MEDLINE/PubMed Journal Browser Search

Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

Title: Control of hyperpnoea and pulmonary gas exchange during prolonged exercise: The role of group III/IV muscle afferent feedback.
Author: Iannetta D, Weavil JC, Laginestra FG, Thurston TS, Broxterman RM, Jenkinson RH, Curtis MC, Chang J, Wan HY, Amann M.
Journal: J Physiol; 2024 Oct; 602(20):5375-5389. PubMed ID: 39316014.
Abstract:
It remains unclear whether feedback from group III/IV muscle afferents is of continuous significance for regulating the pulmonary response during prolonged (>5 min), steady-state exercise. To elucidate the influence of these sensory neurons on hyperpnoea, gas exchange efficiency, arterial oxygenation and acid-base balance during prolonged locomotor exercise, 13 healthy participants (4 females; 21 (3) years, V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}}$ : 46 (8) ml/kg/min) performed consecutive constant-load cycling bouts at ∼50% (20 min), ∼75% (20 min) and ∼100% (5 min) of V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}}$ with intact (CTRL) and pharmacologically attenuated (lumbar intrathecal fentanyl; FENT) group III/IV muscle afferent feedback from the legs. Pulmonary responses were continuously recorded and arterial blood (radial catheter) periodically collected throughout the exercise. Pulmonary gas exchange efficiency was evaluated using the alveolar-arterial P O 2 ${{P}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ difference ( A - a D O 2 ${\mathrm{A - a}}{{D}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ ). There were no differences in any of the variables of interest between conditions before the start of the exercise. Pulmonary ventilation was up to 20% lower across all intensities during FENT compared to CTRL exercise (P < 0.001) and this hypoventilation was accompanied by an up to 10% lower arterial P O 2 ${{P}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ and a 2-4 mmHg higher P C O 2 ${{P}_{{\mathrm{C}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ (both P < 0.001). The exercise-induced widening of A - a D O 2 ${\mathrm{A - a}}{{D}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ was up to 25% larger during FENT compared to CTRL (P < 0.001). Importantly, the differences developed within the first minute of each stage and persisted, or further increased, throughout the remainder of each bout. These findings reflect a critical and time-independent significance of feedback from group III/IV leg muscle afferents for continuously regulating the ventilatory response, gas exchange efficiency, arterial oxygenation and acid-base balance during human locomotion. KEY POINTS: Feedback from group III/IV leg muscle afferents reflexly contributes to hyperpnoea during short duration (i.e. <5 min) locomotor exercise. Whether continuous feedback from these sensory neurons is obligatory to ensure adequate pulmonary responses during steady-state exercise of longer duration remains unknown. Lumbar intrathecal fentanyl was used to attenuate the central projection of group III/IV leg muscle afferents during prolonged locomotor exercise (i.e. 45 min) at intensities ranging from 50% to 100% of V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}}$ . Without affecting the metabolic rate, afferent blockade compromised pulmonary ventilation and gas exchange efficiency, consistently impairing arterial oxygenation and facilitating respiratory acidosis throughout exercise. These findings reflect the time-independent significance of feedback from group III/IV muscle afferents for regulating exercise hyperpnoea and gas exchange efficiency, and thus for optimizing arterial oxygenation and acid-base balance, during prolonged human locomotion.

[Abstract] [Full Text] [Related] [New Search]