Characteristics of lung resistance and elastance associated with tracheal stenosis and intrapulmonary airway narrowing in ex vivo sheep lungs.

BACKGROUND: Understanding the characteristics of pulmonary resistance and elastance in relation to the location of airway narrowing, e.g., tracheal stenosis vs. intrapulmonary airway obstruction, will help us understand lung function characteristics and mechanisms related to different airway diseases. METHODS: In this study, we used ex vivo sheep lungs as a model to measure lung resistance and elastance across a range of transpulmonary pressures (5-30 cmH2O) and ventilation frequencies (0.125-2 Hz). We established two tracheal stenosis models by inserting plastic tubes into the tracheas, representing mild (71.8% lumen area reduction) and severe (92.1%) obstructions. For intrapulmonary airway obstruction, we induced airway narrowing by challenging the lung with acetylcholine (ACh). RESULTS: We found a pattern change in the lung resistance and apparent lung elastance as functions of ventilation frequency that depended on the transpulmonary pressure (or lung volume). At a transpulmonary pressure of 10 cmH2O, lung resistance increased with ventilation frequency in severe tracheal stenosis, whereas in ACh-induced airway narrowing the opposite occurred. Furthermore, apparent lung elastance at 10 cmH2O decreased with increasing ventilation frequency in severe tracheal stenosis whereas in ACh-induced airway narrowing the opposite occurred. Flow-volume analysis revealed that the flow amplitude was much sensitive to ventilation frequency in tracheal stenosis than it was in ACh induced airway constriction. CONCLUSIONS: Results from this study suggest that lung resistance and apparent elastance measured at 10 cmH2O over the frequency range of 0.125-2 Hz can differentiate tracheal stenosis vs. intrapulmonary airway narrowing in ex vivo sheep lungs.

Effects of sitting, supine, and prone postures on nasal patency in individuals with obstructive sleep apnea syndrome.

BACKGROUND: Studies have found that in healthy individuals without nasal disease, changes in posture cause an increase in nasal resistance, especially in the prone posture. Many patients with obstructive sleep apnea syndrome (OSAS) sleep in a prone posture, but no studies have examined the effect of this change in posture on nasal resistance in patients with OSAS. Therefore, we conducted this study to investigate this posture-related physical phenomenon in individuals with OSAS. METHODS: We evaluated the nasal patency of 29 patients diagnosed with OSAS using the visual analog scale (VAS), acoustic rhinometry, and video-endoscopy in the sitting, supine, and prone postures. RESULTS: In the OSAS group, both supine and prone postures significantly influenced subjective nasal blockage and led to a notable reduction in the minimal cross-sectional area (mCSA) as determined by acoustic rhinometry, compared to the sitting posture. The prone posture exhibited a more pronounced effect than the supine posture. Endoscopic evaluations further revealed increased hypertrophy of the inferior turbinate in the supine posture for the right nasal passage and the prone posture for the left. However, no significant differences were observed between the prone and supine postures. CONCLUSION: In OSAS patients, nasal resistance significantly increased in supine and prone postures compared to sitting, with the prone posture showing a greater effect. Clinicians should consider a patient's habitual sleep posture and the effects of postural changes when assessing OSAS severity and devising treatment plans.

Airway mechanics alters generation of cough motor pattern.

Effects of sequential increase in airway resistance: no, low (5 kPa.s/l), high (24 kPa.s/l), and complete block in the inspiratory or expiratory phase of mechanically induced cough on the cough motor pattern were studied in 16 anesthetized (pentobarbital) spontaneously breathing cats (3.70±0.15 kg, 11♂, 5♀). Esophageal pressure and electromyographic activities of the diaphragm during inspiration and abdominal muscles during expiration were analyzed. No significant changes in the number of coughs occurred. Inspiratory occlusion caused a prolongation of cough inspiratory phase, cough inspiratory diaphragm activity, and all cough-related activity. Inspiratory occlusion along with high resistance increased inspiratory esophageal pressure amplitude, total cough cycle duration and the time between maximum activity of the diaphragm and abdominal muscles. High expiratory resistance and occlusion resulted in increased cough expiratory esophageal pressure amplitude, a longer active portion of cough expiration, and cough abdominal activity. Expiratory occlusion also prolonged cough expiratory phase, all cough activity, and total cough cycle. Significantly increased airway resistance and occlusion induce secondary, in addition to mechanical, changes in cough by significantly modulating the generated cough motor pattern. A certain level of resistance appears to be successfully compensated, resulting in minimal changes in coughing characteristics, including expiratory airflow and the rising time of the airflow. Afferent feedback from the respiratory tract, particularly volume feedback, represents a significant factor in modulating cough, mainly under various pathological conditions in the respiratory system.

