Respiratory System Resistance Research Articles

Efficacy of Yiqigubiao pill on chronic obstructive pulmonary disease in rats with the disease induced by lipopolysaccharide and cigarette-smoke fumigation.

To investigate the efficacy of Yiqigubiao pill (YQGB) on chronic obstructive pulmonary disease (COPD) in rats with the COPD induced by lipopolysaccharide (LPS) and cigarette- smoke fumigation. In this study, six groups of rats were set up, including control group, model group, positive control group (aminophylline) and YQGB (high, medium and low doses) groups. Tracheal injection of lipopolysaccharide (LPS) and cigarette-smoke fumigation induced COPD in rats. The general condition, incubation period and coughing times, lung function, level of inflammatory factors, leukocyte condition and pathological changes of bronchus and lung tissue were observed in rats of each group. In the COPD rats, the latent period of coughing was shortened and the cough frequency was increased significantly; the pulmonary function was significantly decreased, which was manifested by the increased lung tissue resistance and respiratory system resistance, and the decreasing percentage of forced expiratory volume and forced expiratory volume in the 0.3 s (FEV0.3/FVC); the contents of tumor necrosis factor-alpha (TNF-α) and interleukin-4 in serum were obviously increased, and the NEUT% in bronchoalveolar lavage fluid was significantly increase. YQGB could obviously prolong the latent period of cough, and reduce the cough frequency and the content of TNF-α in serum. YQGB can also significantly reduce respiratory resistance and increase FEV0.3/FVC value. The results of histopathology showed that YQGB significantly reduced the pathological changes of tracheal mucosa and lung caused by COPD. YQGB obviously increased level of AQP1, which was down-regulated in the COPD rats. YQGB could significantly improve the pulmonary function, reduce inflammation and alleviate lung and bronchial diseases in the COPD rats.

UFP exposure and biomarkers of exposure/effect on small airways in school children

Background/Aim Ultrafine particles (UFP) are of health concern due to their small size and ability to diffuse into the circulatory system once inhaled. However, epidemiological studies of adverse respiratory effects from UFP exposure are uncommon and evidence is varied. There is a scarcity of data on its effects on small airways. We aimed to study associations between UFP exposure and markers of small airways exposure/impacts in school children. Methods We used a time-integrated model for particle number count (PNC) (UFP indicator), which combined measurements at schools and modelled PNC at home using land use and time trends, to assign annual average daily exposure. We measured biomarkers of small airways exposure/impact: respiratory system resistance (Rrs); respiratory system reactance (Xrs); and lung clearance index (LCI); in 577 children recruited from 25 schools. We estimated the effect of exposure to PNC on these outcomes using Bayesian generalised linear mixed effects regression models. Analyses adjusted for potential confounders, using three models: 1) age, sex, height; 2) Model 1 plus BMI, home air conditioning, carpet, garage, gas cooking, gas heating; home flooded or with visible mould (<12 months); blood cotinine levels (ETS); 3) Model 2 plus PM2.5 mass (24 h prior to clinical testing) and annual average daily NO2 exposure. Results The PNC model explained 26% of the variability of PNC measured at the schools. No statistically significant associations were observed between PNC and LCI or Xrs. Protective statistically significant associations were observed for respiratory resistance in Models 1 and 2, but not 3. Conclusions These results do not demonstrate a detrimental effect of UFP on biomarkers of small airways exposure/impact, and the results for resistance (reflecting airway calibre) are counter-intuitive to expected. This might be due to the low predictive capacity of the exposure model, therefore improved exposure measures are needed in future studies.

Biological effects of inhaled hydraulic fracturing sand dust. IV. Pulmonary effects

Hydraulic fracturing creates fissures in subterranean rock to increase the flow and retrieval of natural gas. Sand (“proppant”) in fracking fluid injected into the well bore maintains fissure patency. Fracking sand dust (FSD) is generated during manipulation of sand to prepare the fracking fluid. Containing respirable crystalline silica, FSD could pose hazards similar to those found in work sites where silica inhalation induces lung disease such as silicosis. This study was performed to evaluate the possible toxic effects following inhalation of a FSD (FSD 8) in the lung and airways. Rats were exposed (6 h/d × 4 d) to 10 or 30 mg/m3 of a FSD collected at a gas well, and measurements were performed 1, 7, 27 and, in one series of experiments, 90 d post-exposure. The following ventilatory and non-ventilatory parameters were measured in vivo and/or in vitro: 1) lung mechanics (respiratory system resistance and elastance, tissue damping, tissue elastance, Newtonian resistance and hysteresivity); 2) airway reactivity to inhaled methacholine (MCh); airway epithelium integrity (isolated, perfused trachea); airway efferent motor nerve activity (electric field stimulation in vitro); airway smooth muscle contractility; ion transport in intact and cultured epithelium; airway effector and sensory nerves; tracheal particle deposition; and neurogenic inflammation/vascular permeability. FSD 8 was without large effect on most parameters, and was not pro-inflammatory, as judged histologically and in cultured epithelial cells, but increased reactivity to inhaled MCh at some post-exposure time points and affected Na+ transport in airway epithelial cells.

