Evaluation of a new hyperbaric oxygen ventilator during pressure-controlled ventilation.

Introduction: The stability of a new hyperbaric ventilator (Shangrila590, Beijing Aeonmed Company, Beijing, China) at different clinically relevant pressures in a hyperbaric chamber during pressure-controlled ventilation (PCV) was investigated. Methods: The ventilator was connected to a test lung in the multiplace hyperbaric chamber. The inspiratory pressure (PI) of the ventilator was set to 1.0, 1.5, 2.0, 2.5 and 3.0 kPa (approximately 10, 15, 20, 25 and 30 cmH2O). The compliance and resistance of the test lung were set to 200 mL·kPa⁻¹ and 2 kPa·L⁻¹·s⁻¹, respectively. Experiments were conducted at 101, 203 and 284 kPa ambient pressure (1.0, 2.0 and 2.8 atmospheres absolute respectively). At each of the 5 PI values, the tidal volume (VT), peak inspiratory pressure (Ppeak) and peak inspiratory flow (Fpeak) displayed by the ventilator and the test lung were recorded for 20 cycles. Test lung data were considered the actual ventilation values. The ventilation data were compared among the three groups to evaluate the stability of the ventilator. Results: At every PI, the Ppeak detected by the ventilator decreased slightly with increasing ambient pressure. The Fpeak values measured by the test lung decreased substantially as the ambient pressure increased. Nevertheless, the reduction in VT at 284 kPa and PI 30 cmH2O (compared to performance at 101 kPa) was comparatively small (approximately 60 ml). Conclusions: In PCV mode this ventilator provided relatively stable VT across clinically relevant PI values to ambient pressures as high as 284 kPa. However, because Fpeak decreases at higher ambient pressure, some user adjustment might be necessary for precise VT maintenance during clinical use at higher PIs and ambient pressures.

Optimal Positive End-expiratory Pressure Levels in Tuberculosis-associated Acute Respiratory Distress Syndrome.

BACKGROUND: The objective is to assess lung compliance and identify the optimal positive end-expiratory pressure (PEEP) levels in patients with tuberculosis-associated Acute Respiratory Distress Syndrome (TB-ARDS) compared to non-TB-ARDS patients. METHODS: This observational case-control study utilized electrical impedance tomography to evaluate lung mechanics in 20 TB-ARDS and 20 non-TB-ARDS patients. Participants underwent PEEP titration from 23 to 5 cm H2O in 2 cm H2O decrements. Lung compliance and the rates of hyperdistention and collapse were assessed at each PEEP level. RESULTS: Delta impedance values showed higher amounts in a PEEP range of 11-17 cm H2O and in patients with TB-ARDS (P > 0.05). In addition, both hyperdistention and collapse rates were nonsignificantly higher in TB-ARDS patients (P > 0.05), and the compromised levels of hyperdistention and collapse rates were at 15-17 cm H2O, indicating the most favorable PEEP level. CONCLUSIONS: The observed patterns of hyperdistention and collapse rates across various PEEP levels provide valuable insights into the susceptibility of TB-ARDS patients to barotrauma. Notably, the identified optimal PEEP range between 15 and 17 cm H2O may guide ventilator management strategies in mitigating both hyperdistention and collapse; nonetheless, due to the high variability of lung compliances within groups, we strongly recommend individualized consideration for tailored respiratory support and evaluation.

The relationship between mechanical power normalized to dynamic lung compliance and weaning outcomes in mechanically ventilated patients.

