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Respiratory muscle unloading improves leg muscle oxygenation during exercise in patients with COPD
  1. A Borghi-Silva1,
  2. C C Oliveira1,
  3. C Carrascosa1,
  4. J Maia1,
  5. D C Berton1,
  6. F Queiroga Jr1,
  7. E M Ferreira1,
  8. D R Almeida2,
  9. L E Nery1,
  10. J A Neder1
  1. 1
    Pulmonary Function and Clinical Exercise Physiology Unit, Division of Respiratory Diseases, Department of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil
  2. 2
    Division of Cardiology, Department of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil
  1. Dr J A Neder, Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Respiratory Division, Department of Medicine, Federal University of Sao Paulo – Paulista School of Medicine (UNIFESP-EPM), Rua Professor Francisco de Castro 54, Vila Clementino, CEP 04020-050, São Paulo, Brazil; alberto.neder{at}


Background: Respiratory muscle unloading during exercise could improve locomotor muscle oxygenation by increasing oxygen delivery (higher cardiac output and/or arterial oxygen content) in patients with chronic obstructive pulmonary disease (COPD).

Methods: Sixteen non-hypoxaemic men (forced expiratory volume in 1 s 42.2 (13.9)% predicted) undertook, on different days, two constant work rate (70–80% peak) exercise tests receiving proportional assisted ventilation (PAV) or sham ventilation. Relative changes (Δ%) in deoxyhaemoglobin (HHb), oxyhaemoglobin (O2Hb), tissue oxygenation index (TOI) and total haemoglobin (Hbtot) in the vastus lateralis muscle were measured by near-infrared spectroscopy. In order to estimate oxygen delivery (Do2est, l/min), cardiac output and oxygen saturation (Spo2) were continuously monitored by impedance cardiography and pulse oximetry, respectively.

Results: Exercise tolerance (Tlim) and oxygen uptake were increased with PAV compared with sham ventilation. In contrast, end-exercise blood lactate/Tlim and leg effort/Tlim ratios were lower with PAV (p<0.05). There were no between-treatment differences in cardiac output and Spo2 either at submaximal exercise or at Tlim (ie, Do2est remained unchanged with PAV; p>0.05). Leg muscle oxygenation, however, was significantly enhanced with PAV as the exercise-related decrease in Δ(O2Hb)% was lessened and TOI was improved; moreover, Δ(Hbtot)%, an index of local blood volume, was increased compared with sham ventilation (p<0.01).

Conclusions: Respiratory muscle unloading during high-intensity exercise can improve peripheral muscle oxygenation despite unaltered systemic Do2 in patients with advanced COPD. These findings might indicate that a fraction of the available cardiac output had been redirected from ventilatory to appendicular muscles as a consequence of respiratory muscle unloading.

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  • Funding: Supported by a research grant from Fundação de Amparo à Pesquisa do Estado de São Paulo, São Paulo, Brazil (FAPESP) No 05/00722-0. AB-S is a recipient of a Post-Doctoral Scholarship Grant from FAPESP. JAN is an Established Investigator (level II) of the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil.

  • Competing interests: None.

  • Ethics approval: Patients gave written informed consent and the study protocol was approved by the medical ethics committee of the Federal University of São Paulo/São Paulo Hospital.