Distribution Of Ventilation Research Articles

Evaluation of Regional Pulmonary Ventilation in Spontaneously Breathing Patients with Idiopathic Pulmonary Fibrosis (IPF) Employing Electrical Impedance Tomography (EIT): A Pilot Study from the European IPF Registry (eurIPFreg).

Objectives: In idiopathic pulmonary fibrosis (IPF), alterations in the pulmonary surfactant system result in an increased alveolar surface tension and favor repetitive alveolar collapse. This study aimed to assess the usefulness of electrical impedance tomography (EIT) in characterization of regional ventilation in IPF. Materials and methods: We investigated 17 patients with IPF and 15 healthy controls from the University of Giessen and Marburg Lung Center (UGMLC), Germany, for differences in the following EIT parameters: distribution of ventilation (TID), global inhomogeneity index (GI), regional impedance differences through the delta of end-expiratory lung impedance (dEELI), differences in surface of ventilated area (SURF), as well as center of ventilation (CG) and intratidal gas distribution (ITV). These parameters were assessed under spontaneous breathing and following a predefined escalation protocol of the positive end-expiratory pressure (PEEP), applied through a face mask by an intensive care respirator (EVITA, Draeger, Germany). Results: Individual slopes of dEELI over the PEEP increment protocol were found to be highly significantly increased in both groups (p < 0.001) but were not found to be significantly different between groups. Similarly, dTID slopes were increasing in response to PEEP, but this did not reach statistical significance within or between groups. Individual breathing patterns were very heterogeneous. There were no relevant differences of SURF, GI or CGVD over the PEEP escalation range. A correlation of dEELI to FVC, BMI, age, or weight did not forward significant results. Conclusions: In this study, we did see a significant increase in dEELI and a non-significant increase in dTID in IPF patients as well as in healthy controls in response to an increase of PEEP under spontaneous breathing. We propose the combined measurements of EIT and lung function to assess regional lung ventilation in spontaneously breathing subjects.

Positive End-Expiratory Pressure, Pleural Pressure, and Regional Compliance during Pronation: An Experimental Study.

Rationale: The physiological basis of lung protection and the impact of positive end-expiratory pressure (PEEP) during pronation in acute respiratory distress syndrome are not fully elucidated. Objectives: To compare pleural pressure (Ppl) gradient, ventilation distribution, and regional compliance between dependent and nondependent lungs, and investigate the effect of PEEP during supination and pronation. Methods: We used a two-hit model of lung injury (saline lavage and high-volume ventilation) in 14 mechanically ventilated pigs and studied supine and prone positions. Global and regional lung mechanics including Ppl and distribution of ventilation (electrical impedance tomography) were analyzed across PEEP steps from 20 to 3 cm H2O. Two pigs underwent computed tomography scans: tidal recruitment and hyperinflation were calculated. Measurements and Main Results: Pronation improved oxygenation, increased Ppl, thus decreasing transpulmonary pressure for any PEEP, and reduced the dorsal-ventral pleural pressure gradient at PEEP < 10 cm H2O. The distribution of ventilation was homogenized between dependent and nondependent while prone and was less dependent on the PEEP level than while supine. The highest regional compliance was achieved at different PEEP levels in dependent and nondependent regions in supine position (15 and 8 cm H2O), but for similar values in prone position (13 and 12 cm H2O). Tidal recruitment was more evenly distributed (dependent and nondependent), hyperinflation lower, and lungs cephalocaudally longer in the prone position. Conclusions: In this lung injury model, pronation reduces the vertical pleural pressure gradient and homogenizes regional ventilation and compliance between the dependent and nondependent regions. Homogenization is much less dependent on the PEEP level in prone than in supine positon.

Understanding ATLAS infrastructure behaviour with an Expert System

The ATLAS detector requires a huge infrastructure consisting of numerous interconnected systems forming a complex mesh which undergoes constant maintenance and upgrades. The ATLAS Technical Coordination Expert System provides, by the means of a user interface, a quick and deep understanding of the infrastructure, which helps to plan interventions by foreseeing unexpected consequences, and to understand complex events when time is crucial in the ATLAS control room. It is an object-oriented expert system based on the knowledge composed of inference rules and information from diverse domains such as detector control and safety systems, gas, water, cooling, ventilation, cryogenics, and electricity distribution. This paper discusses the latest developments in the inference engine and the implementation of the most probable cause algorithm based on them. One example from the annual maintenance of the 15°C water circuit chillers is discussed.

