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Needle valves are usually used in flow-metering applications, especially when a constant, calibrated, low flow rate must be maintained for some time, such as the idle fuel flow in a carburettor. Note that the float valve of a carburettor (controlling the fuel level within the carburettor) is not a needle valve, although it is commonly described ...
A hollow needle is advanced through the skin until blood is aspirated. The color of the blood and the rate of its flow help distinguish it from arterial blood (suggesting that an artery has been accidentally punctured). Within North America and Europe, ultrasound use now represents the gold standard for central venous access and skills, with ...
Often expressed in cm/s. This value is inversely related to the total cross-sectional area of the blood vessel and also differs per cross-section, because in normal condition the blood flow has laminar characteristics. For this reason, the blood flow velocity is the fastest in the middle of the vessel and slowest at the vessel wall.
The orientation of the needles takes the normal flow of the blood into account. The "arterial" needle draws blood from the "upstream" location while the "venous" needle returns blood "downstream". This sequence prevents partial recycling of the same blood through the dialysis machine, which would lead to less effective treatment.
Blood is a non-Newtonian fluid. However, often the non-Newtonian effect is very small due to various reasons. Thus, it is important to know about the blood rheology. One of the characteristics of blood that affects the work required to cause the blood to flow through the arteries is the viscosity of blood.
Standard catheter. 1. The catheter itself is composed of (a) a tip for insertion into the vein, (b) wings for manual handling and securing the catheter with adhesives, (c) a valve to allow injection of drugs with a syringe, (d) an end which allows connection to an intravenous infusion line, and capping in between uses.
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Blood viscosity is a measure of the resistance of blood to flow. It can also be described as the thickness and stickiness of blood. This biophysical property makes it a critical determinant of friction against the vessel walls, the rate of venous return, the work required for the heart to pump blood, and how much oxygen is transported to tissues and organs.
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