Stress relaxation of the respiratory system in developing piglets

1992 ◽  
Vol 73 (4) ◽  
pp. 1297-1309 ◽  
Author(s):  
J. J. Perez Fontan ◽  
A. O. Ray ◽  
T. R. Oxland
Keyword(s):  
Stress Relaxation ◽  
Chest Wall ◽  
Respiratory System ◽  
Time Course ◽  
Structural Changes ◽  
Somatic Growth ◽  
Viscoelastic Behavior ◽  
Elastic Recoil ◽  
Pressure Losses ◽  
Double Exponential

To characterize the effect of postnatal development on the viscoelastic behavior of the respiratory system, we quantified the amplitude and time course of stress relaxation in the lungs and chest wall of seven newborn and eight 8-wk-old anesthetized piglets. Stress relaxation was distinguished from other dissipative pressure losses by performing airway occlusions at various constant inspiratory flows and fitting the pressure decays that ensue during the occlusions to a double-exponential function. We found that the amplitude of stress relaxation related linearly to the increase in elastic recoil (and, by extension, in the volume) of the lungs, chest wall, and respiratory system during the inflations preceding the occlusions. On the average, the slope of this relationship was 38–44% lower in the 8-wk-old than in the newborn piglets for the lungs and was not different for the chest wall. The time course of stress relaxation, expressed as a time constant, was not influenced by age. Our results indicate that respiratory system viscoelasticity is sensitive to the geometric and structural changes experienced by the lungs during the period of rapid somatic growth that follow birth in most mammals.

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).

Mechanics of respiratory system in healthy anesthetized humans with emphasis on viscoelastic properties

1993 ◽  
Vol 75 (1) ◽  
pp. 132-140 ◽  
Author(s):  
B. Jonson ◽  
L. Beydon ◽  
K. Brauer ◽  
C. Mansson ◽  
S. Valind ◽  
...  
Keyword(s):  
Respiratory System ◽  
Driving Force ◽  
Viscoelastic Behavior ◽  
Elastic Recoil ◽  
Inspiratory Flow Rate ◽  
Static Compliance ◽  
Viscoelastic System ◽  
Flow Interruption ◽  
In Series ◽  
Flow Dependency

The classic model of the respiratory system (RS) is comprised of a Newtonian resistor in series with a capacitor and a viscoelastic unit including a resistor and a capacitor. The flow interruption technique has often been used to study the viscoelastic behavior under constant inspiratory flow rate. To study the viscoelastic behavior of the RS during complete respiratory cycles and to quantify viscoelastic resistance (Rve) and compliance (Cve) under unrestrained conditions, we developed an iterative technique based on a differential equation. We, as others, assumed Rve and Cve to be constant, which concords with volume and flow dependency of model behavior. During inspiration Newtonian resistance (R) was independent of flow and volume. During expiration R increased. Static elastic recoil showed no significant hysteresis. The viscoelastic behavior of the RS was in accordance with the model. The magnitude of Rve was 3.7 +/- 0.7 cmH2O.l-1 x s, i.e., two times R. Cve was 0.23 +/- 0.051 l/cmH2O, i.e., four times static compliance. The viscoelastic time constant, i.e., Cve.Rve, was 0.82 +/- 0.11s. The work dissipated against the viscoelastic system was 0.62 +/- 0.13 cmH2O x 1 for a breath of 0.56 liter, corresponding to 32% of the total energy loss within the RS. Viscoelastic recoil contributed as a driving force during the initial part of expiration.

