In the medical field, physical terms have been used to explain how the pressures control the body fluid distribution, such as happen on the circulatory and respiratory systems. Pressure is a continuous force determined by some circumstances: Archimedes’ principle talks about how a submerged object can float (physical law of buoyancy). While Pascal’s law explains how pressure is distributed equally throughout a fluid. By last, ideal hydrodynamics is the study of the forces acting on or exerted by fluids.
Last updated: 22 Apr, 2022
Pressure is defined as a continuous physical force that is exerted on or against an object by something that comes in contact with it. It can be described as the force per unit area. This concept is important in medicine, especially when dealing with blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure (cardiovascular system) and with airflow (respiratory system).
Imagine a beach ball full of air. The air inside keeps the ball inflated. Inside the ball, collisions take place against the wall of the ball that apply force. Only those collisions that are perpendicular to the wall have an effect. The air molecules moving along the sidewalls will not influence the balloon staying inflated.
The pressure formula is stated as P = F1 / A where P is the pressure, F1 is the force and A is the area involved. Looking at the units, we get:
(P) = kg / m-s2 = N / m2 = Pascals (Pa)
Pressure is measured in the Pascal units.
When you are standing on Earth, pressure is exerted on you but you don’t feel it. This pressure is referred to as atmospheric pressure Atmospheric pressure The pressure at any point in an atmosphere due solely to the weight of the atmospheric gases above the point concerned. Ventilation: Mechanics of Breathing or Fair (the force that air exerts on a person). The reason you don’t feel atmospheric pressure Atmospheric pressure The pressure at any point in an atmosphere due solely to the weight of the atmospheric gases above the point concerned. Ventilation: Mechanics of Breathing is due to the water and air pressure inside of you pushing outwards. The balance of pressure doesn’t allow a person to feel the force of the air above. Atmospheric pressure Atmospheric pressure The pressure at any point in an atmosphere due solely to the weight of the atmospheric gases above the point concerned. Ventilation: Mechanics of Breathing can be measured in atmospheres or Pascals:
1 atm = 100,000 Pa = 100kPa
When you go underwater, there are two weights acting on you from above: the atmospheric pressure Atmospheric pressure The pressure at any point in an atmosphere due solely to the weight of the atmospheric gases above the point concerned. Ventilation: Mechanics of Breathing and the water pressure. The water pressure is referred to as hydrostatic pressure Hydrostatic pressure The pressure due to the weight of fluid. Edema or Gauge pressure. It is denoted as P = ρ g h, where ρ is the density of the liquid medium, g is the gravitational force, and h is the height of water above the person. So, the total pressure exerted on a person underwater is:
Ptotal = ρ g h + Patm
Hydrostatic pressure Hydrostatic pressure The pressure due to the weight of fluid. Edema
Image by Lecturio.The famous Greek mathematician Archimedes stated that anybody, completely or partially submerged in a fluid at rest, is acted upon by an upward (buoyant) force. This force is equal to the weight of the fluid that the body displaces. Buoyancy occurs because the pressure of the water underneath is greater than the pressure of the water above. When measuring the displaced water, the calculation is based on the volume of the object that was submerged. The pressure acting upward is FB = buoyant force and the pressure acting downward is Fg = gravitational force.
Archimedes’ principle
Image by Lecturio.An object will float if:
FB > Fg
mwater g > mobject g
ρwater V > ρobject V
ρwater > ρobject
Thus buoyancy FB = mdisplaced water g
How much of the object will emerge from the water?
If an object is floating, it will emerge from the water until:
FB = Fg
mwater displaced = mobject
ρwater Vsubmerged = ρobject Vobject
Therefore, for floating objects: Vsubmerged / Vobject = ρobject / ρwater
French scientist Blaise Pascal discovered an interesting phenomenon we now know as Pascal’s law or Pascal’s principle. It states that pressure is equally distributed throughout a fluid. In a fluid at rest in a closed container, a pressure change in one part is transmitted without loss to every part of the fluid and to the walls of the container.
In order to determine the pressures and forces associated with Pascal’s Law, the following must be observed:
Since the pressure is equally distributed throughout a fluid, P1 = P2.
