Negative Expiratory Pressure Technique Research Articles

Phenotyping OSAH patients during wakefulness.

Although currently there are simplified methods to measure the pathophysiological traits that stimulate the occurrence and maintenance of obstructive sleep apnea-hypopnea (OSAH), they remain difficult to implement in routine practice. This pilot study aimed to find a simpler daytime approach to obtain a meaningful, similar pathophysiological phenotypic profile in patients with OSAH. After obtaining diagnostic polygraphy from a group of consecutive patients with OSAH, we performed the dial-down CPAP technique during nocturnal polysomnography and used it as reference method. This allowed assessment of upper airway collapsibility, loop gain (LG), arousal threshold (AT), and upper airway muscle gain (UAG). We compared these results with a daytime protocol based on negative expiratory pressure (NEP) technique for evaluating upper airway collapsibility and UAG, on maximal voluntary apnea for LG, and on clinical predictors for AT. Of 15 patients studied, 13 patients with OSAH accurately completed the two procedures. There were strong (all r2 > 0.75) and significant (all p < 0.001) correlations for each phenotypic trait between the measurements obtained through the reference method and those achieved during wakefulness. It is possible to phenotype patients withOSAH from a pathophysiological point of view while they are awake. Using this approach, cutoff values corresponding to those usually adopted using the reference method can be identified to detect abnormal traits, achieving profiles similar to those obtained through the dial-down CPAP technique.

Non-interventional monitoring of expiratory flow limitation during experimental mechanical ventilation.

BackgroundExpiratory flow limitation (EFL) is common among patients in the intensive care unit under mechanical ventilation (MV) and may have significant clinical consequences. In the present study, we examine the possibility of non-interventional detection of EFL during experimental MV.MethodsEight artificially ventilated New Zealand rabbits were included in the experiments. EFL was induced during MV by application of negative expiratory pressure (−5, −8 and −10 hPa) and detected by the negative expiratory pressure technique. Airway pressure (Paw) and gas flow (V′) were digitally recorded and processed off-line for the evaluation of respiratory mechanics. The method is based on the computation and monitoring of instantaneous respiratory resistance Rrs(t). The resistive pressure (Paw,res(t)) is calculated by subtracting from Paw its elastic component and the end-expiratory pressure, as assessed by linear regression. Then, Rrs(t) is computed as the instant ratio Paw,res(t)/V′(t).ResultsTwo completely different patterns of expiratory Rrs(t) separate the cases with EFL from those without EFL. Small and random fluctuations are noticed when EFL is absent, whereas the onset of EFL is accompanied by an abrupt and continuous rise in Rrs(t), towards the end of expiration. Thus, EFL is not only detected but may also be quantified from the volume still to be expired at the time EFL occurs.ConclusionThe proposed technique is a simple, accurate and non-interventional tool for EFL monitoring during MV.

Study on negative expiratory pressure technique in children with bronchial asthma

To investigate the clinical significance of children bronchial asthma detection by using negative expiratory pressure (NEP) technique. The children with bronchial asthma admitted to Department of Pediatrics of Zhejiang Provincial Integrated Traditional Chinese and Western Medicine Hospital from March 2016 to March 2018 were enrolled. They were divided into mild group (0-4 scores) and severe group (5-12 scores) according to asthma clinical scoring criteria. The children undergoing physical examination at the same period were served as healthy control group. NEP technique and tidal volume (VT) were detected by the pulmonary function instrument. Respiratory flow-volume curves (F-V curves) without NEP were compared with tidal F-V curves after NEP application to assess expiratory flow limitation (EFL). EFL index was calculated according to the percentage of expiratory VT after EFL and expiratory VT when NEP was not used. Pearson correlation method was used to analyze the relationship between EFL index and severity of bronchial asthma. Receiver operating characteristic (ROC) curve was plotted to analyze the value of EFL index in evaluating the severity of bronchial asthma in children. A total of 86 children with bronchial asthma were enrolled in the study, and 84 patients completed the test and 2 children withdrew due to other diseases. Finally, 84 patients were included in the final analysis, including 41 mild and 43 severe children. Forty-two healthy children in the same period were served as healthy control group. There was no significant difference in gender or age among the groups, and no adverse reactions occurred during the test. The EFL index of children with bronchial asthma was significantly higher than that of the healthy control group, and it was increased with the severity of the disease [mild group compared with healthy control group: (30.60±6.03)% vs. (6.64±2.37)%, severe group compared with healthy control group: (33.70±5.41)% vs. (6.64±2.37)%, both P < 0.05]. There was no significant difference in respiratory rate (RR) or VT between mild group or severe group and healthy control group [RR (times/min): 31.45±4.18, 32.81±4.07 vs. 31.97±4.01, VT (mL/kg): 6.29±1.14, 5.96±0.90 vs. 6.30±1.20, all P > 0.05]. It was shown by the correlation analysis that EFL index was positively correlated with the severity of asthma (r = 0.836, P = 0.000). It was shown by ROC curve analysis that the area under ROC curve (AUC) of EFL index for predicting the severity of bronchial asthma in children was 0.801 [95% confidence interval (95%CI) = 0.725-0.878]; when the best cut-off value of EFL index was 29.21%, the sensitivity was 85.7%, the specificity was 69.2%, the positive predictive value was 75.1%, and the negative predictive value was 60.2%. The EFL index measured by NEP technology was closely related to the severity of bronchial asthma. The higher the EFL index, the more serious of the condition. The severity of bronchial asthma could be early judged by EFL index, which provided a basis for the evaluation and treatment of bronchial asthma.