Influence of manikin movement on temperature stratification in a displacement ventilated room

Temperature stratification generally exists in an indoor environment with floor-level air-supply systems, such as displacement ventilation (DV) and underfloor air distribution (UFAD). The systems with vertical temperature differences possess many advantages over mixing ventilation, including lower energy consumption and better indoor air quality. Some dynamic factors, including the movement of the human body, the door opening and closing processes, can disrupt or weaken the temperature stratification. However, the mechanisms by which these factors affect temperature stratification remain unclear. In this study, a series of experiments was conducted to investigate the temperature stratification of the DV system in an environmental chamber by adopting a moving manikin. We employed temperature stratification stability (TSS) and temperature stratification recovery time (TSRT) to quantify the influence of dynamic factors on temperature stratification. The primary and secondary factors which influencing TSS and TSRT were identified using orthogonal experiments among four important indices, i.e. manikin moving velocity (v), manikin moving duration (t), manikin heat generation intensity (P) and air change rate of the chamber (ACH). Results show factors destruct the mean TSS, ranked from the most to least significant, are v, ACH, P and t, and those for mean TSRT are v, t, P and ACH. In the manikin activity area, TSS increases with the vertical height. Manikin moving velocity exerts a primary effect on temperature stratification. There is a negative correlation between Re number and TSS in ourexperiment. The area affected by the movement is observed mainly around the manikin, not the whole chamber. The temperature stratification still exists after the termination of the manikin movement, but is relatively weakened.

Roles of Electrical Impedance Tomography in Determining a Lung Protective Strategy for Acute Respiratory Distress Syndrome in the Era of Coronavirus Disease 2019.

Electrical impedance tomography (EIT) is noninvasive and can be used at the bedside for real-time evaluation to identify ventilation distribution of infected lungs. This review briefly describes the basic principle of EIT and summarizes the latest findings on its potential contribution to lung protective strategies in coronavirus disease 2019 patients. Additionally, experimental approaches for detecting the distribution of pulmonary blood flow in coronavirus disease 2019 patients are presented. The findings underscore the role of EIT in determining lung protective strategies for coronavirus disease 2019-associated acute respiratory distress syndrome.

A Wireless, Low-Power, and Miniaturized EIT System for Remote and Long-Term Monitoring of Lung Ventilation in the Isolation Ward of ICU

Individualized lung-protective ventilation strategy is essential for patients with COVID-19. In this study, a wireless, low-power, and miniaturized electrical impedance tomography (EIT) system was developed for remote and long-term monitoring of lung ventilation for patients with COVID-19 in the isolation ward of ICU. A new strategy of combining filtering and improved voltage-controlled current was employed to design the current source for a simplified system structure, and a new differential receiver circuit consisting of a buffer amplification and a differential amplification was proposed to design the voltage measurement unit for high precision. Moreover, a Bluetooth interface was adopted for wireless data transmission, and components characterized by low power consumption were selected to minimize the system power consumption. The proposed EIT system occupies a total size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.5\times 4.5\times0.6$ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and can work stably within 25 m from the wireless terminal installed with host EIT software. The system has a signal-to-noise of 70 dB at 50 kHz, stability of 0.1% relative change, and power consumption of 114 mW, as tested with a resistor phantom. Furthermore, a comparison between the proposed system and a commercial ICU EIT device was conducted on nine healthy volunteers for ventilation monitoring. The correlation between lung volume and relative impedance changes was higher than 0.9 for both EIT systems ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$p &lt; 0.001$ </tex-math></inline-formula> ). The analysis of the corresponding EIT images revealed that both systems delivered comparable images in terms of linearity, repeatability, and regional ventilation distribution. The test and experimental results suggested that the proposed system could conveniently provide reliable data acquisition (DAQ) for remote and long-term lung ventilation monitoring.

Predictors of functional capacity as measured by the Glittre activities of daily living test in women with rheumatoid arthritis.

