Biomedical subjects

Ahmed Shafik

Publications and source records attributed to Ahmed Shafik.

122 records · Page 7Linked to original sources

PubMed2002

Physiological assessment of the function of the ileocecal junction with evidence of ileocecal junction reflexes.

BACKGROUND: The ileocecal junction (ICJ) appears to be a specialized segment of the gut which regulates the passage of the chyme from the ileum to the cecum. We investigated the response of the ICJ to cecal and ileal distension and the nature of this response (direct or reflex). MATERIAL/METHODS: Nine patients who had early cancer in the proximal transverse colon were studied during right hemicolectomy. The pressure response of the ICJ to cecal and ileal balloon distension was determined before and after cecal and ileal anesthesia. The balloon and manometric catheters were introduced into the cecum and ileum by colotomy and ileotomy, respectively. ICJ length was measured by the pull-through technique. RESULTS: The ICJ high pressure zone had a mean length of 3.6 cm. Chyme flow to the cecum occurred in jets. Large-volume cecal distension caused a significant rise in cecal and ICJ pressures and decreased ileal pressure; the balloon was dispelled to the transverse colon. Large-volume ileal distension caused an increase in ileal pressure, decreased ICJ and cecal pressures, and aboral balloon movement. No pressure response was produced by small volume distension or anesthesia of the cecum or ileum. CONCLUSIONS: Ileal distension is suggested to initiate reflex ICJ and cecal relaxation which is mediated through the 'ileocecal inhibitory reflex' and which allows the chime to pass to the cecum. Cecal distension appears to evoke reflex ileal and ICJ contraction, thus preventing ceco-ileal reflux and allowing time for chyme to accumulate in, and distend, the terminal ileum; we call this reflex the 'ceco-ileal excitatory reflex'. These 2 reflexes are thought to regulate chyme passage through the ICJ.

Adult↗

PubMed2002

Role of the rectosigmoid pacemaker and electric activity in rectal motility: mechanism and clinical significance.

BACKGROUND: The rectum exhibits electric activity in the form of slow waves or pacesetter potentials (PPs) and action potentials (APs), which are suggested to be initiated from a rectosigmoid pacemaker (RSP). We hypothesized that the RSP and electric waves are responsible for rectal motility. This hypothesis was investigated. METHODS: The rectum of 13 mongrel dogs was exposed through an abdominal incision, and 3 electrodes were fixed serially to the rectal serosa. The rectal pressure was measured by a 6 F saline-perfused catheter and the rectal electromechanical response to rectal balloon distension in increments of 5 ml of air was registered. The test was repeated after rectosigmoid junction (RSJ) anesthetization by 20 minutes and 3 hours using xylocaine injection. It was done also after saline instead of xylocaine injection. RESULTS: PPs and APs were recorded and had the same frequency, amplitude and conduction velocity from the 3 electrodes of the same animal. APs occurred randomly and were coupled with elevated rectal pressure. Rectal balloon distension produced increase of the rectal electric activity and pressure, which increased with the increase of the rectal distension until, at a mean volume of 31.2 +/- 5.4 ml, the balloon was expelled to the exterior. RSJ anesthetization abolished the rectal electric waves and effected no balloon expulsion with high volume rectal distension. The rectal waves appeared after waning of the anesthetic effect. Saline injection into the RSJ produced no significant effect on the rectal electromechanical activity. CONCLUSION: Rectal electric waves are suggested to be initiated from the RSP and to be responsible for the rectal motor activity. Incremental rectal balloon distension effected progressive increase of the rectal electromechanical activity until the balloon was expelled to the exterior RSJ anesthetization blocked the electric waves and the electromechanical response to rectal distension. These results have probably clinical significance when performing electrorectograms for various rectal pathologic conditions as well as when applying an artificial pacemaker to the non-contractile rectum.

Action Potentials↗

PubMedDate not supplied

Effect of colonic distention on ileal motor activity with evidence of coloileal reflex.

