Determinants of Exercise Intolerance in Patients with Idiopathic Inflammatory Myopathy

Authors

Nicole Varone, Texas Woman's UniversityFollow
Denis J. Wakeham, Institute for Exercise and Environmental Medicine, University of Texas SouthwesternFollow
Salman Bhai, Institute for Exercise and Environmental Medicine, University of Texas Southwestern Medical CenterFollow
Christopher M. Hearon Jr, Institute for Exercise and Environmental Medicine, University of Texas SouthwesternFollow

Abstract

Idiopathic inflammatory myopathy (IIM) is an inflammatory muscle disease in which patients experience severe exercise intolerance. There is evidence of vasculopathy in patients with IIM, however it is currently unknown whether vascular dysfunction contributes to exercise intolerance in IIM. PURPOSE: This study aims to compare leg hemodynamics and muscle oxygen utilization during isolated single leg knee extension exercise (SLKE) between patients with IIM and healthy controls. METHODS: Ten patients with IIM (age: 52 ± 14 yrs; 4 females; BMI: 32 ± 9 kg/m²) and seven healthy control participants (CON; age: 48 ± 13 yrs; 3 females; BMI: 25 ± 6 kg/m²) performed a SLKE protocol designed to elicit fatigue in 30-minutes. Leg blood flow (LBF; doppler ultrasound), mean arterial pressure (MAP; brachial electro-sphygmomanometry), and venous blood gasses (VBG; femoral venous catheter) were measured at fatigue. We calculated leg arterial-venous oxygen difference (Δa-vO₂; calculated from hemoglobin concentration and arterial oxygen saturation [pulse oximetry] and femoral venous oxygen saturation), leg VO₂ (LVO₂; LBF x Δa-vO₂), and leg vascular conductance (LVC; LBF/MAP). All data between groups were compared using independent samples t-test and are presented as mean ± standard deviation. RESULTS: At fatigue, external work-rate (CON: 34 ± 15 vs. IIM: 25 ± 9 Watts, p = 0.112) and LVO₂ (CON: 313 ± 112 vs IIM: 329 ± 111 ml/min, p = 0.776) were not different between groups. LBF (CON: 2451 ± 773 vs IIM: 3016 ± 997 ml/min, p = 0.229) and MAP (CON: 118 ± 15 vs. IIM: 107 ± 14 mmHg, p = 0.123) were not different between groups at fatigue, but LVC was higher in IIM (CON: 20.9 ± 7.1 vs. IIM: 28.6.0 ± 7.2 ml/min/mmHg, p = 0.044). Also, Δa-vO2 at fatigue tended to be lower in IIM than controls (CON: 12.8 ± 1.7 vs. IIM: 11.0 ± 1.9 dl/ml, p = 0.058). CONCLUSION: Peripheral vascular dysfunction is not a primary contributor to exercise intolerance in patients with IIM. In contrast, the lower Δa-vO2 at fatigue indicates that impaired oxygen extraction is the primary factor limiting exercise tolerance in patients with IIM.

Recommended Citation

Varone, Nicole; Wakeham, Denis J.; Bhai, Salman; and Hearon, Christopher M. Jr (2025) "Determinants of Exercise Intolerance in Patients with Idiopathic Inflammatory Myopathy," International Journal of Exercise Science: Conference Proceedings: Vol. 2: Iss. 17, Article 117.
Available at: https://digitalcommons.wku.edu/ijesab/vol2/iss17/117