Gas pressure, Volume and Flow Measurement

2011 ◽  
Author(s):  
Patrick Magee ◽  
Mark Tooley
Keyword(s):  
Airway Pressure ◽  
Gas Flow ◽  
Intrathoracic Pressure ◽  
Wheatstone Bridge ◽  
External Pressure ◽  
Electrical Circuit ◽  
Gas Pressure ◽  
Positive Pressure ◽  
Electrical Analogy ◽  
Metal Bellows

The physics of pressure, flow and the gas laws have been discussed in Chapter 7 in relation to the behaviour of gas and vapour. This section will focus on the physical principles of the measurement of gas pressure, volume and flow. Unlike a liquid, a gas is compressible and the relationship between pressure, volume and flow depends on the resistance to gas flow (or impedance if there is a frequency dependence between pressure and flow in alternating flow, see Chapter 4 for the electrical analogy of this) in conduits (bronchi, anaesthetic tubing); it also depends on the compliance of structures being filled and emptied (alveoli, reservoir bags, tubing or bellows). Normal breathing occurs by muscular expansion of the thorax, thus lowering the intrathoracic pressure, allowing air or anaesthetic gas to flow towards the alveoli down a pressure gradient from atmospheric pressure. When positive pressure ventilation occurs, gas is ‘pushed’ under pressure into the alveoli. Depending on the exact relationship between the ventilator and the lungs, different relationships exist between airway pressure (rather than alveolar pressure, which cannot easily be measured) and gas flow and volume. Gas pressure measurement devices were traditionally in the form of an aneroid barometer, a hollow metal bellows calibrated for pressure and temperature, which contracts when the external pressure on it increases, and expands when it decreases. The movement is linked to a pointer and indicator dial. It is often more convenient to make the device in the shape of part of a circular section, but the principle is the same. This is what the Bourdon gauge, which commonly measures pressure in gas cylinders, looks like. The detection of movement of the diaphragm of an aneroid barometer can take several forms. The movement can either be linked via a direct mechanical linkage to a pointer, or diaphragm movement can be linked to a capacitative or inductive element in an electrical circuit, such as a Wheatstone bridge. Airway pressure during spontaneous breathing or artificial ventilation is low. The preferred units of measurement are cm H2O and the range of values is between −20 and +20 cmH2O. The aneroid barometer to measure this will therefore be of light construction, using thin copper for the bellows material.

scholarly journals Evaluation of a Humidified Nasal High-Flow Oxygen System, Using Oxygraphy, Capnography and Measurement of Upper Airway Pressures

2011 ◽  
Vol 39 (6) ◽  
pp. 1103-1110 ◽  
Author(s):  
J. E. Ritchie ◽  
A. B. Williams ◽  
C. Gerard ◽  
H. Hockey
Keyword(s):  
Healthy Volunteers ◽  
Airway Pressure ◽  
Gas Flow ◽  
Air Entrainment ◽  
High Flow ◽  
Positive Pressure ◽  
Mean Airway Pressure ◽  
Flow Rates ◽  
Oxygen Fraction ◽  
Airway Pressures

In this study, we evaluated the performance of a humidified nasal high-flow system (Optiflow™, Fisher and Paykel Healthcare) by measuring delivered FiO2 and airway pressures. Oxygraphy, capnography and measurement of airway pressures were performed through a hypopharyngeal catheter in healthy volunteers receiving Optiflow™ humidified nasal high flow therapy at rest and with exercise. The study was conducted in a non-clinical experimental setting. Ten healthy volunteers completed the study after giving informed written consent. Participants received a delivered oxygen fraction of 0.60 with gas flow rates of 10, 20, 30, 40 and 50 l/minute in random order. FiO2, FEO2, FECO2 and airway pressures were measured. Calculation of FiO2 from FEO2 and FECO2 was later performed. Calculated FiO2 approached 0.60 as gas flow rates increased above 30 l/minute during nose breathing at rest. High peak inspiratory flow rates with exercise were associated with increased air entrainment. Hypopharyngeal pressure increased with increasing delivered gas flow rate. At 50 l/minute the system delivered a mean airway pressure of up to 7.1 cmH2O. We believe that the high gas flow rates delivered by this system enable an accurate inspired oxygen fraction to be delivered. The positive mean airway pressure created by the high flow increases the efficacy of this system and may serve as a bridge to formal positive pressure systems.

