Respiratory Muscle Electromyographic Adjustments and Ventilatory Kinetics During Incremental Hypercapnic Stimulation

International Journal of Anatomy and Physiology | Vol. 15, No. 9, September 2026 | pp. 209–220

DOI: 10.46882/2026/IJAP/000185

Article Type: Original Research Article

Title: Respiratory Muscle Electromyographic Adjustments and Ventilatory Kinetics During Incremental Hypercapnic Stimulation

Names of Authors: Liam O. O'Connor¹, Siobhan M. Gallagher²

Authors’ Affiliations: ¹School of Medicine, Physiology Section, University College Dublin, Dublin, Ireland; ²Department of Respiratory Physiology, Galway University Hospital, Galway, Ireland

Abstract:
The neural regulation of respiratory muscles adapts dynamically to rising carbon dioxide levels to stabilize arterial blood gases. This study characterized the recruitment patterns of primary and accessory respiratory muscles during incremental hypercapnic stimulation. Twenty-four healthy subjects (12 males, 12 females, aged 20 to 25 years) underwent a modified Read rebreathing protocol using a gas mixture of 7% CO2 and 93% O2 for 6 minutes. Surface electromyography (sEMG) recorded neural activation of the musculus diaphragm (intercostal spaces), musculus sternocleidomastoideus (SCM), and musculus rectus abdominis. Root mean square (RMS) values of sEMG were calculated and synchronized with ventilation parameters. At baseline (partial pressure of end-tidal CO2, PetCO2 = 38.4 ± 1.2 mmHg), diaphragmatic activity drove tidal ventilation while accessory muscle activity was minimal. When PetCO2 exceeded a threshold of 46.5 ± 1.8 mmHg, a significant exponential increase in diaphragmatic RMS activity was observed (p < 0.01). Recruitment of the SCM muscle rose sharply at PetCO2 levels above 52.0 ± 2.1 mmHg, showing a 4.2-fold increase in electrical activity at peak hypercapnia. Minute ventilation (Ve) correlated strongly with SCM activation (r = 0.84, p < 0.001) in the advanced stages of rebreathing. These electromyographic data demonstrate a tiered activation cascade within the respiratory musculature during hypercapnia, marking the precise chemical thresholds where accessory networks are recruited to support ventilatory demands.

Keywords: Electromyography, Hypercapnia, Diaphragm, Sternocleidomastoideus, Ventilatory Kinetics, Rebreathing

Manuscript Timeline: Received: July 08, 2026; Revised: August 18, 2026; Accepted: September 01, 2026; Published: September 16, 2026

Citation: O'Connor L.O., & Gallagher S.M. (2026). Respiratory Muscle Electromyographic Adjustments and Ventilatory Kinetics During Incremental Hypercapnic Stimulation. International Journal of Anatomy and Physiology, 15(9), 209–220. DOI: 10.46882/2026/IJAP/000185

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