Activity patterns of the diaphragm during voluntary movements in awake cats

Abstract

The diaphragm is an important inspiratory muscle, and is also known to participate in the postural function. However, the activity of the diaphragm during voluntary movements has not been fully investigated in awake animals. In order to investigate the diaphragmatic activity during voluntary movements such as extending or rotating their body, we analyzed the electromyogram (EMG) of the diaphragm and trunk muscles in the cat using a technique for simultaneous recordings of EMG signals and video images. Periodic respiratory discharges occurred in the left and right costal diaphragm when the cat kept still. However, once the cat moved, their periodicity and/or synchrony were sometimes buried by non-respiratory activity. Such non-periodic diaphragmatic activities during voluntary movements are considered as the combination of respiratory activity and non-respiratory activity. Most of the diaphragmatic activities started shortly after the initiation of standing-up movements and occurred after the onset of trunk muscle activities. Those activities were more active compared to the normal respiratory activity. During rotation movements, left and right diaphragmatic activities showed asymmetrical discharge patterns and higher discharges than those during the resting situation. This asymmetrical activity may be caused by taking different lengths of each side of the diaphragm and trunk muscles. During reaching movements, the diaphragmatic activity occurred prior to or with the onset of trunk muscle activities. It is likely that diaphragmatic activities during reaching movements and standing-up movements may have been controlled by some different control mechanisms of the central nervous system. This study will suggest that the diaphragmatic activity is regulated not only by the respiratory center but also by inputs from the center for voluntary movements and/or sensory reflex pathways under the awake condition.

Fig. 1

Positions of EMG electrodes. EMG electrodes are indicated by circles. Dotted lines indicate the border of the latissimus dorsi and external oblique. Thick line indicates the position of the diaphragm. DIA Diaphragm, LD latissimus dorsi, EO external oblique, RA rectus abdominis. These abbreviations are common to all the figures

Fig. 2

EMGs during standing-up movements. Frames indicate the period of standing-up movement from lifting their forelimbs up to putting down. a EMGs from resting (a–c) to standing-up movement (d–h). ‘d’ The onset of the standing-up movement and ‘h’ the end of the standing-up movement. The vertical line and the alphabet correspond with the body positions illustrated on the top of the figure. Asterisks show rhythmic respiratory activities in the diaphragm. b Time scale expanded recording of (a). Asterisks show rhythmic respiratory activities in the diaphragm, and dotted circles indicate the non-respiratory activities. The vertical thick lines indicate the onset of non-respiratory activity of the diaphragm. The arrows indicate onsets of LD and EO activities

Fig. 3

EMGs during rotating movement. Frames indicate the rotating movements (the clockwise rotating movement). The vertical lines and the alphabet show the body positions in accordance with illustration on the top of the figure. The non-respiratory activities when the contralateral diaphragm was not active are indicated by the arrows and the underlines. Black thick underlines the first asymmetrical activity of left diaphragm, white thick underlines the first asymmetrical activity of right diaphragm. Hatched thick underlines the second asymmetrical activity of left diaphragm

Fig. 4

EMGs during reaching movements. Frames indicate the reaching movements. a EMG recordings during reaching movement. b Time scale expanded graph of (a) during reaching movement. ECG signal mixed in the record of right RA. The vertical line ‘c’ indicates the onset of non-respiratory activity of the diaphragm. The arrows indicate onsets of LD and EO activities. The differences in the times of onset between DIA and LD or EO are indicated by horizontal arrows. In this case, onset of the right LD was prior to that of the diaphragm and the onset of left EO was not able to be measured