Pulmonary diffusing capacity, membrane diffusing capacity, and capillary blood volume in children with intractable asthma with and without chronic overinflation of the lungs

Effects of the menstrual cycle on lung function variables in women with asthma

RATIONALE

Angiogenesis is a defining pathologic feature of airway remodeling and contributes to asthma severity. Women experience changes in asthma control over the menstrual cycle, a time when vessels routinely form and regress under the control of angiogenic factors. One vital function modulated over the menstrual cycle in healthy women is gas transfer, and this has been related to angiogenesis and cyclic expansion of the pulmonary vascular bed.

OBJECTIVES

We hypothesized that changes in gas transfer and the pulmonary vascular bed occur in women with asthma over the menstrual cycle and are associated with worsening airflow obstruction.

METHODS

Twenty-three women, 13 with asthma and 10 healthy control subjects, were evaluated over the menstrual cycle with weekly measures of spirometry, gas transfer, nitric oxide, hemoglobin, factors affecting hemoglobin binding affinity, and proangiogenic factors.

MEASUREMENTS AND MAIN RESULTS

Airflow and lung diffusing capacity varied over the menstrual cycle with peak levels during menses that subsequently declined to nadir in early luteal phase. In contrast to healthy women, changes in lung diffusing capacity (DL(CO)) were associated with changes in membrane diffusing capacity and DL(CO) was not related to proangiogenic factors. DL(CO) did not differ between the two groups, although methemoglobin and carboxyhemoglobin were higher in women with asthma than in healthy women.

CONCLUSIONS

Women with asthma experience cyclic changes in airflow as well as gas transfer and membrane diffusing capacity supportive of a hormonal effect on lung function.

Pulmonary capillary blood volume in hyperpnea-induced bronchospasm

Reactive hyperemia of the bronchial circulation has been postulated to contribute to the airway narrowing that occurs following exercise or hyperpnea in subjects with asthma with hyperpnea-induced bronchospasm (HIB). Changes in lung parenchymal mechanics also occur in HIB, including increases in peripheral airway resistance. Since the peripheral airways and lung parenchyma are supplied by the pulmonary circulation, and changes in the pulmonary circulation could alter airway resistance or tissue mechanics, we hypothesized that pulmonary capillary blood flow would increase in association with HIB, resulting in increases in pulmonary capillary blood volume (VC). We measured VC by using two test gases of varying oxygen concentration to determine the diffusing capacity of the lung for carbon monoxide (DL(CO)) before and after a period of hyperpnea in 13 subjects with asthma with HIB and 10 control subjects without asthma. Despite subjects with asthma having a significant fall in FEV(1) following hyperpnea compared with control subjects (DeltaFEV(1) = -26 +/- 12 versus -4 +/- 4%, mean +/- SD, p < 0.001), there was no change in the DL(CO) or VC from baseline values. We conclude that pulmonary capillary blood volume does not change following hyperpnea, and therefore that changes in pulmonary blood flow are not associated with HIB.

Single breath carbon monoxide transfer factor in different forms of chronic airflow obstruction in a general population sample

The single breath transfer factor for carbon monoxide (TLCO), TLCO/alveolar volume (VA), and standard spirometric indices were measured in a survey of the randomly selected population sample of 1174 subjects enrolled in the Tucson epidemiological study of airways obstructive disease. Subjects were subdivided according to whether the FEV1/FVC ratio was under 65%, 65-75%, or over 75%. The influence of smoking on TLCO was accounted for by expressing TLCO as a percentage of the expected value-that is, of the value expected from the reported cigarette consumption. The 63 subjects who gave a history of physician confirmed asthma in reply to a questionnaire tended to have high values for TLCO, even when FEV1/FVC was reduced. In the absence of a given diagnosis of asthma, however, TLCO and TLCO/VA were reduced when the FEV1/FVC ratio was reduced, whether or not a clinical diagnosis of emphysema had been reported. This suggests that these subjects may have undiagnosed emphysema. This cross sectional analysis of our survey data suggests that subjects in our sample with spirometric evidence of chronic airflow obstruction have different forms of disease, characterised by different physiological features, in addition to the different risk factors and clinical courses reported earlier.

Carbon monoxide diffusing capacity, other indices of lung function, and respiratory symptoms in a general population sample

