Volume-time profile during relaxed expiration in the normal dog

1985 ◽  
Vol 59 (3) ◽  
pp. 732-737 ◽  
Author(s):  
J. H. Bates ◽  
M. Decramer ◽  
D. Chartrand ◽  
W. A. Zin ◽  
A. Boddener ◽  
...  
Keyword(s):  
Respiratory System ◽  
Time Course ◽  
Elastic Equilibrium ◽  
Esophageal Pressure ◽  
Time Profile ◽  
Time Interval ◽  
Opening Pressure ◽  
Lung Inflation ◽  
Volume Comparison ◽  
Airway Opening

Airway opening pressure, esophageal pressure, and flow were obtained during relaxed expirations in two normal anesthetized paralyzed dogs. The signal-to-noise ratio in the flow signals was greatly increased by averaging 10 different signals obtained with the same lung inflation volume. Numerical integration of an averaged flow signal then yielded the time course of the volume of the respiratory system above functional residual capacity (the elastic equilibrium volume). Comparison of volume signals obtained with different inflation volumes suggests that the resistance of the respiratory system increases with flow. The flow-volume and semilog volume curves show that expiration is induced by two apparently separate mechanisms: one causes emptying of most of the expired volume over a time interval of much less than 1 s, whereas the other contributes a relatively small amount to the expired volume over a significantly longer time (greater than or equal to 1 s). We postulate the first mechanism to be due to that of the respiratory system behaving like a single unit, with an elastance that is slightly volume dependent, emptying through a single airway which has a resistance that increases with flow. From the nature of airway opening pressure and esophageal pressure measured after occlusion in midexpiration, we conclude that the second mechanism is due to the viscoelastic properties (i.e., creep) of the respiratory system. The properties are manifest mainly in the chest wall.

Measurement of pleural pressure at low and high frequencies in normal rabbits

1987 ◽  
Vol 63 (3) ◽  
pp. 1142-1146 ◽  
Author(s):  
D. A. Chartrand ◽  
T. H. Ye ◽  
J. M. Maarek ◽  
H. K. Chang
Keyword(s):  
Body Surface ◽  
Pressure Transducer ◽  
Esophageal Pressure ◽  
Pleural Pressure ◽  
Opening Pressure ◽  
High Frequencies ◽  
Occlusion Test ◽  
Airway Opening ◽  
Catheter Tip ◽  
The Relationship

In eight tracheotomized adult rabbits placed in the supine position, we employed a catheter-tip piezoresistive pressure transducer to measure esophageal pressure (Pes) and assessed the validity of taking the changes in Pes to be the changes in pleural pressure (Ppl). We applied an occlusion test in which the tracheal cannula was occluded during either spontaneous inspiratory efforts or body surface oscillations ranging from 3 to 50 Hz. The relationship between Pes and airway opening pressure (Pao) was recorded. In all instances, the changes in Pes and Pao were virtually identical in both amplitude and phase. We conclude that, as evaluated by the occlusion test, a catheter-tip pressure transducer placed in the esophagus of rabbits can give adequate estimation of local pleural changes up to at least 50 Hz.

The effect of lung inflation on the inspiratory action of the canine parasternal intercostals

2006 ◽  
Vol 100 (3) ◽  
pp. 858-863 ◽  
Author(s):  
Dimitri Leduc ◽  
André De Troyer
Keyword(s):  
Functional Residual Capacity ◽  
Negative Impact ◽  
Chronic Obstructive ◽  
Electromyographic Activity ◽  
Opening Pressure ◽  
Obstructive Pulmonary Disease ◽  
Lung Inflation ◽  
Airway Opening ◽  
Residual Capacity ◽  
Phrenic Nerves