Effects of allergic airway inflammation and chronic intermittent hypoxia on systemic blood pressure.

Asthma and obstructive sleep apnea (OSA) are highly prevalent chronic conditions, and both are associated with systemic hypertension. Additionally, asthma and OSA reciprocally interact, mutually exacerbating each other. In this study, we tested the effect of allergen-induced lower airway inflammation and concurrent chronic intermittent hypoxia (CIH) on systemic blood pressure (BP), pulmonary function, and proinflammatory cytokines, in a rat model. Brown Norway rats were exposed to 43 days of normoxia (NORM) or CIH, concurrent with weekly house dust mite (HDM) challenges. BP was measured 1 day after the last HDM challenge. On day 44, pulmonary function was tested, and blood for Th-2 and Th-1 cytokine levels was collected. HDM significantly increased mean (P = 0.002), systolic (P = 0.003), and diastolic (P = 0.004) BP compared with saline-challenged controls. Higher mean BP significantly correlated to increased total respiratory system resistance (R2 = 0.266, P = 0.002), driven by an association with parenchymal tissue dampening (R2 = 0.166, P = 0.016). HDM relative to saline-challenged controls increased the expression of serum IL-6 (P = 0.008), but no relationships of systemic BP with IL-6 or any other cytokines were found. CIH did not alter the allergen-induced responses on BP, although it tended to increase the expression of serum IL-6 (P = 0.06) and monocyte chemoattractant protein-1 (MCP-1, P = 0.09), regardless of HDM challenge. Chronic allergen-induced airway inflammation results in systemic hypertension that is correlated to the degree of distal airway obstruction induced by the allergen. These effects do not appear to be explained by the associated systemic inflammation.

Methods to Evaluate Airway Resistance and Lung Compliance During Mechanical Ventilation: A Comparative Study

Mechanical ventilation is a lifesaving activity that is used in critical care management. In such case, monitoring of airway resistance(Raw) and lung compliance(CL) play a major role for diagnosing the lung condition, setting the ventilator parameters, can act as a decision parameter for weaning the patient from the ventilator. Several methods have been described for estimating these respiratory parameters. In this work, a study is conducted to compare two different methods used to calculate airway resistance and lung compliance during mechanical ventilation. Michigan Adult/Infant lung simulator is used to simulate different compliance conditions and Michigan Pneuflo Resistors to simulate different resistance conditions. Flow, volume and pressure data were logged for different set parameters i.e. for different resistance and compliance combinations. Later these data were used to calculate the respiratory system resistance and compliance. Two methods were used to calculate lung parameters, dynamic approach and Least Square fitting(LSF) method(using respiratory system equation of motion). Both methods gave accurate estimate of Raw and CL. But the dynamic approach required respiratory maneuver whereas LSF approach required large datasets to carry out the calculation and the patient should not show any active breathing during evaluation

Using airway resistance measurement to determine when to switch ventilator modes in congenital diaphragmatic hernia: a case report