BACKGROUND: Prolonged mechanical ventilation is associated with an increased risk of mortality in these patients. However, there exists a significant clinical need for novel indicators that can complement traditional weaning evaluation methods and effectively guide ventilator weaning. OBJECTIVES: To investigate the specific relationship between mechanical power normalized to dynamic lung compliance (Cdyn-MP) and weaning outcomes in patients on mechanical ventilation for more than 24 hours, as well as those who underwent a T-tube weaning strategy. METHODS: A retrospective cohort study was conducted using the Medical Information Mart for Intensive Care-IV v1.0 database (MIMIC-IV v1.0). Patients who received invasive mechanical ventilation for more than 24 hours and underwent a T-tube ventilation strategy for weaning were enrolled. Patients were divided into two groups based on their weaning outcome: weaning success and failure. Ventilation parameter data were collected every 4 hours during the first 24 hours before the first spontaneous breathing trial (SBT). RESULTS: Of all the 3,695 patients, 1,421 (38.5%) experienced weaning failure. Univariate logistic regression analysis revealed that the risk of weaning failure increased as the Cdyn-MP level rose (OR 1.34, 95% CI 1.31-1.38, P<0.001). After adjusting for age, body mass index, disease severity, and pre-weaning disease status, patients with high Cdyn-MP quartiles in the 4 hours prior to the SBT had a significantly greater risk of weaning failure than those with low Cdyn-MP quartiles (odds ratio 10.37, 95% CI 7.56-14.24). These findings were robust and consistent in both subgroup and sensitivity analyses. CONCLUSION: The increased Cdyn-MP before SBT was independently associated with a higher risk of weaning failure in mechanically ventilated patients. Cdyn-MP has the potential to be a useful indicator for guiding the need for ventilator weaning and complementing traditional weaning evaluation methods.

Effects of individualised lung-protective ventilation with lung dynamic compliance-guided positive end-expiratory pressure titration on postoperative pulmonary complications of paediatric video-assisted thoracoscopic surgery: protocol for a randomised controlled trial.

INTRODUCTION: Lung-protective ventilation strategies (LPVS) for one-lung ventilation (OLV) in paediatric patients pose greater challenges than in adults. Optimising LPVS for paediatric OLV to mitigate postoperative pulmonary complications (PPCs) has emerged as a current research focal point. However, there remains a divergence of opinions concerning the individualised setting and application of positive end-expiratory pressure (PEEP). Lung dynamic compliance (Cdyn) can serve as a reflection of the lung's physiological state in children during OLV and is a readily obtainable parameter. This study protocol is formulated to assess the effectiveness of Cdyn-guided PEEP titration on PPCs during paediatric OLV. METHODS AND ANALYSIS: This study constitutes a single-centre, prospective, double-blind, randomised controlled trial. The trial aims to recruit 60 paediatric patients scheduled for video-assisted thoracoscopic surgery. These eligible patients will be randomly assigned to either the Cdyn-guided PEEP group or the conventional PEEP group during general anaesthesia for OLV. The primary outcome will involve assessing the incidence of PPCs at 7 days after surgery. Secondary outcomes will encompass the evaluation of the modified lung ultrasound score following surgery, as well as monitoring the oxygenation index, driving pressure and Cdyn during mechanical ventilation. Data collection will be performed by investigators who are kept blinded to the interventions. ETHICS AND DISSEMINATION: The Clinical Trial Ethics Committee at Shenzhen Children's Hospital has conferred ethical approvals for this trial (approval number: 2022076). Results from this trial will be disseminated in peer-reviewed journals and presented at professional symposiums. TRAIL REGISTRATION NUMBER: NCT05386901.

Correlation between normally aerated lung and respiratory system compliance at clinical high positive end-expiratory pressure in patients with COVID-19.

Normally aerated lung tissue on computed tomography (CT) is correlated with static respiratory system compliance (Crs) at zero end-expiratory pressure. In clinical practice, however, patients with acute respiratory failure are often managed using elevated PEEP levels. No study has validated the relationship between lung volume and tissue and Crs at the applied positive end-expiratory pressure (PEEP). Therefore, this study aimed to demonstrate the relationship between lung volume and tissue on CT and Crs during the application of PEEP for the clinical management of patients with acute respiratory distress syndrome due to COVID-19. Additionally, as a secondary outcome, the study aimed to evaluate the relationship between CT characteristics and Crs, considering recruitability using the recruitment-to-inflation ratio (R/I ratio). We analyzed the CT and respiratory mechanics data of 30 patients with COVID-19 who were mechanically ventilated. The CT images were acquired during mechanical ventilation at PEEP level of 15 cmH2O and were quantitatively analyzed using Synapse Vincent system version 6.4 (Fujifilm Corporation, Tokyo, Japan). Recruitability was stratified into two groups, high and low recruitability, based on the median R/I ratio of our study population. Thirty patients were included in the analysis with the median R/I ratio of 0.71. A significant correlation was observed between Crs at the applied PEEP (median 15 [interquartile range (IQR) 12.2, 15.8]) and the normally aerated lung volume (r = 0.70 [95% CI 0.46-0.85], P < 0.001) and tissue (r = 0.70 [95% CI 0.46-0.85], P < 0.001). Multivariable linear regression revealed that recruitability (Coefficient = - 390.9 [95% CI - 725.0 to - 56.8], P = 0.024) and Crs (Coefficient = 48.9 [95% CI 32.6-65.2], P < 0.001) were significantly associated with normally aerated lung volume (R-squared: 0.58). In this study, Crs at the applied PEEP was significantly correlated with normally aerated lung volume and tissue on CT. Moreover, recruitability indicated by the R/I ratio and Crs were significantly associated with the normally aerated lung volume. This research underscores the significance of Crs at the applied PEEP as a bedside-measurable parameter and sheds new light on the link between recruitability and normally aerated lung.

