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.

Measurement of temporal changes in DLSBCO-3EQ from small alveolar samples in normal subjects.

The dynamic changes in CO concentration [CO] during a single breath could be influenced by topographic inhomogeneity in the lung or by peripheral inhomogeneity due to a gas mixing resistance in the gas phase of the lung or to serial gradients in gas diffusion. Ten healthy subjects performed single-breath maneuvers by slowly inhaling test gas from functional residual capacity to one-half inspiratory capacity and slowly exhaling to residual volume with target breath-hold times of 0, 1.5, 3, 6, and 9 s. We calculated the three-equation single-breath diffusing capacity of the lung for CO (DLSBCO-3EQ) from the mean [CO] in both the entire alveolar gas sample and in four successive equal alveolar gas samples. DLSBCO-3EQ from the entire alveolar gas sample was independent of breath-hold time. However, with 0 s of breath holding, from early alveolar gas samples DLSBCO-3EQ was reduced and from late alveolar gas samples it was increased. With increasing breath-hold time, DLSBCO-3EQ from the earliest alveolar gas sample rapidly increased, whereas from the last alveolar gas sample it rapidly decreased such that all values from the small alveolar gas samples approached DLSBCO-3EQ from the entire alveolar sample. These changes correlated with ventilation inhomogeneity, as measured by the phase III He concentration slope and the mixing efficiency, and were larger for maneuvers with inspired volumes to one-half inspiratory capacity vs. total lung capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhalant atopic sensitivity to grasshoppers in research laboratories.

BACKGROUND: Atopic sensitivity to insects, in both occupational and nonoccupational settings, is common. METHODS: A 26-year-old man with atopic asthma experienced worsened asthma and urticaria on exposure to grasshoppers in a research laboratory; he along with 16 other persons who work with grasshoppers from two laboratories and 26 control subjects were studied. The patient underwent a controlled allergen inhalation test with aqueous grasshopper dropping antigen. All subjects were assessed by means of a questionnaire. All but one (who refused because of severe skin reactions after contact with grasshoppers) had skin prick tests with three extracts of grasshopper and with grass pollen, cat dander, and Dermatophagoides farinae. RESULTS: The allergen challenge was positive with an isolated early asthmatic response (23% fall forced expiratory volume in 1 second [FEV1]) at 1:4096 (approximately 25 micrograms/ml), and a borderline fall in provocative concentration of methacholine causing a 20% fall in FEV1. Seven of 16 (43.8%) workers had positive grasshopper skin test results compared with one of 26 (3.8%) control subjects (p = 0.0052). Sensitization occurred even in otherwise nonatopic workers (5 of 12). Symptoms of asthma on exposure (n = 4) correlated better with positive skin test results than did cutaneous symptoms (n = 8). CONCLUSION: Atopic sensitization to grasshoppers in research laboratories is a significant occupational health problem.