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PubMedDate not supplied

[Characterization of the functional interrelationship between the cardiovascular and respiratory systems in children with bronchial asthma in the remission period].

Bronchial asthma is considered to be a psychosomatic disease in the genesis of which the functional instability of the subcortical brain structures and the autonomic nervous system regulating the cardio-respiratory complex play the principal role. The structural interrelationship of the values of the cardiovascular and respiratory systems in children with bronchial asthma in the period of remission was studied. Disorders were revealed in the intersystemic regulation of the functions in relatively normal functioning of each separate system.

Adolescent↗
PubMed1999

Interrupter airway and tissue resistance: errors caused by valve properties and respiratory system compliance.

The interrupter technique is used to determine airway and tissue resistance. Their accuracy is influenced by the technical properties of the interrupter device and the compliance of the respiratory system. We investigated the influence of valve characteristics and respiratory system compliance on the accuracy of determining airway and tissue resistance by means of a computer simulation. With decreasing compliance we found increasing errors in both airway and tissue resistance determination of up to 34 and 71%, respectively. On this basis we developed a new occlusion valve, with special emphasis on rapid closing time and tightness in the closed state to improve the accuracy of resistance determination. The newly developed occlusion device greatly improves the accuracy of airway and tissue resistance determination. We conclude that respiratory system compliance is a limiting factor for the accuracy of the interrupter technique. To apply the interrupter technique in patients with extremely low respiratory system compliances, we need sophisticated technical devices.

Airway Resistance↗
PubMed1982

Excretion-retention diagram to evaluate gas exchange properties of vertebrate respiratory systems.

Excretion [E = (PE - PI)/(PV - PI)] and retention [R = (Pa - PI)/(PV -PI)]are completely model-free defined variables which describe the dual input-output black-box representation of vertebrate respiratory systems under steady-state conditions. In the excretion-retention diagram (E-R diagram), E is plotted as a function of R. The application of the principle of mass conservation confines the possible combinations of E and R for a gas with a blood-gas partition coefficient, lambda, in a respiratory system with an overall ventilation, VT, and an overall perfusion, QT, to E = (lambda QT/VT) (1 - R). In general, E can be described as a continuous function of R. The mathematical formulation of this function depends on the configuration of the respiratory system. Easily recognizable curvatures are obtained for counter-cross, and cocurrent systems with and without parallel inhomogeneities. Visual inspection of actual E and R data displayed in an E-R diagram therefore allows the correct choice of the configuration of the respiratory system to be eventually used for further parameter estimation schemes. The E-R diagram is also a powerful tutorial tool for visualizing the complex relationships between the gas exchange of agents with different physical properties and the consequences of changes in ventilation and perfusion distribution within the respiratory system on gas transport.

Animals↗
PubMed1987

Inverse modeling of dog airway and respiratory system impedances.

Mechanical parameters of the respiratory system are often estimated from respiratory impedances using lumped-element inverse models. One such six-element model is composed of an airway branch [with a resistance (Raw) and inertance (Iaw)] separated from a tissue branch [with a resistance (Rt), inertance (It), and compliance (Ct)] by a shunt compliance representing alveolar gas compression (Cg). Even though the airways are known to have frequency-dependent resistance and inertance, these inverse models have been composed of linear frequency-independent elements. In this study we investigated the use of inverse models where the airway branch was represented by a frequency-independent Raw and Iaw, a Raw that is linearly related to frequency and an Iaw that is independent of frequency, and a system of identical parallel tubes the impedance of which was computed from the tube radius and length. These inverse models were used to analyze airway and respiratory impedances between 2 and 1,024 Hz that were predicted from an anatomically detailed forward model. The forward model represented the airways by an asymmetrically branched network with a terminal impedance representative of known Cg, Rt, It, and Ct. For respiratory impedances between 2 and 128 Hz, all models fit the data reasonably well, and reasonably accurate estimates of Cg, Rt, It, and Ct were extracted from these data. For data above 200 Hz, however, only the multiple-tube model accurately fitted respiratory impedances (Zrs). This model fitted the Zrs data best when composed of 27 tubes, each having a radius of 0.148 cm and a length of 16.5 cm.