To assess the relationships among single-breath diffusing capacity for CO (DLCOsb) (13), respiratory symptoms, and cigarette smoking in a general population sample, the data of 718 men and 894 women 20 yr of age or older were analyzed, and comparisons were performed with flow-volume curve (MEFV) variables and the slope of the alveolar plateau (DN2%/L) as well. Percent predicted DLCOsb and its correction for alveolar volume (DL/VA) were significantly lower in smokers than in nonsmokers. The relationship of presence/absence of respiratory symptoms and cigarette smoking with DLCOsb and DL/VA was significant. DLCO indices were almost always selected as discriminant variables in multivariate analysis between asymptomatic and symptomatic subjects. Poor concordance among lung function tests was evident: in men, 30% with abnormal (i.e., lower than 97.5% percentile) and 21% with normal DLCO indices also had abnormal MEFV parameters and/or DN2%/L. In women, the corresponding figures were 24 and 10%, respectively. In men, when considering only DLCO indices, the percentage of symptomatic subjects with abnormal lung function tests ranged from 33% in those with at least one symptom to 45% in those complaining of dyspnea. When the proportion of symptomatic subjects with DN2%/L and MEFV abnormalities were added, it increased to 56 and 66%, respectively. However, in women the proportion of symptomatic subjects with abnormal lung function indices was very small. These results indicate the usefulness of including CO diffusing capacity in epidemiologic surveys in the detection of abnormalities.

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.

Physiologic characteristics of subjects exhibiting accelerated deterioration of ventilatory function

From a randomly selected community population sample followed with sequential surveys since 1972, 13 subjects who exhibited a mean annual decline in FEV1 greater than 60 ml/yr were drawn for detailed studies of lung function. These subjects had developed clinically significant airway obstruction during this period of follow-up. Clinical evaluation was not successful in characterizing the nature of the disorder. None of the subjects had alpha-1-antitrypsin deficiency. In a small proportion of subjects, elevated total serum immunoglobulin E may have played a role in the obstructive airway disorder. Some subjects exhibited loss of lung elastic recoil and diminished carbon monoxide diffusing capacity suggestive of developing emphysema. Others appeared to have intrinsic airway disease involving large and/or small airways, which may be fixed in some and responsive to bronchodilator in others. Thus, neither the site nor the nature of the disorder inferred from results of physiologic tests was uniform, illustrating the heterogeneous nature of chronic obstructive lung disease.

Evaluation of the single-breath diffusing capacity in asthma and cystic fibrosis

To explain why the single-breath carbon monoxide diffusing capacity (Dsb) was, on the average, elevated in 163 asthmatic subjects and 175 patients with cystic fibrosis, we simulated this elevation in ten normal subjects by having them perform the test for Dsb through an inspiratory obstruction. This resulted in an 18 percent increase in Dsb corrected for pulmonary volume. Inhalation of a bronchodilator drug was associated with relief of obstruction and a fall in the corrected Dsb in 31 asthmatic subjects but did not change either the obstruction or the corrected Dsb in 17 patients with cystic fibrosis. We suggest that elevated Dsb in asthma and cystic fibrosis is partly due to maximal inspiration against obstructed airways. This requires abnormally negative intrathoracic pressures, increasing the pulmonary capillary blood volume, and, thereby, increasing the Dsb.

Single breath transfer factor measured concurrently by two methods in asthmatic and normal subjects

Haydu, S.P. (1974).Thorax, 29, 232-236. Single breath transfer factor measured concurrently by two methods in asthmatic and normal subjects. There have been conflicting reports that the single breath transfer factor for carbon monoxide in asthma may be normal, high or low. To resolve this point the single breath transfer factor was measured in comparable groups of asthmatic and normal subjects. Two methods of calculating the alveolar volume were used, employing multiple breath helium dilution (giving Tl) and single breath helium dilution (giving Tl′).

A higher value was found for Tl than for Tl′ in the asthmatic subjects but a lower value for Tl than Tl′ in the normal subjects. These differences were significant. The largest differences were found in the asthmatic subjects with a large residual volume. There was no significant difference between the asthmatic and normal subjects in the value of Tl and Tl′. As the reports of a raised transfer factor were from workers who used Tl, and this was not confirmed by those who used Tl′, it is concluded that this apparent difference between normal and asthmatic subjects can be explained in some cases by the difference in the methods used.

Pulmonary function in status asthmaticus: effect of therapy

In 11 patients with bronchial asthma, lung volumes, FEV_1·0, PaO₂, and lung diffusing capacity (single breath CO method) were measured in status asthmaticus and after recovery.

Ventilatory capacity improved following therapy. The improvement was associated with a rise in vital capacity and a fall in residual volume, but the total lung capacity might either decrease, increase or remain unchanged.

A decreased value of PaO₂ was found in all patients in status asthmaticus. After treatment PaO₂ increased in all patients. In two of them PaO₂ increased despite the unchanged values of the other parameters of pulmonary function. The improvement of PaO₂ after treatment is considered to be the result of adjustment of perfusion to ventilation.

The lung diffusing capacity was below normal values in three patients before treatment. After treatment the diffusing capacity increased in six patients. The diffusion constant, although within the normal range in status asthmaticus, increased after treatment in one and decreased in three other patients. The decreased diffusing capacity in status asthmaticus is the consequence of a reduced effective alveolar volume due to uneven distribution of ventilation. The changes observed in the diffusion constant following corticotherapy are ascribed to a dependence of this constant on the different level of the alveolar volume at which the single breath test is performed.