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.     

Bronchodilators increase airway instability in cystic fibrosis

Supramaximal flow transients of partial expiratory flow-volume curves are caused by a rapidly emptying compartment. By superimposing a maximal and a series of partial expiratory flow-volume curves, the volume of the flow transient equivalent for the maximal curve was estimated (volume of airway contribution = VACMEFV). This flow transient equivalent is caused by an extra dead space, created in the large airways by a full inspiration. In 18 children with cystic fibrosis (CF), routine pulmonary functions and VACMEFV were measured before and after bronchodilator medication. Baseline VACMEFV correlated directly with the curvilinearity of the flow-volume curve and inversely with the clinical and radiologic score. Significantly, bronchodilator medication improved FVC, FEV1, FEF25-75, VC, PEF, Raw, and also VACMEFV. In 6 children, VEmax25 increased as a result of apparent peripheral bronchodilation. In 3 others, end-expiratory flow increased slightly but the expanded VACMEFV included the measuring point invalidating the measurement. In the remaining 9 patients, VEmax25 decreased after bronchodilator. As an apparent discrepancy, FEV1, FVC, PEF, VC, FEF25-75 increased, and Raw decreased in 4 to 9 patients. The volumes and flow rates measured early in forced expiration and the end-expiratory flow behaved differently because VACMEFV expanded beyond the measuring points of early expiratory and mid-expiratory flow rates. As the bronchodilator rendered the compliant large airways still more distensible, the amount of air emptied from the dead space in early forced expiration increased. Simultaneously, end-expiratory flow decreased because of enhanced airway compression.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spirometry in early childhood in cystic fibrosis patients

BACKGROUND: Spirometry data in cystic fibrosis (CF) patients in early childhood is scarce, and the ability of spirometry to detect airways obstruction is debatable. OBJECTIVE: To evaluate the ability of spirometry to detect airflow obstruction in CF patients in early childhood. METHODS: CF children (age range, 2.5 to 6.9 years) in stable clinical condition were recruited from five CF centers. The children performed guided spirometry (SpiroGame; patented by Dr. Vilzone, 2003). Spirometry indices were compared to values of a healthy early childhood population, and were analyzed with relation to age, gender, and clinical parameters (genotype, pancreatic status, and presence of Pseudomonas in sputum or oropharyngeal cultures). RESULTS: Seventy-six of 93 children tested performed acceptable spirometry. FVC, FEV1, forced expiratory flow in 0.5 s (FEV0.5), and forced expiratory flow at 50% of vital capacity (FEF50) were significantly lower than healthy (z scores, mean +/- SD: - 0.36 +/- 0.58, - 0.36 +/- 0.72, - 1.20 +/- 0.87; and - 1.80 +/- 1.47, respectively; p < 0.01); z scores for FEV1 and FVC were similar over the age ranges studied. However, z scores for FEV0.5 and forced expiratory flow at 25 to 75% of vital capacity were significantly lower in older children compared to younger children (p < 0.001), and a higher proportion of 6-year-old than 3-year-old children had z scores that were > 2 SDs below the mean (65% vs 5%, p < 0.03). Girls demonstrated lower FEF50 than boys (z scores: - 2.42 +/- 1.91 vs - 1.56 +/- 1.23; p < 0.001). Clinical parameters evaluated were not found to influence spirometric indices. CONCLUSIONS: Spirometry elicited by CF patients in early childhood can serve as an important noninvasive tool for monitoring pulmonary status. FEV0.5 and flow-related volumes might be more sensitive than the traditional FEV1 in detecting and portraying changes in lung function during early childhood.     

