What is the role of tests of lung function in the management of infants with lung disease?

This review considers whether there is a role for lung function tests in the clinical management of infants with lung disease. The purpose of testing lung function in older subjects, the tests available for infants, and the practical problems of testing lung function in infants are considered. After reviewing all the facts, we suggest that there are four situations in which lung function testing should be recommended for infants, as follows: (1) the infant who presents with unexplained tachypnea, hypoxia, cough, or respiratory distress in whom a definitive diagnosis is not apparent from physical examination and other, less difficult investigations; (2) the infant with severe, continuous, chronic obstructive lung disease who does not respond to an adequate clinical trial of combined corticosteroid and bronchodilator therapy; (3) the infant with known respiratory disease of uncertain severity in whom there is need to justify management decisions; and (4) research and development. A review of 62 recent publications to determine how lung function tests are being used at the present time showed that they are being used overwhelmingly for research. The role of lung function testing in the clinical management of infants has not been established, and research is needed to clarify this situation. We suggest that such studies should explore the role of lung function tests in infants with specific symptoms, signs, or diagnoses, taking into account information from other types of investigation and the cost/benefit/risk ratios.

Exhaled nitric oxide and asthma in young children

Exhaled nitric oxide (eNO) has been used to diagnose asthma in adults and children using either the slow vital capacity method (SVCm) or, in younger children, the tidal breathing method (TBm). Adenosine 5'-monophosphate (AMP) challenge also has been found to be a sensitive and specific test for the diagnosis of asthma. In the present study, we used the AMP provocation concentration that caused wheezing (PCW) to confirm the diagnosis of asthma (PCW < or = 200 mg/mL). We studied 36 children (2-7 years) with mild intermittent asthma, 13 children (3-7 years) with moderate persistent asthma treated with inhaled steroids, 20 nonasthmatic children (2-7 years) with chronic cough and recurrent pneumonia, and 15 healthy children (4-6 years). Expired gas was collected in collection bags by the TBm, and eNO was measured. We evaluated the efficacy of eNO values in diagnosing asthma. The mean eNO level of the mild intermittent asthmatic children (5.6 +/- 0.4 ppb) not receiving inhaled corticosteroids was significantly higher (ANOVA P < 0.0001) than that of the moderate persistent asthmatics who were treated with inhaled steroids, the nonasthmatic children with chronic cough, and the group of healthy children (3.7 +/- 0.6 ppb, P < 0.05; 3.2 +/- 0.3 ppb, P < 0.001; 2.2 +/- 0.2 ppb, P < 0.001, respectively). The points of intersection for sensitivity and specificity curves of eNO to differentiate mild intermittent asthmatics from nonasthmatic children with chronic cough and from healthy children were 77% and 88% for eNO values of 3.8 ppb and 2.9 ppb, respectively. We conclude that eNO collected by the TBm can differentiate steroid-naive young children with intermittent asthma from healthy children, from nonasthmatic children with chronic cough, and from asthmatic children treated with inhaled steroids.

Can peak expiratory flow measurements estimate small airway function in asthmatic children?

BACKGROUND

Asthma is characterized in part by small airways dysfunction. Peak expiratory flow (PEF) measurement has been suggested by all international guidelines as an important tool in asthma management. The correlation between PEF and FEV(1) but not with forced expired flow at 50% of vital capacity (FEF(50)) is well-established.

STUDY OBJECTIVE

To determine the value of PEF measurement as a predictor of small airways status as expressed by FEF(50).

DESIGN

Analysis of the association between PEF and FEF(50) in single and multiple determinations.

PATIENTS

One hundred eleven asthmatic children (mean age, 11.8 years), grouped in the following way according to FEV(1) values: within normal range (n = 46); mildly reduced FEV(1) (n = 44); and moderately/severely reduced FEV(1) (n = 21).

RESULTS

Overall, FEF(50) and PEF were significantly correlated (r = 0.49; p < 0.0001). However, in 41.6% of the patients, the actual FEF(50) differed by > 20% from the calculated FEF(50). PEF has a high specificity (82.4%) but a poor sensitivity (51.7%) to detect FEF(50) status. PEF was better able to reflect abnormal FEF(50) in the patients with more severe asthma and to reflect normal FEF(50) values in the healthier patients. In patients with multiple measurements (n = 40), the correlation between FEF(50) and PEF was significantly better than that derived from a single determination (multiple measurements r = 0.77; single measurement, r = 0.49).

CONCLUSIONS

Although PEF is an important tool in the management of asthmatic patients, it does not yield a complete picture because it is not sensitive in detecting small airways function. It is best used at home along with regular spirometry measurements at the clinic. PEF may serve as a better index of changes in small airways function once an individual regression is determined.

Plethysmographic measurements of lung volume and airway resistance. ERS/ATS Task Force on Standards for Infant Respiratory Function Testing. European Respiratory Society/ American Thoracic Society

Functional residual capacity (FRC) is the only static lung volume that can be measured routinely in infants. It is important for interpreting volume-dependent pulmonary mechanics such as airway resistance or forced expiratory flows, and for defining normal lung growth. Despite requiring complex equipment, the plethysmographic method for measuring FRC is very simple to apply and, unlike the gas dilution techniques, enables repeat measures of lung volume to be obtained within a few minutes. This method has the further advantage that with suitable adaptations to the equipment, simultaneous measurements of airway resistance can also be obtained. The aim of this paper is to provide recommendations pertaining to equipment requirements, study procedures and reporting of data for plethysmographic measurements in infants. Implementation of these recommendations should help to ensure that such measurements are as accurate as possible and that meaningful comparisons can be made between data collected in different centres or with different equipment. These guidelines cover numerous aspects including terminology and definitions, equipment, data acquisition and analysis and reporting of results and also highlight areas where further research is needed before consensus can be reached.

Methacholine inhalation challenge: a shorter, cheaper and safe approach

Increased nonspecific bronchial hyperresponsiveness to pharmacological agents such as histamine or methacholine (MCh) is a hallmark of asthma. The measurement of airway reactivity is quite sensitive but testing is tedious, and time and money consuming. The present aim was, therefore, to design the shortest possible, yet safe inhalation challenge protocol applicable for a lung function referral centre. All records of studies performed in our institution during 1996 were analyzed retrospectively with a baseline ratio (bl) of forced expiratory volume in one second/forced vital capacity (FEV1/FVC) > or = 0.7 (n=449). It was questioned what the initial dose should be, and whether some inhalation steps could have been skipped without losing pertinent information and/or causing an adverse response (a fall in FEV1 >40%). When unavailable, provocative dose causing a 20% fall in FEV1 (PD20) values were obtained by linear inter- or extrapolation of the existing data. The present study showed that three-fold concentration steps could have been employed with minimal change in outcome. Only 151449 patients (3.3%) would have experienced a severe response. Five subjects (of 169, 3.0%) with FEV1/FVCbl 0.7-0.8 reacted to inhalation up to 0.073 micromol. Four subjects (of 280, 1.4%) with FEV1/ FVCbl> or =0.8 reacted to inhalation up to 0.219 micromol. The authors suggest that: 1) an initial dose of 0.219 micromol (initial concentration= 0.21 mg.mL(-1)) may be used when the baseline ratio of forced expiratory volume in one second to forced vital capacity > or =0.8 and 0.073 micromol (initial concentration=0.07 mg.mL(-1)) when the baseline ratio is <0.8; 2) a tripling dose protocol is easier to perform, cheaper and 30.2%, faster, yet just as safe; and 3) other abbreviated protocols used in epidemiologic settings may not be applicable in a referral centre setting.

