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.

Using Conventional Infant Ventilators at Unconventional Rates

PEDIATRICS ◽  
1984 ◽  
Vol 74 (4) ◽  
pp. 487-492 ◽  
Author(s):  
Stephen J. Boros ◽  
Dennis R. Bing ◽  
Mark C. Mammel ◽  
Erik Hagen ◽  
Margaret J. Gordon
Keyword(s):  
Tidal Volume ◽  
Airway Pressure ◽  
Important Determinant ◽  
Peak Inspiratory Pressure ◽  
Lung Compliance ◽  
Minute Volume ◽  
Inspiratory Pressure ◽  
Positive End Expiratory Pressure ◽  
Inspiratory Time ◽  
Pressure Monitor

The effect of progressive increases in ventilator rate on delivered tidal and minute volumes, and the effect of changing peak inspiratory pressure (Pmax), positive end-expiratory pressure (PEEP), and inspiration to expiration (I:E) ratio at different ventilator rates were examined. Five different continuous-flow, time-cycled, pressure-preset infant ventilators were studied using a pneumotachograph, an airway pressure monitor, and a lung simulator. As rates increased from 10 to 150 breaths per minute, tidal volume stayed constant until 25 to 30 breaths per minute; then progessively decreased. In all, tidal volume began to decrease when proximal airway pressure waves lost inspiratory pressure plateaus. As rates increased, minute volume increased until 75 breaths per minute, then leveled off, then decreased. Substituting helium for O2 increased the ventilator rate at which this minute volume plateau effect occurred. Increasing peak inspiratory pressure consistently increased tidal volume. Increasing positive end-expiratory pressure decreased tidal volume. At rates less than 75 breaths per minute, inspiratory time (inspiration to expiration ratio) had little effect on delivered volume. At rates greater than 75 breaths per minute, inspiratory time became an important determinant of minute volume. For any given combination of lung compliance and airway resistance: (1) there is a maximum ventilator rate beyond which tidal volume progressively decreases and another maximum ventilator rate beyond which minute volume progressively decreases; (2) at slower rates, delivered volumes are determined primarily by changes in proximal airway pressures; (3) at very rapid rates, inspiratory time becomes a key determinant of delivered volume.

Effects of Alterations of Inspiratory and Expiratory Pressures and lnspiratory/Expiratory Ratios on Mean Airway Pressure, Blood Gases, and Intracranial Pressure

PEDIATRICS ◽  
1981 ◽  
Vol 67 (4) ◽  
pp. 474-481
Author(s):  
A. R. Stewart ◽  
N. N. Finer ◽  
K. L. Peters
Keyword(s):  
Intracranial Pressure ◽  
Significant Relationship ◽  
Airway Pressure ◽  
Peak Inspiratory Pressure ◽  
Blood Gases ◽  
Hyaline Membrane Disease ◽  
Positive End Expiratory Pressure ◽  
Mean Airway Pressure ◽  
Hyaline Membrane ◽  
End Tidal

Twenty neonates requiring mechanical ventilation for respiratory failure, including 13 with hyaline membrane disease, were studied to assess the effects of alterations in ventilator settings on mean airway pressure (MAP), blood gases, and intracranial pressure (ICP). The study involved random alterations in peak inspiratory pressure (PIP), positive end-expiratory pressure (PEEP), and inspiratory/expiratory ratio while MAP, Pao2, ICP, and end-tidal Pco2 were continuously monitored. The results showed a significant relationship between MAP and Pao2 that was expressed as the change in Pao2 per millimeter of mercury change in MAP (ΔPa02/ΔMAP) with a mean ΔPao2/ΔMAP of 4.92. The ΔPao2/ΔMAP was highest for changes in PEEP (6.08), followed by PIP (5.07), and inspiratory/expiratory ratio (1.9). There was a significant relationship between alterations in PEEP and PIP vs Paco2 and pH. Increases in PEEP and decreases in PIP resulted in an elevated Paco2 and a lowered pH, and decreases in PEEP and increases in PIP resulted in a decreased Paco2 and an elevated pH. There was no significant relationship between MAP and ICP, but there was a significant association between ΔICP and ΔPaco2 during alterations in PIP (r = .64, P <.001). Increases in PEEP will lead to the greatest increase in Pao2 per change in MAP, followed by increases in PIP and inspiratory /expiratory ratio using a pressure-limited ventilator.

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.