Effects of increasing tidal volume and end-expiratory lung volume on induced bronchoconstriction in healthy humans.

BACKGROUND: Increasing functional residual capacity (FRC) or tidal volume (VT) reduces airway resistance and attenuates the response to bronchoconstrictor stimuli in animals and humans. What is unknown is which one of the above mechanisms is more effective in modulating airway caliber and whether their combination yields additive or synergistic effects. To address this question, we investigated the effects of increased FRC and increased VT in attenuating the bronchoconstriction induced by inhaled methacholine (MCh) in healthy humans. METHODS: Nineteen healthy volunteers were challenged with a single-dose of MCh and forced oscillation was used to measure inspiratory resistance at 5 and 19 Hz (R5 and R19), their difference (R5-19), and reactance at 5 Hz (X5) during spontaneous breathing and during imposed breathing patterns with increased FRC, or VT, or both. Importantly, in our experimental design we held the product of VT and breathing frequency (BF), i.e, minute ventilation (VE) fixed so as to better isolate the effects of changes in VT alone. RESULTS: Tripling VT from baseline FRC significantly attenuated the effects of MCh on R5, R19, R5-19 and X5. Doubling VT while halving BF had insignificant effects. Increasing FRC by either one or two VT significantly attenuated the effects of MCh on R5, R19, R5-19 and X5. Increasing both VT and FRC had additive effects on R5, R19, R5-19 and X5, but the effect of increasing FRC was more consistent than increasing VT thus suggesting larger bronchodilation. When compared at iso-volume, there were no differences among breathing patterns with the exception of when VT was three times larger than during spontaneous breathing. CONCLUSIONS: These data show that increasing FRC and VT can attenuate induced bronchoconstriction in healthy humans by additive effects that are mainly related to an increase of mean operational lung volume. We suggest that static stretching as with increasing FRC is more effective than tidal stretching at constant VE, possibly through a combination of effects on airway geometry and airway smooth muscle dynamics.

Assessment of nasal respiration and three-dimensional airway volume changes in orthognathic surgery patients.

OBJECTIVES: The aim of this study was to evaluate the effect of maxillary movements in orthognathic surgery on nasal airway volume change and its correlation with airflow and resistance. MATERIALS AND METHODS: This study included 25 patients (8 male, 17 female) with Class II (6 patients) or Class III (19 patients) malocclusion. All patients underwent Le Fort I and bilateral sagittal split ramus osteotomy. Nasal airflow and resistance were measured by using rhinomanometry and acoustic rhinometry pre and six months post-operatively. Nasal volume was measured using computed tomography before surgery and six months after surgery. RESULTS: Nasal volume increased in 10 out of 11 patients with CCW (counterclockwise) rotation and decreased in 1 patient while, nasal volume increased in 5 patients with CW (clockwise) rotation and decreased in 9 patients. Superior nasal airway volume increased significantly, while the effects on nasal flow and resistance were not significant. Additionally, no significant correlation was found between airway volume changes and variations in airflow and resistance. CONCLUSION: CCW rotation in orthognathic surgery patients significantly increased superior nasal airway volume but did not improve nasal airway flow and resistance.

Small airway resistance in obese and nonobese patients with obstructive sleep apnea syndrome using impulse oscillometry.