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.

[Analysis of compliance with lung protective mechanical ventilation strategy in patients with acute respiratory distress syndrome].

Objective: To assess the compliance with a lung protective ventilation strategy and to evaluate the relationship with prognosis in patients with acute respiratory distress syndrome (ARDS). Methods: In the prospective multicenter cohort study (CHARDS), patients with ARDS undergoing invasive mechanical ventilation were enrolled to collect essential information, mechanical ventilation data, and prognostic data. Compliance was operationally defined as tidal volume ≤7 ml/kg predicted body weight (PBW) or plateau pressure ≤30 cmH2O or driving pressure≤15 cmH2O. Tidal volume data collected 7 days prior to ventilation after ARDS diagnosis were categorized into four groups: standard group (Group A, 100% compliance), non-standard group (Group B, 50%-99% compliance, Group C,1%-49% compliance,and Group D,totally non-compliant). Plateau pressure and drive pressure measurements were recorded on the first day. Stepwise regression, specifically Logistics regression, was used to identify the factors influencing ICU survival. Results: A total of 449 ARDS patients with invasive mechanical ventilation were included; the proportion of mild, moderate, and severe patients was 71 (15.8%), 198 (44.1%) and 180 (40.1%), respectively. During the first 7 days, a total of 2880 tidal volume measurements were recorded with an average tidal volume of (6.89±1.93) ml/kg PBW. Of these measurements, 53.2% were found to be≤7 ml/kg PBW. The rates of compliance with lung protective mechanical ventilation were 29.8% (134/449), 24.5% (110/449), 23.6% (106/449), and 22% (99/449) in groups A, B, C, and D, respectively. In the standard group, the tidal volume for mild ARDS patients was 18.3%(13/71), while it was 81.7%(58/71)in the non-standard group. Similarly, in patients with moderate ARDS, the tidal volume was 25.8% (51/198) in the standard group, while it was 74.2% (147/198) in the non-standard group. Finally, in patients with severe ARDS, the tidal volume was 38.9% (70/180) in the standard group, while it was 61.1% (110/180) in the non-standard group. Notably, the compliance rate was higher in patients with moderate and severe ARDS in group A compared to patients with mild and moderate ARDS (18.3% vs. 25.8% vs. 38.9%, χ2=13.124, P=0.001). Plateau pressure was recorded in 221 patients, 95.9% (212/221) patients with plateau pressure≤30 cmH2O, and driving pressure was recorded in 207 patients, 77.8% (161/207) patients with a driving pressure ≤15 cmH2O.During the first 7 days, the mortality rate in the intensive care unit (ICU) was lower in the tidal volume standard group compared to the non-standard group (34.6% vs. 51.3%, χ2=10.464, P=0.001). In addition, the in-hospital mortality rate was lower in the standard group compared to the non-standard group (39.8% vs. 57%, χ2=11.016, P=0.001).The results of the subgroup analysis showed that the mortality rates of moderate and severe ARDS patients in the standard group were significantly lower than those in the non-standard group, both in the ICU and in the hospital (all P<0.05). However, there was no statistically significant difference in mortality among mild ARDS patients (all P>0.05). Conclusions: There was high compliance with recommended lung protective mechanical ventilation strategies in ARDS patients, with slightly lower compliance in patients with mild ARDS, and high compliance rates for plateau and drive pressures. The tidal volume full compliance group had a lower mortality than the non-compliance group, and showed a similar trend in the moderate-to-severe ARDS subgroup, but there was no significant correlation between compliance and prognosis in patients with mild ARDS subgroup.

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.

Effect of end-inspiratory pause duration on respiratory system compliance calculation in mechanically ventilated dogs with healthy lungs.

