Effect of inhaled methacholine on inspiratory flow

One hundred consecutive outpatients with symptoms suggestive of asthma who came to the Pulmonary Function Laboratory for a methacholine challenge test were studied. In addition to the forced expiratory maneuvers, forced inspiratory maneuvers were performed before and after the maximal response to methacholine. In 24 patients, the methacholine challenge suggested that they had asthma (forced expiratory volume in 1 s [FEV1] decrease greater than or equal to 20 percent). Six of these 24 patients also had a decrease in maximal forced inspiratory flow (FIFmax) greater than or equal to 20 percent and nine had a decrease in forced inspiratory flow at 50 percent of vital capacity (FIF50) greater than or equal to 20 percent, suggesting that bronchoconstriction can cause decreased inspiratory as well as expiratory flows. In 76 patients, the methacholine challenges were "negative" (FEV1 decrease less than or equal to 20 percent), suggesting that they did not have asthma. Nevertheless, in 11 of these 76 patients the FIFmax decrease was greater than or equal to 20 percent, and in 14 patients the FIF50 decrease was greater than or equal to 20 percent, suggesting that intermittent central airway obstruction is responsible for these patients' symptoms.     

用力吸气流量在COPD和支气管哮喘中的应用

目的 评价用力吸气流量指标在慢性阻塞性肺疾病(COPD)和支气管哮喘中价值。方法 观察COPD80例和支气管哮喘20例在吸入支气管扩张剂后用力吸气流量指标的前后变化。结果 轻度COPD患者和支气管哮喘患者FEV1,FIV1，PEF，PIF，FEF50％，FIF50%指标，在吸入支气管扩张剂前后均有明显的差异。但用力吸气流量指标与用力呼气流量指标在统计学无差别。而中、重度COPD患者FIV1％较FEV1％有显著差异性。结论 在COPD中，在评价支气管的可逆性方面，用力吸气流量具有用力呼气流量同样的效果。甚至在重度COPD患者中．FIV1%比用力呼气流量可能更加敏感。     

Bronchodilator response in residual volume in irreversible airway obstruction

BACKGROUND: Although airway obstruction, as defined by improvement of forced expiratory volume in one second (FEV1) and/or forced vital capacity (FVC), is irreversible in patients with COPD, they clearly seem to benefit from treatment with inhaled bronchodilators. AIMS: To assess the response pattern of residual volume (RV) compared to FEV1 after bronchodilation in patients with reversible and irreversible airway obstruction. METHODS: Changes in static lung volumes were compared with improvement in dynamic lung volumes in 396 consecutive patients undergoing reversibility testing with repeat bodyplethysmography. Reversibility was defined as improvement of FEV1 >200 ml and >12% after inhalation of fenoterol hydrobromide. RESULTS: Irreversibility was found in 297 out of 396 patients with airway obstruction. Except for total lung capacity (TLC), all parameters (residual volume [RV], vital capacity [VC], forced inspiratory vital capacity [IVC], forced vital capacity [FVC], forced expiratory volume in one second [FEV1] and the FEV1/VC ratio) showed statistically significant changes after bronchodilation in 396 patients. The multiple linear regression model adjusted for age, sex and BMI showed a non-linear relationship between DeltaFEV1 or DeltaVC compared to DeltaRV after bronchodilation. If the increase in DeltaFEV1 is lower than 0.1 L, DeltaRV remains constant. However, if the increase in DeltaFEV1 is more than 0.1 L, DeltaRV decreases too. The same is found at an increase in VC of 0.3 L. CONCLUSION: In summary, in patients with irreversible airway obstruction DeltaRV cannot be predicted by DeltaFEV1 or DeltaVC after bronchodilation. Therefore, spirometric assessment should be complemented by bodyplethysmography.     