Background/aim: There is limited information on the pathologic changes in the small airways among obese and nonobese patients with obstructive sleep apnea syndrome (OSAS). Impulse oscillometry (IOS) measures airway resistance and reactance independently of patient effort. This study aimed to compare airway resistance in small airways using IOS between obese and nonobese patients with OSAS. Materials and methods: In this real-life cross-sectional study, demographic information was collected from obese and nonobese subjects diagnosed with moderate and severe OSAS without any other underlying diseases. Spirometry and IOS measurements were conducted, and the values of both groups were statistically analyzed. Results: The nonobese group had a mean age of 45.6 ± 11.7 years (median 45), while the obese group had a mean age of 48.4 ± 9.5 years (median 47.5). The mean body mass index (BMI) for the nonobese group was 26.2 ± 2.1 kg/m2 (median 27 kg/m2), and for the obese group, it was 35.6 ± 6.4 kg/m2 (median 33 kg/m2). Statistically significant differences were observed between the two groups in R5 - R20 percentage, reactance area (AX), and resonant frequency (Fres) values (p < 0.05). Conclusion: Among obese OSAS patients, there is an increase in resistance in small airways as indicated by IOS values. IOS shows promise as a potential screening tool for diagnosing OSAS.

Nasal airway resistance in patients with different degrees of operated unilateral cleft lip: Evaluation of ventilation in 112 patients.

OBJECTIVE: The aim of this study was to compare the nasal airway resistance between the cleft and non-cleft sides in operated unilateral cleft lip (UCL) patients with varying severities at birth, as well as to assess the differences in nasal airway resistance between UCL patients and healthy individuals. METHODS: This retrospective study was conducted on 112 UCL patients who have undergone primary lip reconstructions but not advanced surgeries as the study group and 20 healthy participants as the control group between February 2023 to March 2024. The study group patients were grouped based on the severity of their cleft lip at birth, divided into occult cleft lip group, incomplete cleft lip group, and complete cleft lip group. The anterior rhinomanometry was used to evaluate nasal resistance, including unilateral effective resistances during inspiration (Reffin), expiration (Reffex), and the entire breath (ReffT), as well as unilateral vertex resistance during inspiration (VRin) and expiration (VRex). The Kolmogorov-Smirnov test was used to assess normality. Paired t-tests were utilized to analyze the differences in nasal resistance between the healthy and affected sides within the same group of patients. Student's t-test was used to analyze the differences in nasal resistance among patients with different degrees of cleft lip. A p-value of <0.05 was considered statistically significant. RESULTS: The nasal resistances of the occult cleft and incomplete cleft lip groups showed no significant differences between the cleft and non-cleft sides, and were similar to the control group. However, in the complete cleft lip group, the cleft side nasal resistance was significantly higher than the non-cleft side and control group. Among the groups, the complete cleft lip group had significantly higher nasal resistances on the cleft side for Reffin, VRin, and ReffT compared to the occult cleft group. CONCLUSION: Understanding the nasal resistance of different degrees of operated UCL patients can benefit clinical diagnosis and treatment. Patients with complete cleft lip have more severe nasal obstruction on the cleft side, with greater impact on inhalation than exhalation. For these patients, treatment by an otolaryngologist is recommended to improve nasal airflow.

Elevated neutrophil-to-lymphocyte ratio combined with decreased lymphocyte-to-monocyte ratio is associated with increased peripheral airway resistance in patients with hepatic steatosis.

Although the link between hepatic steatosis and lung function has been confirmed, the focus has largely been on central airways. The association between hepatic steatosis and increased peripheral airway resistance has not yet been explored. Hepatic steatosis and increased peripheral resistance are connected with immunity dysregulation. High neutrophil-to-lymphocyte ratio (NLR) and low lymphocyte-to-monocyte ratio (LMR) have been recognized as indicators of immunity dysregulation. In this study, the association between hepatic steatosis and increased peripheral airway resistance was evaluated, and the effect of immunity dysregulation (high NLR/low LMR) on the increased peripheral airway resistance among patients with hepatic steatosis was explored. In this retrospective study, chest or abdomen CT scans and spirometry/impulse oscillometry (IOS) from 2018 to 2019 were used to identify hepatic steatosis and increased central/peripheral airway resistance in patients. Among 1391 enrolled patients, 169 (12.1%) had hepatic steatosis. After 1:1 age and abnormal ALT matching was conducted, clinical data were compared between patients with and without hepatic steatosis. A higher proportion of patients with hepatic steatosis had increased peripheral airway resistance than those without hepatic steatosis (52.7% vs 40.2%, P = .025). Old age, high body mass index, history of diabetes, and high NLR/low LMR were significantly correlated with increased peripheral airway resistance. The presence of hepatic steatosis is associated with increased peripheral airway. High NLR/low LMR is an independent associated factor of increased peripheral airway resistance in patients with hepatic steatosis. It is advisable for patients with hepatic steatosis to regularly monitor their complete blood count/differential count and undergo pulmonary function tests including IOS.