Negative Expiratory Pressure (NEP) Technique and Anthropometric Derived Indices as Surrogate Markers for Predicting Obstructive Sleep Apnea Syndrome (OSAS)

Introduction: We wondered whether anthropometric, lung function, arterial blood gas (ABG), tidal volume (VT), and Negative Expiratory Pressure (NEP) Technique data could be utilized alone or collectively for predicting the presence of obstructive sleep apnea syndrome (OSAS). Methods: Thirty-eight consecutive subjects (29% females) were referred for symptoms suggestive of OSAS. They had no respiratory or any other system failure. Anthropometric data, VT and lung function measurements were obtained. All subjects underwent overnight polysomnogaphy (PSG). They were also subjected to the NEP technique (-5 cm H2O) in seated and supine positions, specifically investigating the usefulness of known NEP-acquired indices (EFL %, ΔV %, V, NEP 0.5, V0.2%). PSG classified subjects according to Apnea/Hypopnea Index (AHI). Results: Eleven patients had AHI&lt;15, whilst 27 had AHI≥15. Only ΔV % and V,NEP0.5 correlated with AHI in both positions. A Multiple Linear Regression (MLR) model using V,NEP 0.5 in the seated position (V,NEP 0.5se), Neck Circumference (NC), arterial oxygen tension (Pa02), Expiratory Reserve Volume (ERV,% pred), improves AHI prediction (R2 adj =0,814). Conclusions: V,NEP0.5, could identify moderate and severe OSAS in stable patients. MLR models using additional parameters substantially improve AHI prediction.

Effect of pulmonary rehabilitation on tidal expiratory flow limitation at rest and during exercise in COPD patients

We hypothesized that severe COPD patients who present with the disadvantageous phenomenon of Expiratory Flow Limitation (EFL) may benefit as COPD patients without EFL do after implementation of a Pulmonary Rehabilitation (PR) program. Forty-two stable COPD patients were studied at rest and during exercise. EFL and dynamic hyperinflation (DH) were documented using the negative expiratory pressure (NEP) technique and inspiratory capacity (IC) maneuvers, respectively. Patient centered outcomes were evaluated by the Saint-George’s Respiratory Questionnaire (SGRQ) and the mMRC dyspnea scale. Before PR, 16 patients presented with EFL at rest and/or during exercise. After PR, EFL was abolished in 15 out of those 16 EFL patients who exhibited a significant increase in IC values. These were mainly accomplished through a modification of the breathing pattern. In the 26 NFL patients no increase was noted in their IC or a modification of their breathing pattern. However, both NFL and EFL COPD patients improved exercise capacity and patients centered outcomes undergoing the same PR program.

