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PubMed1994

Adequacy of control of asthma in a general practice. Is maximum peak expiratory flow rate a valid index of asthma severity?

OBJECTIVES: To evaluate the adequacy of control of asthma in patients attending a general practice; and to examine the validity of peak expiratory flow rate (PEFR) as an index of asthma severity in the context of general practice. DESIGN: Short-term cohort study using indices derived from two weeks of peak flow monitoring to evaluate asthma control. PARTICIPANTS: Known and newly diagnosed asthmatics aged six years or more who presented during the study period for any reason. They were enrolled if baseline forced expiratory volume in one second (FEV1) increased by 10% or more after the administration of nebulised salbutamol. Children under the age of 12 years with no initial response to bronchodilator were included if an exercise test performed on another day was positive. OUTCOME MEASURES: Peak flow criteria for "mild asthma" in the Asthma Management Plan, 1989 (Med J Aust 1989; 151: 650-653) were used as the initial definition of "adequate control". The definition of "adequate control" was modified to variability less than 20% and a minimum PEFR of 50% or more of mean predicted value. RESULTS: There was no association between variability and maximum PEFR, but variability was strongly correlated with minimum PEFR (R = -0.60; P < 0.0005). Asthma was adequately controlled in 68% of the participants. CONCLUSION: Current guidelines with respect to the peak flow indices used in the classification of the severity of asthma need to be re-evaluated and probably changed for application in general practice.

Asthma↗
PubMed2002

[Evaluation of systematic pulmonary function testing for asthma in children aged three to five years].

UNLABELLED: Pulmonary function testing is not usually done in the preschool child, despite the recent data showing early deterioration in airway function in asthma. METHODS: We evaluated feasibility and clinical interest of flow-volume loop by forced expiratory maneuver and measure of airway resistance by interrupter technique (interrupter resistance), before and after inhalation of salbutamol, in 75 children aged three to five years seen in the ambulatory setting for asthma. RESULTS: Feasibility rate (92%) and reproducibility rate (91%) of those techniques were good, so that 84% of the cases could be exploited (63 children of 75). We found few significant associations between clinical parameters and flow-volume loop. We found a significant association between elevated interrupter resistance at basis and night-symptoms (P = 0.03), between diminished interrupter resistance after salbutamol and exercise-symptoms (P = 0.03), symptoms in the ambulatory setting (P = 0.02) and absence of inhaled corticosteroid treatment (P = 0.046). Pulmonary function testing resulted in treatment modification in 14% of cases. CONCLUSION: Our study shows that flow-volume loop and measure of airway resistance by interrupter technique can be done with a good reproducibility in the preschool child. Interrupter resistance appears to be better correlated than flow-volume loop with usually evaluated clinical parameters.

Asthma↗
PubMed1983

Effects of inhaled budesonide alone and in combination with low-dose terbutaline in children with exercise-induced asthma.

The effect of aerosolized terbutaline in a dose of 32.5 micrograms and its placebo, administered in a double-blind fashion, was studied in 14 children with exercise-induced asthma (EIA) before and during a 4-wk treatment period with aerosolized steroid (budesonide, 400 micrograms/day). Effects were assessed from the changes in peak expiratory flow (PEF), forced expiratory volume in one second (FEV1), and forced expiratory flow (FEF25-75) before and after treadmill exercise challenge. Compared with placebo there was a significant improvement in pulmonary function after terbutaline. During budesonide therapy, pulmonary function improved further, but there was no enhancement of the response to terbutaline. Terbutaline alone, budesonide plus placebo, and budesonide plus terbutaline reduced the exercise-induced fall in FEV1 by 30, 51, and 84%, respectively. The effect of budesonide on EIA was delayed during the 4 wk of treatment as compared with the improvement in resting pulmonary function. The present results suggest that 1 to 4 wk of therapy with inhaled corticosteroids decreases the severity of EIA. Further, the combined effect of inhaled corticosteroid and beta-2 agonist on pulmonary function appears to be additive.

Adolescent↗
PubMed1989

An assessment of peak expiratory flow as a surrogate measurement of FEV1 in stable asthmatic children.

