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Biomedical subjects

W M Sun

Publications and source records attributed to W M Sun.

At least 109 records · Page 6Linked to original sources
PubMed1994

In vitro exposure of tracheobronchial epithelial cells and of tracheal explants to ozone.

An in vitro system for exposing respiratory epithelial cells or explant tissues to ozone has been developed and characterized. This system is designed to generate and monitor consistent, reproducible levels of ozone, over a range of concentrations, in a humidified atmosphere, and to allow an exposure time of 24 h or longer. Based on chemical analysis, highly reproducible concentrations of ozone are delivered throughout the chamber, with a coefficient of variation of < 5% between five replicate vials exposed to 0.5 ppm of ozone for 50 min. The viability of cultured human tracheobronchial epithelial cells, as measured by the ability to oxidize a vital dye, and of rat tracheal epithelium, as measured by total numbers of necrotic cells in tracheal explants, after ozone exposure was examined in this system. Responses of cultured cells to ozone exposure as measured by bioassay were consistent with the observed low level of variability of ozone concentration between replicate incubation dishes or vials. Responses of cultured cells to ozone were proportional to duration of exposure and inversely proportional to the volume of medium covering the cells. We conclude that this newly developed in vitro exposure system will allow relatively simple and convenient exposure of cultured cells or organs to ozone or other gaseous agents under highly controlled and reproducible conditions.

Air Pollution↗
PubMed1994

Anorectal function after restorative proctocolectomy and low anterior resection with coloanal anastomosis.

Anorectal manometry and electromyography were studied in 17 patients before and after restorative proctocolectomy with stapled pouch-anal anastomosis, in ten patients before and after low anterior resection with stapled coloanal anastomosis, and in 35 normal controls. More than 80 per cent of patients in both groups developed abnormal oscillation of anal pressure after operation (amplitude 15-60 (median 25) cmH2O, frequency 4-10 (median 8) per min) and showed no anal relaxation in response to intermittent neorectal distension. All patients lost discriminative rectal sensation and none could perceive a normal desire to defaecate. Patients with postoperative soiling had a greater amplitude of anal pressure oscillation and lower minimum basal pressure, although those who underwent coloanal anastomosis had a greater risk of incontinence because of large asynchronous oscillations in neorectal pressure. The common pathophysiological features after restorative proctocolectomy and coloanal anastomosis probably relate to damage to the autonomic and enteric nerve supplies. The presence of an unstable internal anal sphincter may be an important cause of postoperative nocturnal incontinence.

Adult↗
PubMed1994

Modulation of pumping function of gastric body and antropyloric contractions.

Gastric and antropyloric phasic contractions control transpyloric pulsatile flow, the major mechanism of gastric emptying. Both the occurrence and patterning of phasic gastric contractions are highly modulated by intestinal feedback mechanisms, with resultant variation in gastric emptying. The observed patterns of these contractions can only be plausibly explained by the action of neural influences on gastric motility. These influences derive from several mechanisms driven by intestinal feedback, central nervous system controls, and higher centers, with transmission of signals via intrinsic enteric pathways and extrinsic nerves. It is suggested that the occurrence and patterning of gastric phasic contractions depend on the spatial specificity and local modulation of the intensity of neural stimulation of gastric muscle. The resultant strength of contraction determines the occurrence and timing of lumen occlusion relative to adjacent regions. The timing of lumen occlusion in adjacent regions may be the major determinant of mechanical outcome.

Animals↗
PubMed1994

Effects of duodenal distention on fasting and postprandial antropyloroduodenal motility in humans.

BACKGROUND/AIMS: Mechanoreceptors in the proximal small intestine may play an important role in the regulation of gastric emptying. Balloon distention of the duodenum causes fundic relaxation. The purpose of the present study was to determine the effect of stimulation of duodenal mechanoreceptors on both fasting and postprandial antropyloroduodenal motility in humans. METHODS: Antropyloroduodenal pressures were recorded in 12 healthy volunteers with a sleeve-sidehole assembly, incorporating two balloons 5 and 20 cm distal to the pylorus. Duplicate proximal and distal duodenal balloon distensions with 10, 20, and 30 mL of air for 2.5 minutes were performed separately and in randomized order both during fasting and after a meal. RESULTS: During fasting, proximal and distal distention at all volumes increased the number of isolated pyloric pressure waves (P < 0.05) and basal pyloric pressure (P < 0.05), and the response to proximal distention was greater (P < 0.05). Postprandially, proximal and distal distention increased basal pyloric pressure (P < 0.05) with a greater response to proximal distention (P < 0.05), but had no effect on isolated pyloric pressure waves. Both during fasting and postprandially, there were more synchronous and less antegrade antral waves during distention (P < 0.05). The number of duodenal pressure waves increased during proximal (P < 0.05) but not distal distention. CONCLUSIONS: Stimulation of duodenal mechanoreceptors by balloon distention has significant and region-dependent effects on antropyloroduodenal motility that vary between fasting and postprandial states.

