Malnutrition and peak expiratory flow rate

In order to assess the effects of malnutrition on the growth of lung function, 376 Indian schoolchildren aged 6-12 yrs were studied. Peak expiratory flow rate (PEFR) was measured with a Wright peak flow meter, and nutritional status assessed by calculation of the percentage predicted height for age (HFA) and weight for height (WFH) using Harvard standards. After standardizing for height and sex, the PEFR of 30 wasted children (WFH below 80%) was significantly reduced (p less than 0.01), but that of 135 stunted children (HFA below 90%) was higher than average (p less than 0.05). It is concluded that current malnutrition has a negative effect on PEFR, possibly due to impaired muscle function, but that past or chronic malnutrition affects growth of lung function less than it affects somatic growth.     

Assessment of diurnal variability of peak expiratory flow in stable asthmatics.

Five daily readings of peak expiratory flow (PEF) were obtained for three days on 100 patients with chronic stable asthma. The variability of PEF was calculated as the amplitude percent mean (A%M) from the readings obtained on the third day, and compared to previously reported data from 152 healthy Indian adults. Patients with severe asthma exhibited significantly higher A%M than patients with both mild and moderate asthma (p < 0.05), but there was considerable overlap across disease categories. The area under the receiver operating characteristic curve plotted to assess the performance of PEF variability as a discriminator in diagnosing asthma was 0.826, with best discrimination at a value of 12.5 (sensitivity 0.640, specificity 0.941). Using a cut-off value of 16.5 (as proposed earlier by us) improved specificity to 0.987 but reduced sensitivity to 0.510. Using a traditional cut-off of 20, specificity remained almost unchanged (0.993), but sensitivity dropped further to 0.440. Thus A%M>16.5 is a useful marker of bronchial asthma in epidemiological studies in India. However, its use in population screening, clinical diagnosis, or in the assessment of the severity of asthma in individual patients has serious limitations because of poor sensitivity.     

The effect of dialyzer reuse on peak expiratory flow rate

Peak expiratory flow rates were measured during routine haemodialysis in 18 patients with chronic renal failure who were in receipt of thrice weekly haemodialysis treatment, using both a new cuprophan dialyzer and then the same dialyzer after reprocessing. Acetate buffered dialysate was used on both occasions. The peak expiratory flow rates fell by 10 +/- 0.3%, mean +/- sem, during the first hour of treatment with the new dialyzer, and in seven patients (39%) the fall was greater than 15%. Whereas the reduction in peak expiratory flow rates was significantly less with reuse, 4 +/- 0.1% (P less than 0.5). Similarly, the fall in arterial oxygen tension was also reduced on reuse from 28 +/- 1.2% to 14 +/- 1.3% at 30 min (P less than 0.05) and from 30 +/- 1.4% to 18 +/- 3.1% (P less than 0.05) at 60 min of dialysis. There was also a reduction in the fall in the peripheral platelet count at 30 min of dialysis from 14 +/- 0.8% to 9 +/- 0.4% with reuse (P less than 0.05). However, there was no change in dialysis associated leukopenia with reuse of the dialyzer membrane. These results suggest that reprocessing the dialyzer membrane alters its biocompatibility characteristics resulting in an improvement in biocompatibility and further supports the role of inflammatory cell mediator release in the pathogenesis of dialysis associated hypoxaemia and pulmonary dysfunction during the first hour of dialysis treatment.     

Reproducibility of peak expiratory flow rate measured at home

In 8 stable patients with chronic asthma, the reproducibility of peak expiratory flow rate (PEFR) measured and recorded 4 times per day for longer than 1 month at home and at work was assessed. Average %PEFRs of individuals through the periods observed were higher than 80%, and coefficients of variation were less than 10% regardless of the time measured. This suggested that a decrease in %PEFR more than 10% reflects early phase of deterioration of airways narrowing and frequent measurement of PEFR is essential for long-term management and for self-assessment of chronic asthma.     