Effect of the Ti/Te ratio on mean intratracheal pressure in high-frequency oscillatory ventilation

1998 ◽  
Vol 84 (5) ◽  
pp. 1520-1527 ◽  
Author(s):  
Ulrich Thome ◽  
Frank Pohlandt
Keyword(s):  
High Frequency ◽  
Airway Pressure ◽  
High Frequency Oscillatory Ventilation ◽  
Inspiratory Time ◽  
Mean Airway Pressure ◽  
Air Trapping ◽  
Oscillatory Ventilation ◽  
Mean Pressure ◽  
Oscillation Frequencies ◽  
High Frequency Oscillatory

In high-frequency oscillatory ventilation (HFOV), an adequate mean airway pressure is crucial for successful ventilation and optimal gas exchange, but air trapping cannot be detected by the usual measurement at the y piece. Intratracheal pressures produced by the high-frequency oscillators HFV-Infantstar (IS), Babylog 8000 (BL), and the SensorMedics 3100A (SM) [the latter with either 30% (SM30) or 50% (SM50) inspiratory time] were investigated in four anesthetized tracheotomized female piglets that were 1 day old and weighed 1.6–1.9 kg (mean 1.76 kg). The endotracheal tube was repeatedly clamped while the piglets were ventilated with an oscillation frequency of 10 Hz, and the airway pressure distal of the clamp was recorded as a measure of average intrapulmonary pressure during oscillation. Clamping resulted in a significant decrease of mean airway pressure when the piglets were ventilated with SM30(−0.86 cmH2O), BL (−0.66 cmH2O), and IS (−0.71 cmH2O), but airway pressure increased by a mean of 0.76 cmH2O with SM50. Intratracheal pressure, when measured by a catheter pressure transducer at various oscillation frequencies, was lower than at the y piece by 0.4–0.9 cmH2O (SM30), 0.3–3 cmH2O (BL), and 1–4.7 cmH2O (IS) but was 0.4–0.7 cmH2O higher with SM50. We conclude that the inspiratory-to-expiratory time (Ti/Te) ratio influences the intratracheal and intrapulmonary pressures in HFOV and may sustain a mean pressure gradient between the y piece and the trachea. A Ti/Te ratio < 1:1 may be useful to avoid air trapping when HFOV is used.

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.

Vaporized Perfluorohexane Attenuates Ventilator-induced Lung Injury in Isolated, Perfused Rabbit Lungs

2005 ◽  
Vol 102 (3) ◽  
pp. 597-605 ◽  
Author(s):  
Marcelo Gama de Abreu ◽  
Beate Wilmink ◽  
Matthias Hübler ◽  
Thea Koch
Keyword(s):  
Lung Injury ◽  
Therapy Group ◽  
Peak Inspiratory Pressure ◽  
Thromboxane B2 ◽  
Inspiratory Pressure ◽  
Control Group ◽  
Positive End Expiratory Pressure ◽  
Lung Weight ◽  
Ventilator Induced Lung Injury ◽  
Perfusate Flow

Background The authors tested the hypothesis that administration of vaporized perfluorohexane may attenuate ventilator-induced lung injury. Methods In isolated, perfused rabbit lungs, airway pressure-versus-time curves were recorded. At baseline, peak inspiratory pressure and positive end-expiratory pressure of mechanically ventilated lungs were set to obtain straight pressure-versus-time curves in both the lower and upper ranges, which are associated with less collapse and overdistension, respectively. After that, peak inspiratory pressure and positive end-expiratory pressure were set at 30 cm H2O and 0, respectively, and animals were randomly assigned to one of two groups: (1) simultaneous administration of 14% perfluorohexane vapor in room air (n = 7) and (2) control group-ventilation with room air (n = 7). After 20 min of cycling collapse and overdistension, tidal volume and positive end-expiratory pressure were set back to baseline levels, administration of perfluorohexane in the therapy group was stopped, and mechanical ventilation was continued for up to 60 min. Lung weight, mean pulmonary artery pressure, and concentration of thromboxane B2 in the perfusate were measured. In addition, the distribution of pulmonary perfusate flow was assessed by using fluorescent-labeled microspheres. Results Significantly higher peak inspiratory values developed in control lungs than in lungs treated with perfluorohexane. In addition, upper ranges of pressure-versus-time curves were closer to straight lines in the perfluorohexane group. Lung weight, mean pulmonary arterial pressure, and release of thromboxane B2 were significantly higher in controls than in perfluorohexane-treated lungs. Also, redistribution of pulmonary perfusate flow from caudal to cranial zones was less important in the treatment group. Conclusion The authors conclude that the administration of perfluorohexane vapor attenuates the development of ventilator-induced lung injury in isolated, perfused rabbit lungs.

