Diffusing capacity and over-all ventilation:perfusion in asthma

Pulmonary function in children with persistent tachypnea of infancy

BACKGROUND

Data on the prevalence and type of lung function impairment in preschool and school-aged children previously diagnosed with persistent tachypnea of infancy (PTI) are scarce. Therefore, this study aims to assess pulmonary function in this age group.

METHODS

Children diagnosed with PTI over 3 years old were admitted for follow-up visits and healthy controls were enrolled. The study group included children who were able to complete pulmonary function tests (PFTs). Medical history, physical examination, and pulmonary function (spirometry, body plethysmography, impulse oscillometry, nitrogen multiple breath washout test, diffusing capacity for carbon monoxide [DL_CO ]) were assessed.

RESULTS

Thirty-seven children (26 boys, 11 girls; median age: 5.6 years) diagnosed with PTI and 37 healthy controls were recruited. Forced expiratory volume in 1 s and forced vital capacity were significantly lower (-1.12 vs. 0.48, p = 0.002 and -0.83 vs. 0.31, p = 0.009, respectively); respiratory resistance at 5 Hz (0.06 vs. -0.62, p = 0.003), resonant frequency (1.86 vs. 1.36, p = 0.04), residual volume (RV) (2.34 vs. -1.2, p < 0.0001), RV%TLC (total lung capacity) (2.63 vs. -0.72, p < 0.0001), and specific airway resistance (5.4 vs. 2.59, p = 0.04) were significantly higher in PTI patients as compared with controls (data were presented as median z-score). Air trapping was found in 60.0%, and abnormally high lung clearance index and DL_CO  were found in 73.3% and 90.9% of PTI patients, respectively.

CONCLUSIONS

This study demonstrated that lung function is affected in most children with PTI. PFTs showed that peripheral airways are the major zone of functional impairment.

Static lung volumes and diffusion capacity in adults 30 years after being diagnosed with asthma

Background

Long-term follow-up studies of adults with well-characterized asthma are sparse. We aimed to explore static lung volumes and diffusion capacity after 30 + years with asthma.

Methods

A total of 125 adults with an objectively verified diagnosis of asthma between 1974–1990 at a Danish respiratory outpatient clinic completed a follow-up visit 2017–19. All participants (age range 44–88 years) completed a comprehensive workup and were, based on these assessments, classified as having either active asthma or being in complete remission. The examination program included measurements of static lung volumes and diffusion capacity.

Results

Participants with active asthma were hyperinflated (residual volume/total lung capacity ratio 0.43, 95% CI 0.41—0.45) (RV/TLC ratio) compared with those in remission (RV/TLC ratio 0.38, 95% CI 0.36—0.41) (p < 0.03). A tendency towards higher diffusion capacity per liter lung volume was seen in participants with active asthma (KCO 100% predicted, 95% CI 97—104) compared with those in remission (KCO 94% pred., 95% CI 89—99) (P = 0.10). Longer asthma duration was associated with a higher KCO 0.47% pred./year (95% CI 0.14—0.80), adjusted for age and smoking. Patients on GINA step 4 and 5 treatment were more hyperinflated (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta$$\end{document}Δ RV 14% pred., 95% CI 3—27) and had higher airway resistance (mean 53% pred., 95% CI 9—97) than participants on lower GINA steps. Patients with uncontrolled disease had substantially higher airway resistance (72% pred. 95% CI 20—124) than well-controlled patients.

Conclusion

Thirty years after a confirmed diagnosis of asthma, those continuing to have active asthma and those having severe asthma, have higher diffusion capacity and more hyperinflation than patients in remission.