Association of the forced oscillation technique with negative expiratory pressure in COPD

Expiratory flow limitation (EFL) during tidal breathing is common in patients with severe COPD, and a major determinant of dynamic hyperinflation and exercise limitation. The negative expiratory pressure (NEP) technique has been the gold standard to detect EFL, while the forced oscillation technique (FOT) has also been reported to detect it. However, the association of FOT with NEP is not fully understood. We assessed whether broadband frequency FOT would predict the presence of EFL measured by NEP. FOT, NEP, and spirometry were performed in 51 patients with COPD. The extent of emphysema was measured by high-resolution computed tomography and scored. Fifteen patients were classified into the EFL-positive group and 36 into the EFL-negative group. In multivariate logistic regression analysis, EFL was independently predicted by emphysema score, forced vital capacity, and whole-breath respiratory system reactance at 5Hz (X5). The receiver operator characteristic curve analysis revealed that inspiratory X5 best predicted EFL-positivity. X5-related forced oscillatory parameters are useful for detecting EFL in the management of COPD.

Expiratory flow limitation detected by negative expiratory pressure in children with asthma

Objective The purpose of this study was to evaluate the feasibility of expiratory flow limitation(EFL) detected by negative(NEP) and the correlation between EFL and routine lung function measurements(Forced expiratory volume in first second,FEV1),EFL and MRC dyspnea scale,in patients with stable and acute asthma,to find a simple,reliable and objective method for the diagnosis,differential diagnosis,the severity of disease and evaluation of severity and efficacy of treatment for asthma,and a objective method reflecting the severity of dyspnea.Methods Sixty-four children enrolled in No.306 Hospital of PLA from Jun.to Dec.in 2012 were included in this study.The severity of dyspnea was rated according to the dyspnea scale proposed by the Medical Research Council(MRC).Then routine pulmonary ventilation function tests and NEP technique were performed respectively.Result (1) All asthmatic patients tolerated NEP well.(2) Pulmonary ventilation function tests:The mean FEV1 in 64 was 71.33 ± 13.92％ pred.(3) MRC dyspnea scale:MRC dyspnea scale was 2 in 10,1 in 54 of 64 children with stable asthma.The Spearman' s correlation coefficient of MRC dyspnea scale with FEV1 was-0.635(P ＜0.05).(4)EFL detected by NEP:There were no EFL in 46 children with asthma both in seated and supine positions.There were EFL in 8 children both in seated and supine positions and in 10 only in supine position..The Spearman's correlation coefficient of three-point EFL score with FEV1 and MRC dyspnea scale was-0.607 and 0.964(P ＜ 0.05) respectively.The Spearman's correlation coefficient of five-point EFL score with FEV1 and MRC dyspnea scale was-0.626 and 0.966 (P ＜ 0.05)respectively.Conclusion (1) NEP technique can be used in children with asthma.(2) There was a significant correlation between EFL detected by NEP technique and FEV1.(3) There is a stronger correlation between EFL and MRC dyspnea scale than that between FEV1 and MRC dyspnea scale. Key words: Asthma; Children; Negative expiratory pressure(NEP) ; Expiratory flow limitation(EFL) ; Forced expiratory volume in first second

Divers’ neurobehavioral performance under 4.7 MPa: A real-time monitoring

Patients with COPD exhibit increased inspiratory work and dyspnea due to dynamic hyperinflation caused by expiratory flow limitation. Helium-oxygen mixtures (ie, heliox) have been used in treating these patients on the assumption that, by lowering airway resistance, they might be beneficial.In 22 patients with COPD, the presence of expiratory flow limitation was assessed with patients in the sitting and supine positions using the negative expiratory pressure technique, and the effects of heliox (80% He, 20% O2) on breathing pattern, expiratory flow limitation, and dynamic hyperinflation, evaluated from the change in inspiratory capacity (IC), were measured at rest and were compared with those due to inhaled salbutamol.During air breathing, 13 patients experienced flow limitation while in the sitting position and 18 experienced flow limitation while in the supine position. Neither heliox nor salbutamol therapy changed the breathing pattern in any of the patients, regardless of posture and the presence or absence of expiratory flow limitation. However, in both positions IC increased significantly in most flow-limited patients after bronchodilator administration, but not after heliox administration.Since heliox had no effect on dynamic hyperinflation, the use of this gas mixture, which is costly and cumbersome, does not appear to be beneficial in stable patients with COPD breathing at rest.