BackgroundCongenital diaphragmatic hernia is a deficiency of the fetal diaphragm resulting in herniation of the abdominal viscera into the thoracic cavity. The best method of respiratory management of congenital diaphragmatic hernia is unclear, but high frequency oscillatory ventilation is often used as the initial ventilator mode for severe congenital diaphragmatic hernia. When it becomes impossible to maintain the pre-ductal saturations, the timing of successful switching of the ventilation mode from high frequency oscillatory ventilation to conventional mechanical ventilation remains unclear. Herein, we reported two cases in which airway resistance measurements based on pulmonary function tests were used for making the decision to switch the ventilator mode from high frequency oscillatory ventilation to conventional mechanical ventilation in patients with left isolated congenital diaphragmatic hernia.Case presentationTwo 0-day-old infants with congenital diaphragmatic hernia were admitted to our hospital. In both patients, high frequency oscillatory ventilation was started initially, and the levels of saturation gradually rose within a few hours after birth. After 24 h of high frequency oscillatory ventilation, the level of saturation decreased, and the dissociation of pre-ductal and post-ductal saturation re-occurred. The respiratory-system resistance was 515 and 403 cmH2O·kg/L/s, respectively. Because the respiratory-system resistance was elevated, we decided to change the ventilator mode from high frequency oscillatory ventilation to conventional mechanical ventilation. After switching to conventional mechanical ventilation, the patients’ heart rate and saturation increased immediately.ConclusionsIn patients with congenital diaphragmatic hernia, resistance levels of > 400 cmH2O·kg/L/s may indicate high airway resistance and suggest greater alveolar vibration attenuation. When respiratory-system resistance reaches over 400 cmH2O·kg/L/s, it may be an optimal time for switching from high frequency oscillatory ventilation to conventional mechanical ventilation.

Effect of nasal airway nonlinearities on oscillometric resistance measurements in infants.

Oscillometric measurements of respiratory system resistance (Rrs) in infants are usually made via the nasal pathways, which not only significantly contribute to overall Rrs but also introduce marked flow (V')-dependent changes. We employed intrabreath oscillometry in casts of the upper airways constructed from head CT images of 46 infants. We examined oscillometric nasal resistance (Rn) in upper airway casts with no respiratory flow (R0) and the effect of varying V' on Rn by simulating tidal breathing. A characteristic nonlinear relationship was found between Rn and V', exhibiting segmental linearity and a prominent breakpoint (V'bp) after log-log transformation. V'bp was linearly related to the preceding value of end-expiratory volume acceleration (V″eE; on average r2 = 0.96, P < 0.001). Rn depended on V', and R at end-expiration (ReE) showed a strong dependence on V″eE in every cast (r2 = 0.994, P < 001) with considerable interindividual variability. The intercept of the linear regression of ReE versus V″eE was found to be a close estimate of R0. These findings were utilized in reanalyzed Rrs data acquired in vivo in a small group of infants (n = 15). Using a graphical method to estimate R0 from ReE, we found a relative contribution of V'-dependent nonlinearity to total resistance of up to 33%. In conclusion, we propose a method for correcting the acceleration-dependent nonlinearity error in ReE. This correction can be adapted to estimate R0 from a single intrabreath oscillometric measurement, which would reduce the masking effects of the upper airways on the changes in the intrathoracic resistance.NEW & NOTEWORTHY Oscillometric measurements of respiratory system resistance (Rrs) in infants are usually made via the nasal pathways, which not only significantly contribute to overall Rrs but also introduce marked flow acceleration-dependent distortions. Here, we propose a method for correcting flow acceleration-dependent nonlinearity error based on in vitro measurements in 3D-printed upper airway casts of infants as well as in vivo measurements. This correction can be adapted to estimate Rrs from a single intrabreath oscillometric measurement.

Prenatal exposure to VOCs and NOx and lung function in preschoolers.

Several studies have shown that exposure to air pollutants affects lung growth and development and can result in poor respiratory health in early life. We included a subsample of 772 Mexican preschoolers whose mothers participated in a Prenatal Omega-3 fatty acid Supplements, GRowth, And Development birth cohort study with the aim to evaluate the impact of prenatal exposure to volatile organic compounds and nitrogen oxides on lung function measured by oscillation tests. The preschoolers were followed until 5 years of age. Anthropometric measurements and forced oscillation tests were performed at 36, 48, and 60 months of age. Information on sociodemographic and health characteristics was obtained during follow up. Prenatal exposure to volatile organic compounds and nitrogen oxides was evaluated using a land use regression models and the association between them was tested using a lineal regression and longitudinal linear mixed effect models adjusting for potential confounders. Overall, the mean (standard deviation) of the measurements of respiratory system resistance and respiratory system reactance at 6, 8, and 10 Hz during the follow-up period was 11.3 (2.4), 11.1 (2.4), 10.3 (2.2) and -5.2 (1.6), -4.8 (1.7), and -4.6 hPa s L-1 (1.6), respectively. We found a significantly positive association between respiratory resistance (βRrs6 = 0.011; 95%CI: 0.001, 0.023) (P < .05) and prenatal exposure to nitrogen dioxide and a marginally negatively association between respiratory reactance (βXrs6 = -11.40 95%CI: -25.26, 1.17 and βXrs8 = -11.91 95%CI: -26.51, 1.43) (P = .07) and prenatal exposure to xylene. Prenatal exposure to air pollutants was significantly associated with the alteration of lung function measured by oscillation tests in these preschool children.

