Abstract
The purpose of this study was to determine the effect of respiratory muscle fatigue on intercostal and forearm muscle perfusion and oxygenation in patients with heart failure. Five clinically stable heart failure patients with respiratory muscle weakness (age, 66±12 years; left ventricle ejection fraction, 34±3%) and nine matched healthy controls underwent a respiratory muscle fatigue protocol, breathing against a fixed resistance at 60% of their maximal inspiratory pressure for as long as they could sustain the predetermined inspiratory pressure. Intercostal and forearm muscle blood volume and oxygenation were continuously monitored by near-infrared spectroscopy with transducers placed on the seventh left intercostal space and the left forearm. Data were compared by two-way ANOVA and Bonferroni correction. Respiratory fatigue occurred at 5.1±1.3 min in heart failure patients and at 9.3±1.4 min in controls (P<0.05), but perceived effort, changes in heart rate, and in systolic blood pressure were similar between groups (P>0.05). Respiratory fatigue in heart failure reduced intercostal and forearm muscle blood volume (P<0.05) along with decreased tissue oxygenation both in intercostal (heart failure, -2.6±1.6%; controls, +1.6±0.5%; P<0.05) and in forearm muscles (heart failure, -4.5±0.5%; controls, +0.5±0.8%; P<0.05). These results suggest that respiratory fatigue in patients with heart failure causes an oxygen demand/delivery mismatch in respiratory muscles, probably leading to a reflex reduction in peripheral limb muscle perfusion, featuring a respiratory metaboreflex.
Highlights
Along with a limited ability to increase cardiac output, increased pulmonary capillary pressure and skeletal myopathy, respiratory muscle fatigue is considered a key factor contributing to the diminished exercise capacity observed in patients with heart failure (HF) [1,2]
We tested the hypothesis that there would be a reduction in intercostal muscle oxygenation during respiratory fatigue with onset of the metaboreflex response in www.bjournal.com.br patients with HF
Our results showed a significant reduction in intercostal and forearm muscle oxygen saturation from rest to fatigue in the HF group, which was not observed in the healthy group
Summary
Along with a limited ability to increase cardiac output, increased pulmonary capillary pressure and skeletal myopathy, respiratory muscle fatigue is considered a key factor contributing to the diminished exercise capacity observed in patients with heart failure (HF) [1,2]. The stimulation of ergoreceptors sensitive to accumulation of metabolites within respiratory skeletal muscle reflexively increases sympathetic outflow, which limits the increase of blood flow to working muscle, causing reduced perfusion of locomotor muscles and leading to fatigue [3,4,5]. The proposed trigger for the metaboreflex is accumulation of metabolites within respiratory muscle caused by an oxygen demand/delivery mismatch [3,8], but so far the patterns of respiratory blood flow and oxygenation during respiratory fatigue in patients with heart failure have not been described. This study was designed to determine the effect of respiratory muscle fatigue on intercostal and forearm muscles blood volume and oxygenation in HF patients
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