Although pulmonary involvement is the most common extra-articular manifestation of rheumatoid arthritis (RA), traditional pulmonary function tests (PFTs) do not show a good correlation with the field tests usually performed in these patients. In recent decades, measurement of ventilation distribution heterogeneity through the nitrogen single-breath washout (N2SBW) test and evaluation of functional capacity during exercise using the Glittre activities of daily living test (GA-T) have been increasingly used. Therefore, the objective of this study was to evaluate predictors of GA-T outcomes in women with RA considering demographic, anthropometric, clinical, functional variables, and chest computed tomography (CT) findings. Forty-three women with RA underwent the GA-T, the N2SBW test, spirometry, measurement of the diffusing capacity for carbon monoxide (DLco), measurement of respiratory muscle strength, and evaluation of physical function of the lower and upper limbs through the Health Assessment Questionnaire Disability Index (HAQ-DI). Chest CT scans were analyzed retrospectively. The GA-T time showed significant correlations with the DLco (rs=-0.397, P=0.008), forced vital capacity/DLco (rs=0.307, P=0.044), phase III slope of the N2SBW test (SIIIN2, rs=0.644, P<0.0001), and the HAQ-DI (rs=0.482, P=0.001). Disease extent as assessed by chest CT was associated with the GA-T time. On multiple regression analysis, the SIIIN2 and HAQ-DI were the only predictors of the GA-T time, explaining 40% of its variability. Thus, ventilation distribution heterogeneity and worse physical function substantially explain the variability in GA-T time in women with RA and varying extents of disease on chest CT.

Cardio-Respiratory tolerability of perfluoropropaneEnhanced MRI of pulmonary ventilation

Rationale: Recent advances in perfluoropropane magnetic resonance imaging of the lung have provided the means to assess pulmonary ventilation and gas distribution throughout the pulmonary airways and acini in a non-invasive manner. Objectives: The increased density of the inhaled PFP/O2 gas mixture generates longer wash-in times compared to wash-out while breathing room air and leads to slight increases in airway resistance (Raw) and respiratory effort by the subject during imaging. As a consequence of these gas-related effects, we sought to evaluate the cardio-respiratory tolerability of the PFP/O2 gas mixtures in our sequential breath-hold imaging protocol in normal subjects and subjects with obstructive lung disease. Methods: Tolerability was determined by evaluation of changes in vital signs (Heart Rate, Systolic and Diastolic Blood Pressure, Respiratory Rate and Temperature (otic)) at 3 time points (screening, pre-imaging and post-imaging) Measurements and Main Results: Assessment of vital signs before and after the administration of perfluoropropane gas mixture by matched pair analysis demonstrated statistically different values for Heart rate (Mean Difference =-2.417 bpm), Systolic BP (Mean Difference=6.95 mmHg), Diastolic BP (Mean Difference=3.86 mmHg) and SpO2 (Mean Difference=0.56%) even though these do not represent physiologically significant differences compared to activities of daily living such as climbing a flight of stairs. Conclusions: Our data demonstrate no negative outcomes in using PFP gas to image pulmonary ventilation. The PFP gas mixture is safe, well tolerated, and provides a three dimensional ‘picture’ (representation) of inhaled gas distribution for subject cohorts of normal and obstructive lung disease.

Ultrashort inspiratory times homogenize ventilation distribution in an inhomogeneous two-compartment model of the neonatal lung.

Inhomogeneous lung ventilation and pulmonary air leaks are common adverse effects of mechanical ventilation in preterm infants suffering from respiratory distress syndrome. We hypothesized that shortening of inspiratory times can improve the homogeneity of lung aeration. We assumed that ultrashort inspiratory times lead to a full build-up of pressure in regions with low compliance while maintaining incomplete filling of regions with high compliance. We connected a two-compartment model of the lung with different compliances of the two compartments to a neonatal ventilator. Pressures and flow rates were measured separately for each compartment at inspiratory times ranging from 0.1 to 0.8 s and various combinations of tidal volumes. An inspiratory time of 0.8 s resulted in near total pressure equalization between the airway pressure and the two compartments, as 97% of the maximum applied peak pressure was reached in the low compliance compartment and 95% in the high compliance compartment. The distribution of the tidal volume was proportional to the compartment compliance. Ultrashort inspiratory times lowered the peak pressure and tidal volume in the high compliance compartment but maintained higher pressure and volume in the low compliance compartment. An inspiratory time of 0.2 s resulted in a peak pressure of 80% of peak airway pressure in the low compliance compartment and in 61% of peak airway pressure in the high compliance compartment (p < .001). Ventilation with ultrashort inspiratory times may improve homogeneity of air distribution in inhomogeneous lungs of ventilated preterm or term infants.