Urbanization and the risk of asthma among schoolchildren in the Palestinian Authority

The aim of the present survey was to compare the prevalence of symptoms suggestive of asthma in boys and girls aged 6-7 and 13-14 years in a rural and an urban area in the West Bank. For this purpose, the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire was issued to 970 schoolchildren in the two regions. The response rate was 92.2%. The prevalences of ever wheezing in the urban and rural areas were 16.4% and 12.0%, respectively (p < 0.05); the 12-month prevalences of wheezing were 10.5% and 5.5%, respectively (p < 0.05); the prevalences of more severe wheeze were 4.5% and 1.7%, respectively (p < 0.05); and prevalences of diagnosed asthma were 4.2% and 2.8%, respectively (p = NS). When controlling for age by stratification, the significant association between prevalence rates and place of residence persisted in the 13-14-year age group. These results also show that the prevalence of asthma among Palestinian children is moderately high in comparison with that reported from developing countries, but lower than those reported from Western countries. This survey, the first epidemiological survey on asthma in the West Bank, demonstrates a marked difference between urban and rural areas. The findings emphasize the need for further study of the environmental determinants of the disease among Palestinian children.

Cut-off points defining normal and asthmatic bronchial reactivity to exercise and inhalation challenges in children and young adults

An analysis was undertaken to determine the optimal cut-off separating an asthmatic from a normal response to a bronchial provocation challenge by exercise and the inhalation of methacholine or histamine in children and young adults. Data were extracted, after appropriate correction, from published studies available in Medline of large random populations that complied with preset criteria of suitability for analysis, and the distribution of bronchial reactivity in the healthy population for exercise and inhalation challenges were derived. Studies on the response to exercise and methacholine inhalation in 232 young asthmatics of varying severity were carried out by the authors and the distribution of bronchial reactivity of a young asthmatic population obtained. Comparisons of the sensitivity and specificity of the challenges were aided by the construction of receiver operating characteristic curves. The optimal cut-off point of the fall in forced expiratory volume in one second (FEV1) after exercise was 13%, with a sensitivity (power) of 63% and specificity of 94%. For inhalation challenges, the optimal cut-off point for the dose of methacholine or histamine causing a 20% fall in FEV1 was 6.6 micromol, with a sensitivity of 92% and a specificity of 89%. The cut-off values were not materially affected by the severity of the asthma and provide objective data with which to evaluate the results of bronchial provocation challenges in children and young adults.

Rehabilitation of hypoxemic patients with COPD at low altitude at the Dead Sea, the lowest place on earth

BACKGROUND

In patients with COPD, oxygen therapy has been shown to improve exercise capacity and survival. Increase in barometric pressure at low altitude can serve as a simple way to improve arterial oxygenation in hypoxemic patients. We have tried to evaluate the effect of staying at low altitude on arterial oxygenation and exercise performance in patients with COPD.

PATIENTS AND METHOD

Eleven patients with COPD (9 male, 2 female) aged 38 to 79 years (mean FEV1, 0.96 L; 36% predicted) with hypoxemia (mean PaO2, 54.2+/-8.9 mm Hg) at Jerusalem (altitude 800 m above sea level) were taken down to the Dead Sea area (altitude 402 m below sea level) for 3 weeks. At both locations we tested arterial blood gases, spirometry, progressive exercise, 6-minute walking distance, and sleep oximetry. The study was repeated 2 weeks after returning to Jerusalem.

RESULTS

Spirometry results were unchanged. Mean arterial PaO2 rose from 54.2+/-8.9 mm Hg to 69.5+/-11 at the first week and to 66.6+/-11 at the third week of stay (p<0.001). PaCO2 rose from 43.5+/-9.8 mm Hg to 47.7+/-9 and 49.5+/-8.4 (p<0.006). Six-minute walking distance rose from 337+/-107 m to 449+/-73 and 507+/-91 in the third week (p<0.005). Maximum oxygen consumption (VO2max) rose from 901+/-257 mL/min to 1,099+/-255 and 1,063+/-250 mL/min (p=0.01). Sleep oximetry showed an increase in mean sleep arterial oxygen saturation from 86.0+/-4.3% to 89.9+/-4.2% and 88.3+/-3.0 at 1 and 3 weeks, respectively (p<0.05). Following the return to Jerusalem, arterial gases returned to their baseline levels (PaO2, 52.9+/-9.4 mm Hg) but 6-min walking distance remained significantly high, 453+/-47 (p<0.02), and VO2max remained high as well (1,102+/-357 mL/min), although it did not reach statistical significance.

CONCLUSIONS

Decline to low altitude or staving at high oxygen environment improves arterial oxygenation and exercise capacity in hypoxemic patients residing in moderate or high altitude. Low altitude (or pressurized wards) can improve pulmonary rehabilitation of hypoxemic patients with COPD.

Comparison of respiratory inductance plethysmography with thoracoabdominal compression in bronchial challenges in infants and young children

Respiratory inductance plethysmography measuring thoracoabdominal asynchrony (TAA) has been claimed to be a useful tool for measuring changes in airway resistance in infants. In this study we evaluated the response to methacholine by thoracoabdominal compression and respiratory inductance plethysmography. Seventeen infants (mean age, 13.1 +/- 4.7 mo) with recurrent episodes of cough or wheeze underwent bronchial challenge with inhaled methacholine. Lung function was evaluated by measuring maximal expiratory flow at resting lung volume (VmaxFRC), and the degree of TAA was measured by phase angle (theta). Methacholine was inhaled for 1 min during tidal breathing using increasing doubling concentrations until a fall of at least 40% in VmaxFRC was achieved (final concentration). All infants responded to the final concentration of methacholine by a significant fall in VmaxFRC (from 31 +/- 10 to 12 +/- 5 ml/s/kg, p < 0.001). All but one infant responded to methacholine at the final concentration with a significant increase in phase angle (median theta increased from 11.7 to 31.7 degrees, p < 0.001). In two other infants there was an early response in theta compared with the response in VmaxFRC. Phase angle increase after methacholine was expressed as Z-scores (the difference between postmethacholine theta and postbuffer theta divided by the standard deviation of postbuffer theta). An increase of at least 2.0 Z-scores in theta was observed at the same concentration of methacholine when VmaxFRC fell by at least 40% in 15 of the 17 infants (88%). We conclude that respiratory inductance plethysmography is a sensitive method to measure bronchial reactivity to methacholine in most of the infants studied (14 of 17, 82%). A concentration of methacholine causing an increase in theta of at least 2.0 standard deviations above baseline is equivalent to the concentration causing a 40% fall in VmaxFRC.

Home recording of PEF in young asthmatics: does it contribute to management?

