Postural disturbances resulting from unilateral and bilateral diaphragm contractions: a phrenic nerve stimulation study

Thoracoabdominal breathing movements are a complex source of postural disturbance, but there are contradictory reports in the literature with inspiration described as having either a backward or a forward disturbing effect. To elucidate the mechanisms underlying this phenomenon, the present study studied the postural disturbance caused by isolated contractions of the diaphragm. Eight male and four female healthy subjects followed an original paradigm of phrenic nerve stimulation (bilateral and unilateral) and “diaphragmatic” voluntary sniff maneuvers in the seated and standing postures. Center of gravity (CG) acceleration was calculated from force plate recordings, and respiratory kinematics were assessed with thoracic and abdominal sensor belts. CG and respiratory signals revealed that, while seated, bilateral phrenic stimulation and sniff maneuvers consistently produced expansion of the abdomen associated with a forward peak of CG acceleration. In the standing posture, the direction of the CG peak was reversed and always directed backward. Unilateral phrenic stimulation induced an additional medial-lateral acceleration of the CG, directed toward the nonactive side while seated, but in the opposite direction while standing. These results suggest that isolated diaphragmatic contractions produce a constant disturbing pattern for a given posture, but with opposite effects between standing and seated postures. This could be related to the different biomechanical configuration of the body in each posture, corresponding to distinct kinematic patterns of the osteoarticular chain. In addition, the lateral component of the CG acceleration induced by unilateral diaphragm contractions could be clinically relevant in patients with hemidiaphragm paralysis.

The Effects of Moving Environments on Thoracolumbar Kinematics and Foot Center of Pressure When Performing Lifting and Lowering Tasks

The purpose of this study was to examine how wave-induced platform motion effects postural stability when handling loads. Twelve participants (9 male, 3 female) performed a sagittal lifting/lowering task with a 10 kg load in different sea conditions off the coast of Halifax, Nova Scotia, Canada. Trunk kinematics and foot center of force were measured using the Lumbar Motion Monitor and F-Scan foot pressure system respectively. During motion conditions, significant decreases in trunk velocities were accompanied by significant increases in individual foot center of pressure velocities. These results suggest that during lifting and lowering loads in moving environments, the reaction to the wave-induced postural disturbance is accompanied by a decrease in performance speed so that the task can be performed more cautiously to optimize stability.

Effects of Long Duration and Repeated Exposures in an Immersive Virtual Envionment on Postural Stability

Postural disturbance following virtual environment (VE) exposure has been reported in many studies. Some suggest that postural disturbance could be a pre-cursor of or highly related to simulator sickness (SS). Few studies have addressed long duration exposure and multi-sessions in SS and postural disturbance. This study investigated effects of long duration and repeated exposure to an immersive VE on postural disturbance. The results suggested larger postural disturbance 24 hours and 48 hours after the first VE exposure. However, differences between postural disturbance magnitudes pre- and post- exposure within a day decreased after 48 hours. Differential effects were associated with different postural stances were also found. Suggestions for further research are addressed.