Chyme delivery from the ileum to the colon is controlled by various neurologic and hormonal factors, many of which remain to be identified. In this report we investigated the effect of colonic distention on ileal motility with the aim of identifying the mechanism of chyme delivery from the ileum to the colon. The right colon of 16 healthy volunteers (12 men and 4 women; mean age 36+/-9 years standard deviation) was distended by a balloon that was filled with saline solution in increments of 20 ml. The pressure response of the terminal ileum to the colonic distention was recorded by a saline-perfused tube. The test was repeated in nine subjects after the colonic segment around the balloon was anesthetized by xylocaine injection into the colonic wall. Twenty and 40 ml colonic distention produced no significant ileal pressure response. Colonic distention with 60 ml produced an increase in colonic pressure (P<0.05), as measured by intraballoon pressure, and a decrease in ileal pressure (P<0.05); a similar response was achieved with 80 ml distention. At 100 ml colonic distention, the balloon was dispelled to the transverse colon. Distention up to 100 ml of the anesthetized colonic segment produced no significant colonic or ileal pressure response. The flow of chyme from the small to the large gut appears to be controlled by a reflex mechanism that we call the "coloileal reflex." Whenever the right colon is distended with a substantial volume of chyme that increases the intraluminal pressure, it is suggested that ileal relaxation occurs, which delays the emptying of chyme from the ileum.

Adult↗

PubMedDate not supplied

Role of tunica albuginea in erection: is it a dynamic or a static role?

The tunica albuginea (TA) of the penis is claimed to share in erectile mechanism by compressing the emissary veins passing through it. Apparently this claim is theoretical as no experimental studies could be traced in literature proving this concept. We investigated the hypothesis that TA acts as a cover to corpora cavernosa (CC) and spongiosa (CS) and does not have an active role in erectile mechanism. Penises of 9 dogs were degloved and TA was divided at upper, middle and lower 1/3 of the penis. The intracorporal and glans penis (GP) pressures were measured in the TA-covered and non-covered parts of CC and CS in the flaccid and erectile phases. Sham operation, without performing the TA incisions, was done in 7 control animals. In the test animals, intracorporal pressure (ICP) in the non-TA covered corpora and in GP recorded in flaccid phase a mean of 12.2 +/- 0.8 cmH2O for CC and 11.3 +/- 0.7 cmH2O for the CS and GP, and in the erectile phase 98.4 +/- 8.6 and 76.2 +/- 9.3 cmH2O, respectively. There was no significant difference between covered and non-covered corpora or between test and control animals. In conclusion, the TA seems to act as a cover to the corporal tissue. Its absence did not change ICP.

Animals↗

PubMedDate not supplied

Conjoint corpora cavernosa and its role in erection.

The two penile corpora cavernosa (CC) remain as separate structures along the penile shaft. During our study of 28 cadavers, we came across three cadavers in which the two CCs were fused together forming a single tubular structure; this article discusses these three cadaveric specimens. The cadavers were aged 52, 36, and 12 years. After penile degloving, the dorsal groove on the penile shaft was absent. In two of the cadavers, multiple transverse cut-sections in the penile shaft showed that the two CCs were united into one single tubular structure that extended from the symphysis pubis to the glans penis. The cut section was kidney-shaped, with the corpus spongiosum lying under cover of the concave surface. No intercavernosal septum was identified. The transverse cut-section of the third cadaveric specimen revealed an incomplete fusion of the two CCs. An intercavernosal septum was present in its upper part, but absent in its lower part where the two CCs were fused together. In all three cadaveric specimens, the CCs showed a normal histologic pattern and the corpus spongiosum was morphologically normal. Based on biomechanical principles, we theorize that the blood volume occupying the two CCs would be greater, the penile rigidity stronger, and the penetration force more powerful in the two separate CCs as normal than in the two CCs if fused. However, further studies involving large number of cases are needed.

Adult↗

PubMedDate not supplied

Effect of straining on the lower esophageal sphincter: identification of the "straining-esophageal reflex" and its role in gastroesophageal competence mechanism.