Diurnal variation of peak expiratory flow rate in asthmatic children

A diurnal variation in peak expiratory flow rate (PEFR) has been described in normal and asthmatic adults. This variation has been apparent in data reported from children, but the rhythm has not been characterized. Sixty-eight asthmatic children recorded PEFR three times a day for 4 weeks at home. Data were analyzed using paired t-tests, cosinor analysis, and spectral analysis. Fifty subjects (73.5%) had significant diurnal variations in PEFR on paired t-tests. Mean amplitude, derived from cosinor analysis, was 22.6% (SD = 13.2%) of mean PEFR. The trough of the PEFR rhythm occurred at 0345 hours for the group. Spectral analysis confirmed that the major component of the variation in PEFR was due to a rhythm with a period of 24 hours. The amplitude of the diurnal variation was not related to the subjects' age, sex, or medications taken but was inversely related to mean lung function (expressed as percentage predicted).     

The distribution of peak expiratory flow variability in a population sample

Although serial peak expiratory flow (PEF) measurements are often used to assess the variability of airflow obstruction, the range of values to be expected in the general population has never been defined, nor is there any consensus as to how PEF variability should be expressed. We have compared PEF recordings made by 121 subjects selected at random from the population of a small town (Group A) and 221 subjects selected because of wheeze in the last year (Group B). Subjects were asked to record PEF every 2 h during waking hours for 7 days using a mini-Wright peak flow meter. Seven indices of PEF variability were derived for each subject and the range for each index determined. All indices showed a positively skewed distribution in the random sample. Two variability indices, standard deviation percent mean and amplitude percent mean, provided the greatest separation between subjects with both a diagnosis of asthma and wheeze in the last year and subjects with neither feature and also provided the highest intra-class correlation coefficients. We conclude that amplitude percent mean and standard deviation percent mean provide the best means of expressing PEF variability for epidemiological purposes, but that amplitude percent mean is more easily derived and appears to be the index of choice. PEF variability has a continuous distribution in the general population and no clear-cut division between asthmatic and nonasthmatic subjects can be defined.     

Comparison of bronchial reactivity and peak expiratory flow variability measurements for epidemiologic studies.

Inclusion of a standardized measurement of airway function is important in epidemiologic studies of asthma to facilitate comparison between different studies. Bronchial reactivity is widely used in such studies, but measurement of peak expiratory flow (PEF) variability has a number of potential advantages. We compared PEF variability with methacholine challenge tests in a community population sample. Subjects selected at random (n = 95) and on the basis of having experienced wheeze in the last 12 months (n = 130) performed a challenge test with methacholine to a maximum dose of 12.25 mumol and made serial PEF recordings every 2 h for a week. PEF variability was expressed as mean daily maximum amplitude as a percentage of the mean (amplitude % mean). Increased bronchial reactivity and PEF variability were arbitrarily defined as values above the 10th or below the 90th percentiles in the random sample. A measurement of amplitude % mean was available from all 225 subjects, whereas only 115 (51%) had a measurable PD20 methacholine. PD20 measurements correlated weakly but significantly with amplitude % mean (r = -0.44, p less than 0.001). Increased values of both bronchial reactivity and PEF variability were related to the presence of respiratory symptoms in the week before testing. Asthma was more strongly related to increased bronchial reactivity than to PEF variability. Both measurements showed a strong association with atopy and the intraclass correlation coefficients (ratio of between-subject to total variance) were similar for both.(ABSTRACT TRUNCATED AT 250 WORDS)     

The concentration of hydrogen peroxide in exhaled air depends on expiratory flow rate.

Hydrogen peroxide (H2O2) is known to be detectable in exhaled air. The present study aimed to determine whether the concentration of exhaled H2O2 depends on expiratory flow rate in order to make inferences on the site of its production within the lung. Breath condensate was collected in cooled Teflon tubes, at three different expiratorv flow rates, in 15 healthy or mild asthmatic subjects. Tests were repeated 2-5 times to assess reproducibility. Mean+/-SEM concentrations of H2O2 at flow rates of 140, 69 and 48 mL.s(-1) were 0.12+/-0.02, 0.19+/-0.02 and 0.32+/-0.03 microM, respectively. These values differed significantly from each other (p<0.001). For comparison, average coefficients of variability within repeated measurements at each of the three flow rates were 68, 62 and 82%, respectively. These data demonstrate that the concentration of exhaled hydrogen peroxide depends on expiratory flow rate. Since flow dependence is an indicator of production within the airways, this result suggests that, to a large extent, the exhaled hydrogen peroxide originates within the airways. However, even under strictly controlled conditions, a high degree of variability persists, which may limit the usefulness of exhaled hydrogen peroxide as a marker of airway inflammation.     

