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Respiratory Muscle Unloading Improves Leg Muscle Oxygenation During Exercise in Patients with COPD
  1. AUDREY BORGHI-SILVA
  1. Federal University of Sao Paulo, Brazil
    1. Cristino C Oliveira
    1. Federal University of Sao Paulo, Brazil
      1. Cláudia Carrascosa
      1. Federal University of Sao Paulo, Brazil
        1. Joyce Maia
        1. Federal University of Sao Paulo, Brazil
          1. Danilo Berton
          1. Federal University of Sao Paulo, Brazil
            1. Fernando Queiroga
            1. Federal University of Sao Paulo, Brazil
              1. Elaoara Ferreira
              1. Federal University of Sao Paulo, Brazil
                1. Dirceu Ribeiro
                1. Federal University of Sao Paulo, Brazil
                  1. Luiz Nery
                  1. Federal University of Sao Paulo, Brazil
                    1. J Alberto Neder (albneder{at}pneumo.epm.br)
                    1. Federal University of Sao Paulo, Brazil

                      Abstract

                      Background: Respiratory muscle unloading during exercise could improve locomotor muscle oxygenation due to increased systemic oxygen delivery (higher cardiac output and/or CaO2) in patients with chronic obstructive pulmonary disease (COPD).

                      Methods: Sixteen non-hypoxaemic males (FEV1= 42.2 ± 13.9 % pred) 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 deoxy-hemoglobyn [HHb], oxi-Hb [O2Hb], tissue oxygenation index (TOI) and total Hb [Hbtot] in the vastus lateralis were measured by near-infrared spectroscopy. In order to estimate systemic 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 to sham. 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, i.e., DO2est remained unchanged with PAV (p>0.05). Interestingly, however, leg muscle oxygenation 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 to sham ventilation (p<0.01).

                      Conclusions: Respiratory muscle unloading during high-intensity exercise can improve peripheral muscle oxygenation despite an unaltered systemic DO2 in patients with advanced COPD. These findings might indicate that a fraction of the available cardiac output had been redirected from the ventilatory to the appendicular muscles as a consequence of the respiratory muscle unloading.

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