The lower esophagus is intra-abdominal and exposed to intra-abdominal pressure (IAP) variations that may lead to gastroesophageal reflux (GER). We investigated the hypothesis that the lower esophageal sphincter (LES) undergoes phasic contraction on IAP increase, with a resulting inhibition of the stress GER. The study comprised 17 subjects (age 42.3 +/- 8.7 SD yr, 10 men, 7 women) who were scheduled for surgical repair of abdominal hernia. The patients had no swallowing problems. The electromyographic (EMG) activity of the LES and pressure within the LES were recorded at rest and during increased IAP (coughing, straining). The recording was repeated after LES anesthetization or saline infiltration. The LES EMG at rest showed regular slow waves (SWs), superimposed on or followed by random action potentials (APs). Coughing or straining induced increase of the SWs parameters and also of the APs; although the increase with straining was less than with coughing, the difference was insignificant. Coughing or straining increased the LES pressure significantly (p < .05, p < .05, respectively). Ten minutes after LES anesthetization, coughing or straining did not produce significant LES EMG or pressure changes, while saline infiltration of LES caused LES response similar to preinjection. Thus, coughing and straining effected an increase of the LES EMG activity and pressure, an action presumably mediated through a reflex that we call the "straining-esophageal reflex." This reflex seems to be evoked during increased intra-abdominal pressure and to effect LES contraction, thus, sharing with other factors in prevention of gastroesophageal reflux.

Abdomen↗

PubMedDate not supplied

Physioanatomic study of the diaphragmatic crura: the identification of autonomous "gastroesophageal sphincter".

It is claimed that the right diaphragmatic crus forms a loop sphincter around the lower esophagus. We investigated the hypothesis that the loop-shaped muscle does not belong to the diaphragmatic crura either anatomically or physiologically and is considered an autonomous muscle. Thirty-two cadaveric specimens (20 males, 12 females, 22 adults, mean age 36.2 +/- 11.8 years, 10 mature neonatal deaths) fixed in 10% formalin were studied anatomically. Electrophysiologic study was performed in 14 subjects (8 men, 6 women, mean age 36.6 +/- 8.2 years) scheduled for laparatomy. The loop muscle was stimulated by needle electrode, and response from the muscle and right crus was recorded by two electrodes. The test was repeated using an electrode into the left crus. Response of the loop muscle to individual stimulation of right and left crus was also registered. Muscle bundles formed a U-shaped loop around the lower esophagus, with the two limbs inserted into the 1st lumbar vertebra. An "esophago-sphincteric space" existed between the two limbs anterior to the esophagus. Three patterns of loop insertion were identified: classic, limb fusion, and limb crossing. The two crura were tendinous from their vertebral attachment, became fleshy, and fanned out proximally to merge with the fleshy diaphragm proper. Stimulation of loop muscle affected significant increase of its electric activity but had no effect on right or left crus. Crural stimulation produced significant increase of their electric activity and no effect on the loop muscle. Muscle fibers surrounding the lower esophagus formed a U-shaped loop. The loop arrangement seems to play significant role in competent mechanism of the gastroesophageal junction. Anatomic and electrophysiologic evidence suggest that the loop muscle is an autonomous muscle that surrounds the lower esophagus and is not derived from the diaphragmatic crura. We call this muscle "striated gastroesophageal sphincter".

Adult↗

PubMedDate not supplied

Interstitial cells of cajal in patients with constipation due to total colonic inertia.

Colonic wall contains interstitial cells of Cajal. In view of studies demonstrating that Cajal cells generate electric waves which are presumably responsible for colonic motor activity, and that these waves are absent in total colonic inertia, we investigated the hypothesis that colonic Cajal cells might be disordered in patients with total colonic inertia. The study comprised 28 patients (age 41.6 +/- 8.2 SD years, 19 women, 9 men) with total colonic inertia in whom total colectomy was performed. Colonic specimens obtained from normal segments of the excised colon of 24 cancer patients acted as controls. Specimens were subjected to c-kit immunohistochemistry. Controls for antisera specificity consisted of tissue incubated with normal rabbit serum that had been substituted for the primary antiserum. C-kit-positive branched Cajal-like cells were detected in the musculature of the normal colonic segments. They were distinguishable from the C-kit-negative smooth muscle cells and the C-kit-positive but unbranched mast cells. No Cajal cells were detected in colon of total colonic inertia patients. The absence of Cajal cells in patients with total colonic inertia can be assumed to explain the absence of electric waves and motile activity previously reported in these patients. Further studies are needed to investigate the cause of Cajal-cell absence.

