Neuromuscular transmission in hypoxemic patients with chronic obstructive pulmonary disease

Impact of obstructive sleep apnea on neuromuscular transmission- a descriptive study

Objective: Obstructive sleep apnea (OSA) is a sleep disorder accompanied by intermittent hypoxia. Neuromuscular transmission (NT) is known to be disturbed under chronic hypoxia. In this descriptive study, it has been aimed to test NT under intermittent hypoxia in OSA. Methods: Thirty-nine newly diagnosed OSA patients without any comorbidities or conditions that alter NT were included in the study. Jitter analysis was performed using a concentric needle electrode. Results: The mean jitter value of 39 OSA patients was 25.9 ± 3.7 μs. When compared to the mean reference jitter values, patients in the present study had significantly higher jitter (p < 0.001). Seven (17.9%) patients met the electrophysiological criteria for NT failure. Conclusion: The authors propose that intermittent hypoxia can be the trigger for NT failure in OSA. The interaction between increased oxidative stress and disturbed mitochondrial functions may also contribute.

Neuromuscular efficiency is impaired during exercise in COPD patients

AIM

to analyze respiratory and peripheral neuromuscular efficiency during exercise in COPD.

METHODS

COPD patients (VEF₁ = 39.25 ± 13.1 %) were paired with healthy subjects. It was performed cardiopulmonary exercise test with simultaneously electromyography (EMG). Respiratory neuromuscular efficiency was determined by relationship between tidal volume and diaphragm EMG. Peripheral neuromuscular efficiency was determined by relationship between power output and vastus lateralis EMG.

RESULTS

Healthy subjects presented higher respiratory neuromuscular efficiency at moderate, heavy and maximum exercise intensities compared to COPD (p < 0.05). Healthy subjects presented higher peripheral neuromuscular efficiency at light, moderate, heavy and maximum exercise intensities compared to COPD (p < 0.001). Dynamic hyperinflation presented correlation with respiratory and peripheral neuromuscular efficiency (r = -0.73 and r = -0.76, p < 0.001).

CONCLUSION

COPD patients have lower respiratory neuromuscular efficiency at moderate exercise intensity and lower peripheral neuromuscular efficiency at light exercise intensity. Dynamic hyperinflation affects respiratory and peripheral neuromuscular efficiency.

Circulating Biomarkers of Accelerated Sarcopenia in Respiratory Diseases

Skeletal muscle dysfunction is a critical finding in many respiratory diseases. However, a definitive biomarker to assess muscle decline in respiratory diseases is not known. We analyzed the association of plasma levels of glycoprotein Dickkopf-3 (Dkk-3), c-terminal agrin fragment-22 (CAF22) and microRNAs miR-21, miR-134a, miR-133 and miR-206 with hand-grip strength (HGS) and appendicular skeletal mass index (ASMI) in male, 54-73-year-old patients with chronic obstructive pulmonary diseases (COPD), asthma or pulmonary TB (n = 83-101/group). Patients with respiratory diseases showed a reduction in HGS and gait speed, while a reduction in ASMI was only found in patients with pulmonary TB. Among the sarcopenia indexes, HGS showed the strongest correlation with plasma CAF22, miR-21 and miR-206 levels while ASMI showed the strongest correlation with Dkk-3 and miR-133 in respiratory diseases. We found a modest-to-significant increase in the plasma markers of inflammation, oxidative stress and muscle damage, which had varying degrees of correlations with Dkk-3, CAF22 and selected micro RNAs (miRs) in respiratory diseases. Taken together, our data show that plasma levels of Dkk-3, CAF22 and selected miRs can be useful tools to assess accelerated sarcopenia phenotype in the elderly with respiratory diseases.

Effect of 6-minute walk test on neuromuscular properties of patients with chronic obstructive pulmonary disease

OBJECTIVE

The objective of this study was to evaluate the neuromechanical properties of the knee extensor muscles before and after the 6-minute walk test (6MWT) in chronic obstructive pulmonary disease (COPD) patients and control subjects.

MATERIALS AND METHODS

COPD patients from the Department of Pulmonology of the Hospital de Clinicas de Porto Alegre and age- and sex-matched control volunteers without COPD were included in this study. Body composition and lower limb strength assessed by maximal voluntary isometric contraction (MVIC) of the knee extensors) were assessed before and after the 6MWT. The total reaction time (TRT), premotor time (PMT) and motor time (MT) were assessed using surface electromyography of the rectus femoris and vastus lateralis knee extensor muscles.

RESULTS

Eighteen patients COPD patients (10 men, FEV₁ 36 ± 12% of predicted) and 8 control subjects (5 men, FEV₁ 82 ± 7% of predicted) were included. COPD patients had lower muscle strength before (21.77 ± 7.86 kg) and after the 6MWT (11.16 ± 4.70 kg) compared with control subjects (33.50 ± 14.01 kg before; 29.25 ± 16.66 kg after). After the 6MWT, COPD patients showed a significant reduction in the MVIC and a significant increase in the TRT and PMT, which did not occur in control subjects. The reaction time parameters were higher in COPD patients after the 6MWT compared with control subjects. The TRT (r = -0.535, P < 0.005) and PMT (r = -0.549, P < 0.005) were inversely correlated with the MVIC after the 6MWT.

CONCLUSIONS

Neuromuscular changes associated with upper motor neuron activation contribute to MVIC impairment in COPD patients after performing a functional test.