Effects of Controlled Voluntary Increase in the Ventilatory Demand on Respiratory System Resistance in Healthy and Non-Cystic Fibrosis Bronchiectasis Subjects: A Cross-Sectional Study

IntroductionBronchiectasis patients may present a reduced functional capacity due to an increase in the ventilatory demand during exercise. ObjectiveTo evaluate the effects of controlled voluntary hyperinflation and increased respiratory rate on the mechanics of the respiratory system, simulating what happens during exercise, in bronchiectasis and healthy subjects. MethodsBronchiectasis (n=30) and healthy (n=16) subjects were evaluated by impulse oscillometry (IOS) during a baseline condition, and in controlled conditions with baseline (b) tidal volume (V) and hyperinflation (H), with respiratory rates at 30(R30) and 40(R40) bpm, in a random order. The mixed effects and a significance level at 0.05 were used for comparisons. ResultsResistance at 5Hz (R5), and at minus 20Hz (R5–R20), in kPa/L/s, were higher in subjects with bronchiectasis in all experimental conditions (p<0.05). For the bronchiectasis group, R5 and R5-20 increased with R increase at V (VRb versus VR30 and VR40; VR30 versus VR40; R5, R20 and R5-20 increased with R increase at H (HRb versus HR40; HR30 versus HR40). For the same R, there was a decrease with H compared to V (HRb versus VR30 and VR40; and HR30 versus VR30 and VR40). For the healthy group, only R20 showed differences (HR30 versus HR40; HR40 versus VR40). ConclusionThe tachypnea increases the resistance and reactance of the respiratory system in bronchiectasis patients, and the voluntary hyperinflation caused attenuates this increase. These results can guide the development of strategies to reduce the limitation of physical activity in patients with bronchiectasis.

Folium Sennae and emodin reverse airway smooth muscle contraction.

The objective of this project was to find a bronchodilatory compound from herbs and clarify the mechanism. We found that the ethanol extract of Folium Sennae (EEFS) can relax airway smooth muscle (ASM). EEFS inhibited ASM contraction, induced by acetylcholine, in mouse tracheal rings and lung slices. High-performance liquid chromatography assay showed that EEFS contained emodin. Emodin had a similar reversal action. Acetylcholine-evoked contraction was also partially reduced by nifedipine (a selective inhibitor of L-type voltage-dependent Ca2+ channels, LVDCCs), YM-58483 (a selective inhibitor of store-operated Ca2+ entry, SOCE), as well as Y-27632 (an inhibitor of Rho-associated protein kinase). In addition, LVDCC- and SOCE-mediated currents and cytosolic Ca2+ elevations were inhibited by emodin. Emodin reversed acetylcholine-caused increases in phosphorylation of myosin phosphatase target subunit 1. Furthermore, emodin, in vivo, inhibited acetylcholine-induced respiratory system resistance in mice. These results indicate that EEFS-induced relaxation results from emodin inhibiting LVDCC, SOCE, and Ca2+ sensitization. These findings suggest that Folium Sennae and emodin may be new sources of bronchodilators.

Measuring lung mechanics of expiratory tidal breathing with non-invasive breath occlusion

Background and objectiveLung mechanics measurements provide clinically useful information about disease progression and lung health. Currently, there are no commonly practiced methods to non-invasively measure both resistive and elastic lung mechanics during tidal breathing, preventing the important information provided by lung mechanics from being utilised. This study presents a novel method to easily assess lung mechanics of spontaneously breathing subjects using a dynamic elastance, single-compartment lung model.MethodsA spirometer with a built-in shutter was used to occlude expiration during tidal breathing, creating exponentially decaying flow when the shutter re-opened. The lung mechanics measured were respiratory system elastance and resistance, separated from the exponentially decaying flow, and interrupter resistance calculated at shutter closure. Progressively increasing resistance was added to the spirometer mouthpiece to simulate upper airway obstruction. The lung mechanics of 17 healthy subjects were successfully measured through spirometry.ResultsN = 17 (8 female, 9 male) healthy subjects were recruited. Measured decay rates ranged from 5 to 42/s, subjects with large variation of decay rates showed higher muscular breathing effort. Lung elastance measurements ranged from 3.9 to 21.2 cmH_2O/L, with no clear trend between change in elastance and added resistance. Resistance calculated from decay rate and elastance ranged from 0.15 to 1.95 cmH_2Os/L. These very small resistance values are due to the airflow measured originating from low-resistance areas in the centre of airways. Occlusion resistance measurements were as expected for healthy subjects, and increased as expected as resistance was added.ConclusionsThis test was able to identify reasonable dynamic lung elastance and occlusion resistance values, providing new insight into expiratory breathing effort. Clinically, this lung function test could impact current practice. It does not require high levels of cooperation from the subject, allowing a wider cohort of patients to be assessed more easily. Additionally, this test can be simply implemented in a small standalone device, or with standard lung function testing equipment.

