by aggregating and forming fibers in the opening of a wound which trap red blood cells to form a scab.

Circulation

The circulatory system consists of several fundamental parts. Blood is the serological fluid that provides the medium of transport. The heart is a pump that provides a sufficient pressure to carry the blood from one organ to another. The heart pumps blood into arteries, which distribute blood to organs. The blood flows into successively smaller arteries until it reaches tiny vessels called capillaries, and moves through the capillary walls. The blood then flows into a successively larger network of veins that ultimately return the blood to the organs such as the heart.

Thus, veins carry blood toward the heart and arteries carry it away from the heart. Because of this, not all arteries carry oxygenated blood. There are two major exceptions, where arteries are carrying deoxygenated blood. The pulmonary artery carries deoxygenated blood from the heart to the lungs for oxygen access. The umbilical arteries carry deoxygenated blood away from the baby’s body to the placenta for oxygen

Our circulation includes a separate pulmonary circuit to the lungs in addition to our main body circuit. One potential weak point in the circulatory system is the aorta: the main artery to the body. One of the first arteries to branch off is the coronary artery, which supplies blood to the heart muscle itself so it can pump. The coronary artery goes around the heart like a crown. A blockage of the coronary artery or one of its branches can cause portions of the heart to die if they don’t get nutrients and oxygen. This is referred to as a coronary heart attack.

The heart is responsible for providing the energy to pump the blood. The heart provides the pressure necessary to propel the blood throughout the body. If the heart does not continue its cycle of contraction and relaxation, then the blood stops flowing and the body cells are unable to obtain nutrients and eliminate wastes.

The heart contains a series of valves and chambers which could potentially malfunction over time due to illness, disease, birth defects, and/or physiological deterioration. The arteries are like muscles which have thick elastic walls that can become clogged over time. If arteries become hardened and less resilient, they are less likely to function properly. Potential build-up of cholesterol plaque may cause the arteries to contract, or even close.

Acidity

Normal blood pH is maintained between 7.35 and 7.45 by the regulatory systems. The lungs regulate the amount of carbon dioxide in the blood and the kidneys regulate the bicarbonate. When the pH decreases to below 7.35, a condition of acidosis is present (see author Michael Crichton’s “The Andromeda Strain”). This means that the hydrogen ions are increased and that pH and bicarbonate ions are decreased. I.E. A greater number of hydrogen ions [or (+) protons] are present in the blood than can be absorbed by the buffer systems.

Vigorous exercise causes an increase in the amount of carbon dioxide in the blood because muscles are oxidizing glucose sugars more rapidly. When certain brain cells sense a lower pH, nerve impulses are sent more frequently to the diaphragm causing a more rapid and forceful retraction. This results in more rapid, deeper breathing. This increase in the rate of air exchange means that carbon dioxide is lost from the lungs more rapidly. When exercise stops, the carbon dioxide level drops, blood pH rises, and breathing eventually returns to normal.

Alternatively, alkalosis results when the pH is above 7.45. This condition results when the buffer base (bicarbonate ions) is greater than normal and the concentration of hydrogen ions is decreased.

Both acidosis and alkalosis can be of two different types: respiratory and metabolic. Respiratory acidosis or alkalosis is caused by various malfunctions of the lungs. Metabolic acidosis or alkalosis is caused by various metabolic disorders which result in an excessive build up or loss of acids or bases.

Absorption / Color

In humans and other hemoglobin-using creatures, oxygenated blood is bright red. This is due to oxygenated iron (like rust) in the red blood cells. Deoxygenated blood is a darker shade of red, which can be seen during blood donation and when venous blood samples are taken. However, due to an optical effect caused by the way in which light penetrates through the skin, veins typically appear blue in color. This has led to a common misconception that venous blood is blue before it is exposed to air. Another reason for this misconception is that medical charts always show venous blood as blue in order to distinguish it from arterial blood which is depicted as red on the same chart. A rare exception is the blood of horseshoe crabs -- which is blue. This is a result of its high content in copper-based hemocyanin instead of the iron-based hemoglobin found, for example, in humans.