Sex differences in asthma control, lung function and exacerbations: the ATLANTIS study.

BACKGROUND: Asthma is a heterogeneous disease with a prevalence and severity that differs between male and female patients. QUESTION: What are differences between male and female patients with asthma with regard to asthma control, lung function, inflammation and exacerbations? METHODS: We performed a post hoc analysis in the ATLANTIS (Assessment of Small Airways Involvement in Asthma) study, an observational cohort study including patients with asthma from nine countries with a follow-up of 1 year during which patients were characterised with measures of large and small airway function, questionnaires, inflammation and imaging. We compared differences in baseline characteristics and longitudinal outcomes between male and female patients with asthma. RESULTS: 773 patients were enrolled; 450 (58%) of these were female. At baseline, female patients with asthma were in higher Global Initiative for Asthma (GINA) steps (p=0.042), had higher Asthma Control Questionnaire 6 (F: 0.83; M: 0.66, p<0.001) and higher airway resistance as reflected by uncorrected impulse oscillometry outcomes (ie, R5-R20: F: 0.06; M: 0.04 kPa/L/s, p=0.002). Male patients with asthma had more severe airway obstruction (forced expiratory volume in 1 s/forced vital capacity % predicted: F: 91.95; M: 88.33%, p<0.01) and more frequently had persistent airflow limitation (F: 27%; M: 39%, p<0.001). Blood neutrophils were significantly higher in female patients (p=0.014). With Cox regression analysis, female sex was an independent predictor for exacerbations. INTERPRETATION: We demonstrate that female patients are in higher GINA steps, exhibit worse disease control, experience more exacerbations and demonstrate higher airway resistance compared with male patients. The higher exacerbation risk was independent of GINA step and blood eosinophil level. Male patients, in turn, have a higher prevalence of persistent airflow limitation and more severe airflow obstruction. These findings show sex can affect clinical phenotyping and outcomes in asthma. TRIAL REGISTRATION NUMBER: NCT02123667.

Flow interruption compared to forced oscillatory maneuvers and esophageal balloon/pneumotachography for measurement of respiratory resistance in the horse.

Pulmonary function testing is critical to the diagnosis of equine asthma (EA), an important cause of respiratory disease in the horse, but its clinical use has remained elusive, unfortunately, due to the complexity of reference methods, esophageal balloon/pneumotachography (EBP), and forced oscillatory mechanics (FOM), so we sought a noninvasive, portable method for use in horses through rapid interruption of airflow for equilibration of alveolar pressure with proximal airway pressure, termed flow interruption (FI). Resistance (RINT) was computed as the relationship between the change in pressure at the nose before and immediately after interruption and flow immediately before interruption. A pilot study in five healthy university-owned animals using EBP and FI showed good correspondence between the two methods: RINT (0.33 ± 0.05 cmH2O/L/s) and RL (0.31 ± 0.06 cmH2O/L/s). In two separate populations of client-owned horses, with random assignment of methods to FI versus EBP (n = 8), RINT showed good correlation with RL in horses (rs = 0.995, P = 0.0002) and accords with RL, with no significant difference between RINT and RL. Using FOM (n = 12), RINT (0.67 ± 0.31 cmH2O/L/s) has good correlation with RRS measured with FOM (r = 0.834, P = 0.0001), but is consistently smaller than RRS (0.74 ± 0.33 cmH2O/L/s). Histamine bronchoprovocation (HBP) was performed in a subset of these horses: FI classified one horse in six as less reactive than did EBP, and FI classified one horse in seven as less reactive than did FOM.NEW & NOTEWORTHY We developed and document for the first time the use of flow interruption for the rapid and noninvasive measurement of resistance in equine patients and demonstrated short- and long-term stability and accuracy in comparison with the reference methods.

