Performance Evaluation of Tattoo Skin Electrodes for Measuring Respiratory Muscle Activity in Healthy Subjects

Measuring respiratory muscle activity is essential for assessing chronic respiratory diseases and neuromuscular disorders, and can be performed by means of surface electromyography (sEMG) over lower intercostal spaces, in an easy and noninvasive manner. While sEMG signals are usually recorded using commercial wired Ag/AgCl electrodes and complex acquisition setups, tattoo skin electrodes are currently emerging as a new wearable technology to measure electrophysiological signals. This study aims to evaluate the performance of tattoo skin electrodes for sEMG recording over lower intercostal spaces to measure respiratory muscle activity. In-lab tests were performed in 6 healthy participants, using two different tattoo sensors for recording four lower right intercostal space sEMG signals, corresponding to inter-electrode distances of 1.35, 2, 2.7, and 4.05 cm, during various respiratory maneuvers. Tattoo measurements of respiratory muscle activity were compared with reference measurements obtained with commercial Ag/AgCl electrodes and a respiratory band signal. Tattoo measurements showed very strong correlations (r from 0.858 to 0.931) and good-to-excellent agreement (ICC_2,1 from 0.759 to 0.919) with reference measurements, regardless of the inter-electrode distance. These results demonstrate that tattoo sensors are a promising alternative to commercial Ag/AgCl electrodes for measuring respiratory muscle activity in real-world settings.Clinical Relevance- Tattoo sensors are a promising wearable technology for measuring respiratory muscle activity, being thinner and more flexible than commercial Ag/AgCl electrodes, and allowing the design of skin conformable electrode arrays. The use of this technology represents a clear advance towards continuous, noninvasive, and remote monitoring of patients with respiratory muscle weakness under free-living conditions, which would improve assessment of disease progression and the efficacy of therapeutic interventions.