The value of home monitoring of peak expiratory flow (PEF) as part of an action plan for asthma management in children and young adults is uncertain. We sought to determine whether home recording of PEF benefited asthma management and whether any contribution was affected by the severity of the asthma. Twenty-eight children and young adults with asthma of different severity (mean age 14 yrs; 95% confidence interval (95% CI) 12-16 yrs) recorded their symptoms, drug consumption and PEF twice daily for a mean of 82 days over a 12 week period, and attended the laboratory every 2 weeks for measurement of lung function. The number of individual patients with significant correlations for laboratory lung function tests compared with ambulatory PEF and diary scores averaged over the preceeding 2 weeks was low in all severity groups. When measured in the laboratory, PEF meter readings correlated poorly with PEF measured by spirometry. The proportion of patients with significant correlations for PEF, symptoms and rescue bronchodilator use on a day-to-day basis was 70-80% in the group of severe asthmatics and significantly less in the mild asthmatics. In a subgroup of 14 patients who were sick on a mean of 19 days, the mean difference in PEF between well and sick days was 14% of predicted. Diurnal PEF variation correlated poorly with other parameters in all groups. It is concluded that PEF monitoring adds little to daily recording of symptoms and bronchodilator use in the management of young patients with severe asthma, and it is too insensitive to register meaningful clinical changes in those with milder asthma.

Functional residual capacity (FRC) measurements by plethysmography and helium dilution in normal infants

Comparative measurements of functional residual capacity (FRC) made by plethysmography (FRCpleth) and by helium dilution (FRCHe) were obtained on 27 infants and young children without known pulmonary disease (14 males, 13 females; 4 weeks-26 months; mean age 32.2 weeks) while under chloral hydrate sedation. Clinical histories, clinical examinations, and pulmonary functions were normal for all members of the group. FRCpleth, whether measured near end expiration (EE) or near end inspiration (EI), and corrected to mean expiratory levels of at least 3 breathing cycles, was consistently and significantly greater than FRCHe. Comparative values for mean (+/- standard deviation) were FRCpleth EE, 182.0 (+/- 79.7) mL and FRCpleth El, 171.8 (+/- 77.4) mL vs. FRCHe, 154 (+/- 72.2) mL, P < 0.0001 and P < 0.005, respectively. Normalizing values by weight, FRCpleth EE was 23.8 mL/kg (+/- 5.3) vs. FRCHe, 20.2 (+/- 4.7) mL/kg, mean (+/- standard deviation). The difference between FRCpleth and FRCHe, expressed as FRCpleth - FRCHe/FRCpleth x 100, was 9% for occlusions at end inspiration and 16% for occlusions at end expiration. The following equations describe our FRC results in relation to length: In (FRCHe) = 2.74 x ln (length) - 6.53 r2 = 0.781 slope = 2.74 +/- 0.29 SE Y intercept = 6.53 +/- 1.12 SE ln (FRCPleth EI) = 2.69 x ln (length) - 6.21 r2 = 0.752 slope = 2.69 +/- 0.31 SE Y intercept = 6.21 +/- 1.29 SE The difference between FRCpleth and FRCHe was more marked when occlusions were performed at end expiration than at end inspiration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine, methacholine, and exercise challenges in children with asthma or paediatric chronic obstructive pulmonary disease

BACKGROUND

Bronchial hyperreactivity to methacholine is present in children with asthma and other types of paediatric chronic obstructive pulmonary disease (COPD), while hyperreactivity to exercise is more specific for asthma. Adenosine 5'-monophosphate (AMP) is a potent bronchoconstrictor and, like exercise, may provoke asthma by activating mast cells. This study investigated the suitability of AMP as a specific challenge for asthma in children.

METHODS

Bronchial provocation challenges with methacholine and AMP were performed in a double blind fashion using tidal breathing in 51 children with asthma, 21 with paediatric COPD of various types, and in 19 control children. Each subject also underwent a standardised exercise challenge after inhalation challenges were completed. Sensitivity and specificity curves were constructed and the intersection point of sensitivity and specificity for each type of challenge was determined.

RESULTS

When the asthmatic patients were compared with the children with COPD, the intersection points for AMP, exercise and methacholine were 90%, 85%, and 50%, respectively. When compared with the controls the same intersection points were 98%, 84%, and 92%, and when children with paediatric COPD were compared with controls they were 55%, 50%, and 82%.

CONCLUSIONS

Methacholine distinguishes both asthma and paediatric COPD from controls with a sensitivity of 82-92%, but does not distinguish between asthma and paediatric COPD; exercise and AMP distinguish asthma from controls with a sensitivity and specificity of 84-98% but they also distinguish asthma from paediatric COPD with a sensitivity and specificity of 85-90%. AMP inhalation is a practical aid for diagnosing asthma and distinguishing it from COPD in children of all ages.

Effect of natural oxygen enrichment at low altitude on oxygen-dependent patients with end-stage lung disease

OBJECTIVE

To assess the effect of lowering altitude to that of the lowest place on earth (Dead Sea) on arterial oxygenation and exercise performance in patients with hypoxemia and end-stage lung disease.

DESIGN

A cohort of 10 patients.

SETTING

Pulmonary function laboratories in Jerusalem, Israel, and at the Dead Sea.

PATIENTS

10 patients with end-stage lung disease who were receiving long-term oxygen therapy. The 4 males and 6 females were 12 to 77 years old. Four patients had chronic obstructive pulmonary disease; 2 had cystic fibrosis; 3 had pulmonary fibrosis; and 1 had pulmonary hypertension (thromboembolic). Mean forced vital capacity was 1.54 L (54% of predicted value) and mean forced expiratory volume in 1 second was 0.85 L (35% of predicted value).

MEASUREMENTS

Spirometry, blood gas analysis, progressive exercise testing, and sleep oximetry were done in Jerusalem (altitude, 800 m above sea level; barometric pressure, 696 mm Hg); the same measurements were done 6 days after arrival at the Dead Sea (altitude, 402 m below sea level; barometric pressure, 800 mm Hg) and then 7 to 14 days later in Jerusalem.

RESULTS

Arterial oxygenation increased from a median partial pressure of arterial oxygen of 51.6 mm Hg in Jerusalem to 67.0 mm Hg at the Dead Sea, an increase of 15.2 mm Hg (95% CI of paired difference, 4.1 to 20.4 mm Hg; P = 0.001). Partial pressure of arterial carbon dioxide increased from a median of 43.2 to 45.9 mm Hg, an increase of 2.7 mm Hg (CI, 0.5 to 6.4 mm Hg; P = 0.004), with a borderline significant change in the alveolar-arterial gradient. Arterial oxygen saturation increased from a median of 87.7% to 92.8%, a change of 4.8% (CI, 1.9% to 9.8%; P = 0.003). Exercise performance also improved as maximum oxygen uptake increased from a median of 827 mL/min to 1056 mL/min, an increase of 203 mL/min (CI, 54 to 388 mL/min; P = 0.006). Sleep oximetry also improved as median arterial oxygen saturation measured during sleep increased from 85% to 90%, a change of 5% (CI, 2% to 7%; P = 0.005), and percentage of sleep time with an oxygen saturation rate of 90% or more increased from a median of 24% to 73%, a change of 49% (CI, 20% to 87%; P = 0.02). No change in spirometry was noted. All patients felt less dyspneic and reported improved functional capacity with reduced need for oxygen.

