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Journal of Clinical Sleep Medicine :... Mar 2016Lung mechanics in the overlap of COPD and sleep apnea impact the severity of sleep apnea. Specifically, increased lung compliance with hyperinflation protects against...
STUDY OBJECTIVES
Lung mechanics in the overlap of COPD and sleep apnea impact the severity of sleep apnea. Specifically, increased lung compliance with hyperinflation protects against sleep apnea, whereas increased airway resistance worsens sleep apnea. We sought to assess whether the expiratory time constant, which reflects lung mechanics, is associated with sleep apnea severity in such patients.
METHODS
Polysomnographies in 34 subjects with the overlap syndrome were reviewed. Three time constants were measured for each of up to 5 stages (wake, NREM stages, and REM). The time constants were derived by fitting time and pressure coordinates on the expiratory portion of a nasal pressure signal along an exponentially decaying equation, and solving for the time constant. Demographics, morphometrics, wake end-tidal CO2, right diaphragmatic arc on a chest radiograph, and the apnea-hypopnea index (AHI) were recorded.
RESULTS
The time constant was not associated with age, gender, body mass index, right diaphragmatic arc, or wake end-tidal CO2, and was not significantly different between sleep stages. A mean time constant (TC) was therefore obtained. Subjects with a TC > 0.5 seconds had a greater AHI than those with a TC ≤ 0.5 seconds (median AHI 58 vs. 18, respectively, p = 0.003; Odds ratio of severe sleep apnea 10.6, 95% CI 3.9-51.1, p = 0.005).
CONCLUSIONS
A larger time constant in the overlap syndrome is associated with increased odds of severe sleep apnea, suggesting a greater importance of airway resistance relative to lung compliance in sleep apnea causation in these subjects.
Topics: Aged; Airway Resistance; Exhalation; Female; Humans; Male; Polysomnography; Pulmonary Disease, Chronic Obstructive; Respiration; Respiratory Function Tests; Severity of Illness Index; Sleep Apnea Syndromes; Sleep Stages; Time
PubMed: 26414979
DOI: 10.5664/jcsm.5576 -
BMC Pulmonary Medicine Nov 2019The expiratory time constant (RC), which is defined as the product of airway resistance and lung compliance, enable us to assess the mechanical properties of the...
BACKGROUND
The expiratory time constant (RC), which is defined as the product of airway resistance and lung compliance, enable us to assess the mechanical properties of the respiratory system in mechanically ventilated patients. Although RC could also be applied to spontaneously breathing patients, little is known about RC calculated from the maximal expiratory flow-volume (MEFV) curve. The aim of our study was to determine the reference value for RC, as well as to investigate the association between RC and other respiratory function parameters, including the forced expiratory volume in 1 s (FEV)/ forced vital capacity (FVC) ratio, maximal mid-expiratory flow rate (MMF), maximal expiratory flow at 50 and 25% of FVC (MEF and MEF, respectively), ratio of MEF to MEF (MEF/MEF).
METHODS
Spirometric parameters were extracted from the records of patients aged 15 years or older who underwent pulmonary function testing as a routine preoperative examination before non-cardiac surgery at the University of Tokyo Hospital. RC was calculated in each patient from the slope of the descending limb of the MEFV curve using two points corresponding to MEF and MEF. Airway obstruction was defined as an FEV/FVC and FEV below the statistically lower limit of normal.
RESULTS
We retrospectively analyzed 777 spirometry records, and 62 patients were deemed to have airway obstruction according to Japanese spirometric reference values. The cut-off value for RC was 0.601 s with an area under the receiver operating characteristic curve of 0.934 (95% confidence interval = 0.898-0.970). RC was strongly associated with FEV/FVC, and was moderately associated with MMF and MEF. However, RC was less associated with MEF and MEF/MEF.
CONCLUSIONS
Our findings suggest that an RC of longer than approximately 0.6 s can be linked to the presence of airway obstruction. Application of the concept of RC to spontaneously breathing subjects was feasible, using our simple calculation method.
