Pressure measurement
Paul Grimshaw, Michael Cole, Adrian Burden, Neil Fowler in Instant Notes in Sport and Exercise Biomechanics, 2019
Another common unit used to describe pressure is the pascal (Pa), which represents the pressure created by a 1 N force acting on a 1 m2 area. As 1 pascal represents a relatively low force spread over a large area, it is more common to report kilopascals (kPa), where 1 kPa is equivalent to 1000 pascals. An alternative to reporting pressure in pascals is to compare the measured pressure with the ambient pressure caused by the Earth’s atmosphere. The pressure caused by the weight of the air in the Earth’s atmosphere is referred to as atmospheric or barometric pressure. Imagine a column with a cross-sectional area of 1 m2 that extends from the Earth’s surface to the edge of the atmosphere. This column will contain a certain number of air particles that will collectively create a force due to their weight, their density and their distance from the Earth’s surface. The standard atmosphere is a unit of pressure that represents one normal atmosphere and is defined as: 1 Atmosphere = 101325 Pa or 101.325 kPa
Physiological Mechanisms for the Action of Pulmonary Surfactant
Jacques R. Bourbon in Pulmonary Surfactant: Biochemical, Functional, Regulatory, and Clinical Concepts, 2019
When surfactants act at liquid surfaces, the molecules locate at the liquid-air interface with their polar groups in the aqueous phase and their nonpolar groups orientated toward the air, as shown in Figure 1a. This location of an orientated monolayer reduces surface energy and, hence, the surface tension (γ) which can be measured directly by a number of methods described later. Traditionally, monolayers of surfactant are studied on a Langmuir trough, as illustrated in Figure 3. When the surface area is changed, the surfactant molecules tend to reequilibrate on the long term with those distributed as micelles in the liquid phase — known as the aqueous hypophase — eventually reaching an equilibrium surface tension. On the short term, they undergo compression, exerting a surface pressure (Π) resisting further compression as the surface area is reduced, just as gas molecules in a cylinder resist compression by a piston. The surface pressure is thus related to the surface pressure as:
Cortical Deafness (Plus Other Central Hearing Disorders)
Alexander R. Toftness in Incredible Consequences of Brain Injury, 2023
The ability to interpret sound is absolutely incredible from a physical standpoint. You've probably heard the term “sound wave” before, but let's take a moment to explore it. In order to hear something, you first need a vibrating object. In the case of a guitar, it's the string wiggling back and forth. Next, the guitar string smacks air molecules around in a particular pattern, causing those air molecules to bump into other molecules which continue the pattern. This causes the molecules to bunch up close together in some places and spread out away from each other in the places in between, creating pressure. Because the molecules are moving, there is change in pressure over time. When this whole assembly of moving pressure thwaps up against the inside of the ear, what has essentially happened is that the vibration from the guitar has jumped into the tiny bones inside of your head, specifically the inner ear bones called ossicles. Your ear bones then turn that vibration into waves of fluid which travel into a circular structure in your inner ear called the cochlea. The cochlea converts the fluid waves into tiny amounts of electricity depending on the change in pressure over time. All of that is the easy part of hearing sound.
Airflow through the supraglottis during inspiration
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
L. Reid, M. Hayatdavoodi, S. Majumdar
Figure 10(a) shows the pressure force acting on the regions of interest presented in Figure 2. The pressure force is obtained by p is the pressure, and A is the surface area. The pressure forces in all hypopharyngeal subdivisions are positive at Q = 30 L/min then become negative at higher flow rates Q > 120 L/min in the UH and MH. The LH region exhibits a positive normal force at all flow rates in the LH, which peaks at 180 L/min with an average pressure of 84 Pa over the region. The high-pressure observed in the LH, occurs due to collision of the epiglottic jet against the downstream wall before it is redirected anteriorly through laryngeal inlet. The maximal negative forces were observed in the ULA and URA regions at all flow rates, shown in Figure 10(a). These regions include the lateral margins of the epiglottic tip where peak velocities are observed in Figure 6. In Figure 10(a), the URP and ULP regions demonstrate inconsistency in their normal force values as higher flow rates are applied to the inlet. The URP has relatively low positive normal force at flow rates up to Q = 180 L/min, but at Q = 240 L/min drops significantly and becomes negative. The normal force of the ULP region is positive at low flow rates, which become negative at Q > 120 L/min and reaches a peak negative value at Q = 180 L/min.
Applications of computational fluid dynamics to congenital heart diseases: a practical review for cardiovascular professionals
Published in Expert Review of Cardiovascular Therapy, 2021
Gianluca Rigatelli, Claudio Chiastra, Giancarlo Pennati, Gabriele Dubini, Francesco Migliavacca, Marco Zuin
The main flow phenomena in this field that can be characterized by CFD and the corresponding hemodynamic quantities of interest are reported in Table 1. The hemodynamic parameters derived from both pressure and velocity fields are analyzed. The pressure in the vessels and chambers is expressed in pascal (Pa) or mmHg, according to the International System of Units. The vorticity magnitude (expressed in 1/s) is defined as the magnitude of the vorticity vector; the vorticity vector is a measure of the rotation of a fluid element as it moves through the domain and it may be representative of pathological conditions when far from the baseline [14]. The wall shear stress (WSS) (expressed in Pa), is defined as the frictional force of the flowing blood along the wall surface per unit area. WSS values deflecting from a baseline value are indexes of abnormalities leading to thrombus formation, abnormal vessel modeling and pathological remodeling, arterial damage [15]. Another important quantity to be evaluated is the power (energy per unit time, measured in watt) dissipated when the blood flows in arteries. Minimizing this loss of energy when designing or re-routing the blood in surgical connections is an index of a good streamlining of the blood [4].
Adduction-Induced Strain on the Optic Nerve in Primary Open Angle Glaucoma at Normal Intraocular Pressure
Published in Current Eye Research, 2021
Robert A. Clark, Soh Youn Suh, Joseph Caprioli, JoAnn A. Giaconi, Kouros Nouri-Mahdavi, Simon K. Law, Laura Bonelli, Anne L. Coleman, Joseph L. Demer
The rationale for the current study, and its relationship to primary open angle glaucoma (POAG), requires context of some biomechanical definitions. Tensile force applied to any material produces elongation; in biomechanics, this elongation is termed “strain.” A given tensile force applied to a highly elastic, soft material produces a larger strain (relative elongation, often expressed in percent of original length) than that force applied to a stiffer, less elastic material that consequently experiences less strain. Conversely, less tensile force is required for a given elongation applied to the highly elastic, soft material, while greater tensile force is required when applied to the stiffer, less elastic material. In biomechanics, “stress” is defined as force divided by the cross-sectional area of the piece of material acted upon. Stress has the same units as hydrostatic pressure. For example, the common intraocular pressure (IOP) unit of 1 mmHg is the equivalent of 133 Pascal, a metric unit defined as 1 Newton (kg-m/s2) force per square meter. Thus, IOP is a stress applied to the ON from inside the eye, while adduction applies a physically identical type of stress to the ON, but from outside the eye.
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