CHANGES IN THE COMPONENTS OF THE DIFFUSING CAPACITY IN PULMONARY SARCOIDOSIS

An open-circuit method for determining lung diffusing capacity during exercise: comparison to rebreathe

To avoid limitations associated with the use of single-breath and rebreathe methods for assessing the lung diffusing capacity for carbon monoxide (DlCO) during exercise, we developed an open-circuit technique. This method does not require rebreathing or alterations in breathing pattern and can be performed with little cognition on the part of the patient. To determine how this technique compared with the traditional rebreathe (DlCO,RB) method, we performed both the open-circuit (DlCO,OC) and the DlCO,RBmethods at rest and during exercise (25, 50, and 75% of peak work) in 11 healthy subjects [mean age = 34 yr (SD 11)]. Both DlCO,OCand DlCO,RBincreased linearly with cardiac output and external work. There was a good correlation between DlCO,OCand DlCO,RBfor rest and exercise (mean of individual r2= 0.88, overall r2= 0.69, slope = 0.97). DlCO,OCand DlCO,RBwere similar at rest and during exercise [e.g., rest = 27.2 (SD 5.8) vs. 29.3 (SD 5.2), and 75% peak work = 44.0 (SD 7.0) vs. 41.2 ml·min−1·mmHg−1(SD 6.7) for DlCO,OCvs. DlCO,RB]. The coefficient of variation for repeat measurements of DlCO,OCwas 7.9% at rest and averaged 3.9% during exercise. These data suggest that the DlCO,OCmethod is a reproducible, well-tolerated alternative for determining DlCO, particularly during exercise. The method is linearly associated with cardiac output, suggesting increased alveolar-capillary recruitment, and values were similar to the traditional rebreathe method.

Primary care paradigm for management of sarcoidosis, Part 2

Sarcoidosis is a systemic granulomatous disease of undetermined etiology in which the immune system is overstimulated. Management of the patient with sarcoidosis entails continuity of patient care far beyond disease, even into remission. Care is comprehensive, including all involved organ systems, coordination of specialty consultations and services, and includes diagnostic tests. Therapeutic decisions are the responsibility of the primary care practitioner. Prognosis of sarcoidosis is not uniformly good. Patients can die. Subacute sarcoidosis patients usually do not require pharmacologic therapy. Chronic sarcoidosis may require long-term treatment for years to indefinitely. Corticosteroids are still the drugs of choice and other therapy is now available. Health organizations and private nonprofit support groups are available for patient education and assistance. Close support must still come from the family unit. Sarcoidosis may occur in family members in different cohorts at all ages in life and in any racial or ethnic group. The second in a two-part series on management of the patient with sarcoidosis, this article describes coordination of care and considers community, prevention, and family aspects of the disease.

Volume adjustment of mechanics and diffusion in interstitial lung disease. Lack of clinical relevance

Relationships of lung mechanics and diffusion to lung volume were examined in 38 patients with interstitial lung disease to determine whether patterns of reduction relate to severity of disease, distinguish histologic characteristics or predict prognosis for reversibility. Normal volume-related values for both mechanics and diffusion were seen throughout the range of severity of disease. The ratio of mechanics to lung volume did not correlate with the ratio of diffusion to lung volume in the same patient. Volume relationships of mechanics and diffusion failed to distinguish pathologic predominance of fibrosis or inflammation/granulomas. These ratios failed to predict reversibility in patients who had repeated tests. These results suggest that in patients with interstitial lung disease the significance of "volume-adjustment" of mechanics and diffusion should be viewed with caution; these parameters do not appear to contribute to the assessment of pathophysiology or correlate with clinical spectrum of interstitial lung diseases.

Regional extravascular density and fractional blood volume of the lung in interstitial disease

Regional lung density (g lung/ml thoracic volume) and fractional pulmonary blood volume (ml blood/ml thoracic volume) have been measured by positron tomography in 10 patients with interstitial disease. From the measurements regional extravascular lung density (g tissue and interstitial water/ml thoracic volume) was derived, providing a non-invasive measurement of the interstitial reaction. Extravascular lung density was increased and large regional variations were observed. Fractional blood volume was reduced in patients with pulmonary fibrosis. In two patients with sarcoidosis, a reduction in extravascular lung density occurred after treatment with oral prednisone. Abnormalities in extravascular lung density and fractional blood volume correlated with abnormalities shown by tests of overall pulmonary function.