Peripheral and proximal lung ventilation in asthma: Short-term variation and response to bronchodilator inhalation

The relative involvement of the large and small airways in asthma is not clear. Hyperpolarized gas magnetic resonance imaging (MRI) provides high-resolution 3-dimensional images of ventilation distribution that can be quantified by the ventilated volume percentage (VV%) of the lungs. Our aims were to (1) quantify the baseline reproducibility of VV%, (2) assess the ventilation distribution between the proximal and peripheral lungs, and (3) investigate regional ventilation response to bronchodilator inhalation in a cohort of patients with asthma. A total of 33 patients with poorly controlled, moderate-to-severe asthma were scanned with hyperpolarized 3He MRI. Two image data sets were acquired at baseline, and 1 image data set was acquired after bronchodilator inhalation. Images were divided into proximal and peripheral regions for analysis. Bland-Altman analysis showed strong reproducibility of VV% (bias= 0.12%; LOA= -1.86% to 2.10%). VV% variation at baseline was greater in the periphery than in the proximal lung. The proximal lung was better ventilated than the peripheral lung. Ventilation increased significantly in response to bronchodilator inhalation, globally and regionally, and the ventilation increase in response to bronchodilator inhalation was greater in the peripheral lung than in the proximal lung. Hyperpolarized gas MRI was more sensitive to changes in response to bronchodilator inhalation (58%) than spirometry (33%). The peripheral lung showed reduced ventilation and a greater response to bronchodilator inhalation than the proximal lung. The high level of baseline reproducibility and sensitivity of hyperpolarized gas MRI to bronchodilator reversibility suggests that it is suitable for low subject number studies of therapy response.

Comparative effects of flow vs. volume-controlled one-lung ventilation on gas exchange and respiratory system mechanics in pigs

BackgroundFlow-controlled ventilation (FCV) allows expiratory flow control, reducing the collapse of the airways during expiration. The performance of FCV during one-lung ventilation (OLV) under intravascular normo- and hypovolaemia is currently unknown. In this explorative study, we hypothesised that OLV with FCV improves PaO2 and reduces mechanical power compared to volume-controlled ventilation (VCV). Sixteen juvenile pigs were randomly assigned to one of two groups: (1) intravascular normovolaemia (n = 8) and (2) intravascular hypovolaemia (n = 8). To mimic inflammation due to major thoracic surgery, a thoracotomy was performed, and 0.5 μg/kg/h lipopolysaccharides from Escherichia coli continuously administered intravenously. Animals were randomly assigned to OLV with one of two sequences (60 min per mode): (1) VCV–FCV or (2) FCV–VCV. Variables of gas exchange, haemodynamics and respiratory signals were collected 20, 40 and 60 min after initiation of OLV with each mechanical ventilation mode. The distribution of ventilation was determined using electrical impedance tomography (EIT).ResultsOxygenation did not differ significantly between modes (P = 0.881). In the normovolaemia group, the corrected expired minute volume (P = 0.022) and positive end-expiratory pressure (PEEP) were lower during FCV than VCV. The minute volume (P ≤ 0.001), respiratory rate (P ≤ 0.001), total PEEP (P ≤ 0.001), resistance of the respiratory system (P ≤ 0.001), mechanical power (P ≤ 0.001) and resistive mechanical power (P ≤ 0.001) were lower during FCV than VCV irrespective of the volaemia status. The distribution of ventilation did not differ between both ventilation modes (P = 0.103).ConclusionsIn a model of OLV in normo- and hypovolemic pigs, mechanical power was lower during FCV compared to VCV, without significant differences in oxygenation. Furthermore, the efficacy of ventilation was higher during FCV compared to VCV during normovolaemia.