A stepwise lung recruitment maneuver using I-gel can improve respiratory parameters: A prospective observational study.

I-gel has been used in various clinical situations. The study investigated alterations in respiratory parameters following a stepwise lung recruitment maneuver (LRM) using the i-gel. The research involved 60 patients classified as American Society of Anesthesiologists class I-II, aged 30 to 75 years, undergoing elective urologic surgery. Various respiratory parameters, including lung compliance, airway resistance, leak volume, airway pressure, and oxygen reserve index, were recorded at different time points: before LRM, immediately after LRM, and at 5, 15, and 30 minutes after LRM, as well as at the end of the surgery. The primary outcome was to assess an improvement in lung compliance. Dynamic lung compliance (mean ±â€…SD) was significantly increased from 49.2 ±â€…1.8 to 70.15 ±â€…3.2 mL/cmH2O (P < .05) after LRM. Static lung compliance (mean ±â€…SD) was increased considerably from 52.4 ±â€…1.7 to 65.0 ±â€…2.5 mL/cmH2O (P < .05) after the LRM. Both parameters maintained a statistically significant increased status for a certain period compared to baseline despite a decreased degree of increment. Airway resistance (mean ±â€…SD) was significantly reduced after the LRM from 12.05 ±â€…0.56 to 10.41 ±â€…0.64 L/cmH2O/s (P < .05). Stepwise LRM using i-gel may improve lung compliance and airway resistance. Repeated procedures could lead to prolonged improvements in respiratory parameters.

Numerical simulation of the influence of nasal cycle on nasal airflow.

To study the characteristics of nasal airflow in the presence of nasal cycle by computational fluid dynamics. CT scan data of a healthy Chinese individual was used to construct a three-dimensional model of the nasal cavity to be used as simulation domain. A sinusoidal airflow velocity is set at the nasal cavity entrance to reproduce the breathing pattern of a healthy human. There was a significant difference in the cross-sectional area between the two sides of the nasal cavity. Particularly, the decongested side is characterized by a larger cross-section area, and consequently, by a larger volume with respect to the congested side. The airflow velocity, pressure, and nasal resistance were higher on the congested narrow side. The temperature regulation ability on the congested narrow side was stronger than that on the decongested wider side. During the nasal cycle, there are differences in the nasal cavity function between the congested and decongested sides. Therefore, when evaluating the impact of various factors on nasal cavity function, the nasal cycle should be considered.

Continuous estimation of respiratory system compliance and airway resistance during pressure-controlled ventilation without end-inspiration occlusion.

BACKGROUND: Assessing mechanical properties of the respiratory system (Cst) during mechanical ventilation necessitates an end-inspiration flow of zero, which requires an end-inspiratory occlusion maneuver. This lung model study aimed to observe the effect of airflow obstruction on the accuracy of respiratory mechanical properties during pressure-controlled ventilation (PCV) by analyzing dynamic signals. METHODS: A Hamilton C3 ventilator was attached to a lung simulator that mimics lung mechanics in healthy, acute respiratory distress syndrome (ARDS) and chronic obstructive pulmonary disease (COPD) models. PCV and volume-controlled ventilation (VCV) were applied with tidal volume (VT) values of 5.0, 7.0, and 10.0 ml/kg. Performance characteristics and respiratory mechanics were assessed and were calibrated by virtual extrapolation using expiratory time constant (RCexp). RESULTS: During PCV ventilation, drive pressure (DP) was significantly increased in the ARDS model. Peak inspiratory flow (PIF) and peak expiratory flow (PEF) gradually declined with increasing severity of airflow obstruction, while DP, end-inspiration flow (EIF), and inspiratory cycling ratio (EIF/PIF%) increased. Similar estimated values of Crs and airway resistance (Raw) during PCV and VCV ventilation were obtained in healthy adult and mild obstructive models, and the calculated errors did not exceed 5%. An underestimation of Crs and an overestimation of Raw were observed in the severe obstruction model. CONCLUSION: Using the modified dynamic signal analysis approach, respiratory system properties (Crs and Raw) could be accurately estimated in patients with non-severe airflow obstruction in the PCV mode.