Human blood is always red. The tone is bright red when it is oxygenated (or oxygen rich) and a darker red when it's lacking oxygen (or oxygen poor). De-oxygenated blood only appears to be blue, largely because it is being viewed through many layers of translucent (partially transmitting) skin cells.

Longer (redder) wavelengths can penetrate more deeply into the skin than shorter, bluer wavelengths before reflecting out. A vein looks blue because red light travels far enough into the skin to be absorbed by the blood in the vein. If the blood vessel is far enough below the skin, however, blue light -- which would normally also be absorbed by the vein -- reflects out of the skin before reaching the vein. So the light reflecting from tissue over the vein contains less red light than blue light, giving the vein a bluish cast or hue.

I.E. Oxygen poor blood is most definitely NOT blue. It is a sort of purplish / maroon color at best. In order to see the vein at all, light has to go through the skin and hit the blood in the vein. The blood absorbs certain colors of light, and reflects others back through the skin. The combination of these effects (absorption by oxygen poor blood & absorption and deflection in the skin) yields a blue color.

The color of blood comes from the red blood cells (RBC's or erythrocytes --> disk-shaped particles in electron micrograph shown above) which make up about 40% of blood by volume. This is readily apparent in a simple centrifuge test. Each red blood cell is filled with hemoglobin -- the protein which carries oxygen to tissues and carries carbon dioxide away from tissues.

Hemoglobin carries oxygen by using heme, a large ring-like molecule which has at its center a single atom of iron (Fe) , which is what actually binds to the oxygen to form an iron (hydr) oxide complex. The chemical property of heme that gives it these abilities is in the many double covalent bonds that form the ring. These double bonds can be shifted into many different 'resonant' configurations.

When oxygen binds to the iron atom in heme, the iron atom (or ion) changes its shape slightly. This alters the resonance of the heme molecule. This new resonance gives off a different frequency of light, so the perceived color of the heme shifts from dark red to bright red. When the oxygen is released into the tissues, the iron goes back to its original shape, and the heme returns to its normal resonance, so the color goes back from scarlet to maroon.

Although blood has a high absorption in a very broad region (300 – 900 nm) it has a strong and narrow absorption band with a maximum centered around 415 nm.

In the absorption spectrum depicted above, note that the absorption is the weakest above 600 nm. This results in the reflection of visible light and the appearance of red wavelengths of the visible spectrum.

Hortola, P.
"SEM Analysis of Red Blood Cells in Aged Human Bloodstains"
Forensic Sci.Int. Vol. 55, p. 139 (1992)
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Identification of Blood

The Luminol test

The most widely used method for finding invisible blood is through the use of a chemical developer such as Luminol, or 5-Amino-2,3-dihydro-1,4-phthalazinedione (C8H7N3O2).

The Luminol must first be activated with an oxidant. Usually, a solution of hydrogen peroxide (H2O2) and a hydroxide salt in water is used as the activator. In the presence of a catalyst (e.g. the iron compounds found in human hemoglobin) the hydrogen peroxide is decomposed to form oxygen and water:

H2O2 --> O2 + H20

A two-part formula is mixed just prior to use, and is then sprayed on the surfaces being examined. The Luminol reacts with the iron complex in the blood's hemoglobin to produce a self-luminescence. I.E. The bloodstains literally glow in the dark with a faint bluish light.

The amount of catalyst necessary for the reaction to occur is very small relative to the amount of luminol, allowing the detection of even trace amounts of blood. The bluish glow only lasts for about 30 seconds. Detecting the glow requires a fairly dark room. Any glow detected may be documented by a long exposure photograph.

The Luminol test is extremely sensitive, and is capable of detecting bloodstains dilutes up to 300,000 times. For this reason, spraying large areas such as carpets, walls, flooring, or the interior of a vehicle may reveal blood traces or patterns that would have gone unnoticed under normal lighting conditions. In addition, it will not interfere with any subsequent DNA testing that may be carried out in a forensic laboratory.

