Dynamic Respiratory Mechanics Research Articles

Electrical Impedance Tomography during Abdominal Laparoscopic Surgery: A Physiological Pilot Study

Background: Both general anesthesia and pneumoperitoneum insufflation during abdominal laparoscopic surgery can lead to atelectasis and impairment in oxygenation. Setting an appropriate level of external PEEP could reduce the occurrence of atelectasis and induce an improvement in gas exchange. However, in clinical practice, it is common to use a fixed PEEP level (i.e., 5 cmH2O), irrespective of the dynamic respiratory mechanics. We hypothesized setting a PEEP level guided by EIT in order to obtain an improvement in oxygenation and respiratory system compliance in lung-healthy patients than can benefit a personalized approach. Methods: Twelve consecutive patients scheduled for abdominal laparoscopic surgery were enrolled in this prospective study. The EIT Timpel Enlight 1800 was applied to each patient and a dedicated pneumotachograph and a spirometer flow sensor, integrated with EIT, constantly recorded respiratory mechanics. Gas exchange, respiratory mechanics and hemodynamics were recorded at five time points: T0, baseline; T1, after induction; T2, after pneumoperitoneum insufflation; T3, after a recruitment maneuver; and T4, at the end of surgery after desufflation. Results: A titrated mean PEEP of 8 cmH2O applied after a recruitment maneuver was successfully associated with the “best” compliance (58.4 ± 5.43 mL/cmH2O), with a low percentage of collapse (10%), an acceptable level of hyperdistention (0.02%). Pneumoperitoneum insufflation worsened respiratory system compliance, plateau pressure, and driving pressure, which significantly improved after the application of the recruitment maneuver and appropriate PEEP. PaO2 increased from 78.1 ± 9.49 mmHg at T0 to 188 ± 66.7 mmHg at T4 (p < 0.01). Other respiratory parameters remained stable after abdominal desufflation. Hemodynamic parameters remained unchanged throughout the study. Conclusions: EIT, used as a non-invasive intra-operative monitor, enables the rapid assessment of lung volume and regional ventilation changes in patients undergoing laparoscopic surgery and helps to identify the “optimal” PEEP level in the operating theatre, improving ventilation strategies.

Establishment of a digital remote platform for respiratory support and intelligent early warning in intensive care units

During the disease progression or treatment of critically ill patients with lung injury, the changes in respiratory mechanics are continuous and dynamic. Establishing a digital platform for respiratory support in the ICU, which enables the continuous recording, dynamic analysis, and real-time alerting of numerical and waveform data from mechanical ventilation, can help intensivists improve their understanding of "dynamic respiratory mechanics", improve respiratory therapy and patient outcomes, as well as reduce workload and increase work efficiency. The construction of a dedicated database for mechanical ventilation, based on ventilator waveforms provides essential data support for projects such as respiratory mechanics data algorithm models. This will facilitate the establishment of an auxiliary decision-making system, enable the realization of intelligent mechanical ventilation, and create a new era of dynamic respiratory mechanics.

The role of inspiratory capacity and tidal flow in diagnosing exercise ventilatory limitation in Cystic Fibrosis

BackgroundExercise ventilatory limitation conventionally defined by reduced breathing reserve (BR) may underestimate the effect of lung disease on exercise capacity in patients with mild to moderate obstructive lung diseases. ObjectiveTo investigate whether ventilatory limitation may be present despite a normal BR in Cystic Fibrosis (CF). MethodsTwenty adult CF patients (age 16-58y) with a wide range of pulmonary obstruction severity completed a symptom-limited incremental exercise test on a cycle ergometer. Operating lung volumes were derived from inspiratory capacity (IC) measurement during exercise and exercise tidal flow volume loop analysis.Results: six patients had a severe airway obstruction (FEV1<45% predicted) and conventional evidence of ventilatory limitation (low BR). Fourteen patients had mild to moderate-severe airway obstructive (FEV1 46–103% predicted), and a normal BR [12–62 L/min, BR% (17–40)]. However, dynamic respiratory mechanics demonstrated that even CF patients with mild to moderate-severe lung disease had clear evidence of ventilatory limitation during exercise. IC was decreased by (median) 580 ml (range 90–1180 ml) during exercise, indicating dynamic hyperinflation. Inspiratory reserve volume at peak exercise was 445 ml (241–1350 ml) indicating mechanical constraint on the respiratory system. The exercise tidal flow met or exceeded the expiratory boundary of the maximal flow volume loop over 72% of the expiratory volume (range 40–90%), indicating expiratory flow limitation. ConclusionReduced BR as a sole criterion underestimates ventilatory limitation during exercise in mild to moderate-severe CF patients. Assessment of dynamic respiratory mechanics during exercise revealed ventilatory limitation, present even in patients with mild obstruction.

