Total Respiratory System Research Articles

Changes in the mechanical properties of the respiratory system during the development of interstitial lung edema

BackgroundPulmonary edema induces changes in airway and lung tissues mechanical properties that can be measured by low-frequency forced oscillation technique (FOT). It is preceded by interstitial edema which is characterized by the accumulation of extravascular fluid in the interstitial space of the air-blood barrier. Our aim was to investigate the impact of the early stages of the development of interstitial edema on the mechanical properties of the respiratory system.MethodsWe studied 17 paralysed and mechanically ventilated closed-chest rats (325–375 g). Total input respiratory system impedance (Zrs) was derived from tracheal flow and pressure signals by applying forced oscillations with frequency components from 0.16 to 18.44 Hz distributed in two forcing signals. In 8 animals interstitial lung edema was induced by intravenous infusion of saline solution (0.75 ml/kg/min) for 4 hours; 9 control animals were studied with the same protocol but without infusion. Zrs was measured at the beginning and every 15 min until the end of the experiment.ResultsIn the treated group the lung wet-to-dry weight ratio increased from 4.3 ± 0.72 to 5.23 ± 0.59, with no histological signs of alveolar flooding. Resistance (Rrs) increased in both groups over time, but to a greater extent in the treated group. Reactance (Xrs) did not change in the control group, while it decreased significantly at all frequencies but one in the treated. Significant changes in Rrs and Xrs were observed starting after ~135 min from the beginning of the infusion. By applying a constant phase model to partition airways and tissue mechanical properties, we observed a mild increase in airways resistance in both groups. A greater and significant increase in tissue damping (from 603.5 ± 100.3 to 714.5 ± 81.9 cmH2O/L) and elastance (from 4160.2 ± 462.6 to 5018.2 ± 622.5 cmH2O/L) was found only in the treated group.ConclusionThese results suggest that interstitial edema has a small but significant impact on the mechanical features of lung tissues and that these changes begin at very early stages, before the beginning of accumulation of extravascular fluid into the alveoli.

Decreased Respiratory Compliance in Infants Less Than or Equal to 32 Weeks' Gestation, Delivered More Than 7 Days After Antenatal Steroid Therapy

Our objective was to compare the pulmonary function (respiratory compliance) of infants who were < or = 32 weeks' gestation and delivered > 7 days after a single course of antenatal steroids versus infants who were delivered 1 to 7 days after a single course of antenatal steroids. A prospective cohort study of respiratory system compliance was conducted of infants < or = 32 weeks' gestation within 72 hours of life and before surfactant therapy if needed. The study (remote) group was composed of infants who were treated with antenatal steroids > 7 days before delivery and the comparison group (ideal group) of matched infants who were treated with antenatal steroids 1 to 7 days before delivery. Respiratory system compliance was measured with the single-breath occlusion technique. Twenty-eight remotely treated infants and 28 ideally treated infants were studied. The remote group had a significantly lower respiratory system compliance per kilogram and total respiratory system compliance when compared with the ideal antenatal steroids group. Within the remote group, infants who received antenatal steroids 8 to 14 days (n = 10) before delivery had a significantly higher respiratory system compliance and a trend to less surfactant need (10% vs 33%) as compared with infants who received antenatal steroids > 14 days (n = 18) before delivery. Infants who were < or = 32 weeks' gestation and remotely treated with antenatal steroids (average 21 days) had a significantly lower respiratory compliance compared with matched infants who were ideally treated with antenatal steroids. We speculate that the lower respiratory system compliance may reflect the dissipation of beneficial effects of antenatal steroids on pulmonary function when delivery occurs > 7 days after therapy and particularly when therapy is > 14 days before delivery.

The chest wall in acute lung injury/acute respiratory distress syndrome

There has recently been renewed interest in the chest wall during mechanical ventilation, related to lung-protective ventilation strategies, as well as in the role of abdominal pressure in many facets of critical illness. The purpose of this review is to address relevant issues related to the chest wall and mechanical ventilation, particularly in patients with acute lung injury/acute respiratory distress syndrome. In mechanically ventilated patients with acute lung injury, intra-abdominal pressure is an important determinant of chest wall compliance. With elevated intra-abdominal pressure, the compliance of the chest wall and total respiratory system is decreased, with a relatively normal compliance of the lungs. The lung compression effects of increased intra-abdominal pressure may lead to a loss of lung volume with atelectasis. An appropriate level of positive end-expiratory pressure is necessary to counterbalance this collapsing effect on the lungs. Also, the stiff chest wall results in a lower transpulmonary pressure during positive-pressure ventilation. As chest wall compliance may have important clinical implications during positive-pressure ventilation, the physiology of this effect should be considered, particularly in patients with acute lung injury and increased abdominal pressure.