OBJECTIVE: To compare respiratory system compliance (CRS), expressed per kilogram of bodyweight (CRSBW), calculated without end-inspiratory pause (EIP) and after three EIP times (0.2, 0.5 and 1 seconds) with that after 3 second EIP (considered the reference EIP for static CRS) and to determine the EIP times that provided CRSBW values in acceptable agreement with static CRSBW during controlled mechanical ventilation (CMV) in anaesthetized dogs. STUDY DESIGN: Prospective, randomized, nonblinded, crossover clinical study. ANIMALS: A group of 24 client-owned dogs with healthy lungs undergoing surgery in lateral recumbency. METHODS: During CMV in dogs undergoing general anaesthesia, five EIPs [0 (no EIP), 0.2, 0.5, 1 and 3 seconds] were consecutively applied in random order. Tidal volume (Vt) was set at 10 mL kg-1 and positive end-expiratory pressure (PEEP) was not applied. Respiratory rate and inspiratory time were established according to each EIP time, setting EIP between 0 and 50% of the inspiratory time. The CRSBW was calculated as [expired Vt/(plateau pressure - PEEP)]/bodyweight and recorded every 15 seconds for 2 minutes after a 5 minute equilibration period with each EIP. One-way anova for repeated measures and the Bland-Altman analysis were used to compare CRSBW and evaluate agreement between EIP times, respectively. RESULTS: The CRSBW was significantly greater as the EIP time increased up to 1 second (p < 0.05). In the Bland-Altman analysis, none of the tested EIPs (0, 0.2, 0.5 and 1 seconds) provided 95% confidence intervals for limits of agreement within the maximum allowed difference considered for acceptable agreement with 3 second EIP. CONCLUSIONS: and clinical relevance An EIP ≤ to 1 second does not provide a CRSBW value in acceptable agreement with static CRSBW in healthy dogs. Besides, the application of an EIP ≤ to 0.5 seconds underestimates the static CRSBW to an increasing extent as the EIP time decreases.

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.

The Effect of Recruitment Maneuver on Static Lung Compliance in Patients Undergoing General Anesthesia for Laparoscopic Cholecystectomy: A Single-Centre Prospective Clinical Intervention Study.

Background and Objectives: The aim of this study was to examine whether the use of an alveolar recruitment maneuver (RM) leads to a significant increase in static lung compliance (Cstat) and an improvement in gas exchange in patients undergoing laparoscopic cholecystectomy. Material and Methods: A clinical prospective intervention study was conducted. Patients were divided into two groups according to their body mass index (BMI): normal-weight (group I) and pre-obese and obese grade I (group II). Lung mechanics were monitored (Cstat, dynamic compliance-Cdin, peak pressure-Ppeak, plateau pressure-Pplat, driving pressure-DP) alongside gas exchange, and hemodynamic changes (heart rate-HR, mean arterial pressure-MAP) at six time points: T1 (induction of anesthesia), T2 (formation of pneumoperitoneum), T3 (RM with a PEEP of 5 cm H2O), T4 (RM with a PEEP of 7 cm H2O), T5 (desufflation), and T6 (RM at the end). The RM was performed by increasing the peak pressure by +5 cm of H2O at an equal inspiration-to-expiration ratio (I/E = 1:1) and applying a PEEP of 5 and 7 cm of H2O. Results: Out of 96 patients, 33 belonged to group I and 63 to group II. An increase in Cstat values occurred after all three RMs. At each time point, the Cstat value was measured higher in group I than in group II. A higher increase in Cstat was observed in group II after the second and third RM. Cstat values were higher at the end of the surgical procedure compared to values after the induction of anesthesia. The RM led to a significant increase in PaO2 in both groups without changes in HR or MAP. Conclusions: During laparoscopic cholecystectomy, the application of RM leads to a significant increase in Cstat and an improvement in gas exchange. The prevention of atelectasis during anesthesia should be initiated immediately after the induction of anesthesia, using protective mechanical ventilation and RM.

Acute Respiratory Distress Syndrome: Definition, Diagnosis, and Routine Management.

Acute respiratory distress syndrome (ARDS) is an acute inflammatory lung injury characterized by severe hypoxemic respiratory failure, bilateral opacities on chest imaging, and low lung compliance. ARDS is a heterogeneous syndrome that is the common end point of a wide variety of predisposing conditions, with complex pathophysiology and underlying mechanisms. Routine management of ARDS is centered on lung-protective ventilation strategies such as low tidal volume ventilation and targeting low airway pressures to avoid exacerbation of lung injury, as well as a conservative fluid management strategy.