Adult↗
PubMed1994

Ozone, NO, and NO2: oxidant air pollutants and more.

This article reviews the acute and chronic toxicity of the three oxidant air pollutants ozone, nitric oxide (NO), and nitrogen dioxide (NO2). The toxicity of binary mixtures of NO2 with other inhaled agents is also discussed. Newer studies are emphasized, especially those published in the last 5 years or still in press. Very recent data from our laboratory that suggest a new cellular mechanism of importance in lung injury in animals exposed to mixtures of ozone and NO2 that may have general relevance with regard to the effects of oxidant air pollutants on the lung are also presented.

Air Pollutants↗
PubMed1994

Stereospecific effects of intraduodenal tryptophan on pyloric and duodenal motility in humans.

BACKGROUND: L-Tryptophan delays gastric emptying in animals to a greater extent than D-tryptophan, but none of the possible motor mechanisms responsible for this stereospecific effect have been evaluated. METHODS: In 11 healthy volunteers antropyloroduodenal pressures were recorded in the fasted state with a sleeve/sidehole manometric assembly during 20-min intraduodenal infusions (2 ml.min-1) of isotonic L- and D-tryptophan (50 mM, pH 5.7) and normal saline (pH 5.5), given in randomized order. RESULTS: Intraduodenal L-tryptophan increased basal pyloric pressure (p < 0.05), whereas D-tryptophan had no effect. In contrast, L- and D-tryptophan both stimulated (p < 0.05) localized phasic pyloric pressure waves, and there was no significant difference in the responses. The number of duodenal pressure waves was greater during infusion of L-tryptophan than during D-tryptophan (p < 0.05). CONCLUSION: We conclude that intraduodenal tryptophan has stereospecific effects on pyloric and duodenal motility. Although the precise contribution of these differential effects to gastric emptying remains to be clarified, they may be partially responsible for the differences in gastric emptying of D-tryptophan and L-tryptophan.

Adult↗
PubMed1994

[Modelling the general relative risk models in case-control studies of primary hepatocellular carcinoma].

This paper was to analyse the effect of risk factors of primary hepatocellular carcinoma (PHC). The analysis was carried on using the family of relative risk functions to asses which scale could better explain the risk structure underlying the data. The results showed that the risk factors of PHC in south area of China were HBV infection, family history of PHC, drank pond-ditch water, while the risk factors of PHC in north area were HBV infection, family history of PHC, history of hepatitis, drank alcohol. The results suggested that the combined effect of risk factors was near to multiplicative. Being able to discriminate between risk structures has important implications on causal interpretation and public health practice.

Carcinoma, Hepatocellular↗
PubMed1994

[Interaction among the relative risk factors of primary liver cancer in a case-control study].

This paper evaluates the combined effect of HBsAg, drinking water and aflatoxin B1 (AFB1) on the primary hepatocellular carcinoma (PHC) in a case-control study which was carried out in Fusui, Guangxi. We used relative risk model (from subadditive to supermultiplicative) to fit the relationship. The results showed that the combined effect of HBsAg infection and drinking pond-ditch water is nearly multiplicative, and the combined effect of HBsAg infection and AFB1 intake as well as drinking pond-ditch water and AFB1 intake were nearly additive.

Aflatoxin B1↗
PubMed1994

Specificity and directionality of thiol effects on sinusoidal glutathione transport in rat liver.