Effects of Nanoparticles on Lung Physiology in the Presence or Absence of Antigen

Ambient particulate matter (PM) exacerbates allergic airway diseases. Our previous study showed that diesel exhaust particles, the main constituents in urban PM, enhance airway hyperresponsivness in mice. In addition, health effects of PM with a diameter of less than 100 nm, called nanoparticles, have been reported, and we have also demonstrated that carbon nanoparticles exacerbate antigen-related airway inflammation. The present study investigates the effects of pulmonary exposure to two sizes of carbon nanoparticles on lung physiology and lung expression of Muc5ac in the presence or absence of antigen in mice. Nanoparticles alone or ovalbumin (OVA) alone moderately enhanced cholinergic airway reactivity, as assessed by total respiratory system resistance (R) and Newtonian resistance (Rn). In the nanoparticle + OVA groups, all the parameters for lung responsiveness, such as R, compliance, elastance, Rn, tissue damping, and tissue elastance, were worse than those in the vehicle group, the corresponding nanoparticle groups or the OVA group. The lung mRNA level for Muc5ac was significantly higher in the OVA group than in the vehicle group, and further increased in the nanoparticle + OVA groups than in the OVA or the nanoparticle groups. These data suggest that carbon nanoparticles can enhance lung hyperresponsiveness, especially in the presence of antigen. The effects may be mediated, at least partly, through the enhanced lung expression of Muc5ac.

Biologically variable ventilation improves gas exchange and respiratory mechanics in a model of severe bronchospasm*

Mechanical ventilation can be lifesaving for status asthmaticus, but how best to accomplish mechanical ventilation is unclear. Biologically variable ventilation (mechanical ventilation that emulates healthy variation) and conventional control mode ventilation (monotonously regular) were compared in an animal model of bronchospasm to determine which approach yields better gas exchange and respiratory mechanics. A randomized prospective trial of biologically variable ventilation vs. control mode ventilation in swine. University research laboratory. Eighteen farm-raised pigs. Methacholine was administered as a nebulized aerosol to initiate bronchospasm, defined as doubling of peak inspiratory pressure and respiratory system resistance, and then randomized (n = 9 each group) to either continue control mode ventilation or switch to biologically variable ventilation at the same minute ventilation. Over the next 4 hrs, hemodynamics, blood gases, respiratory mechanics, and carbon dioxide expirograms were recorded hourly. At end-experiment, tracheobronchial lavage was undertaken to determine interleukin-6 and -10 concentrations. Measurements of physiologic variables and inflammatory cytokines showed that biologically variable ventilation significantly improved gas exchange, with greater arterial oxygen tensions (p = .006; group x time interaction), lower arterial carbon dioxide tensions (p = .0003; group effect), lower peak inspiratory pressures (p = .0001; group x time), greater static compliance (p = .0001; group x time), greater dynamic compliance (p = .0001; group x time), and lower total respiratory system resistance (p = .028; group x time), compared with conventional ventilation. The appearance of inflammatory cytokines in bronchoalveolar lavage fluid (interleukin-6 and -10) was not affected by mode of ventilation. In this experimental model, biologically variable ventilation was superior to control mode ventilation in terms of gas exchange and respiratory mechanics during severe bronchospasm.

Effects of naphthoquinone on airway responsiveness in the presence or absence of antigen in mice

We have recently demonstrated that naphthoquinone (NQ), one of extractable chemical compounds of diesel exhaust particles (DEP), enhances antigen-related airway inflammation with goblet cell hyperplasia in mice (Inoue et al. in Eur Respir J 209(2):259-267, 2007). Further, NQ has enhanced lung expressions of interleukin (IL)-4 and IL-5. However, the effects of NQ on other cardinal features of asthma have not been completely investigated. The aim of the present study was to evaluate the effects of NQ on airway responsiveness on the model. Vehicle, NQ, ovalbumin (OVA), or NQ + OVA was administered intratarcheally to ICR mice for 6 weeks. Twenty-four hours after the last instillation, lung histology, lung functions such as total respiratory system resistance (R) and Newtonian resistance (R (n)), and protein level of IL-13 and mRNA level for MUC5AC in the lung were examined. Repetitive exposure to NQ aggravated antigen-related lung inflammation. NQ alone enhanced R and R (n) as compared to vehicle without statistical significance. OVA alone or NQ plus OVA showed increases in R and R (n), which was prominent in NQ plus OVA (P < 0.05 vs. vehicle). Combined exposure to NQ and OVA elevated the levels of IL-13 and MUC5AC in the lung as compared with exposure to NQ or OVA alone. These results indicate that NQ can enhance airway hyperresponsiveness in the presence or absence of an antigen. Also, amplified lung expressions of IL-13 and MUC5AC might partly contribute to the deterioration of asthma features by NQ.