The Kastle-Meyer Color Test uses a solution of phenolphthalein and hydrogen peroxide on a piece of filter paper, and when blood of any quantity is present, it turns pink. However, it also turns pink in the presence of potatoes or horseradish, so care must be taken at the scene.

Sometimes microcrystalline tests are also performed. The two most often used are the Takayama test and the Teichmann test. Both add specific chemicals to the blood to make it form crystals with hemoglobin derivatives. These tests are also sensitive to other materials that may be present in a bloodstain.

In the past 40 years, several studies have been conducted on the sensitivity and specificity of presumptive tests for blood. Grodsky, et al. (1) presented a comparative study of benzidine, leucomalachite green and phenolphthalein. They used blood solutions to test the sensitivity of the reagents rather than using a dry bloodstains, which are the usual form in which blood is tested in forensic science laboratories.

In 1960, Hunt et al. (2) conducted a survey of the orthotolidine (OTL), leucomalachite green (LMG), phenolphthalein (PhTh) and 'Luminol' tests. They determined that phenolphthalein was sensitive for blood in the solution form at dilutions of 1:10,000,000. But they also reported negative results with this test when applied directly to small spots of blood. An evaluation of the tetramethylbenzidine (TMB) test was reported by Garner, et al. (3) in 1976. They observed no significant differences between the benzidine and tetramethylbenzidine (TMB) in tests in either sensitivity or specificity. Higaki, et al. (4) compared the phenolphtalein and benzidine tests as presumptive tests. Their results indicate that plant peroxidases contribute to false positive results in the benzidine test only.

More recently, Cox (5, 6) focused on the four presumptive tests for blood, using phenolphtalein (PhTh), tetramethylbenzidine (TMB), leucomalachite green (LMG), and orthotolidine (OTL). His findings indicate that the TMB and OTL are the most sensitive of the group, and also the most likely to produce interference color reactions with plant peroxidases. The LMG test is the least sensitive of the four examined. The PhTh and LMG are the most specific of the four examined.

Moreover, the PhTh test is the best single test, based on its sensitivity of 1:10,000 with stained filter paper and cotton cloth and on the failure of the reagent to react with plant peroxidases.

However, the LMG Test is more commonly used by governmental agencies such as the FBI. In the LMG test, ionic iron forms chelate (ring) structures with many organic compounds. Often iron-chelates possess catalytic activity in oxidation reactions. One example of such a biological catalyst is peroxidase (12), which decomposes hydrogen peroxide to form free hydroxyl radicals:

H2O2 + Peroxidase --> (OH-)

The heme group of hemoglobin (Hb) possesses a peroxidase-like activity, which may catalyze the breakdown of hydrogen peroxide. In the presence of LMG, Hb catalyzes the oxidation of its colorless form into the blue green oxidized state.

LMG (colorless) + Hb --> Oxidized MG (blue green)

If no other organic oxidizable compound, such as LMG, is present, these radicals decompose to form water and oxygen.

The Takayama Test, an alternative presumptive test, was first suggested by the researcher of the same name in 1912. The test is based on the reaction of pyridine with hemoglobin to form hemochromogen crystals. This test was first notes in the literature by Donogany (7), who also suggested its application to the problem of the legal identification of blood. A number of reagents and/or methods have been suggested, as reviewed by Dilling in 1910 (8), and later by Mahler (9). The method was not introduced into the European literature until 1922 by Strassman (10). The procedure has remained virtually unchanged to the present. (Most of the early work is published in German).

Takayama is a crystal test used for the confirmation of the presence of blood on samples that screened positive with LMG. Hemochromogens are compounds of ferro (iron) protoporphyrin in which the residual valences of a heme complex are occupied by nitrogenous bases (e.g. pyridine).

