Effects of respiratory muscle work on respiratory and locomotor blood flow during exercise

Abstract

Manipulating the work of breathing (WOB) during near-maximal exercise influences leg blood flow, but the effects on respiratory muscle blood flow are equivocal. We sought to simultaneously assess leg and respiratory muscle blood flow during intense exercise while manipulating WOB. We hypothesized that: (i) increasing the WOB would increase respiratory muscle blood flow and decrease leg blood flow, and (ii) decreasing the WOB would decrease respiratory muscle blood flow and increase leg blood flow. Eight healthy subjects (n = 5 m, n = 3 W) performed a maximal cycle test (Day 1) and a series of constant-load exercise trials at 90% of peak work rate (Day 2). On Day 2, WOB was assessed with oesophageal balloon catheters and was: increased (via resistors), decreased (via proportional assist ventilation), or unchanged (control) during the trials. Blood flow was assessed using near-infrared spectroscopy optodes placed over quadriceps and the sternocleidomastoid muscles, coupled with a venous indocyanine green dye injection. Changes in WOB were significantly and positively related to changes in respiratory muscle blood flow (r = 0.73), whereby increasing the WOB increased blood flow. Conversely, changes in WOB were inversely related to changes in locomotor blood flow (r = 0.57), whereby decreasing the WOB increased locomotor blood flow. Oxygen uptake was not different during the control and resistor trials (3.8 ± 0.9 vs. 3.7 ± 0.8 l min⁻¹, P > 0.05), but was lower on the PAV trial (3.4 ± 0.7 l min⁻¹, P < 0.05) compared to control. Our findings support the concept that respiratory muscle work significantly influences the distribution of blood flow to both respiratory and locomotor muscles.

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