Flow-volume curve abnormalities and obstructive sleep apnea syndrome

Recent reports have suggested that flow volume curve abnormalities may be of interest in the diagnosis of obstructive sleep apnea syndromes by showing either extrathoracic airway obstruction (ratio of expiratory flow to inspiratory flow at 50 percent of forced vital capacity [FEF50/FIF50] exceeding 1) or upper airway fluttering (indicated by a sawtooth aspect on the mid-half of the inspiratory part of the curve) or both. In our study, 57 patients referred for a suspected sleep apnea syndrome (SAS) underwent conventional spirometry, assessment of flow-volume curves, ENT examination, and polysomnography. Thirty patients had an obstructive SAS, four patients a central SAS, and 23 patients no SAS. Signs of upper airway fluttering (the sawtooth sign) were present in 61 percent of the patients with obstructive SAS and in 46 percent of the patients without obstructive SAS (central SAS or no SAS). Signs of extrathoracic upper airway obstruction (FEF50/FIF50 greater than 1) were present in 67 percent of the patients with obstructive SAS and in 71 percent of the patients without obstructive SAS. These results suggest that upper airway abnormalities, as reflected by abnormal flow volume curves, are not always associated with obstructive SAS; they favor the hypothesis of a central component in the mechanism of upper airway occlusion during sleep.     

Comparison of maximal midexpiratory flow rate and forced expiratory flow at 50% of vital capacity in children

BACKGROUND: The mid-portion of the maximal expiratory flow-volume (MEFV) curve is often described by values of the mean forced expired flow as lung volume decreases from 75% to 25% of vital capacity (ie, forced expiratory flow, midexpiratory phase [FEF(25-75)]). It is common practice to report also forced expired flow at 50% of vital capacity (FEF(50)). STUDY OBJECTIVE: To investigate whether FEF(50) and FEF(25-75) are highly correlated or whether the difference between them reflects a degree of airways obstruction. Also, we wanted to investigate the correlation between the two in cases of irregularly shaped MEFV curves (ie, "saw-toothing"). DESIGN: Analysis of the correlation between FEF(50) and FEF(25-75) in a single determination. We assessed the relationship between the FEF(50)/FEF(25-75) ratio and the degree of airways obstruction, as reflected by other traditional parameters such as FEV(1), FEV(1)/FVC ratio, and specific airway conductance (SGaw). PATIENTS: There were 1,350 forced expiratory maneuvers performed by children with a broad range of pulmonary abnormalities. RESULTS: FEF(50) correlated with FEF(25-75) as follows: FEF(50) (L/s) = 0.041 + 1.136*FEF(25-75)(L/s); r(2) = 0.956; standard error of the estimate = 0.013; p < 0.0001. The FEF(50)/FEF(25-75) ratio remained stable and did not correlate with FEV(1) (r = 0.12), FEV(1)/FVC ratio (r = 0.11), or SGaw (r = 0.02; difference not significant). The correlation between FEF(25-75) and FEF(50) was similar for both the smooth curve (r = 0.97) and the irregular curve (r = 0.96). CONCLUSIONS: Although not identical, FEF(25-75) and FEF(50) are highly correlated, and the ratio of the two is fairly constant. Therefore, the practice of reporting both of them is unnecessary. We suggest that it is reasonable to prefer FEF(50).     

Upper airways obstruction with bilateral vocal cord paralysis.

In ten patients with bilateral vocal cord paralysis, we demonstrated variable extrathoracic airway obstruction. The ratio of forced expiratory flow at 50 percent vital capacity to forced inspiratory flow at the same lung volume (VE50/VI50) was 1.65 +/- 0.77 (mean +/- 1 SD). There was marked variability of inspiratory flow obstruction with a mean VI50 of 1.63 +/- 0.75 liters/ sec and a range from 0.9 liters/sec to 3.2 liters/sec. Nine of the ten patients required tracheostomy for symptoms of dyspnea. Follow-up flow volume loops were obtained to document the effects of surgical intervention and tracheostomy.     

The interpretation of the spirogram. How accurate is it for 'obstruction'?