Topics: Adolescent; Airway Obstruction; Exhalation; Feasibility Studies; Female; Humans; Lung; Male; Maximal Expiratory Flow-Volume Curves; Predictive Value of Tests; Preoperative Period; ROC Curve; Reference Values; Retrospective Studies; Spirometry; Surgical Procedures, Operative
PubMed: 31711456
DOI: 10.1186/s12890-019-0976-6 -
Analytical and Bioanalytical Chemistry Apr 2012Propofol in exhaled breath can be detected and monitored in real time by ion molecule reaction mass spectrometry (IMR-MS). In addition, propofol concentration in exhaled...
Propofol in exhaled breath can be detected and monitored in real time by ion molecule reaction mass spectrometry (IMR-MS). In addition, propofol concentration in exhaled breath is tightly correlated with propofol concentration in plasma. Therefore, real-time monitoring of expiratory propofol could be useful for titrating intravenous anesthesia, but only if concentration changes in plasma can be determined in exhaled breath without significant delay. To evaluate the utility of IMR-MS during non-steady-state conditions, we measured the time course of both expiratory propofol concentration and the processed electroencephalography (EEG) as a surrogate outcome for propofol effect after an IV bolus induction of propofol. Twenty-one patients scheduled for routine surgery were observed after a bolus of 2.5 mg kg(-1) propofol for induction of anesthesia. Expiratory propofol was measured using IMR-MS and the cerebral propofol effect was estimated using the bispectral index (BIS). Primary endpoints were time to detection of expiratory propofol and time to onset of propofol's effect on BIS, and the secondary endpoint was time to peak effect (highest expiratory propofol or lowest BIS). Expiratory propofol and changes in BIS were first detected at 43 ± 21 and 49 ± 11 s after bolus injection, respectively (P = 0.29). Peak propofol concentrations (9.2 ± 2.4 parts-per-billion) and lowest BIS values (23 ± 4) were reached after 208 ± 57 and 219 ± 62 s, respectively (P = 0.57). Expiratory propofol concentrations measured by IMR-MS have similar times to detection and peak concentrations compared with propofol effect as measured by the processed EEG (BIS). This suggests that expiratory propofol concentrations may be useful for titrating intravenous anesthesia.
Topics: Adult; Aged; Anesthetics, Intravenous; Breath Tests; Exhalation; Female; Humans; Kinetics; Male; Mass Spectrometry; Middle Aged; Propofol; Time Factors
PubMed: 22370587
DOI: 10.1007/s00216-012-5856-3 -
Expiratory Resistances Prevent Expiratory Diaphragm Contraction, Flow Limitation, and Lung Collapse.American Journal of Respiratory and... May 2020Tidal expiratory flow limitation (tidal-EFL) is not completely avoidable by applying positive end-expiratory pressure and may cause respiratory and hemodynamic...
Tidal expiratory flow limitation (tidal-EFL) is not completely avoidable by applying positive end-expiratory pressure and may cause respiratory and hemodynamic complications in ventilated patients with lungs prone to collapse. During spontaneous breathing, expiratory diaphragmatic contraction counteracts tidal-EFL. We hypothesized that during both spontaneous breathing and controlled mechanical ventilation, external expiratory resistances reduce tidal-EFL. To assess whether external expiratory resistances ) affect expiratory diaphragmatic contraction during spontaneous breathing, ) reduce expiratory flow and make lung compartments more homogeneous with more similar expiratory time constants, and ) reduce tidal atelectasis, preventing hyperinflation. Three positive end-expiratory pressure levels and four external expiratory resistances were tested in 10 pigs after lung lavage. We analyzed expiratory diaphragmatic electric activity and respiratory mechanics. On the basis of computed tomography scans, four lung compartments-not inflated (atelectasis), poorly inflated, normally inflated, and hyperinflated-were defined. Consequently to additional external expiratory resistances, and mainly in lungs prone to collapse (at low positive end-expiratory pressure), ) the expiratory transdiaphragmatic pressure decreased during spontaneous breathing by >10%, ) expiratory flow was reduced and the expiratory time constants became more homogeneous, and ) the amount of atelectasis at end-expiration decreased from 24% to 16% during spontaneous breathing and from 32% to 18% during controlled mechanical ventilation, without increasing hyperinflation. The expiratory modulation induced by external expiratory resistances preserves the positive effects of the expiratory brake while minimizing expiratory diaphragmatic contraction. External expiratory resistances optimize lung mechanics and limit tidal-EFL and tidal atelectasis, without increasing hyperinflation.