Intermittent CPAP limits hyperoxia-induced lung damage in a rabbit model of bronchopulmonary dysplasia.

A significant proportion of preterm infants develop bronchopulmonary dysplasia (BPD) leading to poor lifelong respiratory health. Limited treatment options exist with continuous positive airway pressure (CPAP) ventilation being one of the few associated with diminished BPD. However, little is known about the effect of the distending pressure of CPAP on the developing lung exposed to hyperoxia. We aimed to identify the functional and structural effects of CPAP in a preterm hyperoxia rabbit model of BPD. Premature rabbit pups were randomized to normoxia, hyperoxia (≥95% O2), or hyperoxia plus 4 h daily CPAP [fraction of inspired oxygen (FiO2) 0.95, 5 cmH2O]. On day 7 postdelivery we performed invasive pressure-volume- and forced oscillation-based pulmonary function tests, before lung harvest for histological evaluation. Alveolar and vascular morphology, airway smooth muscle content, respiratory epithelium height, extracellular matrix components, and inflammatory cytokine expression were quantified. Hyperoxia-reared pups had restrictive lungs: alveolar walls were thickened, with the lung parenchymal tissue, collagen content, and airway smooth muscle content increased. In addition, peripheral pulmonary artery wall thickness was increased. CPAP increased alveolar recruitment and limited the structural effect of hyperoxia on the respiratory epithelium and pulmonary arteries. Additionally, CPAP improved lung function, mitigating hyperoxia-associated changes to respiratory system resistance, tissue damping, and tissue elastance. Hyperoxia disrupted functional and structural lung development. Daily intermittent CPAP limited hyperoxia-associated decreased lung function and attenuated structural changes to pulmonary arteries and respiratory epithelium while having no structural alveolar consequences. The mechanism by which CPAP has these beneficial effects needs further investigation.

Bronchodilator Response Assessed by the Forced Oscillation Technique Identifies Poor Asthma Control With Greater Sensitivity Than Spirometry

Persistent bronchodilator response (BDR) following diagnosis of asthma is an underrecognized treatable trait, associated with worse lung function and asthma control. The forced oscillation technique (FOT) measures respiratory system impedance, and BDR cutoffs have been proposed for healthy adults; however, the relevance in asthma is unknown. We compared BDR cutoffs, using FOT and spirometry, in asthma and the relationship with asthma control. Data from patients with asthma who withheld bronchodilator medication for at least 8h before a tertiary airway clinic visit were reviewed. All subjects performed FOT and spirometry before and after salbutamol administration, and completed the Asthma Control Test. FOT parameters examined included respiratory system resistance (R5) and reactance (X5) at 5Hz, and area under the reactance curve (AX). BDR was defined by standard recommendations for spirometry and based on the 95th percentile of BDR in healthy adults for FOT. Fifty-two subjects (18 men; mean age, 53 ± 18 years) were included. BDR was identified more frequently by FOT than spirometry (54%vs27%of subjects). BDR assessed by X5 and AX, but not R5, was associated with spirometric BDR (χ2, P< .01) and correlated with asthma control (X5: rs= -0.36, P< .01; AX: rs= 0.34, P= .01). BDR measured by reactance parameters identified more subjects with poor asthma control than did spirometry (AX, 69%vsspirometry, 41%). BDR assessed by FOT can identify poor asthma control. Reactance parameters were more sensitive in identifying poor asthma control than spirometry, supporting the use of FOT to complement spirometry in the clinical management of asthma.

Respiratory mechanics during initial lung aeration at birth in the preterm lamb.