We examined the relationship over 24 hours between percent-predicted values (PPV) of peak expiratory flow (PEF) and forced expiratory volume in one second (FEV1) in a group of 23 stable untreated asthmatic children 6 to 17 years of age by means of regression analysis as well as the percentage difference between the PPV of these two measurements. Although the Pearson correlation coefficient between the PPV was consistently high, ranging between 0.854 and 0.892, the assumption that such a finding substantiates the substitution of PEF for FEV1 is called into question. Over 50 percent of the subjects displayed a 10 percent or greater difference in the PPV between the two measurements, regardless of the time of day the two respiratory variable were determined, while over one-third of all subjects evidenced a 20 percent or greater discrepancy between the PPV of the two measures. While, on a group basis, there was no statistically significant difference in the mean percentage difference over 24 hours between the PPV of FEV1, when compared with the corresponding measurement of PEF, reliance on PEF alone in individual subjects may result in a false impression of the patency of the airways in comparison to the FEV1.

Adolescent↗
PubMedDate not supplied

[Forced expiration index, signal and noise].

Although forced expiration measurements are extensively used, there is no general agreement concerning the best way to quantify the data. In this context, it may be of interest to examine indices from the point of view of their signal/noise ratio. The signal depends upon the actual sensitivity of the index to the kind of abnormality which is to be detected. In general, the relationship between signal and degree of abnormality is strongly non-linear, so that sensitivity is not a constant. The noise depends upon the kind of investigation which is made. When a subject is compared to himself (bronchomotor challenge, follow-up studies, etc.), it is mainly due to intraindividual variability. FEV1 is an example of index with a low sensitivity to peripheral airway abnormality, but a high reproducibility, so that its signal/noise ratio for paired measurements is comparatively good. When two groups are to be compared, the relevant noise is interindividual variability. Coefficient of variation of transit times and slope ratios are quite effective in detecting abnormalities in young smokers, probably because their sensitivity to mild peripheral airway disease is large compared to their interindividual variability. It follows that, according to the type of study, as well as to the nature and extent of abnormality, many indices may qualify as being the best.

Forced Expiratory Flow Rates↗
PubMed1982

Respiratory heat and water loss during exercise in patients with asthma. Effect of repeated exercise challenge.

A study was performed to investigate the loss of heat and water from the airways during repeated exercise challenge. Twenty-six asthmatic patients performed 6-8 min exercise on a bicycle ergometer at a workload equivalent to 57-85% of their predicted maximum working capacity. Sixteen patients performed two exercise tests separated by 40-52 min. Exercise-induced asthma (EIA) occurred in all patients after initial challenge but eight had significant protection from EIA following a second challenge. This protection was not associated with a reduction in heat and water loss from the airways during exercise. A further 10 patients performed two exercise tests 2-3 h apart. The second test was preceded by the administration of 200 microgram salbutamol aerosol. There was no significant difference between the two tests in loss of heat and water from the airways during exercise. Exercise-induced asthma occurred in all patients after the initial challenge but was inhibited by the salbutamol after the second challenge. Thus the reduction in EIA as a result of a refractory period or in response to aerosol salbutamol is not due to changes in heat and water loss from the airways during exercise.

Adolescent↗
PubMed1987

Intravenous methylprednisolone efficacy in status asthmaticus of childhood.

Forty-nine nonsteroid-dependent children hospitalized with status asthmaticus were randomized to receive IV placebo or methylprednisolone treatment (1 mg/kg every six hours). All patients received nebulized isoetharine inhalations and continuous IV aminophylline infusion. Twenty-four hours after admission, the methylprednisolone-treated patients demonstrated a greater rate of improvement in their clinical scoring index than did placebo-treated children. However, the duration of hospital stay was not significantly shortened. Twenty-eight of the patients performed serial bedside spirometry at 0, 12, 24, and 36 hours after admission. The methyl-prednisolone-treated patients experienced a more rapid recovery from peripheral airway obstruction as measured by forced expiratory flow rate during 25% to 75% of forced vital capacity (FEF25-75). The magnitude and rate of improvement in FEF25-75 was significantly greater at 36 hours (P less than .05) and independent of changes in peak expiratory flow rate, forced vital capacity, or forced expiratory volume in the first second of forced vital capacity. Placebo-treated patients had a higher incidence of asthma relapse within 4 weeks of discharge (eight v two relapses, P less than .05). Findings of this study indicate that IV corticosteroid therapy is beneficial in treating pediatric status asthmaticus.