In rats the sinusoidal glutathione (GSH) carrier transports GSH bidirectionally, and its activity is influenced by the thiol-disulfide status; the Vmax of sinusoidal GSH efflux was increased by dithiothreitol (DTT) and decreased by cystine. In the present work we examined the specificity and directionality of the thiol effect. Using in situ perfused livers, we found that 1 mM DTT and other dithiols, including 1,2-ethanedithiol, 1,3-propanedithiol, and 1,4-butanedithiol, stimulated sinusoidal GSH efflux by 200-500% but dihydrothioctic acid, which is negatively charged, had no effect. Uncharged or positively charged monothiols (2 mM), such as dimercaprol, monothioglycerol, 2-mercaptoethanol, 3-mercapto-2-butanol, 1-mercapto-2-propanol, and cysteamine, also exerted a stimulatory effect on sinusoidal GSH efflux. In contrast, monothiols containing a negatively charged substituent, such as penicillamine, captopril, N-acetylcysteine, mercaptopropionylglycine, mercaptoethanesulfonic acid, mercaptoacetic acid, and mercaptopropionic acid, had no effect. The thiol moiety was essential for activity, inasmuch as ethanol, propanol, propanediol, and glycerol had no effect on sinusoidal GSH efflux. The effect of DTT or cystine pretreatment (2 mM or 0.5 mM, respectively, for 30 min) on GSH uptake was then examined using cultured rat hepatocytes. The linear rate of [35S]GSH uptake and the concentration dependence were measured after cells were pretreated with acivicin (0.5 mM, for 15 min) and buthionine sulfoximine (10 mM, 15 min), to prevent breakdown and resynthesis of GSH from precursors, respectively. Uptake buffer also contained 20 mM alpha-(methylamino)isobutyric acid and 20 mM threonine (inhibitors of amino acid transport systems A and ASC, respectively), to prevent uptake of cysteine. Pretreatment with DTT decreased the Vmax of GSH uptake by approximately 50% (control Vmax value, 24 nmol/10(6) cells/30 min), whereas the Km remained unaffected (approximately 8 mM). Cystine pretreatment had no influence on GSH uptake but inhibited efflux. In conclusion, the presence of at least one thiol group and the absence of negative charge are required to stimulate sinusoidal GSH efflux. The direction of GSH transport is modulated by the thiol-disulfide status, so that thiol reduction changes the GSH transporter from a bidirectional GSH transporter into a preferentially unidirectional (outward) transporter by inhibiting uptake while stimulating efflux and thiol oxidation favors inward transport by inhibiting only efflux.

Analysis of Variance↗
PubMed1993

Effect of food and anti-cholinergic drugs on the pattern of rectosigmoid contractions.

The colonic response to a meal is often used to test the effect of drugs on colonic motility, but this test is hindered by its inconsistency. This study has used multiple manometric sensors situated in the rectosigmoid region to investigate whether recording of the site and type of contraction offers a clear discrimination of the colonic response to a meal and the effect of drugs. Two studies were carried out on 16 healthy volunteers. Before the meal, rectosigmoid motility consisted mainly of isolated contractions occurring in a single manometric channel. The motility index increased in every subject after the meal (p < 0.05), but this increase entirely consisted of a massive increase in contractions occurring simultaneously in three or more manometric channels (multiple channel contractions), the number increasing from 9 per hour preprandially to 57 per hour (p < 0.01). There was a concomitant decrease in the number of the single channel contractions from 65 to 56 per hour. In a second study an infusion of an antispasmodic drug, mebeverine hydrochloride, into the sigmoid colon of healthy volunteers stopped the postprandial increase in the multiple channel contractions and prevented the significant rise in the motility index. The decrease in single channel contractions was unaffected. These results show that the colonic response to a meal consists of a change in the pattern of rectosigmoid contractions and suggest that multiple channel contractions may be a more sensitive indicator of the effect of a meal on the rectosigmoid colon than the motility index.

Adult↗
PubMed1992

Haemorrhoids are associated not with hypertrophy of the internal anal sphincter, but with hypertension of the anal cushions.

A combined manometric and ultrasonographic study of the internal anal sphincter was carried out in 20 patients with haemorrhoids and 20 age-matched normal controls. Mean(s.e.m.) basal anal pressure was significantly higher in patients than in controls, 62(4) versus 45(6) cmH2O (P less than 0.05), although there were no significant differences in mean maximum basal and squeeze pressures. During rectal distension 90 per cent of patients showed no reduction in anal pressure in the outermost anal channel, although the internal sphincter electromyogram was suppressed and the external sphincter electromyogram did not necessarily increase above baseline. The mean(s.e.m.) maximum residual pressure was significantly higher in patients, 70(6) versus 45(6) cmH2O (P less than 0.05). Direct pressure measurement in anal cushions exhibited abnormally high median pressure in patients compared with controls, 35 versus 10 cmH2O (P less than 0.001). Pressures recorded during coughing and straining were also significantly higher in patients than in controls (P less than 0.001). Ultrasonographic study of the anal canal revealed a clear image of the internal sphincter, the thickness of which could easily be measured. The mean(s.e.m.) thickness of the sphincter was not significantly different, 2.3(0.2) versus 2.1(0.1) mm, between patients with haemorrhoids and controls (P = 0.18). The absence of any significant differences in the internal sphincter thickness between normal subjects and patients with haemorrhoids suggests that the high anal pressure in patients with haemorrhoids is of vascular origin.

