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Biomedical subjects

Ahmed Shafik

Publications and source records attributed to Ahmed Shafik.

At least 91 records · Page 5Linked to original sources
PubMed2003

Effect of straining on perineal muscles and their role in perineal support: identification of the straining-perineal reflex.

OBJECTIVE: The functional activity of the superficial (STPM) and deep (DTPM) transverse perineal muscles is poorly addressed in the literature. We investigated the hypothesis that these muscles act to support the perineum during increased intraabdominal pressure (IAP). METHODS: 46 healthy volunteers (mean age 30.4 +/- 1.2 y, 20 nulliparous women) were studied. The IAP was recorded by a manometric catheter introduced into the rectum. The response of the perineal muscles to straining (sudden by coughing and slow by Valsalva's maneuver) was registered by a needle electrode inserted into the STPM and DTPM separately. The response was recorded again after individual anesthetization of the perineal muscles and rectum using Xylocaine. The test was repeated using saline instead of Xylocaine and was performed on both sides. RESULTS: Straining (sudden or slow sustained) effected increase of the rectal pressure and the motor unit action potentials of both perineal muscles. The higher rectal pressure was increased by straining, the higher the motor unit action potentials increased MUAPs. The latency showed a gradual decrease upon incremental rectal pressure elevation. The perineal muscles did not respond to straining after individual anesthetization of the rectum and perineal muscles, but did respond to saline administration. The response was similar from muscles on both sides. CONCLUSIONS: Perineal muscle contraction on straining postulates a reflex relationship that we call the "straining-perineal reflex." We suggest that this reflex, which results in perineal muscle contraction, supports the perineum against the increased IAP induced by straining and the tendency of the perineum to descend. The results warrant further study of the role of the straining-perineal reflex in the genesis of perineal functional disorders.

Adult↗
PubMed2003

Overactive bladder inhibition in response to pelvic floor muscle exercises.

A recent study by the senior author demonstrated that striated urethral sphincter contraction effected the inhibition of vesical contraction and suppression of the desire to micturate, an action suggested to be mediated through the "voluntary urinary inhibition reflex". We hypothesized that the effect of pelvic floor muscle (PFM) exercises on the overactive bladder was mediated through this reflex action. The current communication investigates this hypothesis. A total of 28 patients (mean age 44.8+/-10.2 years, 18 men, 10 women) with overactive bladder and 17 healthy volunteers (mean age 42.6+/-9.8 years, 12 men, 5 women) were enrolled in the study. The vesical and posterior urethral pressures were determined before and after vesical filling reached the volume at which urge in control subjects, and involuntary voiding in the patients, occurred. Intra-abdominal pressure was recorded to obtain detrusor pressure readings. The bladder was refilled to the above volume and the subject asked to hold PFM contractions for 10 s during which the vesical and posterior urethral pressures were recorded. In healthy volunteers, the mean detrusor and posterior urethral pressures at urge to void were 30.6+/-4.8 SD and 18.7+/-3.3 cm H(2)O, respectively. On PFM contraction, the detrusor pressure declined to 11.6+/-1.4 cm H(2)O (P<0.01) and urethral pressure increased to 139.8+/-17.4 cm H(2)O (P<0.001). In patients, the mean detrusor and posterior urethral pressure readings when the bladder was filled to the volume which induced involuntary incontinence, were 28.2+/-4.2 and 17.3+/-3.4 cm H(2)O, respectively; on PFM contractions, the detrusor pressure decreased to 10.6+/-2.1 cm H(2)O (P<0.01), while urethral pressure increased to 86.6+/-7.9 cm H(2)O (P<0.001) and voiding did not occur. In conclusion, PFM contractions led to a decline of detrusor and increase of urethral pressures and suppressed the micturition reflex. These contractions appear to induce their effect by preventing internal sphincter relaxation produced by the micturition reflex. Failure of the internal sphincter to relax seems to cause reflex detrusor relaxation, an action presumably mediated through the "voluntary urinary inhibition reflex". The results of the current study encourage the treatment of overactive bladder with PFM contractions.

Adult↗
PubMed2003

Etiology of the resting myoelectric activity of the levator ani muscle: physioanatomic study with a new theory.