CONCLUSION

Descent to low altitude can improve arterial oxygenation, exercise performance, and sleep oximetry and consequently the quality of life in patients with hypoxemia and advanced lung disease.

Computerized respiratory muscle training in children with Duchenne muscular dystrophy

The present study describes the use of simple video games for a 5-week regimen of respiratory muscle training in 15 patients with Duchenne muscular dystrophy (DMD) at various stages of the disease. The games were re-arranged to be operated and driven by the respiratory efforts of the patient and to incorporate accurate ventilation and time measurements. Improvement in respiratory performance was determined by maximum voluntary ventilation (MVV), maximal achieved ventilation (VEmax) during a progressive isocapnic hyperventilation manoeuvre (PIHV) and the PIHV duration. The actual training period was 23 +/- 4 days (mean +/- S.D.) at ventilatory effort of 46 +/- 6% MVV, for 10 +/- 3 min day-1. Patients with moderate impairment of lung function tests (LFT) showed an improvement in MVV, VEmax, and duration of PIHV of 12 +/- 7% (p < 0.02), 53 +/- 25% (p < 0.001) 57 +/- 21% (p < 0.01), respectively. Improvements correlated with actual training time and ventilation level, %MVV, but negatively correlated with years of immobilization and with the initial MVV. We conclude that computerized respiratory games may be applied for breathing exercises and may improve respiratory performance in recently immobilized children with DMD who have moderate impairment of LFT.

Comparison of airway resistance and total respiratory system resistance in infants

Airway resistance (Raw) can be measured throughout the respiratory cycle by whole body plethysmography. Total resistance of the respiratory system (Rrs) can be measured from the relaxed expiration that follows end inspiratory occlusion. The purpose of this study was to compare the two methods in normal infants and in infants with airway obstruction of different types and severity. Fifteen infants with essentially normal lungs aged 24.6 +/- 18.0 (SD) wk, nine infants with congenital stridor aged 36.0 +/- 17.3 wk, and eleven wheezy infants aged 20.1 +/- 11.3 wk had simultaneous measurements of Raw and Rrs. Rrs was similar to Raw both during inspiration and expiration in the normal infants, to all expiratory Raw in those with congenital stridor, and to all inspiratory and early expiratory Raw in the wheezy infants. Raw was markedly and significantly higher than Rrs during mid and late inspiration in infants with congenital stridor and during late expiration in the wheezy infants. We conclude that Rrs is a good estimate of Raw in normal infants and of early expiratory Raw in all infants. In infants with airway obstruction, Rrs does not reveal the dynamic changes in Raw during tidal breathing, nor can it differentiate between infants with upper and lower airway obstruction.

Bronchial provocation determined by breath sounds compared with lung function

Bronchial provocation testing with methacholine was undertaken in 15 children aged 5 to 8 years with obstructive lung disease, mostly asthma (13/15). The methacholine was inhaled during two minutes of tidal breathing in increasing concentrations. After each inhalation, lung function was measured and clinical signs recorded independently by two observers unaware of each other's results. The logarithm of the concentration of methacholine which caused wheezing over the trachea correlated closely with the logarithm of the concentration of methacholine causing a 20% fall in the forced expiratory volume in one second (FEV1) but was 52% greater on average. At the end of the test there was a mean (SD) fall in FEV1 of 33.3 (7.4)% and a fall in oxygen saturation of 5.2 (3.1)%. Bronchial provocation testing by listening for wheeze over the trachea is a safe technique, which correlates with objective measures of lung function in young children.

Nonspecific bronchial reactivity in asthmatic children depends on severity but not on age

Bronchial reactivity to inhaled methacholine was measured by the steady-state tidal breathing method in asthmatic children aged 1 to 17 yr. The children were divided into three clinical groups according to their minimal therapeutic requirements: mild asthma, children requiring infrequent treatment with inhaled beta-agonists (81 patients); moderate asthma, children requiring daily preventive treatment with either cromolyn sodium or slow-release theophylline (67 patients); and severe asthma, children requiring daily preventive treatment with oral or inhaled steroids (34 patients). They were also divided into three age groups: from 1 to 6 yr, tested by using bronchial provocation with tracheal auscultation (BPTA) to determine the methacholine concentration causing wheezing (PCW); and from 7 to 11 yr and 12 to 17 yr, using lung function testing to determine the concentration causing a 20% fall in FEV1 (PC20). For the whole group the mean level of bronchial reactivity to methacholine correlated inversely with the severity of bronchial asthma according to the minimal drug requirements (p less than 0.0001) and was similar over the whole age range (p less than 0.9965) for each severity grouping. In the older children the difference between moderate and severe asthma was not significant, but this may have been a result of the effect of corticosteroids in the severe group. We concluded that age has no significant effect on the methacholine response in asthmatic children over a wide age range.

Effect of hyperoxia on bronchial response to inhaled methacholine

Bronchial reactivity to methacholine (MCH) under normoxic and hyperoxic conditions was studied in a double-blind controlled study in 10 normal subjects and nine asthmatic patients. The normal volunteers were challenged while breathing dry, 21% and 100% O2, and the maximal percent falls in forced expired volume in is (FEV1) following inhalation of the highest concentration of MCH (64 mg/ml) were 8 +/- 5% and 9 +/- 8%, respectively; P = NS. The asthmatic patients had their MCH challenge breathing the same gas composition and the provocative concentrations that caused a 20% fall in FEV1 (PC20) were 0.18 mg/ml (range 0.06-5.73) and 0.25 mg/ml (range 0.07-8.49), respectively, which were statistically not significantly different. We conclude that in humans, 100% O2 does not affect bronchial reactivity to MCH.

Corticosteroids do not affect the clinical or physiological status of infants with bronchiolitis

The treatment of infants aged 1.5-11.0 months suffering from acute bronchiolitis with a combination of inhaled albuterol and systemic corticosteroids or inhaled albuterol and placebo was compared in 50 infants in a double blind study. The mean initial clinical score and the rate of improvement was similar in the two groups. The mean +/- SD hospital stay was 5.0 +/- 1.2 days for the steroid group and 5.2 +/- 1.7 days for the placebo group. Lung function was measured in 14 infants (7 from each group) and showed evidence of increased lung volumes and severe airway obstruction in the acute stage (the mean values for the steroid group were: TGV, 31 mL/kg; SGaw, 0.104 L/s.cmH2O; VmaxFRC, 12.9 mL/s/kg; for the placebo group: TGV, 35 mL/kg; SGaw, 0.104 L/s.cmH2O; VmaxFRC, 8.5 mL/s/kg) which had improved 2-4 weeks later (steroid group: TGV, 25 mL/kg; SGaw, 0.168 L/s.cmH2O; VmaxFRC, 21.6 mL/s/kg; -placebo group: TGV, 24 mL/kg, SGaw, 0.198 L/s.cmH2O, VmaxFRC, 17.5 mL/s/kg). There were no significant differences of thoracic gas volume, specific airway conductance, and forced expiratory flow at resting lung volume between the two groups, either in the acute or convalescent stages. We conclude that corticosteroids do not change the rate of clinical improvement in acute bronchiolitis, nor do they effect lung function 2-4 weeks later.

