Respiratory muscle unloading improves leg muscle oxygenation during exercise in patients with COPD
- A Borghi-Silva1,
- C C Oliveira1,
- C Carrascosa1,
- J Maia1,
- D C Berton1,
- F Queiroga Jr1,
- E M Ferreira1,
- D R Almeida2,
- L E Nery1,
- J A Neder1
- 1Pulmonary Function and Clinical Exercise Physiology Unit, Division of Respiratory Diseases, Department of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil
- 2Division of Cardiology, Department of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil
- 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}pq.cnpq.br
- Received 10 September 2007
- Accepted 16 April 2008
- Published Online First 20 May 2008
Abstract
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.
Footnotes
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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.
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Competing interests: None.
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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.