Of all the striated muscles in the bodies of mammals, only the pelvic floor muscles, which include the levator ani (LA), have resting electric activity. The cause and function of this resting myoelectric activity are not exactly known. The current study investigated the effect of intraabdominal pressure (IAP) and visceral weight on the electromyographic (EMG) activity of the LA, seeking to elucidate its cause and function. A series of 18 subjects (12 women, 6 men, mean age 38.6 years) were subjected to laparoscopic cholecystectomy for calcular cholecystitis. Prior to cholecystectomy, the resting LA EMG and IAP were recorded with the patient in the recumbent and erect positions. During laparoscopic cholecystectomy, the IAP was elevated by CO2 insufflation in increments of 5 cm of H(2)O, and the LA EMG activity was recorded for the recumbent and vertical positions during inflation and after deflation at the end of the operation. In 5/18 patients in whom laparoscopic cholecystectomy was extended to open cholecystectomy, the IAP and LA EMG were also registered. The study also included histologic examination of the LA muscle from 15 cadavers (7 adults, 8 neonates). Levator ani EMG increased ( p < 0.05) on standing. At operation, IAP elevation was associated with a significant increase of LA EMG activity. On deflation, the IAP and LA EMG activity level returned to the pre-insufflation state. In open cholecystectomy, the IAP was zero and the LA EMG recorded no activity for the recumbent position, but there was an activity for the vertical position. Histologically, the lateral part of the LA in the adult cadavers consisted solely of skeletal muscle fibers. Proceeding medially, smooth muscle fibers started to appear and gradually increase until, at the midportion, the LA split into two layers, a deep layer consisting of smooth muscle fibers and a superficial layer consisting of skeletal fibers. In neonates, the LA was composed of purely skeletal muscle fibers. The LA EMG activity seems to be related to both the IAP and the visceral weight. It is probably attributable to the presence of smooth muscle bundles in the LA muscle. The LA EMG activity increased with the elevation of the IAP and visceral weight, which resulted in increased muscle tone to oppose the augmented pressure or weight. This effect seems to be mediated through the straining-levator reflex. A chronic increase of IAP or visceral overload is suggested to affect muscle integrity and function.

Abdomen↗
PubMed2003

Colonic pacing in the treatment of patients with irritable bowel syndrome: technique and results.

The treatment of the irritable bowel syndrome (IBS) is not entirely satisfactory as the exact cause of the condition has not been revealed. We have demonstrated in a recent study that the IBS exhibited a "tachyarrhythmic" electromyographic pattern; the wave rhythm was irregular and wave variables were higher than those of the healthy volunteers. We suggested that a disorder of the colonic pacemaker discharges these abnormal waves thereby causing the motor disorders of IBS. In another study, we determined the colonic pacing parameters needed to modulate the disordered pacemaker. In the current communication we investigated the effect of colonic pacing, using these parameters, on the EMG activity of the sigmoid colon (SC) and on the clinical manifestations of patients with IBS. A pacemaker was implanted in a subcutaneous pocket in the inguinal area and its two leads were hooked to the colosigmoid junction. The effect of colonic pacing on the SC EMG activity was investigated by inserting two recording electrodes into the SC muscle. The patients were then trained for home pacing after removal of the 2 recording electrodes. Nine patients (age 42.7 +/- 4.2 years, 6 women) with IBS were studied. The pre-pacing tachyarrhythmic pattern of EMG was recorded. On colonic pacing, the slow wave rhythm became regular and wave variables were normalized; the symptoms of the IBS improved. The optimal parameters used for pacing comprised an amplitude of 6 mA, a pulse width of 150 ms and a frequency of 25% higher than that of the basal colonic waves. In 7/9 patients the improvement of symptoms continued when pacing was ceased after 6 months of daily pacing; the pacemaker was removed after 3 months of non-pacing. In 2/9 patients, pacing needed to be continued because the symptoms recurred each time the pacing was ceased. In conclusion, colonic pacing succeeded in normalizing the tachyarrhythmic pattern and relieving the symptoms of the IBS. No complications were encountered and the method was well accepted and tolerated. Further studies on a large group of patients are required.

Adult↗
PubMed2003

Electric activity of the colon in subjects with constipation due to total colonic inertia: an electrophysiologic study.