Adolescent↗
PubMed1975

Evaluation of bronchial drainage in patients with cystic fibrosis.

Examined in this study are the results of six tests of pulmonary function immediately preceding and following bronchial drainage in twenty-six patients with cystic fibrosis. Highly significant increases averaging 5.67, 4.13, 13.47, and 6.98 percent occurred in peak expiratory flow rate, forced vital capacity, expiratory reserve volume, and inspiratory capacity respectively. Significant increases in peak expiratory flow rate, forced vital capacity, and inspiratory capacity were observed in a subgroup of six of the above patients who had evidence of bronchospasm. The authors conclude that bronchial drainage will produce significant increases in routine pulmonary function values. The results suggest that this treatment is most effective in clearing the larger, more proximal, airways and is of benefit even in the presence of clinical bronchospasm.

Adolescent↗
PubMed1986

In vivo human tracheal pressure-area curves using computerized tomographic scans. Correlation with maximal expiratory flow rates.

In order to develop a simple technique to measure in vivo pressure-area (P-A) curves of the extrathoracic trachea in humans, we studied 14 normal male subjects. Valsalva and Mueller maneuvers were performed at FRC, and tracheal cross-sectional area (TXSA) was measured using computed tomography. Extrathoracic tracheal transmural pressure (TMP) was obtained as airway opening minus atmospheric pressure (Pat). Tracheal "compliance" (TC) was measured on the "inflation" limb of the P-A curve. Tracheal compliance was not a significant predictor of maximal expiratory flow rates, and TXSA at zero TMP was a significant predictor of peak expiratory flow rate but not of FEV1 or Vmax50. P-A curves showed an unexpected configuration characterized by a plateau or an increase in TXSA with TMP lower than -15 cm H2O. P-A curves obtained in 5 subjects using extrathoracic esophageal pressure as tracheal external pressure instead of atmospheric pressure did not show a plateau or an increase in TXSA with Mueller maneuvers. In these 5 subjects, TC using esophageal pressure rather than Pat did not aid in the prediction of flow. We conclude that extrathoracic tracheal external pressure is not Pat because this pressure is probably affected by transmission of pleural pressure to the cervical interstitial tissue as well as by the contraction of cervical accessory inspiratory muscles. Therefore, true tracheal compliance cannot be simply measured since it requires placement of an esophageal balloon.

Adult↗
PubMed2004

Expiratory effort enhancement and peak expiratory flow in humans.

Peak expiratory flow (PEF) has previously been considered an effort-dependent, non flow-limited parameter that is constrained by the force-velocity relationship of the respiratory muscles. It has also been assumed that, if the muscles were able to augment the expiratory pressure, the PEF would increase. We tested the validity of this notion in normal volunteers who were able to enhance their expiratory pressure with maneuvers utilizing the stretch-shortening cycle (greater force when contractions were immediately preceded by eccentric contractions). Five healthy volunteers [35 (2) years] performed two successive maximal expiratory flow-volume maneuvers (MEFV) in rapid sequence. MEFV1 was a standard maneuver, whereas MEFV2 included a forceful inspiration to total lung capacity; a strategy designed to augment expiratory pressure via the stretch-shortening cycle. Neither maneuver included a post-inspiratory pause. We measured PEF, esophageal pressure (P(es)), and the electromyographic activity of the abdominal muscles. Compared to MEFV1, MEFV2 produced greater activation of the abdominal muscles during inspiration (eccentric contraction), greater peak expiratory P(es), greater rate of rise of P(es), shorter time to PEF, but similar PEF. Our findings directly demonstrate the inability of the augmented expiratory effort to increase PEF and thus support the notion that PEF is determined by a flow-limiting mechanism and not by the velocity of muscle shortening.

Adult↗
PubMed1982

Comparison of peak expiratory flow and FEV1 admission criteria for acute bronchial asthma.