Since pressure is related to force and area, then the following relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship occurs:
F1 / A1 = F2 / A2, thus there is equal force per unit area.
Pascal’s law is useful in machinery that uses hydraulics (the science involving the mechanical properties and uses of liquids). In these scenarios, one can gain a mechanical advantage by making one area greater than another, such that:
F2 = F1 (A2 / A1)
Pascal’s law
Image by Lecturio.Hydrodynamics is the branch of science concerned with forces acting on or exerted by fluids and the forces acting on solid bodies, immersed and in motion. Hydrodynamics contains six different parts: ideal flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure, flow rate Flow rate maximum flow the ventilator will deliver a set tidal volume in liters per minute Invasive Mechanical Ventilation, continuity, Bernoulli’s principle Bernoulli’S Principle Wheezing, Venturi effect Venturi effect High-velocity blood flow through the left ventricular outflow tract during systole creates negative pressure, pulling the mitral valve leaflets toward the ventricular septum and pressing the leaflets against it. Hypertrophic Cardiomyopathy, and Pitot tube.
Ideal flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure deals with an ideal fluid— one that is incompressible, not viscous, and laminar without turbulence. Liquids do not have the ability to be compressible, unlike gases. The flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure in liquids occurs due to the lack of viscosity. The ideal flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure must be laminar and orderly without turbulence or chaos. In general, laminar flow Laminar flow Vascular Resistance, Flow, and Mean Arterial Pressure occurs at lower velocities and is smooth, not rough.
The flow rate Flow rate maximum flow the ventilator will deliver a set tidal volume in liters per minute Invasive Mechanical Ventilation is the amount of fluid that flows at a given time. It is calculated as follows:
Flow rate Flow rate maximum flow the ventilator will deliver a set tidal volume in liters per minute Invasive Mechanical Ventilation = Volume per second
Q = Volume / Time = (Area x Distance) / Time
Thus, the flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure Q = Area x Velocity (Q = A v) since velocity = distance / time
When a fluid is in motion, it must move in such a way that mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast is conserved. If the flow rate Flow rate maximum flow the ventilator will deliver a set tidal volume in liters per minute Invasive Mechanical Ventilation is too low, a vacuum situation will occur. If the flow rate Flow rate maximum flow the ventilator will deliver a set tidal volume in liters per minute Invasive Mechanical Ventilation is too high, overlap will occur.
Q1 = Q2 and A1 v1 = A2 v2
Daniel Bernoulli explained an important principle in fluid dynamics. His principle stated that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy. At any portion along the tube, energy is conserved.
P1 + ½ ρ v12 + ρ g h1 = P2 + ½ ρ v22 + ρ g h2
The Venturi effect Venturi effect High-velocity blood flow through the left ventricular outflow tract during systole creates negative pressure, pulling the mitral valve leaflets toward the ventricular septum and pressing the leaflets against it. Hypertrophic Cardiomyopathy is the reduction in fluid pressure that results when a fluid flows through a constricted section of a pipe. The constricted area will have a higher velocity but a lower pressure in a given system. In fluid dynamics, a fluid’s velocity must increase as it passes through a narrowing or constricted section of pipe (according to the principle of mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast continuity).
However, the fluid’s static pressure must decrease according to the principle of conservation of mechanical energy ( Bernoulli’s principle Bernoulli’S Principle Wheezing, stated above). Thus, in a constricted section of pipe, fluid will have a higher velocity and lower pressure; and in a wider section of pipe, the fluid will have higher pressure and lower velocity.
A pitot tube is a pressure measuring instrument used to measure fluid flow velocity Flow velocity Vascular Resistance, Flow, and Mean Arterial Pressure. The basic setup consists of a tube pointing directly into the fluid flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure. As this tube contains fluid, pressure can be measured. The moving fluid is brought to rest (stagnates) as there is no outlet to allow flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure to continue. This pressure is the stagnation pressure, or total pressure, of the fluid.
Using Bernoulli’s principle Bernoulli’S Principle Wheezing, we know that stagnation pressure = static pressure + dynamic pressure.
Ptotal = Pstatic + ½ ρ v2
Solving for velocity, v = √( (2 (Ptotal – Pstatic)) / ρ)
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