Qualitative Components of Dyspnea during Incremental Exercise across the COPD Continuum.

Evaluation of the intensity and quality of activity-related dyspnea is potentially useful in people with chronic obstructive pulmonary disease (COPD). The present study sought to examine associations between qualitative dyspnea descriptors, dyspnea intensity ratings, dynamic respiratory mechanics, and exercise capacity during cardiopulmonary exercise testing (CPET) in COPD and healthy controls. In this cross-sectional study, 261 patients with mild-to-very severe COPD (forced expiratory volume in 1 s, 62 ± 25%pred) and 94 age-matched controls (forced expiratory volume in 1 s, 114 ± 14%pred) completed an incremental cycle CPET to determine peak oxygen uptake (V˙O2peak). Throughout exercise, expired gases, operating lung volumes, and dyspnea intensity were assessed. At peak exercise, dyspnea quality was assessed using a modified 15-item questionnaire. Logistic regression analysis revealed that among 15 dyspnea descriptors, only those alluding to the cluster "unsatisfied inspiration" were consistently associated with an increased likelihood for both critical inspiratory mechanical constraint (end-inspiratory lung volume/total lung capacity ratio ≥0.9) during exercise and reduced exercise capacity (V˙O2peak < lower limit of normal) in COPD (odds ratio (95% confidence interval), 3.26 (1.40-7.60) and 3.04 (1.24-7.45), respectively; both, P < 0.05). Thus, patients reporting "unsatisfied inspiration" (n = 177 (68%)) had an increased relative frequency of critical inspiratory mechanical constraint and low exercise capacity compared with those who did not select this descriptor, regardless of COPD severity or peak dyspnea intensity scores. In patients with COPD, regardless of disease severity, reporting descriptors in the unsatisfied inspiration cluster complemented traditional assessments of dyspnea during CPET and helped identify patients with critical mechanical abnormalities germane to exercise intolerance.

Evaluation of Dynamic Respiratory Mechanical Abnormalities During Conventional CPET.

Assessment of the ventilatory response to exercise is important in evaluating mechanisms of dyspnea and exercise intolerance in chronic cardiopulmonary diseases. The characteristic mechanical derangements that occur during exercise in chronic respiratory conditions have previously been determined in seminal studies using esophageal catheter pressure-derived measurements. In this brief review, we examine the emerging role and clinical utility of conventional assessment of dynamic respiratory mechanics during exercise testing. Thus, we provide a physiologic rationale for measuring operating lung volumes, breathing pattern, and flow–volume loops during exercise. We consider standardization of inspiratory capacity-derived measurements and their practical implementation in clinical laboratories. We examine the evidence that this iterative approach allows greater refinement in evaluation of ventilatory limitation during exercise than traditional assessments of breathing reserve. We appraise the available data on the reproducibility and responsiveness of this methodology. In particular, we review inspiratory capacity measurement and derived operating lung volumes during exercise. We demonstrate, using recent published data, how systematic evaluation of dynamic mechanical constraints, together with breathing pattern analysis, can provide valuable insights into the nature and extent of physiological impairment contributing to exercise intolerance in individuals with common chronic obstructive and restrictive respiratory disorders.

Deterioration of Nighttime Respiratory Mechanics in COPD: Impact of Bronchodilator Therapy

