Exercise testing in pulmonary sarcoidosis

Recent developments in the physiological assessment of sarcoidosis: clinical implications

PURPOSE OF REVIEW

This review emphasizes key findings in physiologic research of sarcoidosis reported over the past year.

RECENT FINDINGS

Sarcoidosis, a multiorgan disease involving the formation of epithelioid-cell granulomas, is characterized by reduced lung volumes, compliance, and diffusion capacity (D(L)CO), and, in a small number of cases, by airflow limitation. Recent studies do not show a close relationship between changes in lung volume and radiographic stage. Fatigue and exercise limitation are characteristic of this condition, and can be assessed by health-related quality of life (HRQOL) instruments. Recent investigations have focused on the evaluation of the extent of parenchymal and nodal inflammatory activity by PET using 18F-fluorodeoxyglucose (FDG-PET imaging). Pulmonary hypertension in advanced cases of sarcoidosis contributes to increased physical impairment, and decreased HRQOL and survival. It is best associated with ambulatory desaturation, reduced D(L)CO, and abnormal cardiopulmonary exercise testing findings indicative of pulmonary vascular disease. If pulmonary hypertension is suspected, it should be screened for by echocardiography and confirmed by right heart catheterization. Selected patients with progressive disease unresponsive to medical therapy or with severe pulmonary hypertension should be considered for lung transplantation. Current criteria for lung transplantation include New York Heart Association functional class III-IV, pulmonary hypertension, and/or right atrial pressure at least 15  mmHg.

SUMMARY

Periodic assessment of HRQOL measures, exercise-induced hypoxemia, and right-sided cardiac pressures for pulmonary hypertension provides, to date, the best insight into the magnitude of physiologic impairment, serving as guideposts for management (including lung transplantation) and prognosis.

Membrane and Capillary Blood Components of Diffusion Capacity of the Lung for Carbon Monoxide in Pulmonary Sarcoidosis

BACKGROUND

Resting pulmonary diffusing capacity of the lung for carbon monoxide (DLCO) is known to be the best predictor of arterial desaturation during exercise in patients with sarcoidosis. However, the relative contribution of each of the two components of DLCO-alveolar membrane diffusing capacity (Dm) and pulmonary capillary blood volume (Vc)-remains unclear.

STUDY OBJECTIVES

To evaluate which component is responsible for the decrease of resting DLCO in patients with sarcoidosis, and to determine which resting pulmonary function test, including Dm and Vc, is the best predictor of gas exchange abnormalities during submaximal exercise.

DESIGN

Prospective analysis of patients referred to our department of respiratory medicine.

PATIENTS

Twenty four patients with pulmonary sarcoidosis were separated into two groups according to chest radiographic findings: group 1, stages 2 and 3 (n = 15); group 2, stage 4 (n = 9). All the patients completed pulmonary function tests (flows, volumes, single-breath DLCO, transfer coefficient [Ka], Dm, Vc) and submaximal exercise (two steady-state levels of mild and moderate exercise corresponding respectively to a target oxygen consumption of approximately 10 to 15 mL/min/kg).

RESULTS

DLCO was reduced in the two groups (group 1, 63 +/- 16% of predicted; group 2, 64 +/- 16% of predicted). Dm was severely decreased (group 1, 58 +/- 24% of predicted; group 2, 51 +/- 15% of predicted), whereas Vc was unchanged or only mildly decreased (group 1, 81 +/- 18% of predicted; group 2, 85 +/- 28% of predicted). Whatever the group of patients and the exercise level, Dm and DLCO were the strongest predictors (p < 0.001) of gas exchange abnormalities. Ka or volumes were weak predictors, and Vc or flows were not related with exercise gas exchange.

CONCLUSIONS

This study demonstrates that a decrease in Dm mostly accounts for resting DLCO reduction, and that Dm as well as DLCO are highly predictive of gas exchange abnormalities at exercise in patients with sarcoidosis.

Recruitment of lung diffusing capacity: update of concept and application

Lung diffusing capacity (DL) for carbon monoxide (DLCO), nitric oxide (DLNO) or oxygen (DLO2) increases from rest to peak exercise without reaching an upper limit; this recruitment results from interactions among alveolar volume (VA), and cardiac output (q), as well as changing physical properties and spatial distribution of capillary erythrocytes, and is critical for maintaining a normal arterial oxygen saturation. DLCO and DLNO can be used to interpret the effectiveness of diffusive oxygen transport and track structural alterations of the alveolar-capillary barrier, providing sensitive noninvasive indicators of microvascular integrity in health and disease. Clinical interpretation of DL should take into account Q in addition to VA and hemoglobin concentration.

