Application Of Negative Expiratory Pressure Research Articles

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.

Upper Airway Collapsibility Assessed by Negative Expiratory Pressure while Awake is Associated with Upper Airway Anatomy.

There is a growing interest to develop a simple method to characterize the mechanisms leading to upper airway collapse in order to guide treatment options in patients with obstructive sleep apnea (OSA). Critical closing pressure (Pcrit) during sleep is able to predict the anatomical component of OSA. However, Pcrit is a laborious method that is only used for research purposes. The application of negative expiratory pressure (NEP) is a simple method to assess upper airway collapsibility that can be easily performed during wakefulness. We hypothesized that NEP will be, similarly to Pcrit, associated with upper airway anatomy assessed by computed tomography (CT) scan. Patients under investigation for OSA underwent polysomnography, CT of the upper airway, NEP while awake, and Pcrit during sleep. NEP was performed with -5 cm H2O in supine position using a nasal mask. Pcrit was measured during sleep induced by low doses of midazolam. Twenty-eight male subjects were studied (age 45 ± 13 y, body mass index 29.4 ± 4.9 kg/m2, apnea-hypopnea index (AHI) 30 ± 26, range 2 to 86 events/h). NEP and Pcrit were similarly associated with tongue area (r = 0.646 and r = 0.585), tongue volume (r = 0.565 and r = 0.613) and pharyngeal length (r = 0.580 and r = 0.611), respectively (p < 0.05 for all comparisons). NEP and Pcrit were also significantly correlated with AHI (r = 0.490 and r = 0.531). NEP and Pcrit were significantly higher in patients with severe OSA than the remaining population. NEP is a simple and promising method that is associated with the anatomical component of upper airway collapsibility. NEP may be valuable to select patients for noncontinuous positive airway pressure alternative therapies for OSA.

Biphasic intra-thoracic pressure regulation augments cardiac index during porcine peritonitis: a feasibility study

Preservation of cardiac output (CO) and pulmonary artery pressure (PAP) is vital to maintaining tissue oxygenation in sepsis. This feasibility study tested the hypothesis that therapeutic intra-thoracic pressure regulation (tIPR), delivered with a novel device, was designed to non-invasively enhance venous return by creating sub-atmospheric intra-thoracic pressure during the expiratory phase of mechanical ventilation, improves CO without fluid resuscitation in a porcine E. coli peritonitis model of sepsis. Seven pigs were intubated, anaesthetized and instrumented with a Swan-Ganz and femoral artery catheter. After a 30 min basal period, a fibrin clot containing 4–5 × 109 cfu kg−1 E. coli O111.B4 was implanted in the peritoneum. One hour after clot implantation, tIPR was utilized for 30 min and then removed from the ventilator circuit for 30 min. This tIPR cycle was repeated 4-times. Changes in haemodynamic parameters were calculated by comparing pre-tIPR values to peak values during tIPR administration. Following peritonitis, tIPR significantly increased the peak cardiac index (mean ± SEM) (14.8 ± 2.6 vs 7.9 ± 2.3 ml kg−1) and mean arterial pressure (10.2 ± 1.5 vs 4.9 ± 1.1 mmHg) and simultaneously decreased PAP (−7.7 ± 1.5 vs −2.7 ± 0.8 mmHg). These results support the feasibility of the concept that therapeutic application of negative expiratory pressure may provide a non-invasive and complementary approach to increase cardiac output and organ perfusion in the setting of septic shock.

Observational study on efficacy of negative expiratory pressure test proposed as screening for obstructive sleep apnea syndrome among commercial interstate bus drivers - protocol study