Adult↗

PubMedDate not supplied

The "opening time" and "pelvic floor electromyographic lag time": two novel tools in the assessment of the anorectal evacuation time.

Rectal evacuation necessitates rectal contraction and pelvic floor muscles relaxation; it is not known which action precedes the other. We investigated the hypothesis that pelvic floor muscles relaxation precedes rectal contraction so that rectal contents find the anal canal already opened. Electromyographic activity of the external anal sphincter as well as anal and rectal pressures were recorded during rectal balloon distension and evacuation. Pelvic floor muscles electromyographic lag time (time from start of pelvic floor muscles relaxation to start of evacuation) and opening time (time from start of rectal contraction to start of evacuation) were measured. Rectal balloon distension in increments of 20 mL up to 100 mL effected progressive increase of both external anal sphincter electromyography and anal pressure. At 120 mL balloon distension up to 180 mL, external anal sphincter electromyography and anal pressure exhibited gradual decrease whereas rectal pressure showed no changes. At 200 to 220 mL rectal balloon distension, rectal pressure increased and anal pressure decreased, while external anal sphincter showed no electromyographic activity; rectal balloon was expelled. The opening time recorded a mean of 1.8 +/- 0.7 s and pelvic floor muscles electromyographic lag time of 2.2 +/- 0.9; the two recordings showed no significant difference (p > .05). These, two diagnostic tools in anorectal investigations are presented: the opening time and pelvic floor muscles electromyographic lag time. Pelvic floor muscles relaxation preceded rectal contraction. As there is no significant difference between opening time and pelvic floor muscles electromyographic lag time, it appears easier to apply the latter as it is simple, objective, and noninvasive.

Adult↗

PubMedDate not supplied

Effect of external anal sphincter contraction on the ischiocavernosus muscle and its suggested role in the sexual act.

Whereas the bulbocavernosus muscle shares its contractile activity with the external anal sphincter (EAS), the response of the ischiocavernosus muscle (ICM) to EAS contraction could not be traced in the literature. We investigated the hypothesis that the ICM contracts reflexly upon EAS contraction. The response of the ICM to EAS squeeze and stimulation was recorded in 21 healthy volunteers (13 men, 8 women, age 36.8 +/- 10.7 [SD] years). An electromyographic (EMG) needle (stimulating) electrode was introduced into the EAS and another (recording) one was inserted into the ICM. The test was repeated after individual anesthetization of the EAS and ICM and after muscle infiltration with normal saline instead of lidocaine. EAS electrostimulation (10 stimuli, 200 micros duration, 0.2 Hz frequency, 0-100 mA intensity) produced an increase of ICM EMG activity to a mean of 267.8 +/- 42.7 microV, whereas anal squeeze effected an increase to a mean of 224.5 +/- 45.3 microV. The ICM did not respond to stimulation of the EAS after individual anesthetization of the ICM and EAS, but it did after saline infiltration. The results were reproducible. ICM contracted upon EAS contraction. This effect seems to be mediated through a reflex that we call "anocavernosal excitatory reflex." The ICM lever action is suggested to share in the erectile mechanism by elevating the penile shaft to above the horizontal level. The reflex may prove of diagnostic significance in sexual function disorders, a point that needs further study.

Adult↗

PubMedDate not supplied

Colosigmoid junction: a study of its functional activity with identification of a physiologic sphincter and involvement in reflex actions.

