Neuromuscular Stimulation of Quadriceps in Patients Hospitalised during an Exacerbation of COPD: A Comparison of Low (35 Hz) and High (50 Hz) Frequencies

Abstract

Neuromuscular electrical stimulation (NMES) has shown to improve skeletal muscle strength and exercise capacity in stable patients with chronic obstructive pulmonary disease (COPD). Variations in NMES protocols are considerable. We aimed to compare changes in muscle strength after high-frequency and low-frequency NMES in patients admitted to hospital with an acute exacerbation of COPD. Patients were referred for inpatient (IP) rehabilitation during hospitalisation for an acute worsening of their COPD. They received 30-minute daily NMES to both quadriceps at a frequency of 35 or 50 Hz. NMES intensity was titrated to patients' tolerance. Isometric quadriceps muscle strength and endurance walking (ESWT) time were measured at baseline and on hospital discharge. A total of 10 patients in each treatment group underwent NMES during hospitalisation (mean [SD] age 68.0 [±7.4] years, FEV1 0.99 L [±0.58], FEV1/FVC 47% [± 27%], MRC 5 [IQR ±1]). There were no significant differences in baseline characteristics between groups. Muscle strength (legs combined) increased in both groups regardless of the NMES frequency used (35 Hz--3.8 ± 4.9; 50 Hz--3.4 ± 5.5 kg). This was only significant within the 35 Hz group. The change in ESWT also showed a trend to increase in both groups (35 Hz--109 ± 92.7; 50 Hz--145.6 ± 94.7). There was no significant difference between groups for either outcome. NMES is a feasible intervention to improve muscle strength in a cohort of patients admitted with an exacerbation of COPD. The response appears to be independent of the frequency used and both were well-tolerated.