A vagal reflex evoked by airway closure.

Airway integrity must be continuously maintained throughout life. Sensory neurons guard against airway obstruction and, on a moment-by-moment basis, enact vital reflexes to maintain respiratory function1,2. Decreased lung capacity is common and life-threatening across many respiratory diseases, and lung collapse can be acutely evoked by chest wall trauma, pneumothorax or airway compression. Here we characterize a neuronal reflex of the vagus nerve evoked by airway closure that leads to gasping. In vivo vagal ganglion imaging revealed dedicated sensory neurons that detect airway compression but not airway stretch. Vagal neurons expressing PVALB mediate airway closure responses and innervate clusters of lung epithelial cells called neuroepithelial bodies (NEBs). Stimulating NEBs or vagal PVALB neurons evoked gasping in the absence of airway threats, whereas ablating NEBs or vagal PVALB neurons eliminated gasping in response to airway closure. Single-cell RNA sequencing revealed that NEBs uniformly express the mechanoreceptor PIEZO2, and targeted knockout of Piezo2 in NEBs eliminated responses to airway closure. NEBs were dispensable for the Hering-Breuer inspiratory reflex, which indicated that discrete terminal structures detect airway closure and inflation. Similar to the involvement of Merkel cells in touch sensation3,4, NEBs are PIEZO2-expressing epithelial cells and, moreover, are crucial for an aspect of lung mechanosensation. These findings expand our understanding of neuronal diversity in the airways and reveal a dedicated vagal pathway that detects airway closure to help preserve respiratory function.

Effect of decreasing PEEP on hyperinflation and collapse in COVID-19: A computed tomography study.

BACKGROUND: High positive end-expiratory pressure (PEEP>10 cmH2O) is commonly used in mechanically ventilated hypoxemic patients with COVID-19. However, some epidemiological and physiological studies indirectly suggest that using a lower PEEP may primarily and beneficially decrease lung hyperinflation in this population. Herein we directly quantified the effect of decreasing PEEP from 15 to 10 cmH2O on lung hyperinflation and collapse in mechanically ventilated patients with COVID-19. METHODS: Twenty mechanically ventilated patients with COVID-19 underwent a lung computed tomography (CT) at PEEP of 15 and 10 cmH2O. The effect of decreasing PEEP on lung hyperinflation and collapse was directly quantified as the change in the over-aerated (density below -900 HU) and non-aerated (density above -100 HU) lung volumes. The net response to decreasing PEEP was computed as the sum of the change in those two compartments and expressed as the change in the "pathologic" lung volume. If the pathologic lung volume decreased (i.e., hyperinflation decreased more than collapse increased) when PEEP was decreased, the net response was considered positive; otherwise, it was considered negative. RESULTS: On average, the ratio of arterial tension to inspiratory fraction of oxygen (PaO2:FiO2) in the overall study population was 137 (119-162) mmHg. In 11 (55%) patients, the net response to decreasing PEEP was positive. Their over-aerated lung volume decreased by 159 (98-186) mL, while the non-aerated lung volume increased by only 58 (31-91) mL. In nine (45%) patients, the net response was negative. Their over-aerated lung volume decreased by 46 (18-72) mL, but their non-aerated lung volume increased by 107 (44-121) mL. CONCLUSION: In 20 patients with COVID-19 the net response to decreasing PEEP, as assessed with lung CT, was variable. In approximately half of them it was positive (and possibly beneficial), with a decrease in hyperinflation larger than the increase in collapse.

Mucopolysaccharidosis (MPS IIIA) mice have increased lung compliance and airway resistance, decreased diaphragm strength, and no change in alveolar structure.