A narrative review of electrical impedance tomography in lung diseases with flow limitation and hyperinflation: methodologies and applications

Electrical impedance tomography (EIT) is a functional radiation-free imaging technique that measures regional lung ventilation distribution by calculating the impedance changes in the corresponding regions. The aim of the present review was to summarize the current literature concerning the methodologies and applications of EIT in lung diseases with flow limitation and hyperinflation. PubMed was searched up to May 2020 to identify studies investigating the use of EIT in patients with asthma, bronchiectasis, bronchitis, bronchiolitis, chronic obstructive pulmonary disease, and cystic fibrosis. The extracted data included study design, EIT methodologies, interventions, validation and comparators, population characteristics, and key findings. Of the 44 included studies, seven were related to simulation, animal experimentation, or reconstruction algorithm development with evaluation on patients; 27 studies had the primary objective of validating EIT technique and measures including regional ventilation distribution, regional EIT-spirometry parameters, end-expiratory lung impedance, and regional time constants; and 10 studies had the primary objective of applying EIT to monitor the response to therapeutic interventions, including various ventilation supports, patient repositioning, and airway suctioning. In pediatric and adult patients, EIT has been successfully validated for assessing spatial and temporal ventilation distribution, measuring changes in lung volume and flow, and studying regional respiratory mechanics. EIT has also demonstrated potential as an alternative or supplement to well-established measurement modalities (e.g., conventional pulmonary function testing) to monitor the progression of obstructive lung diseases, although the existing literature lacks prediction values as references and lacks clinical outcome evidence.

Lobar Ventilation in Patients with COPD Assessed with the Full-Scale Airway Network Flow Model and Xenon-enhanced Dual-Energy CT.

Background The full-scale airway network (FAN) flow model shows excellent agreement with limited functional imaging data but requires further validation prior to clinical use. Purpose To validate the ventilation distributions computed with the FAN flow model with xenon ventilation from xenon-enhanced dual-energy (DE) CT in participants with chronic obstructive pulmonary disease (COPD). Materials and Methods In this prospective study, the FAN model extracted structural data from xenon-enhanced DE CT images of men with COPD scanned between June 2012 and July 2013 to compute gas ventilation dynamics. The ventilation distributions on the middle cross-section plane, percentage lobar ventilation, and ventilation heterogeneity quantified by the coefficient of variation (CV) were compared between xenon-enhanced DE CT imaging and the FAN model. The relationship between the ventilation parameters with the densitometry and pulmonary function test results was demonstrated. The agreements and correlations between the parameters were measured using the concordance correlation coefficient and the Pearson correlation coefficient. Results Twenty-two men with COPD (mean age, 67 years ± 7 [standard deviation]) were evaluated. The percentage lobar ventilation computed with FAN showed a strong positive correlation with xenon-enhanced DE CT data (r = 0.7, P < .001). Ninety-five percent of lobar ventilation CV differences lay within 95% confidence intervals. Correlations of the percentage lobar ventilation were negative for percentage emphysema (xenon-enhanced DE CT: r = -0.38, P < .001; FAN: r = -0.23, P = .02) but were positive for percentage normal tissue volume (xenon-enhanced DE CT: r = 0.78, P < .001; FAN: r = 0.45, P < .001). Lung CVs of FAN revealed negative correlations with the spirometry results (CVFAN vs percentage predicted forced expiratory volume in 1 second: r = -0.75, P < .001; CVFAN vs ratio of forced expiratory volume in 1 second to forced vital capacity: r = -0.67, P < .001). Conclusion The full-scale airway network modeled lobar ventilation in patients with chronic obstructive pulmonary disease correlated with the xenon-enhanced dual-energy CT imaging data. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Parraga and Eddy in this issue.

Comparative studies on isothermal attachment ventilation based on vertical walls, square and circular columns