Assessment of airway function in young children with asthma: comparison of spirometry, interrupter technique, and tidal flow by inductance plethsmography

The assessment of airway function in young children requires adaptation of techniques designed for adults and/or application of techniques that do not require complex respiratory maneuvers. We sought to assess two methods of measuring airway function: time to peak expiratory flows as a ratio of expiratory time (T(PTEF)/T(E)), derived from respiratory inductance plethysmography, and total respiratory resistance by the interrupter technique (Rint), both obtained during quiet tidal breathing. Both techniques were referenced to FEV1 and flow at 50% expired volume (FEF50) from conventional spirometry in 30 children aged 4-8 years (median age, 6.9; range, 4.5-8.5 years) with a physician diagnosis of asthma and who were able to perform FEV1 with a repeatability of at least 8%. T(PTEF)/T(E) and Rint were performed in random order followed by spirometry, in order to reduce the possible effects of pulmonary stretch on tidal breathing measures. Coefficients of variation (CV) and mean absolute change/baseline standard deviation were derived for each measurement. Baseline FEV1 did not correlate significantly with T(PTEF)/T(E) (r = 0.025), but did correlate with Rint (r = 0.737, P < 0.001); respective relationships for change after bronchodilator were r = 0.09 (ns) and r = 0.64 (P < 0.001). FEF50 also correlated significantly with Rint (R = 0.769, P < 0.001) but not with T(PTEF)/T(E). FEV1 and FEF50 both increased postbronchodilator, with respective mean changes of 11.4% and 28% (P < 0.001), while Rint decreased by 24.3% (P < 0.001). No significant changes were noted for T(PTEF)/T(E). T(PTEF)/T(E) derived from inductance plethysmography does not detect mild airway obstruction or modest changes in airway caliber following bronchodilator in young children with asthma. The interrupter technique may have a role in assessing baseline airway function and response to therapy in children unable to perform reliable spirometry, and/or when the investigator wishes to avoid the possible influence of forced maneuvers on airway tone.     

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).     

Ratio between forced expiratory flow between 25% and 75% of vital capacity and FVC is a determinant of airway reactivity and sensitivity to methacholine

STUDY OBJECTIVE: The ratio between forced expiratory flow between 25% and 75% of vital capacity (FEF(25-75)) and FVC is thought to reflect dysanapsis between airway size and lung size. A low FEF(25-75)/FVC ratio is associated with airway responsiveness to methacholine in middle-aged and older men. The current study was designed to assess this relationship in both male and female subjects over a broader range of ages. STUDY DESIGN: Data analysis of consecutive subjects who had a >or= 20% reduction in FEV(1) after 相似文献   

Timing and driving components of the breathing strategy in children with cystic fibrosis during exercise

The aim of this study was twofold: first, to determine the breathing strategies of children with cystic fibrosis (CF) during exercise, and secondly, to see if there was a correlation with lung function parameters. We determined the tension-time index of the inspiratory muscles (T(T0.1)) during exercise in nine children with CF, who were compared with nine healthy children with a similar age distribution. T(T0.1) was determined as followed T(T0.1) = P0.1/PImax . T(I)/T(TOT), where P0.1 is mouth occlusion pressure, PImax is maximal inspiratory pressure, and T(I)/T(TOT) is the duty cycle. CF children showed a significant decrease of their forced expiratory volume in 1 sec (FEV1), forced vital capacity (FCV), and FEV1/FVC, whereas the residual volume to total lung capacity ratio (RV/TLC) ratio and functional residual capacity (FRC) were significantly increased (P < 0.001). Children with CF showed mild malnutrition assessed by actual weight expressed by percentage of ideal weight for height, age, and gender (weight/height ratio; 82.3 +/- 3.6%). Children with CF showed a significant reduction in their PImax (69.3 +/- 4.2 vs. 93.8 +/- 7 cmH2O). We found a negative linear correlation between PImax and weight/height only in children with CF (r = 0.9, P < 0.001). During exercise, P(0.1), P0.1/PImax, and T(T0.1) were significantly higher, for a same percent maximal oxygen uptake in children with CF. On the contrary, T(I)/T(TOT) ratio was significantly lower in children with CF compared with healthy children. At maximal exercise, children with CF showed a T(T0.1) = 0.16 vs. 0.14 in healthy children (P < 0.001). We observed at maximal exercise that P0.1/PImax increased as FEV1/FVC decreased (r = -0.90, P < 0.001), and increased as RV/TLC increased (r = 0.92, P < 0.001) only in children with CF. Inversely, T(I)/T(TOT) decreased as FEV1/FVC decreased (r = 0.89, P < 0.001), and T(I)/T(TOT) decreased as RV/TLC increased (r = -0.94, P < 0.001). These results suggest that children with CF adopted a breathing strategy during exercise in limiting the increase of the duty cycle. Two determinants of this strategy were degrees of airway obstruction and hyperinflation.     