Transfer coefficients better reflect emphysematous changes than carbon monoxide diffusing capacity in obstructive lung diseases

The overlap between asthma and chronic obstructive pulmonary disease (COPD) has attracted the interest of pulmonary physicians; thus, measurement of carbon monoxide diffusion capacity (DLco) and/or transfer coefficients (Kco, DLco/V_A) may become valuable in clinical settings. How these parameters behave in chronic obstructive lung diseases is poorly understood. We predicted that Kco might more accurately reflect emphysematous changes in the lungs than DLco. We examined DLco and Kco in nonsmokers and smokers with asthma and investigated their relationships with forced expiratory volume in 1 s (%FEV₁) by group. We then selected nonsmokers (As-NS) and smokers with asthma (As-Sm) in both groups and those with COPD while controlling for the degree of airflow limitation across groups. Emphysema volumes [%lung attenuation volume (%LAV)] and percentage of cross-sectional area of small pulmonary vessels <5 mm² (%CSA_<5) were measured by computed tomography. In As-NS, %Kco was significantly higher when FEV₁% was reduced, but such a correlation was not seen in As-Sm. %Kco successfully differentiated among the three groups when airflow limitation levels were matched. However, %DLc, was significantly reduced only in patients with COPD. Both %LAV and %CSA_<5 were better correlated with %Kco than with %DLco. There was discordance between %DL_CO and %Kco in As-Sm, which was not seen in As-NS. Overall, %Kco better reflects emphysematous changes in obstructive lung diseases than %DLco. NEW & NOTEWORTHY Despite differing behaviors of %Kco and %DLco in several diseases, the characteristics of these parameters have not been fully examined in smokers with asthma. Here, we demonstrated that %Kco is a more sensitive parameter of pathophysiology, better reflecting emphysematous changes in chronic obstructive lung diseases overall, compared with %DLco. Thus, more precise interpretations of %DLco and %Kco may provide clues for understanding the pathophysiology of obstructive lung diseases.

Early life exposure to allergen and ozone results in altered development in adolescent rhesus macaque lungs

In rhesus macaques, previous studies have shown that episodic exposure to allergen alone or combined with ozone inhalation during the first 6 months of life results in a condition with many of the hallmarks of asthma. This exposure regimen results in altered development of the distal airways and parenchyma (Avdalovic et al., 2012). We hypothesized that the observed alterations in the lung parenchyma would be permanent following a long-term recovery in filtered air (FA) housing. Forty-eight infant rhesus macaques (30 days old) sensitized to house dust mite (HDM) were treated with two week cycles of FA, house dust mite allergen (HDMA), ozone (O3) or HDMA/ozone (HDMA+O3) for five months. At the end of the five months, six animals from each group were necropsied. The other six animals in each group were allowed to recover in FA for 30 more months at which time they were necropsied. Design-based stereology was used to estimate volumes of lung components, number of alveoli, size of alveoli, distribution of alveolar volumes, interalveolar capillary density. After 30 months of recovery, monkeys exposed to HDMA, in either group, had significantly more alveoli than filtered air. These alveoli also had higher capillary densities as compared with FA controls. These results indicate that early life exposure to HDMA alone or HDMA+O3 alters the development process in the lung alveoli.

Asthma outcomes: pulmonary physiology

BACKGROUND

Outcomes of pulmonary physiology have a central place in asthma clinical research.

OBJECTIVE

At the request of National Institutes of Health (NIH) institutes and other federal agencies, an expert group was convened to provide recommendations on the use of pulmonary function measures as asthma outcomes that should be assessed in a standardized fashion in future asthma clinical trials and studies to allow for cross-study comparisons.

METHODS

Our subcommittee conducted a comprehensive search of PubMed to identify studies that focused on the validation of various airway response tests used in asthma clinical research. The subcommittee classified the instruments as core (to be required in future studies), supplemental (to be used according to study aims and in a standardized fashion), or emerging (requiring validation and standardization). This work was discussed at an NIH-organized workshop in March 2010 and finalized in September 2011.

RESULTS

A list of pulmonary physiology outcomes that applies to both adults and children older than 6 years was created. These outcomes were then categorized into core, supplemental, and emerging. Spirometric outcomes (FEV(1), forced vital capacity, and FEV(1)/forced vital capacity ratio) are proposed as core outcomes for study population characterization, for observational studies, and for prospective clinical trials. Bronchodilator reversibility and prebronchodilator and postbronchodilator FEV(1) also are core outcomes for study population characterization and observational studies.

