Is colour flow imaging needed to exclude clinically significant valvular regurgitation in adult patients undergoing transthoracic echocardiography?

OBJECTIVE

To establish whether clinically significant aortic and mitral valvular regurgitation can be excluded in adult patients undergoing transthoracic echocardiography without using colour flow imaging.

SETTING

Sunnybrook Health Science Centre, a tertiary referral centre with full cardiovascular services affiliated with the University of Toronto, Toronto, Ontario.

DESIGN

Logistic regression models were developed from a retrospective review of 14,051 unselected consecutive echocardiograms from 1991 through 1994. The dependent variable was more than mild aortic or mitral valvular regurgitation. Independent variables included age, sex and various functional and structural measures obtained during routine two-dimensional echocardiography. The negative predictive values and sensitivity of the models were estimated.

INTERVENTION

The number of patients correctly classified by these models, as well as the proportion for whom the colour flow imaging did not add to the baseline echocardiogram, was determined. Nonparametric bootsrapping was used to obtain confidence intervals for these statistics.

MAIN RESULTS

Ten models were developed, with negative predictive values ranging from 96.2% to 100%. Incorporation of such decision aids into the software of echocardiographic machinery would help echocardiographers to rule out significant aortic or mitral regurgitant lesions. In practices where colour flow imaging is routinely employed, 40% fewer procedures could be performed.

CONCLUSIONS

Models based on simple demographic and two-dimensional echocardiographic variables can reliably exclude significant valvular regurgitation and could potentially reduce the volumes and costs of colour flow imaging. Given the widespread diffusion of colour Doppler imaging, the models may also be helpful to avoid misinterpretation of flow imaging results, by defining subgroups in whom the prior probability of significant aortic or mitral regurgitation is extremely low.

Human beta-defensin-1 is a salt-sensitive antibiotic in lung that is inactivated in cystic fibrosis

A human bronchial xenograft model was used to characterize the molecular basis for the previously described defect in bacterial killing that is present in the cystic fibrosis (CF) lung. Airway surface fluid from CF grafts contained abnormally high NaCl and failed to kill bacteria, defects that were corrected with adenoviral vectors. A full-length clone for the only known human beta-defensin (i.e., hBD-1) was isolated. This gene is expressed throughout the respiratory epithelia of non-CF and CF lungs, and its protein product shows salt-dependent antimicrobial activity to P. aeruginosa. Antisense oligonucleotides to hBD-1 ablated the antimicrobial activity in airway surface fluid from non-CF grafts. These data suggest that hBD-1 plays an important role in innate immunity that is compromised in CF by its salt-dependent inactivation.

Assessment of diurnal variation of cerebrospinal fluid tryptophan and 5-hydroxyindoleacetic acid in healthy human females

The role of serotonin (5-HT) in the pathogenesis and treatment of major neuropsychiatric disorders, including mood and anxiety disorders, continues to be the subject of extensive research. Previous studies examining central 5-HT functioning measured cerebrospinal fluid (CSF) levels of 5-hydroxyindoleacetic acid (5-HIAA) by using single or multiple lumbar punctures. A number of investigators have demonstrated the feasibility of continuous CSF sampling via an indwelling lumbar catheter to study CSF neurochemistry in healthy subjects and patients with neuropsychiatric illness. Four healthy female volunteers, aged 21-34 years, underwent continuous CSF sampling. CSF was collected at a constant rate of 1 ml every 10 minutes over a 30-hour period, with levels of tryptophan (TRP) and 5-HIAA measured every hour. Plasma was also obtained hourly for TRP determination. The results of this study indicate that CSF 5-HIAA, CSF TRP, and plasma TRP levels showed variation over time, but failed to show diurnal fluctuation. Intra-individual coefficients of variation determined for CSF 5-HIAA, CSF TRP, and plasma TRP ranged from 9.2 to 14.9%, 8.8 to 14.6%, and 14.7 to 19.0%, respectively. Continuous CSF sampling is safe and feasible in humans, and may prove useful for studies of central 5-HT neurotransmission in neuropsychiatric illness.

Pathogenesis of Tourette's syndrome

This review presents a models of disease pathogenesis in the context of CNS development. It begins with an exploration of the clinical features and natural history of Tourette's syndrome. This is followed by a consideration of the role of genetic and nongenetic factors. An effort is then made to review the anatomical organization of the basal ganglia and related cortical sites. These circuits are intimately involved in the normal processing of sensorimotor, cognitive, and emotionally laden information. Evidence implicating these circuits in the pathobiology of Tourette's syndrome is then considered. The review closes with the prospects for advances in interdisciplinary research and therapeutics using this model as a guide.