Effects of Components Derived from Diesel Exhaust Particles on Lung Physiology Related to Antigen

Our previous study has shown that diesel exhaust particles (DEP), main constituents in ambient particulate matters (PM), enhance airway hyperresponsivness in a murine model of allergic asthma (Takano et al., 1998). However, it remains unknown which components in DEP are responsible for the enhancement. The present study investigated the effects of repeated pulmonary exposure to DEP components (extracted organic chemicals in DEP; DEP-OC, carbonaceous nuclei of DEP after extraction; washed DEP) on lung physiology in the presence or absence of antigen. ICR mice were divided into six experimental groups. Vehicle, DEP components, ovalbumin (OVA), or DEP components plus OVA was administered intratrachally for 6 weeks. Twenty-four hr after the last instillation, cholinergic lung reactivity was examined. DEP components alone did not induce any facilitation of lung function as compared to vehicle alone. The values of total respiratory system resistance (R), elastance (E), Newtonian resistance (Rn), tissue damping (G), and tissue elastance (H) were higher and the value of compliance (C) was lower in the OVA or the DEP component + OVA groups than in the vehicle group. In particular, the hyperreactivity was most prominent in the washed DEP + OVA group. The values in the DEP-OC + OVA group were not significantly different from those in the OVA group. These data suggest that carboneous component in DEP, rather than organic chemical one, can be attributable to the enhancement of lung hyperresponsiveness in allergic asthma.

Non-invasive measurement of total respiratory compliance and resistance in cats

We adapted non-invasive techniques developed for human infants to measure total respiratory system compliance (Crs) and resistance (Rrs) in 21 healthy cats. The animals breathed through a face mask attached to a respiratory circuit and measurements were taken of changes in lung volume and airway pressure during brief occlusions of the airway at different lung volumes. The slope of the plot of change in volume against airway pressure yielded the multiple occlusion Crs with a mean (+/-95%CI) value of 6.8 (6.3-7.3) ml/cm H2O. In 12 animals measurements were made by the single breath technique in which occlusion was made early in expiration and on release, a plot of the subsequent relaxed expiratory flow and volume yielded the time constant (taurs), Crs and Rrs with mean (+/-95%CI) values of 0.27 (0.22-0.31) s, 7.0 (6.1-7.8) ml/cm H2O, and 38.7 (33.7-43.6) cm H2O/l/s, respectively. Rrs was significantly correlated inversely with forced expiratory flow at resting lung volume (V'maxFRC).

Effect of aging on respiratory system physiology and immunology

With the looming expansion of the elderly population of the US, a thorough understanding of "normal" aging-related changes on the respiratory system is paramount. The respiratory system undergoes various anatomical, physiological and immunological changes with age. The structural changes include chest wall and thoracic spine deformities which impairs the total respiratory system compliance leading to increase work of breathing. The lung parenchyma loses its supporting structure causing dilation of air spaces: "senile emphysema". Respiratory muscle strength decreases with age and can impair effective cough, which is important for airway clearance. The lung matures by age 20-25 years, and thereafter aging is associated with progressive decline in lung function. The alveolar dead space increases with age, affecting arterial oxygen without impairing the carbon dioxide elimination. The airways receptors undergo functional changes with age and are less likely to respond to drugs used in younger counterparts to treat the same disorders. Older adults have decreased sensation of dyspnea and diminished ventilatory response to hypoxia and hypercapnia, making them more vulnerable to ventilatory failure during high demand states (ie, heart failure, pneumonia, etc) and possible poor outcomes.