CONCLUSIONS

The subcommittee considers pulmonary physiology outcomes of central importance in asthma and proposes spirometric outcomes as core outcomes for all future NIH-initiated asthma clinical research.

Lung gas transfer in children with sickle cell anaemia

The impact of sickle cell anaemia (SCA) on respiratory function of children must be determined if their management is to be optimised. Pulmonary diffusing capacity (DL(CO)), corrected for haemoglobin (DL(COc)), therefore was assessed in 24 children with SCA and 24 ethnic matched controls, mean age 11 (range 7-16) years. To determine if any differences found correlated with other measures of lung function, spirometry was undertaken and lung volumes assessed. The SCA children compared to the controls had lower weight (p=0.01), body mass index (p=0.002), DL(CO) (p<0.0001), K(CO) (p=0.003), V(CSB) (p=0.01), FEV(1) (p<0.0001) and FVC (p<0.0001), but greater K(COc) (p=0.001). K(COc) results correlated significantly with PEF (r=-0.58, p=0.02), but not TLC(pleth) (p=0.36), FEV(1) (0.39) or FVC (p=0.36). In conclusion, when corrected for haemoglobin levels, the SCA children compared to controls of similar age had elevated gas transfer per unit lung volume results. Our results suggest this abnormality is independent of other lung function abnormalities.

Diffusing Capacity for Nitric Oxide and Carbon Monoxide in Patients With Diffuse Parenchymal Lung Disease and Pulmonary Arterial Hypertension

BACKGROUND

The passage of carbon monoxide (CO) through the alveolocapillary membrane and into the plasma and intraerythrocytic compartments determines the diffusing capacity of the lung for CO (DLCO) as defined by the Roughton and Forster equation. On the other hand, the single-breath diffusing capacity of the lung for nitric oxide (DLNO) is thought to represent the true membrane diffusing capacity because of its very high affinity for hemoglobin (Hb) and its independence from pulmonary capillary blood volume. Therefore, the DLNO/DLCO ratio can be used to differentiate between thickened alveolocapillary membranes (both DLNO and DLCO are decreased, and the DLNO/DLCO ratio is normal) and decreased perfusion of ventilated alveoli (the DLNO less decreased than the DLCO; therefore, the DLNO/DLCO ratio is high) in patients with pulmonary disease.

STUDY DESIGN

We measured the combined values of DLCO and DLNO in 41 patients with diffuse parenchymal lung disease (DPLD), 26 patients with pulmonary arterial hypertension (PAH), and 71 healthy subjects.

RESULTS

The DLCO (corrected to the standard Hb value) was lowered in the DPLD group (64% of predicted) and in the PAH group (64% of predicted), and was normal in the control group (105% of predicted). The DLNO/DLCO ratio in patients with PAH (4.98) was significantly higher than that in patients with DPLD (4.56) and in healthy subjects (4.36).

CONCLUSION

The DLNO/DLCO ratio is significantly higher in patients with PAH than in healthy subjects, although this ratio cannot be applied as a screening test to discriminate between patients with DPLD and PAH as the overlap between these groups is too large.

Clinical practice guidelines: medical follow-up of patients with asthma--adults and adolescents

The follow-up of patients with asthma should focus on asthma control (disease course over a number of weeks).

Clinical significance of elevated diffusing capacity

STUDY OBJECTIVE

Single-breath diffusing capacity of the lung for carbon monoxide (DLCO) is used as a pulmonary function test (PFT) to assess gas transfer in the lungs. The implications of a low DLCO are well-recognized, but the clinical significance of a high DLCO is not clear. The aim of this study was to identify the clinical correlates of a high DLCO.