A normal FEV1/VC ratio does not exclude airway obstruction

BACKGROUND: A decreased forced expiratory volume in 1 s/vital capacity (FEV(1)/VC) ratio is the hallmark of the definition of airway obstruction. We recently suggested that a lung function pattern, we called small airways syndrome (SAOS), has a normal FEV(1)/VC and total lung capacity (TLC) and reflects obstruction of small airways. OBJECTIVES: To substantiate our hypothesis we measured and compared lung function tests including maximal expiratory flow rates (MEFR), sensitive indicators of airway obstruction, in SAOS subjects and in matched controls. METHODS: We selected 12 subjects with the pattern of SAOS, but without chronic lung or heart disease (average age: 40.7 +/- 7.8 years) and 36 age-matched subjects with normal lung function (42.8 +/- 6.3 years). We measured static and dynamic lung volumes, MEFR and lung diffusing capacity (DL(CO)). RESULTS: SAOS subjects were heavier smokers (p < 0.05) and body mass index was less than in control subjects (p < 0.01). Both FEV(1)/VC ratio and TLC were comparable in the two groups. However, FEV(1), VC, DL(CO), and MEFR were lower and residual volume (RV) and RV/TLC ratio were higher (p < 0.05) in the SAOS group than in the control one. Furthermore, the MEFR curve of the SAOS group was displaced to the left without any change in slope, suggesting premature airway closure. CONCLUSION: Our results suggest that a normal FEV(1)/VC ratio does not exclude airway obstruction. A decrease of FEV(1), provided TLC is normal, reflects small airway obstruction.     

Assessing bronchodilator responsiveness in infants using partial expiratory flow-volume curves

Our objective was to compare the effectiveness of maximum forced expiratory flow measured at functional residual capacity (V'maxFRC) and the ratio of flow at 75% of the forced expiratory volume to peak forced expiratory flow (FEF(75)/FEF(peak)) for detecting bronchodilator-related changes in wheezy infants. In 55 infants (mean age, 7.8 +/- 3.1 months) with a history of recurrent wheezing, V'maxFRC and FEF(75)/FEF(peak) were measured at baseline and 15 min following nebulized albuterol. Mean results from 4 baseline and 4 postalbuterol partial expiratory flow-volume curves were compared at baseline and following bronchodilator challenge. The strength (relative effect size) of each measure for assessing change was quantified by dividing the mean of the pre- to postdifferences by the standard deviation of the differences. Mean percent predicted V'maxFRC was 41.3 +/- 34.3% at baseline and 44.4 +/- 34.0% following albuterol. Mean FEF(75)/FEF(peak) was 26.7 +/- 13.4% at baseline and 35.8 +/- 14.3% following albuterol. The mean percent change from baseline [(post-pre)/pre] in percent predicted V'maxFRC was 18.3 +/- 39.3, and for FEF(75)/FEF(peak), it was 44.1 +/- 36.8. The change in FEF(75)/FEF(peak) following albuterol was significantly greater than the change in V'maxFRC (P < 0.0001). The relative effect size for mean percent change from baseline in V'maxFRC was 0.47, and for FEF(75)/FEF(peak), 1.20. Changes in FEF(75)/FEF(peak) appear to differentiate changes in airway function following administration of a bronchodilator better than do changes in V'maxFRC.     

