General theory of frictional heating with application to rubber friction.

The energy dissipation in the contact regions between solids in sliding contact can result in high local temperatures which may strongly effect friction and wear. This is the case for rubber sliding on road surfaces at speeds above 1 mm s(-1). We derive equations which describe the frictional heating for solids with arbitrary thermal properties. The theory is applied to rubber friction on road surfaces and we take into account that the frictional energy is partly produced inside the rubber due to the internal friction of rubber and in a thin (nanometer) interfacial layer at the rubber-road contact region. The heat transfer between the rubber and the road surface is described by a heat transfer coefficient which depends on the sliding speed. Numerical results are presented and compared to experimental data. We find that frictional heating results in a kinetic friction force which depends on the orientation of the sliding block, thus violating one of the two basic Leonardo da Vinci 'laws' of friction.

Clinical features, diagnostic and therapeutic approaches to haematogenous vertebral osteomyelitis.

This article review the clinical features and the diagnostic approach to haematogenous vertebral osteomyelitis in order to optimise treatment strategies and follow-up assessment. Haematogenous spread is considered to be the most important route: the lumbar spine is the most common site of involvement for pyogenic infection and the thoracic spine for tuberculosis infection. The risk factors for developing haematogenous vertebral osteomyelitis are different among old people, adults and children: the literature reports that the incidence seems to be increasing in older patients. The source of infection in the elderly has been related to the use of intravenous access devices and the asymptomatic urinary infections. In young patients the increase has been correlated with the growing number of intravenous drug abusers, with endocarditis and with immigrants from areas where tuberculosis is still endemic. The onset of symptoms is typically insidious with neck or back pain often underestimated by the patient. Fever is present in 10-45% of patients. Spinal infections may cause severe neurological compromise in few cases, but mild neurological deficit, limited to one or two nerve roots, was detected in 28-35% of patients. The diagnosis of haematogenous vertebral osteomyelitis may be very difficult, as the symptoms can be sometimes not specific, vague or almost absent. The usual delay in diagnosis has been reported to be two to four months, despite the use of imaging techniques: in the early diagnosis of vertebral ostemyelitis is important the role of bone scintigraphy. The general principles for the management of spine infections are non operative, consisting of external immobilization and intravenous antibiotics, followed by oral antibiotics. Indications for surgery should be given in case of absence of clinical improvement after 2-3 weeks of intravenous antibiotics, persistent back pain and systemic effects of chronic infection and with presence or progression of neurological deficit in elderly or in cervical infection. Chronic ostemyelitis may require surgery in case of a development of biomechanical instability and/or a vertebral collapse with progressive deformity.

Management of severe ulcerative colitis with the help of high resolution ultrasonography.

OBJECTIVES: The prognosis of attacks of ulcerative colitis is clearly linked to the extent and activity of the disease. The aim of this study was to investigate the value of high resolution ultrasonography in assessing both the extent and activity of severe ulcerative colitis and its response to medical treatment. METHODS: Fifty-seven consecutive patients affected by a severe (32 patients) or moderately severe (25 patients) attack of ulcerative colitis underwent ultrasonographic examination. The ultrasonographic extent of the disease was evaluated in 32 patients by comparing ultrasonography and scintigraphy. RESULTS: Compared with scintigraphy, sensitivity, specificity, and overall accuracy of ultrasonographic extent were 89%, 100%, and 91%, respectively. These results were also confirmed in a subgroup of patients submitted to surgery, comparing ultrasonographic and scintigraphic data versus specimens. Using the ultrasonographic score of activity, it was possible to discriminate severe and moderately severe attacks with a specificity, sensitivity, and diagnostic accuracy of 96%, 90.3%, and 92.9% respectively. A close correlation was also found between ultrasonographic and scintigraphic activity (r = 0.78; p < 0.001). After 10 days of intensive treatment, the ultrasonographic activity significantly decreased in severe and moderate groups (p < 0.001) and in both subgroups of nonoperated patients (p < 0.001) but not in operated patients (p = NS). CONCLUSIONS: High resolution ultrasonography can be useful in assessing both extent and activity of severe ulcerative colitis, in monitoring the patient's condition, and in objectively evaluating the response to medical therapy.

111In-octreotide scintigraphy in endocrine tumors. Preliminary data.

