Mean Pressure Responses Research Articles

Distributed occupant-seat interactions as an objective measure of seating comfort

An automotive seat must provide the occupant with a comfortable environment in which driving can be performed in a safe and comfortable manner. The characterisation of the interactions between the occupant and the seat under various conditions thus constitutes an important goal for enhancing the knowledge of essential design factors that could yield improved seating comfort. This paper investigates the occupant-seat interactions through measurements and analyses of the distributed contact force, contact area and peak and mean pressure responses at the body-seat-pan and body-backrest interfaces of three different automotive seats. User’s perceived comfort levels for various seating configurations were acquired through a survey and results were analysed through analytical hierarchy process (AHP) in order to derive a quantitative expression for the perceived comfort level. A strong correlation between perceived comfort and the peak and mean pressures on the seat-pan enabled us to derive an explicit formulation of seating comfort.

Functional Impact of the Rhabdosphincter Branch of the Pelvic Nerve on the Membranous Urethra in Comparison to That of the Pudendal Nerve in Male Rabbits

Introduction: The innervation of the membranous urethra (MU) is still under debate. We analysed the functional effects of electrostimulation of the rhabdosphincter branch of the pelvic nerve (RBP) on the MU in a standardized male rabbit model, paying attention both to the efferent and the possible afferent effects of stimulation. Material and Methods: Six male rabbits (chinchilla bastards) were included in this study. Pudendal nerve branches as well as pelvic nerve branches were exposed bilaterally in all animals. Randomized electrostimulation trials of both the pudendal nerve fibres and the RBP were carried out using a biphasic signal (0.3 mA, 200 μs). The stimulation frequency ranged from 10 to 40 Hz in a randomized pattern. Changes in MU pressure were measured urodynamically. The pressure changes occurring as a result of stimulation were compared in both nerve structures. At the end of the stimulation trial, the RBP and the pudendal nerve were dissected at different positions before repeating the stimulation and the MU pressure recording. Results: The mean MU baseline pressure without stimulation was 24 cm H₂O (range 21–27) in all animals. During unilateral pudendal stimulation, the mean pressure response rose by highly significant values (p < 0.005) compared to baseline. The pressure response was frequency dependent. Stimulation of the RBP resulted in a small but significant change of the MU pressure in the lower frequency range (10 and 20 Hz) (p > 0.05). On performing stimulation at higher frequencies, there was no significant difference from baseline. The pressure response of the MU during stimulation of the intact RBP did not differ significantly from the response after dissection of the RBP. However, after dissecting the pudendal nerve, the MU pressure response to RBP stimulation was diminished. Conclusion: Our results confirm the primacy of the pudendal nerve in the innervation of the MU. Stimulation of the RBP, however, may produce an afferent signal which is transmitted to the pudendal nerve, thus resulting in a pressure increase of the MU and contributing towards continence. We showed the importance of the RBP to maintain full urinary continence in rabbits. Our results suggest that substantially higher continence rates can be achieved through a nerve-sparing procedure in radical prostatectomy. Nerve-sparing radical prostatectomy incidentally also protects the RBP from injury.

Nerves at the Ventral Prostatic Capsule Contribute to Erectile Function: Initial Electrophysiological Assessment in Humans

BackgroundRecent microanatomical studies have identified a significant amount of nerve fibers along the ventral circumference of the prostate capsule and confirmed the concept of a periprostatic nerve network. However, functional investigations have not yet proved whether nerve fibers distributed on the prostate capsule, particularly those outside the neurovascular bundle (NVB), contribute to erection. ObjectiveTo confirm whether nerve fibers distributed on the prostate capsule contribute to erectile function, the present study was performed using electrophysiologic testing. Design, setting, and participantsThe circumference of the prostate capsule was electrically stimulated during radical retropubic prostatectomy (RRP) in 12 patients with clinically localized prostate cancer (PCa). We defined the ventromedian circumference of the prostate capsule as the 12 o’clock position and the posterolateral position of the typical NVB as the 5 o’clock position. Periprostatic nerve fibers at the 12, 1, 2, 3, 4, and 5 o’clock positions of the midprostate were stimulated using bipolar electrodes. MeasurementsChanges in pressure at the middle of the urethra were measured using an inserted balloon catheter to detect increases in cavernosal pressure. Results and limitationsAlthough the study included only 12 patients, every stimulation at all positions between 1 and 5 o’clock evoked urethral pressure responses in all patients. Mean pressure response was most powerful for 5 o’clock stimulation and decreased with stimulated points further from the 5 o’clock position. ConclusionsWe demonstrated that electrostimulation at not only the posterolateral but also the anterior and lateral circumference of the prostate capsule can increase cavernosal pressure. These findings indicate that the periprostatic nerve network contributes to erections.

Posterior sagittal anorectoplasty in anorectal anomalies: clinical, manometric and profilometric evaluation.