The accuracy of the spirogram in detecting or excluding airway obstruction based on airflow limitation was assessed prospectively in 200 subjects, 74 with obstruction and 126 without it. The diagnosis of airway obstruction was based on a combination of clinical and body plethysmographic data. The ratio of forced expiratory volume in 1 s to forced vital capacity (FEV1/FVC %) had a sensitivity of 0.82 and a specificity of 0.98. A fixed lower limit seemed better than a lower limit based on prediction formulas. Because specificity is so much higher than sensitivity, less precise clinical information is required to confirm the presence of obstruction if FEV1/FVC % is abnormal than is needed to exclude obstruction if FEV1/FVC % is normal. Using a combination of FEV1/FVC % and the ratio of forced expiratory flow (FEF) at 50% of FVC gave a higher sensitivity with a comparable specificity when compared with FEV1/FVC % used alone. A normal value for FEF between 25% and 75% of FVC virtually ruled out obstruction, but low values had poor specificity.     

Severe asthma associated with myasthenia gravis and upper airway obstruction.

An unusual association of asthma and myasthenia gravis (MG) complicated by tracheal stenosis is reported. The patient was a 35-year-old black woman with a history of severe asthma and rhinitis over 30 years. A respiratory tract infection triggered a life-threatening asthma attack whose treatment required orotracheal intubation and mechanical ventilatory support. A few weeks later, tracheal stenosis was diagnosed. Clinical manifestations of MG presented 3 years after her near-fatal asthma attack. Spirometry showed severe obstruction with no response after inhalation of 400 microg of albuterol. Baseline lung function parameters were forced vital capacity, 3.29 L (105% predicted); forced expiratory volume in 1 second (FEV1), 1.10 L (41% predicted); maximal midexpiratory flow rate, 0.81 L/min (26% predicted). FEV1 after administration of albuterol was 0.87 L (32% predicted). The patient's flow-volume loops showed flattened inspiratory and expiratory limbs, consistent with fixed extrathoracic airway obstruction. Chest computed tomography scans showed severe concentric reduction of the lumen of the upper thoracic trachea.     

Should forced expiratory volume in six seconds replace forced vital capacity to detect airway obstruction?

It has been suggested that forced expiratory volume in six seconds (FEV(6)) should be substituted for forced vital capacity (FVC) to measure fractions of timed expired volume for airflow obstruction detection. The present authors hypothesised that this recommendation might be questionable because flow after 6 s of forced expiration from more diseased lung units with the longest time constants was most meaningful and should not be ignored. Furthermore, previous studies comparing FEV(6) and FVC included few subjects with mild or no disease. The present study used spirometric data from the USA Third National Health and Nutrition Evaluation Survey with prior published ethnicity- and sex-specific equations for FEV(1)/FEV(6), FEV(1)/FVC and FEV(3)/FVC, and new equations for FEV(3)/FEV(6), all derived from approximately 4,000 adult never-smokers aged 20-80 yrs. At 95% confidence intervals, 21.3% of 3,515 smokers and 41.3% of smokers aged >51 yrs had airway obstruction; when comparing FEV(1)/FEV(6) with FEV(1)/FVC, 13.5% were concurrently abnormal, 1.5% were false positives and 4.1% were false negatives; and when comparing FEV(3)/FEV(6) with FEV(3)/FVC, 11.6% were concurrently abnormal, 3.3% were false positives and 5.7% were false negatives. Substituting forced expiratory volume in six seconds for forced vital capacity to determine the fractional rates of exhaled volumes reduces the sensitivity of spirometry to detect airflow obstruction, especially in older individuals and those with lesser obstruction.     

Determination of bronchodilation in the clinical pulmonary function laboratory. Role of changes in static lung volumes

Improved airway resistance following bronchodilator inhalation is not always accompanied by improvement in forced expiratory flow. We studied 241 patients with airways obstruction to learn whether changes in static lung volumes (vital capacity and function residual capacity measured by body plethysmography [FRCB]) would reveal bronchodilation not demonstrated by expiratory flow rates (the ratio of forced vital capacity at one second to the total forced vital capacity [FEV1/FVC]), and the forced expiratory flow for the midportion of the forced vital capacity (FEF25--75%). A significant fall in Raw occurred in 129 patients, 46 of whom had a significant increase in vital capacity (mean of + 465 ml +/- 43, P less than 0.001) and a fall in FRCB (mean of -763 ml +/- 78 P less than 0.001) with no change in FEV1/FVC% of FEF25--75%. We interpret these data to indicate that improvement in static lung volumes can reflect bronchodilation in the absence of improved expiratory flow.     