Comparison of the single breath and volume recruitment techniques in the measurement of total respiratory compliance in anesthetized infants and children

Total respiratory compliance (Crs) has not previously been measured from the static pressure-volume (P-V) curve during spontaneous breathing in anesthesized infants and children. A single breath test and a volume recruitment maneuver for measuring Crs were applied to 18 infants and children breathing spontaneously during halothane anesthesia in order to determine the usefulness and reliability of these noninvasive tests for measuring static compliance during anesthesia. Crs from the single breath test (Crssb) was determined from the mask pressure plateau (P) during a brief end-inspiratory airway occlusion and the lung volume (V) from the passive expiration following release of the occlusion. Crs from the volume recruitment maneuver (Crsvr) was determined from P and V during a series of expiratory occlusions at progressively higher lung volumes. The P-V curves fit a polynomial curve with the convexity toward the pressure axis in most patients, and Crsvr was the tangent to the curve in the mid-tidal range. The tallest four patients did not show respiratory muscle relaxation during the occlusions with either test, and the single breath test could not be completed in an additional two patients. In the 12 patients (59-89 cm in height) in whom both tests were successful, Crssb correlated with, and was similar to, Crsvr. The intrasubject coefficient of variation was less with the single breath test (9.4 +/- 6.7%) than with the volume recruitment maneuver (15.0 +/- 7.1%). The authors conclude that both tests are simple, reliable, and rapid and give similar results for Crs in spontaneously breathing children (59-89 cm in height) anesthetized with halothane.

Differential lung function in an infant with the Swyer-James syndrome

A previously healthy two year old boy had an adenoviral infection at the age of 13 months and developed hyperlucency of the left lung, chronic respiratory distress, and failure to thrive. Bronchodilators and steroid treatment had no effect. Radionuclide lung scans using an intravenous bolus of xenon-133 both before and after treatment showed substantially reduced function on the hyperlucent side and modestly reduced function on the other side. Fibreoptic bronchoscopy showed no structural abnormalities. Partial forced expiratory flow volume (PEFV) curves, generated from end inspiration by rapid compression of the chest wall with an inflatable jacket, were obtained from the total respiratory system and from each lung separately by inflating a Fogarty catheter in the contralateral mainstem bronchus. Expiratory flow rates and volumes during both tidal breathing and PEFV manoeuvres were considerably decreased in the hyperlucent lung. PEFV curves from the "healthy" right lung and from the total respiratory system were similar in shape and showed a moderately obstructive pattern. The right lung ventilated about four times as much as the left when measured by bronchospirometry and about three times as much when measured by the radionuclide technique. The lung scans appeared to reflect adequately the functional abnormality in this infant with the Swyer-James syndrome.

Immediate effect of various treatments on lung function in infants with cystic fibrosis

The immediate effect of four different modes of treatment was assessed by lung function tests on 19 infants with cystic fibrosis (CF) during the first year of life. The regimens were applied in a randomized fashion and consisted of aerosol inhalation of salbutamol (n = 8; SAL), aerosol inhalation of N-acetyl cysteine (n = 5; AC), chest physiotherapy (n = 6; CPT), and combined treatment with aerosol inhalation of SAL and AC followed by CPT (n = 6; COMB). Pulmonary function was measured before and shortly after therapy with each mode of treatment. Thoracic gas volume (Vtg) and specific airway conductance (SGaw) were measured by an infant whole body plethysmograph, and forced expiratory flow at resting lung volume (VmaxFRC) was determined with a thoraco-abdominal squeeze jacket. There was no correlation between baseline lung function and changes in any parameter due to treatment. Overall group comparison showed that the combined therapy resulted in a significant improvement in lung function when compared to any of the three treatments applied separately. There was no significant change in lung volumes in any individual group, but SGaw and VmaxFRC showed a small but significant improvement following the COMB treatment when compared with AC or CPT.

Drive and timing components of respiration in young children following induction of anaesthesia with halothane or ketamine

Timing and drive components of respiration were studied in 18 young children following induction of anaesthesia with ketamine and were compared with results from ten children following induction of anaesthesia with halothane. During one minute of quiet breathing, signals from a pneumotachograph attached to the anaesthetic mask were analysed for tidal volume (Vt), respiratory frequency (f), minute volume (Ve), inspiratory and expiratory times (Ti, Te) and flow pattern. Following induction of anaesthesia with ketamine, children breathed more slowly and deeply than children receiving halothane, but there was no significant difference in Ve or in Vt/Ti, suggesting that respiratory drive was similar in the two groups of children. In the children receiving ketamine, Ti was more than twice as long, and thus the ratio Ti/Te was significantly increased, in comparison with the group receiving halothane. In addition to the prolonged Ti in the children induced with ketamine, there was a more rapid increase in volume in early inspiration than in late inspiration, which is an apneustic breathing pattern. There was a slower decrease in volume in early expiration, with occasional early expiratory breath holding lasting up to three seconds, in the ketamine-induced children. The unique breathing pattern demonstrated with ketamine, consisting of large Vt, increased Ti/Te ratio, apneustic inspiratory pattern, and expiratory braking, contributed to an increased mean lung volume above functional residual capacity, of 2.40 ml.kg-1 body weight, in comparison to 1.27 ml.kg-1 in the children receiving halothane.

Lung function in infants with cystic fibrosis

Lung function was measured in 28 infants with cystic fibrosis and repeated in 17 of the infants during the first year of life. Thoracic gas volume (TGV) and specific airway conductance (sGaw) were measured plethysmographically and maximum forced expiratory flow at functional residual capacity (VmaxFRC) was derived from the partial expiratory flow-volume curve. At the time of the initial evaluation respiratory function was correlated with the clinical condition of the infants but not with age. There was a good correlation between sGaw and VmaxFRC when both were expressed as percentages of the predicted normal values. On the basis of the normal range for sGaw the infants were divided into two groups. Group A (n = 9), who had normal sGaw, were younger and had a lower clinical score and normal VmaxFRC and TGV values. Group B (n = 19), who had low sGaw, had increased TGV and decreased VmaxFRC. There was no correlation with age for any measure of lung function for the population as a whole. Repeat testing was undertaken at intervals in 17 representative infants. In most of these infants the relation between sGaw and VmaxFRC was maintained; there was no evidence that VmaxFRC was affected before sGaw. There was no functional evidence that the earliest changes in cystic fibrosis occur in small airways, as reflected by changes in VmaxFRC in infancy.

