Chronic sustained hypoxia alters the pattern of diaphragm electrical activity in anaesthetized rats

Chronic sustained hypoxia (CSH) is known to induce functional and structural changes in the respiratory system. The diaphragm, as the main inspiratory muscle of mammals, is particularly important in the neuromotor regulation of respiration. Diaphragm electromyography (dEMG) records the sum of motor unit action potentials (MUAP) and provides information regarding motor unit recruitment and frequency coding during muscle contraction. We aimed to assess changes in dEMG activity following CSH. Herein, eight male Wistar rats (2-3 months) were subjected to CSH (10 ± 0.5% O₂) for 10 successive days. In vivo dEMG recording was employed to assess changes in the diaphragm electrical activity. Filtered and rectified dEMGs were used for further analyses. Findings showed that CSH for 10 consecutive days significantly changed the pattern of dEMG signals. The slope of the rising phase of RMS-enveloped dEMG bursts was much steeper in CSH rats compared to normoxic control rats (rise time: 373 vs. 286 ms; P = 0.005). Burst frequency significantly decreased following CSH (59 vs. 42 bursts/min; P = 0.0001), which was associated with a significant increase in burst amplitude (P = 0.039) and inter-burst duration (0.65 vs. 0.88 s; P = 0.041). Power spectral density analyses showed that the mean frequency (293 vs. 266 Hz; P = 0.033) and high-frequency to low-frequency power ratio (P = 0.009) of dEMG signals significantly declined in CSH rats. Notably, the regularity of frequency and amplitude of dEMG signals did not change significantly following CSH.