Responses to progressive exercise in subjects with chronic dyspnea and inspiratory muscle weakness

Abstract

Abstract Introduction Inspiratory muscle weakness (IMW) is a potential cause of exertional dyspnea frequently under‐appreciated in clinical practice. Cardiopulmonary exercise testing (CPET) is usually requested as part of the work‐up for unexplained breathlessness, but the specific pattern of exercise responses ascribed to IMW is insufficiently characterized. Objectives To identify the physiological and sensorial responses to progressive exercise in dyspneic patients with IMW without concomitant cardiorespiratory or neuromuscular diseases. Methods Twenty‐three subjects (18 females, 55.2 ± 16.9 years) complaining of chronic daily life dyspnea (mMRC = 3 [2‐3]) plus maximal inspiratory pressure < the lower limit of normal and 12 matched controls performed incremental cycling CPET. FEV1/FVC<0.7, significant abnormalities in chest CT or echocardiography, and/or an established diagnosis of neuromuscular disease were among the exclusion criteria. Results and Conclusion Patients presented with reduced aerobic capacity (peak V̇O2: 79 ± 26 vs 116 ± 21 %predicted), a tachypneic breathing pattern (peak breathing frequency/tidal volume = 38.4 ± 22.7 vs 21.7 ± 14.2 breaths/min/L) and exercise‐induced inspiratory capacity reduction (‐0.17 ± 0.33 vs 0.10 ± 0.30 L) (all P < .05) compared to controls. In addition, higher ventilatory response (ΔV̇E/ΔV̇CO2 = 34.1 ± 6.7 vs 27.0 ± 2.3 L/L) and symptomatic burden (dyspnea and leg discomfort) to the imposed workload were observed in patients. Of note, pulse oximetry was similar between groups. Reduced aerobic capacity in the context of a tachypneic breathing pattern, inspiratory capacity reduction and preserved oxygen exchange during progressive exercise should raise the suspicion of inspiratory muscle weakness in subjects with otherwise unexplained breathlessness.

Keywords

• exercise test
• maximal respiratory pressures
• muscle weakness
• respiration disorders
• respiratory function tests
• respiratory muscles