Obstructive and restrictive spirometric patterns: fixed cut-offs for FEV1/FEV6 and FEV6.

The purpose of this study was to determine fixed cut-off points for forced expiratory volume in one second (FEV(1))/FEV(6) and FEV(6) as an alternative for FEV(1)/forced vital capacity (FVC) and FVC in the detection of obstructive and restrictive spirometric patterns, respectively. For the study, a total of 11,676 spirometric examinations, which took place on Caucasian subjects aged between 20-80 yrs, were analysed. Receiver-operator characteristic curves were used to determine the FEV(1)/FEV(6) ratio and FEV(6) value that corresponded to the optimal combination of sensitivity and specificity, compared with the commonly used fixed cut-off term for FEV(1)/FVC and FVC. The data from the current study indicate that FEV(1)/ FEV(6) <73% and FEV(6) <82% predicted can be used as a valid alternative for the FEV(1)/FVC <70% and FVC <80% pred cut-off points for the detection of obstruction and restriction, respectively. The statistical analysis demonstrated very good, overall, agreement between the two categorisation schemes. For the spirometric diagnosis of airway obstruction (prevalence of 45.9%), FEV(1)/FEV(6) sensitivity and specificity were 94.4 and 93.3%, respectively; the positive and negative predictive values were 92.2 and 95.2%, respectively. For the spirometric detection of a restrictive pattern (prevalence of 14.9%), FEV(6) sensitivity and specificity were 95.9 and 98.6%, respectively; the positive and negative predictive values were 92.2 and 99.3%, respectively. This study demonstrates that forced expiratory volume in one second/forced expiratory volume in six seconds <73% and forced expiratory volume in six seconds <82% predicted, can be used as valid alternatives to forced expiratory volume in one second/forced vital capacity <70% and forced vital capacity <80% predicted, as fixed cut-off terms for the detection of an obstructive or restrictive spirometric pattern in adults.     

Upper airway anesthesia induces airflow limitation in awake humans.

Upper airway receptors are thought to contribute to upper airway stability by reducing collapsing forces. Their activity can be abolished by topical anesthesia. We have measured in 16 healthy volunteers (mean +/- SD age, 23.7 +/- 1.6 yr) specific airway conductance (SGaw), maximal inspiratory (MIFR) and expiratory (MEFR) flow rates before and 15, 35, and 45 min after extensive upper airway anesthesia (UAA) with 10% lidocaine. Average values of MIFR decreased (p less than 0.01) 15 min after UAA, but they returned to or near to control values at 45 min: MIF25 (4.8 versus 6.0 L/s); MIF50 (5.1 versus 6.2 L/s); MIF75 (4.4 versus 5.3 L/s). Transient decreases in flow (V) rates, reaching zero flow in some subjects, were observed in 13 subjects during forced inspiratory vital capacity (FIVC) maneuvers and in seven subjects during forced expiratory vital capacity (FEVC) maneuvers. MEFR at 25, 50, and 75% FVC, SGaw, and FVC did not change after anesthesia. Simultaneous measurements of supraglottic pressure, V, and lung volume in 12 of the 16 subjects showed that the site of flow limitation was localized at the level of the glottis in all except one subject in whom there was both a glottic and a supraglottic obstruction. We conclude that extensive upper airway anesthesia induced a profound but transitory upper airway obstruction during FIVC and FEVC maneuvers. These findings are compatible with the concept of reflex regulation of upper airway caliber.     

Small airways in progressive systemic sclerosis (PSS).