A more recent paper (13) provides an analysis of conditions affecting the rate of formation of the hemochromogen crystals using oxygen-free reagents. In these experiments, the traditional Takayama reagent is made by combining deionized water (H2O), sodium hydroxide (NaOH), a saturated dextrose (glucose) solution, and pyridine. This reagent is stable for several weeks is kept refrigerated. Low temperatures, however, increase the solubility of gases (such as oxygen) in solution. The aqueous components of Takayama's reagent were rendered oxygen-free by boiling, then cooling in the absence of oxygen. In addition, oxygen 'scavengers' such as dithiothreitol, sodium dithionite, mercaptoethanol, and dithioerythritol, react with and remove dissolved oxygen form solution (11).

Hatch concludes that Takayama's reagent forms hemochromogen crystals from dried bloodstains faster in the absence of oxygen (13). Moreover, heat is not required to initiate this crystallization. Both of these facts make the oxygen free agent more convenient to use. It is also better for the analysis of small, or dilute blood stains, where diffusion losses incident to long incubation times (or heat induced fluid movements) can reduce heme concentrations enough to inhibit of prevent the formation of crystals.

Finally, it may be necessary in certain cases to determine if the body fluid is of human (or higher primate) origin. In the Ouchterlony Precipitin Test, soluble antigens form the sample react with antibodies in a gel medium. Antigen-antibody complexes will form and increase to a size at which point they are no longer soluble and precipitate out in the form of a visible white line in the gel medium. (*Note: The RT-PCR quantification system which is higher primate specific may be used in lieu of OPT when sample size or volume is limited.)

1) Grodsky, M., et al.

"Simplified Preliminary Blood Testing"

J. Criminal Law, Criminology and Police Science, Vol. 42, p 95 (1951)

2) Hunt, A.C., et al.

"The Identification of Human Stains - A Critical Survey"

J. Forensic Medicine, Vol. 7, p.122 (1960)

3) Garner, D.D., et al.

"An Evaluation of Tetramethylbenzadine as a Presumptive Test for Blood"

J. Forensic Sci., Vol. 21, p. 816 (1976)

4) Higaki, R.S., et al.

"Sensitivity, Stability and Specificity of Phenolphthalein as an Indicator Test for Blood"

Canadian Society of Forensic Science Journal, Vol. 9, p. 97 (1976)

5) Cox, M.

"Effect of Fabric Washing on the Presumptive Identification of Bloodstains"

J. Forensic Sci., Vol. 35, p.1335 (1990)

6) Cox. M.

"A Study of the Sensitivity and Specificity of Four Presumptive Tests for Blood"

J. Forensic Sci., Vol. 36, p.1503 (1991)

7) Donogany, Z.

"Darstellung von Hamochromogenkrystllen"

Zentralbaltt fur Physiolgie, Vol. 6, p.629 (1893)

8) Dilling, W.J.

Atlas der Kristalfromen und der Absorpionsbander der Hamochrmogene

T. Enke, Stuttgart (1920)

9) Mahler, K.

"Der Wert der Mikrokristallographischen Proben fur forenischen Blutnachweis"

Duetsche Zeitschift fuer die Gesante Gerichtliche Medizin, Vol. 2, p. 671 (1923)

10) Strassman, G.

"Darstellung der Hamochromogenkristalle nach Takayama"

Muenchener Medizinische Wochenschrift, Vol. 69, p. 116 (1922)

11) Evelyn, K.A., et al.

"Microdetermination of Oxyhemoglobin, Methomoglobin, & Sulfhemoglobin in a Single Sample of Blood"

J. Biol. Chem. Vol. 126, p. 655 (1938)

12) Blake, E.T. and Dillon, D.J.

"Microorganisms and the Presumptive Tests for Blood"

J. Police Science Admin., Vol. 19, p. 395 (1980)

13) Hatch, A.L.