Dynamic pulmonary hyperinflation occurs without expiratory flow limitation in chronic heart failure during exercise

To assess the occurrence of tidal expiratory flow limitation (EFL) and/or dynamic pulmonary hyperinflation (DH) in chronic heart failure (CHF) during exercise 15 patients with stable systolic CHF, aged 69±6yr, underwent pulmonary function testing and incremental cardio-pulmonary exercise testing. They subsequently performed constant load exercise testing at 30, 60 and 90% of respective maximum workload. At each step the presence of EFL, by negative expiratory pressure technique, and changes in inspiratory capacity (IC) were assessed. Ejection fraction amounted to 36±6% and V˙O2, peak (77±19% pred.) was reduced. EFL was absent at any step during constant load exercise. In 6 patients IC decreased more than 10% pred. at highest step. Only in these patients TLC, FRC, RV FEF25–75% and DLCO were decreased at rest. V˙O2, peak correlated with DLCO, TLC and IC at rest and with IC (r2=0.59; p<0.001) and decrease in IC (r2=0.44; p<0.001) at 90% of maximum workload. During exercise CHF patients do not exhibit EFL, but some of them develop DH that is associated with lower V˙O2, peak.

Expiratory Flow Limitation in Obstructive Sleep Apnea and COPD: A Quantitative Method to Detect Pattern Differences Using the Negative Expiratory Pressure Technique.

Background:Expiratory flow limitation (EFL), determined by the negative expiratory pressure (NEP) technique, can exhibit overlapping patterns in COPD, obstructive sleep apnea (OSA) and non-OSA obesity. We assessed the ability of a quantitative method to assess EFL to discriminate COPD from obese and OSA patients during NEP (-2 to -3 cm H2O) testing.Methods:EFL was quantified by measuring the area under the preceding control tidal breath (Vt) subtended by the NEP curve (%AUC). To quantify mean lost flow, the ratio of %AUC to percentage of control Vt over which EFL occurred (%EFL) (= %AUC/%EFL) was computed. Percent EFL, %AUC, and %AUC/%EFL was compared in 42 patients with COPD, 28 obese subjects without OSA, 50 with OSA (26 mild-moderate, 24 severe) and 19 control subjects, in seated and supine postures.Results:All patients exhibited %EFL values significantly higher than control subjects, corrected for age and gender (ANOVA). All but the COPD group exhibited higher %EFL while supine, but not %AUC or %AUC/%EFL. Amongst seated subjects, %EFL was highest in COPD, and amongst supine groups, it was greatest in OSA and COPD. %AUC/%EFL was significantly higher in mild-moderate OSA than in COPD only while seated. %AUC or %AUC/%EFL did not discriminate amongst other cohorts in either posture.Conclusions:Computation of %EFL helps distinguish EFL in COPD, obese and OSA patients from those of control subjects. Computation of %AUC and %AUC/%EFL is useful in determining the magnitude of extrathoracic FL in individuals with obesity and OSA, but does not distinguish between cohorts.

Manual compression of the abdomen to assess expiratory flow limitation during mechanical ventilation

PurposeThe aim of this study was to evaluate the manual compression of the abdomen (MCA) during expiration as a simple bedside method to detect expiratory flow limitation (EFL) during daily clinical practice of mechanical ventilation (MV). MethodsWe studied 44 semirecumbent intubated and sedated critically ill patients. Flow-volume loops obtained during MCA were superimposed upon the preceding breaths and recorded with the ventilator. Expiratory flow limitation was expressed as percentage of expiratory tidal volume without any increase in flow during MCA (MCA [%VT]). In the first 13 patients, MCA was validated by comparison with the negative expiratory pressure (NEP) technique. Esophageal pressure changes during MCA and intrinsic positive end-expiratory pressure were also recorded in all the patients. ResultsManual compression of the abdomen and NEP agreed in all cases in detecting EFL with a bias of −0.16%. Percentage of expiratory tidal volume without any increase in flow during MCA is highly correlated with percentage of expiratory tidal volume without any increase in flow during NEP (n = 13, P < .0001, r2 = 0.99) and intrinsic positive end-expiratory pressure (n = 44, P < .001, r2 = 0.78), with a good repeatability (n = 44; within-subject SD, 5.7%) and reproducibility (n = 13; within-subject SD, 2.41%). Two third of the patients were flow limited, among whom one third had no previously known respiratory disease. ConclusionsManual compression of the abdomen provides a simple, rapid, and safe bedside reliable maneuver to detect and quantify EFL during mechanical ventilation.