PATIENTS AND METHODS

We identified 245 patients with a high DLCO (ie, > 140% predicted) and a matched group of 245 patients with normal DLCO (ie, 85 to 115% predicted), who were selected from a laboratory database of 45,000 patients tested between January 1997 and December 1999. We compared the demographic features, clinical diagnoses, and PFT data between the two groups.

SETTINGS

Large multispecialty group practice.

RESULTS

The patients in the high DLCO group were heavier (mean [+/- SD] weight, 96.0 +/- 22.9 vs 85.0 +/- 21.3 kg, respectively; p < 0.001), had a higher mean body mass index (32.9 +/- 7.4 vs 29.4 +/- 6.4 kg/m(2), respectively; p < 0.001), larger body surface area (p < 0.001), and larger mean total lung capacity (p = 0.007) and alveolar volume (p < 0.001). The clinical diagnoses of obesity (p < 0.001) and asthma (p < 0.001) were more common among patients with high DLCO values. The majority of patients (62%) with a high DLCO had a diagnosis of obesity, asthma, or both. Polycythemia, hemoptysis, and left-to-right shunt were uncommon.

CONCLUSION

A high DLCO on a PFT is most frequently associated with large lung volumes, obesity, and asthma. Other conditions are much less common. A clinical condition, which typically reduces DLCO, may deceptively normalize DLCO in such patients.

Partial pulmonary sympathetic denervation by thoracoscopic D2-D3 sympathicolysis for essential hyperhidrosis: effect on the pulmonary diffusion capacity

In patients with essential hyperhidrosis (EH), a pathological condition characterized by increased activity of the upper dorsal sympathetic ganglia D2-D3, anatomical interruption at the D2-D3 level by thoracoscopic sympathicolysis (TS) is a safe and effective treatment. The D2 and D3 ganglia, however, are also in the pathway of sympathetic lung innervation, which may influence the pulmonary diffusion capacity for carbon monoxide (expressed as transfer factor for CO:TLCO, and as transfer coefficient for CO:KCO). We therefore studied the effect of TS on TLCO and KCO in 50 EH patients: compared with pre-operative values, both TLCO (-6.7%, P < 0.001) and KCO (-4.2%, P = 0.002) were significantly decreased at 6 weeks after bilateral TS, an effect which was independent of the smoking status of the patients. In order to explain this phenomenon, the following pharmacological interventions were studied: (1) oral beta 1 + 2-adrenoreceptor blockade with propranolol caused a comparable decrease of TLCO (-6.3%) and KCO (-7.5%) in matched normal subjects, but had no effect on TLCO and KCO in EH patients prior to TS; and (2) subsequent inhalation of the beta 2-adrenoreceptor agonist salbutamol in a dosage suspected to cause alveolar beta-receptor stimulation had no effect on TLCO and KCO, neither in the normal subjects, nor in EH patients (before and after TS). Although the exact mechanism of the TS-induced decrease in TLCO and KCO remains speculative, these findings suggest that they may be related to a beta 1-adrenoreceptor-mediated change in pulmonary capillary membrane permeability, although TS-induced changes in pulmonary blood flow or an interplay of both mechanisms cannot be excluded.

Clinical correlates of an elevated diffusing capacity for carbon monoxide corrected for alveolar volume

The diffusing capacity for carbon monoxide is partially dependent on lung volume at which it is measured. As a consequence, the diffusing capacity for carbon monoxide is often indexed to the simultaneously measured lung volume (VA), giving rise to the term DL/VA. This reflects the diffusing capacity of carbon monoxide per unit area of lung parenchyma. The authors investigated the pulmonary function of 18 patients who had an elevated DL/VA in order to identify factors that could account for this abnormality. Sixteen of the 18 had a reduction in vital capacity. The vital capacity was reduced because of obesity, pleural disease, and diaphragmatic dysfunction. Eight of nine patients with a body mass index > 30 kg/m2 had a reduction in vital capacity. On the basis of these findings, we believe that an elevated DL/VA should alert the physician to the possibility of 1) an increase in pulmonary capillary blood volume (Vc) (obesity, polycythemia, negative pleural pressure), and 2) reduced VA that does not directly affect the pulmonary capillary bed (pleural disease, neuromuscular disease).