Ventilation and air distribution methods play an important role in indoor air quality and thermal environments. Effective airflow distribution within indoor environments has always been a great cause of concern. Attachment ventilation has drawn considerable interest since it is more energy efficient and space saving than traditional mixing or displacement ventilation methods. As a newly developed and applied attachment ventilation method, vertical wall-based attachment ventilation (WAV) was first proposed in the 1990’s by the authors. Later, the concepts of square column-based attachment ventilation (SAV) and circular column-based attachment ventilation (CAV) were also presented to meet the needs of more industrial applications. In this paper, three attachment ventilation methods— i.e., WAV, SAV and CAV are compared based on experimental studies and numerical simulations. For the vertical attachment region, semi-theoretical equations characterizing the dimensionless centerline velocity of WAV, SAV and CAV are proposed. The velocity profiles of all three types of attachment ventilation methods are similar. Of the three attachment ventilation methods, for the same distance y* along the attached wall measured from the slot inlet, the dimensionless centerline velocity of WAV is the largest, while those of SAV and CAV remain almost identical. In the horizontal air reservoir region (air lake zone), the semi-theoretical equations to predict dimensionless centerline velocity also are presented. The results show that for the same distance x normal to the wall/column, the dimensionless centerline velocity of WAV is the largest, followed by SAV and CAV. Additionally, unified semi-theoretical equations are presented for predicting the jet centerline velocity decay of attachment ventilation, which is helpful for the design of air distribution systems in heating, ventilation and air conditioning (HVAC) engineering applications.

Nasal high flow higher than 60\xa0L/min in patients with acute hypoxemic respiratory failure: a physiological study

BackgroundNasal high flow delivered at flow rates higher than 60 L/min in patients with acute hypoxemic respiratory failure might be associated with improved physiological effects. However, poor comfort might limit feasibility of its clinical use.MethodsWe performed a prospective randomized cross-over physiological study on 12 ICU patients with acute hypoxemic respiratory failure. Patients underwent three steps at the following gas flow: 0.5 L/kg PBW/min, 1 L/kg PBW/min, and 1.5 L/kg PBW/min in random order for 20 min. Temperature and FiO2 remained unchanged. Toward the end of each phase, we collected arterial blood gases, lung volumes, and regional distribution of ventilation assessed by electrical impedance tomography (EIT), and comfort.ResultsIn five patients, the etiology was pulmonary; infective disease characterized seven patients; median PaO2/FiO2 at enrollment was 213 [IQR 136–232]. The range of flow rate during NHF 1.5 was 75–120 L/min. PaO2/FiO2 increased with flow, albeit non significantly (p = 0.064), PaCO2 and arterial pH remained stable (p = 0.108 and p = 0.105). Respiratory rate decreased at higher flow rates (p = 0.014). Inhomogeneity of ventilation decreased significantly at higher flows (p = 0.004) and lung volume at end-expiration significantly increased (p = 0.007), but mostly in the non-dependent regions. Comfort was significantly poorer during the step performed at the highest flow (p < 0.001).ConclusionsNHF delivered at rates higher than 60 L/min in critically ill patients with acute hypoxemic respiratory failure is associated with reduced respiratory rate, increased lung homogeneity, and additional positive pressure effect, but also with worse comfort.

Vaping disrupts ventilation-perfusion matching in asymptomatic users.

Inhalation of e-cigarette's aerosols (vaping) has the potential to disrupt pulmonary gas exchange, but the effects in asymptomatic users are unknown. We assessed ventilation-perfusion (V̇A/Q̇) mismatch in asymptomatic e-cigarette users, using magnetic resonance imaging (MRI). We hypothesized that vaping induces V̇A/Q̇ mismatch through alterations in both ventilation and perfusion distributions. Nine young, asymptomatic "Vapers" with >1-yr vaping history, and no history of cardiopulmonary disease, were imaged supine using proton MRI, to assess the right lung at baseline and immediately after vaping. Seven young "Controls" were imaged at baseline only. Relative dispersion (SD/means) was used to quantify the heterogeneity of the individual ventilation and perfusion distributions. V̇A/Q̇ mismatch was quantified using the second moments of the ventilation and perfusion versus V̇A/Q̇ ratio distributions, log scale, LogSDV̇, and LogSDQ̇, respectively, analogous to the multiple inert gas elimination technique. Spirometry was normal in both groups. Ventilation heterogeneity was similar between groups at baseline (Vapers, 0.43 ± 0.13; Controls, 0.51 ± 0.11; P = 0.13) but increased after vaping (to 0.57 ± 0.17; P = 0.03). Perfusion heterogeneity was greater (P = 0.04) in Vapers at baseline (0.53 ± 0.06) compared with Controls (0.44 ± 0.10) but decreased after vaping (to 0.42 ± 0.07; P = 0.005). Vapers had greater (P = 0.01) V̇A/Q̇ mismatch at baseline compared with Controls (LogSDQ̇ = 0.61 ± 0.12 vs. 0.43 ± 0.12), which was increased after vaping (LogSDQ̇ = 0.73 ± 0.16; P = 0.03). V̇A/Q̇ mismatch is greater in Vapers and worsens after vaping. This suggests subclinical alterations in lung function not detected by spirometry.NEW & NOTEWORTHY This research provides evidence of vaping-induced disruptions in ventilation-perfusion matching in young, healthy, asymptomatic adults with normal spirometry who habitually vape. The changes in ventilation and perfusion distributions, both at baseline and acutely after vaping, and the potential implications on hypoxic vasoconstriction are particularly relevant in understanding the pathogenesis of vaping-induced dysfunction. Our imaging-based approach provides evidence of potential subclinical alterations in lung function below thresholds of detection using spirometry.