Pulmonary sarcoidosis after ten to twenty years

One hundred and fifty-nine patients with Pulmonary Sarcoidosis have been studied ten to 20 years after diagnosis with a 90 per cent follow-up of survivors. Among the 76 patients with a mean follow-up of 22.5 years there is radiological evidence of pulmonary fibrosis in 13 and respiratory function tests revealed 12 with a transfer factor of less than 80 per cent of predicted. Of the further 83 patients followed to ten years there was radiological evidence of pulmonary fibrosis in five and a reduced transfer factor in four. Thirty-one patients received Prednisolone for various complications due to Sarcoidosis. There is no evidence of late respiratory disability. The complications and causes of death at ten and 20 years are examined and among the latter eight developed various forms of malignant disease. Since 1973 a further 139 patients have been studied, i.e. a total of 298 and two of these died from progressive Sarcoidosis despite corticosteroid treatment. Six patients have developed late autoimmune diseases.

A standardised method of estimating KCO on exercise

This study was designed to standardise a progressive exercise test for the assessment of change in carbon monoxide transfer coefficient (KCO) with exercise and to examine the variation between subjects and the reproducibility within subjects. Normal subjects exercised on a bicycle ergometer while ventilation, heart rate, and expired gas concentrations were recorded continuously. Preliminary studies showed that reduction of the breath hold time to six seconds made measurements of KCO during heavy exercise more comfortable without affecting the result. When KCO was measured immediately after exercise it was lower than when measured during exercise. KCO was measured in 50 normal subjects at rest and at three different work loads maintained for three minutes with a pause of five minutes between each. The relationships between KCO and both oxygen consumption and work load were linear in all subjects but the relationship between KCO and heart rate was distorted by high resting heart rates in some subjects. The mean slope of the relationship between KCO and oxygen consumption (VO2) was steeper in women than in men (mean slopes 0.627 and 0.348 mmol min-1 kPa-1 l-1 per 1 min-1 respectively), and the same was true for the relationship between KCO and work rate. The heart rate rose more steeply in relation to VO2 in women, so that the relationship of KCO to heart rate was similar in men and women (mean slope 0.01 mmol min-1 kPa-1 l-1 per beat min-1). Repeat studies on five occasions in five individuals gave coefficients of variation for the slopes of the relationships between KCO and VO2, work rate, and heart rate of 5-10%.

Sarcoidosis. An updated review

Sarcoidosis, a multisystem disease of unknown cause characterized by the formation of noncaseating granulomas, may involve any organ of the body, but the commonest sites of predilection are the lungs, lymph nodes, skin, and eyes. Sarcoidosis can be associated with polyclonal hyperglobulinemia, hypercalcemia, hypercalciuria, circulating immune complexes, cutaneous anergy, and in vitro depressed cell-mediated immunity. Recent studies of the cellular composition and cellular interactions of sarcoid-involved tissue have resulted in some insight into the pathophysiology of the disease. In early stages the predominance of activated T-helper cells in affected sites may account for many of the immunologic aberrations. The production of macrophage chemotactic substances by these cells may be the initial stimulus for the formation of the granuloma. The natural history of the disease is highly variable; the acute forms tend to resolve spontaneously, whereas the chronic forms rarely involute. Although multiple therapeutic modalities have been used and some have reportedly been effective, systemic corticosteroids remain the most effective available therapeutic agents.

Lung transfer factor and KCO at cardiac frequency 100 beats/min as a guide to impaired function of lung parenchyma

Transfer factor (TL) and KCO have been measured by the single breath carbon monoxide method in 39 patients with confirmed or suspected lung disease, mostly of occupational origin, and 37 healthy subjects. TL and KCO at an exercise cardiac frequency of 100 beats/min (TL100 and KCO100) and the slopes of the regression of exercise transfer factor and KCO on exercise cardiac frequency (delta TL/delta fC and delta KCO/delta fC) were obtained. The discriminatory performance of these indices in detecting defective gas transfer was compared with that of TL and KCO at rest (TLrest and KCOrest). The slope indices did not distinguish between healthy subjects and patients with emphysema or conditions of the lung parenchyma, including asbestosis. The slope indices also failed to distinguish between individuals with normal and abnormal gas transfer at rest. The indices TL100 and KCO100 contributed additional information not contained in the indices at rest and they merit further study.