Diffusing capacity in the clinical assessment of chronic airflow limitation

CAL remains an important cause of morbidity and mortality. The diffusing capacity has ranked high in the assessment of CAL because it represents the best pulmonary function test to assess the integrity of the pulmonary capillary bed. Unfortunately, numerous physiologic, pathologic, and technical factors affect the test, thus limiting its sensitivity and specificity. HRCT techniques offer the potential to assess the extent of emphysema more accurately, but the technique requires greater standardization and is more expensive and less noninvasive than DLcoSB testing. Although the CIBA symposium considered DLcoSB "essential" in the investigation of the CAL patient, 16 the use of conventional DLcoSB testing in the seated position at rest is not currently advised as a routine screening procedure. The test must be performed in a center with high degree of quality control, and the results can be of value only by integrating the result into a comprehensive clinical assessment. Within this context, conventional DLcoSB testing may provide limited information about the extent of emphysema because reductions in DLcoSB correlate with the extent of emphysema by HRCT. When DLcoSB is normal, it may point in the direction of considering asthma as the cause of the airflow limitation. It may also provide information about disease severity and prognosis in O2-dependent CAL patients. The test should be a part of the investigation of the patient with unexplained dyspnea. It remains controversial how emphysema correlates with the degree of impairment in CAL, and further work needs to be done to clarify this relationship. This requires a reexamination of current CT methods 110 and the relationship between DLcoSB, structural changes in the lung, and HRCT evidence of emphysema. Refinements in DLcoSB testing methods, such as the measurement of DLcoSB-3EQ are linked to rapidly responding CO analyzers and computer-driven software, which will potentially improve the accuracy and reproducibility of the test, particularly in the presence of airway obstruction and nonuniform distribution of ventilation. Such refinements, which offer the possibility that tests of diffusion could become more useful markers of disease, include measuring DLcoSB when the pulmonary capillary recruitment is near maximal (head-down position, exercise), enhancing the sensitivity of the test to alterations in the lung periphery, standardizing previous volume history, developing more precise corrections for Hb and COHb, and developing an index of diffusion nonuniformity.

Single breath diffusing capacity for carbon monoxide in stable asthma

BACKGROUND

Single breath diffusing capacity for carbon monoxide (Dco) is commonly used as a simple method of assessing overall pulmonary gas exchange properties. Studies of Dco in bronchial asthma have yielded conflicting results.

OBJECTIVE

To study Dco and to determine the factors influencing Dco in patients with asthma.

METHODS

Dco was prospectively measured in 80 consecutive never-smoker patients with uncomplicated stable asthma. The topographic distribution of lung perfusion was determined in 10 asthmatics and 10 controls, with a 133Xe radionuclide scan.

RESULTS

The mean (SD) value of Dco was increased to 117 (17) percent of predicted values; individual values were either within or above normal limits; diffusion was also elevated at 116 (19) percent after correction for alveolar volume (transfer coefficient, D/VA). The Dco was not correlated with atopic status, duration of asthma, or results of spirometric tests; there was a weak negative correlation between D/VA and FEV1 or residual volume. There was a better perfusion of the upper zones of the lungs in asthmatics as compared with controls. Among the asthmatics, there was a strong positive correlation between Dco and the apex to base perfusion ratio (r = 0.975).

CONCLUSIONS

Dco is normal or high among never smoker patients with uncomplicated asthma; elevated Dco may be attributed to a better perfusion of the apices of teh lungs; the latter could result from two mutually nonexclusive mechanisms: an increase in pulmonary arterial pressure and/or a more negative pleural pressure generated during inspiration as a consequence of bronchial narrowing. The unexpected finding of high Dco should raise the possibility of bronchial asthma in patients with otherwise undiagnosed conditions.