Mucopolysaccharidosis type IIIA (MPS IIIA) is characterized by neurological and skeletal pathologies caused by reduced activity of the lysosomal hydrolase, sulfamidase, and the subsequent primary accumulation of undegraded heparan sulfate (HS). Respiratory pathology is considered secondary in MPS IIIA and the mechanisms are not well understood. Changes in the amount, metabolism, and function of pulmonary surfactant, the substance that regulates alveolar interfacial surface tension and modulates lung compliance and elastance, have been reported in MPS IIIA mice. Here we investigated changes in lung function in 20-wk-old control and MPS IIIA mice with a closed and open thoracic cage, diaphragm contractile properties, and potential parenchymal remodeling. MPS IIIA mice had increased compliance and airway resistance and reduced tissue damping and elastance compared with control mice. The chest wall impacted lung function as observed by an increase in airway resistance and a decrease in peripheral energy dissipation in the open compared with the closed thoracic cage state in MPS IIIA mice. Diaphragm contractile forces showed a decrease in peak twitch force, maximum specific force, and the force-frequency relationship but no change in muscle fiber cross-sectional area in MPS IIIA mice compared with control mice. Design-based stereology did not reveal any parenchymal remodeling or destruction of alveolar septa in the MPS IIIA mouse lung. In conclusion, the increased storage of HS which leads to biochemical and biophysical changes in pulmonary surfactant also affects lung and diaphragm function, but has no impact on lung or diaphragm structure at this stage of the disease.NEW & NOTEWORTHY Heparan sulfate storage in the lungs of mucopolysaccharidosis type IIIA (MPS IIIA) mice leads to changes in lung function consistent with those of an obstructive lung disease and includes an increase in lung compliance and airway resistance and a decrease in tissue elastance. In addition, diaphragm muscle contractile strength is reduced, potentially further contributing to lung function impairment. However, no changes in parenchymal lung structure were observed in mice at 20 wk of age.

Albuterol Delivery via In-Line Intrapulmonary Percussive Ventilation Superimposed on Invasive Ventilation in an Adult Lung Model.

BACKGROUND: Intrapulmonary percussive ventilation (IPV) is frequently used for airway clearance, together with delivery of aerosolized medications. Drug delivery via IPV alone increases with decreasing percussion frequency and correlates with tidal volume ([Formula: see text]), whereas drug delivery via IPV during invasive ventilation is not well characterized. We hypothesized that drug delivery via IPV-invasive ventilation would differ from IPV alone due to control of ventilation by invasive ventilation. METHODS: An adult ventilator circuit was used for IPV-invasive ventilation. A normal or a diseased lung model was configured to airway resistance of 5 cm H2O/L/s and lung compliance of 100 mL/cm H2O or to airway resistance of 20 cm H2O/L/s and lung compliance of 50 mL/cm H2O, respectively. The ventilator settings were the following: pressure control continuous mandatory ventilation mode, 10 breaths/min; PEEP, 5 cm H2O; [Formula: see text], 0.21; inspiratory time, 1 s; no bias flow; and inspiratory pressure, 10 or 15 cm H2O for the normal or the diseased lung model, respectively, to reach [Formula: see text] 500 mL with IPV off. Albuterol nebulized from an IPV device was captured in a filter placed before the lung model and quantitated by spectrophotometry. RESULTS: The maximum efficiency of albuterol delivery via IPV-invasive ventilation was not different from that via IPV alone (mean ± SD of loading dose, 3.7 ± 0.2% vs 4.2 ± 0.3%, respectively; P = .12). The mean ± SD albuterol delivery efficiency with IPV-invasive ventilation was lower for the diseased lung model versus the normal model (1.6 ± 0.3% vs 3.2 ± 0.5%; P < .001), which increased with decreasing percussion frequency. In contrast, the mean ± SD [Formula: see text] was lower for the normal lung model versus the diseased model (401 ± 14 mL vs 470 ± 11 mL; P < .001). CONCLUSIONS: Albuterol delivery via IPV-invasive ventilation was modulated by percussion frequency but was not increased with increasing [Formula: see text]. The delivery efficiency was not sufficiently high for clinical use, in part due to nebulizer retention and extrapulmonary deposition.

Relationship between Static Lung Compliance and Extubation Failure in Postoperative Cardiac Surgery Patients. / Relação entre a Complacência Pulmonar Estática e a Falha de Extubação em Pacientes Pós-Operatório de Cirurgia Cardíaca.