Chest wall and respiratory system mechanics in cats: effects of flow and volume

1988 ◽  
Vol 64 (6) ◽  
pp. 2636-2646 ◽  
Author(s):  
T. Kochi ◽  
S. Okubo ◽  
W. A. Zin ◽  
J. Milic-Emili
Keyword(s):  
Chest Wall ◽  
Time Constant ◽  
Flow Rate ◽  
Respiratory System ◽  
Flow Resistance ◽  
Stress Adaptation ◽  
Inspiratory Flow Rate ◽  
Intrinsic Resistance ◽  
Pressure Losses ◽  
Airway Occlusion

The effects of inspiratory flow rate and inflation volume on the resistive properties of the chest wall were investigated in six anesthetized paralyzed cats by use of the technique of rapid airway occlusion during constant flow inflation. This allowed measurement of the intrinsic resistance (Rw,min) and overall dynamic inspiratory impedance (Rw,max), which includes the additional pressure losses due to time constant inequalities within the chest wall tissues and/or stress adaptation. These results, together with our previous data pertaining to the lung (Kochi et al., J. Appl. Physiol. 64: 441–450, 1988), allowed us to determine Rmin and Rmax of the total respiratory system (rs). We observed that 1) Rw,max and Rrs,max exhibited marked frequency dependence; 2) Rw,min was independent of flow (V) and inspired volume (delta V), whereas Rrs,min increased linearly with V and decreased with increasing delta V; 3) Rw,max decreased with increasing V, whereas Rrs,max exhibited a minimum value at a flow rate substantially higher than the resting range of V; 4) both Rw,max and Rrs,max increased with increasing delta V. We conclude that during resting breathing, flow resistance of the chest wall and total respiratory system, as conventionally measured, includes a significant component reflecting time constant inequalities and/or stress adaptation phenomena.

Respiratory mechanics in adult rats hypoxic in the neonatal period

1989 ◽  
Vol 66 (4) ◽  
pp. 1772-1778 ◽  
Author(s):  
S. Okubo ◽  
J. P. Mortola
Keyword(s):  
Respiratory System ◽  
Structural Changes ◽  
Chronic Hypoxia ◽  
Respiratory Mechanics ◽  
Neonatal Period ◽  
Somatic Growth ◽  
Tail Length ◽  
Newborn Rats ◽  
Pulmonary Resistance ◽  
Adult Rats

Newborn rats were exposed to 10% O2 from 24 h to 6 days after birth, then returned to normoxia and examined at 50 days of age, i.e., after reaching sexual maturity. Despite the important impairment in somatic growth during hypoxia, at 50 days body weight and nose-tail length were as in control rats never exposed to hypoxia. Hypoxic rats had a bigger chest, with larger anteroposterior diameter, larger surface area of the muscle component of the diaphragm, and heavier and more expanded lungs. None of these structural changes were observed in a third group of rats, which were exposed for 6 days to hypoxia between 35 and 42 days of age, i.e., at a much more advanced stage of postnatal development. In addition, hypoxic rats had higher compliance of the respiratory system and of the lung and lower total pulmonary resistance than control rats. Frequency dependence of compliance was not different. We conclude that in the rat the structural changes induced by neonatal chronic hypoxia are not resolved by the return to normoxia but persist at least until postpuberty with modifications of the mechanical properties of the respiratory system.

Statics of the respiratory system and growth: an experimental and allometric approach

1981 ◽  
Vol 241 (5) ◽  
pp. R336-R341 ◽  
Author(s):  
J. T. Fisher ◽  
J. P. Mortola
Keyword(s):  
Body Weight ◽  
Body Size ◽  
Chest Wall ◽  
Respiratory System ◽  
Age Groups ◽  
Weight Ratio ◽  
Lung Compliance ◽  
Elastic Recoil ◽  
Lung Weight ◽  
Residual Capacity

Static mechanical properties of the respiratory system have been examined during growth. Static inflation limb pressure-volume curves were obtained in rats and rabbits of three age groups, newborn, 2 wk, and adult. Lung weight-to-body weight ratio (LW/BW) decreased with age. Functional residual capacity (FRC) decreased with age when expressed per unit BW but increased when expressed per unit LW. Elastic recoil pressure of the lung at FRC increased during growth. Respiratory system and chest wall compliance per unit body weight (Crs/BW, Cw/BW) decreased during growth while lung compliance (CL/LW) increased. Examination of the newborn and adult allometric functions with respect to each other, suggests that, in general, changes in respiratory variables during growth are age dependent rather than size dependent. The slopes of these functions during growth tend to be less than the allometric slopes found in either the newborn or adult. In the adult the respiratory system and lung-specific compliances are interspecific constants, whereas chest wall specific compliance decreases with body size. In contrast, all the specific compliances of the newborn are size independent. The allometric ratio of Cw to CL decreases with body size in the adult, whereas this ratio is larger in the newborn and is an interspecific constant.