Computational haemodynamics in cerebral aneurysm custom models based on different reconstructive methodologies

The dynamic mechanical properties of the respiratory system reflect the ensemble behavior of its constituent structural elements. This study assessed the appropriateness of constant-phase descriptions of respiratory tissue viscoelasticity at various distending pressures. We measured the mechanical input impedance (Z) of the lungs, chest wall and total respiratory system in 12 dogs at mean airway pressures from 5 to 30 cm H2O. Each Z was fitted with a constant-phase model which provided estimates tissue damping (G), elastance (H), and hysteresivity (η = G/H). Both G and H sharply increased with increasing distending pressure for the lungs and chest wall, while η attained a minimum near 15–20 cm H2O. Model fitting errors for the lungs and total respiratory system increased for distending pressures greater than 20 cm H2O, indicating that constant-phase descriptions of parenchymal and respiratory system viscoelasticty may be inappropriate at volumes closer to total lung capacity. Such behavior may reflect alterations in load distribution across various parenchymal stress-bearing elements.

Effects of Lung Squeezing Technique on Lung Mechanics in Mechanically-Ventilated Preterm Infants with Respiratory Distress Syndrome

Effects of conventional chest physiotherapy on preterm infants may be compromised due to the maturation difference in immature lungs. The lung squeezing technique (LST) has been shown to be beneficial in correcting atelectasis in preterm infants. The purpose of this study was to investigate the effects of LST on the parameters of lung mechanics in preterm infants on mechanical ventilation. LST was used as an intervention to improve the distribution of ventilation in infants with respiratory distress syndrome. Eleven preterm infants on mechanical ventilation were enrolled. Serial measurements on static respiratory system compliance (Crs) and resistance (Rrs) by an airway occlusion technique with passive flow-volume analysis were performed before and immediately after LST, and repeated 4 hours later to assess the carryover effect. Crs improved by 21% (0.92 ± 0.37 mL/cmH 2 O/kg vs. baseline 0.76 ± 0.33 mL/cmH 2 O/kg, p = 0.023) immediately after LST. Split group analysis showed that only the lower Crs group had a significant carryover effect at 4 hours post-LST (p = 0.046). LST increases total respiratory system compliance, possibly through decompression of the overdistended lung units and recruitment of atelectatic alveoli. Rrs showed no significant change after LST. Individual trends of decreased Rrs were observed in infants with obvious secretion. The effect of LST on respiratory system resistance needs to be further explored by recruiting other disease conditions that present with pulmonary secretions.

Changes in respiratory mechanics with increasing degrees of airway obstruction in COPD: Detection by forced oscillation technique

The Forced Oscillation Technique (FOT) is a method for non-invasively assessing respiratory mechanics during spontaneous breathing, demanding little cooperation. The aim of this study was to test the ability of FOT to describe the changes in respiratory mechanics in progressive COPD. The study was performed in a control group formed by 21 healthy subjects and 79 outpatients with COPD, which were classified by spirometry, according to the degree of airway obstruction, in mild, moderate and severe groups. Resistive impedance data were submitted to linear regression analysis over the 4-16 Hz frequency range, which yielded the total respiratory system resistance extrapolated at 0 Hz (R0), the respiratory system conductance (Grs), mean respiratory resistance (Rm), and the resistance/frequency slope (S). Reactance data were interpreted using the mean values (Xm) over the 4-32 Hz frequency range, the dynamic compliance (Crs,dyn), the dynamic elastance (E(rs,dyn)), and the resonant frequency (fr) data. Considering the control and mild groups, the increase of airway obstruction resulted in a significant increase of R0 (P<0.008), Rm (P<0.001), and a significant reduction in Grs (P<0.002). Reactive parameters, Crs, dyn and Ers,dyn also presented significant modifications. The subsequent increase (mild to moderate) showed a significant raise of R(0) (P<0.007), S (P<0.001), and a reduction in Grs (P<0.015), while significant increases in Xrs (P<0.001), and Ers,dyn (P<0.02), and also a reduction in Crs, dyn (P<0.02) were also observed. In contrast to earlier stages, in the late stage of the airway obstruction increase (moderate to severe obstruction), resistive parameters did not present statistically significant modifications, while significant modifications were observed in Xrs (P<0.02), Crs, dyn (P<0.003) and Ers,dyn (P<0.003). The results of this study demonstrated that the FOT is useful for detecting the respiratory mechanics modifications in COPD patients. The initial phases of airway obstruction in COPD can be described mainly by resistive parameters, while in more advanced phases, reactive parameters seem to be more useful. Since the FOT has the advantage of being a simple method, such a technique may give a significant clinical contribution, representing an alternative and/or complement to the evaluation of respiratory mechanics by means of forced expiration.