A large number of endocrine tumors express somatostatin receptors, and the use of radiolabeled somatostatin analogs has been recently introduced for their localization. Using in vivo scintigraphy with 111In-pentetreotide, primary tumor localizations were demonstrated in 3/3 carcinoids (2 intestinal carcinoids and 1 lung ACTH-secreting carcinoid; in 2 patients liver metastases larger than 1 cm were visualized), in 1/1 GH-secreting pituitary macroadenoma, and in 1/1 thyroid localization of MTC. Bone and/or lymph node metastases were imaged in 2/4 patients previously treated for MTC, with persistently high CT and CEA levels; in the other 2 patients the other scintigraphic techniques were also negative. Octreotide scintigraphy was negative in 2/2 insulinomas and in 2/2 ACT-producing pituitary adenomas. In 2 patients with carcinoid syndrome and 1 patient with Cushing syndrome due to ectopic ACTH, octreotide therapy induced a significant decrease in tumoral markers. Our preliminary data are in agreement with the results of larger series reported in literature: octreotide scintigraphy is a useful noninvasive tool to detect endocrine tumors expressing somatostatin receptors, particularly for carcinoids. It is of great use in the differential diagnosis of Cushing syndrome due to ectopic ACTH. Moreover, 111In-pentetreotide scintigraphy may be useful in selecting patients who may benefit from octreotide therapy to control hormonal hypersecretion effects.

Diagnostic protocol in prosthetic loosening.

The authors report the results they obtained in 35 cases studied based on a protocol to identify prosthetic loosening and to preoperatively establish its possible septic etiology. After clinical and radiographic assessment, the protocol called for a total body bone scan with Tc 99 m which, in positive cases, were associated laboratory tests and further instrumental testing (CT, bone scan and needle aspiration). Thanks above all to bone scan with labelled granulocytes the protocol provided high accuracy (91.4%) in preoperatively identifying the causes of infection.

Lactulose hydrogen breath test in orocecal transit assessment. Critical evaluation by means of scintigraphic method.

Orocecal transit time can be studied easily using the hydrogen breath test with lactulose, but the method has some important limitations. The orocecal transit time of 10 patients suffering from irritable bowel syndrome was measured twice, at a one-week interval, by breath test and scintigraphy simultaneously using an aqueous solution of 20 g lactulose containing 74 MBq of [99mTc]DTPA. Abdominal radioactivity and alveolar hydrogen values obtained every 5 min were noted and used to obtain the following: orocecal transit time by the two methods; ileocecal lactulose flow; total and per gram of lactulose hydrogen production; mean hydrogen concentration during the right colon filling; and measurement error of the breath test with respect to the scintigraphy. In the case of the breath test, the orocecal transit time intrapatient reproducibility was better (coefficient of variation = 13.5%) when a hydrogen threshold increment of 5 ppm was used; the best correlation with the scintigraphic measurement was observed at this threshold (r = 0.90, P < 0.001). The breath test overestimated orocecal transit time with the error correlating negatively and significantly with the total hydrogen production and, particularly, the mean hydrogen concentration (r = 0.79, P < 0.01): for a mean hydrogen concentration of more than 15 ppm, the error was negligible, while within this value there was a noticeable overestimation. To conclude, the lactulose hydrogen breath test is capable of giving an accurate measurement of orocecal transit time if a hydrogen threshold increment of 5 ppm is chosen and if the mean hydrogen concentration in the first 30 min of the right colon filling is taken into account.

Absence of histopathological changes of ileum and colon in functional chronic diarrhea associated with bile acid malabsorption, assessed by SeHCAT test: a prospective study.

OBJECTIVES: Chronic diarrhea of unknown origin is often associated with bile acid malabsorption, the pathogenetic role of which is uncertain. The aim of this study was to identify morphological abnormalities in the ileal and colonic mucosa in patients with this disorder. METHODS: We performed a prospective and blinded histopathological study (between June 1991 and November 1992) of endoscopic biopsies of the distal ileum and colon of 23 patients suffering from chronic diarrhea of unknown origin. In 14, the SeHCAT (75-selena-homo-cholic acid taurine) test was abnormal owing to bile acid malabsorption; in the other nine, the diarrhea control group, the test results were normal. A detailed evaluation of surface epithelium, immune response and inflammatory changes was made. RESULTS: in two patients and two controls, mild villous atrophy was observed; there was also slight inflammation of the ileal and colonic mucosa occurring with the same frequency in both groups. A slight replacement of goblet cells was more evident in the diarrhea control group. CONCLUSIONS: Chronic diarrhea of unknown origin associated with bile acid malabsorption does not involve specific morphological changes of ileal or colonic mucosa, and its pathogenesis must be looked for in dysfunction of the ileum and/or colon.

Bile acid malabsorption in AIDS-associated chronic diarrhea: a prospective 1-year study.