Topics: Animals; Diaphragm; Disease Models, Animal; Exhalation; Lung; Muscle Contraction; Positive-Pressure Respiration; Pulmonary Atelectasis; Pulmonary Ventilation; Respiration, Artificial; Respiratory Distress Syndrome; Respiratory Mechanics; Swine; Tomography, X-Ray Computed
PubMed: 32150440
DOI: 10.1164/rccm.201909-1690OC -
Experimental Physiology Oct 2015What is the central question of this study? Does the induction of a model of lung injury affect the expiratory time constant (τE) in terms of either total duration or... (Comparative Study)
Comparative Study
What is the central question of this study? Does the induction of a model of lung injury affect the expiratory time constant (τE) in terms of either total duration or morphology? Does ventilation with gases of different densities alter the duration or morphology of τE either before or after injury? What is the main finding and its importance? The use of sulfur hexafluoride in ventilating gas mixtures lengthens total expiratory time constants before and after lung injury compared with both nitrogen and helium mixtures. Sulfur hexafluoride mixtures also decrease the difference and variability of τE between fast- and slow-emptying compartments before and after injury when compared with nitrogen and helium mixtures. Acute lung injury is characterized by regional heterogeneity of lung resistance and elastance that may lead to regional heterogeneity of expiratory time constants (τE). We hypothesized that increasing airflow resistance by using inhaled sulfur hexafluoride (SF6) would lengthen time constants and decrease their heterogeneity in an experimental model of lung injury when compared with nitrogen or helium mixtures. To overcome the limitations of a single-compartment model, we employed a multisegment model of expiratory gas flow. An experimental model of lung injury was created using intratracheal injection of sodium polyacrylate in anaesthetized and mechanically ventilated female Yorkshire-cross pigs (n = 7). The animals were ventilated with 50% O2 and the remaining 50% as nitrogen (N2), helium (He) or sulfur hexafluoride (SF6). Values for τE decreased with injury and were more variable after injury than before (P < 0.001). Values for τE increased throughout expiration both before and after injury, and the rate of increase in τE was lessened by SF6 (P < 0.001 when compared with N2 both before and after injury). Altering the inhaled gas density did not affect indices of oxygenation, dead space or shunt. The use of SF6 in ventilating gas mixtures lengthens total expiratory time constants before and after lung injury compared with both N2 and He mixtures. Importantly, SF6 mixtures also decrease the difference and variability of τE between fast- and slow-emptying compartments before and after injury when compared with N2 and He mixtures.
Topics: Acrylic Resins; Acute Lung Injury; Administration, Inhalation; Animals; Disease Models, Animal; Exhalation; Female; Gases; Helium; Lung; Models, Biological; Nitrogen; Respiration, Artificial; Specific Gravity; Sulfur Hexafluoride; Sus scrofa; Time Factors
PubMed: 26289254
DOI: 10.1113/EP085205 -
Journal of Pharmaceutical and... Oct 2021The advantages that on-line breath analysis has shown in different fields have already made it stand as an interesting tool for pharmacokinetic studies. This review... (Review)
Review
The advantages that on-line breath analysis has shown in different fields have already made it stand as an interesting tool for pharmacokinetic studies. This review summarizes recent progress in the field, diving into the different analytical methods and the different advantages and hurdles encountered. We conclude that there is a wealth of limitations in the application of this technique, and key aspects like standardization are still outstanding. Nevertheless, this is an experimental field that has not yet been fully explored; and the advantages it offers for animal welfare, decrease in the amount of drug needed in experimental studies, and complementary insights to current pharmacological studies, warrant further exploration. Further studies are needed to overcome current limitations and incorporate this technique into the toolbox of pharmacological studies, both at an industrial and academic level.
Topics: Animals; Breath Tests; Exhalation; Reference Standards
PubMed: 34403867
DOI: 10.1016/j.jpba.2021.114311 -
Pediatric Pulmonology Feb 2020Mechanical insufflation-exsufflation (MI-E) is recommended for subjects of all ages with neuromuscular disorders (NMDs) and weak cough. There is a lack of knowledge on...