Application of impulse oscillometry in cystic fibrosis patients

Impulse oscillometry (IOS) measures the total respiratory system impedance (Z) at incremental frequencies during normal tidal breathing. Our aim was to establish the total respiratory impedance and how IOS measurements relate to conventional lung function indices in patients with cystic fibrosis (CF). Results from spirometry, static lung volumes and IOS (R, X, Z, resonant frequency (FR) and reactance area 5Hz — FR (AX)) were compared in 66 adult CF patients recruited from CF Care Centre of Moscow. Patients had airway obstruction (FEV1 = 57 % pred.), hyperinflation (RV = 253 % pred., FRC = 158 % pred., RV / TLC = 52 %). IOS demonstrated a frequency dependent increase in R (R5 = 173 % pred., R20 = 140 % pred.) and a decrease in X (X5 = –0,23 kPa/L / s) with a shift in FR to higher frequencies (FR = 18 Hz, AX = 1,4 kPa / L). There were significant correlations between FR, X20, R5, R20, AX and conventional lung function indices (FEV1 = – 0,74; 0,78; –0,42; –0,31 and –0,76 respectively). The data indicate that measurement of reactance and FR may reflect the degree of airway obstruction. IOS is an effort independent measurement that could be used in clinical routine especially in patients with severe lung diseases.

Assessment of Pulmonary Function in COPD

Pulmonary function testing is used in the diagnosis of chronic obstructive pulmonary disease (COPD) and the staging of COPD severity. The current diagnostic criterion for airflow obstruction is a ratio of forced expiratory volume in 1 second (FEV (1)) to forced vital capacity (FVC) < 70%. However this absolute definition can lead to false-negative determinations in younger patients and false-positive determinations in the elderly. Nevertheless, screening spirometry is advocated and becomes feasible in the physician office setting with the availability of compact, relatively affordable apparatus that meets the appropriate technical specifications. Spirometry should be complemented by measurement of lung volumes using body plethysmography in those with evidence of airflow obstruction. Small airways disease can be detected by various techniques that measure airway and total respiratory system resistance. There is renewed interest in the forced oscillation technique and impulse oscillometry because of their noninvasiveness and potential ability to distinguish small from larger airway disease. Finally, pulmonary function testing has an important role in preoperative risk assessment; for example, in patients being considered for lung volume reduction surgery or resection of a lung nodule.

A Mechanistic Model for Quasistatic Pulmonary Pressure-Volume Curves for Inflation

A mechanistic model of the respiratory system is proposed to understand differences in quasistatic pressure-volume (p-V) curves of the inflation process in terms of the alveolar recruitment and the elastic distension of the wall tissues. In the model, a total respiratory system consists of a large number of elements, each of which is a subsystem of a cylindrical chamber fitted with a piston attached to a spring. The alveolar recruitment is simulated by allowing a distribution of the critical pressure at which an element opens; while the wall distension is represented by the piston displacement. Relations are derived between parameters in the error-function p-V model equation and properties of the mechanistic model The parameters of the model-based p-V equation are determined for clinical data sets of patients with acute respiratory distress syndrome.

Small size at birth and greater postnatal weight gain: relationships to diminished infant lung function.

Recent evidence suggests that impaired lung development is linked with diminished lung function and an increased risk of chronic obstructive airway disease in adulthood. To examine environmental influences on early lung development, we measured lung function in 131 normal-term infants aged 5-14 weeks. Adjusting for age at measurement, FEV at 0.4 seconds fell by 4.4% for each standard deviation decrease in birth weight (p = 0.047); when adjusted for FVC, FEV at 0.4 seconds was not related to birth weight but fell by 3.2% per standard deviation increase in infant weight gain (p = 0.001). Age- and sex-adjusted total respiratory system compliance fell by 7.0% per standard deviation decrease in birth weight (p < 0.001) but was not related to infant weight gain. In univariate analyses, age-adjusted forced expiratory flow at functional residual capacity was not related to birth weight, but decreased by 11.0% per standard deviation increase in infant weight gain (p = 0.007). The respiratory rate rose by 5.1% per standard deviation increase in infant weight gain (p = 0.001). Lung function measurements were not related to infant feeding. The observations suggest that lower rates of fetal growth and higher rates of early infancy weight gain are associated with impaired lung development.

Detection of expiratory flow limitation in COPD using the forced oscillation technique.