"A Modified Reagent for the Confirmation of Blood"

J. Forensic Sci., Vol. 38, p. 1502 (1993)

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Bloodstain Pattern Analysis

Hemotaphonomy is the study of bloodstains. The focus is on the changes in appearance and size of the cellular components, as well as the characteristics of their cell position and appearance in function of the superficial topography and composition of the substrate. This science was founded in 1992 during cytomorphological researches on red blood cells in bloodstains.

Bloodstain pattern evidence is often present at the scene of a crime of violence. The shape and distribution of blood droplets can often assist in reconstructing how the crime occurred. The shape and appearance of bloodstains and smears can give useful information about the crime. Such considerations have important implications for any investigator who seeks to trace the direction, dropping distance, and angle of impact if a bloodstain. Some of these observations may be summarized as follows:

1) Blood is a very uniform material from an aerodynamic standpoint. Its rheological properties are not affected to any significant degree by age or gender. Blood is shed from a body at constant temperature and is normally exposed to an external environment for a very short time. Thus, atmospheric pressure, temperature and humidity have no measurable effect on its behavior.

2) The diameter of a blood spot is of little or no value in estimating the distance it has fallen after the first 5 or 6 feet. Beyond this distance, the change is too slight to be reliable. Similarly, the edge characteristics (or “scallops”) of blood spots have no meaning or value unless the effect of the target surface is well known.

3) The degree of spatter of a single blood drop depends far more upon the smoothness of the target surface than the distance the drop falls. The more coarse the surface, the more likely the droplet will be ruptured and spatter.

A blotter, for example, will cause a drop to spatter to a considerable extent at a distance of merely 18 inches, whereas a drop falling over 100 feet will not spatter at all if it lands on glass or other smooth surfaces. In general, the harder and less porous the surface, the less spatter results.

The shape of the blood drop itself can reveal significant information. The proportions of the drops can reveal the energy needed to disburse it in those dimensions. The shape of the stain can illustrate the direction in which it was traveling and angle at which it struck the surface. Choosing several stains, and using basic trigonometric functions, enables us to do a three dimensional recreation of the area of origin from which a blood-letting event occurred.

The disruption of a blood drop on impact with a surface is directly related to the texture of the surface. "A smooth surface, such as glass, will provide the recording of a stain with clean edges and shapes of proper geometric proportion. A rough surface, like concrete, will break the surface tension irregularly and generate a star burst, or spinning effect. An experienced analyst is able to use some of the most disrupted stains to recreate the event. Arterial spurts, for example, when compared with the anatomical location of the injury may provide information about the position when the injury was inflicted and any subsequent movement by the injured party. Castoff patterns, or drops that are thrown off of a swinging instrument in the arc of the swing, can illustrate the position of the assailant when swinging a knife, or club.

The shape of a blood drop can reveal a lot about the conditions in which it fell. Given the many variations in what can happen at a crime scene, the experts don't necessarily all agree, but a flexible rule of thumb with a generally smooth and non-porous surface might be the following:

1) If blood falls a short distance--around twelve inches?at a 45-degree angle, the marks tend to be circular.

2) If blood drops fall several feet straight down, the edges may become crenellated, and the farther the distance from the source to the surface, the more pronounced the crenellation.

3) A height of six feet or more can produce small spurts that radiate out from the main drop.

4) If there are many drops less than an eighth of an inch across, with no larger drop, then it may be concluded that the blood spatter probably resulted from an impact.

5) If the source was in motion when the blood leaked or spurted, or if the drops flew through the air and hit an angled surface, the drops generally look like stretched-out exclamation marks. The end of the stain that has the smallest size blob indicates the direction in which the source was moving.

It must be emphasized that blood pattern analysis is a complicated discipline and requires experience with many different situations to learn to do an accurate reading. While any of the above statements may be true, there can also be exceptions, and all interpretations are contingent on the factors that make up the context of the crime scene, most specifically the surface on which the blood made an impact.