Role of Positive End-Expiratory Pressure and Regional Transpulmonary Pressure in Asymmetrical Lung Injury.

Rationale: Asymmetrical lung injury is a frequent clinical presentation. Regional distribution of Vt and positive end-expiratory pressure (PEEP) could result in hyperinflation of the less-injured lung. The validity of esophageal pressure (Pes) is unknown.Objectives: To compare, in asymmetrical lung injury, Pes with directly measured pleural pressures (Ppl) of both sides and investigate how PEEP impacts ventilation distribution and the regional driving transpulmonary pressure (inspiratory - expiratory).Methods: Fourteen mechanically ventilated pigs with lung injury were studied. One lung was blocked while the contralateral one underwent surfactant lavage and injurious ventilation. Airway pressure and Pes were measured, as was Ppl in the dorsal and ventral pleural space adjacent to each lung. Distribution of ventilation was assessed by electrical impedance tomography. PEEP was studied through decremental steps.Measurements and Results: Ventral and dorsal Ppl were similar between the injured and the noninjured lung across all PEEP levels. Dorsal Ppl and Pes were similar. The driving transpulmonary pressure was similar in the two lungs. Vt distribution between lungs was different at zero end-expiratory pressure (≈70% of Vt going in noninjured lung) owing to different respiratory system compliance (8.3 ml/cm H2O noninjured lung vs. 3.7 ml/cm H2O injured lung). PEEP at 10 cm H2O with transpulmonary pressure around zero homogenized Vt distribution opening the lungs. PEEP ≥16 cm H2O equalized distribution of Vt but with overdistension for both lungs.Conclusions: Despite asymmetrical lung injury, Ppl between injured and noninjured lungs is equalized and esophageal pressure is a reliable estimate of dorsal Ppl. Driving transpulmonary pressure is similar for both lungs. Vt distribution results from regional respiratory system compliance. Moderate PEEP homogenizes Vt distribution between lungs without generating hyperinflation.

Physiological effects of different recruitment maneuvers in a pig model of ARDS

BackgroundIn acute respiratory distress syndrome (ARDS), lung recruitment maneuvers can recruit collapsed alveoli in gravity-dependent lung regions, improving the homogeneity of ventilation distribution. This study used electrical impedance tomography to investigate the physiological effects of different recruitment maneuvers for alveolar recruitment in a pig model of ARDS.MethodsARDS was induced in ten healthy male pigs with repeated bronchoalveolar lavage until the ratio of arterial partial pressure of oxygen (PaO2) of fraction of inspired oxygen (P/F) was < 100 mmHg and remained stable for 30 min (TARDS). ARDS pigs underwent three sequential recruitment maneuvers, including sustained inflation, increments of positive end-expiratory pressure (PEEP), and pressure-controlled ventilation (PCV) applied in random order, with 30 mins at a PEEP of 5 cmH2O between maneuvers. Respiratory mechanics, hemodynamics, arterial blood gas, and electrical impedance tomography were recorded at baseline, TARDS, and before and after each recruitment maneuver.ResultsIn all ten pigs, ARDS was successfully induced with a mean 2.8 ± 1.03 L bronchoalveolar lavages. PaO2, P/F, and compliance were significantly improved after recruitment with sustained inflation, increments of PEEP or PCV (all p < 0.05), and there were no significant differences between maneuvers. Global inhomogeneity index significantly decreased after recruitment with sustained inflation, increments of PEEP, or PCV. There were no significant differences in global inhomogeneity before or after recruitment with the different maneuvers. The decrease in global inhomogeneity index (ΔGI) was significantly greater after recruitment with increments of PEEP compared to sustained inflation (p = 0.023), but there was no significant difference in ΔGI between increments of PEEP and PCV or between sustained inflation and PCV.ConclusionSustained inflation, increments of PEEP, and PCV increased oxygenation, and regional and global compliance of the respiratory system, and decreased inhomogeneous gas distribution in ARDS pigs. Increments of PEEP significantly improved inhomogeneity of the lung compared to sustained inflation, while there was no difference between increments of PEEP and PCV or between sustained inflation and PCV.