Inflation induces a marked decrease in the lung-expanding ability of the diaphragm, but its effect on the parasternal intercostal muscles is uncertain. To assess this effect, the phrenic nerves and the external intercostals were severed in anesthetized, vagotomized dogs, such that the parasternal intercostals were the only muscles active during inspiration, and the endotracheal tube was occluded at different lung volumes. Although the inspiratory electromyographic activity recorded from the muscles was constant, the change in airway opening pressure decreased with inflation from −7.2 ± 0.6 cmH2O at functional residual capacity to −2.2 ± 0.2 cmH2O at 20-cmH2O transrespiratory pressure ( P < 0.001). The inspiratory cranial displacement of the ribs remained virtually unchanged, and the inspiratory caudal displacement of the sternum decreased moderately. However, the inspiratory outward rib displacement decreased markedly and continuously; at 20 cmH2O, this displacement was only 23 ± 2% of the value at functional residual capacity. Calculations based on this alteration yielded substantial decreases in the change in airway opening pressure. It is concluded that, in the dog, 1) inflation affects adversely the lung-expanding actions of both the parasternal intercostals and the diaphragm; and 2) the adverse effect of inflation on the parasternal intercostals is primarily related to the alteration in the kinematics of the ribs. As a corollary, it is likely that hyperinflation also has a negative impact on the parasternal intercostals in patients with chronic obstructive pulmonary disease.

Pliometric activity of inspiratory muscles: maximal pressure-flow curves

1987 ◽  
Vol 62 (1) ◽  
pp. 322-327 ◽  
Author(s):  
G. P. Topulos ◽  
M. B. Reid ◽  
D. E. Leith
Keyword(s):  
Respiratory System ◽  
Flow Characteristics ◽  
Esophageal Pressure ◽  
Flow Curves ◽  
Reduced Pressure ◽  
Pressure Flow ◽  
Inspiratory Muscles ◽  
Airway Opening ◽  
Maximal Pressure ◽  
Force Velocity

We tested the hypothesis that inspiratory muscles, like other skeletal muscles, would exert greater force under pliometric conditions (being lengthened while active) than under isometric or miometric (active shortening) conditions. Maximal inspiratory pressure-flow curves of the respiratory system are analogous to the force-velocity curves for isolated muscle (Agostoni and Fenn, J. Appl. Physiol. 15:349–353, 1960). We measured esophageal pressure (Pes) and plethysmographic flow (V) at relaxation volume of the respiratory system in six trained subjects inspiring maximally through graded resistors (miometric), against a closed airway (isometric), and while constant expiratory flows were forced by a reduced pressure source at the airway opening (pliometric). Pes varied inversely with V and this trend continued into the pliometric range. In addition we found that the pressure-flow characteristics of the rib cage and of the abdomen are similar to those for the chest wall as a whole. The mechanical and energetic advantages of muscle activity under pliometric conditions may be available to some inspiratory muscles in both normal and pathological situations.

scholarly journals In Vitro Estimation of Relative Compliance during High-Frequency Oscillatory Ventilation

2021 ◽  
Vol 11 (3) ◽  
pp. 899
Author(s):  
Jan Matejka ◽  
Martin Rozanek ◽  
Jakub Rafl ◽  
Petr Kudrna ◽  
Karel Roubik
Keyword(s):  
Physical Model ◽  
Respiratory System ◽  
High Frequency ◽  
High Frequency Oscillatory Ventilation ◽  
Opening Pressure ◽  
Respiratory System Mechanics ◽  
Oscillatory Ventilation ◽  
Airway Opening ◽  
High Frequency Oscillatory

High-frequency oscillatory ventilation (HFOV), which uses a small tidal volume and a high respiratory rate, is considered a type of protective lung ventilation that can be beneficial for certain patients. A disadvantage of HFOV is its limited monitoring of lung mechanics, which complicates its settings and optimal adjustment. Recent studies have shown that respiratory system reactance (Xrs) could be a promising parameter in the evaluation of respiratory system mechanics in HFOV. The aim of this study was to verify in vitro that a change in respiratory system mechanics during HFOV can be monitored by evaluating Xrs. We built an experimental system consisting of a 3100B high-frequency oscillatory ventilator, a physical model of the respiratory system with constant compliance, and a system for pressure and flow measurements. During the experiment, models of different constant compliance were connected to HFOV, and Xrs was derived from the impedance of the physical model that was calculated from the spectral density of airway opening pressure and spectral cross-power density of gas flow and airway opening pressure. The calculated Xrs changed with the change of compliance of the physical model of the respiratory system. This method enabled monitoring of the trend in the respiratory system compliance during HFOV, and has the potential to optimize the mean pressure setting in HFOV in clinical practice.

