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Concepts in Human Factors Engineering (Part 7 of 11)
By Dennis R Andrews PhD, PSP, CECD (ExpertPages member profile page)
The transportation system carries the much needed material and nutrients throughout the body. This transportation system is known as the blood and lymphatic systems. The blood system carries oxygen from the lungs to areas of the body to metabolize and energize the body. Nutrients from the food we eat are also circulated to the cells for use as an energy source. The byproduct of the metabolism is carbon dioxide, water and heat. We previously discussed the need to expel carbon dioxide and heat as a major function to keep the body healthy.
|Concepts in Human Factors Engineering is a series containing eleven articles:|
Blood is often said to be the fluid of life. Blood comprises approximately 10 percent of the total body fluid volume. Blood volume must be maintained in order to stabilize the blood pressure. If a large open wound or a blood vessel were to rupture blood loss would be rapid and large. The normal person can loose approximately 10 percent of the total volume of their blood fluid without the possibility of critical stress. Approximately 20 percent of the total volume would begin to seriously affect the function of the body in terms of breathing and blood pressure. As one approaches 40 percent or above critical and fatal affects will appear to stabilize the body and regain control blood must be infused immediately.
As we know there are four blood types A, B, AB and O. It is important to know your blood type and some people carry their blood type in their wallet or on a chain around the neck with other valuable health information. The blood types are not all interchangeable and can have devastating effects if there is a mix-up. Plasma in the blood carries away unwanted byproducts. Red blood cells are the actual vehicles which carrying the oxygen throughout the body.
The lymphatic system consists of capillaries found in most tissues. This system is totally independent and closed from the blood transportation system. The lymphatic system has capillaries, which are thin enough to allow large protein molecules to enter. When stretched the system is much like fluid under high-pressure. The pump for this system is created as the lymph is stretched and contracted the fluid can also be moved by the surrounding vessels near the muscle. The pump volume varies considerably due to its purpose, which is to drain excessive fluid protein, which may accumulate in the tissue. Swelling of the lower limbs is an indication of the lack of movement over long periods of time, such as a long movie or plane ride.
Muscles and vital organs require a different blood supply and large demands require the transportation system, also known as the circulatory system for our purpose, to function efficiently and properly. The circulatory system is a closed system within the human body activated by the heart which could be considered as two fluid pumps, one for incoming fluid and one for outgoing, also known as ventricles. The output of the heart pump is affected by the number of contractions and the pressure from these contractions. The volume of the pump can be termed in units called minute volume. It is said that the cardiac output is five liters per minute for an adult at rest. It is crucial to remember that a stronger healthy heart can pump more volume than is usually needed. This is one reason why as we get older our stamina drops and we get out of breath from moderate exertion, which in our earlier years would have been an easy exercise. As blood and oxygen is pumped through the system it can permeate the muscle tissue and consequently the pressure will drop. The difference in pressure in the artery and vein aid in the transportation of the volume of blood. Veins transport blood to the heart and arteries transport blood away from heart. Blood flow is directly correlated with the strength of the heart pump, physical properties of the blood such as viscosity and the condition of our pipes or blood vessels. In other words blood flow depends on strength of the blood being pushed and the friction against this force.
In summary the blood flow is totally dependent upon the condition of the heart, which depends upon the force required, pressure, viscosity of the blood and the condition of the arteries and veins. When one or all of these are under stress the blood pressure will rise and may be life-threatening if the rise is to rapid or the pressure is too great. We know that during work the blood flow will be much greater than when we are at rest. The condition of the working parts must be in top condition given our age for maximum efficiency and work. It is estimated that the blood supply to the muscle increases fivefold during heavy exercise or work. Ironically the blood supply to the kidneys and the digestive tract is reduced 6/7 fold. Oxygen, which must be carried throughout the body by the blood, increases thirty fold from rest do to heavy exercise. Heart rate or beats per minute range from 60/78 at rest and increases three times during heavy exercise. Cardiac output is a measurement of the volume of blood per minute; the volume would increase during strenuous exercise. Stroke volume is the amount of blood exiting the left side of the heart during each ventricle contraction this can increase three times for heavy work. Blood pressure is the reading relating to the arteries at rest a good reading would be 70 over 120. The first reading is the diastole and second reading is the systole. Systole is the beginning of the heart muscle contraction and diastole is the beginning of its relaxation.