Upper Airway Collapsibility During Wakefulness in Children with Sleep Disordered Breathing, as Determined by the Negative Expiratory Pressure Technique

Upper airway (UA) collapsibility is a major factor in the pathophysiology of sleep disordered breathing (SDB). We hypothesized that the negative expiratory pressure (NEP) technique could distinguish between normal children and children with SDB even during wakefulness. During wakefulness, NEP of -5 and -10 cm H(2)O was applied during expiration in seated and supine positions. UA muscle activity (EMG) was measured using intra-oral electrodes. Sleep laboratory. Twenty children with snoring, 20 with obstructive sleep apnea syndrome (OSAS), and 20 controls. The ratio of the area under the expiratory flow-volume curve during NEP compared to tidal breathing (RatioNEP) was calculated. Similarly, EMG area under the curve during NEP as a ratio of baseline was measured (RatioEMG). There were significant differences in RatioNEP between controls and snorers and controls and OSAS, at both pressures, in both the seated and supine positions; P < 0.0001 for all (e.g., RatioNEP at -5 cm H(2)O, seated: 1.8 ± 0.5, 2.1 ± 0.4, and 3.0 ± 0.6 for OSAS, snorers, and controls, respectively). However, no significant differences were found between snorers and OSAS. For RatioEMG, no significant differences were found between groups. RatioNEP distinguishes between normal children and children with SDB, be it snoring or OSAS, indicating that these children have a more collapsible UA even during wakefulness. However, it does not differentiate between snorers and OSAS, highlighting the important role of UA muscle activity during sleep. NEP technique does not elicit a different UA muscle activity response between controls and children with SDB.

Blunted respiratory-related evoked potential in awake obstructive sleep apnoea subjects: A NEP technique study

Objective Respiratory-related evoked potentials (RREP) elicited by transmural pressure in obstructive sleep apnoea (OSA) subjects have reported conflicting data. Different features of pressure stimuli and/or in the timing of stimuli application seem to account for these contradictory results. The negative expiratory pressure (NEP) technique, highly reproducible in terms of rise time and pressure values, allows to minimize the methodological confounding factors. We determined whether the afferent activity from the upper airway (UA) is altered in OSA subjects. Methods RREP potentials were examined in 10 OSA and in 12 non-apnoeic awake subjects by means of the NEP technique. Results All controls showed a cortical response to all pressure stimuli. All OSA subjects showed responses to −5 and −10 cmH 2O whereas six of them showed no responses to −1 cmH 2O. The amplitude of the P22, N45 and P85 components of the RREP was significantly reduced in OSA with respect to the controls in response to both the −5 and −10 cmH 2O stimuli. We found no significant differences in latencies. Conclusions Awake OSA subjects had a raised threshold to pressure stimuli and blunted respiratory-related evoked potentials. Significance These data indicate a deficit in afferent activity in the UA.

Reproducibility of the negative expiratory pressure technique in detecting expiratory flow limitation on chronic obstructive pulmonary disease patients

To evaluate the reproducibility of Negative Expiratory Pressure (NEP) technique in detecting expiratory flow limitation (EFL) on chronic obstructive pulmonary disease (COPD) patients. EFL was evaluated with NEP technique in 72 subjects having stable COPD on two occasions. Agreement between testing occasions was assessed with the κ statistic for the 3-point and 5-point EFL scores, and with paired t-test for FL index. On the first testing occasion, 18 subjects had no EFL, 18 subjects had EFL in the supine position, and 36 subjects in the sitting and the supine position. Using the 3-point score, agreement was present in 58 of the 72 subjects at time 2 (κ = 0.69, P<0.001), indicating a substantial agreement was found. Using the 5-point score, agreement was seen in 52 of the 72 subjects (κ = 0.65, P<0.001), also indicating a substantial agreement. The difference of FL index between the first and the second occasion was significant in both the sitting (P<0.05) and supine (P<0.05) positions. Both 3-point and 5-point scores provided a reproducible assessment of EFL on COPD patients but the FL index seemed less reproducible. More research were needed before NEP technique was promoted to be used clinically.