Respiratory mechanics and intrinsic PEEP during ketamine and halothane anesthesia in young children

Static compliance of the respiratory system (Crs) was measured by the interrupter technique in 18 anesthetized children to compare the effects of ketamine on Crs with those of halothane. Crs was the slope of the pressure-volume (P-V) curve obtained by repeated brief airway occlusions throughout relaxed expiration, and the intercept of the P-V curve on the pressure axis was the intrinsic positive end-expiratory airway pressure (PEEPi). Expiratory time (Te) was measured during a period of quiet breathing, and the passive expiratory time constant (tau) was measured during the relaxed expiration after an end-inspiratory occlusion. Nine children were anesthetized with a continuous infusion of ketamine and a matching group of nine children inhaled halothane in oxygen. Crs was significantly greater in the ketamine group (22.8 +/- 6.2 ml/cm H2O) than in the halothane group (15.7 +/- 5.5 ml/cm H2O). The tau value was also significantly greater in the ketamine group. Mean PEEPi in the ketamine group was 2.3 +/- 1.8 cm H2O and in the halothane group was 0.4 +/- 0.8 cm H2O. PEEPi correlated inversely with Te/tau according to a logarithmic function. It was concluded that, in children anesthetized with ketamine, Crs is significantly greater than that in children anesthetized with halothane, and the resultant prolongation of tau and decreased Te/tau with ketamine anesthesia lead to increased PEEPi.

Respiratory heat/water loss alone does not determine the severity of exercise-induced asthma

Respiratory heat loss (RHL) or water loss (RWL) have been proposed as possible triggering factors in exercise and hyperventilation-induced asthma (EIA and HIA). It has recently been demonstrated that exercise intensity and climatic factors are both important in determining the severity of EIA. Eight young asthmatics performed both exercise and isocapnic hyperventilation (IHV) manoeuvres under identical climatic conditions, as part of our investigation of these interactive factors which determine the severity of the asthmatic response. It was found that, when challenged at low ventilatory levels, exercise produced a significantly attenuated asthmatic response compared to IHV. The fall in forced expired volume in 1 sec (delta FEV1) following exercise was 15 +/- 4% as compared with 27 +/- 3% after IHV (p less than 0.002). It is concluded that while the hypernoea in exercise may serve as a trigger, exercise per se introduces an additional factor which serves to limit the full response seen with IHV. This attenuated response is revealed at low ventilatory levels but is masked at high levels.

Respiratory heat/water loss alone does not determine the severity of exercise-induced asthma

Respiratory heat loss (RHL) or water loss (RWL) have been proposed as possible triggering factors in exercise and hyperventilation-induced asthma (EIA and HIA). It has recently been demonstrated that exercise intensity and climatic factors are both important in determining the severity of EIA. Eight young asthmatics performed both exercise and isocapnic hyperventilation (IHV) manoeuvres under identical climatic conditions, as part of our investigation of these interactive factors which determine the severity of the asthmatic response. It was found that, when challenged at low ventilatory levels, exercise produced a significantly attenuated asthmatic response compared to IHV. The fall in forced expired volume in 1 sec (delta FEV1) following exercise was 15 +/- 4% as compared with 27 +/- 3% after IHV (p less than 0.002). It is concluded that while the hypernoea in exercise may serve as a trigger, exercise per se introduces an additional factor which serves to limit the full response seen with IHV. This attenuated response is revealed at low ventilatory levels but is masked at high levels.

Exercise intensity determines and climatic conditions modify the severity of exercise-induced asthma

Recent studies have shown some evidence that exercise-induced asthma (EIA) may not be entirely explained by respiratory heat loss (RHL). We investigated the interrelationship between heat exchange, exercise intensity and EIA. In order to differentiate between the effects of RHL and exercise intensity, we arranged for tests to be performed with the same RHL, but with different intensities of exercise and inspired air conditions. Each of 8 asthmatic children exercised twice in random order for 6 min on a cycle ergometer. One test consisted of exercise performed at a greater level of effort while breathing room air, mean (+/- SE) air conditions being 25.0 +/- 0.4 degrees C and 15.7 +/- 0.2 mg H2O/L. The other test was performed at a lesser level of effort while breathing cold (0.0 +/- 0.5 degrees C) and dry air (O mg H2O/L). The mean ratio of minute ventilations in the 2 exercise tests was 1.78 +/- 0.03, but the RHL was similar in both tests. The EIA after the exercise at the greater level was more severe than after the lesser level, the percent fall in FEV2 from baseline being 36 +/- 7% and 21 +/- 5%, respectively (p less than 0.025). We conclude that the exercise level has a major role in determining the severity of EIA and that climatic conditions act as modifying factors.

Partial forced expiratory flow-volume curves in young children during ketamine anesthesia

Maximal flows at functional residual capacity (VmaxFRC) from partial forced expiratory flow-volume (PEFV) curves were obtained in 14 normal preschool children (8 boys, 6 girls) of average age 44 mo, under general anesthesia before elective surgery. PEFV curves were generated from end inspiration by rapid compression of the chest wall with an inflatable jacket. VmaxFRC, expressed in milliliter per second, correlated linearly with height, weight, age, and FRC in milliliter and milliliters per kilogram. The best correlation of VmaxFRC (ml/s) was to height to the power of 2.47, which agrees with the results predicted by wave-speed theory. Mean FRC-corrected VmaxFRC was 2.42 +/- 0.50 (SD) FRC's/s with no significant difference between boys (2.35 FRC's/s) and girls (2.51 FRC's/s). There was no correlation between lung-size corrected VmaxFRC and height, weight, or age, but it tended to decrease with increasing FRC. The intersubject variability for VmaxFRC was reduced by normalizing for FRC, and was significantly better than that reported for awake children. This can be attributed to the greater control over volume history and more reliable maximal flow generation during anesthesia. The intrasubject coefficient of variation (CV) for VmaxFRC was 12.2%, and the intersubject CV was 20.0%. The difference may represent the variability due to dysanapsis. It is concluded that dysanapsis is not a prominent factor in children of this age group. In addition, the similarity of the regression equation for VmaxFRC vs. height to that of FRC vs. height supports the concept of equidimensional growth of the airways and lung parenchyma.

A non-invasive method for measuring inspiratory muscle fatigue during progressive isocapnic hyperventilation in man

Eleven normal adults each performed a ten minute progressive isocapnic hyperventilation (PIHV) test in which ventilatory levels were increased every two minutes. All subjects exhibited mechanical fatigue by failing to maintain the target of 80% of maximum voluntary ventilation (MVV). The mean ventilation at this level was 67.5 +/- 1.4% MVV. This fatigue was accompanied by a fall in transdiaphragmatic pressure. During the test the EMG of the sternomastoid (SM) was monitored by surface electrodes and was analyzed using fast-fourier transform. The centroid frequency (Fc) fell as ventilation increased, and correlated negatively with the inability to achieve target ventilation(r = -0.99, p less than 0.015). Five subjects performed the test while the diaphragmatic EMG was recorded from an oesophageal electrode (DIes) and from surface electrodes (DIs). The Fc of DIes fell with increasing ventilation levels (r = -0.95, p less than 0.05) and there was a correlation between the Fc changes of both DIes and the SM (r = -0.92, p less than 0.001). The Fc of DIs did not correlate with either mechanical performance or the Fc of DIes, because of contamination of surface signals by signals from expiratory muscles. It is concluded that the PIHV along with surface monitoring of EMG activity from the sternomastoid can serve as a non-invasive method for evaluating inspiratory muscle fatigue.