Determinants of gas flow through a bronchopleural fistula

1989 ◽  
Vol 67 (4) ◽  
pp. 1591-1596 ◽  
Author(s):  
M. C. Walsh ◽  
W. A. Carlo
Keyword(s):  
Airway Pressure ◽  
Gas Flow ◽  
Bronchopleural Fistula ◽  
Peak Inspiratory Pressure ◽  
Intrathoracic Pressure ◽  
Transpulmonary Pressure ◽  
Inspiratory Pressure ◽  
Positive End Expiratory Pressure ◽  
Inspiratory Time ◽  
Mean Airway Pressure

To assess the determinants of bronchopleural fistula (BPF) flow, we used a surgically created BPF to study 15 anesthetized intubated mechanically ventilated New Zealand White rabbits. Mean airway pressure and intrathoracic pressure were evaluated independently. Mean airway pressure was varied (8, 10, or 12 cmH2O) by independent manipulations of either peak inspiratory pressure, positive end-expiratory pressure, or inspiratory time. Intrathoracic pressure was varied from 0 to -40 cmH2O. BPF flow varied directly with mean airway pressure (P less than 0.001). However, at constant mean airway pressure, BPF flow was not influenced independently by changes in peak inspiratory pressure, positive end-expiratory pressure, or inspiratory time. Resistance of the BPF increased as intrathoracic pressure became more negative. Despite increased resistance, BPF flow also increased. BPF resistance was constant over the range of mean airway (P less than 0.01) pressures investigated. Our data document the influence of mean airway pressure and intrathoracic pressure on BPF flow and suggest that manipulations which reduce transpulmonary pressure will decrease BPF flow.

scholarly journals The Effect of Sustained Positive Airway Pressure on Derived Cardiac Output in Children

1994 ◽  
Vol 22 (1) ◽  
pp. 30-34 ◽  
Author(s):  
J. B. Clough ◽  
A. W. Duncan ◽  
P. D. Sly
Keyword(s):  
Cardiac Output ◽  
Stroke Volume ◽  
Airway Pressure ◽  
Positive Airway Pressure ◽  
Intrathoracic Pressure ◽  
Continuous Variable ◽  
Positive Pressure ◽  
Age Related ◽  
Pulsed Wave Doppler ◽  
Doppler Techniques

It is well established that the improvement in gas exchange that occurs with positive pressure ventilation may come at the expense of a decrease in cardiac output and oxygen delivery. Clinical observation suggests that children and infants may be more resistant than adults to the falls in cardiac output induced by positive airway pressure. The aims of this study were to quantify the effect of a sustained increase in intrathoracic pressure on cardiac output and stroke volume, and to determine whether this change is age-related. Twenty-eight children undergoing general anaesthesia were studied. Cardiac output was derived using pulsed wave Doppler techniques at four different levels of sustained positive airway pressure, and stroke volume was calculated. The relationship between airway pressure and both cardiac output and stroke volume was examined using a general linear model which included age as a continuous variable. Cardiac output decreased with increasing levels of sustained positive airway pressure (P=0.001). The fall in SV for a given airway pressure increased with increasing age (P=0.02). The mechanisms responsible for the increase of the magnitude of the fall in stroke volume with age remain to be elucidated.

scholarly journals Self-Consistent Modeling of Electrode Motion in a Model Circuit Breaker

2019 ◽  
Vol 6 (1) ◽  
pp. 99-102
Author(s):  
R. Fuchs
Keyword(s):  
Gas Flow ◽  
Low Voltage ◽  
Circuit Breaker ◽  
Computational Grid ◽  
Electrical Circuit ◽  
Gas Pressure ◽  
Circuit Breakers ◽  
Self Consistent ◽  
Coupled Solution ◽  
Model Circuit

<span lang="EN-US">Numerical simulations of low-voltage circuit breakers require a coupled solution of gas flow, electromagnetism, electrical circuit, and other aspects. Including electrode motion is challenging because the computational grid is deformed and data is to be exchanged among dedicated solvers. A central issue is to keep them synchronized. This is addressed with a single framework that allows for a continuously morphing grid and accounting for the cumulative effects of mechanics, Lorentz force, and gas pressure. It is shown that gas pressure has negligible effect.</span>

Nasal Intermittent Positive Pressure Ventilation versus Continuous Positive Airway Pressure and Apnea of Prematurity: A Systematic Review and Meta-Analysis

2021 ◽  
Author(s):  
Bayane Sabsabi ◽  
Ava Harrison ◽  
Laura Banfield ◽  
Amit Mukerji
Keyword(s):  
Systematic Review ◽  
Continuous Positive Airway Pressure ◽  
Airway Pressure ◽  
Primary Outcome ◽  
Positive Pressure Ventilation ◽  
Positive Airway Pressure ◽  
Meta Analysis ◽  
Intermittent Positive Pressure Ventilation ◽  
Positive Pressure ◽  
Apnea Of Prematurity