BACKGROUND: Idiopathic constipation may result from colonic inertia, which affects the whole colon or is localized to an area of the colon. The colon exhibits electric activity in the form of slow waves or pacesetter potentials (PPs) and action potentials (APs), which are coupled with elevated colonic pressure. The APs are claimed to be responsible for colonic motor activity. HYPOTHESIS: Colonic electric activity is disordered in patients with constipation due to colonic inertia. METHODS: Electric activity was studied in 11 patients with colonic inertia and constipation (mean +/- SD age, 42.8 +/- 6.6 years; 7 women) who underwent total colectomy. Eight volunteers who had no gastrointestinal complaints (mean +/- SD age, 40.6 +/- 5.8 years; 5 women) acted as controls. Control subjects underwent laparotomy for hernia repair (n = 7 patients) and for removal of a mesenteric cyst (n = 1 patient). During the operation, 2 monopolar silver-silver chloride electrodes were applied to the cecum and the ascending, transverse, descending, and sigmoid colon. RESULTS: Electric waves (PPs and APs) were recorded from all parts of the colon in control subjects. The waves were monophasic, negatively deflected, and had regular rhythm. The wave variables from the 2 electrodes of each segment of the colon were identical and reproducible. They progressively increased aborally. In the colonic inertia group, 5 patients had recorded waves from the cecum and ascending colon but no waves from the rest of the colon. The wave variables were significantly lower than those of the controls (P =.02). In the remaining 6 patients, no waves were registered from the whole colon. CONCLUSIONS: Regular electric waves were recorded from the colons of control subjects. The aboral increase of their frequency, amplitude, and conduction velocity suggests that colonic motile activity increases analward, reaching its maximum in the sigmoid colon to expel its solid contents. We postulate that constipation in patients with colonic inertia is attributable to weak or absent electric activity, the cause of which is unknown. A disorder of the interstitial cells of Cajal, which generate electric activity, is suggested to have a role in inducing diminished or absent colonic motor activity, a point that should be investigated.

Action Potentials↗
PubMed2003

Identification of a sphincter at the sigmoidorectal canal in humans: histomorphologic and morphometric studies.

In a recent study we demonstrated that the rectosigmoid junction is a large bowel segment 2.8 +/- 0.9 cm in length, which we have termed the 'sigmoidorectal canal' (SRC). In that study we showed that the SRC exerted increased intraluminal pressure, contained a thick, circular, smooth muscle layer, and reacted to sigmoid colon (SC) and rectal contraction by relaxation and contraction, respectively. These findings suggest the existence of an anatomical sphincter at the SRC. To investigate this hypothesis, in the present study we carried out a morphometric (quantitative) analysis of the musculature of the SC, SRC, and rectum. Twenty-two cadavers (13 male, 9 female; mean age = 32.3 +/- 17.6 years) were investigated. Histomorphologic studies comprised staining transverse (15 cadavers) and longitudinal (7 cadavers) sections from the SC, SRC, and rectum. Specimens were stained with H&E, Masson's trichrome, and silver stains. Morphometric studies, using image analyzer computer equipment, measured the muscle thickness of the muscularis externa (ME) of the SC, SRC, and rectum. The ME of the SRC was markedly thickened compared to the ME of the SC or rectum. In 16 specimens, the increased thickness involved mainly the circular muscle layer and in six specimens both the circular and longitudinal layers. Connective tissue septa connected the adventitia with the submucosa: these 'adventitial septa' contained nerve ganglia. 'Localized bundles' of smooth muscle fibers were detected between the circular muscle fibers. The morphometric findings showed that the mean thickness of the circular muscle layer measured 440.3 +/- 80.1 microm in the SC, 1166.1 +/- 255.4 microm in the SRC, and 394.9 +/- 123.9 microm in the rectum. This study strongly suggests the presence of an anatomic sphincter at the SRC. This sphincter may explain the higher pressure at the SRC and the response of the SRC to rectal and SC contractions. The localized smooth muscle bundles in the ME may represent a rectosigmoid pacemaker.

Adolescent↗
PubMed2003

Effect of perineal compression on the rectal tone: a study of the mechanism of action.

PURPOSE: Digital pressure on the perineum was reported to result in an increase of the rectal tone. This effect has been related to a reflex action named perineorectal reflex but was not verified. The mechanism of action of perineal pressure on the rectal tone was studied. METHODS: Eighteen healthy volunteers (mean age +/- standard deviation, 39.7 +/- 11.8 years; 10 males) were studied. The barostat system used consisted of a polyethylene balloon connected to a strain gauge and a computer-controlled, air-injection system. The balloon was introduced into the rectum, and the rectal tone was assessed by recording the balloon volume variations in response to digital pressure on the perineum. The test was repeated after individual anesthetization of perineum and rectum. It was performed again using normal saline instead of Xylocaine. RESULTS: During perineal pressure, all the volunteers exhibited rectal tone increase with a mean decrease in the balloon volume of 72.3 +/- 14.7 percent. There was no significant difference (P > 0.05) in the rectal tone response between females and males nor between young and elderly patients. The mean latency was 17.3 +/- 1.8 ms. Perineal pressure 20 minutes after individual anesthetization of perineum and rectum effected no significant rectal tone changes. The response returned after the anesthetic effect had waned. The rectal tone response after saline administration was similar to that before administration. CONCLUSION: The study has shown that rectal tone increase during digital perineal pressure represents most probably a reflex action. This was evidenced by absence of rectal tone response on individual anesthetization of the assumed two arms of the reflex arc: perineum and rectum. The perineorectal reflex may be of diagnostic significance in rectal motor disorders and has the potential to be used as an investigative tool, provided further studies are performed to prove these points.