The role of computer games in measuring spirometry in healthy and "asthmatic" preschool children

STUDY OBJECTIVES: To explore the role of respiratory interactive computer games in teaching spirometry to preschool children, and to examine whether the spirometry data achieved are compatible with acceptable criteria for adults and with published data for healthy preschool children, and whether spirometry at this age can assess airway obstruction. DESIGN: Feasibility study. SETTINGS: Community kindergartens around Israel and a tertiary pediatric pulmonary clinic. PARTICIPANTS: Healthy and asthmatic preschool children (age range, 2.0 to 6.5 years). INTERVENTION: Multi-target interactive spirometry games including three targets: full inspiration before expiration, instant forced expiration, and long expiration to residual volume. MEASUREMENTS AND RESULTS: One hundred nine healthy and 157 asthmatic children succeeded in performing adequate spirometry using a multi-target interactive spirometry game. American Thoracic Society (ATS)/European Respiratory Society spirometry criteria for adults for the start of the test, and repeatability were met. Expiration time increased with age (1.3 +/- 0.3 s at 3 years to 1.9 +/- 0.3 s at 6 years [+/- SD], p < 0.05). FVC and flow rates increased with age, while FEV1/FVC decreased. Healthy children had FVC and FEV1 values similar to those of previous preschool studies, but flows were significantly higher (> 1.5 SD for forced expiratory flow at 50% of vital capacity [FEF50] and forced expiratory flow at 75% of vital capacity [FEF75], p < 0.005). The descending part of the flow/volume curve was convex in 2.5- to 3.5-year-old patients, resembling that of infants, while in 5- to 6-year-old patients, there was linear decay. Asthma severity by Global Initiative for Asthma guidelines correlated with longer expiration time (1.7 +/- 0.4 s; p < 0.03) and lower FEF50 (32 to 63%; p < 0.001) compared to healthy children. Bronchodilators improved FEV1 by 10 to 13% and FEF50 by 38 to 56% of baseline. CONCLUSIONS: Interactive respiratory games can facilitate spirometry in very young children, yielding results that conform to most of the ATS criteria established for adults and published data for healthy preschool children. Spirometric indexes correlated with degree of asthma severity.     

The interrupter technique to assess airway responsiveness in children with cystic fibrosis

The aim of this study was to assess the validity of the interrupter technique (Rint) in measuring airway responsiveness in children with cystic fibrosis. Fifty children (aged 6-16 years) with cystic fibrosis performed six Rint measurements followed by three acceptable forced expiratory maneuvers. Each child then inhaled 5 mg of nebulized salbutamol by facemask. After 20 min the Rint and forced expiratory measurements were repeated. In the population as a whole a moderate but significant correlation between inverse Rint and FEV1 values was observed, both before and after inhaled bronchodilator (r=0.71 and 0.72, respectively, P < 0.001). However, when changes in Rint and FEV1 readings following inhaled bronchodilator were examined, no relationship was seen. Indeed, the two methods identified completely different subsets of children as being bronchodilator responsive. These results indicate that although a relationship exists between Rint and FEV1 in the whole population, this is not the case in individual children. Rint and FEV1 reflect different aspects of lung function. It is not appropriate to use Rint as a simple alternative for FEV1 in children with cystic fibrosis when assessing airway responsiveness.     

Should flow-volume loop be monitored in sleep apnea patients treated with continuous positive airway pressure?