Effect of lung lavage on the stress relaxation of the respiratory system

1993 ◽  
Vol 75 (4) ◽  
pp. 1536-1544 ◽  
Author(s):  
J. J. Perez Fontan
Keyword(s):  
Stress Relaxation ◽  
Respiratory System ◽  
Time Course ◽  
Lung Lavage ◽  
Elastic Recoil ◽  
Lung Inflation ◽  
Pressure Losses ◽  
Elastic Stresses ◽  
Double Exponential ◽  
Before And After

To test the hypothesis that lowering the concentrations of surfactant molecules at the gas-liquid interface increases viscoelastic dissipation in the lungs, the amplitude and time course of stress relaxation were quantified before and after lavage of the lungs with warm saline in five newborn and five 8-wk-old anesthetized piglets. Stress relaxation was separated from other dissipative pressure losses by fitting the pressure decays that follow airway occlusions performed during a period of constant inspiratory flow to a double-exponential regression. The amplitude of stress relaxation (defined by the term of the regression with the longest time constant) related linearly to the changes in respiratory system volume and elastic recoil preceding the occlusions both before and after the lavage. Lung lavage increased the slope of both relationships without altering the time course of the relaxations. In addition to being consistent with the proposed hypothesis, these results suggest that viscoelastic pressure losses remain linked to the elastic stresses generated during lung inflation, as proposed by Fredberg and Stamenovic's structural dumping theory (J. Appl. Physiol. 67: 2408#x2013;2419, 1989).

Effects of surface tension and viscosity on airway reopening

1990 ◽  
Vol 69 (1) ◽  
pp. 74-85 ◽  
Author(s):  
D. P. Gaver ◽  
R. W. Samsel ◽  
J. Solway
Keyword(s):  
Surface Tension ◽  
Fluid Viscosity ◽  
Opening Pressure ◽  
Viscous Forces ◽  
Considerable Portion ◽  
Airway Opening ◽  
Wall Compliance ◽  
Large Opening ◽  
Surface Tension Forces ◽  
The Relationship

We studied airway opening in a benchtop model intended to mimic bronchial walls held in apposition by airway lining fluid. We measured the relationship between the airway opening velocity (U) and the applied airway opening pressure in thin-walled polyethylene tubes of different radii (R) using lining fluids of different surface tensions (gamma) and viscosities (mu). Axial wall tension (T) was applied to modify the apparent wall compliance characteristics, and the lining film thickness (H) was varied. Increasing mu or gamma or decreasing R or T led to an increase in the airway opening pressures. The effect of H depended on T: when T was small, opening pressures increased slightly as H was decreased; when T was large, opening pressure was independent of H. Using dimensional analysis, we found that the relative importance of viscous and surface tension forces depends on the capillary number (Ca = microU/gamma). When Ca is small, the opening pressure is approximately 8 gamma/R and acts as an apparent “yield pressure” that must be exceeded before airway opening can begin. When Ca is large (Ca greater than 0.5), viscous forces add appreciably to the overall opening pressures. Based on these results, predictions of airway opening times suggest that airway closure can persist through a considerable portion of inspiration when lining fluid viscosity or surface tension are elevated.

Flow and volume dependence of expiratory resistance in anesthetized cats

1989 ◽  
Vol 67 (3) ◽  
pp. 1013-1019 ◽  
Author(s):  
M. Skaburskis ◽  
F. Shardonofsky ◽  
J. Milic-Emili
Keyword(s):  
Respiratory System ◽  
Volume Flow ◽  
Flow Profile ◽  
Pressure Flow ◽  
Lung Inflation ◽  
Mechanically Ventilated ◽  
Volume Dependence ◽  
Flow Dependence ◽  
Lung Deflation ◽  
Respiratory Muscle Activity