What hinders pulmonary gas exchange and changes distribution of ventilation in immobilized white rhinoceroses (Ceratotherium simum) in lateral recumbency?

This study used electrical impedance tomography (EIT) measurements of regional ventilation and perfusion to elucidate the reasons for severe gas exchange impairment reported in rhinoceroses during opioid-induced immobilization. EIT values were compared with standard monitoring parameters to establish a new monitoring tool for conservational immobilization and future treatment options. Six male white rhinoceroses were immobilized using etorphine, and EIT ventilation variables, venous admixture, and dead space were measured 30, 40, and 50 min after becoming recumbent in lateral position. Pulmonary perfusion mapping using impedance-enhanced EIT was performed at the end of the study period. The measured impedance (∆Z) by EIT was compared between pulmonary regions using mixed linear models. Measurements of regional ventilation and perfusion revealed a pronounced disproportional shift of ventilation and perfusion toward the nondependent lung. Overall, the dependent lung was minimally ventilated and perfused, but remained aerated with minimal detectable lung collapse. Perfusion was found primarily around the hilum of the nondependent lung and was minimal in the periphery of the nondependent and the entire dependent lung. These shifts can explain the high amount of venous admixture and physiological dead space found in this study. Breath holding redistributed ventilation toward dependent and ventral lung areas. The findings of this study reveal important pathophysiological insights into the changes in lung ventilation and perfusion during immobilization of white rhinoceroses. These novel insights might induce a search for better therapeutic options and is establishing EIT as a promising monitoring tool for large animals in the field.NEW & NOTEWORTHY Electrical impedance tomography measurements of regional ventilation and perfusion applied to etorphine-immobilized white rhinoceroses in lateral recumbency revealed a pronounced disproportional shift of the measured ventilation and perfusion toward the nondependent lung. The dependent lung was minimally ventilated and perfused, but still aerated. Perfusion was found primarily around the hilum of the nondependent lung. These shifts can explain the gas exchange impairments found in this study. Breath holding can redistribute ventilation.

The effect of turbulence on natural ventilation of a proposed octagonal greenhouse in a transient flow

This study presents the effect of openings on the ventilation rate of an experimental proposed octagonal greenhouse in a transient flow. Furthermore, it makes a comparison between the free ventilation of the proposed greenhouse with an Arc greenhouse with two-dimensional computational fluid dynamic simulation. To simulate airflow in the Arc greenhouse, we selected a one-side roof vent openings, butterfly-type side vent openings and one-side-face to face-roof vent openings as opening designs. Moreover, two octagonal greenhouse portions were selected due to changes in cross-sectional area. The results showed that the average wind speed in the greenhouse equipped with butterfly-type side vent opening was higher than other greenhouses, but the temperature of air inlet was distributed less slowly. To illustrate the accuracy, the computational fluid dynamic results, which include wind speed and temperature, were compared with the measured values from the proposed octagonal greenhouse. Moreover, this study investigates the effect of greenhouse shape and openings on turbulence formation and the effect of turbulence on greenhouse climate. After 10 min of simulation, the average total temperature in the greenhouses with butterfly-type side vent openings and one-side-face to face-roof vent openings models had still not reached the outside air temperature. Based on observations, like the average total temperature, the average total airflow velocity was also close in both sides of the octagonal greenhouse. The simulation results show that the speed of free ventilation and temperature distribution in the proposed octagonal greenhouse were higher than the Arc greenhouse with other openings design.