Animals↗
PubMed2003

Effects of EDTA- and sulfite-containing formulations of propofol on respiratory system resistance after tracheal intubation in smokers.

BACKGROUND: The formulation of sulfite-containing propofol (SCP) has not been thoroughly investigated in patients with the extensive smoking history for the effects on the total respiratory system resistance after tracheal intubation. However adverse effects, including acute asthma and bronchospasm, have been reported with several other parenteral formulations of drugs containing sulfite as preservative. Therefore, the aim of this prospective randomized and double blind study was to investigate the effects of EDTA-containing propofol (ECP) and SCP on total respiratory system resistance (Rrs) in patients with the prolonged smoking history and undergoing propofol-based total intravenous anesthesia with tracheal intubation. METHODS: 40 patients scheduled for general anesthesia were enrolled into the study. Anesthesia was induced with either 2 mg/kg ECP, or 2 mg/kg SCP followed by vecuronium (0.1 mg/kg) to ensure complete neuromuscular relaxation for the time of the study. Maintenance anesthesia was continued with propofol infusion at 0.15 mg/kg/min for the first 15 min after intubation. Total respiratory system resistance (Rrs), was measured continuously for 10 min postintubation. RESULTS: The analysis of repeated Rrs measurements taken every minute for 10 min postintubation revealed trend consisting of higher Rrs in the SCP group when compared to the ECP group. The statistical analysis of the data performed using repeated measures analysis of covariance demonstrated statistically significant effect (P < 0.05) of the treatment group factor (SCP vs. ECP) and the time factor (time after intubation) on the postintubation Rrs. CONCLUSION: The total respiratory system resistance measured repeatedly for 10 min after tracheal intubation in patients with smoking history is significantly elevated after induction with SCP than after induction with ECP. The preservative used for propofol formulation may alter the effects of propofol on the total respiratory system resistance in smokers.

Adult↗
PubMed1988

Cellular defense of the avian respiratory system: influx and nonopsonic phagocytosis by respiratory phagocytes activated by Pasteurella multocida.

Poultry have a very limited number of resident macrophages in the normal steady-state respiratory tract. Thus, poultry must rely heavily on active migration of phagocytic cells to the lungs and air sacs in defending against respiratory pathogens. Intratracheal administration of a live, apathogenic Pasteurella multocida vaccine (Choloral; Clemson University strain) increased the number of avian respiratory phagocytes (ARP; obtained by lavage of lungs and air sacs) within 24 h by 3 orders of magnitude compared with the number of ARP obtained from mock-inoculated controls and from nonreacting chickens. Chickens yielding a high number of ARP did not show any sign of respiratory disease. Flow cytometric analysis of ARP that were exposed to 20 nonopsonized fluorescent microspheres per ARP for 30 min at 37 degrees C demonstrated a fivefold increase in the percentage of actively phagocytic cells in the ARP populations of stimulated chickens compared with the percentage of phagocytic ARP for mock-inoculated control birds. The phagocytic capacity (relative number of engulfed microspheres) of ARP from stimulated birds doubled during the same time. The flow cytometric observations were confirmed by fluorescence microscopy. These results indicate that activation by avirulent replicating agents of phagocytic cells of chicken to migrate to the respiratory tract may be a means of defending poultry against air sacculitis and pneumonia.

Animals↗
PubMed1988

Cellular defense of the avian respiratory system: effects of Pasteurella multocida on respiratory burst activity of avian respiratory tract phagocytes.