BackgroundObstructive sleep apnea (OSA) is a respiratory disease characterized by the collapse of the extrathoracic airway and has important social implications related to accidents and cardiovascular risk. The main objective of the present study was to investigate whether the drop in expiratory flow and the volume expired in 0.2 s during the application of negative expiratory pressure (NEP) are associated with the presence and severity of OSA in a population of professional interstate bus drivers who travel medium and long distances.Methods/DesignAn observational, analytic study will be carried out involving adult male subjects of an interstate bus company. Those who agree to participate will undergo a detailed patient history, physical examination involving determination of blood pressure, anthropometric data, circumference measurements (hips, waist and neck), tonsils and Mallampati index. Moreover, specific questionnaires addressing sleep apnea and excessive daytime sleepiness will be administered. Data acquisition will be completely anonymous. Following the medical examination, the participants will perform a spirometry, NEP test and standard overnight polysomnography. The NEP test is performed through the administration of negative pressure at the mouth during expiration. This is a practical test performed while awake and requires little cooperation from the subject. In the absence of expiratory flow limitation, the increase in the pressure gradient between the alveoli and open upper airway caused by NEP results in an increase in expiratory flow.DiscussionDespite the abundance of scientific evidence, OSA is still underdiagnosed in the general population. In addition, diagnostic procedures are expensive, and predictive criteria are still unsatisfactory. Because increased upper airway collapsibility is one of the main determinants of OSA, the response to the application of NEP could be a predictor of this disorder. With the enrollment of this study protocol, the expectation is to encounter predictive NEP values for different degrees of OSA in order to contribute toward an early diagnosis of this condition and reduce its impact and complications among commercial interstate bus drivers.Trial registrationRegistro Brasileiro de Ensaios Clinicos (local acronym RBEC) [Internet]: Rio de Janeiro (RJ): Instituto de Informaçao Cientifica e Tecnologica em Saude (Brazil); 2010 - Identifier RBR-7dq5xx. Cross-sectional study on efficacy of negative expiratory pressure test proposed as screening for obstructive sleep apnea syndrome among commercial interstate bus drivers; 2011 May 31 [7 pages]. Available from http://www.ensaiosclinicos.gov.br/rg/RBR-7dq5xx/.

Teste de pressão negativa expiratória: um novo método simples para identificar pacientes com risco para apneia obstrutiva do sono

The objective of this article was to describe a new method for assessing expiratory flow limitation during spontaneous breathing, using the negative expiratory pressure test to identify patients at risk for obstructive sleep apnea. Upper airway collapsibility is evaluated by measuring decreases in flow and in expired volume in the first 0.2 seconds after negative expiratory pressure application at 10 cmH₂O. The negative expiratory pressure test is easily applied and could be adopted for the evaluation of expiratory flow limitation caused by upper airway obstruction in patients with obstructive sleep apnea.

Upper airway dynamics during negative expiratory pressure in apneic and non-apneic awake snorers

BackgroundThe ability of negative expiratory pressure (NEP) technique to differentiate between awake snorers with and without obstructive sleep apnea-hypopnea (OSAH) was investigated.MethodsForty-eight subjects with sleep disordered breathing (SDB) and 7 healthy subjects, as non-snorer controls, underwent the NEP application of -5 and -7 cmH2O in the seated and supine position during wakefulness, after performing a sleep study. The upper airway collapsibility was assessed by computing the volume exhaled during the first 0.5 sec. (V,NEP0.5) and 1 sec. (V,NEP1) following the NEP start.ResultsPatients with severe (AHI ≥ 30) (n = 19) and mild-to-moderate (AHI <30 and >5) (n = 15) OSAH had lower V,NEP0.5 (340 ± 88 ml) as compared to snorers (AHI ≤ 5) (n = 14) (427 ± 101 ml; p < 0.01) and controls (n = 7) (492 ± 69 ml; p < 0.001) in the supine position with NEP -5 cmH2O. Less significant differences among the different groups were observed for V,NEP0.5 in the seated position with NEP -5 cmH2O and in both positions with NEP -7 cmH2O (only OSAH patients vs controls, p < 0.001). Similar results were obtained for V,NEP1 in either position by using both NEP -5 cmH2O and -7 cmH2O. In spite of this, a substantial overlapping of V,NEP0.5 and V,NEP1 between snorers and OSAH patients did not allow to identify a reliable diagnostic cut-off level. An inverse correlation with AHI was found for V,NEP0.5 in the supine position with NEP -5 cmH2O (rs = -0.46, p < 0.05) in severe OSAH patients.ConclusionThe awake OSAH patients exhibit values of V,NEP0.5 and V,NEP1 lesser than those of awake snorers. The NEP technique, however, appears to have a limited usefulness as clinical tool for routine screening of the OSAH patients during wakefulness.

Expiratory muscles modulate negative expiratory pressure-induced flow during muscular exercise

The recruitment of expiratory muscles during exercise might be altered by the application of negative expiratory pressure (NEP) inducing a feature of expiratory flow limitation (EFL) called muscle EFL. To check this hypothesis EFL and expiratory muscle EMG (ExpEMG) were measured at rest and during exercise in eight healthy subjects. Six subjects performed isocapnic hyperventilation. At 5hPa NEP, 5/8 subjects had EFL during exercise. This limitation disappeared when NEP value was increased and did not appear during isocapnic hyperventilation. During exercise, in limited subjects, ExpEMG was significantly reduced during expiration with NEP as compared to control. Gastric pressure measured in a limited subject increased during expiration but less with NEP than without it, while this pressure measured in another, non-limited, subject decreased. An inhibitory reflex due to negative pressure could be responsible for muscle EFL by reducing expiratory muscle activity. The response to NEP during exercise should be interpreted with caution.