Obstructive disease involving peripheral airways has been noted in diffuse interstitial pulmonary disease, including sarcoidosis and cryptogenic fibrosing alveolitis. The possibility of obstruction of small airways in progressive systemic sclerosis (PSS) has been suggested by widespread bronchiolectasis and peribronchial fibrosis noted at necropsy. We performed pulmonary function studies in 39 subjects (22 nonsmokers and 17 smokers) with PSS, most of whom had functional evidence of interstitial pulmonary involvement (increased static recoil pressure and reduced diffusing capacity). The 1 second forced expiratory volume to forced vital capacity ratio (FEV1:FVC) was normal in all subjects. Although the severity of the restrictive process was greater in nonsmokers compared with that in smokers, the maximal mid-expiratory flow rate, closing volume, closing capacity, volume of isoflow, change in maximal expiratory flow at 50 per cent of vital capacity during 80 per cent helium--20 per cent oxygen breathing compared with air breathing (delta Vmax50), ratio of dynamic to static lung compliance at different breathing frequencies and upstream airway conductance at static recoil pressures of 5 and 10 cm H2O were nearly always normal in the nonsmokers but were frequently abnormal in the smokers with PSS. These findings suggest that diffuse interstitial pulmonary disease due to PSS generally does not lead to functional evidence of obstruction in peripheral airways and that when the latter is found it can likely be attributed to the effects of concomitant cigarette smoking.     

Effects of inhaled steroids on methacholine-induced bronchoconstriction and gas trapping in mild asthma.

According to a recent hypothesis, airway smooth muscle regulates airway calibre mostly at high lung volume, whereas the mucosa and adventitia dimensions dominate at low lung volumes. It was thought that if inhaled steroids decrease the thickness of airway wall in asthma, then forced vital capacity (FVC), which reflects the functional changes at low lung volume, should decrease less during induced bronchoconstriction than flow at high volume. The study was conducted in 31 mild asthmatics under control conditions and during a methacholine challenge before and after 4-weeks treatment with inhaled fluticasone dipropionate (1.5 mg daily, 16 patients) or placebo (15 patients). After fluticasone dipropionate treatment, control forced expiratory volume in one second (FEV1), and maximal flow at 50% of control FVC during forced expiration after a maximal (V'max,50) and a partial inspiration (V'p,50) significantly increased. During methacholine challenge, FVC decreased less than did FEV1 or V'max,50, and so did inspiratory vital capacity compared to V'p,50. Both the provocative dose of methacholine causing a 20% fall in FEV1 and the bronchodilator effect of deep inhalation significantly increased. The latter was assessed by means of the regression coefficient of all V'max,50 plotted against V'p,50. No significant changes in these parameters occurred after placebo. These data show that inhaled steroids remarkably blunt the occurrence of gas trapping during induced bronchoconstriction in mild bronchial asthma, possibly due to their effect on airway wall remodelling.     

Density-dependence of maximal expiratory flow and its correlation with small airway disease in smokers

Density-dependence of maximal expiratory flow was measured in 110 patients prior to resection for peripheral coin lesions. The resected lung or lobe was examined morphologically and graded for emphysema, membranous bronchiolitis, and respiratory bronchiolitis. Density dependence did not decrease with increasing airway obstruction, and there was no relationship between density-dependence and peripheral airway abnormality or emphysema in the group as a whole. When patients were arbitrarily divided into those with forced expiratory volume in one second (FEV1) greater than 80% predicted (n = 80) and FEV1 less than 80% predicted (n = 30), density-dependence correlated significantly and negatively with membranous bronchiolitis in those with FEV1 greater than 80% predicted and significantly but positively in those with more advanced airway obstruction. We conclude that density-dependence of maximal expiratory flow is not an accurate predictor of peripheral airway abnormality in patients with mild to moderate air-flow obstruction.     