The respiratory tract of healthy chickens contain few free-residing phagocytic cells. Intratracheal inoculation with Pasteurella multocida stimulated a significant (P less than 0.05) migration of cells to the lungs and air sacs of White Rock chickens within 2 hours after inoculation. We found the maximal number of avian respiratory tract phagocytes (22.9 +/- 14.0 x 10(6] at 8 hours after inoculation. Flow cytometric analysis of these cells revealed 2 populations on the basis of cell-size and cellular granularity. One of these was similar in size and granularity to those of blood heterophils. Only this population was capable of generating oxidative metabolites in response to phorbol myristate acetate. The ability of the heterophils to produce hydrogen peroxide, measured as the oxidation of intracellularly loaded 2',7'-dichlorofluorescein, decreased with time after inoculation. These results suggest that the migration of heterophils, which are capable of high levels of oxidative metabolism, to the lungs and air sacs may be an important defense mechanism of poultry against bacterial infections of the respiratory tract.

Animals↗
PubMed1995

Mortality of copper cadmium alloy workers with special reference to lung cancer and non-malignant diseases of the respiratory system, 1946-92.

OBJECTIVES: To identify and quantify any relations between occupational exposure to cadmium oxide fume and mortalities from lung cancer and from chronic non-malignant diseases of the respiratory system. METHODS: The mortality experience of 347 copper cadmium alloy workers, 624 workers employed in the vicinity of copper cadmium alloy work (vicinity workers), and 521 iron and brass foundry workers (all men) was investigated for the period 1946-92. All subjects were first employed in these types of work in the period 1922-78 and for a minimum period of one year at one of two participating factories. Two analytical approaches were used, indirect standardisation and Poisson regression. RESULTS: Compared with the general population of England and Wales, mortality from lung cancer among copper cadmium alloy workers was close to expectation (observed deaths 18, expected deaths 17.8, standardised mortality ratio (SMR) 101, 95% confidence interval (95% CI) 60 to 159). A significant excess was shown for lung cancer among vicinity workers but not among iron and brass foundry workers (vicinity workers: observed 55, expected 34.3, SMR 160, 95% CI 121 to 209, P < 0.01; iron and brass foundry workers: observed 19, expected 17.8, SMR 107, 95% CI 64 to 167). Increased SMRs for non-malignant diseases of the respiratory system were shown for each of the three groups (alloy workers: observed 54, expected 23.5, SMR 230, 95% CI 172 to 300, P < 0.001; vicinity workers: observed 71, expected 43.0, SMR 165, 95% CI 129 to 208, P < 0.001; iron and brass foundry workers: observed 34, expected 17.1, SMR 199, 95% CI 137 to 278, P < 0.01). Work histories of the copper cadmium alloy workers were combined with independent assessments of cadmium exposures over time to develop individual estimates of cumulative exposure to cadmium; this being a time dependent variable. Poisson regression was used to investigate risks of lung cancer and risks of chronic non-malignant diseases of the respiratory system in relation to three levels of cumulative cadmium exposure (< 1600, 1600-4799, > or = 4800 micrograms.m-3.y). After adjustment for age, year of starting alloy work, factory, and time from starting alloy work, there was a significant positive trend (P < 0.01) between cumulative exposure to cadmium and risks of mortality from chronic non-malignant diseases of the respiratory system. Relative to a risk of unity for the lowest exposure category, risks were 4.54 (95% CI 1.96 to 10.51) for the middle exposure category and 4.74 (95% CI 1.81 to 12.43) for the highest exposure category. There was a non-significant negative trend between cumulative cadmium exposure and risks of mortality from lung cancer. Relative to a risk of unity for the lowest exposure category, risks were 0.85 (95% CI 0.27 to 2.68) for the middle exposure category and 0.81 (95% CI 0.18 to 3.73) for the highest exposure category. Similar findings were obtained when adjustment was made for age only. CONCLUSIONS: The findings are consistent with the hypothesis that exposure to cadmium oxide fume increases risks of mortality from chronic non-malignant diseases of the respiratory system. The findings do not support the hypothesis that exposure to cadmium oxide fume increases risks of mortality for lung cancer.

Alloys↗
PubMed1992

Effects of longitudinal laparotomy on respiratory system, lung, and chest wall mechanics.