Measurement characteristics of peak expiratory flow

STUDY OBJECTIVES: To evaluate features of the peak expiratory flow (PEF) test protocol, and to characterize patterns of reproducibility in multiple PEF measurements. DESIGN: Cross-sectional study. SETTING: University population. PARTICIPANTS: Two hundred twenty-three healthy adults. INTERVENTIONS: Participants recorded five PEF measurements in each of five sessions per day for 1 week. Measurements and results: Patterns of within-session variability were characterized using a reproducibility criterion based on a large percentage difference between best trials and evidence of a maneuver-induced bronchospasm (MIB) indicated by successive drops of PEF values in a session. Although the maximum PEF value in a session occurred on the fourth or fifth trial 32% of the time, the change in PEF values was small. Supervision was associated with small improvements in level and reproducibility. Using a cutoff of 5% for defining reproducibility, 15% of all sessions were not reproducible. When averaged over each subject, 9% of the cohort had a mean difference > 5%. Overall, MIB was unusual and observed in 8% of all test sessions; however, MIB was more common among asthmatics and subjects with wheeze, atopy, or allergies than subjects without. By contrast, poor reproducibility was more common among smokers and subjects with cough and phlegm. CONCLUSIONS: These results illustrate that it may be unnecessary to supervise all sessions or collect more than three efforts. Results also suggest that reproducibility reflects smoking-related abnormalities, whereas MIB may reflect airways hyperresponsiveness.     

Reference values for peak expiratory flow rate in adults of African descent

Substantial racial differences in the values of peak expiratory flow (PEF) rate have been noted by several workers in the past. It has also been noted that applying prediction formulae derived from a Caucasian population overestimated the PEF values in Black Africans by 12%-15%. Yet reference values used up until the present, even among Black populations, are based on such formulae. This study provides new reference values for use in the Black population. They were obtained by using curvilinear formulae derived from the study of 1009 normal adult Nigerians (668 men and 341 women) between the ages of 15 years and 82 years, living and/or working in Port Harcourt, Nigeria and its hinterland.     

Environmental exposure to air pollution and allergens and peak flow changes.

Laboratory-based studies have shown that ozone and nitrogen dioxide can potentiate the effect of allergen in sensitized asthmatic subjects, but it is not known whether this interaction is important under natural exposure conditions. Thirty-five subjects with clinical diagnoses of asthma or chronic obstructive pulmonary disease and with a provocative dose causing a 20% fall in forced expiratory volume in one second methacholine <12.25 micromol (using the Yan method) kept peak expiratory flow (PEF) records for a 4-week period during late summer, with concurrent measurement of spore and pollen counts and pollution levels. Multiple regression analysis was then used to determine the effect on PEF of aeroallergen, and of the interaction between aeroallergen and pollutant levels. A statistically significant interaction was demonstrated between total spore count and ozone, but not nitrogen dioxide. Mean PEF fell in association with increasing spore count (same-day and 24-h lag level) and PEF variability increased with increasing spore count (24-h lag level only); both changes were greater the higher the prior ozone level. These results suggest that ozone can potentiate the effect of aeroallergens in subjects with bronchial hyperreactivity under natural exposure conditions. However, the effect was small, and the clinical significance of the interaction requires further study.     

Assessing symptoms and peak expiratory flow rate as predictors of asthma exacerbations

