FESAM: Functional Electrical Stimulation of Abdominal Muscles

The application of engineering control theory to biological systems is a challenge. Often, in initial engineering models or designs of systems to exert control over a certain aspect or part of a biological system, other control loops may be in operation within the biological system that are not accounted for. When the operation of such unconsidered hidden loops reveals themselves, this presents an opportunity to expand knowledge of biological control systems. A complimentary pair of reflexes involved in respiration was described by Hering and Breuer in 1868. Since that time, the manifestation of these reflexes has been controversial. In a recent group of studies seeking to apply an open-loop control system to assist or restore ventilation by electrically stimulating abdominal muscles, unexpected experimental results led to a more thorough study of the potential presence of the Hering-Breuer deflationary reflex in adult human subjects. This paper describes experiments in which abdominal compression (both manual and by electrical stimulation of abdominal muscles) provide evidence supporting the presence of the deflationary reflex control loop in adult human subjects. The results can be utilized to develop a comprehensive model of the human respiratory system considering both chemical and mechanical feedback. Index Terms — respiration, reflex, control, electrical stimulation. GLOSSARY OF SYMBOLS AND ABBREVIATIONS EEV: End Expiratory Volume ECG: Electrocardiogram EMG: Electromyogram DEMG: Diaphragmatic EMG f: Frequency of respiration FESAM: Functional Electrical Stimulation of Abdominal Muscles FRC: Functional Residual Capacity IAPR: Intermittent Abdominal Pressure Regulation IPPV Intermittent Positive Pressure Ventilation MV: Mechanical Ventilation The orginal manuscript received on the February 14 2002. The manuscript accepted in the final form on the April 24 2002. Thomas Ch. Fuhr is with the Institute of Automatic Control Engineering, Technical University of Munich, Germany, e-mail: [email protected] Robert Jaeger is with the Research Service, Department of Veterans Affairs, USA, E-mail: [email protected] MinV: Minute Ventilation SCI: Spinal Cord Injury sd: Standard Deviation Ttot.cond : Time Duration of a single breath; if specified, experimental condition is normal or compressed