A New Method of Negative Expiratory Pressure Test Analysis Detecting Upper Airway Flow Limitation To Reveal Obstructive Sleep Apnea

Expiratory flow limitation (EFL) by negative expiratory pressure (NEP) testing, quantified as the expiratory flow-limited part of the flow-volume curve, may be influenced by airway obstruction of intrathoracic and extrathoracic origins. NEP application during tidal expiration immediately determines a rise in expiratory flow (V) followed by a short-lasting V drop (deltaV), reflecting upper airway collapsibility. This study investigated if a new NEP test analysis on the transient expiratory DeltaV after NEP application for detection of upper airway V limitation is able to identify obstructive sleep apnea (OSA) subjects and its severity. Thirty-seven male subjects (mean +/- SD age, 46 +/- 11 years; mean body mass index [BMI], 34 +/- 7 kg/m2) with suspected OSA and with normal spirometric values underwent nocturnal polysomnography and diurnal NEP testing at - 5 cm H2O and - 10 cm H2O in sitting and supine positions. deltaV (percentage of the peak V [%Vpeak]) was better correlated to apnea-hypopnea index (AHI) than the EFL measured as V, during NEP application, equal or inferior to the corresponding V during control (EFL), and expressed as percentage of control tidal volume (%Vt). AHI values were always high (> 44 events/h) in subjects with BMI > 35 kg/m2, while they were very scattered (range, 0.5 to 103.5 events/h) in subjects with BMI < 35 kg/m2. In these subjects, AHI still correlated to deltaV (%Vpeak) in both sitting and supine positions at both NEP pressures. OSA severity is better related to deltaV (%Vpeak) than EFL (%Vt) in subjects referred to sleep centers. DeltaV (%Vpeak) can be a marker of OSA, and it is particularly useful in nonseverely obese subjects.

Extrathoracic Expiratory Flow Limitation in Obesity and Obstructive and Restrictive Disorders: Effects of Increasing Negative Expiratory Pressure

The negative expiratory pressure (NEP) technique is used to detect intrathoracic expiratory flow limitation (EFL) in patients with respiratory disorders. Application of NEP may result in a sustained decrease of flow below control as a result of upper airway collapse, which may invalidate interpretation of the test. This response to NEP is common in patients with obstructive sleep apnea syndrome (OSAS). The prevalence of this phenomenon, however, has not been studied in healthy subjects and patients with obstructive and restrictive disorders without OSAS. The purpose of this study was as follows: (1) to assess the effects of increasing NEP levels on upper airway patency, and (2) to determine the factors that predispose to intrathoracic flow limitation or upper airway collapse during NEP application in different postures in healthy nonobese and obese subjects, and in patients with obstructive and restrictive respiratory disorders. Fifty-six patients with obstructive airway disease (21 patients with COPD, 16 patients with simple chronic bronchitis, and 19 patients with asthma) were compared with 47 patients with restrictive respiratory disorders, 20 nonobese and healthy subjects, and 9 obese subjects (body mass index > 30) without a history of snoring or OSAS. NEP at levels of 5 cm H(2)O, 10 cm H(2)O, and 15 cm H(2)O were applied at the mouth immediately after the onset of tidal expiration while seated and supine. Intrathoracic EFL was defined as no change in expiratory flow over any portion of the immediately preceding control breath. Upper airway collapse or narrowing was detected when flows decreased below those of the control breath. Ten patients (18%) with obstructive airway disease (7 patients with COPD) exhibited EFL at NEP of 5 cm H(2)O (4 patients were supine only, and 6 patients were both supine and sitting). No patient with restrictive disorders or healthy obese and nonobese subjects presented EFL at NEP of 5 cm H(2)O. In almost all subgroups, both seated and supine, subjects exhibited a transient decrease of flow below control immediately after the application of NEP in occasional breaths. As NEP increased, the number of subjects who exhibited this response in occasional breaths declined, while the number of subjects who displayed this pattern in all breaths increased. Conversely, there were very few subjects in each subgroup who exhibited a sustained decrease in flow below control in occasional breaths at NEP at 5 cm H(2)O, and only one healthy obese subject who displayed this response in all breaths in supine position only. In general, an increase in NEP resulted in only rare instances of sustained decrease in flow below control in all breaths. While transient decreases in flow exhibited immediately after the onset of NEP in all breaths are common and become more prevalent as NEP is increased beyond 5 cm H(2)O, there are only rare instances of sustained decrease in flow below control throughout expiration at all levels of NEP tested, indicating an appropriate upper airway dilator response that maintains patency. Thus, in subjects without OSAS, assessment of intrathoracic EFL with NEP is valid in almost all instances.