In six sedated, anesthetized, paralyzed, and mechanically ventilated guinea pigs, total respiratory system (RT,rs), lung, and chest wall resistances and respiratory system (Est,rs), lung, and chest wall (Est,w) elastances were determined before and after longitudinal laparotomy. Furthermore the resistances were also split into their initial and difference components, with the former reflecting the Newtonian resistances and the latter representing the viscoelastic/inhomogeneous pressure dissipations in the system. For such purpose the end-inflation occlusion during constant inspiratory flow method was used. During laparotomy, a statistically significant increase in respiratory system difference resistance (from 0.086 to 0.101 cmH2O.ml-1.s) significantly augmented RT,rs (from 0.157 to 0.167 cmH2O.ml-1.s). The former was entirely secondary to a significant increase in chest wall difference resistance (0.019 to 0.034 cmH2O.ml-1.s), which naturally raised chest wall total resistance (from 0.030 to 0.047 cmH2O.ml-1.s). Est,rs and Est,w also increased (14.7 and 13.1%, respectively) after abdominal incision. It can be concluded that the midline xiphipubic laparotomy accompanied by the bilateral ventrodorsal infracostal incision increases RT,rs as a consequence of augmented chest wall difference resistance and Est,rs as a result of higher Est,w.

Airway Resistance↗
PubMed1981

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

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.

Aging↗
PubMedDate not supplied

Cellular defense of the avian respiratory system: protection against Escherichia coli airsacculitis by Pasteurella multocida-activated respiratory phagocytes.

The concept of nonspecific cellular defense of the respiratory system of poultry against respiratory pathogens by "preventive activation" of avian respiratory phagocytes (ARPs) was tested in an in vivo protection trial. Chickens were stimulated intratracheally by Pasteurella multocida Choloral vaccine strain. Seven hours later, these and mock-inoculated control chickens were challenged with pathogenic Escherichia coli via the air-sac route. Stimulated chickens had a 25-fold-elevated number of ARPs compared with mock-inoculated control chickens. The proportion of active phagocytes and the phagocytic capacity of these cells was higher in the ARP populations of stimulated chickens than in the ARP populations of control chickens. In vivo protection against E. coli air-sac infection was demonstrated by reduction of morbidity and mortality rates, diminished weight loss, and lower scores of gross and histopathological lesions of P. multocida-stimulated chickens compared with mock-inoculated controls.

Air Sacs↗
PubMedDate not supplied

Influence of the viscoelastic properties of the respiratory system on the energetically optimum breathing frequency.

We hypothesized that the viscoelastic properties of the respiratory system should have significant implications for the energetically optimal frequency of breathing, in view of the fact that these properties cause marked dependencies of overall system resistance and elastance on frequency. To test our hypothesis we simulated two models of canine and human respiratory system mechanics during sinusoidal breathing and calculated the inspiratory work (WI) and pressure-time integral (PTI) per minute under both resting and exercise conditions. The two models were a two-compartment viscoelastic model and a single-compartment model. Requiring minute alveolar ventilation to be fixed, we found that both models predicted almost identical optimum breathing frequencies. The calculated PTI was very insensitive to increases in breathing frequency above the optimal frequencies, while WI was found to increase slowly with frequency above its optimum. In contrast, both WI and PTI increased sharply as frequency decreased below their respective optima. A sensitivity analysis showed that the model predictions were very insensitive to the elastance and resistance values chosen to characterize tissue viscoelasticity. We conclude that the WI criterion for choosing the frequency of breathing is compatible with observations in nature, whereas the optimal frequency predictions of the PTI are rather too high. Both criteria allow for a fairly wide margin of choice in frequency above the optimum values without incurring excessive additional energy expenditure. Furthermore, contrary to our expectations, the viscoelastic properties of the respiratory system tissues do not pose a noticeable problem to the respiratory controller in terms of energy expenditure.

Animals↗
PubMed2003

Influence of respiratory system impedance on volume and pressure delivered at the Y piece in ventilated infants.