All classifications of bloodstain patterns help in the reconstruction of the events. Spatter patterns give the nature of the force and positioning of the victim when shot or bludgeoned. Castoff patterns reveal the positioning and the possible size of the assailant. One also gets an indication of the size of the instrument swung and whether the swinger is left- or right-handed. Transfer patterns and hemorrhage or drip patterns give the direction of movement after blood is shed and can give an indication of timeframes. Arterial spurting can give the position, movement and seriousness of the injury, while 'shadows'---the absence of blood where one would expect to find it---suggest movement or removal of objects and changes to the scene.

Directionality

Spots of blood may be used to determine the directionality of the falling liquid drop that produced them. Their shape frequently permits an estimate as to their velocity and/or impact angle and/or the distance traveled from source to final location (see figure above).

Directionality of a small bloodstain is easily determined, provided that the investigator recognizes the difference between an independent spatter and a castoff or satellite thrown from a larger drop. Small independent stains have a uniform taper resembling a teardrop. The pointed end will always point toward their direction of travel.

Castoff droplets produce a tadpole-like, long narrow stain with a well-defined “head”. The sharper end of these stains always points back towards their origin. Because these satellite spatters travel only a very short distance, the large drop can almost always be traced.

Point of Convergence

The origin of a blood spatter in a two-dimensional configuration can be established by drawing straight lines through the long axis (or length) of several individual bloodstains. The intersection or point of convergence of the lines represents the point from which the blood emanated.

By drawing a line through the long axis (or lengths) of a group of bloodstains (see figure above), the point of convergence can be determined. The convergence point, or point of origin, is the point (or points) where the lines drawn through the group of droplet stains intersect with each other (see figure below).

The area of origin is the area in three-dimensional space where the blood source was located at the time of the bloodletting incident. The area of origin includes the area of convergence with a third dimension in the z direction. Since the z-axis is perpendicular to the floor, the area of origin has three dimensions and is a volume.

The term point of origin has also been accepted to mean the same thing. However it has been argued, there are problems associated to this term. First, a blood source is not a point source. To produce a point source the mechanism would have to be fixed in three-dimensional space and have an aperture where only a single blood droplet is released at a time, with enough energy to create a pattern. This does not seem likely. Second, bodies are dynamic. Aside from the victim physically moving, skin is elastic and bones break. Once a force is applied to the body there will be an equal and opposite reaction to the force applied by the attacker. Part of the force will move the blood source, even a millimetre, and change the origin while it is still producing blood. So the source becomes contained in a three-dimensional volume.

Impact Angle

It is possible to measure the impact angle of blood on a flat surface by measuring the degree of circular distortion of the stain. A drop of blood striking a surface at right angles gives rise to a nearly circular stain. As the angle decreases, the stain becomes elongated in shape. By accurately measuring the length and width of a bloodstain, the impact angle can be calculated using basic trigonometric functions. It can be shown that the sine of the impact angle (lpha):

$\sin \alpha = \left( \frac{w}{l} \right)$

= sine of the angle of impact

= ratio of [width / length ] of droplet

Not every result of BPA will qualify as incontrovertible evidence, but the following are some things a bloodstain pattern analyst may be able to determine conclusively and state as fact:

Location and description of individual stains and patterns,
Mechanism that created the stains,
Direction a blood droplet was traveling (by calculating angles of impact),
Area of origin (location of blow into blood source),
Type of object used in attack (edged, blunt, firearm, etc.),
Minimum number of blows,
The presence of a subject at a scene,
Positioning of the victim, suspect, and objects during events, and
The sequence of events.

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Blood Pressure

Rev. Stephen Hales (1677 -1761) studied the role of fluids and vapors (air, water and blood) in the maintenance of both plant and animal life. He gave accurate accounts of the movements of water in plants, blood in animals, and demonstrated the absorption of air in the circulatory systems of both plants and animals.