Determinants of end expiratory volume in young children during ketamine or halothane anesthesia

The expiratory time (Te) and the rate of lung emptying in expiration are important determinants of functional residual capacity (FRC) in infants. In order to determine whether these factors also influence FRC in children during anesthesia, 20 preschool children were studied, 10 while receiving ketamine, and 10 during halothane anesthesia. Te was measured during quiet breathing and the passive expiratory time constant (tau) was determined from the passive expiratory flow volume (V/V) curve following a brief end inspiratory airway occlusion. The number of time constants available for expiration, Te/tau, was then calculated. The difference between FRC and the relaxation volume of the respiratory system (Vrs) (FRC-Vrs) was measured by extrapolating the linear segment of the V/V curve to zero flow, and measuring FRC-Vrs. During ketamine anesthesia, tau was markedly prolonged (1.15 s, range 0.73-2.29 s), with the result that Te/tau was, in all subjects, less than 2. Children anesthetized with halothane had shorter tau (0.38 s, range 0.24-0.65 s), and Te/tau was more than 2 in most subjects. FRC-Vrs was significantly greater in the subjects from the ketamine group (203 ml, range 115-392 ml) than in those from the halothane group (32 ml, range 1-71 ml). For the 20 subjects, there was a significant relationship between FRC-Vrs (ml) and Te/tau described by the equation. FRC-Vrs = 845.0e-1.28(Te/tau) The authors conclude that, in children during ketamine anesthesia, tau is prolonged and, in these children, the relationship of Te to tau is an important determinant of FRC-Vrs. Te/tau was not related causally to FRC-Vrs in the halothane group.(ABSTRACT TRUNCATED AT 250 WORDS)

Expiratory volume clamping: a new method to assess respiratory mechanics in sedated infants

During breathing under sedation via a two-way valve, airflow (V), volume (delta V), and airway pressure (P) were recorded in eight normal (N) infants, seven with reversible obstructive airway disease (ROAD), and seven with chronic lung disease (CLD). Intermittently, expiratory volume clamping (EVC) was applied, involving selective occlusion of the expiratory valve for three to five breaths. The latter produced cumulative increases in delta V that, due to progressive recruitment of the Hering-Breuer reflex, were accompanied by increasing expiratory plateaus in P (i.e., apneas). The resultant passive inflation delta V-P relationships were closely approximated by the expression: delta V = aP2 + bP + c, wherein a represented the pressure-related changes in chord compliance (Crs), b the Crs at P = 0, and c the difference between the dynamic end-expiratory and relaxation volumes of the respiratory system. Relative to N, the ROAD and CLD infants had significantly reduced weight-specific values of a/kg, their b/kg values were increased, whereas the c/kg measurements did not significantly vary. Moreover, for each subject we determined the net Crs/kg obtaining at P = 20 cmH2O (i.e., Crs20/kg), an estimate of the net deflation compliance; the passive respiratory time constant (tau rs) based on the slope of the expired delta V/V relationship; and the respiratory system conductance (Grs/kg). Relative to N, the mean Crs20/kg was significantly reduced only in the infants with CLD and, due to increases in tau rs, both patient groups depicted significantly diminished values of Grs/kg, suggesting the presence of airways obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional residual capacity in healthy preschool children lying supine

Functional residual capacity (FRC) was measured by the closed-circuit helium dilution method in 41 supine healthy children 1 month to 8 yr of age. In 20 children, the measurement was carried out while they were awake, and in the others, who were less cooperative, testing was done during ketamine anesthesia before elective surgery. There was no significant difference in the FRC values between these groups, and they were subsequently analyzed as a single group. For males and females separately and combined, FRC correlated significantly with height, age, and weight, both with linear and nonlinear regression analyses. No significant difference between the sexes was found. The best correlation of FRC was with height; the linear equation being FRC (ml) = -457.3 + 8.8 X height (cm) (r2 = 0.662), and the nonlinear equation being FRC (ml) = 0.0052 X [height (cm)]2.44 (r2 = 0.827).

Lung function in infancy and childhood following neonatal intensive care

Pulmonary function studies were performed in 11 neonatal intensive care survivors both during infancy and later in childhood. Lung function was compared with the respiratory support given in the neonatal period. The mean +/- SE thoracic gas volume was 96 +/- 4% predicted in infancy and rose to 122 +/- 8% predicted during childhood (P less than 0.005). The specific airway conductance (SGaw) in infancy was 57 +/- 7% predicted and rose to 90 +/- 8% predicted in childhood (P less than 0.0025). Abnormalities in SGaw were found only in ventilated infants, and there was a negative logarithmic correlation between the treatment score in the neonatal period and the SGaw in both infancy and childhood. The data indicate a long-term improvement in airway conductance of moderately affected infants with the development of mild hyperinflation in childhood possibly resulting from residual small airway abnormalities despite a symptomless clinical course. The residual abnormalities in prematurely born infants were in proportion to the intensity of treatment required in the neonatal period.

Effect of heart weight on distribution of lung surface pressures in vertical dogs

In head-up dogs the vertical gradient of transpulmonary pressure (VGTP) disappears after pneumothorax develops. Our laboratory recently confirmed that the heart moves downward and posteriorly with pneumothorax. To study the extent to which the heart is supported by the lungs, we used a linear elasticity model and finite-element analysis. The lung and heart were assumed to be symmetric along a vertical axis. Reported values of the elastic properties of lung and heart were assigned. The model was generated first without the heart, using the lung alone. The heart was then added to the model. Finally, heart weight was doubled. Adding the heart caused the VGTP to increase; doubling the heart weight further increased the VGTP. These increases were more pronounced at higher lung volumes. Lung inflation was accompanied by an upward displacement of the heart. Inclusion of the heart caused increased inhomogeneities in regional volume distribution. The effect of heart weight may in part explain why the VGTP in the head-up dog is greater than that predicted by lung density.

Nemaline myopathy as a cause of sleep hypoventilation

Two siblings, a 14.5-year-old boy and his 11.5-year-old sister, with congenital nemaline myopathy presented with severe respiratory failure and, in the case of the older patient, with cor pulmonale and systemic hypertension. The children were treated initially by continuous mechanical ventilation, but after a few weeks they only required ventilation at night. At the start of treatment, both were found to have a decreased ventilatory response to CO2 which apparently improved during 4 to 5 years of follow-up treatment. It has not been possible to wean them from nocturnal mechanical ventilation, but during the daytime they attend school and function almost normally. It is postulated that respiratory failure in nemaline myopathy may not be related to the severity of the muscle weakness but may result from a disturbance of the feedback required for normal control of breathing.

Can thoracic gas volume be measured in infants with airways obstruction?