COPD is associated with nighttime respiratory symptoms, poor sleep quality, and increased risk of nocturnal death. Overnight deterioration of inspiratory capacity (IC) and FEV1 have been documented previously. However, the precise nature of this deterioration and mechanisms by which evening bronchodilation may mitigate this occurrence have not been studied. What is the effect of evening dosing of dual, long-acting bronchodilation on detailed nocturnal respiratory mechanics and inspiratory neural drive (IND)? A double-blind, randomized, placebo-controlled crossover study assessed the effects of evening long-acting bronchodilation (aclidinium bromide/formoterol fumarate dihydrate: 400/12 μg) or placebo on morning trough IC (12h after the dose; primary outcome) and serial overnight measurements of spirometry, dynamic respiratory mechanics, and IND (secondary outcomes). Twenty participants with COPD (moderate/severe airway obstruction and lung hyperinflation) underwent serial measurements of IC, spirometry, breathing pattern, esophageal and transdiaphragmatic pressures, and diaphragm electromyography (diaphragmatic electromyography as a percentage of maximum; IND) at 6 time points from 0 to 12h after the dose and compared with sleeping IND. Compared with placebo, evening bronchodilation was not associated with increased morning trough IC 12h after the dose (P= .48); however, nadir IC (lowest IC, independent of time), peak IC, area under the curve for 12h after the dose, and IC for 10h after the dose were improved (P< .05). During placebo, total airways resistance, lung hyperinflation, IND, and tidal esophageal and transdiaphragmatic pressure swings all increased significantly overnight compared with baseline evening values; however, each of these parameters improved with bronchodilator treatment (P< .05) with no change in ventilation or breathing pattern. Respiratory mechanics significantly deteriorated at night during placebo. Although the morning trough IC was unchanged, evening bronchodilator treatment was associated consistently with sustained overnight improvements in dynamic respiratory mechanics and inspiratory neural drive compared with placebo CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT02429765.

Aging effects on airflow dynamics and lung function in human bronchioles.

Background and objectiveThe mortality rate for patients requiring mechanical ventilation is about 35% and this rate increases to about 53% for the elderly. In general, with increasing age, the dynamic lung function and respiratory mechanics are compromised, and several experiments are being conducted to estimate these changes and understand the underlying mechanisms to better treat elderly patients.Materials and methodsHuman tracheobronchial (G1 ~ G9), bronchioles (G10 ~ G22) and alveolar sacs (G23) geometric models were developed based on reported anatomical dimensions for a 50 and an 80-year-old subject. The aged model was developed by altering the geometry and material properties of the model developed for the 50-year-old. Computational simulations using coupled fluid-solid analysis were performed for geometric models of bronchioles and alveolar sacs under mechanical ventilation to estimate the airflow and lung function characteristics.FindingsThe airway mechanical characteristics decreased with aging, specifically a 38% pressure drop was observed for the 80-year-old as compared to the 50-year-old. The shear stress on airway walls increased with aging and the highest shear stress was observed in the 80-year-old during inhalation. A 50% increase in peak strain was observed for the 80-year-old as compared to the 50-year-old during exhalation. The simulation results indicate that there is a 41% increase in lung compliance and a 35%-50% change in airway mechanical characteristics for the 80-year-old in comparison to the 50-year-old. Overall, the airway mechanical characteristics as well as lung function are compromised due to aging.ConclusionOur study demonstrates and quantifies the effects of aging on the airflow dynamics and lung capacity. These changes in the aging lung are important considerations for mechanical ventilation parameters in elderly patients. Realistic geometry and material properties need to be included in the computational models in future studies.

Advances in the Evaluation of Respiratory Pathophysiology during Exercise in Chronic Lung Diseases.

Dyspnea and exercise limitation are among the most common symptoms experienced by patients with various chronic lung diseases and are linked to poor quality of life. Our understanding of the source and nature of perceived respiratory discomfort and exercise intolerance in chronic lung diseases has increased substantially in recent years. These new mechanistic insights are the primary focus of the current review. Cardiopulmonary exercise testing (CPET) provides a unique opportunity to objectively evaluate the ability of the respiratory system to respond to imposed incremental physiological stress. In addition to measuring aerobic capacity and quantifying an individual's cardiac and ventilatory reserves, we have expanded the role of CPET to include evaluation of symptom intensity, together with a simple “non-invasive” assessment of relevant ventilatory control parameters and dynamic respiratory mechanics during standardized incremental tests to tolerance. This review explores the application of the new advances in the clinical evaluation of the pathophysiology of exercise intolerance in chronic obstructive pulmonary disease (COPD), chronic asthma, interstitial lung disease (ILD) and pulmonary arterial hypertension (PAH). We hope to demonstrate how this novel approach to CPET interpretation, which includes a quantification of activity-related dyspnea and evaluation of its underlying mechanisms, enhances our ability to meaningfully intervene to improve quality of life in these pathologically-distinct conditions.

