Respiratory responses to voluntary and reflexly-induced stepping movements in normal subjects and spinal patients

In the present study, the mechanisms of interaction between the breathing and stepping movements were investigated. The investigations were carried out in 8 normal subjects and 4 individuals with complete spinal cord lesion. Additionally, experimental studies were performed in 7 decerebrate and 4 spinal cats. Involuntary reflex stepping movements in the air were induced by vibrators attached above a tendon of m. rectus femoris and m. biceps femoris. In the spinal patients, epidural stimulation was carried out with electrodes located in the posterior epidural space at the vertebral level Th11. It was found that voluntary-induced stepping, which are accompanied by visceral reactions, were mediated by the central mechanisms. Changes in breathing pattern in response to vibration-induced involuntary stepping movements point up to the peripheral component being predominant in such interactions. In the spinal patients under epidural spinal cord stimulation delivered below the site of injury, the reaction in the cardio-respiratory system was abolished. Vibrations to the leg muscles also did not evoke respiratory responses. However, in the condition of forced breathing such vibrations evoked the rhythmic bursting EMG activity in m. rectus femoris, which was in harmony with the breathing rhythm. The results confirmed the presence of an interaction between breathing and stepping generators. This interaction is underlain both by central and peripheral components.