Anorectal malformations comprise a spectrum of anomalies that continue to be difficult to treat, even today. The aim was to evaluate the fecal continence of children who underwent posterior sagittal anorectoplasty due to anorectal malformations, via computerized anorectal manometry and profilometry. Prospective study at Universidade Federal de São Paulo. 82 patients (56.1% boys; 43.9% girls) of mean age 85.5 months were evaluated. They were divided into continent, partially continent and incontinent groups. Age, sex, manometric variables and profilometric parameters were studied. The results were statistically analyzed. Among the 82 patients, 37.8% were continent, 25.6% were partially continent and 36.6% were incontinent. The overall mean resting pressure was 22 mmHg, and the means for the continent, partially continent and incontinent groups were, respectively, 30.7 mmHg, 23 mmHg and 14.7 mmHg. The overall mean pressure response to voluntary contraction was 56 mmHg, and the means for the groups were 65.4 mmHg, 55.8 mmHg and 46.6 mmHg, respectively. The rectosphincteric reflex was absent in 82.9% of the cases. In the profilometry analysis for all patients together, blue (20 to 50 mmHg) and yellow (50 to 80 mmHg) were predominant, and there was a similar distribution for the continent and partially continent patients. However, among the incontinent patients, green (< 20 mmHg) and blue prevailed. Manometric and computerized profilometric analyses were an excellent method for postoperative evaluations on patients with intermediate and high anorectal anomalies, and for therapeutic planning.

Impact of Electrostimulation of Neurovascular Bundles and Pudendal Nerves on the Membranous Urethra in Male Rabbits

The pathophysiology of post-prostatectomy incontinence is supposed to be multifactorial. The impact of the neurovascular bundles on sphincter function is still under debate. We clarified the impact of cavernous nerves function on the MU. We compared MU pressure responses in male rabbits following electrophysiological stimulation trials on the neurovascular bundles vs pudendal nerve stimulation. Six male Chinchilla Bastard rabbits were included in this study. Pudendal and cavernous nerve branches were exposed bilaterally in all animals. Randomized electrostimulation of pudendal nerve fibers and the cavernous nerves, as confirmed by erection,) were done using a biphasic signal form of 0.3 mA for 200 microseconds. Stimulation frequency was changed in a randomized pattern from 10 to 40 Hz. Changes in MU pressure were measured urodynamically via a transurethral microtip catheter placed in the MU. Stimulation responses of the 2 nerve structures were compared. Mean baseline pressure in the MU without stimulation was 23 cm H(2)O (range 20 to 25) in all animals. During unilateral pudendal stimulation the mean pressure response increased highly significantly to 33, 43, 59 and 60 cm H(2)O at 10, 20, 30 and 40 Hz, respectively (p <0.005). In contrast, compared to baseline pressure cavernous nerve stimulation did not result in any significant changes in proximal urethral pressure (mean 23 cm H(2)O, range 20 to 25, p >0.05). Our results confirm the primacy of the pudendal nerve in the external urethral sphincter innervation. In contrast, stimulation of the cavernous nerves did not produce any pressure changes in the MU. These results confirm that the neurovascular bundles have no functional impact on the MU.

Smooth muscle role on pulmonary arterial function during acute pulmonary hypertension in sheep.

We determined the wall mechanical response of the pulmonary artery (PA) to acute pulmonary hypertension induced pharmacologically and by an occlusion maneuver, to study the vascular response of the local segment and its influence in the whole pulmonary circulation. Pulmonary pressure and diameter were measured in six anaesthetized sheep under steady-state conditions. Transient hypertension in the PA was induced by phenylephrine (PHE) and a high pressure (HP) mechanical occlusion aimed at producing the same pulse and mean pressure responses. A viscoelastic arterial wall model was applied and the elastic (E(pd)) and viscous (micro) indexes were obtained. The micro/E(pd) ratio was adopted to quantify the damping performance of the arterial wall segment. The diastolic time constant was used as an indicator of the whole pulmonary buffering function. The systemic pressure was always measured. The pulmonary mean, systolic and pulse pressure increases (P < 0.05) were similar during PHE and HP, with respect to control. PHE also induced a systemic pressure rise (P < 0.05). The E(pd) elastic index increased during HP (P < 0.05) and tended to increase during PHE with respect to control. The viscous index micro only increased with PHE (P < 0.05) with respect to control and occlusion. The diastolic time constant increased with PHE with respect to control (P < 0.05). A pressure rise in the PA, induced by an occlusion maneuver, increased local stiffness. Similar pressure rises with smooth muscle activation (PHE), produced both a stiffness and viscous index increase. In PHE resistance increases more than compliance decreases so that the global net effect is a longer decay time. Smooth-muscle activation enhances the local damping effect (micro/E(pd)), concomitant with the buffering function improvement.