Abstract
Idiopathic inflammatory myopathies involve skeletal muscles and can be associated with interstitial lung disease and/or heart dysfunction, which may reduce exercise capacity. We aimed to clarify cardiopulmonary factors affecting the 6-min walk distance in patients who were able to walk without leg pain or fatigue. Twenty-three patients with inactive adult idiopathic inflammatory myopathies, and 18 age- and gender-matched healthy controls were evaluated for hemodynamic responses using noninvasive impedance cardiography during the 6-min walk test. The patients were also examined by the pulmonary function test for forced vital capacity and diffusing capacity for carbon monoxide (DLCO), and by echocardiography for left ventricular ejection fraction and right ventricular systolic pressure. Interstitial lung disease was diagnosed in 19 patients using high-resolution computed tomography. There was no difference in 6-min walk distance or cardiac output after walking between the patients and healthy controls. However, stroke volume during the 6-min walk test was significantly lower in the patients than in healthy controls, suggesting malfunction in the heart. Moreover, the increased heart rate matched the cardiac output. Spearman’s correlation analysis demonstrated a correlation between 6-min walk distance and stroke volume, cardiac output after walking and DLCO, but not left ventricular ejection fraction or right ventricular systolic pressure, as this study lacked the patients with pulmonary hypertension. In conclusion, impaired DLCO due to interstitial lung disease was suggested to be a fundamental parameter affecting exercise capacity, in addition to heart involvement, in patients with idiopathic inflammatory myopathies.
Highlights
Interstitial lung disease is a common extra-muscular complication of idiopathic inflammatory myopathies, and lowdiffusing capacity for carbon monoxide (DLCO) is known to increase the risk of mortality [1, 2]
Heart involvement in idiopathic inflammatory myopathies was detected by cardiac magnetic resonance tomography [5] or echocardiography [6], and these findings may lead to therapeutic treatment for the cause of morbidity [7]
It may be difficult to clarify cardiac parameters likely associated with exercise capacity using conventional echocardiography; when cardiac impairment was assessed by global longitudinal strain measurement, subclinical heart disease was found in up to 50% of patients [9]
Summary
Interstitial lung disease is a common extra-muscular complication of idiopathic inflammatory myopathies, and lowdiffusing capacity for carbon monoxide (DLCO) is known to increase the risk of mortality [1, 2]. Referring to other estimates for cardiac parameters, recent studies have demonstrated that impedance cardiography with real-time monitoring can noninvasively evaluate hemodynamic responses during the 6MWT [10, 11]. Pulmonary hypertension patients with a normal ejection fraction had a lower stroke volume (SV) and cardiac index (CI) compared with healthy controls during walking [10], and patients with chronic obstructive disease exhibited slower responses to increasing cardiac output (CO) [11]. The maximal CO in patients with pulmonary hypertension was observed during the 6MWT by the inert gas rebreathing method [12] These noninvasive methods may be available for evaluation of hemodynamic responses during walking to examine the relation between exercise capacity and heart involvement in patients with idiopathic inflammatory myopathies. We compared measurements obtained from patients and age- and gender-matched healthy controls during the 6MWT using noninvasive impedance cardiography
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