OBJECTIVES: In patients with chronic diarrhea associated with acquired immunodeficiency syndrome, bile acid malabsorption, very rarely investigated, may have an important pathogenetic role. METHODS: In this 1-yr prospective study, 15 patients with AIDS-associated chronic diarrhea and 10 AIDS-controls were studied for bile acid malabsorption by means of the SeHCAT abdominal retention test. The patients with diarrhea underwent the glucose hydrogen breath test to identify any bacterial proliferation in the small bowel. RESULTS: In the chronic diarrhea group, only one case of small bowel bacterial overgrowth, and seven cases (47%) with generally severe bile acid malabsorption, were observed. Among the controls, only one had an abnormal low SeHCAT retention. In both cases with Cryptosporidium infection, the SeHCAT test was pathological. CONCLUSIONS: These data are of clinical importance for the pathogenetic study of AIDS-associated chronic diarrhea and for specific treatment with cholestyramine.

Technetium-99m hexamethyl propylene amine oxime granulocyte scintigraphy in Crohn's disease: diagnostic and clinical relevance.

Scintigraphy with autologous granulocytes labelled by technetium-99m hexamethyl, propylene amine oxime (99mTc-HMPAO) was performed in 103 Crohn's disease patients and 52 healthy controls. In 31 patients endoscopic and histologic activity was compared with scan activity index. In the 98 patients with a positive scan, the extent of Crohn's disease, assessed by scintigraphy, was compared with that evaluated by small bowel x ray or colonoscopy with biopsies. In 48 patients, Crohn's disease activity index, activity index, simple index, erythrocyte sedimentation rate, C-reactive protein were correlated with the scan results. In 16 patients the five parameters and scan were repeated after treatment with methyl-prednisolone (10 cases), enteral nutrition (3), and 5-acetylsalicylic acid (3). The results showed that 99mTc-HMPAO granulocyte scan had a 95% sensitivity and 100% specificity to detect active inflammation; it correctly showed an abscess or a fistula in all the 24 cases found. The correlation between histological inflammatory activity and scan activity index was highly significant (r = 0.85; p < 0.01), less significant (r = 0.65; p < 0.01) between endoscopy and scan activity index. The evaluation for the extent of Crohn's disease by scan was completely correct in the small bowel (100%) and 93% correct in the large bowel. No correlation was seen between the three clinical activity parameters and scanning; in more than 80% of the cases in remission on the basis of a clinical or laboratory index, scintigraphy remained positive. Medical treatment was effective on the clinical indices but not on the active inflammation in the ileum, whereas it led to a negative scan in 5/11 cases in the large intestine. Scintigraphy with 99mTc-HMPAO granulocyte plays an important part in Crohn's disease for the diagnosis of complications, for activity and assessment of the extent, and for the treatment results evaluation.

Scintigraphic study of gastrointestinal transit and disintegration sites of mesalazine tablets labeled with technetium-99m.

Tablets of mesalazine covered with a pH-dependent coating (Pentacol), labeled by an original technique with technetium-99m, were administered to 12 patients, 9 with Crohn's disease, 3 of which recurrent, 1 with ulcerative colitis, and 2 with irritable bowel syndrome, with the aim of verifying in vivo the intestinal site of disintegration and how the contents spread throughout the intestine. In all cases the tablet was broken down in the distal ileum at extremely variable intervals, from 5 to 27 h, and the contents spread into the nearby loops and into the colon. The notable differences in the residence time of the whole tablet in the ileum can be explained by differences in adhesion to the inflamed mucosa and by a lower pH in the part of the ileum affected by the disease.

Post-cholecystectomy diarrhea: evidence of bile acid malabsorption assessed by SeHCAT test.

Although bile acid malabsorption (BAM) in post-cholecystectomy diarrhea (PCD) is a well-known clinical condition, its true etiopathogenetic role is not entirely clear. The SeHCAT (23-selena-25-homotaurocholic acid) test, a simple and reliable BAM test, was performed in 33 cholecystectomized patients, 26 with chronic diarrhea. The test revealed a marked degree of BAM in 25/26 cases. Cholestyramine in doses of 2-12 g/day was effective in 23/25, ineffective in two, and was not tolerated in one patient. When treatment was suspended, diarrhea recurred in nine, whereas bowel habit remained regular in 60%, with brief sporadic episodes of diarrhea in the other cases. The SeHCAT test was repeated in 11 cases after cholestyramine treatment interruption, and revealed the normalization of parameters in two patients and an improvement in three. We conclude that BAM is an important etiopathogenetic factor in PCD that responds favorably to cholestyramine. In 60% of the cases, it resolved diarrhea definitively, although without eliminating BAM in all cases: this suggests that existence of other factors associated with BAM. The SeHCAT test is essential for a differential diagnosis between PCD and the irritable bowel syndrome.