Respiratory dynamics and dead space to tidal volume ratio of volume-controlled versus pressure-controlled ventilation during prolonged gynecological laparoscopic surgery.

Laparoscopic operations have become longer and more complex and applied to a broader patient population in the last decades. Prolonged gynecological laparoscopic surgeries require prolonged pneumoperitoneum and Trendelenburg position, which can influence respiratory dynamics and other measurements of pulmonary function. We investigated the differences between volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) and tried to determine the more efficient ventilation mode during prolonged pneumoperitoneum in gynecological laparoscopy. Twenty-six patients scheduled for laparoscopic radical hysterectomy combined with or without laparoscopic pelvic lymphadenectomy were randomly allocated to be ventilated by either VCV or PCV. Standard anesthesic management and laparoscopic procedures were performed. Measurements of respiratory and hemodynamic dynamics were obtained after induction of anesthesia, at 10, 30, 60, and 120min after establishing pneumoperitoneum, and at 10min after return to supine lithotomy position and removal of carbon dioxide. The logistic regression model was applied to predict the corresponding critical value of duration of pneumoperitoneum when the Ppeak was higher than 40cmH2O. Prolonged pneumoperitoneum and Trendelenburg position produced significant and clinically relevant changes in dynamic compliance and respiratory mechanics in anesthetized patients under PCV and VCV ventilation. Patients under PCV ventilation had a similar increase of dead space/tidal volume ratio, but had a lower Ppeak increase compared with those under VCV ventilation. The critical value of duration of pneumoperitoneum was predicted to be 355min under VCV ventilation, corresponding to the risk of Ppeak higher than 40cmH2O. Both VCV and PCV can be safely applied to prolonged gynecological laparoscopic surgery. However, PCV may become the better choice of ventilation after ruling out of other reasons for Ppeak increasing.

Time-varying respiratory system elastance: a physiological model for patients who are spontaneously breathing.

BackgroundRespiratory mechanics models can aid in optimising patient-specific mechanical ventilation (MV), but the applications are limited to fully sedated MV patients who have little or no spontaneously breathing efforts. This research presents a time-varying elastance (Edrs) model that can be used in spontaneously breathing patients to determine their respiratory mechanics.MethodsA time-varying respiratory elastance model is developed with a negative elastic component (Edemand), to describe the driving pressure generated during a patient initiated breathing cycle. Data from 22 patients who are partially mechanically ventilated using Pressure Support (PS) and Neurally Adjusted Ventilatory Assist (NAVA) are used to investigate the physiology relevance of the time-varying elastance model and its clinical potential. Edrs of every breathing cycle for each patient at different ventilation modes are presented for comparison.ResultsAt the start of every breathing cycle initiated by patient, Edrs is < 0. This negativity is attributed from the Edemand due to a positive lung volume intake at through negative pressure in the lung compartment. The mapping of Edrs trajectories was able to give unique information to patients’ breathing variability under different ventilation modes. The area under the curve of Edrs (AUCEdrs) for most patients is > 25 cmH2Os/l and thus can be used as an acute respiratory distress syndrome (ARDS) severity indicator.ConclusionThe Edrs model captures unique dynamic respiratory mechanics for spontaneously breathing patients with respiratory failure. The model is fully general and is applicable to both fully controlled and partially assisted MV modes.

Monitoring of intratidal lung mechanics: a Graphical User Interface for a model-based decision support system for PEEP-titration in mechanical ventilation

In mechanical ventilation, a careful setting of the ventilation parameters in accordance with the current individual state of the lung is crucial to minimize ventilator induced lung injury. Positive end-expiratory pressure (PEEP) has to be set to prevent collapse of the alveoli, however at the same time overdistension should be avoided. Classic approaches of analyzing static respiratory system mechanics fail in particular if lung injury already prevails. A new approach of analyzing dynamic respiratory system mechanics to set PEEP uses the intratidal, volume-dependent compliance which is believed to stay relatively constant during one breath only if neither atelectasis nor overdistension occurs. To test the success of this dynamic approach systematically at bedside or in an animal study, automation of the computing steps is necessary. A decision support system for optimizing PEEP in form of a Graphical User Interface (GUI) was targeted. Respiratory system mechanics were analyzed using the gliding SLICE method. The resulting shapes of the intratidal compliance-volume curve were classified into one of six categories, each associated with a PEEP-suggestion. The GUI should include a graphical representation of the results as well as a quality check to judge the reliability of the suggestion. The implementation of a user-friendly GUI was successfully realized. The agreement between modelled and measured pressure data [expressed as root-mean-square (RMS)] tested during the implementation phase with real respiratory data from two patient studies was below 0.2mbar for data taken in volume controlled mode and below 0.4mbar for data taken in pressure controlled mode except for two cases with RMS<0.6mbar. Visual inspections showed, that good and medium quality data could be reliably identified. The new GUI allows visualization of intratidal compliance-volume curves on a breath-by-breath basis. The automatic categorisation of curve shape into one of six shape-categories provides the rational decision-making model for PEEP-titration.