Expiratory flow limitation (EFL) during tidal breathing is a major determinant of dynamic hyperinflation and exercise limitation in chronic obstructive pulmonary disease (COPD). Current methods of detecting this are either invasive or unsuited to following changes breath-by-breath. It was hypothesised that tidal flow limitation would substantially reduce the total respiratory system reactance (Xrs) during expiration, and that this reduction could be used to reliably detect if EFL was present. To test this, 5-Hz forced oscillations were applied at the mouth in seven healthy subjects and 15 COPD patients (mean +/- sD forced expiratory volume in one second was 36.8 +/- 11.5% predicted) during quiet breathing. COPD breaths were analysed (n=206) and classified as flow-limited if flow decreased as alveolar pressure increased, indeterminate if flow decreased at constant alveolar pressure, or nonflow-limited. Of these, 85 breaths were flow-limited, 80 were not and 41 were indeterminate. Among other indices, mean inspiratory minus mean expiratory Xrs (deltaXrs) and minimum expiratory Xrs (Xexp,min) identified flow-limited breaths with 100% specificity and sensitivity using a threshold between 2.53-3.12 cmH2O x s x L(-1) (deltaXrs) and -7.38- -6.76 cmH2O x s x L(-1) (Xexp,min) representing 6.0% and 3.9% of the total range of values respectively. No flow-limited breaths were seen in the normal subjects by either method. Within-breath respiratory system reactance provides an accurate, reliable and noninvasive technique to detect expiratory flow limitation in patients with chronic obstructive pulmonary disease.

Tracking of airway and tissue mechanics during TLC maneuvers in mice.

A tracking impedance estimation technique was developed to follow the changes in total respiratory impedance (Zrs) during slow total lung capacity maneuvers in six anesthetized and mechanically ventilated BALB/c mice. Zrs was measured with the wave-tube technique and pseudorandom forced oscillations at nine frequencies between 4 and 38 Hz during inflation from a transrespiratory pressure of 0-20 cmH2O and subsequent deflation, each lasting for approximately 20 s. Zrs was averaged for 0.125 s and fitted by a model featuring airway resistance (Raw) and inertance, and tissue damping and elastance (H). Lower airway conductance (Glaw) was linearly related to volume above functional residual capacity (V) between 0 and 75-95% maximum V, with a mean slope of dGlaw/dV = 13.6 +/- 4.6 cmH2O-1. s-1. The interdependence of Raw and H was characterized by two distinct and closely linear relationships for the low- and high-volume regions, separated at approximately 40% maximum V. Comparison of Raw with the highest-frequency resistance of the total respiratory system revealed a marked volume-dependent contribution of tissue resistance to total respiratory system resistance, resulting in the overestimation of Raw by 19 +/- 8 and 163 +/- 40% at functional residual capacity and total lung capacity, respectively, whereas the lowest frequency reactance was proportional to H; these findings indicate that single-frequency resistance values may become inappropriate as surrogates of Raw when tissue impedance is changing.

Tracking variations in airway caliber by using total respiratory vs. airway resistance in healthy and asthmatic subjects.

An index of airway caliber can be tracked in near-real time by measuring airway resistance (Raw) as indicated by lung resistance at 8 Hz. These measurements require the placing of an esophageal balloon. The objective of this study was to establish whether total respiratory system resistance (Rrs) could be used rather than Raw to track airway caliber, thereby not requiring an esophageal balloon. Rrs includes the resistance of the chest wall (Rcw). We used a recursive least squares approach to track Raw and Rrs at 8 Hz in seven healthy and seven asthmatic subjects during tidal breathing and a deep inspiration (DI). In both subject groups, Rrs was significantly higher than Raw during tidal breathing at baseline and postchallenge. However, at total lung capacity, Raw and Rrs became equivalent. Measured with this approach, Rcw appears volume dependent, having a magnitude of 0.5-1.0 cmH2O. l-1. s during tidal breathing and decreasing to zero at total lung capacity. When resistances are converted to an effective diameter, Rrs data overestimate the increase in diameter during a DI. Simulation studies suggest that the decrease in apparent Rcw during a DI is a consequence of airway opening flow underestimating chest wall flow at increased lung volume. We conclude that the volume dependence of Rcw can bias the presumed net change in airway caliber during tidal breathing and a DI but would not distort assessment of maximum airway dilation.

Effects of EDTA- and Sulfite-containing Formulations of Propofol on Respiratory System Resistance after Tracheal Intubation in Smokers

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. 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. 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. 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.