Assessing nasal airway resistance and symmetry: An approach to global perspective through computational fluid dynamics.

This study aimed to explore the variability in nasal airflow patterns among different sexes and populations using computational fluid dynamics (CFD). We focused on evaluating the universality and applicability of dimensionless parameters R (bilateral nasal resistance) and ϕ (nasal flow asymmetry), initially established in a Caucasian Spanish cohort, across a broader spectrum of human populations to assess normal breathing function in healthy airways. In this retrospective study, CT scans from Cambodia (20 males, 20 females), Russia (20 males, 18 females), and Spain (19 males, 19 females) were analyzed. A standardized CFD workflow was implemented to calculate R-ϕ parameters from these scans. Statistical analyses were conducted to assess and compare these parameters across different sexes and populations, emphasizing their distribution and variances. Our results indicated no significant sex-based differences in the R parameter across the populations. However, moderate sexual dimorphism in the ϕ parameter was observed in the Cambodian group. Notably, no geographical differences were found in either R or ϕ parameters, suggesting consistent nasal airflow characteristics across the diverse human groups studied. The study also emphasized the importance of using dimensionless variables to effectively analyze the relationships between form and function in nasal airflow. The observed consistency of R-ϕ parameters across various populations highlights their potential as reliable indicators in both medical practice and further CFD research, particularly in diverse human populations. Our findings suggest the potential applicability of dimensionless CFD parameters in analyzing nasal airflow, highlighting their utility across diverse demographic and geographic contexts. This research advances our understanding of nasal airflow dynamics and underscores the need for additional studies to validate these parameters in broader population cohorts. The approach of employing dimensionless parameters paves the way for future research that eliminates confounding size effects, enabling more accurate comparisons across different populations and sexes. The implications of this study are significant for the advancement of personalized medicine and the development of diagnostic tools that accommodate individual variations in nasal airflow.

Effects of adenoid hypertrophy on nasopharyngeal airway ventilation: A computational fluid dynamics study.

OBJECTIVES: Adenoid hypertrophy causes impaired nasopharyngeal airways (NA) ventilation. However, it is difficult to evaluate the ventilatory conditions of NA. Therefore, this study aimed to analyze the nasopharyngeal airway resistance (NARES) based on computational fluid dynamics simulations and the nasopharyngeal airway depth (NAD) and adenoid hypertrophy grade measured on cephalometric cone-beam computed tomography images and determine the relationship between NAD and grade and NARES to ultimately assess using cephalometric measurements whether NA has airway obstruction defects. METHODS: Cephalogram images were generated from cone-beam computed tomography data of 102 children (41 boys; mean age: 9.14 ± 1.43 years) who received orthodontic examinations at an orthodontic clinic from September 2012 to March 2023, and NAD and adenoid grade and NARES values were measured based on computational fluid dynamics analyses using a 3D NA model. Nonlinear regression analyses were used to evaluate the relationship between NARES and NAD and correlation coefficients to evaluate the relationship between grade and NARES. RESULTS: NARES was inversely proportional to the cube of NAD (R2 = 0.786, P < 0.001), indicating a significant relationship between these variables. The resistance NARES increased substantially when the distance NAD was less than 5 mm. However, adenoid Grade 4 (75 % hypertrophy) was widely distributed. CONCLUSIONS: These study findings demonstrate that the ventilatory conditions of NA can be determined based on a simple evaluation of cephalogram images. An NAD of less than 5 mm on cephalometric images results in NA obstruction with substantially increased airflow resistance.

Functional analysis of airway remodeling is related with fibrotic mediators in asthmatic children.