Effect of Preceding Inspiratory Speed and End-Inspiratory Pause on Forced Expiratory Manoeuvre in Healthy Subjects and Chronic Obstructive Pulmonary Disease Patients

Background: Lower peak expiratory flow (PEF) and forced expiratory volume in 1 s (FEV₁) have been consistently found after slow inspiration with end-inspiratory pause (EIP). Objectives: It was the aim of this study to establish the respective influence of the speed of preceding inspiration (SPI) and EIP on the parameters obtained from the following expiratory forced vital capacity (FVC) manoeuvre. Methods: In 8 healthy subjects and 12 patients with chronic obstructive pulmonary disease (COPD), a number of inspirations with different SPI and EIP were performed. In the subsequent FVC manoeuvre, maximal expiratory flows, including PEF, and maximal expired volumes at different times, including FEV₁, were measured. For each FVC manoeuvre, peak expiratory time, expired volume at PEF (as % of FVC), flow limitation by the negative expiratory pressure technique and FVC were checked to be sure of achieving a similar expiratory effort and starting inflation lung volume. Results: The highest values of PEF and FEV₁ were found in normal subjects and COPD patients after fastest SPI without EIP (p < 0.001). In normal subjects, no significant PEF and FEV₁ changes during FVC manoeuvre were observed with different SPI, in the absence of EIP. In contrast, inspirations with slower SPI (inspiratory time >2 s) without EIP were followed by lower PEF in COPD patients (p < 0.05). As compared with inspirations without EIP, those with a presence of EIP were invariably followed by lower PEF and FEV₁, both in normal subjects and in COPD patients (p < 0.05). Conclusions: The effect of SPI on subsequent PEF and FEV₁ is irrelevant in healthy subjects as well as in COPD patients, unless SPI is too slow (inspiratory time >2 s), while any EIP decreases these indices in all individuals.

Negative Expiratory Pressure (NEP) Parameters Can Predict Obstructive Sleep Apnea Syndrome in Snoring Patients

The objective of this study was to assess whether parameters of the negative expiratory pressure (NEP) technique are able to detect obstructive sleep apnea syndrome (OSAS) in snoring patients. A cross-sectional study included 42 OSAS patients diagnosed by polysomnography (PSG), 34 simple snorers, and 32 healthy subjects. Lung function was measured by using a plethysmograph and the NEP technique was performed with the patient in the seated and supine positions in a random order. The depression was fixed to 5 cmH(2)O. All patients had normal forced expiratory flow/volume loops. Apneic patients had lower Dflow in both positions with a number of oscillations on the expiratory curve obtained with NEP and an expiratory flow limitation (EFL) in the supine position higher than that of other groups (p < 0.05). Changing from the sitting to the supine position raised the EFL of the three groups, with a significant decrease in Dflow and an increase in the number of oscillations in snoring and OSAS patients (p < 0.05). The analysis of variance showed that only the number of oscillations was significantly different between apneic and snoring patients. NEP constitutes a simple and useful tool for the screening OSAS by EFL, especially the number of oscillations obtained with NEP.

Reproducibility of the Negative Expiratory Pressure Technique in COPD

Tidal expiratory flow limitation (EFL) contributes to chronic dyspnea and exercise intolerance in COPD patients. It can be assessed with the negative expiratory pressure (NEP) technique and is expressed as either the percentage of the tidal volume over which EFL occurs (EFL%Vt) or according to more detailed three-point or five-point scoring systems. The aim of this study was to evaluate the reproducibility of the NEP technique in COPD patients. Tidal EFL was evaluated with NEP in 18 subjects with stable COPD (FEV(1) range, 18 to 75% predicted) on two occasions (mean retest interval, 8.2 days) by the same rater. Agreement between testing occasions was assessed with the kappa statistic for the 3-point and 5-point EFL scores, and with the coefficient of repeatability for EFL%Vt. On the first testing occasion, nine subjects had no EFL, four subjects had EFL in the supine position, and five subjects had EFL in the sitting and the supine position. Using the 3-point score, agreement was present in 14 of 18 subjects at time 2 (kappa = 0.66), indicating substantial agreement. Using the 5-point score, agreement was seen in 13 of 18 subjects (kappa = 0.61), also indicating substantial agreement. The reproducibility of EFL%Vt measurements was lower than that required to reliably detect clinical change in both the sitting and supine positions (coefficient of repeatability, 37% and 58%, respectively). The 3-point and 5-point scores provide a reproducible assessment of EFL in COPD patients. The classification of EFL as a percentage of tidal volume is less reproducible, and large changes are required to be confident that real clinical change has occurred.