Time-Varying Respiratory Elastance for Spontaneously Breathing Patients

Respiratory mechanics models can be used to optimise patient-specific mechanical ventilation (MV), but are limited to fully sedated MV patients who are not spontaneously breathing. This research presents a non-invasive model-based method to determine respiratory mechanics of spontaneously breathing MV patients. Patient-specific respiratory mechanics of 22 spontaneously breathing patients are described using a single compartment lung model with time-varying elastance (Edrs). The normalised Edrs trajectories and the area under the curves (AUCEdrs) are calculated using clinical data from 22 patients ventilated using pressure support (PS) and neurally adjusted ventilatory assist (NAVA). Edrs trajectories are also compared between ventilation modes. Edrs for PS ventilation were significantly higher compared to NAVA (p < 0.05). Edrs trajectories were more variable during NAVA than PS (p < 0.05). 20 of 22 patients had AUCEdrs > 25 cmH2Os/l. The AUCEdrs is a surrogate of elastance, and thus can be used as a respiratory failure severity indicator. This non-invasive model-based approach captures unique dynamic respiratory mechanics for spontaneously breathing patients during PS and NAVA. The model is fully general and is applicable to both fully controlled and partially assisted MV modes, with the resulting potential to standardise treatment for all MV patients.

Physiological mechanisms of sex differences in exertional dyspnoea: role of neural respiratory motor drive

What is the central question of this study? Does the combination of a higher neural respiratory drive and greater dynamic mechanical ventilatory constraints during exercise in healthy women versus men form the mechanistic basis of sex differences in activity-related dyspnoea? What is the main finding and its importance? Sex differences in activity-related dyspnoea in health primarily reflected the awareness of a higher neural respiratory drive needed to achieve any given ventilation during exercise in the setting of relatively greater dynamic mechanical ventilatory constraints in women. These findings may have implications for our understanding of the mechanisms of sex differences in exertional dyspnoea in variants of health (e.g. the elderly) and in patients with cardiorespiratory disease. The purpose of this study was to elucidate the physiological mechanisms of sex differences in exertional dyspnoea. We compared detailed measures of neural respiratory motor drive [diaphragmatic EMG (EMGdi) expressed as a percentage of maximal EMGdi (EMGdi%max)], breathing pattern, operating lung volumes, dynamic respiratory mechanics [tidal oesophageal (P(oes,tida)l%peak) and transdiaphragmatic pressure swings (P(di,tidal)%peak) expressed as a percentage of their respective peak values] and sensory intensity and unpleasantness ratings of dyspnoea during symptom-limited incremental cycle exercise in healthy young women (n = 25) and men (n = 25). The tidal volume to forced vital capacity ratio (V(T)%FVC), breathing frequency, EMGdi%max, P(oes,tidal)%peak, P(di,tidal)%peak and sensory intensity and unpleasantness ratings of dyspnoea were higher, while dynamic inspiratory capacity and inspiratory reserve volume were lower at a standardized absolute ventilation of 55 l min(-1) during submaximal exercise in women versus men (all P < 0.05). In contrast, sex had no demonstrable effect on the inter-relationships between exercise-induced increases in V(T)%FVC, EMGdi%max and sensory intensity and unpleasantness ratings of dyspnoea. The results of this study suggest that sex differences in the intensity and unpleasantness of exertional dyspnoea in health are likely to reflect the awareness of a relatively higher neural respiratory motor drive (or EMGdi%max) needed to achieve any given ventilation during exercise in the setting of relatively greater dynamic mechanical constraints on V(T) expansion in women.