Ventilatory defect in coal workers with simple pneumoconiosis: early detection of functional abnormalities

Airway obstruction is a prominent feature in coal workers' pneumoconiosis (CWP). However, many patients with CWP have even demonstrated a normal forced vital capacity (FVC) and forced expiratory volume in 1s (FEV1). The purpose of this study was to evaluate the ventilatory defect by spirometry and search for parameters, other than FVC and FEV1, suitable for early detection of pulmonary impairment in CWP. A sample of 227 coal miners was selected from the medical clinics of two teaching hospitals. Maximal expiratory flow volume measurement and determination of functional residual capacity (FRC) and residual volume (RV) were carried out with an automated plethysmograph. The prevalence of airway obstruction (FEV1/FVC < 70%) in this sample of miners was 52.9% (120/227). There was a progression of functional impairment with the transition from category 0 to categories 2 and 3, no matter what the miners smoking habits. All of the 107 non-obstructed miners had a normal FVC and FEV1. However, the mean values for FEF25-75% (mean forced expiratory flow during the middle half of FVC) and Vmax50 (maximal expiratory flow rate at 50% FVC) were abnormally low, and RV was already elevated, in those non-obstructed subjects with category 1 simple pneumoconiosis. A borderline abnormally elevated FRC in the miners with radiological category 3 of CWP was also noted. We conclude that the Vmax50, FEF25-75%, and RV appeared to be the discriminative indices for detecting early ventilatory defect in non-obstructed patients with simple CWP. Further studies is still needed to clarify the cause of small airway dysfunction.     

Bronchial responsiveness, oscillations of peak flow rate and symptoms in patients with mitral stenosis.

To better characterize airway hyperresponsiveness reported in cardiac patients questionnaire-recorded symptoms, bronchial responsiveness to methacholine (Mch) and to ultrasonically nebulized distilled water (UNDW), diurnal oscillations of peak expiratory flow (PEF) rate were evaluated in 32 patients with moderate mitral stenosis. Twenty patients were responsive to Mch (defined as provocative dose producing a 20% fall in forced expiratory volume in one second (PD20 FEV1) less than 3.2 mg) (geometric mean PD20 FEV1 851 +/- 154 micrograms SE). Only two patients showed a fall in FEV1 greater than 20% after UNDW challenge. Patients responsive to Mch challenge had lower FEV1 as percentage of vital capacity (FEV1/VC) (80 +/- 4.8 vs 83 +/- 3.8%, p less than 0.05), higher coefficient of variation of PEF (CV-PEF) (7.1 +/- 2.8 vs 5 +/- 2.4, p less than 0.05) and higher prevalence of wheeze (70 vs 25%, p less than 0.05) in comparison with patients non-responsive to Mch challenge. CV-PEF was significantly related to FEV1 (r = 0.347, p less than 0.05) and maximal expiratory flow at 50% expired volume (MEF50) (r = 0.405, p less than 0.05). The probability of responding to Mch bronchial challenge increased proportionally with the increase in CV-PEF and the decrease in FEV1, FEV1/VC and MEF50. Airway hyperresponsiveness of patients with mitral stenosis seems to be more similar to that reported in bronchitic than in asthmatic patients.     

Airway dysfunction in patients with Parkinson's disease

To investigate pulmonary function abnormalities in Parkinson's disease (PD), we obtained maximal inspiratory and expiratory flow-volume curves in 63 patients (59 under treatment) with different stages of the disease, not filtered for respiratory symptoms. PD severity was evaluated by the Unified PD Rating Scale, the Webster's scale, and Hoehn and Yahr staging. Patients with more severe PD had lower percentage forced vital capacity (FVC%), and peak inspiratory and expiratory flows. Those with fluctuations and/or dyskinesias had lower FVC% and percentage forced expiratory flow volume in 1 sec (FEV₁%). There were a number of weak but significant correlations between PD scales and spirographic parameters. Thirty one patients (49.2%) had pathological flow-volume curves. The clinical profile and the duration of the disease did not influence the pattern of the curve. Physiologic evidence of upper airway obstruction was observed in 3 cases. A spirometric restrictive ventilatory defect (FEV₁/FVC higher than or equal to 80%) was observed in 54 patients (85%), while generalized airway obstruction was present only in one nonsmoker. We conclude that abnormal flow-volume loop contour is a frequent finding in PD. This probably reflects involvement of the upper airway musculature, that in some patients can produce upper airway obstruction. Generalized airflow limitation is not an important characteristic of PD. By contrast, a restrictive spirometric defect, probably due to incoordinated expiratory effort or abnormally low chest wall compliance, is the main spirometric finding in these patients. Offprint requests to: J. L. Izquierdo-Alonso     