Adenosine diphosphate inhibits the serotonin transporter

Adenosine 5'-diphosphate (ADP) caused rapid and significant reductions in the rates of [3H]serotonin uptake observed for human platelets, human platelet vesicles, and rat brain synaptic vesicles. Estimated Vmax values in platelets (N = 15). platelet vesicles (N = 3), and synaptic vesicles (N = 3) exposed to 100 microM ADP were 42.3 +/- 11.4%, 78.8 +/- 1.4%, and 56.8 +/- 9.9% of control values, respectively. The EC50 values observed for ADP in platelets and platelet vesicles were 10-24 microM. Exposure to 100 microM ADP had small, inconsistent effects on KM values observed for the platelet transporter. ADP (100 microM) caused only a slight competitive inhibition of the platelet membrane binding of [3H]citalopram, a ligand for the 5HT uptake site of the transporter (5.0% displacement of 1.0 nM [3H]citalopram, 13% increase in apparent KD). The ADP analogue 2-methylthioADP caused similar decreases in the rates of platelet [3H]serotonin uptake, while a number of other related compounds had little or no effect on rates of platelet uptake. The ADP-effect on uptake was rapid, occurring in less than 2.5 s. and was additive with reductions produced by protein kinase C (PKC) activation. The ADP-induced decreases in uptake did not appear to occur through the ADP receptor or known platelet second messenger systems. The exact mechanism of the ADP-effect and its functional significance remain to be determined.

Delayed-type hypersensitivity in mast cell-deficient mice: dependence on platelets for expression of contact sensitivity

Previous studies of cutaneous T cell-mediated responses in mice have obtained pharmacologic, morphologic, and immunologic evidence pointing to a critical role for local mast cells in release of the vasoactive amine serotonin (5-HT) to mediate early, initiating events that are required for elicitation of these responses. However, the role of mast cells in initiating these T cell-mediated cutaneous responses has been questioned due to the presence of relatively intact delayed-type hypersensitivity responses, such as contact sensitivity (CS), in mast cell-deficient mice whose skin contains only 1 % normal mast cell numbers. The contribution of other potential local sources of 5-HT, such as circulating platelets, at the site of a delayed-type hypersensitivity or CS response in these mast cell-deficient strains, has not been investigated. Therefore, we studied the effect of systemic platelet depletion, produced with an anti-platelet Ab, on blood and tissue levels of 5-HT, and on in vivo T cell-mediated cutaneous sensitivity responses, in W/Wv and Sl/Sld mast cell-deficient mice. The results showed that: 1) platelet depletion severely reduced whole blood 5-HT; 2) tissue levels of 5-HT, in mast cell-deficient mice, depended in large part on the presence of circulating platelets, and 3) specific depletion of platelets markedly suppressed CS responses in both W/Wv and Sl/Sld mast cell-deficient mice, and only moderately reduced CS in normal +/+ congenic mast cell-sufficient controls, but did not decrease CS in beige mice, with platelet granules that are defective in storage of 5-HT. We concluded that platelets may provide 5-HT crucial for the initiation of cutaneous T cell-mediated immune responses, such as CS.

Delayed-type hypersensitivity in mast cell-deficient mice: dependence on platelets for expression of contact sensitivity

Previous studies of cutaneous T cell-mediated responses in mice have obtained pharmacologic, morphologic, and immunologic evidence pointing to a critical role for local mast cells in release of the vasoactive amine serotonin (5-HT) to mediate early, initiating events that are required for elicitation of these responses. However, the role of mast cells in initiating these T cell-mediated cutaneous responses has been questioned due to the presence of relatively intact delayed-type hypersensitivity responses, such as contact sensitivity (CS), in mast cell-deficient mice whose skin contains only 1 % normal mast cell numbers. The contribution of other potential local sources of 5-HT, such as circulating platelets, at the site of a delayed-type hypersensitivity or CS response in these mast cell-deficient strains, has not been investigated. Therefore, we studied the effect of systemic platelet depletion, produced with an anti-platelet Ab, on blood and tissue levels of 5-HT, and on in vivo T cell-mediated cutaneous sensitivity responses, in W/Wv and Sl/Sld mast cell-deficient mice. The results showed that: 1) platelet depletion severely reduced whole blood 5-HT; 2) tissue levels of 5-HT, in mast cell-deficient mice, depended in large part on the presence of circulating platelets, and 3) specific depletion of platelets markedly suppressed CS responses in both W/Wv and Sl/Sld mast cell-deficient mice, and only moderately reduced CS in normal +/+ congenic mast cell-sufficient controls, but did not decrease CS in beige mice, with platelet granules that are defective in storage of 5-HT. We concluded that platelets may provide 5-HT crucial for the initiation of cutaneous T cell-mediated immune responses, such as CS.

