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Wednesday, February 26, 2014

Physic's Lexicon

1.  Laminar flow:  Also called streamline flow.  Fluid flows in streamline patterns.  The flow is straight, orderly and smooth.  There is no swirling of the fluid.  Molecular movement is smooth and straight.  fluid runs in straight lines parallel to the pipe walls.  Pressure through the tube is therefore based on Poiseulle's Law.  Normal breathing is often considered laminar flow.  While taking in a breathing treatment, a smooth laminar flow is essential for equal distribution of medicine through the air passages

2.  Poiseulle's Law:  States that the pressure needed for fluid to flow through a tube is directly proportional to the viscosity of the fluid, the length of the tube, and the rate of flow.  If the fluid is thick, if the tube is long, or if the tube is long, or if the tube radius is decreased higher pressures will be needed*.  Bronchospasm, increased secretions, increased viscosity of secretions, and tumors all might change the bronchiole tubes in such a way as to require greater pressures during ventilation.

3.  Turbulant flow:  The flow is not laminar.  The fluid through a tube eddies and swirls.  Molecular movement is chaotic.  Poiseulle's Law is no longer under effect during this type of flow.  It also includes chaotic changes in pressure and velocity.  Inhaling rapidly can cause turbulent flow, and so can crying, laughing, sneezing, etc.  In this way, turbulent flow results in poor distribution of medicine along the air passages.  It causes much of the medicine to impact in the larger airways instead of getting to the deeper air passages where it's needed.

4.  Transitional flow:  Also called tracheobronchial flow.  This is a mixture of both laminar and turbulent flow.  Pressure is based on laminar and turbulent gradients.  An example of this type of flow is where the air passages fork, such as at the corina.  When smooth laminar flow suddenly hits the corina it becomes turbulent.

5.  Toricelli's Law:  It was created by 17th century physician Evalgelista Toricelli.  He postulated that the speed of fluid through an opening is directly relative to the height of fluid above the opening.  For example, he believed if a tiny hole was made in the bottom of a cup, and the cup was filled to the top with water, that water would pour from the hole at the same speed as it would if it were poured at the height of the top of the cup. This was an early variety of the Bernoulii principle

6.  Bernoulli principle:  It was created by 18th century mathematician and physicist Daniel Bernoulli.  When fluid flow horizontally, as the velocity of the fluid increases the static pressure will decrease.  A couple examples will help you visualize this effect.  1)  The shape of an airplane wing is such that air traveling over the wing must flow faster than air under the wing.  The drop in pressure over the wing causes lift.  2)  Nebulizers allow air to flow through a narrowing in a tube.  This narrow passage causes that air to increase in velocity, and this causes a drop in pressure that causes fluid from the cup to be drawn into the flow.  This causes the mist that the patient inhales.

7.  Venturi principle:  Similar to the Bernoulli effect, or another variation of it.  It was developed in the 18th century by Giovanni Venturi.  If you insert an opening just distal to a narrowing in the tube, the drop in pressure caused by the increased velocity of the fluid through the narrowing will cause fluid to be entrained into the flow.  The design of the venuri (the opening) will allow for the amount of fluid entrained to remain constant.  This principle is applied in Venturi mask to assure a patient gets an accurate and desired FiO2.


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