OBJECTIVES: Tidal volume (VT) delivered to infants' airways are overestimated and pressure underestimated when measured in the ventilator and not at the Y piece. This study aimed at evaluating the influence of respiratory system impedance on expiratory VT (VTE) and pressure measurement difference. DESIGN: Prospective observational study. SETTING: Pediatric intensive care unit at a university hospital. PATIENTS: Data were collected between February 2000 and October 2001 for 30 infants (range, 1-23 months) ventilated in the pressure-controlled or volume-controlled mode. INTERVENTIONS: Measurements of VTE, pressure obtained at the same time at the Y piece and on the ventilator Servo 300, were collected in ventilated infants. Respiratory system impedance was calculated from data obtained at the Y piece. Circuit compliance was measured in vitro. VTEs were corrected for compressible volume. MEASUREMENTS AND RESULTS: VTEs were overestimated by the Servo 300 in the pressure-controlled and volume-controlled modes (from 5% to 62% of the value displayed on Servo 300). Maximal inspiratory pressures were underestimated by the Servo 300 in the pressure-controlled mode (difference from -2 to +19 cm H(2)O). Measurement difference increased with increasing respiratory system impedance. Ventilator VTE corrected for circuit compliance did not offer a sufficiently accurate estimation of VTE at the Y piece. CONCLUSIONS: VT and pressure measurements must be performed at the Y piece, especially in infants with increased respiratory system impedance (i.e., decreased respiratory system compliance or increased resistance). Correcting VTE for circuit compliance cannot replace measurement of VT at the Y piece.

Airway Resistance↗
PubMed1991

Two-compartment modelling of respiratory system mechanics at low frequencies: gas redistribution or tissue rheology?

The mechanical properties of the respiratory system are generally inferred from measurements of pressure and flow at the airway opening. Traditionally, these measurements have been related through a single-compartment model of the respiratory system. Recently, however, there has been considerable interest in modelling low-frequency respiratory mechanics in terms of two compartments, since this gives a much improved description of experimental data. In this paper we consider two classes of two-compartment models that are compatible with pressure-flow relationships of air measured at the airway opening. One type of model accounts for regional ventilation inhomogeneity in the lung in terms of two alveolar compartments. The other type of model considers pulmonary ventilation to be homogeneous, while the tissues of the respiratory system are modelled as being viscoelastic. In normal dogs, the appropriate two-compartment model has been shown to be the viscoelastic model. In the case of abnormal physiology, however, one must invoke a model having both viscoelastic tissues and ventilation inhomogeneities. Additional experimental data are required in order to identify such a model, and to quantify these two phenomena.

Airway Resistance↗
PubMed2002

Functional residual capacity and compliance of the respiratory system after surfactant treatment in premature infants with severe respiratory distress syndrome.

UNLABELLED: To understand the mechanisms behind improved oxygenation after intratracheal surfactant instillation, the immediate and late effects on lung volume and compliance of the respiratory system (CRS) were analysed. Infants received modified porcine surfactant (Curosurf) or modified bovine surfactant (Alveofact). Measurements of functional residual capacity (FRC) and CRS were successfully performed in 90 ventilated preterm infants (birth weight 1264 +/- 435 g; gestational age 28.2 +/- 2.5 weeks) with severe respiratory distress syndrome. FRC and CRS were measured during mechanical ventilation prior to and 1, 3, 6, 24, 48, 72, 96, 120 and 168 h after surfactant replacement. Oxygenation rapidly improved. FRC increased significantly from 7.64 +/- 1.58 ml/kg to 15.35 +/- 3.27 ml/kg (P < 0.01) at 1 h after surfactant instillation. CRS remained virtually unchanged during the first hours after surfactant replacement and a concomitant decrease in specific compliance was seen. CONCLUSION: the changes in lung function following surfactant treatment can only be explained by initial stabilisation of already aerated alveoli followed by recruitment of new gas exchange units as mechanisms involved in mediating the effect of surfactant on gas exchange. However, since no significant correlation between changes in functional residual capacity and improvement in arterial-to-alveolar oxygen tension ratio was seen, other effects of surfactant must be considered. These include local and/or systemic changes in haemodynamics.