Strategies for improving prescribing practice

Drug therapy is an integral component of modern medical care, and practising physicians are faced with the difficult task of keeping up with rapid changes in pharmacologic treatments. Recent evidence indicates that prescribing practice is often inconsistent with criteria for safety and effectiveness. Surveys indicate that community-based physicians are not satisfied with current sources of information on prescription drugs. The dissemination of printed material alone does not lead to improved prescribing practice, but specific education and feedback strategies can. To improve prescribing practice in Canada we need to systematically evaluate strategies to change prescribing behaviour, to design quality assurance programs based on proven strategies and to develop collaboration and cooperation among providers, manufacturers, governments and the public.

Appropriateness in health care delivery: definitions, measurement and policy implications

A major focus of the current health care debate is the notion that a substantial proportion of the health care delivered in Canada is inappropriate. There are two types of appropriateness: appropriateness of a service and appropriateness of the setting in which care is provided (i.e., inpatient v. outpatient or home care). Measuring both types objectively requires the comparison of observed patterns of care with explicit criteria for appropriate care. The few studies of appropriateness conducted in Canada have shown that inappropriate services are provided and inappropriate settings are used. Reducing inappropriate health care delivery could involve active strategies for the implementation of guidelines and better cooperation and coordination within the health care system. However, lower rates of health care delivery or even inappropriate health care will not necessarily translate into higher quality care or lower costs overall.

Recent findings on preventable hospitalizations

Disparities in health outcomes for low-income populations as documented by rates of preventable hospital admission remains large in the United States, even with the moderate expansion of Medicaid and efforts at the state and local levels to improve primary care services that began in the mid-1980s. These differences in outcome for rich and poor are not an isolated phenomenon of a few old and decaying Northeast urban centers but are documented in a broad range of urban areas. Much smaller differences are found in urban areas in Ontario, where universal coverage may help to reduce barriers to care.

Regionalization of cardiac surgery in the United States and Canada. Geographic access, choice, and outcomes

OBJECTIVE

To determine how regionalization of facilities for coronary artery bypass surgery (CABS) affects geographic access to CABS and surgical outcomes.

DESIGN

Computerized hospital discharge records were used to measure hospital CABS volume and in-hospital post-CABS mortality rates. Relationships between surgical volume and age- and sex-adjusted mortality rates were compared using chi 2 tests. Small-area analysis of the association between CABS rates and distances to nearest CABS hospital was performed using multivariate linear regression methods.

SETTING

All nonfederal hospitals in New York, California, Ontario, Manitoba, and British Columbia.

PATIENTS

All adult residents of the five jurisdictions who underwent CABS in a hospital in their jurisdiction from 1987 through 1989.

RESULTS

In New York and Canada, approximately 60% of all CABS operations took place in hospitals performing 500 or more CABS operations per year, compared with only 26% in California. The highest mortality rates were found among California hospitals performing fewer than 100 CABS operations per year (adjusted 14-day in-hospital mortality was 4.7% compared with 2.4% in high-volume California hospitals, P < .001). The percentage of the population residing within 25 miles of a CABS hospital was 91% in California, 82% in New York, and less than 60% in Canada. Eliminating very low-volume (< 100 cases per year) CABS hospitals in California would increase travel distances to a CABS hospital only slightly for a small number of residents. The Canadian degree of regionalization was not associated with lower CABS rates within provinces for populations living at more remote distances from the nearest CABS hospital.

CONCLUSION

Regionalization of CABS facilities in New York and Canada largely avoids the problem of low-volume outlier hospitals with high postoperative mortality rates found in California. New York has avoided the redundancy of facilities that exists in California while still providing residents a geographically convenient selection of CABS hospitals. Stricter regionalization in Canada may leave residents with a more narrow choice of facilities, but does not disproportionately affect access to surgery for populations living at remote distances from CABS facilities.