The colosigmoid junction (CSJ) marks the termination of the descending colon (DC) and the beginning of the sigmoid colon (SC); it is a fixed area in the retroperitoneum. At this site where two functionally different areas meet, we hypothesized the presence at the CSJ of a physiologic sphincter that regulates the passage of gut contents from the DC to the SC. This hypothesis was investigated for this communication. Eight subjects (mean age 36.6 +/- 4.7 SD years, 6 women) were studied during surgical repair of incisional hernia or laparotomy. The pressure responses of the CSJ to individual distension of the DC and SC were recorded. A balloon-ended tube was introduced per annum to lie in the DC or SC, and the pressure in the DC, CSJ, and SC was measured by saline-perfused catheters. To study whether the CSJ response to individual DC or SC distension was a direct or reflex action, the test was repeated in six of eight patients after separate anesthetization of the DC, CSJ, and SC. The CSJ had a higher pressure than that of the DC or SC; the high-pressure zone measured a mean of 2.1 +/- 0.9 cm. High-volume DC distension effected a significant DC pressure rise (p <.001) and a CSJ pressure decline (p <.05), which lasted a mean of 7.2 +/- 1.2 s. In contrast, the CSJ responded to big volume SC distension by significant pressure elevation (p <.001) which was also momentary. Small volume distension of the DC or SC effected no significant CSJ pressure response (p >.05). The CSJ pressure did not respond to distension of the anesthetized DC or SC. Likewise, the anesthetized CSJ did not react to DC or SC distension. When the test was repeated using saline instead of xylocaine, the CSJ pressure response was similar to that without saline injection. The CSJ is a high pressure zone with a measurable length. It reacts to DC or SC balloon distension by dilatation or narrowing, respectively. These findings presumably denote the existence of a "physiologic sphincter" at the CSJ, which appears to regulate the passage of colonic contents to the SC. We postulate that the CSJ pressure response to DC or SC distension is reflex and mediated through the "colosigmoid reflexes." The role of the colosigmoid sphincter and reflexes in colonic motility disorders remains to be investigated.

Adult↗

PubMedDate not supplied

Electrophysiologic identification of the location of the colonic pacemakers in humans: further study.

We recently defined the sites of four colonic pacemakers that appear to generate the electric waves assumed to be responsible for the colonic motility. We hypothesized that a dysfunction of one or more of these pacemakers might interfere with the generation of electric waves and the colonic motility. This hypothesis was investigated in the current communication. The tests were performed during the repair of huge incisional hernia of 8 subjects (5 F, 3 M; mean age 42.8 +/- 3.3 SD years). Two electrodes were applied to each of the terminal ileum (TI), cecum (C), and ascending (AC), transverse (TC), descending (DC), and sigmoid (SC) colon. The electric activity of the TI and the various colonic segments was recorded using surface silver-silver chloride electrodes applied to the colon. The site of change of the wave variables between the TI and the C and between the different other colonic segments was determined by changing the position of the electrodes placed over the segments to be examined. Presumably, the sites where the wave variables changed represent the potential location of the pacemakers. We anesthetized these sites individually by injection of 2% Xylocaine, and then recorded the electric activity after 20 min in all the subjects and after 2 h in only 5 subjects. Electric waves in the form of pacesetter and action potentials were recorded from the TI and the colon. The sites of potential pacemakers could be defined at the ileocecal and cecocolonic junctions, at the mid third of the TC, and at the colosigmoid junction. Anesthetization of the cecal pole resulted in disappearance of the cecal electric waves, with persistence of the waves from the other colon segments. Anesthetization of the cecocolonic junction eliminated the electric waves of the AC and the right half of the TC, while the waves in the rest of the colon persisted. The remaining two pacemaker sites produced similar results when anesthetized. The electric waves reappeared after the anesthetic effect had waned. Thus, the colon possesses at least four pacemakers that appear to mediate the colonic motor activity. Individual pacemaker block by anesthetization effected disappearance of electric waves in the relative colonic segment, which reappeared after waning of the anesthetic effect. The disappearance of these waves upon pacemaker anesthetization supports a relationship between the pacemakers at the anesthetized site and the electric waves. The electric waves seem to be generated by these pacemakers. We suggest that colonic inertia, segmental or total, results from the dysfunction of one or more pacemakers, and that an artificial pacemaker could be applied for the treatment of such conditions. These suggestions need to be further studied.

Action Potentials↗

PubMedDate not supplied

Study of the effect of jejuno-ileal distension on the motor activity of the stomach with evidence of "entero-gastric inhibitory reflex".