Active and passive respiratory mechanics in anesthetized dogs

1986 ◽  
Vol 61 (5) ◽  
pp. 1647-1655 ◽  
Author(s):  
W. A. Zin ◽  
A. Boddener ◽  
P. R. Silva ◽  
T. M. Pinto ◽  
J. Milic-Emili
Keyword(s):  
Chest Wall ◽  
Respiratory System ◽  
Power Functions ◽  
Intrinsic Resistance ◽  
Pressure Losses ◽  
Inspiratory Muscles ◽  
Anesthetized Dogs ◽  
Force Velocity ◽  
Spontaneously Breathing ◽  
Active Impedance

In six spontaneously breathing anesthetized dogs (pentobarbital sodium, 30 mg/kg) airflow, volume, and tracheal and esophageal pressures were measured. The active and passive mechanical properties of the total respiratory system, lung, and chest wall were calculated. The average passive values of respiratory system, lung, and chest wall elastances amounted to, respectively, 50.1, 32.3, and 17.7 cmH2O X l-1. Resistive pressure-vs.-flow relationships for the relaxed respiratory system, lung, and chest wall were also determined; a linear relationship was found for the former (the total passive intrinsic resistance averaged 4.1 cmH2O X l-1 X s), whereas power functions best described the others: the pulmonary pressure-flow relationship exhibited an upward concavity, which for the chest wall presented an upward convexity. The average active elastance and resistance of the respiratory system were, respectively, 64.0 cmH2O X l-1 and 5.4 cmH2O X l-1 X s. The greater active impedance reflects pressure losses due to force-length and force-velocity properties of the inspiratory muscles and those due to distortion of the respiratory system from its relaxed configuration.

Absolute intraesophageal pressure at functional residual capacity in frequency

1981 ◽  
Vol 51 (2) ◽  
pp. 270-275 ◽  
Author(s):  
P. Helms ◽  
C. S. Beardsmore ◽  
J. Stocks
Keyword(s):  
Chest Wall ◽  
Wall Thickness ◽  
Respiratory System ◽  
Functional Residual Capacity ◽  
Esophageal Pressure ◽  
Elastic Recoil ◽  
Residual Capacity ◽  
The Mean ◽  
Intraesophageal Pressure

Absolute intraesophageal pressure at functional residual capacity (FRC) has been estimated in 15 infants (age 1-30 wk) by the extrapolation of the esophageal pressure-volume relationships to zero balloon volume by use of air-filled balloons in their ranges of infinite compliance. The pressure-volume relationships of the esophageal balloons (length 3.5-5.0 cm, perimeter 1.7-2.5 cm, wall thickness 0.045-0.075 mm) were determined in air and in erect and horizontal positions under water, the behavior of the balloons placed horizontally under water closely approximated that of the balloons in vivo. The mean absolute intraesophageal pressure at FRC was -1.44 cmH2O in eight normal infants and -1.56 cmH2O in seven convalescent infants with a variety of cardiorespiratory disorders. The less negative absolute end-expiratory esophageal pressure in infants when compared with that in adults can be explained by changes in lung elastic recoil, chest wall recoil, or a combination of these factors during the development and growth of the respiratory system from birth to adulthood.