OBJECTIVE: To investigate peak expiratory flow rate (PEFR) and quality of life scores for their ability to predict exacerbations of asthma. PARTICIPANTS AND METHODS: We identified adults who received oral or inhaled asthma medications from 36 community drugstores. We administered the McMaster Asthma Quality of Life Questionnaire (AQLQ) and measured PEFR, defining "red zone" (highest risk) as a PEFR < 50% of each patient's expected value based on gender, age, and height. We identified asthma exacerbations (breathing-related emergency department visits and hospitalizations) within 4 and 12 months after enrollment and used proportional hazards regression to assess the ability of PEFR and AQLQ scores to predict exacerbations, controlling for clinical and demographic factors. RESULTS: A red zone PEFR was a significant univariable predictor of exacerbations within 12 months (hazard ratio [HR], 1.8; 95% confidence interval [CI], 1.1 to 3.0; P =.027). However, neither a red zone PEFR, the raw PEFR, or percent of predicted maximal PEFR were significantly predictive when controlling for AQLQ scores, clinical characteristics, or demographic data (P >.2). However, the 4 subscales of the AQLQ were each significant univariable and multivariable predictors of asthma exacerbations. For example, the overall AQLQ scale had a multivariable HR of 0.63 (95% CI, 0.46 to 0.87; P =.005) for exacerbations occurring within 4 months and 0.66 (95% CI, 0.54 to 0.82; P <.001) within 12 months. CONCLUSIONS: PEFR added no predictive information to that contained in AQLQ scores and clinical and demographic data. These results support the National Institutes of Health asthma guidelines' recommendation for routinely assessing symptoms but not PEFR.     

Inter-session reproducibility of peak expiratory flow with standardized expiratory maneuvers

BACKGROUND: In adults performing forceful expiratory maneuvers, the length of post-inspiratory pause prior to forced expiration may influence the subsequently measured peak expiratory flow (PEF) and increase its variability. We investigated the effects of two different lengths of breath-hold at total lung capacity (TLC) on the short-term reproducibility of PEF in healthy volunteers. METHODS: Forty-six healthy volunteers (age 34.6+/-8.5; 23 men) performed a series of maximal forceful expirations in two different test sessions, separated by approximately 2 weeks. In each test-session, PEF was measured with two different types of maneuvers. One maneuver (P) included a brief (<2s) post-inspiratory pause at TLC prior to forced expiration, whereas the second maneuver (NP) included no pause at TLC. The speed of inspiration to TLC was fast and similar for both maneuvers. In a given test session, all volunteers performed four efforts for each type of maneuver. The highest PEF for each maneuver was used for analysis. The Bland-Altman statistical analysis was used to determine inter-session reproducibility of PEF. RESULTS: Within-maneuver analysis of the between-test session reproducibility of PEF showed that neither maneuver systematically biased the measured PEF (mean difference 0.02L/s for the P and 0.17L/s for the NP maneuver). Inter-maneuver between-test session analysis similarly showed that neither maneuver introduced a systematic bias in the maximal PEF (mean difference ranged from -0.15 to -0.01L/s). The limits of agreement were comparable in all maneuver-pair analyses. CONCLUSIONS: Forceful expiratory maneuvers with or without a brief (<2s) pause at TLC produce comparable PEF values in test-retest sessions.     

Comparison of peak expiratory flow variability between workers with work-exacerbated asthma and occupational asthma

BACKGROUND: Peak expiratory flow (PEF) monitoring is frequently used to diagnose occupational asthma (OA). The variability of PEF between periods at work and away from work has not been described in workers with work-exacerbated asthma (WEA). We sought to assess and compare the diurnal variability of PEF during periods at and away from work between subjects with OA and WEA. METHODS: Workers referred for work-related asthma underwent PEF monitoring for 2 weeks at and away from work. The diagnostic of OA or WEA was subsequently made according to the respective positivity or negativity of the specific inhalation challenges. PEF mean diurnal variability was calculated during periods at and away from work. PEF graphs were also interpreted using direct visual analysis by five observers and using a computer program (Oasys-2, Expert System ) [available at: http://www.occupationalasthma.com]. RESULTS: Thirty-four subjects were investigated (WEA, n = 15; OA, n = 19). There was a greater variability of PEF at work than away from work in both OA (19.8 +/- 8.7% vs 10.7 +/- 6.3%, p < 0.001) and WEA (14.2 +/- 4.8% vs 10.6 +/- 5.6%, p = 0.02). However, the magnitude of the variability was higher in OA than in WEA (p = 0.02). The visual interpretation of PEF or the Oasys-2 program failed to distinguish WEA from OA. CONCLUSION: Although workers with OA showed a higher PEF variability than workers with WEA when at work, clinicians were unable to reliably differentiate OA from WEA using the visual interpretation of PEF graphs or the computerized analysis.