Post-surgical deep vein thrombosis prevention: evaluation of the risk/benefit ratio of fractionated and unfractionated heparin.

An open controlled study was carried out to assess the efficacy and tolerance of a new low molecular weight heparin for the prevention of post-surgical deep vein thrombosis and pulmonary embolism. Forty-five patients undergoing abdominal surgery mainly for neoplasm, gallstones and gastric ulcers were administered 7,500 AXaU of low molecular weight heparin subcutaneously, 2 hours before surgery and once a day for 7 days after. Heparin calcium (15,000 IU subcutaneously per day) was used as a comparison drug in 45 control subjects, matched for age, sex and type of operation. Deep vein thrombosis was identified with clinical parameters, radio-labelled fibrinogen uptake test, echo-doppler and venography; pulmonary embolism with clinical examination, chest X-rays and/or scintigraphy. No episodes of deep vein thrombosis occurred in the low molecular weight heparin-treated patients, whilst there was 1 episode, without pulmonary embolism, in the control group. The consumption of blood and haemoderivatives for transfusions was higher in the heparin calcium group. Only in this group, furthermore, did 5 patients have to suspend antithrombotic treatment due to severe haemorrhages. General tolerance of the two drugs was identical and very good.

75Se HCAT test in the detection of bile acid malabsorption in functional diarrhoea and its correlation with small bowel transit.

The purpose of this study was to evaluate whether bile acid malabsorption assessed by the 75SeHCAT test, had a pathogenetic role in functional chronic diarrhoea and to ascertain whether the small bowel transit time (SBTT) could be correlated with the 75SeHCAT test results. The test was based on the counting of the abdominal retention of a 75-selenium labelled homotaurocholic acid. The 75SeHCAT test was carried out in a control group of 23 healthy adults and in 46 patients, 38 of whom were suffering from irritable bowel syndrome (IBS) of diarrhoeic form and eight patients who had undergone cholecystectomy and were suffering from chronic diarrhoea. Faecal bile acid loss was determined in nine patients, and in 14, serum bile acid increase after a standard meal was measured. In 17, SBTT was studied by hydrogen breath test after lactulose administration (21 g in 300 ml water). In 15 patients, choledochocaecal transit time was estimated by Tc99m-HIDA (111 MBq) cholescintigraphy. In 20 of 46 subjects, 75SeHCAT retention was below normal level, and in 19 cholestyramine administration relieved diarrhoea. 75SeHCAT results were related to faecal bile acid loss, while no correlation was found with serum bile acids and SBTT. The data suggest a possible wider use of the 75SeHCAT test in chronic diarrhoea to estimate bile acid malabsorption in irritable bowel syndrome, diarrhoeic form, and provide an effective treatment. In our patients small bowel transit velocity does not seem to be a pathogenetic factor of bile acid malabsorption.

Scintigraphic evaluation of enterogastric reflux using 75Se-HCAT: methodology and first clinical observations.

The aim of this study was to assess the possibility of detecting enterogastric reflux (EGR) by 75Se-HCAT cholescintigraphy. The lowest detectable activity in the gastric area at different concentrations of the radiotracer in the gallbladder was preliminary measured both in a plastic phantom and in an in vivo model. Ten patients were studied after a single oral administration of 1480 KBq 75Se-HCAT. Gamma camera imaging was carried out for five consecutive days during both fasting and after meal ingestion. In our in vivo model an EGR corresponding to 1% of gallbladder content on day one and 8% on day five was detected. In three out of five patients in whom bile was present in the stomach at endoscopy, 75Se-HCAT cholescintigraphy demonstrated an EGR, while in three out of five patients in whom endoscopy was negative, 75Se-HCAT cholescintigraphy detected EGR either during fasting or after meal ingestion. As EGR is not constant, 75Se-HCAT may be a useful tracer of bile to detect EGR over a prolonged period of time and in different physiological conditions.

Scintigraphic study of the evolution of cortical homografts in the treatment of fractures.

Twelve patients who had undergone osteosynthesis with a metal plate combined with a frozen homoplastic bone graft for the treatment of fractures or pseudarthrosis were subjected to bone scintigraphy with 99 Tc MDP. This investigation showed the graft to be a site of early and specific accumulation of the tracer. This finding supports early colonization of the graft by vascular structures and osteoblastic cells. In view of the small number of cases studied and our incomplete knowledge of the metabolic processes involved these considerations must remain hypotheses but given the excellent clinical results obtained, the relationships between homoplastic bone and host bone merit further investigation.