BACKGROUND/AIMS: In chronic constipation due to delayed colonic transit, stasis of the ileal contents with resulting ileal distension may occur. The current study investigated the effect of ileal and jejunal distension on the gastric motility, aiming at elucidating the possible existence of a relationship and its role in the flow through the gut. METHODOLOGY: The response of the gastric pressure to ileal and jejunal balloon distension in increments of 2 mL of saline was recorded in 12 mongrel dogs. The test was repeated after separate local anesthetization of the ileum, jejunum and stomach. RESULTS: 2- and 4-mL ileal balloon distension produced no significant gastric pressure response, while 6- and up to 10-mL distension effected decrease of the antral and corporeal pressures (p < 0.05, p < 0.05, respectively). Jejunal distension produced a gastric pressure decline (p < 0.05) with 4 and up to 10 mL of saline. The gastric pressure decrease did not show significant changes with the various distending volumes. It was maintained as long as ileal or jejunal distension was continued. Distension of the anesthetized ileum or jejunum caused no gastric pressure changes, nor did ileal or jejunal distension produce pressure changes in the anesthetized stomach. CONCLUSIONS: The gastric pressure decline and presumably hypotonia upon ileal or jejunal distension with big volumes postulate a reflex relationship which we call "entero-gastric inhibitory reflex". The small intestine is suggested to slow down gastric emptying through this reflex. A balance is thus created between chyme delivery from the stomach and chyme processing by the small intestine. Reflex derangement in neurogenic and myogenic diseases may result in gastrointestinal disorders, a point that needs to be investigated.

Animals↗

PubMedDate not supplied

Treatment of irritable bowel syndrome with colonic pacing: evaluation of pacing parameters required for correction of the "tachyarrhythmia" of the IBS.

BACKGROUND/AIMS: A recent study of the electromyographic (EMG) activity of irritable bowel syndrome (IBS) has shown that the frequency, amplitude and conduction velocity of the slow waves (SWs) of the sigmoid colon (SC) were significantly higher in IBS patients than in the healthy volunteers. The SW rhythm was irregular. A "tachyarrhythmic pattern" was characteristic of the IBS. The SC pressure in the IBS was also significantly higher than that of the healthy controls. We suggested that the cause of IBS is related to an aberrant focus in one or more of the colonic pacemakers which possibly triggers abnormal impulses to the colon. We hypothesized that stimulation of the pacemaker which delivers electric waves to the SC, may correct the abnormal electric waves and eliminate the IBS symptoms. In this communication we tried to define the adequate pacing parameters necessary for normalization of the tachyarrhythmic pattern of the electric waves in IBS. METHODOLOGY: Nineteen subjects with IBS were divided into a study group (age 48.6+/-9.8 years; 7 women, 4 men) and a control group (age 47.6+/-9.2 years; 5 women, 3 men). The study also included 8 healthy volunteers (47.9+/-9.7 years; 5 women). Three 28-gauge cardiac pacing electrodes were used: one for pacing applied to the pacemaker at the colosigmoid junction (CSJ) and 2 for recording applied to the SC mucosa. In the study group, the CSJ electrode was stimulated using an electrical stimulator which delivered a constant current. The optimal pacing parameters had been determined after repeated trials with different variables. In the control group, recording was done without pacemaker activation. The SC pressure was measured by a 10-F saline-perfused tube. RESULTS: In the healthy volunteers, the basal SWs were regular and followed or superimposed by action potentials (APs). Pacing produced a significant increase in the SW variables and SC pressure; the latency was 20.3+/-3.6 s. The study and the control group exhibited a basal tachyarrhythmic pattern and a significantly higher SC pressure than the healthy volunteers. Pacing of the study group effected lowering of the SW variables and SC pressure which did not show a significant difference against those of the healthy volunteers at rest. The optimal pacing parameters comprised an amplitude of 6 mA, a pulse width of 150 ms and a 25% higher frequency than that of the already recorded basal colonic waves. The control group showed no change in the tachyarrhythmic pattern. CONCLUSIONS: CS pacing parameters were identified and succeeded in normalizing the tachyarrhythmic pattern of the IBS. We suggest that this method be used for the treatment of patients with IBS when other measures have failed to cure the condition.

Adult↗