Respiratory-related evoked potential and upper airway transmural pressure change by using the negative expiratory pressure (NEP) device.

Several studies have previously shown respiratory related evoked potentials (RREP) in humans elicited by mechanical stimuli applied on upper airways (UA). According to us, heterogeneous findings, concerning latencies and amplitudes, have been reported because of the different timing of stimuli application during the respiratory cycle and/or features of pressure stimuli. Therefore we evaluated the cortical response evoked by transmural pressure changes at the mouth induced by a negative expiratory pressure (NEP) device. RREP were recorded in 22 healthy non-obese, non-snoring volunteers. The subjects were studied awake in seated position during quiet breathing. Three different pressure levels were applied, in a random order, 200 ms after the beginning of expiration. Cortical electrical responses were recorded from scalp electrodes at Fz, Cz, and Pz scalp location (international 10-20 system) referenced to the linked earlobes. RREP responses consisted of two negative (N45, N120) and two positive (P22, P85) waves. There was no significant effect of pressure or electrode on component latencies. The P22 wave (PRESSURE: F(df 2,42)=6.66, P<0.01), the N45 wave (PRESSURE: F(df 2,42)=16.51, P<0.001), and the P85 wave (PRESSURE: F(df2,42)=15.15, P<0.001) increased significantly theyr amplitude with increasing from pressure stimuli 1 to 10 cmH2O. The present results suggest that the UA NEP application in humans is a reliable way of evoking cortical responses. The experimental features that we described allow us to minimize the confounding factors in evaluating RREPs. The NEP device appears to be a useful tool for investigation of the neurobiology of UA sensation in humans.

Does negative expiratory pressure influence performances of spirometry in older patients?

The aim of this study is to assess the influence of the negative expiratory pressure (NEP) technique on the performance of maximal expiratory manoeuvre in elderly patients. Firstly, the authors studied how NEP (at 5 and 10 cmH2O, NEP5 and NEP10) influences forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) in 60 young healthy volunteers, in order to assess the fluctuations of the method. In the second part of the study, 65 successive elderly inpatients (>70 yrs old) were examined. In this group, 15 elderly patients were unable to perform the manoeuvre, 27 had a normal function, 14 had a lung function with obstructive pattern and nine with restrictive pattern. In young subjects, FVC during NEP5 and NEP10 compared to baseline values was 101+/-5%, and 103+/-5%, respectively, and FEV1 was 100+/-4% and 101+/-5%, respectively. In elderly patients with normal function, FVC during NEP5 and NEP10 compared to baseline values was 99+/-14% and 109+/-23%, respectively, and FEV1 was 97+/-9% and 104+/-13%, respectively. There were no relevant effects of the NEP application on FVC or FEV1 values in elderly patients with an obstructive or restrictive pattern. In elderly patients, the use of the negative expiratory pressure technique during maximal expiratory manoeuvres provides little complementary information compared to a classical manoeuvre. The negative expiratory pressure technique did not modify the initial diagnosis when compared with the classical manoeuvre.

Evaluation of flow limitation in elderly patients unable to perform a forced expiratory maneuver.

The assessment of pulmonary function in elderly persons is not often easy in the clinical practice because of poor patient collaboration. A new technique, negative expiratory pressure (NEP), should provide a simple, rapid and non-invasive method for detecting flow limitation without collaboration of the patients. Our aim was to investigate whether it is possible to detect an expiratory flow limitation during resting breathing with NEP in elderly patients unable to perform a forced expiratory maneuver. In 15 elderly inpatients (4 males and 11 females, mean age 83+/-4.7 SD years) unable to realize the classical forced expiratory maneuver because of poor coordination or cognitive disturbance, we applied the NEP technique during spontaneous breathing. NEP application during resting breathing was easily and rapidly performed in all cases without side effects. During NEP (-5cmH2O and NEP -10cmH2O), 6 and 5/15 patients were flow limited; mean flow limitation was 60+/-9% and 70+/-15% respectively. These results were reproducible with repeated NEP tests. Application of negative pressure at the mouth during tidal expiration provides a simple method for detecting expiratory flow limitation during spontaneous breathing in elderly patients with poor collaboration.