Nasal continuous positive airway pressure (nCPAP) has been widely established in the treatment of obstructive sleep apnea syndrome (OSAS). However, only few studies have evaluated long-term effects of this treatment on lung function. This study assesses the effect of nCPAP on lung function parameters and response to bronchodilators in 50 OSAS patients. Spirometry and arterial blood gas measurements were performed before starting nCPAP and after 16.8 +/- 8 months of treatment. Of the 50 study patients (55 +/- 12 years, with an apnea/hypopnea index of 47 +/- 34h(-1)), 15 had asthma, 13 had chronic obstructive pulmonary disease (COPD) and 22 had no obstructive airway disease (NOAD). In the entire population, significant decreases in FEF50 (from 69 +/- 38% to 61 +/- 30%, P < 0.005), FEF25 (from 53 +/- 34% to 46 +/- 28%, P < 0.05) and FEF25-75 (from 65 +/- 33% to 57 +/- 27%, P < 0.005) were observed after treatment. No impairment of lung function was found in COPD and asthmatic patients. In contrast, lung function was changed in the NOAD group where FEF50, FEF25 and FEF25-75 as well as FEV1 and FEV1/VC ratio were significantly reduced. Moreover, bronchial hyperresponsiveness occurred in five of 22 patients of this group. These results suggest that tolerance of nCPAP should be handled by long-term follow-up of flow-volume loops.     

Pulmonary function characteristics in patients with different patterns of methacholine airway hyperresponsiveness

STUDY OBJECTIVES: The American Thoracic Society guidelines for methacholine-induced airway hyperresponsiveness include a > or = 20% reduction in FEV(1) or a > or = 40% reduction in specific airway conductance (sGaw). The objectives of the current study are to assess the concordance between these two criteria and to characterize the pulmonary function and respiratory symptoms of patients with different patterns of methacholine hyperresponsiveness. STUDY DESIGN: A prospective study of 248 consecutive patients referred for methacholine bronchoprovocation testing. RESULTS: Positive methacholine hyperresponsiveness was noted in 179 patients; 139 patients (78%) had a > or = 20% reduction in FEV(1), whereas 40 patients (22%) had a > or = 40% reduction in sGaw alone without a significant change in FEV(1). The former group had the following: (1) higher baseline lung volumes, (2) lower baseline values of FEV(1) and sGaw, (3) forced expiratory flow between 25% and 75% of vital capacity (FEF(25-75))/FVC ratios compared to patients with a reduction in sGaw alone (0.72 +/- 0.26 vs 0.97 +/- 0.28, mean +/- SD; p < 0.0001), and (4) more frequent presence of wheezing and chest tightness (p < 0.05). CONCLUSIONS: First, a substantial number of patients have a reduction in SGaw alone in response to methacholine, and secondly, this response is seen in patients with a higher FEF(25-75)/FVC ratio. Since the FEF(25-75)/FVC ratio is thought to be an index of airway size relative to lung size, we speculate that the larger intrinsic airway size relative to lung size may explain the differences in baseline parameters and patterns of methacholine hyperresponsiveness.     

Home versus hospital intravenous antibiotic therapy for acute pulmonary exacerbations in children with cystic fibrosis

To compare the effectiveness of home versus hospital intravenous (IV) antibiotic therapy for acute pulmonary exacerbations in children with cystic fibrosis (CF). A retrospective chart review was performed of 143 encounters for pulmonary exacerbations in 50 patients with CF. All encounters were categorized into two groups based on location of completion of antibiotic therapy: hospital group completed treatment in hospital (n = 64), home group completed treatment at home (n = 79). Percent change was calculated for forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1), forced expiratory flow rate between 25 percent and 75 percent of vital capacity (FEF(25-75%)), maximum forced expiratory flow (FEF(max)), oxygen saturation (O2 SAT), and weight. Means of percent change (PC) from the beginning to the end of IV antibiotic treatment in outcome variables were compared. Total duration of treatment was compared between the two groups. The two groups had no significant differences at baseline in all outcome variables. Treatment of exacerbations in both groups resulted in significant improvement of lung function, O2 SATS, and weight (P 相似文献   

Assessing the usefulness of outcomes measured in a cystic fibrosis treatment trial