Adult↗
PubMed1992

Anorectal function in patients with complete supraconal spinal cord lesions.

Anorectal manometry and sphincter electromyography were performed in 23 patients with complete supraconal traumatic spinal injuries and 30 age and sex matched control subjects. Basal pressures in the spinal group were similar to those in normal subjects but conscious control of sphincter activity was abolished in all spinal patients. Discriminant rectal sensation was also abolished during rectal distension, but 40% of patients experienced a dull pelvic ache at maximum levels of distension. Phasic rectal contraction and anal relaxation were present but exaggerated and induced at lower distending volumes than in normal subjects. The configuration of the rectal pressure/volume relationship was linear in patients compared with a reversed 'S' shape in normal subjects. The external anal sphincter response to rectal distension was noticeably attenuated, reinforcing the view that this spinal reflex is heavily modulated by supraspinal centres under normal circumstances. The external anal sphincter response to increases in abdominal pressure was also attenuated, and the anal pressures were strongly correlated with the level of the lesion and the abdominal pressure the patient could generate. No spinal patient showed a decrease in external anal sphincter activity during straining 'as if to defecate.' The exaggerated anorectal smooth muscle responses to rectal distension and the attenuated external sphincter response explain why patients with complete supraconal spinal lesions experience uncontrollable reflex defecation, while the persistance of external and sphincter contraction and the absence of any external anal sphincter relaxation during straining 'as if to defecate' might explain the difficulty that these patients have in consciously expelling rectal contents.

Adolescent↗
PubMed1992

Utility of a combined test of anorectal manometry, electromyography, and sensation in determining the mechanism of 'idiopathic' faecal incontinence.

Combined tests of anorectal manometry, sphincter electromyography and rectal sensation were carried out in 302 patients with faecal incontinence (235 women, 67 men). The results obtained were compared with 65 normal subjects (35 women, 30 men). A mechanism for incontinence was identified in all and the majority of patients had more than one abnormality. Two hundred and seventy eight patients (92%) had a weak external anal sphincter, 185 of these (67%, mostly women) also showed abnormal perineal descent, and 14 women showed clinical evidence of sphincter damage as a result of obstetric trauma. Ten per cent of patients with impaired external anal sphincter contraction showed associated evidence of spinal disease (impaired rectal sensation plus attenuated or enhanced reflex external anal sphincter activity). Unlike the other groups, the 'spinal' group contained equal numbers of men and women. Ninety seven patients (32%) had evidence of a weak internal anal sphincter. The external sphincter was also very weak and 92% of these patients also had perineal descent. Eighty two patients (27%) showed an unstable internal sphincter, characterised by prolonged 'spontaneous' anal relaxation under resting conditions and an abnormal reduction in anal pressure after conscious contraction of the sphincter or an increase in intraabdominal pressure. One hundred and forty two patients (47%) had a hypersensitive rectum associated with enhanced anorectal responses to rectal distension. All these patients had an abnormally weak external sphincter, suggesting that the hypersensitive or 'irritable' rectum should not be regarded as a cause of faecal incontinence unless accompanied by external sphincter weakness. Twenty four patients (8%) showed a normal basal and squeeze pressures and impaired rectal sensation; six showed giant rectal contractions during rectal distension. The results show that idiopathic faecal incontinence is not caused by a single abnormality, and it is suggested that combined anorectal manometry, electromyography, and sensory testing is a useful technique to identify the causes of faecal incontinence and provide a basis for appropriate treatment.

Adolescent↗
PubMed1991

Reflex anal dilatation: effect of parting the buttocks on anal function in normal subjects and patients with anorectal and spinal disease.