Hales is credited for carrying out the first catheterization of the heart of a living animal for a definite experimental purpose. In doing so, he developed the first precise definition of the capacity of a heart. He bled a sheep to death and then led a gun-barrel from the neck vessels into the still-beating heart. Through this, he filled the hollow chambers with molten wax and then measured (from the resultant cast) the volume of the heartbeat and the minute-volume of the heart, which he calculated from the pulse-beat.

In 1711, Hales began his studies on blood pressure. True to his mechanistic views, he carefully measured the blood pressure of three horses and produced the first recorded estimates of blood pressure. Furthermore, he studied the pulse rates of various-sized animals and measured the heart's capacity to pump blood through the pulmonary veins. (Hales also studied the effects of heat, cold, and various drugs on the blood vessels and experimented with animal reflexes.)

In 1733, a 10-foot high vertical glass tube was connected by means of a goose's trachea (which on account of its flexibility served in lieu of rubber tubing) to a brass cannula inserted into the animal's artery. When the blood was permitted to flow from the artery into the vertical tube it rose rapidly (but with fluctuating progress) until it reached a height of 8 feet and 3 inches. It then continued to oscillate above and below this level with each beat of the heart. For his work he received the Copley Prize in 1739. The essence of his work has since been re-published, and can be found under:

Hales, S.
"An Account of Some Hydraulic and Hydrostatic Experiments made on the Blood Vessels of Animals"
J. Clinic. Monit. Comp., Vol. 16, p. 45 (2000)

Best, C.H., Taylor, N.B. (5^th Edition)

Physiological Basis of Medical Practice

Williams and Wilkins Co. (Baltimore, 1950)

High blood pressure is quickly becoming a major problem in our society. According to recent estimates by the national Center for Health Statistics, nearly one in three U.S. adults has high blood pressure, but because there are no symptoms, nearly one-third of these people don't know they have it (NCHS, 2005). In fact, many people have high blood pressure for years without knowing it. Uncontrolled high blood pressure can lead to stroke, heart attack, heart failure or kidney failure. This is why high blood pressure is often called the "silent killer." The only way to tell if you have high blood pressure is to have your blood pressure checked often, which should be done with more frequency than during an annual physical.

Some of the factors that cause high blood pressure are poor or abnormal kidney functionality, problems associated with structural irregularities of blood vessels, and when arteries narrow because of plaque build up. Some physical factors which influence blood pressure include the following:

1) Rate of pumping

In the circulatory system, this rate is called heart rate, the rate at which blood (the fluid) is pumped by the heart. The higher the heart rate, the higher (potentially, assuming no change in stroke volume) the blood pressure.

2) Volume of fluid or blood volume

The more blood present in the body, the higher the rate of blood return to the heart and the resulting cardiac output. There is some relationship between dietary salt intake and increased blood volume, potentially resulting in higher blood pressure, though this varies with the individual and is highly dependent on autonomic nervous system response.

3) Resistance

In the circulatory system, this is the resistance of the blood vessels. The higher the resistance, the higher the blood pressure. Resistance is related to size (the larger the blood vessel, the lower the resistance), as well as the smoothness of the blood vessel walls. Smoothness is reduced by the buildup of fatty deposits on the arterial walls. Substances called vasoconstrictors can reduce the size of blood vessels, thereby increasing blood pressure. Vasodilators (such as nitroglycerin) increase the size of blood vessels, thereby decreasing blood pressure. Some types of omega-6 fatty acids, particularly from olive oil, have been known to increase vascular smoothness.

4) Viscosity

If the blood gets thicker, the result is an increase in blood pressure. Certain medical conditions can change the viscosity of the blood. For instance, low red blood cell concentration, anemia, reduces viscosity, whereas increased red blood cell concentration increases viscosity. Viscosity also increases with blood sugar concentration (visualize pumping syrup). It had been thought that aspirin and related "blood thinner" drugs decreased the viscosity of blood, but studies found that they act by reducing the tendency of the blood to clot instead.