Exercise testing in pulmonary sarcoidosis

The change in transfer coefficient (Kco) with increasing heart rate during exercise was studied in 25 normal subjects and in 21 patients with pulmonary sarcoidosis. The slope of the Kco response against heart rate was found to be 0·0053 mmol min⁻¹ kPa⁻¹ l⁻¹ per beat in the normal group but in many of the patients was two standard deviations or more below this normal slope, even when their routine function tests were normal. This response of Kco to exercise is a more sensitive index of changed function than more routine function tests in pulmonary sarcoidosis.

Membrane diffusing capacity and pulmonary capillary volume in rheumatoid disease

In some patients with rheumatoid disease gas transfer across the lungs is abnormal. We measured the membrane component of gas transfer (Dm) and pulmonary capillary volume (Vc) in 48 patients with rheumatoid arthritis and in 48 normal volunteers matched for age, sex, and smoking habits. Volunteers had normal chest radiographs and normal forced expiratory volume in one second and vital capacity. There were no significant differences between the rheumatoid and control groups for Dm. Mean Vc in rheumatoid male smokers (64.0 ml, SD 16.5) was significantly lower than in control male smokers (76.3 ml, SD 18.0 p less than 0.05). In rheumatoid female smokers mean Vc (43.4 ml, SD 13.3) was significantly lower than in rheumatoid female non-smokers (58.4 ml, SD 15.4 p less than 0.01). There was no significant difference between rheumatoid and control female non-smokers (mean Vc 58.4 ml and 60.7 ml respectively). Significant differences in Vc in terms of per cent predicted normal were found between patients receiving corticosteroids and those not receiving corticosteroids or penicillamine (p less than 0.02) and between patients with nodules and those without (p less than 0.05). Patients with persistently low transfer factor for five years had a significantly lower Vc (p less than 0.02). There was no consistent correlation between Dm and Vc and dynamic compliance or static recoil pressure. It appears that the abnormality of transfer factor in rheumatoid disease previously demonstrated is caused by reduction of Vc. It seems that involvement of pulmonary blood vessels occurs in patients with nodules and is suppressed by treatment with corticosteroids.

Use of pulmonary function tests in the management of sarcoidosis

The literature on pulmonary function testing in sarcoidosis is critically reviewed. The results indicate that pulmonary function tests are not a reliable means for detecting the presence of parenchymal sarcoidosis, nor do they provide an accurate estimate of the extent of parenchymal disease. There are at present no known pulmonary function criteria that allow the clinician to predict the natural cause of pulmonary sarcoidosis or the response to therapy. The major value of pulmonary function testing is to assess changes in the disease course of the individual patient through sequential measurements. Currently there is no conclusive evidence that measurements of arterial blood gas tensions or pulmonary compliance add significantly to the sensitivity and specificity of the vital capacity and diffusing capacity in the management of sarcoidosis.

Prolonged treatment of pulmonary sarcoidosis with corticosteroids

The results are described of prolonged corticosteroid treatment in 52 patients with pulmonary sarcoidosis observed for a mean duration of 10·5 years from diagnosis. Twenty of the patients were treated for less than one year, the remainder for a mean of five years. The mean length of observation after discontinuing treatment was 5·5 years. Selection of patients for treatment was based on (1) evidence from radiographic observation, even for two years or more, that the disease was progressive so that spontaneous remission was improbable; and (2) evidence of disturbed lung function, especially the onset of dyspnoea or an impaired diffusing capacity. Treatment, conveniently with prednisone at a maintenance dose of about 15 mg. daily, should be continued for at least a year and often for much longer until withdrawal is not followed by radiographic relapse. Such treatment does not increase the chance of a complete remission even when given at an early stage of the disease; and relief of dyspnoea is unpredictable and seldom considerable. But prolonged treatment will halt progressive lung destruction and appears to curb the eventual mortality.