Effect of liquid inflation on the viscoelastic behavior of the lungs in developing piglets

1994 ◽  
Vol 77 (4) ◽  
pp. 1653-1658 ◽  
Author(s):  
J. La Rocca ◽  
J. J. Perez Fontan
Keyword(s):  
Stress Relaxation ◽  
Time Constant ◽  
Lung Volume ◽  
Inflation Rate ◽  
Viscoelastic Behavior ◽  
Transpulmonary Pressure ◽  
Liquid Interface ◽  
Developmental Changes ◽  
Elastic Recoil ◽  
Airway Opening

Viscoelastic dissipation through stress relaxation decreases during the first weeks after birth in the piglet's lungs (J. Appl. Physiol. 73: 1297–1309, 1992). To characterize the mechanism of this decrease, we compared the stress relaxation undergone by the lungs of six newborn and six 9-wk-old piglets when the airway opening was occluded in the course of air and saline inflations. The amplitude of stress relaxation, determined from the mono-exponential decay ultimately adopted by the transpulmonary pressure during the occlusions, related linearly to the increases in lung elastic recoil preceding the occlusions. The slope of this relationship was greater in the newborn than in the 9-wk-old piglets during air inflations and similar at the two ages during saline inflations. Both the ratio of stress relaxation to elastic recoil and the time constant of the relaxations were similar during air and saline inflations and were independent of inflation rate and lung volume at the start of the inflations. These findings indicate that the postnatal decrease in stress relaxation is caused primarily by developmental changes in the geometry of the gas-liquid interface. They are also consistent with the notion that the viscoelastic stresses generated by the gas liquid interface and lung tissue are well matched for a given elastic recoil.

Postnatal growth rate and gonadal development in circadian tau mutant hamsters reared in constant dim red light

Reproduction ◽  
2000 ◽  
pp. 327-330 ◽  
Author(s):  
RJ Lucas ◽  
JA Stirland ◽  
YN Mohammad ◽  
AS Loudon
Keyword(s):  
Time Course ◽  
Red Light ◽  
Somatic Growth ◽  
Postnatal Growth ◽  
Gonadal Development ◽  
Testicular Development ◽  
Wild Type ◽  
Similar Time ◽  
Syrian Hamsters ◽  
Body Weights

The role of the circadian clock in the reproductive development of Syrian hamsters (Mesocricetus auratus was examined in wild type and circadian tau mutant hamsters reared from birth to 26 weeks of age under constant dim red light. Testis diameter and body weights were determined at weekly intervals in male hamsters from 4 weeks of age. In both genotypes, testicular development, subsequent regression and recrudescence exhibited a similar time course. The age at which animals displayed reproductive photosensitivity, as exhibited by testicular regression, was unrelated to circadian genotype (mean +/- SEM: 54 +/- 3 days for wild type and 59 +/- 5 days for tau mutants). In contrast, our studies revealed a significant impact of the mutation on somatic growth, such that tau mutants weighed 18% less than wild types at the end of the experiment. Our study reveals that the juvenile onset of reproductive photoperiodism in Syrian hamsters is not timed by the circadian system.

Effects of accelerator type on stress relaxation behavior and network structure of aged natural rubber/chloroprene rubber vulcanizates

2016 ◽  
Vol 49 (5) ◽  
pp. 381-396 ◽  
Author(s):  
Farzad A Nobari Azar ◽  
Murat Şen
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Network Structure ◽  
Structural Changes ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Rubber Blends ◽  
Chloroprene Rubber ◽  
Weather Changes ◽  
Behavior Network

Natural rubber/chloroprene rubber (NR/CR) blends are among the commonly used rubber blends in industry and continuously are exposed to severe weather changes. To investigate the effects of accelerator type on the network structure and stress relaxation of unaged and aged NR/CE vulcanizates, tetramethyl thiuram disulfide, 2-mercaptobenzothiazole, and diphenyl guanidine accelerators have been chosen to represent fast, moderate, and slow accelerator groups, respectively. Three batches have been prepared with exactly the same components and mixing conditions differing only in accelerator type. Temperatures scanning stress relaxation and pulse nuclear magnetic resonance techniques have been used to reveal the structural changes of differently accelerated rubber blends before and after weathering. Nonoxidative thermal decomposition analyses have been carried out using a thermogravimetric analyzer. Results indicate that there is a strong interdependence between accelerator type and stress relaxation behavior, network structure, cross-linking density, and aging behavior of the blends. Accelerator type also affects decomposition energy of the blends.

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