Anal dilatation in response to gentle parting of the buttocks has been advocated as a sign of sexual abuse in children, but nothing is known of the physiology of this response or its existence in normal subjects, in patients with spinal disease, and in patients with a weak sphincter and whether it can be elicited after training. To answer these questions we investigated the effect of parting the buttocks on anal function. Combined anal manometry and electromyography was conducted in six normal subjects (five men, one woman, aged 19-53 years), in 18 patients with faecal incontinence (three men, 15 women, aged 30-80 years), and in seven paraplegic patients (six men, one woman, aged 25-36 years), in four of whom the posterior sacral roots had been cut. Parting the buttocks in normal subjects reduced the pressure in the anal canal from 102 (20) to 14 (3) cm H2O (mean (SEM), p less than 0.00001), but did not cause the anus to gape. This drop in pressure was associated with increased electrical activity in the external anal sphincter. Normal subjects could consciously relax the external anal sphincter and reduce the anal pressure but not so as to result in anal gaping during traction on the buttocks, even after anal dilatation. Stimulation of the anal lining by moving a probe in and out of the anal canal increased the activity of the external anal sphincter, raising anal pressures. Paraplegic patients who had lost conscious control of their external sphincters showed anal gaping when the buttocks were parted. A similar phenomenon was seen in patients with faecal incontinence who had weakness of the external anal sphincter, while incontinent patients with weakness of both sphincters showed anal gaping even at rest. Inasmuch as the results of our study can be applied to children, the data suggest that reflex anal dilatation should only be used to support a diagnosis of sexual abuse if sphincter function is otherwise normal and there is no evidence of cerebrospinal disease. Although our results do not support the notion that children could become so conditioned to repeated digital or penile penetration of the anus that they can cause the anus to gape when the buttocks are parted, neither do they exclude it.

Adult↗
PubMed1990

Control of defecation in patients with spinal injuries by stimulation of sacral anterior nerve roots.

OBJECTIVE: To observe the effects of stimulation of the sacral anterior roots on anorectal and low colonic pressures and to programme implanted stimulators to produce defecation. DESIGN: Prospective study of 12 consecutive patients. SETTING: Spinal injuries unit and university gastrointestinal physiology department. PATIENTS: 12 Patients with complete supraconal spinal cord lesions. Their injuries had been sustained at least two years before the study. INTERVENTIONS: A Brindley-Finetech intradural sacral anterior root stimulator was implanted in all patients. Three months postoperatively the stimulator settings were adjusted after measurement of simultaneous anorectal and low colonic pressures. MAIN OUTCOME MEASURES: Full defecation. RESULTS: Six patients achieved complete rectal evacuation of faeces using the implant and subsequently did not require manual help for defecation. For all but one of the patients the total time taken to complete defecation was reduced, and all were free from constipation, the most prevalent gastrointestinal symptom in patients with spinal injuries. CONCLUSIONS: Sacral anterior root stimulators can be programmed to achieve complete unassisted defecation and can considerably improve the quality of life of patients with spinal injuries.

Adult↗
PubMed1990

Hypertensive anal cushions as a cause of the high anal canal pressures in patients with haemorrhoids.

Anorectal manometry and electrophysiology studies were conducted in 25 men with non-prolapsing haemorrhoids, ten men with prolapsing haemorrhoids, and 20 age-matched normal men. Mean(s.e.m.) minimum basal pressures were significantly higher in patients with non-prolapsing haemorrhoids than in normals (61(5) versus 43(7) cmH2O; P less than 0.05) or patients with prolapsing haemorrhoids (55(4) cmH2O; P less than 0.05). There were no significant differences in maximum basal pressures and maximum squeeze pressures. During rectal distension, all normal subjects showed relaxation in all anal channels. However, 92 per cent of patients with non-prolapsing haemorrhoids and 40 per cent of patients with prolapsing haemorrhoids showed no relaxation in the outer anal channels, even when relaxation occurred in the inner anal channels; internal sphincter electrical slow waves were suppressed and the integrated electrical activity of the external sphincter had returned to predistension values. Maximum residual anal pressures during balloon distension were significantly higher in patients with non-prolapsing haemorrhoids than normals (75(7) versus 45(7) cmH2O; P less than 0.01), or patients with prolapsing haemorrhoids (53(3) cmH2O; P less than 0.05). When subjects increased intra-abdominal pressure rectal pressure was significantly higher in patients with non-prolapsing haemorrhoids than in normal subjects (157(10) versus 105(15) cmH2O; P less than 0.05), but not in patients with prolapsing haemorrhoids (126(14) cmH2O). Resting anal cushion pressures in patients with non-prolapsing or prolapsing haemorrhoids were much higher than normal capillary or venous pressure and significantly higher than those recorded in normals (median 35, 35 versus 10 cmH2O; P less than 0.0001). Pressures recorded during coughing (60, 60 versus 30 cmH2O) and straining (78, 80 versus 55 cmH2O) were also significantly higher (P less than 0.0001) in patients than in normals. Pressures after straining were higher than those recorded before (38 versus 29 cmH2O; P less than 0.05) in 60 per cent of patients but no normal subjects and took 18-36 s to return to baseline. This study suggests that the abnormally high pressures in the anal canal in patients with haemorrhoids may be related to an increased vascular pressure in the anal cushions.

Action Potentials↗