BACKGROUND: Asthmatic children present variable degrees of airway inflammation, remodeling, and resistance, which correlate with disease control and severity. The chronic inflammatory process of the airway triggers airway remodeling, which reflects the degree of airway resistance. Pro-inflammatory and pro-fibrotic mediators are centrally involved in this process. OBJECTIVE: To investigate whether the levels of pulmonary and systemic pro-inflammatory and pro-fibrotic mediators present a correlation with the resistance of the respiratory system and of the proximal and distal airways. METHODS: 39 Asthmatic children (persistent mild and moderate) and 39 non-asthmatic children (both between 6 and 13 years old) were evaluated for anthropometric characteristics, lung function and mechanics, and pulmonary and systemic immune responses. RESULTS: Asthmatic children showed an increased number of blood eosinophils (p < 0.04), basophils (p < 0.04), monocytes (p < 0.002) and lymphocytes (p < 0.03). In addition, asthmatic children showed impaired lung function, as demonstrated by FEV1 (p < 0.0005) and FEV1/FVC (p < 0.004), decreased total resistance of the respiratory system (R5Hz; p < 0.009), increased resistance of the proximal airways (R20Hz; p < 0.02), increased elastance (Z5Hz; p < 0.02) and increased reactance (X5Hz; p < 0.002) compared to non-asthmatic children. Moreover, the following inflammatory factors were significantly higher in asthmatic than non-asthmatic children: GM-CSF in the breath condensate (BC) (p < 0.0001) and in the serum (p < 0.0001); TGF-beta in the BC (p < 0.0001) and in the serum (p < 0.004); IL-5 in the BC (p < 0.02) and in the serum (p < 0.01); IL-4 in the serum (p < 0.0002). CONCLUSIONS: Impulse oscillometry is a sensitive method to detect airway resistance in persistent mild and moderate asthmatic children, an event followed by increased levels of pro-inflammatory and pro-fibrotic mediators.

Impact of posture and CPAP on nasal airflow.

Obstructive sleep apnea (OSA) patients who use continuous positive airway pressure (CPAP) often complain of nasal dryness and nasal obstruction as side effects of CPAP. The physiological mechanisms by which CPAP may cause nasal dryness and nasal obstruction remain poorly understood. It has been hypothesized that CPAP interferes with the nasal cycle, abolishing the resting phase of the cycle and leading to nasal dryness. We performed rhinomanometry measurements in 31 OSA patients sitting, laid supine, and supine after 10 min of CPAP at 10 cmH2O. A posture change from sitting to supine led to more symmetric airflow partitioning between the left and right nostrils in the supine position. CPAP did not have a significant impact on nasal resistance, unilateral airflows, or airflow partitioning. Our results suggest that airflow partitioning becomes more symmetric immediately after changing to a supine position, while CPAP had no effect on nasal airflow, thus preserving the nearly symmetric airflow partitioning achieved after the posture change.

Impact of palatopharyngeal sizes changing on pharyngeal airflow fluctuation and airway vibration in a pediatric airway.

Snoring is common in children and is associated with many adverse consequences. One must study the relationships between pharyngeal morphology and snoring physics to understand snoring progression. Although some model studies have provided fluid-structure interaction dynamic descriptions for the correlation between airway size and snoring physics, the descriptions still need to be further investigated in patient-specific airway models. Fluid-structure interaction studies using patient-specific airway structures complement the above model studies. Based on reported cephalometric measurement methods, this study quantified and preset the size of the palatopharynx airway in a patient-specific airway and investigated how the palatopharynx size affects the pharyngeal airflow fluctuation, soft palate vibration, and glossopharynx vibration with the help of a verified FSI method. The results showed that the stenosis anterior airway of the soft palate increased airway resistance and airway resistance fluctuations, which can lead to increased sleep effort and frequent snoring. Widening of the anterior airway can reduce airflow resistance and avoid obstructing the anterior airway by the soft palate vibration. The pharyngeal airflow resistance, mouth inflow proportion, and soft palate apex displacement have components at the same frequencies in all airway models, and the glossopharynx vibration and instantaneous inflow rate have components at the same frequencies, too. The mechanism of this same frequency fluctuation phenomenon can be explained by the fluid-structure interaction dynamics of an ideal coupled model consisting of a flexible plate model and a collapsible tube model. The results of this study demonstrate the potential of FSI in studying snoring physics and clarify to some degree the mechanism of airway morphology affecting airway vibration physics.

Respiratory and chest wall mechanics in very preterm infants.