Does the Respiratory System Limit Exercise in Mild Chronic Obstructive Pulmonary Disease?

It is not known if abnormal dynamic respiratory mechanics actually limit exercise in patients with mild chronic obstructive pulmonary disease (COPD). We reasoned that failure to increase peak ventilation and Vt in response to dead space (DS) loading during exercise would indicate true ventilatory limitation to exercise in mild COPD. To compare the effects of DS loading during exercise on ventilation, breathing pattern, operating lung volumes, and dyspnea intensity in subjects with mild symptomatic COPD and age- and sex-matched healthy control subjects. Twenty subjects with Global Initiative for Chronic Obstructive Lung Disease stage I COPD and 20 healthy subjects completed two symptom-limited incremental cycle exercise tests, in randomized order: unloaded control and added DS of 0.6 L. Peak oxygen uptake and ventilation were significantly lower in COPD than in health by 36% and 41%, respectively. With added DS compared with control, both groups had small decreases in peak work rate and no significant increase in peak ventilation. In health, peak Vt and end-inspiratory lung volume increased significantly with DS. In contrast, the COPD group failed to increase peak end-inspiratory lung volume and had a significantly smaller increase in peak Vt during DS. At 60 W, a 50% smaller increase in Vt (P < 0.001) in response to added DS in COPD compared with health was associated with a greater increase in dyspnea intensity (P = 0.0005). These results show that the respiratory system reached or approached its physiologic limit in mild COPD at a lower peak work rate and ventilation than in healthy participants. Clinical trial registered with www.clinicaltrials.gov (NCT 00975403).

Analysis of Dynamic Respiratory Mechanics Profits from Breathing-Phase Selective Filtering

Analysis of Dynamic Respiratory Mechanics Profits from Breathing-Phase Selective Filtering

Structural Identifiability and Practical Applicability of an Alveolar Recruitment Model for ARDS Patients

Patient-specific mathematical models of respiratory mechanics can offer substantial insight into patient state and pulmonary dynamics that are not directly measurable. Thus, they offer significant potential to evaluate and guide patient-specific lung protective ventilator strategies for acute respiratory distress syndrome (ARDS) patients. To assure bedside applicability, the model must be computationally efficient and identifiable from the limited available data, while also capturing dominant dynamics and trends observed in ARDS patients. In this study, an existing static recruitment model is enhanced by considering alveolar distension and implemented in a novel time-continuous dynamic respiratory mechanics model. The model was tested for structural identifiability and a hierarchical gradient descent approach was used to fit the model to low-flow test responses of 12 ARDS patients. Finally, a comprehensive practical identifiability analysis was performed to evaluate the impact of data quality on the model parameters. Identified parameter values were physiologically plausible and very accurately reproduced the measured pressure responses. Structural identifiability of the model was proven, but practical identifiability analysis of the results showed a lack of convexity on the error surface indicating that successful parameter identification is currently not assured in all test sets. Overall, the model presented is physiologically and clinically relevant, captures ARDS dynamics, and uses clinically descriptive parameters. The patient-specific models show the ability to capture pulmonary dynamics directly relevant to patient condition and clinical guidance. These characteristics currently cannot be directly measured or established without such a validated model.

Assessment of a volume-dependent dynamic respiratory system compliance in ALI/ARDS by pooling breathing cycles

New methods were developed to calculate the volume-dependent dynamic respiratory system compliance (Crs) in mechanically ventilated patients. Due to noise in respiratory signals and different characteristics of the methods, their results can considerably differ. The aim of the study was to establish a practical procedure to validate the estimation of intratidal dynamic Crs. A total of 28 patients from intensive care units of eight German university hospitals with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) were studied retrospectively. Dynamic volume-dependent Crs was determined during ongoing mechanical ventilation with the SLICE method, dynostatic algorithm and adaptive slice method. Conventional two-point compliance C2P was calculated for comparison. A number of consecutive breathing cycles were pooled to reduce noise in the respiratory signals. Crs-volume curves produced with different methods converged when the number of pooling cycles increased (n ≥ 7). The mean volume-dependent Crs of 20 breaths was highly correlated with mean C2P (C2P,mean = 0.945 × Crs,mean − 0.053, r2 = 0.968, p < 0.0001). The Bland–Altman analysis indicated that C2P,mean was lower than Crs,mean (−2.4 ± 6.4 ml cm−1 H2O, mean bias ± 2 SD), but not significant according to the paired t-test (p > 0.05). Methods for analyzing dynamic respiratory mechanics are sensitive to noise and will converge to a unique solution when the number of pooled cycles increases. Under steady-state conditions, assessment of the volume-dependent Crs in ALI/ARDS patients can be validated by pooling respiratory data of consecutive breaths regardless of which method is applied. Confidence in dynamic Crs determination may be increased with the proposed pooling.