Forced expiratory volume in 1s (FEV(1)) is the usual primary outcome variable in clinical trials in cystic fibrosis (CF). Usually, several secondary outcomes are also measured. We assessed which secondary outcomes are likely to give additional clinically useful information about treatment effects, in order to inform the design of future studies. The study was performed as part of a trial comparing daily rhDNase with alternate day rhDNase and hypertonic saline in CF. The primary outcome was FEV(1). Secondary outcomes were forced vital capacity (FVC), forced expiratory flow at 25-75% of forced vital capacity (FEF(25-75)), number of pulmonary exacerbations, weight gain, quality of life (QOL), and exercise tolerance. The usefulness of each secondary outcome was investigated by assessing if the change in that outcome over the treatment period could be predicted from the primary outcome. Change in FEV(1) correlated with changes in FVC (r(2)=0.76, P=0.001), FEF(25-75) (r(2)=0.64, P=0.001), weight (r(2)=0.08, P=0.001), and change in oxygen saturation with exercise (r(2)=0.08, P=0.001). However, it did not correlate with changes in visual analogue score (VAS) with exercise, QOL, nor with the occurrence of pulmonary exacerbations. Only the outcomes QOL and VAS with exercise actually provided additional information to FEV(1) in this study.     

Digital clubbing and pulmonary function abnormalities in children with lung disease

Digital clubbing and pulmonary function tests were measured in children, adolescents, and adults with chronic lung diseases to determine pulmonary function correlates with a quantitative measure of clubbing. The group had a mean age of 13.8 +/- 6.0 (SD) years, mean PaO2 of 81 +/- 21 mm Hg, and mean FEV1 of 60% +/- 26% predicted. Digital clubbing was diagnosed in 43 cases when the distal phalangeal depth to interphalangeal depth (DPD/IPD) ratio, measured on a finger cast, was greater than or equal to 1 (greater than 3 SD above mean from 85 controls; no history of pulmonary disease; mean age, 14.8 +/- 7.6). The PaO2 of patients with digital clubbing was 69.4 +/- 2.1 (SEM) mm Hg compared with 88.3 +/- 1.3 mm Hg in those without digital clubbing (P less than 0.0001). Digital clubbing was present in 39 of the 84 (46%) hypoxic patients (PaO2 less than or equal to 88) but only four of the 78 (5%) normoxic patients (P less than 0.0001). The DPD/IPD ratio was negatively correlated with PaO2 in subjects with cystic fibrosis and interstitial fibrosis. Weak negative correlations were seen for all other subjects except asthmatics. Overall, the DPD/IPD ratio was significantly correlated with PaO2 (r = -0.53; P less than 0.0001). The DPD/IPD ratio was correlated with other lung function abnormalities (increased RV, decreased FEV1, and FEF25%-75%) only for the subjects with cystic fibrosis. We conclude that digital clubbing is associated with hypoxemia and airway obstruction. The relation is seen most clearly in subjects with cystic fibrosis, possibly reflecting the prolonged duration of hypoxemia. Digital clubbing is rarely seen in normoxic subjects.     

Exercise-induced bronchospasm in children: comparison of FEV1 and FEF25-75% responses

The response of asthmatic children to exercise has usually been evaluated by forced expiratory volume in 1 sec (FEV(1)). We reasoned that other respiratory indexes derived from the forced vital capacity maneuver such as forced expiratory flow between 25-75% of vital capacity (FEF(25-75%)) would add significant information in the evaluation of the relationship between asthma severity and response to exercise. We studied 164 children with intermittent (n = 63), mild persistent (n = 30), moderate persistent (n = 40), and severe persistent asthma (n = 31). Subjects exercised for 6 min on a cycle ergometer at 80% of their maximum heart rate, and spirometry was performed before and 5, 10, and 20 min after exercise. There was good correlation between changes in FEV(1) and FEF(25-75%) after exercise (r = 0.60, P < 0.001 for intermittent asthma and r = 0.80, P < 0.001 for severe persistent asthma). The presence of a fall in both FEV(1) (>/=10%) and in FEF(25-75%) (>/=26%) when compared to a decrease in only one of these two indexes was significantly greater in children with more severe asthma (60.0% for intermittent asthma and 94.4% for severe persistent asthma, P = 0.022). FEF(25-75%) can decrease in response to exercise without changes in FEV(1), mainly in children with mild asthma. In the evaluation of the response to exercise in children with different asthma severities, more than one maximum expiratory flow-volume parameter should be used.     