In practice, each individual's autonomic nervous system responds to and regulates all these interacting factors so that, although the above issues are important, the actual blood pressure response of a given individual varies widely because of both split-second and slow-moving responses of the nervous system and end organs. These responses are very effective in changing the variables and resulting blood pressure from moment to moment.

Also, venous pressure is the blood pressure in a vein or in the atria of the heart. It is much less than arterial blood pressure, with common values of 5 mmHg in the right atrium and 8 mmHg in the left atrium. Measurement of pressures in the venous system and the pulmonary vessels plays an important role in intensive care medicine but requires invasive techniques.

*Note: In a human, the normal level of pressure is considerably less than this (5 - 6 feet) but in cases of hypertension may be as high as 13 feet. The pressure varies within fairly narrow limits in different warm-blooded species, and there is little or no relationship between the size of an animal and the height of its blood pressure.

The pressure in a rat's arteries is actually somewhat higher than that in human vessels and the arterial pressure of a mouse is probably little different from that of an elephant. The blood pressure is, in general, higher in birds than in mammals whereas that of cold-blooded animals is only ~ 1/3.

Relative levels in mm Hg:
Frog: 43
Turtle: 44
Mouse: 113
Robin: 118
Rat: 187
Canary: 220

Aronson, S.M.
"The Determination of Blood Pressure"
R.I. Med., Vol. 76, p. 217 (1993)
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Blood Transfusion

The volume of blood in typical human being is approximately 4 - 5 liters for women and 5 - 6 liters for men, depending on individual body weight. This accounts for about 8% of the total body weight. A blood loss of 1.5 liters is required to cause physical incapacitation. A 40 % blood volume loss is required to produce irreversible shock -- or death.

Blood transfusion has become an increasingly controversial issue. Recent studies have indicated that ICU and overall mortality rates and organ dysfunction rates were significantly higher in critically ill patients who received red blood cell (RBC) transfusions. RBC transfusion and supplementation with iron and/or vitamins are the usual therapies if the hemoglobin concentration drops below a critical level. In this case, several factors such as age, cardiac performance, expected blood loss, and sometimes even religion influence the decision to transfuse a patient.

Several authors point out that there are no general guidelines for the optimal hemoglobin or vol % RBCs in ICU patients. While a low hemoglobin concentration impairs oxygen availability to the tissues, a high percentage of RBCs may be unfavorable from a rheological point of view (fluid physics: high viscosity).

In one study, the effect of stored blood transfusion on oxygen delivery in patients with sepsis (bacteria in the bloodstream) was studied. Not only is there little evidence that blood transfusion augments systematic oxygen delivery in septic patients, a recent study demonstrated the significant relationship of RBC transfusion to post-operative bacterial infection.

The kidney plays a central role in RBC production in adults. The kidneys detect low levels of oxygen in the blood and release erythropoietin (EPO), a glycol-protein hormone which circulates to the bone marrow and stimulates the production of RBC's. An analysis of the relationship between EPO dose and the increase in red blood cell production has demonstrated a good correlation. Blood cell expansion occurs by day 3 during EPO treatment of non-anemic patients who are iron replete. Despite normal iron stores, some patients have difficulty providing sufficient iron for the necessary RBC production. The maximum acute erythropoietic response in EPO treated patients with measurable storage iron have been obtained by using a synthetic protein which is a combination of EPO and glycose sugar.

In the production of a new RBC substitute ("Polyheme") for artificial oxygenation, Northfield Labs bursts open red blood cells in giant metal vats, freeing the hemoglobin molecules inside. The downside is that free hemoglobin molecules are known to be dangerous -- seeping into the walls of blood vessels and causing inflammation. The company links the molecules to each other by a simple polymerization process, claiming that this removes the hemoglobin's toxicity. But after 10 out of the 81 patients who received the blood substitute suffered heart attacks within 7 days (and 2 of those died) there would appear to be some doubt.

McLelland, E.R. Ed.
"Shock and Blood Transfusion"
Selected Readings in General Surgery
Vol. 32 (January, 2006)