One hundred nine episodes of acute bronchial asthma were studied utilizing PEFR and FEV1 measurements to determine objective patient disposition criteria. Of patients with both a pre-treatment PEFR less than 100 L/min, and a post-treatment value less than 300 L/min, 92% required admission or had an unsuccessful OPD course. Of patients with a pre-treatment PEFR less than 100 L/min and an improvement less than 60 L/min after initial terbutaline, 85% were admitted or had problems after discharge. PEFR correlated well with FEV1 at all stages of treatment.

Acute Disease↗
PubMed1992

Evaluation of mean transit time in children as an indicator of airways obstruction.

Mean transit time was evaluated as a test of pulmonary function in normal and asthmatic children. It was found to be independent of body size and negatively correlated with PEFR, FEV1 and FVC in normal children. Mean transit time was less sensitive in detecting the effects of bronchodilator therapy in asthmatic children than other simpler tests of lung function. The range of normal was so wide that there was no clear demarcation between normal and abnormal. The degree of overlap makes isolated tests of mean transit time of little diagnostic value. It is therefore concluded that mean transit time though it theoretically offers the attractive advantage of being a sensitive indicator of both large and small airways obstruction, is unlikely to play a major part in the routine evaluation of lung function in asthmatic children.

Adolescent↗
PubMed1980

Usefulness of forced expiration slope ratios for detecting mild airway abnormalities.

To assess their value for early recognition of airway abnormalities, forced expiration slope ratios as recently defined by Mead, were measured at 5 lung volumes in 114 healthy nonsmokers and in 76 cigarette smokers. In healthy nonsmokers, slope ratios were independent of sex and body height, but were significantly correlated with age. They tended to be higher at low lung volume, particularly in older subjects. In male smokers with a tobacco consumption of less than 5 pack-years, slope ratios were increased at both ends of the volume range, suggesting nonhomogeneous lung emptying and peripheral airway obstruction. With increasing tobacco consumption, slope ratios tended to return to normal values at low lung volume, perhaps because of airway closure. In female smokers, slope ratios were decreased at high lung volume and increased at low lung volume, suggesting that both central and peripheral airways were abnormal. Mead's analysis appeared to be a useful tool for discussing the data in terms of functional abnormalities. However, because of their large variability, slope ratios were not as successful as transit time indices for recognizing abnormal subjects.

Adult↗
PubMed1985

Increase in tracheal size with age. Implications for maximal expiratory flow.

Because mechanical properties of central airways play an important role in determining maximal expiratory flow, we examined how tracheal size and maximal expiratory flow changed with age in 50 asymptomatic men, 19 to 61 yr of age, who were lifelong nonsmokers. Cross-sectional area (X-SA) of the intrathoracic trachea was estimated from posteroanterior and lateral chest radiographs taken at full inflation. Maximal expiratory flow-volume curves and spirometry were measured by standard techniques. Tracheal X-SA averaged 2.81 cm2 (SD, 0.38) at mean age 21.1 yr and 3.22 cm2 (SD,0.41) at mean age 52.5 yr, and correlated with peak expiratory flow (PEF) (r = 0.522, p less than 0.001) and FEV1 (r = 0.437, p = less than 0.01) (both expressed as percent predicted values based on age and height). These relationships were weaker than previously described in young men. The results suggest that with increasing age, large airways lose elastic recoil, as previously described for the air spaces. Aging changes in the airways may offset the unfavorable effects of loss of lung recoil and account for the relatively good preservation of PEF and the lack of rise in airways resistance with increasing age.

Adult↗
PubMed1990

[Standardization of forced spirometry. Analysis of the basal pulmonary function (PEF, FEF2575, FEF50) in a selected group of children].

This is a study of the ventilatory function (FEF2575, FEF50, PEF) by dry spirometer Vitalograph in 1,566 children of both sexes with ages ranging from 7 to 14 years; 1,156 children (73.6%) were selected as reference population. Height was the biometric parameter with the greatest correlation to the functional variables studied in both sexes, except to PEF in females. Significant differences were observed in functional variables between male and female subjects. Multiple and simple linear regression equations and percentiles tables for each sex are presented.

Adolescent↗