Despite recent insights into the dynamic processes during lung aeration at birth, several aspects remain poorly understood. We aimed to characterize changes in lung mechanics during the first inflation at birth and their relationship to changes in lung volume. Intubated preterm lambs (gestational age, 124-127 days; n = 17) were studied at birth. Lung volume changes were measured by electrical impedance tomography (VLEIT). Respiratory system resistance (R5) and oscillatory compliance (Cx5) were monitored with the forced oscillation technique at 5 Hz. Lambs received 3-7 s of 8 cmH2O of continuous distending pressure (CDP) before delivery of a sustained inflation (SI) of 40 cmH2O. The SI was then applied until either Cx5 or the VLEIT or the airway opening volume was stable. CDP was resumed for 3-7 s before commencement of mechanical ventilation. The exponential increases with time of Cx5 and VLEIT from commencement of the SI were characterized by estimating their time constants (τCx5 and τVLEIT, respectively). During SI, a fast decrease in R5 and an exponential increase in Cx5 and VLEIT were observed. Cx5 and VLEIT provided comparable information on the dynamics of lung aeration in all lambs, with τCx5 and τVLEIT being highly linearly correlated (r2 = 0.87, P < 0.001). Cx5 and VLEIT decreased immediately after SI. Despite the standardization of the animal model, changes in Cx5 and R5 both during and after SI were highly variable. Lung aeration at birth is characterized by a fast reduction in resistance and a slower increase in oscillatory compliance, the latter being a direct reflection of the amount of lung aeration.

Non-invasive measurement of tidal breathing lung mechanics using expiratory occlusion

A great amount of research looks at whether information about lung mechanics can be obtained using spirometry, as these mechanics give clinically useful information about lung condition and disease progression. This study uses a time-varying elastance, single compartment lung model to calculate lung mechanics of 15 tidally breathing healthy subjects. A plethysmograph with a built-in shutter was used to induce an exponentially decaying airflow. Lung elastance and respiratory system resistance were separated from the decay rate of flow caused by the shutter. Occlusion resistance was calculated at shutter closure. To simulate upper airway obstruction, progressively larger resistances were added to the plethysmograph mouthpiece.Decay rates measured ranged from 5-42, with large intra-subject variation associated with muscular breathing effort. Measured lung elastance ranged from 3.9-21.2 cmH2O/L and often remained constant as resistance was increased. Resistance calculated from the decay rate was very small, ranging from 0.15-1.95 cmH2Os/L. The low resistance is due to the airflow measured originating from low resistance areas in the centre of airways. Occlusion resistance measurements were as expected for healthy subjects, and followed the expected resistance trend as resistance was increased.

Effect of Endotracheal Tube Size, Respiratory System Mechanics, and Ventilator Settings on Driving Pressure.

We sought to investigate factors that affect the difference between the peak inspiratory pressure measured at the Y-piece under dynamic flow conditions and plateau pressure measured under zero-flow conditions (resistive pressure) during pressure controlled ventilation across a range of endotracheal tube sizes, respiratory mechanics, and ventilator settings. In vitro study. Research laboratory. None. An in vitro bench model of the intubated respiratory system during pressure controlled ventilation was used to obtain the difference between peak inspiratory pressure measured at the Y-piece under dynamic flow conditions and plateau pressure measured under zero-flow conditions across a range of endotracheal tubes sizes (3.0-8.0 mm). Measurements were taken at combinations of pressure above positive end-expiratory pressure (10, 15, and 20 cm H2O), airway resistance (no, low, high), respiratory system compliance (ranging from normal to extremely severe), and inspiratory time at constant positive end-expiratory pressure (5 cm H2O). Multiple regression analysis was used to construct models predicting resistive pressure stratified by endotracheal tube size. On univariate regression analysis, respiratory system compliance (β -1.5; 95% CI, -1.7 to -1.4; p < 0.001), respiratory system resistance (β 1.7; 95% CI, 1.5-2.0; p < 0.001), pressure above positive end-expiratory pressure (β 1.7; 95% CI, 1.4-2.0; p < 0.001), and inspiratory time (β -0.7; 95% CI, -1.0 to -0.4; p < 0.001) were associated with resistive pressure. Multiple linear regression analysis showed the independent association between increasing respiratory system compliance, increasing airway resistance, increasing pressure above positive end-expiratory pressure, and decreasing inspiratory time and resistive pressure across all endotracheal tube sizes. Inspiratory time was the strongest variable associated with a proportional increase in resistive pressure. The contribution of airway resistance became more prominent with increasing endotracheal tube size. Peak inspiratory pressures measured during pressure controlled ventilation overestimated plateau pressure irrespective of endotracheal tube size, especially with decreased inspiratory time or increased airway resistance.

Reproducibility of respiratory mechanics measurements in patients on invasive mechanical ventilation.