Adult↗
PubMed2003

Study of the role of the second defecation reflex: anorectal excitatory reflex in the pathogenesis of constipation.

BACKGROUND: Previous studies have shown that anal distension caused rectal contraction, an action mediated through the anorectal excitatory reflex. Anal anesthetization aborted rectal contraction and rectal evacuation was induced by excessive straining. We investigated the hypothesis that inhibition or absence of the anorectal excitatory reflex could lead to constipation. METHODS: We studied 18 patients (mean age +/- SD: 40.6 +/- 5.8 years, 14 women) with rectal inertia, 14 (41.7 +/- 6.6 years, 12 women) with puborectalis paradoxical syndrome, and 10 healthy volunteers (37.9 +/- 4.8 years, 8 women). The rectum was filled with normal saline until urge and then evacuated; residual fluid was calculated. The anal and rectal pressure response to anal balloon distension in increments of 2 mL of saline was recorded by a two-channel microtip catheter. RESULTS: In the healthy volunteers, saline was evacuated as a continuous stream without straining except occasionally at the start of evacuation; no residual fluid was encountered. Anal balloon distension effected notable rectal pressure increase. In rectal inertia patients, evacuation occurred in small fluid gushes produced with excessive straining; residual fluid of large volume was collected. Anal balloon distension up to 10 mL produced no notable rectal pressure changes. The patients with PPS failed to evacuate more than a few mL of fluid despite excessive straining; the volume of residual fluid was considerable. Anal balloon distension caused a notable rectal pressure rise. The results were reproducible. CONCLUSIONS: These results suggest that the defecation reflexes (rectoanal and anorectal) are absent in rectal inertia patients and this presumably denotes a neurogenic disorder. The anorectal reflex is active in puborectalis paradoxical syndrome, but the rectoanal reflex is not, indicating a possible myogenic defect in the puborectalis muscle.

Adult↗
PubMed2003

Effect of perineal compression on vesical motor activity.

OBJECTIVE: It has been reported that digital pressure on the perineum inhibits bladder contraction; however, the mechanism is not fully understood. We investigated the hypothesis that this mechanism may be reflex in nature. MATERIAL AND METHODS: A total of 21 healthy volunteers (13 males; mean age 42.3 +/- 11.8 years) were studied. A barostat system consisting of a balloon-ended catheter connected to a strain gauge and air-injection system was used to assess vesical tone. The catheter was introduced into the urinary bladder and the balloon was inflated with 150 ml of air. Digital pressure was exerted on the perineum and the vesical tone was simultaneously assessed by recording the balloon volume variations, expressed as the percentage change from the baseline volume. The test was repeated after separate anesthetization of the perineum and bladder with xylocaine and after using normal saline instead of xylocaine. RESULTS: Digital pressure on the perineum effected a significant decrease in vesical tone, which ranged from 42% to 84% (mean 67.5% +/- 12.5%) of the baseline value. The mean latency was 18.6 +/- 2.6 ms. There was no significant difference between men and women in terms of vesical tone response to perineal pressure. Digital perineal pressure applied 20 min after individual anesthetization of the perineum and bladder produced no significant changes in vesical tone. The response returned after the anesthetic effect had waned. The vesical tone response following saline administration was similar to that before administration. CONCLUSIONS: Vesical tone decrease in response to digital pressure on the perineum suggests a reflex relationship which was absent on individual anesthetization of the two possible arms of the reflex arc: the perineal skin and urinary bladder. We call this relationship the "perineovesical reflex". This reflex may have the potential to be used as an investigative tool in the diagnosis of vesical motor disorders.

Adult↗
PubMed2003

Role of sympathetic innervation in the defecation mechanism: a novel concept of its function.