In five anesthetized paralyzed cats, mechanically ventilated with tidal volumes of 36–48 ml, the isovolume pressure-flow relationships of the lung and respiratory system were studied. The expiratory pressure was altered between 3 and -12 cmH2O for single tidal expirations. Isovolume pressure-flow plots for three lung volumes showed that the resistive pressure-flow relationships were curvilinear in all cases, fitting Rohrer's equation: P = K1V + K2V2, where P is the resistive pressure loss, K1 and K2 are Rohrer's coefficients, and V is flow. Values of K1 and K2 declined with lung inflation, consistent with the volume dependence of pulmonary (RL) and respiratory system resistances (Rrs). During lung deflation against atmospheric pressure, RL and Rrs tended to remain constant through most of expiration, resulting in a nearly linear volume-flow relationship. In the presence of a fixed respiratory system elastance, the shape of the volume-flow profile depended on the balance between the volume and the flow dependence of RL and Rrs. However, the flow dependence of RL and Rrs indicates that their measured values will be affected by all factors that modify expiratory flow, e.g., respiratory system elastance, equipment resistance, and the presence of respiratory muscle activity.

A model for the relation between respiratory neural and mechanical outputs. III. Validation

1981 ◽  
Vol 51 (4) ◽  
pp. 990-1001 ◽  
Author(s):  
M. Younes ◽  
W. Riddle ◽  
J. Polacheck
Keyword(s):  
Respiratory System ◽  
Pressure Wave ◽  
Time Course ◽  
Present Report ◽  
Occlusion Pressure ◽  
Single Breath ◽  
Wave Forms ◽  
Inspiratory Activity ◽  
Good Agreement

In the preceding two communications we described a model for the relation between respiratory neural and mechanical outputs. In the present report we test the accuracy of the model in predicting volume and flow from occlusion pressure wave forms, and vice versa. We performed single-breath airway occlusions in 21 unconscious subjects and determined the time course of occlusion pressure. We also measured the passive properties of the respiratory system. The time course of volume and flow was predicted from the occlusion pressure wave forms, and the results were compared with the spontaneous breaths immediately preceding occlusion. Inspiratory duration, shape and amplitude of occlusion-pressure wave forms, and the passive properties of the respiratory system varied widely among subjects. There was good agreement between predicted and observed values in all cases. Except for some prolongation of inspiration (Hering-Breuer reflex), diaphragmatic activity did not change during occlusion. Since occlusion pressure is proportional to inspiratory activity, we conclude that the model described provides a good approximation of the relation between inspiratory activity and spirometric output.

Airway pressures in an asymmetrically branched airway model of the dog respiratory system

1984 ◽  
Vol 57 (4) ◽  
pp. 1222-1230 ◽  
Author(s):  
Andrew C. Jackson ◽  
Mehrdad Tabrizi ◽  
Michael I. Kotlikoff ◽  
Jon R. Voss
Keyword(s):  
Respiratory System ◽  
High Frequency ◽  
High Frequency Ventilation ◽  
Tissue Properties ◽  
Pressure Distributions ◽  
Lumped Parameter ◽  
Airway Opening ◽  
Frequency Ventilation ◽  
Lung Periphery ◽  
Airway Model

A computer model of the mechanical properties of the dog respiratory system based on the asymmetrically branching airway model of Horsfield et al. (11) is described. The peripheral ends of this airway model were terminated by a lumped-parameter impedance representing gas compression in the alveoli, and lung and chest wall tissue properties were derived from measurements made in this laboratory. Using this model we predicted the respiratory system impedance and the distribution of pressures along the airways in the dog lung. Predicted total respiratory system impedances for frequencies between 4 and 64 Hz at three lung volumes were found to compare quite closely to measured impedances in dogs. Serial pressure distributions were found to be frequency-dependent and to result in higher pressures in the lung periphery than at the airway opening at some frequencies. The implications of this fading for high-frequency ventilation are discussed. impedance; high-frequency ventilation; central airway resistance; respiratory system resistance; airway pressure distribution; distribution of ventilation Submitted on November 14, 1983 Accepted on May 8, 1984

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