ObjectiveTo evaluate the intra- and interexaminer reproducibility of measurements of the resistance and static and dynamic compliance of the respiratory system in patients on mechanical ventilation.MethodsThis was an analytical study conducted with individuals aged ≥ 18 years who were on invasive mechanical ventilation and had no clinical diagnosis of respiratory system disease and/or chest abnormality. Three measurements of respiratory mechanics were performed with a 1-minute interval between them. The first and third measurements were performed by examiner A, the second by examiner B. The values for the resistance and static and dynamic compliance of the respiratory system were compared using the intraclass correlation coefficient.ResultsA total of 198 measurements of respiratory mechanics were performed for 66 patients on mechanical ventilation. The patients had a mean age of 52.6 ± 18.6 years and a mean body mass index of 21.6 ± 2.1kg/m2; a surgical profile (61.5%) and female sex (53.8%) were predominant. Mean values were obtained for the three measurements of respiratory system resistance (A1: 15.7 ± 6.8cmH2O/L/s; B1: 15.7 ± 6.4cmH2O/L/s and A2: 15.9 ± 6.2cmH2O/L/s), respiratory system static compliance (A1: 42.1 ± 13.7mL/cmH2O; B1: 42.4 ± 14.6mL/cmH2O and A2: 42.2 ± 14.5mL/cmH2O) and respiratory system dynamic compliance (A1: 21.3 ± 7.3mL/cmH2O; B1: 21.4 ± 7.5mL/cmH2O and A2: 21.3 ± 6.2mL/cmH2O). The intraclass correlation coefficient was also calculated for respiratory system resistance (R = 0.882 and p = 0.001; R = 0.949 and p = 0.001 - interexaminer A1 versus B and B versus A2, respectively; R = 0.932 and p = 0.001 - intraexaminer); respiratory system static compliance (R = 0.951 and p = 0.001; R = 0.958 and p = 0.001 - interexaminer A1 versus B and B versus A2, respectively; R = 0.965 and p = 0.001 - intraexaminer) and respiratory system dynamic compliance (R = 0.957 and p = 0.001; R = 0.946 and p = 0.001 - interexaminer A1 versus B and B versus A2, respectively; R = 0.926 and p = 0.001 - intraexaminer).ConclusionThe measurements of resistance and static and dynamic compliance of the respiratory system show good intra- and interexaminer reproducibility for ventilated patients.

Regression Equations of Respiratory Impedance Measured by Forced Oscillation Technique for Indian Children.

To develop regression equations of within and whole-breath respiratory impedance for Indian children aged 5 to 17 y. A prospective cross-sectional study was carried out in 5 to 17 y old school children of Bhopal, India. Healthy children were identified by physical examination and by administering questionnaire. The respiratory system resistance (Rrs) and reactance (Xrs) were measured at frequency of 5, 11, and 19Hz by forced oscillation technique (FOT). The regression equations of within and whole-breath Rrs and Xrs were developed separately for boys and girls by multiple linear regression models. Total 336 children were recruited and data of 320 healthy children (boys - 159), standing height of 146.1 ± 16.6cm and body mass index of17.2 ± 2.9kg/m2 were included in the analysis. The mean respiratory system resistance at 5Hz (R5) and respiratory system reactance at 5Hz (X5) of the children, irrespective of gender were 5.46 ± 2.10 cmH2O/L/s and - 1.43 ± 0.85 cmH2O/L/s respectively. Boys of age 16 y and older had significantly smaller Rrs as compared to girls of corresponding age (p < 0.05). The standing height of children had the highest predictive power, followed by age in the regression model. With an increase in standing height, the magnitude of both Rrs and Xrs values of children decrease. The bodyweight of children had a negligible contribution to the regression models. The regression equations of within- and whole-breath Rrs and Xrs of Indian children aged 5 to 17 y are presented for the first time. The R5 values of Indian children were comparable to children of other ethnicities.