BACKGROUND: Static lung compliance, which is seriously affected during surgery, can lead to respiratory failure and extubation failure, which is little explored in the decision to extubate after cardiac surgery. OBJECTIVE: To evaluate static lung compliance in the postoperative period of cardiac surgery and relate its possible reduction to cases of extubation failure in patients submitted to the fast-track method of extubation. METHODS: Patients undergoing cardiac surgery using cardiopulmonary bypass (CPB) at a state university hospital admitted to the ICU under sedation and residual block were included. Their static lung compliance was assessed on the mechanical ventilator using software that uses least squares fitting (LSF) for measurement. Within 48 hours of extubation, the patients were observed for the need for reintubation due to respiratory failure. The level of significance adopted for the statistical tests was 5%, i.e., p<0.05. RESULTS: 77 patients (75.49%) achieved successful extubation and 25 (24.51%) failed extubation. Patients who failed extubation had lower static lung compliance compared to those who succeeded (p<0.001). We identified the cut-off point for compliance through analysis of the Receiver Operating Characteristic Curve (ROC), with the cut-off point being compliance <41ml/cmH2O associated with a higher probability of extubation failure (p<0.001). In the multiple regression analysis, the influence of lung compliance (divided by the ROC curve cut-off point) was found to be 9.1 times greater for patients with compliance <41ml/cmH2O (p< 0.003). CONCLUSIONS: Static lung compliance <41ml/cmH2O is a factor that compromises the success of extubation in the postoperative period of cardiac surgery.

FUNDAMENTO: Pouco explorada na decisão de extubação no pós-operatório de cirurgia cardíaca, a complacência pulmonar estática seriamente afetada no procedimento cirúrgico pode levar à insuficiência respiratória e à falha na extubação. OBJETIVO: Avaliar a complacência pulmonar estática no pós-operatório de cirurgia cardíaca e relacionar sua possível redução aos casos de falha na extubação dos pacientes submetidos ao método fast-track de extubação. MÉTODOS: Foram incluídos pacientes que realizaram cirurgia cardíaca com uso de circulação extracorpórea (CEC) em um hospital universitário estadual admitidos na UTI sob sedação e bloqueio residual. Tiveram sua complacência pulmonar estática avaliada no ventilador mecânico por meio do software que utiliza o least squares fitting (LSF) para a medição. No período de 48 horas após a extubação os pacientes foram observados respeito à necessidade de reintubação por insuficiência respiratória. O nível de significância adotado para os testes estatísticos foi de 5%, ou seja, p<0,05. RESULTADOS: Obtiveram sucesso na extubação 77 pacientes (75,49%) e falharam 25 (24,51%). Os pacientes que falharam na extubação tiveram a complacência pulmonar estática mais baixa quando comparados aos que tiveram sucesso (p<0,001). Identificamos o ponto de corte para complacência por meio da análise da curva Receiver Operating Characteristic Curve (ROC) sendo o ponto de corte o valor da complacência <41ml/cmH2O associado com maior probabilidade de falha na extubação (p<0,001). Na análise de regressão múltipla, verificou-se a influência da complacência pulmonar (dividida pelo ponto de corte da curva ROC) com risco de falha 9,1 vezes maior para pacientes com complacência <41ml/cmH2O (p< 0,003). CONCLUSÕES: A complacência pulmonar estática <41ml/cmH2O é um fator que compromete o sucesso da extubação no pós-operatório de cirurgia cardíaca.

A novel adaptive filter with a heart-rate-based reference signal for esophageal pressure signal denoising.

Esophageal pressure (Peso) is one of the most common and minimally invasive methods used to assess the respiratory and lung mechanics in patients receiving mechanical ventilation. However, the Peso measurement is contaminated by cardiogenic oscillations (CGOs), which cannot be easily eliminated in real-time. The field of study dealing with the elimination of CGO from Peso signals is still in the early stages of its development. In this study, we present an adaptive filtering-based method by constructing a reference signal based on the heart rate and sine function to remove CGOs in real-time. The proposed technique is tested using clinical data acquired from 20 patients admitted to the intensive care unit. Lung compliance ( QUOTE ) and esophageal pressure swings (△Pes) are used to evaluate the performance and efficiency of the proposed technique. The CGO can be efficiently suppressed when the constructional reference signal contains the fundamental, and second and third harmonic frequencies of the heart rate signal. The analysis of the data of 8 patients with controlled mechanical ventilation reveals that the standard deviation/mean of the QUOTE is reduced by 28.4-79.2% without changing the QUOTE and the △Pes measurement is more accurate, with the use of our proposed technique. The proposed technique can effectively eliminate the CGOs from the measured Peso signals in real-time without requiring additional equipment to collect the reference signal.