Alternative methods for assessing bronchodilator reversibility in chronic obstructive pulmonary disease

BACKGROUNDBronchodilator reversibility testing is recommended in all patients with chronic obstructive pulmonary disease (COPD) but does not predict improvements in breathlessness or exercise performance. Two alternative ways of assessing lung...

Alternative methods for assessing bronchodilator reversibility in chronic obstructive pulmonary disease

BACKGROUNDBronchodilator reversibility testing is recommended in all patients with chronic obstructive pulmonary disease (COPD) but does not predict improvements in breathlessness or exercise performance. Two alternative ways of assessing lung mechanics—measurement of end expiratory lung volume (EELV) using the inspiratory capacity manoeuvre and application of negative expiratory pressure (NEP) during tidal breathing to detect tidal airflow limitation—do relate to the degree of breathlessness in COPD. Their usefulness as end points in bronchodilator reversibility testing has not been examined.METHODSWe studied 20 patients with clinically stable COPD (mean age 69.9 (1.5) years, 15 men, forced expiratory volume in one second (FEV1) 29.5 (1.6)% predicted) with tidal flow limitation as assessed by their maximum flow-volume loop. Spirometric parameters, slow vital capacity (SVC), inspiratory capacity (IC), and NEP were measured seated, before and after nebulised saline, and at intervals after 5 mg nebulised salbutamol and 500 μg nebulised ipratropium bromide. The patients attended twice and the treatment order was randomised.RESULTSMean FEV1, FVC, SVC, and IC were unchanged after saline but the degree of tidal flow limitation varied. FEV1improved significantly after salbutamol and ipratropium (0.11 (0.02) l and 0.09 (0.02) l, respectively) as did the other lung volumes with further significant increases after the combination. Tidal volume and mean expiratory flow increased significantly after all bronchodilators but breathlessness fell significantly only after the combination treatment. The initial NEP score was unrelated to subsequent changes in lung volume.CONCLUSIONSNEP is not an appropriate measurement of acute bronchodilator responsiveness. Changes in IC were significantly larger than those in FEV1and may be more easily detected. However, our data showed no evidence for separation of “reversible” and “irreversible” groups whatever outcome measure was adopted.

Forced expiratory maneuvers in very young children. Assessment of flow limitation.

The application of negative expiratory pressure (NEP) to the airway opening during forced expiratory maneuvers has recently been described as a noninvasive method to assess whether flow limitation is achieved in adults. This methodology has great potential for extending the measurement of forced expiratory maneuvers to young children who may not produce maximal efforts as reproducibly as adults. We used NEP to assess flow limitation in 10 children between 3 and 5 yr of age. NEP was well tolerated by all subjects. With the application of NEP, there was not a step increase in flow, a finding consistent with flow limitation for the subjects. In addition to visual inspection, we proposed a method to quantify the change in flow during a short NEP. The flow-volume curves obtained with and without NEP were visually the same, other than the flow transients produced by NEP. The calculated values of FVC and FEF25-75 were not significantly different when measured from flow- volume curves with and without NEP. There was a statistically significant increase in FEV1 with NEP; however, the group mean increase in FEV1 was less than 2%. We conclude that NEP may be a useful technique to determine whether flow limitation has been achieved in young children performing forced expiratory maneuvers.

Detection of expiratory flow limitation during exercise in COPD patients.

The negative expiratory pressure (NEP) method was used to detect expiratory flow limitation at rest and at different exercise levels in 4 normal subjects and 14 patients with chronic obstructive pulmonary disease (COPD). This method does not require performance of forced expirations, nor does it require use of body plethysmography. It consists in applying negative pressure (-5 cmH2O) at the mouth during early expiration and comparing the flow-volume curve of the ensuing expiration with that of the preceding control breath. Subjects in whom application of NEP does not elicit an increase in flow during part or all of the tidal expiration are considered flow limited. The four normal subjects were not flow limited up to 90% of maximal exercise power output (Wmax). Five COPD patients were flow limited at rest, 9 were flow limited at one-third Wmax, and 12 were flow limited at two-thirds Wmax. Whereas in all patients who were flow limited at rest the maximal O2 uptake was below the normal limits, this was not the case in most of the other patients. In conclusion, NEP provides a rapid and reliable method to detect expiratory flow limitation at rest and during exercise.