Delivery of positive end-expiratory pressure to preterm lambs using common resuscitation devices

2018 ◽  
Vol 104 (1) ◽  
pp. F83-F88 ◽  
Author(s):  
Marta Thio ◽  
Jennifer A Dawson ◽  
Kelly J Crossley ◽  
Timothy J Moss ◽  
Charles C Roehr ◽  
...  
Keyword(s):  
Gas Flow ◽  
Inflation Rate ◽  
Neonatal Resuscitation ◽  
Peak Inspiratory Pressure ◽  
Limited Information ◽  
Positive End Expiratory Pressure ◽  
Inflation Rates ◽  
Range Difference ◽  
The Mean

BackgroundIn neonatal resuscitation, a ventilation device providing positive end-expiratory pressure (PEEP) is recommended. There is limited information about PEEP delivery in vivo, using different models of self-inflating bag (SIB) at different inflation rates and PEEP settings.MethodsWe compared PEEP delivery to intubated preterm lambs using four commonly available models of paired SIBs and PEEP valves, with a T-piece, with gas flow of 8 L/min. Peak inspiratory pressure inflations of 30 cmH2O, combined with set PEEP of 5, 7 and 10 cmH2O, were delivered at rates of 20, 40 and 60/min. These combinations were repeated without gas flow. We measured mean PEEP, maximum and minimum PEEP, and its difference (PEEP reduction).ResultsA total of 3288 inflations were analysed. The mean PEEP delivered by all SIBs was lower than set PEEP (P<0.001), although some differences were <0.5 cmH2O. In 55% of combinations, the presence of gas flow resulted in increased PEEP delivery (range difference 0.3–2 cmH2O). The mean PEEP was closer to set PEEP with faster inflation rates and higher set PEEPs. The mean (SD) PEEP reduction was 3.9 (1.6), 8.2 (1.8), 2 (0.6) and 1.1 (0.6) cmH2O with the four SIBs, whereas it was 0.5 (0.2) cmH2O with the T-piece.ConclusionsPEEP delivery with SIBs depends on the set PEEP, inflation rate, device model and gas flow. At recommended inflation rates of 60/min, some devices can deliver PEEP close to the set level, although the reduction in PEEP makes some SIBs potentially less effective for lung recruitment than a T-piece.

Optimal Mean Airway Pressure during High-frequency Oscillation

2001 ◽  
Vol 94 (5) ◽  
pp. 862-869 ◽  
Author(s):  
Sven Goddon ◽  
Yuji Fujino ◽  
Jonathan M. Hromi ◽  
Robert M. Kacmarek
Keyword(s):  
Acute Respiratory Distress Syndrome ◽  
Respiratory Distress Syndrome ◽  
High Frequency ◽  
Airway Pressure ◽  
Distress Syndrome ◽  
High Frequency Oscillation ◽  
Positive End Expiratory Pressure ◽  
Mean Airway Pressure ◽  
Frequency Oscillation ◽  
Initial Injury

Background A number of groups have recommended setting positive end-expiratory pressure during conventional mechanical ventilation in adults at 2 cm H2O above the lower corner pressure (P(CL)) of the inspiratory pressure-volume (P-V) curve of the respiratory system. No equivalent recommendations for the setting of the mean airway pressure (Paw) during high-frequency oscillation (HFO) exist. The authors questioned if the Paw resulting in the best oxygenation without hemodynamic compromise during HFO is related to the static P-V curve in a large animal model of acute respiratory distress syndrome. Methods Saline lung lavage was performed in seven sheep (28+/-5 kg, mean +/- SD) until the arterial oxygen partial pressure/fraction of inspired oxygen ratio decreased to 85+/-27 mmHg at a positive end-expiratory pressure of 5 cm H2O (initial injury). The PCL (20+/-1 cm H2O) on the inflation limb and the point of maximum curvature change (PMC; 26+/-1 cm H2O) on the deflation limb of the static P-V curve were determined. The sheep were subjected to four 1-h cycles of HFO at different levels of Paw (P(CL) + 2, + 6, + 10, + 14 cm H2O), applied in random order. Each cycle was preceded by a recruitment maneuver at a sustained Paw of 50 cm H2O for 60 s. Results High-frequency oscillation with a Paw of 6 cm H2O above P(CL) (P(CL) + 6) resulted in a significant improvement in oxygenation (P &lt; 0.01 vs. initial injury). No further improvement in oxygenation was observed with higher Paw, but cardiac output decreased, pulmonary vascular resistance increased, and oxygen delivery decreased at Paw greater than P(CL) + 6. The PMC on the deflation limb of the P-V curve was equal to the P(CL) + 6 (r = 0.77, P &lt; 0.05). Conclusion In this model of acute respiratory distress syndrome, optimal Paw during HFO is equal to P(CL) + 6, which correlates with the PMC.

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