Showing papers by "Warren M. Grill published in 2003"

Using external anal sphincter activity to detect the onset of bladder contractions

Abstract: Individuals with spinal cord injury or neurological disorders may develop, involuntary bladder contraction at low volumes (bladder hyper-reflexia), which can lead to significant health problems. Current devices can eliminate nascent contractions through continuous stimulation, but do not have a means to detect the onset of bladder contraction to stimulate conditionally. The objective of this study is to determine the relationship between the activity of the external anal sphincter (EAS) and hyper-reflexive bladder contraction, and to use the relationship to develop a model to detect the onset of a bladder contraction. Bladder pressure and EAS EMG were recorded in four intact male cats. There was little EAS activity during the bladder contraction and more activity between contractions (p<0.001). A model was developed to predict the onset of a bladder contraction using the EAS EMG activity. The model calculated the onset of bladder contraction on average 4.8 seconds after the contraction started with an average increase in pressure of 8.7 cmH/sub 2/O. There existed a phasic relationship between the bladder and the EAS, which enabled the prediction model to detect the onset of a bladder contraction. The EAS EMG can be used as a trigger to deliver conditional inhibitory stimulation of the bladder.

Experimental and biomechanical model force fields produced by intraspinal microstimulation of the cat lumbar spinal cord

Abstract: Using a biomechanical model of the cat hindlimb, we studied patterns of endpoint forces created by all muscle combinations of fourteen selected muscles, and compared them to the force patterns produced by intraspinal microstimulation of the lumbar spinal gray matter. We ran the model with two different activation schemes for the muscles. The first run used combinations of the fourteen selected muscles stimulated at the same level of activation. The second run used combinations where muscle forces were normalized to produce the same maximum end-point force. These results were compared to force field patterns obtained experimentally during intraspinal microstimulation. Although there were slight variations in the force patterns produced, both methods converged to four dominant patterns. When muscles in the model were normalized, some force patterns were found that were not observed experimentally. These results show the significance of specific levels of muscle activation to the production of the experimental patterns.

Stimulation of the deep perineal nerve elicits bladder contractions

Abstract: Spinal cord injury (SCI) eliminates voluntary control of bladder function. This study examined the ability to elicit and sustain bladder contractions with deep perineal nerve (DP) stimulation in 3 cats. The DP was stimulated at 2, 10, 20, 33, and 40 Hz over a range of bladder volumes before and after SCI. DP stimulation elicited bladder contractions pre- and post-spinal transection and was dependent on bladder volume and stimulation frequency. Bladder contractions were only evoked above a threshold bladder volume, which decreased post-spinalization. Both pre- and post-transection, bladder contractions were evoked at stimulation frequencies (2 Hz - 40 Hz), however frequencies of 20 Hz or greater were more effective at sustaining contractions. Post-transection, stimulation frequencies of 33 Hz or greater evoked greater bladder pressures than lower frequencies. Stimulation of the proximal, but not distal DP after DP-transection elicited contractions, demonstrating that the response was afferent mediated. Neural prostheses able to evoke sustained bladder contractions could restore bladder control and provide substantial clinical benefit to individuals with SCI.