Pulmonary gas exchange during histamine-induced bronchoconstriction in asthmatic subjects

Bronchial provocation for testing airway hyperreactivity is now well-established. However, the effects of histamine-induced bronchoconstriction on pulmonary gas exchange in man have not been systematically studied. We empirically noted marked decreases in PaO2 in some asthmatic subjects following induced bronchoconstriction. Nine subjects with mild, stable asthma were studied, each on two separate days. The first determined the dose of inhaled histamine necessary to decrease FEV1 by 20 percent and the relationship to lung volume and to pulmonary resistance by the interrupter technique (Rint). On the second day arterial blood gases, ventilation, Rint, and the anatomic (VDan) and physiologic (VDphys) dead spaces were measured simultaneously. There was a significant (p less than 0.05), profound fall in PaO2 (mean, -21.8 mm Hg) and in P(A-a)O2 (mean +14.7 mm Hg) within 5 min after bronchoconstriction, associated with a significant (p less than 0.05) increase in respiratory frequency (mean +5.1 min-1); and decrease in tidal volume (mean, -0.3 L). The ratio VDphys/VT increased significantly (p less than 0.05; mean change, +0.08) even though VDan and VDphys did not. Bronchoconstriction induced the broadening of ventilation (V)/perfusion (Q) ratios, with, most likely, an increase in areas of high V/Q. Histamine-induced bronchoconstriction in mild asthma results in a marked fall in PaO2 due to induced V/Q inequality. Therefore, histamine airway challenge should be used with caution in patients with any preexisting hypoxemia.

Carbon monoxide diffusing capacity in asthmatic patients with mild airflow limitation

The aim of this study was to test the hypothesis that carbon monoxide diffusing capacity (DCO) is elevated in asthmatic patients with minimal airflow limitation and/or hyperinflation; the latter factors should reduce the possibility of technical errors in the measurement of DCO. In ten asthmatic and ten healthy subjects, DCO and its components, membrane diffusing capacity (Dm) and pulmonary capillary blood volume (Qc) were measured by the single-breath method. Values were normalized for alveolar volume (VA). The mean DCO/VA was higher in the asthma groups as was the Qc/VA. The Dm/Qc was also higher in the asthma group. In the asthmatic but not the healthy subjects, both DCO/VA and Qc/VA were negatively correlated with the forced expiratory flow at 50 percent of vital capacity and peak inspiratory flow rate. Thus, DCO/VA may be increased in asthmatic patients with only mild airflow limitation; this may be due to an elevated capillary blood volume.

Effect of high negative inspiratory pressure on single breath CO diffusing capacity

We measured the single breath diffusing capacity for carbon monoxide (DLcoSB) using a three-equation method to describe CO uptake in 10 normal seated subjects who either voluntarily inhaled slowly (0.5 L/sec) to total lung capacity (TLC), or inhaled slowly to TLC with maximal effort through a high inspiratory resistance which created high negative inspiratory pressure. Subjects then immediately exhaled slowly at a voluntarily controlled exhaled flow. Single breath maneuvers were performed in duplicate both with and without high negative inspiratory pressure while subjects were seated upright at rest and during steady-state bicycle exercise. We found that high negative inspiratory pressure increased DLcoSB by 10.5 +/- 4.9% (mean +/- 1 SD) at rest (P less than 0.001). In 7 subjects low level exercise alone increased DLcoSB by a similar amount (12.1 +/- 7.3%; P = 0.005). In six of the subjects there was a significant correlation between the increase in DLcoSB during high negative inspiratory pressure at rest and the increase in DLcoSB during steady-state exercise (r = 0.89; P less than 0.01). During steady-state exercise, high negative inspiratory pressure further increased DLcoSB 6.4 +/- 6.3% compared to exercise alone (P = 0.05). We conclude that the increase in DLcoSB with high negative inspiratory pressure at rest is a simple reproducible method of assessing recruitment of the pulmonary capillary bed in man.