Expiratory Flow Limitation in Patients with Pleural Effusion

Background: Expiratory flow limitation (EFL) is one of the main mechanisms contributing to dyspnea in patients with chronic obstructive pulmonary disease but has not been explored in patients with pleural effusion. Objectives: It was the aim of this study to determine whether patients with pleural effusion exhibit EFL and to investigate the effect of therapeutic thoracentesis on EFL. Patients and Methods: The study was performed on 21 patients with pleural effusion who were subjected to thoracentesis and measurement of pleural pressure (PP). Spirometry and estimation of flow limitation by the negative expiratory pressure technique were performed before and after thoracentesis. Results: Statistically significant differences were observed in all spirometric parameters. No correlation between the increase in lung volumes and flows and any of the aspirated fluid parameters was observed. Before thoracentesis, 14 out of 21 patients were flow limited, compared with 7 patients after thoracentesis (χ² = 6.151, p = 0.013). Mean values of flow limitation before and after thoracentesis differed significantly. The decrease in flow limitation did not correlate with the increase in the spirometric parameters, the aspirated fluid volume or PP decrease. Conclusions: In the majority of patients with pleural effusion, flow limitation improves after thoracentesis. Flow limitation may be a contributing factor to the sensation of dyspnea in these patients.

A new method to detect expiratory flow limitation in chronic obstructive pulmonary disease patients

To explore the significance of negative expiratory pressure (NEP) technique in detecting expiratory flow limitation (EFL) in the chronic obstructive pulmonary disease (COPD) patients. NEP technique was performed on 54 COPD patients, 45 males and 9 females, aged 69+/-10 (Group A), 8 COPD patients who failed to receive the routine pulmonary function tests (Group B), and 10 normal controls. The subjects in 3 groups, matched in age, height, body weight, and educational level, underwent 5-point EFL scoring, Medical Research Council (MRC) dyspnea scoring, 6-min walk distance scoring, and routine pulmonary ventilation function test. EFL was detected in 41 of the 54 COPD patients in Group A. NEP test was successfully performed on the 8 patients of Group B, and 7 of them were found as with EFL. The level of forced expired volume in one second percentage (FEV1%) of the patients with the EFL scores of 2, 3, and 4 were 55.71%+/-11.77%, 41.21%+/-13.69%, and 29.84%+/-11.65% respectively, all significantly lower that of the 0-score group (83.76%+/-16.44%, all P<0.05). Multiple stepwise regression analysis showed that only 5-point EFL score, FEV1%, and 6-min walking distance were associated with MRC dyspnea score, and the 5-point EFL score showed the best associativity with dyspnea. As compared with FEV(1pred)%, 5-point EFL scoring is more reliable in evaluating the dyspnea of COPD patients, it is simple and doesn't't require any cooperation on the part of the patients. NEP technique can be applied in the COPD patients who fail to receive the routine pulmonary function tests.

Hyperinflation and its management in COPD

Chronic obstructive pulmonary disease (COPD) is characterized by poorly reversible airflow limitation. The pathological hallmarks of COPD are inflammation of the peripheral airways and destruction of lung parenchyma or emphysema. The functional consequences of these abnormalities are expiratory airflow limitation and dynamic hyperinflation, which then increase the elastic load of the respiratory system and decrease the performance of the respiratory muscles. These pathophysiologic features contribute significantly to the development of dyspnea, exercise intolerance and ventilatory failure. Several treatments may palliate flow limitation, including interventions that modify the respiratory pattern (deeper, slower) such as pursed lip breathing, exercise training, oxygen, and some drugs. Other therapies are aimed at its amelioration, such as bronchodilators, lung volume reduction surgery or breathing mixtures of helium and oxygen. Finally some interventions, such as inspiratory pressure support, alleviate the threshold load associated to flow limitation. The degree of flow limitation can be assessed by certain spirometry indexes, such as vital capacity and inspiratory capacity, or by other more complexes indexes such as residual volume/total lung capacity or functional residual capacity/total lung capacity. Two of the best methods to measure flow limitation are to superimpose a flow-volume loop of a tidal breath within a maximum flow-volume curve, or to use negative expiratory pressure technique. Likely this method is more accurate and can be used during spontaneous breathing. A definitive definition of dynamic hyperinflation is lacking in the literature, but serial measurements of inspiratory capacity during exercise will document the trend of end-expiratory lung volume and allow establishing relationships with other measurements such as dyspnea, respiratory pattern, exercise tolerance, and gas exchange.