Environmental Tobacco Smoke Affects Lung Function of Preschoolers With Asthma Even After a Decade

To evaluate whether early tobacco smoke exposure has a long-term effect on lung function.Children (n = 105; mean age: 5.62 years) with a history of wheeze and bronchodilator response had been previously enrolled for a study evaluating the association between maternal smoking and preschool asthma. Children could not have taken corticosteroids in the previous 6 months nor have had a respiratory tract infection in the previous 2 weeks. These children were evaluated at a follow-up visit 10 years after the initial enrollment (n = 64; mean age: 14.22 years).The cohort in this study had been assessed at enrollment for environmental tobacco smoke exposure by urinary cotinine and questionnaires. At both enrollment and the 10-year follow-up, fractional exhaled nitric oxide (FeNO), impulse oscillometry (IOS), blood eosinophil counts, and allergic sensitization to indoor and outdoor aeroallergens were assessed. At the 10-year follow-up, children also performed spirometry and a methacholine challenge. Results were compared between enrollment and follow-up.At the 10-year follow-up, fewer children wheezed in the previous year (11% vs 83%), whereas more children had positive allergy testing results (92% vs 70%). Blood eosinophil count, FeNO, and total respiratory system resistance (resistance at 5 Hz [R5]), one of the IOS indices, were all decreased at follow-up. Forty-three percent of parents stopped smoking during the 10 years. Approximately one-third of children reported asthma symptoms and the need for asthma medications in the previous 2 months at the follow-up visit. None reported smoking. Being overweight correlated with forced expiratory volume in 1 second and/or forced vital capacity and the IOS indices (R5 and area under reactance), at the follow-up visit but did not correlate with the preschool urinary cotinine levels. However, preschool urinary cotinine levels did significantly correlate with increased FeNO scores, blood eosinophils, and R5 and decreased reactance (by 5) at the follow-up. No significant correlation was seen with forced expiratory volume in 1 second or methacholine challenge.Early tobacco smoke exposure is linked to the presence of airway inflammation and decreased lung function in older children with a history of asthma.Limitations included the lack of a control asthma group without preschool exposure to tobacco smoke, the small sample size, and lack of interval assessment during the 10-year period to evaluate the potential confounding effect of other environmental factors, socioeconomic factors, or the development of other comorbidities. The study also did not consider whether aeroallergen sensitization had an impact on lung function over time. IOS is not as commonly performed as spirometry for the assessment of asthma, so the use of IOS in assessing and managing asthma in a clinical practice needs further validation. Nevertheless, this study provides further proof that early exposure to tobacco smoke in childhood potentially has long-term negative health effects.

Obesity alters the topographical distribution of ventilation and the regional response to bronchoconstriction.

Obesity is associated with reduced operating lung volumes that may contribute to increased airway closure during tidal breathing and abnormalities in ventilation distribution. We investigated the effect of obesity on the topographical distribution of ventilation before and after methacholine-induced bronchoconstriction using single-photon emission computed tomography (SPECT)-computed tomography (CT) in healthy subjects. Subjects with obesity (n = 9) and subjects without obesity (n = 10) underwent baseline and postbronchoprovocation SPECT-CT imaging, in which Technegas was inhaled upright and followed by supine scanning. Lung regions that were nonventilated (Ventnon), low ventilated (Ventlow), or well ventilated (Ventwell) were calculated using an adaptive threshold method and were expressed as a percentage of total lung volume. To determine regional ventilation, lungs were divided into upper, middle, and lower thirds of axial length, derived from CT. At baseline, Ventnon and Ventlow for the entire lung were similar in subjects with and without obesity. However, in the upper lung zone, Ventnon (17.5 ± 10.6% vs. 34.7 ± 7.8%, P < 0.001) and Ventlow (25.7 ± 6.3% vs. 33.6 ± 5.1%, P < 0.05) were decreased in subjects with obesity, with a consequent increase in Ventwell (56.8 ± 9.2% vs. 31.7 ± 10.1%, P < 0.001). The greater diversion of ventilation to the upper zone was correlated with body mass index (rs = 0.74, P < 0.001), respiratory system resistance (rs = 0.72, P < 0.001), and respiratory system reactance (rs = -0.64, P = 0.003) but not with lung volumes or basal airway closure. Following bronchoprovocation, overall Ventnon increased similarly in both groups; however, in subjects without obesity, Ventnon only increased in the lower zone, whereas in subjects with obesity, Ventnon increased more evenly across all lung zones. In conclusion, obesity is associated with altered ventilation distribution during baseline and following bronchoprovocation, independent of reduced lung volumes.NEW & NOTEWORTHY Using ventilation SPECT-computed tomography imaging in healthy subjects, we demonstrate that ventilation in obesity is diverted to the upper lung zone and that this is strongly correlated with body mass index but is independent of operating lung volumes and of airway closure. Furthermore, methacholine-induced bronchoconstriction only occurred in the lower lung zone in individuals who were not obese, whereas in subjects who were obese, it occurred more evenly across all lung zones. These findings show that obesity-associated factors alter the topographical distribution of ventilation.