Thoracic gas volume (Vtg) was measured in a whole-body, infant plethysmograph in 46 infants with recurrent wheezing after bronchiolitis, 25 infants with cystic fibrosis, and 6 infants without overt lung disease during the first 13 months of life. When related to weight or length, 56.5% of the bronchiolitic infants had low Vtg values, which were more than 2 SD below their predicted normal. The Vtg of the other groups was normal or above. The bronchiolitic infants with Vtg values in the normal range had more severe airways obstruction and it is probable that their Vtg values were also underestimated. Investigation of possible sources of technical or experimental error failed to reveal any explanation for the low Vtg in the bronchiolitic infants. In 5 infants, Vtg determined plethysmographically was correlated linearly to functional residual capacity determined by helium dilution, although Vtg values were greater in all. The administration of albuterol or treatment with steroids failed to make significant changes in Vtg in the bronchiolitic infants. It is suggested that there is a physiologic basis for the presumed underestimation of Vtg in wheezy infants after bronchiolitis, either because of uneven alveolar pressure changes within the chest leading to the effective exclusion of a portion of the lung volume or because there are some alveolar units with very low compliance that change little in volume during respiratory efforts against an occlusion. These results call into question the validity of the plethysmographic measurement of Vtg or airway resistance in these infants. If the error in Vtg is due to uneven alveolar pressure changes, it is suggested that the calculated specific airway conductance is probably correct.

Airway resistance measurements throughout the respiratory cycle in infants

Using a constant-volume infant whole-body plethysmograph containing a heated rebreathing bag, we have been able to measure airway resistance (Raw) throughout the respiratory cycle using a computer-based technique. Data from the plethysmograph transducers are sampled at 60 Hz for the calculations and Raw is calculated at each point sampled during the breath, with appropriate corrections for absolute lung volume. It was found that in most cases Raw varied less with respect to tidal volume than to tidal flow. Various patterns of Raw change in relation to tidal volume were found. These included an elevated but relatively constant resistance, a progressively rising expiratory resistance, and in 3 infants with laryngomalacia, a progressively rising inspiratory resistance. It was also found that the dynamic performance of the rebreathing bag was such that considerable errors would occur if apparatus resistance was assumed to be constant and so the actual apparatus resistance at each point was subtracted from the total resistance to give Raw. In conclusion, Raw is not constant throughout the respiratory cycle in infants and the pattern of change conveys additional information.

The functional response of infants with persistent wheezing to nebulized beclomethasone dipropionate

Lung function was measured in nine infants, ages 15-36 weeks, who had persistent wheezing, apparently following acute bronchiolitis, before and after 2 weeks of treatment with either inhaled nebulized beclomethasone dipropionate (BDP) or placebo in a randomized, double blind, crossover trial. The effect of nebulized albuterol (Salbutamol) was measured before and after the steroid treatment. Thoracic gas volume (TGV) and specific airway conductance (SGaw) were determined using a whole body plethysmograph, and forced expiratory flow at resting lung volume (VmaxFRC) was determined with a thoracoabdominal compression jacket. All infants had marked airways obstruction before treatment with mean +/- SE VmaxFRC of 24 +/- 4% predicted and SGaw of 37 +/- 5% predicted. Two weeks of placebo treatment had no significant effect on lung function, but after 2 weeks of BDP inhalation there was a significant rise in SGaw to 61 +/- 7% (P less than 0.005). VmaxFRC increased to 42 +/- 13% but the difference did not reach significance. Respiratory rate and clinical score for retractions and wheezing also fell significantly with BDP therapy (P less than 0.01 and P less than 0.001 respectively). Albuterol had no effect on lung function either before or during steroid therapy. Steroids may have a role in the management of persistent wheezing following bronchiolitis.

Flow-pressure looping during plethysmography in wheezy infants

Marked looping of the expiratory portion of the flow-pressure relationship was noted in some infants during measurements of airway resistance in a whole-body plethysmograph while the respired air was maintained at body temperature and humidity. An investigation of 13 infants who had varying degrees of airway obstruction showed that there was a negative correlation (r = 0.72) between the severity of the looping and specific airway conductance (SGaw). An even stronger correlation (r = 0.85) was found between the tangent of the angle of phase lag between flow and pressure (theta) and the forced expiratory time constant (t) obtained from the partial forced expiratory flow-volume curve. Such a relationship would be predicted from a model in which the lung behaved as a simple electrical resistance-capacitance network during expiration. It is suggested that the looping is the result of small airway closure during expiration in wheezy infants, with a consequent rise in resistance and prolongation of the time constant of the lung.

Influence of the heart on the vertical gradient of transpulmonary pressure in dogs

Estimations were made of the vertical gradient of transpulmonary pressure (VGTP) from measurements of esophageal pressure in nine head-up dogs at functional residual capacity (FRC) when alive, when dead, and after total bilateral pneumothorax. The VGTP of 0.4 cmH2O/cm height in the alive state was abolished by pneumothorax, and roentgenograms showed that the heart moved in a caudal-dorsal direction. There was a small but significant increase in the VGTP on going from FRC to near total lung capacity (TLC) in alive head-up dogs. In eight dead head-up dogs heart weight was increased by replacing various amounts of heart blood with Hg. The VGTP was significantly increased from 0.28 to 0.51 cmH2O/cm height. The fractional increase in the VGTP was similar to the fractional increase in heart weight. In five dogs extrapolation to zero heart weight gave an average VGTP of 0.14 cmH2O/cm height. We conclude that the lungs help support the heart in the head-up dog and that the VGTP is in part determined by the pressure distribution required for this support.

Relation between efficacy of sodium cromoglycate and baseline lung function in exercise- and hyperventilation-induced asthma

The protective effect of sodium cromoglycate (SCG) against exercise- and hyperventilation-induced asthma with respect to basal lung function was investigated in young asthmatics. The subjects performed standardized exercise or isocapnic hyperventilation challenge tests breathing cold dry air; in each case the effect of SCG was compared with that of a placebo in a double-blind fashion. With exercise as the challenge in 24 subjects, there was a strong positive correlation between the protective effect of SCG and the basal level of lung function. Using hyperventilation as the challenge in 11 subjects, there was no such correlation, but excluding two known placebo responders, there was a negative correlation between the protective effect of SCG and basal lung function. There findings suggest that exercise and hyperventilation operate differently in inducing asthma.

Refractory period following induced asthma: contributions of exercise and isocapnic hyperventilation

To compare the refractory period that follows exercise and isocapnic hyperventilation, 10 asthmatic children performed two pairs of challenge tests in random order at least six hours apart. In pair A a hyperventilation challenge was followed by an exercise challenge and in pair B the order was reversed. Both pairs of tests were done while the children were breathing cold dry air. Tests were matched in terms of work load, ventilation, and end tidal carbon dioxide tension (PCO2). The mean percentage fall in FEV1 (delta FEV1) after the first challenge (hyperventilation) of pair A and the first challenge (exercise) of pair B were the same (30% (SEM 2%)) and 30% (4%) respectively). The mean delta FEV1 of the exercise test following hyperventilation in pair A and of hyperventilation following exercise in pair B was 22% (4%) and 18% (4%) respectively. Both these latter results were significantly lower than the respective delta FEV1 when the challenge was the first test of the pair. Although the mean refractoriness index (reduction in induced asthma in the second test of each pair compared with the first test) was greater when exercise was the first challenge, the difference was not significant.