Dynamic respiratory mechanics and exertional dyspnoea in pulmonary arterial hypertension

Patients with pulmonary arterial hypertension (PAH) may exhibit reduced expiratory flows at low lung volumes, which could promote exercise-induced dynamic hyperinflation (DH). This study aimed to examine the impact of a potential exercise-related DH on the intensity of dyspnoea in patients with PAH undergoing symptom-limited incremental cardiopulmonary cycle exercise testing (CPET). 25 young (aged mean±sd 38±12 yrs) nonsmoking PAH patients with no evidence of spirometric obstruction and 10 age-matched nonsmoking healthy subjects performed CPET to the limit of tolerance. Ventilatory pattern, operating lung volumes (derived from inspiratory capacity (IC) measurements) and dyspnoea intensity (Borg scale) were assessed throughout CPET. IC decreased (i.e. DH) progressively throughout CPET in PAH patients (average 0.15 L), whereas it increased in all the healthy subjects (0.45 L). Among PAH patients, 15 (60%) exhibited a decrease in IC throughout exercise (average 0.50 L), whereas in the remaining 10 (40%) patients IC increased (average 0.36 L). Dyspnoea intensity and ventilation were greater in PAH patients than in controls at any stage of CPET, whereas inspiratory reserve volume was lower. We conclude that DH-induced mechanical constraints and excessive ventilatory demand occurred in these young nonsmoking PAH patients with no spirometric obstruction and was associated with exertional dyspnoea.

Lung Physiology and Obesity: Anesthetic Implications for Thoracic Procedures

Obesity is a worldwide health problem affecting 34% of the American population. As a result, more patients requiring anesthesia for thoracic surgery will be overweight or obese. Changes in static and dynamic respiratory mechanics, upper airway anatomy, as well as multiple preoperative comorbidities and altered drug metabolism, characterize obese patients and affect the anesthetic plan at multiple levels. During the preoperative evaluation, patients should be assessed to identify who is at risk for difficult ventilation and intubation, and postoperative complications. The analgesia plan should be executed starting in the preoperative area, to increase the success of extubation at the end of the case and prevent reintubation. Intraoperative ventilatory settings should be customized to the changes in respiratory mechanics for the specific patient and procedure, to minimize the risk of lung damage. Several non invasive ventilatory modalities are available to increase the success rate of extubation at the end of the case and to prevent reintubation. The goal of this review is to evaluate the physiological and anatomical changes associated with obesity and how they affect the multiple components of the anesthetic management for thoracic procedures.

Respiratory Consequences of Mild-to-Moderate Obesity: Impact on Exercise Performance in Health and in Chronic Obstructive Pulmonary Disease.

In many parts of the world, the prevalence of obesity is increasing at an alarming rate. The association between obesity, multiple comorbidities, and increased mortality is now firmly established in many epidemiological studies. However, the link between obesity and exercise intolerance is less well studied and is the focus of this paper. Although exercise limitation is likely to be multifactorial in obesity, it is widely believed that the respiratory mechanical constraints and the attendant dyspnea are important contributors. In this paper, we examined the evidence that critical ventilatory constraint is a proximate source of exercise limitation in individuals with mild-to-moderate obesity. We first reviewed existing information on exercise performance, including ventilatory and perceptual response patterns, in obese individuals who are otherwise healthy. We then considered the impact of obesity in patients with preexisting respiratory mechanical abnormalities due to chronic obstructive pulmonary disease (COPD), with particular reference to the effect on dyspnea and exercise performance. Our main conclusion, based on the existing and rather sparse literature on the subject, is that abnormalities of dynamic respiratory mechanics are not likely to be the dominant source of dyspnea and exercise intolerance in otherwise healthy individuals or in patients with COPD with mild-to-moderate obesity.