Do NHLBI lung function criteria apply to children? A cross‐sectional evaluation of childhood asthma at National Jewish Medical and Research Center, 1999–2002

Although National Heart Lung Institute (NHLBI) guidelines categorize asthma severity based on spirometry, few studies have evaluated the utility of these spirometric values in grading asthma severity in children. Asthma is thought to be progressive, but little is known about the loss of lung function in childhood. This study sought to determine the spirometric indices in children from 4-18 years of age. Retrospective cross-sectional analysis was performed on all spirometries done in children at the National Jewish Medical and Research Center from 1999-2002. In total, 2,728 children performed 24,388 measures. The mean +/- SD values for forced vital capacity (FVC), forced expired volume in 1 sec (FEV(1)), FEV(1)/FVC ratio, and forced expiratory flow (FEF)(25-75) were 92.7 +/- 16.2, 92.2 +/- 18.0, 85.3 +/- 9.3, and 78.0 +/- 36.5 percent predicted, respectively. Seventy-seven percent of FEV(1) values were >/= 80%, 18.6% were between 60-80%, and 3.1% were <60% of predicted. FEV(1) was highest in 5-year-old children; it declined thereafter, reaching a nadir at 11 years, followed by a partial recovery from 12-18 years. Expressed in liters, FEV(1) values were lower than expected at every age, with the greatest difference at 18 years. FEV(1)/FVC ratios declined through childhood, suggesting impaired airway but not lung growth in children with asthma. In conclusion, the majority of asthmatic children attending a tertiary care facility had FEV(1) values within normal range. With increasing age, the increase in FEV(1) lags behind that of nonasthmatics, so that by 18 years, maximum FEV(1) is impaired. The NHLBI FEV(1) cutoff values do not appear to accurately stratify pediatric asthma, and no useful FEV(1) cutoff could be generated.     

Comparison of normal infants and infants with cystic fibrosis using forced expiratory flows breathing air and heliox

SUMMARY. The detection of early airway disease in infants with cystic fibrosis (CF) may lead to earlier intervention and an improved prognosis. We hypothesized that the ratio of maximal expiratory flows while breathing a mixture of helium and oxygen (heliox) and air, referred to as density dependence (DD), would identify early airway disease in infants with CF who have normal lung function. We also hypothesized that these infants with CF might be better differentiated from normal infants when the flows breathing heliox are compared instead of room air flows. We evaluated 10 infants with CF and 21 infants without CF and with normal lung function, defined as a forced vital capacity (FVC) and forced expiratory flows between 25-75% of expired volume (FEF(25-75)) of greater than 70% predicted (z-score > -2.0). Full forced expiratory maneuvers by the rapid thoracic compression technique were obtained while breathing room air and then heliox. Flow at 50% and 75% of expired volume (FEF(50), FEF(75)), FEF(25-75), and FVC were calculated from the flow volume curve with patients and control subjects breathing each gas mixture. The ratio of heliox to air flow at FEF(50) and FEF(75) was calculated (DD(50), DD(75)), and the point where the two flow-volume curves crossed (V(iso) V') was also measured. DD parameters did not distinguish the infants with CF from the infants without CF; length-adjusted FEF(50) breathing air was significantly lower in the infants with CF compared to the infants without CF (P < 0.05). Length-adjusted flows breathing heliox did not distinguish the two groups. We conclude that the lower FEF(50) value may reflect early airway obstruction in healthy infants with CF, and that measurements obtained with the less dense gas mixture did not improve detection of airway disease in this age group.