Acute and chronic pulmonary function changes in allergic bronchopulmonary aspergillosis

Pulmonary functions of patients with allergic bronchopulmonary aspergillosis were studied during an acute episode (n = 6); during a mean follow-up period of 44 months (range four months--14.8 years) (n = 16); and for any correlation between duration of ABPA and asthma with the total lung capacity (helium dilution), 1 second forced expiratory volume (FEV1), vital capacity, 1 second forced expiratory volume-forced vital capacity ratio (FEV1:FVC per cent) and diffusing capacity of carbon monoxide (DL:CO) (single breath) for the entire group (n = 22). All patients were treated with corticosteroids (intermittent or continuous) and bronchodilators. For the 16 patients, slopes using linear regression analysis were determined from the function as per cent predicted versus time in months from diagnosis and then analyzed for significance. Significant functional loss was shown in three of 16 patients for FEV1, two of 16 patients for vital capacity, one of 16 patients for FEV1:FVC per cent, none of 10 patients for DL:CO and one of 10 patients for total lung cital capacity, FEV1:FVC per cent and the duration of asthma or allergic bronchopulmonary aspergillosis was found by multiple regression analysis correcting for age and smoking (mean 4.24 years; range 0.3 to 14.8 years). Roentgenographic criteria and blood eosinophilia were used to define a "flare" of allergic bronchopulmonary aspergillosis. The six patients during a flare showed a significant reduction in total lung capacity (P less than 0.001), vital capacity (P less than 0.05), FEV1 (P less than 0.01) and DL:CO (P less than 0.001) which uniformly returned to baseline values during steroid therapy. The FEV1:FVC per cent remained unaltered. These findings, contrary to suggestions in the literature, indicate that in the majority of our patients there was no significant progressive functional deterioration after diagnosis. However, during acute episodes of allergic bronchopulmonary aspergillosis, transient reduction of volumes and DL:CO were uniformly present.

Large airway constriction in allergic rhinitis

Extensive pulmonary function tests, including most of the sensitive new techniques capable of detecting small airways obstruction, were performed in 16 asymptomatic patients with allergic rhinitis and 31 normal control subjects. Mean flow rates, lung volumes, and results of tests measuring airways closure, distribution of ventilation, and diffusing capacity for carbon monoxide/alveolar volume did not differ significantly between the groups. Airways resistance (RAW) was significantly higher and specific conductance (SGAW) was significantly lower in subjects with rhinitis. Following administration of nebulized isoproterenol, RAW decreased (p less than 0.001) and SGAW increased (p less than 0.001) to mean values statistically indistinguishable from results obtained in control subjects. Individual results were normal for all tests except RAW and SGAW which were both abnormal in 3 subjects with rhinitis. The results of this investigation indicate that asymptomatic subjects with allergic have large airway (trachea and/or major bronchi) narrowing due to bronchoconstriction and no evidence of diffuse, or small airways, obstruction.

Cardiopulmonary effects of long-term bronchodilator administration

Because of reports of drug tolerance occurring with chronic use of adrenergic agents in asthma, we investigated cardiopulmonary responsiveness to ephedrine and to the beta-2 agent, tebutaline, following chronic drug administration for periods up to one year. With chronic drug administration baseline (prior to daily medication) FEV increased 19% in the terbutaline group and 3.5% in the ephedrine group. An additional increase of FEV above baseline of 23% for terbutaline and 12% for ephedrine was noted after daily medication. Terbutaline also had a longer duration of effect; peak response after ephedrine occurred at 2 hr while terbutaline effect was maximal at 3 to 4 hr. There was no evidence for reduced responsiveness to the bronchodilator actions of either drug at any time. Despite prolonged use, both drugs continue to increase heart rate and pulse pressure moderately following ingestion, with a peak effect occurring at 3 hr; however, pulse pressure widened after terbutaline because of a diastolic fall, while the major effect of ephedrine was to increase systolic pressure. Baseline blood pressure, particularly diastolic, declined progressively with continued drug use. No evidence of cardiac, ehpatic, renal, or ophthalmologic toxicity or change in need for other bronchodilator agents was noted during the study with either drug.