BACKGROUND/OBJECTIVE: Because the role of sympathetic innervation in the defecation mechanism is still vague and unidentified, this study was performed to investigate this issue. METHODS: The effect of individual administration of alpha- and beta-adrenoceptor blocking agents (3 mg/kg phentolamine mesylate and 1 mg/kg propranolol hydrochloride, respectively) and the effect of thoracolumbar sympathectomy on anal and rectal pressures was studied in 13 mongrel dogs. Pressures were measured by a 2-channel microtip catheter. Bilateral thoracolumbar sympathectomy was performed by excising the sympathetic ganglia from T11 to L2. Incremental rectal filling using a rectal balloon with simultaneous anal and rectal pressure measurements was continued until balloon expulsion was achieved. RESULTS: Rectal balloon distension with 30 to 40 mL of saline affected rectal pressure increase (P < 0.001 ), anal pressure decrease (P < 0.01), and balloon expulsion. Following administration of either phentolamine or propranolol or after thoracolumbar sympathectomy, rectal pressure declined (P < 0.05), but anal pressure showed no change (P > 0.05). At a rectal balloon volume of 50 to 60 mL of saline, rectal pressure increased (P < 0.001), anal pressure decreased (P < 0.01), and the balloon was expelled. CONCLUSION: Sympathetic rectal innervation may have a role during both the filling and evacuation phases of the defecation mechanism. During rectal filling, it most likely maintains rectal compliance. During evacuation in cases of rectal sympathetic block or denervation, a larger volume than usual of rectal distension is needed to induce rectal contraction and evacuation.

Adrenergic alpha-Antagonists↗
PubMed2003

Role of positive anorectal feedback in rectal evacuation: the concept of a second defecation reflex: the anorectal reflex.

BACKGROUND/OBJECTIVE: The present study investigated the hypothesis that rectal contraction is maintained by positive anorectal feedback elicited by continuous passage of stools through the rectal neck (anal canal), and that cessation of stool passage aborts rectal contraction. METHODS: Anal and rectal pressures were measured in 18 healthy volunteers (mean age = 38.6 years; 10 men, 8 women) during evacuation of saline infused into the rectum. Residual fluid volume was calculated. The test was repeated after separate application of lidocaine or bland gel to the rectal neck. RESULTS: On evacuation, fluid emanated from the rectal neck in continuous flow with no, or mild, straining. No residual saline was collected from 16 of 18 participants. After anal anesthetization, evacuation occurred in gushes induced with excessive straining; residual fluid was huge. Repetition of the test 2 hours after anesthetization produced the same results as before anesthetization. Bland gel applied to the rectal neck yielded results similar to those before gel application. CONCLUSION: Rectal contraction at defecation is suggested to be maintained by positive anorectal feedback evoked by continuous passage of stool through the rectal neck. This feedback appears to be affected through an anorectal excitatory reflex (ARR), which produces rectal contraction upon stimulation of anal stretch receptors. Abortion of this reflex by anal anesthetization seems to result in failure of the rectum to contract and in excessive straining to achieve rectal evacuation. ARR thus is suggested to be a second defecation reflex necessary to continue defecation, whereas the rectoanal inhibitory reflex is the primary reflex. The role of the ARR in pathogenesis of constipation and its utility in spinal cord injury need to be investigated.

Adult↗
PubMed2003

Effect of urethral dilation on vesical motor activity: identification of the urethrovesical reflex and its role in voiding.

PURPOSE: We investigated the hypothesis that mild urethral distention, which presumably occurs during the passage of urine through the urethra, stimulates stretch receptors in the urethral wall, leading reflexively to vesical contraction. MATERIALS AND METHODS: We evaluated 9 male and 10 female healthy volunteers with a mean age +/- SD of 39.6 +/- 8.3 years. The posterior urethra was distended by a balloon filled with saline in 1 ml. increments up to 6 ml., while recording vesical pressure. The test was repeated after individual anesthetization of the urethra and bladder. RESULTS: Vesical pressure increased significantly at 1 and 2 ml. urethral distention (p <0.01). Increases in urethral distention effected further vesical pressure elevation (p <0.001), although there was no significant difference in distention at 3 to 6 ml. (p >0.05). No significant vesical pressure response of the individually anesthetized urethra or bladder occurred during urethral distention. CONCLUSIONS: Urethral distention is thought to cause vesical contraction through the stimulation of urethral stretch receptors. Vesical contraction at urethral distention postulates a reflex relationship that was abolished by individual anesthetization of the urethra and bladder. This relationship, which we call the urethrovesical reflex, appears to have a role in maintaining vesical contraction during voiding. Further studies are required to investigate the role of this reflex in voiding disorders.

Adult↗