Mechanical insufflation-exsufflation (MI-E) is recommended for subjects of all ages with neuromuscular disorders (NMDs) and weak cough. There is a lack of knowledge on the optimal treatment settings for young children. This study aims to determine the MI-E settings providing high expiratory airflow while using safe inspiratory volumes, and to identify possible limits where the benefit of incrementing the MI-E settings to achieve a higher expiratory airflow, decreased. Using an MI-E device and a lung model imitating a 1-year-old child with NMD, we explored the impact of 120 combinations of MI-E pressure and time settings on maximal expiratory airflow and inspiratory volume. High expiratory airflows were achieved with several pressure and time combinations where the exsufflation pressure, followed by insufflation pressure and time, had the greatest impact. The benefit of incrementing the settings to increase the expiratory airflow leveled off for the insufflation pressure and time, but not for the exsufflation pressure. Given exsufflation pressure of -40 or -50 cmH O and insufflation time longer than 1 second, a plateau in the expiratory airflow curve was present at insufflation pressures from 25 cmH O, whereas a plateau in the inspired volume curve occurred at insufflation pressures from 35 cmH O. The present neuromuscular pediatric lung model study showed that expiratory pressure impacts expiratory airflow more than inspiratory pressure and time. An inspiratory and expiratory pressure set between 20 to 30 and -40 cmH O, respectively, and an inspiratory time longer than 1 second may be considered as a basis when titrating MI-E settings in young children with NMD. The findings must be confirmed in clinical trials.
Topics: Cough; Exhalation; Humans; Infant; Insufflation; Models, Biological; Neuromuscular Diseases; Pulmonary Ventilation
PubMed: 31856413
DOI: 10.1002/ppul.24606 -
Critical Care (London, England) May 2024Tidal expiratory flow limitation (EFL) complicates the delivery of mechanical ventilation but is only diagnosed by performing specific manoeuvres. Instantaneous analysis...
BACKGROUND
Tidal expiratory flow limitation (EFL) complicates the delivery of mechanical ventilation but is only diagnosed by performing specific manoeuvres. Instantaneous analysis of expiratory resistance (Rex) can be an alternative way to detect EFL without changing ventilatory settings. This study aimed to determine the agreement of EFL detection by Rex analysis and the PEEP reduction manoeuvre using contingency table and agreement coefficient. The patterns of Rex were explored.
METHODS
Medical patients ≥ 15-year-old receiving mechanical ventilation underwent a PEEP reduction manoeuvre from 5 cmHO to zero for EFL detection. Waveforms were recorded and analyzed off-line. The instantaneous Rex was calculated and was plotted against the volume axis, overlapped by the flow-volume loop for inspection. Lung mechanics, characteristics of the patients, and clinical outcomes were collected. The result of the Rex method was validated using a separate independent dataset.
RESULTS
339 patients initially enrolled and underwent a PEEP reduction. The prevalence of EFL was 16.5%. EFL patients had higher adjusted hospital mortality than non-EFL cases. The Rex method showed 20% prevalence of EFL and the result was 90.3% in agreement with PEEP reduction manoeuvre. In the validation dataset, the Rex method had resulted in 91.4% agreement. Three patterns of Rex were identified: no EFL, early EFL, associated with airway disease, and late EFL, associated with non-airway diseases, including obesity. In early EFL, external PEEP was less likely to eliminate EFL.
CONCLUSIONS
The Rex method shows an excellent agreement with the PEEP reduction manoeuvre and allows real-time detection of EFL. Two subtypes of EFL are identified by Rex analysis.
TRIAL REGISTRATION
Clinical trial registered with www.thaiclinicaltrials.org (TCTR20190318003). The registration date was on 18 March 2019, and the first subject enrollment was performed on 26 March 2019.
Topics: Humans; Male; Female; Respiration, Artificial; Middle Aged; Aged; Tidal Volume; Positive-Pressure Respiration; Exhalation; Adult
PubMed: 38773629
DOI: 10.1186/s13054-024-04953-9 -
Critical Care (London, England) Feb 2013We hypothesized the expiratory time constant (ƬE) may be used to provide real time determinations of inspiratory plateau pressure (Pplt), respiratory system compliance...
INTRODUCTION
We hypothesized the expiratory time constant (ƬE) may be used to provide real time determinations of inspiratory plateau pressure (Pplt), respiratory system compliance (Crs), and total resistance (respiratory system resistance plus series resistance of endotracheal tube) (Rtot) of patients with respiratory failure using various modes of ventilatory support.