Objective The study aimed to systematically review and analyze the impact of nasal intermittent positive pressure ventilation (NIPPV) versus continuous positive airway pressure (CPAP) on apnea of prematurity (AOP) in preterm neonates. Study Design In this systematic review and meta-analysis, experimental studies enrolling preterm infants comparing NIPPV (synchronized, nonsynchronized, and bi-level) and CPAP (all types) were searched in multiple databases and screened for the assessment of AOP. Primary outcome was AOP frequency per hour (as defined by authors of included studies). Results Out of 4,980 articles identified, 18 studies were included with eight studies contributing to the primary outcome. All studies had a high risk of bias, with significant heterogeneity in definition and measurement of AOP. There was no difference in AOPs per hour between NIPPV versus CPAP (weighted mean difference = −0.19; 95% confidence interval [CI]: −0.76 to 0.37; eight studies, 456 patients). However, in a post hoc analysis evaluating the presence of any AOP (over varying time periods), the pooled odds ratio (OR) was lower with NIPPV (OR: 0.46; 95% CI: 0.32–0.67; 10 studies, 872 patients). Conclusion NIPPV was not associated with decrease in AOP frequency, although demonstrated lower odds of developing any AOP. However, definite recommendations cannot be made based on the quality of the published evidence. Key Points

Care of the Neonate on Nasal Continuous Positive Airway Pressure: A Bedside Guide

2018 ◽  
Vol 37 (1) ◽  
pp. 24-32
Author(s):  
Jennifer M. Guay ◽  
Dru Carvi ◽  
Deborah A. Raines ◽  
Wendy A. Luce
Keyword(s):  
Continuous Positive Airway Pressure ◽  
Respiratory Distress ◽  
Parent Education ◽  
Airway Pressure ◽  
Positive Airway Pressure ◽  
Clinical Manifestations ◽  
Neonatal Morbidity ◽  
Intermittent Positive Pressure Ventilation ◽  
Positive Pressure ◽  
Team Approach

Respiratory distress continues to be a major cause of neonatal morbidity. Current neonatal practice recommends the use of nasal continuous positive airway pressure (nCPAP) in the immediate resuscitation and continued support of neonates of all gestations with clinical manifestations of respiratory distress. Despite the many short- and long-term benefits of nCPAP, many neonatal care units have met resistance in its routine use. Although there have been numerous recent publications investigating the use and outcomes of various modes of nCPAP delivery, surfactant administration, mechanical ventilation, and other forms of noninvasive respiratory support (high-flow nasal cannula, nasal intermittent positive pressure ventilation), there has been a relative lack of publications addressing the practical bedside care of infants managed on nCPAP. Effective use of nCPAP requires a coordinated interprofessional team approach, ongoing assessment of the neonate, troubleshooting the nCPAP circuit, and parent education.

Pressure Assisted Sintering of an Aluminium Alloy

2009 ◽  
Vol 618-619 ◽  
pp. 627-630
Author(s):  
Stephen J. Bonner ◽  
Graham B. Schaffer ◽  
Ji Yong Yao
Keyword(s):  
Aluminium Alloy ◽  
Gas Flow ◽  
Isothermal Holding ◽  
Horizontal Tube ◽  
Elevated Pressure ◽  
Nitrogen Pressure ◽  
Gas Pressure ◽  
Densification Rate ◽  
Conventional Press ◽  
Gas Pressures

An aluminium alloy was sintered using a conventional press and sinter process, at various gas pressures, to observe the effect of sintering gas pressure on the densification rate. Compacts of aluminium alloy 2712 (Al-3.8Cu-1Mg-0.7Si-0.1Sn) were prepared from elemental powders and sintered in a horizontal tube furnace under nitrogen or argon at 590°C for up to 60 minutes, and air cooled. The gas flow was adjusted to achieve specific gas pressures in the furnace. It has been found that increasing the nitrogen pressure at the start of the isothermal holding stage to 160kPa increased the densification rate compared to standard atmospheric pressure sintering. Increasing the nitrogen pressure further, up to 600kPa, had no additional benefit. The densification rate was increased significantly by increasing the gas pressure to 600kPa during both heating and isothermal holding. Under argon the elevated pressure did not increase the densification rate. Results seem to suggest that the beneficial effect of the elevated pressure on the rate of densification is related to nitride formation.

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