Female↗
PubMed1993

Effects of thoracotomy on respiratory system, lung, and chest wall mechanics.

Nineteen rats were sedated, anesthetized, paralyzed, and mechanically ventilated. The respiratory, lung, and chest wall elastances (Est-rs, Est-L, Est-w); respiratory system, pulmonary, and chest wall total resistances (Rtot-rs, Rtot-L, Rtot-w); respiratory system, pulmonary, and chest wall initial resistances (Rinit-rs, Rinit-L, Rinit-w); and respiratory system, pulmonary, and chest wall difference resistances (Rdiff-rs, Rdiff-L, Rdiff-w) were determined before and after thoracotomy using the end-inflation occlusion method. Rinit reflects the Newtonian resistances and Rdiff represents the viscoelastic/inhomogeneous pressure dissipations in the system. Rtot = Rinit+Rdiff, ie, total resistance. The animals were submitted to either anterolateral thoracotomy (group A, n = 7), median sternotomy (group B, n = 6), or median sternotomy under PEEP while the lungs were exposed (group C, n = 6). In groups A and B, statistically significant increases in Rdiff-rs significantly augmented Rtot-rs. The former results were entirely secondary to significant increases in Rdiff-L, which naturally raised Rtot, L. Resistance was not altered in group C rats. Thus, anterolateral thoracotomy and median sternotomy increases Rtot-rs as a consequence of augmented Rdiff-L, but this finding could be prevented by the use of PEEP. Est-rs and Est-L increased in the three groups after surgery. Groups D and E were comprised of four animals each. Both underwent median sternotomy and in group E, PEEP was applied. Histopathologic examination of the lungs demonstrated a higher degree of lung collapse in group D.

Animals↗
PubMed1992

Stress relaxation of the respiratory system in developing piglets.

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.

Animals↗
PubMed1986

A comparative analysis of contractile characteristics of the diaphragm and of respiratory system mechanics.

The mean inspiratory flow rate (VT/TI) is used as an index of central respiratory 'drive', and, at rest, it varies interspecifically in proportion to body weight (BW) raised to the 0.74 power (Boggs and Tenney, 1984). VT/TI is determined by the level of central neural respiratory output, the velocity of contraction of respiratory muscles, and the mechanical characteristics of the respiratory system. We have examined the last two factors in 13 species ranging in weight from 0.025 to 515 kg. We determined the 'effective' inspiratory mechanical characteristics of the respiratory system (time constant, resistance, and compliance) and the time course of diaphragmatic contraction during bilateral supramaximal phrenic nerve stimulation in anesthetized animals. We also measured passive expiratory mechanical variables and made morphometric measurements of the diaphragm. We found that VT/TI during phrenic nerve stimulation was proportional to BW0.82. The 'effective' respiratory time constant (tau'rs) and passive expiratory time constant (tau rs) scaled in proportion to body weight with nearly similar exponents: tau'rs alpha BW0.26 and tau rs alpha BW0.21. In addition, the time constant of diaphragmatic contraction (tau mc) was proportional to BW0.20. Inspiratory time is proportional to tau'rs and tau mc, and tidal volume during stimulation was almost directly proportional to body weight. Thus, interspecific changes in VT/TI during stimulation were related to interspecific changes in the mechanical characteristics of the respiratory system and the velocity of muscular contraction. We conclude that interspecific changes in VT/TI need not reflect interspecific variation in central respiratory drive under resting conditions. We found that diaphragm weight and volume and diaphragm muscle thickness were geometrically similar in all species studied. Inspiratory pressure is an interspecific constant; therefore, by the Law of Laplace, smaller animals must develop greater tension per unit of muscle mass.

Airway Resistance↗