Maximum inspiratory muscle endurance capacity during resistive loading in chronic obstructive pulmonary disease

In 10 patients with stable severe chronic obstructive pulmonary disease (COPD) we evaluated the relationship between the degree of airway obstruction and hyperinflation, and the maximum inspiratory muscle endurance capacity during added inspiratory resistive loading. We measured the ratio of forced expiratory volume in 1 s to forced vital capacity (FEV1/FVC) and airway resistance (Raw) as indices of airway obstruction, and the ratio of functional residual capacity to total lung capacity (FRC/TLC) as an index of hyperinflation. The mean resting transdiaphragmatic pressure to its maximum (Pdi/Pdimax), the tension time index of the diaphragm, and the maximum transdiaphragmatic pressure (Pdimax) were also determined. Following 15 min of resting breathing, the patients breathed through added inspiratory resistances which were progressively increased every 3 min until exhaustion. Maximum endurance capacity (ECmax) was defined as the product of the esophageal pressure - time integral and frequency at the maximum load sustainable for 3 min. ECmax correlated significantly with Raw (r = -0.67, p less than 0.04). The addition of FRC/TLC to the analysis resulted in a significant increase in the correlation coefficient (r = 0.86, p less than 0.01). ECmax did not correlate with FEV1/FVC. Both resting Pdi/Pdimax and Pdimax independently influenced ECmax. In addition, Pdimax correlated significantly with FRC/TLC, and resting Pdi/Pdimax with Raw. We conclude that in stable patients with severe COPD, both airway obstruction and hyperinflation affect maximum inspiratory muscle endurance capacity during inspiratory resistive loading.     

An isoflow-volume technique for assessing airway dynamics in children and adults

BACKGROUND: We propose a new approach to the measurement of small airway function as an alternative to recordings of maximal expiratory flow-volume (MEFV) curves. OBJECTIVES: A newly developed technique to record isoflow-volume (IFV) curves to be tested against maximal respiratory flow curves. METHODS: An isoflow whistle (IFW; Iflopen) measures the length of a constant expiration after full inspiration. The note of the whistle enables a subject to generate an even expiration, and the isoflow maintenance times at 1 l x s(-1) (IFMT1) and 2 l x s(-1) (IFMT2) are recorded. The accuracy and reproducibility of the IFV technique were evaluated in 17 healthy adults (age 17-55 years) and in 14 asthmatic children (age 6-14 years). Comparisons with standard lung function parameters, such as forced expiratory volume in 1 s (FEV1), maximal expiratory flow at 50% (MEF50) and 25% (MEF25) vital capacity and peak expiratory flow (PEF), obtained with a Wright Peakflow Meter were undertaken in 102 healthy (aged 8-14 years) and 101 asthmatic children (aged 6-17 years). A bronchial challenge test was performed in 13 asthmatic children. RESULTS: The expired volume measured by the IFW showed an acceptable agreement with that of a pneumotachograph (mean error of 4.32% for IFMT1 and 5.93% for IFMT2). In healthy and in asthmatic children, the correlations between FEV1 and IFMT1 or IFMT2 (r = 0.92 and 0.94, respectively) were found to be greater than that between FEV1 and PEF (r = 0.68). During bronchial challenge tests in 13 asthmatic children, the FEV1 decreased to 69% of baseline and IFMT1 to 58% of baseline. CONCLUSIONS: The IFV technique accurately measured airway obstruction and closely followed changes in standard parameters of the MEFV curve.