Data on static compliance of the chest wall (Ccw) in preterm infants are scarce. We characterized the static compliance of the lung (CL) and Ccw to determine their relative contribution to static compliance of the respiratory system (Crs) in very preterm infants at 36 wk postmenstrual age (PMA). We also aimed to investigate how these compliances were influenced by the presence of bronchopulmonary dysplasia (BPD) and impacted breathing variables. Airway opening pressure, esophageal pressure, and tidal volume (VT) were measured simultaneously during a short apnea evoked by the Hering-Breuer reflex. We computed tidal breathing variables, airway resistance (R), and dynamic lung compliance (CL,dyn), inspiratory capacity (IC), and Crs, CL, and Ccw. Functional residual capacity was assessed by the multiple breath washout technique (FRCmbw). Breathing variables, compliances, and lung volumes were adjusted for body weight. Twenty-three preterm infants born at 27.2 ± 2.0 wk gestational age (GA) were studied at 36.6 ± 0.6 wk PMA. Median and interquartile range (IQR) Crs/kg is 0.69 (0.6), CL/kg 0.95 (1.0), and Ccw/kg 3.0 (2.4). Infants with BPD (n = 11) had lower Crs/kg (P = 0.013), CL/kg (P = 0.019), and Ccw/kg (P = 0.027) compared with infants without BPD. Ccw/CL ratio was equal between groups. FRCmbw/kg (P = 0.044) and IC/kg (P = 0.005) were decreased in infants with BPD. Infants with BPD have reduced static compliance of the respiratory system, the lungs, and chest wall. Decreased Crs, CL, and Ccw in infants with BPD explain the lower FRC and IC seen in these infants.NEW & NOTEWORTHY Data on chest wall compliance in very preterm infants in the postsurfactant era are scarce. To our knowledge, we are the first group to report data on static respiratory system compliance (Crs), lung compliance (CL), and chest wall compliance (Ccw) in preterm infants with and without bronchopulmonary dysplasia (BPD) in the postsurfactant era.

Effect of increased resistance on dynamic compliance assessed by two clinical monitors during volume-controlled ventilation: A test-lung study.

OBJECTIVE: To evaluate the effect of increased respiratory system resistance (RRS) on dynamic compliance (Cdyn) assessed by the NM3 monitor (Cdyn(NM3)) and the E-CAiOV module (Cdyn(ECAiOV)). STUDY DESIGN: Prospective laboratory study. METHODS: A training test lung (TTL) simulated the mechanical ventilation of a mammal with 50 and 300 mL tidal volumes in three conditions of RRS [normal (RBL), moderately increased (R1) and severely increased (R2)] and a wide range of clinically relevant Cdyn. Simulations at increased RRS were paired with simulations at RBL with the same static compliance for comparisons. Pearson's correlation coefficient and concordance correlation coefficient between the measurements at RBL with the ones with increased RRS were calculated. Bland-Altman plots were also used to evaluate the agreement of Cdyn(ECAiOV) and Cdyn(NM3) at RBL (control values) with their paired values at R1 and R2. Relative bias and limits of agreement (LOAs) were calculated and LOAs larger than 30% were considered unacceptable. Trending ability of Cdyn(NM3) and Cdyn(ECAiOV) were evaluated by polar plots. Values of p < 0.05 were considered significant. RESULTS: The effect of increased RRS was more pronounced for Cdyn(ECAiOV) than for Cdyn(NM3). Unacceptable agreement was only observed in Cdyn(NM3) at R2 in the 300 mL simulation (bias = -18.3% and lower LOA = -45%). For Cdyn(ECAiOV), agreement was unacceptable for all tested RRS in both simulations, being the worst at R2 in the 300 mL simulation (bias = -54.7% and lower LOA = -100.2%). Both levels of increased RRS caused poor trending ability for Cdyn(ECAiOV), whereas the same effect was only observed for Cdyn(NM3) at R2. CONCLUSIONS AND CLINICAL RELEVANCE: In the presence of increased RRS, Cdyn estimated by the NM3 monitor presented better capability to distinguish between changes in RRS from changes in respiratory system compliance.