METHODS
Adults (n = 92) with acute respiratory failure were categorized into four groups depending on the mode of ventilatory support ordered by attending physicians, i.e., volume controlled-continuous mandatory ventilation (VC-CMV), volume controlled-synchronized intermittent mandatory ventilation (VC-SIMV), volume control plus (VC+), and pressure support ventilation (PSV). Positive end expiratory pressure as ordered was combined with all aforementioned modes. Pplt, determined by the traditional end inspiratory pause (EIP) method, was combined in equations to determine Crs and Rtot. Following that, the ƬE method was employed, ƬE was estimated from point-by-point measurements of exhaled tidal volume and flow rate, it was then combined in equations to determine Pplt, Crs, and Rtot. Both methods were compared using regression analysis.
RESULTS
ƬE, ranging from mean values of 0.54 sec to 0.66 sec, was not significantly different among ventilatory modes. The ƬE method was an excellent predictor of Pplt, Crs, and Rtot for various ventilatory modes; r2 values for the relationships of ƬE and EIP methods ranged from 0.94 to 0.99 for Pplt, 0.90 to 0.99 for Crs, and 0.88 to 0.94 for Rtot (P <0.001). Bias and precision values were negligible.
CONCLUSIONS
We found the ƬE method was just as good as the EIP method for determining Pplt, Crs, and Rtot for various modes of ventilatory support for patients with acute respiratory failure. It is unclear if the ƬE method can be generalized to patients with chronic obstructive lung disease. ƬE is determined during passive deflation of the lungs without the need for changing the ventilatory mode and disrupting a patient's breathing. The ƬE method obviates the need to apply an EIP, allows for continuous and automatic surveillance of inspiratory Pplt so it can be maintained ≤ 30 cm H₂O for lung protection and patient safety, and permits real time assessments of pulmonary mechanics.
Topics: Adult; Aged; Exhalation; Female; Humans; Lung Compliance; Male; Middle Aged; Positive-Pressure Respiration; Respiration, Artificial; Respiratory Distress Syndrome; Tidal Volume; Time Factors
PubMed: 23384402
DOI: 10.1186/cc12500 -
Journal of Exposure Science &... Sep 2022Expiratory events, such as coughs, are often pulsatile in nature and result in vortical flow structures that transport expiratory particles. The World Health...
BACKGROUND
Expiratory events, such as coughs, are often pulsatile in nature and result in vortical flow structures that transport expiratory particles. The World Health Organization recommends wearing face masks to reduce the airborne transmission of diseases such as SARS-CoV-2 (COVID-19). However, masks are not perfect as flow leakage occurs around the mask, and their effectiveness under realistic (multi-pulse) coughing conditions is unknown.
OBJECTIVE
To assess the influence of expiratory flow pulsatility on the effectiveness of a surgical face mask by quantifying and classifying the flow leakage around the mask.
METHODS
A custom-built pulsatile expiratory flow simulator is used to generate single- and multi-pulsed coughing events. Flow visualization and particle image velocimetry are used to assess the penetration distance and volume of leakage flow at the top and sides of a surgical mask.
RESULTS
Leakage flow velocity profiles at the top and sides of a surgical mask take the form of a wall jet and a free-shear jet, respectively. Multi-pulsed expiratory flow events are found to generate greater leakage flow around the mask than single-pulsed events.
SIGNIFICANCE
For the first time, the leakage volume of a surgical mask is shown to be correlated to the pulsatile nature of a cough.
IMPACT STATEMENT
The novelties of this study are: First, flow field measurements are used to quantify and classify the leakage flow fields around the top and sides of a surgical mask, providing a benchmark for quantitative modeling of leakage flow velocity profiles. Second, the influence of pulsatility on the effectiveness of surgical face masks is studied by quantifying the leakage volume. For the first time, the leakage volume of a surgical mask is shown to be correlated to the pulsatile nature of a cough, as multi-pulsed expiratory flow events are found to generate greater flow leakage around the mask than single-pulsed events.
Topics: COVID-19; Cough; Exhalation; Humans; Masks; SARS-CoV-2
PubMed: 35132199
DOI: 10.1038/s41370-022-00416-x