Acute and chronic effects of fluoxetine and haloperidol on mouse brain serotonin and norepinephrine turnover

Evidence from clinical studies suggests that the noradrenergic system may play a role in the pathophysiology of antidepressant- and neuroleptic-induced akathisia. In limited previous neurochemical research, acute treatment with selective serotonin reuptake inhibitors (SSRIs) has been reported to increase rat brain norepinephrine (NE) turnover or release. We have examined the neurochemical effects of 2 hr, 4 day, and 20 day treatment with the SSRI fluoxetine, and the neuroleptic haloperidol, on regional brain monoamine metabolism. Short and long-term fluoxetine treatment produced substantial decreases (to 65-79% of control) in serotonin (5HT) turnover. However no effects of fluoxetine on mouse brain NE turnover--as assessed by forebrain, hypothalamus, and hindbrain 3-methoxy-4-hydroxyphenylglycol (MHPG) levels or MHPG/NE ratios--were observed. Acute (2 hr) fluoxetine also did not alter regional NE turnover in rat brain. In contrast, haloperidol tended to increase MHPG levels and MHPG/NE ratios in the mouse brain regions studied. The persistence of decreased 5HT turnover during fluoxetine treatment, the lack of an effect of fluoxetine on NE turnover, and the increased NE turnover seen after haloperidol may have important implications regarding drug responsivity and the mechanism of akathisia induction.

Plasma androgens in autism

Plasma levels of testosterone and the adrenal androgen dehydroepiandrosterone sulfate (DHEA-S) were measured in male autistic subjects (31 prepubertal, 8 postpubertal), mentally retarded/cognitively impaired subjects (MR, 12 prepubertal), and normal control subjects (NC, 10 prepubertal, 11 postpubertal). Mean levels of plasma testosterone were similar in the postpubertal autistic (4.54 +/- 1.12 ng/ml) and postpubertal NC (5.02 +/- 1.87 ng/ml) groups. Plasma DHEA-S levels in postpubertal autistic (2170 +/- 1020 ng/ml) and postpubertal NC (1850 +/- 777 ng/ml) groups also were not significantly different. Similarly, no significant group differences were seen for testosterone or DHEA-S in the prepubertal autistic, MR, or NC individuals, although prepubertal MR individuals with cerebral palsy did have increased plasma DHEA-S levels compared to age-matched MR or NC individuals. Significant negative correlations were found between testosterone and whole blood serotonin (5-HT) levels in the combined (all subjects, all ages) groups and in the autistic group, suggesting that the effect of puberty on whole blood 5-HT may deserve further study. Data indicate that altered secretion of the androgens is not a common feature of autism. However, abnormalities of adrenal androgen secretion may be present in individuals with cerebral palsy.

A role for platelet release of serotonin in the initiation of contact sensitivity

Finding contact sensitivity (CS) responses that were fairly normal in ear swelling, and in serotonin (5-HT) dependence in mast-cell-deficient mice, led to experiments to determine whether platelets supplemented mast cells as a source of 5-HT in CS. Severe depletion of platelets, and consequently blood 5-HT, with antiplatelet antibody, strongly inhibited CS, especially in mast-cell-deficient mice, suggesting that platelets supplemented mast cells. Furthermore, human platelets sensitized in vitro with anti-(tri-nitro-phenyl) IgE, and transferred intravenously together with isolated late-acting effector T cells, provided CS initiation due to local 5-HT release. Similar, IgE-dependent in vitro release of 5-HT was C dependent. These findings establish the importance of antigen-specific platelet release of 5-HT in CS initiation.

Cerebrospinal fluid biogenic amines in obsessive compulsive disorder, Tourette's syndrome, and healthy controls

To examine the role of noradrenergic, dopaminergic, and serotonergic mechanisms in the pathobiology of obsessive compulsive disorder (OCD) and Tourette's syndrome (TS), concentrations of tyrosine (TYR), norepinephrine (NE), 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), homovanillic acid (HVA), tryptophan (TRP), and 5-hydroxyindoleacetic acid (5-HIAA) were measured in the lumbar cerebrospinal fluid (CSF) of 39 medication-free OCD patients, 33 medication-free TS patients, and 44 healthy volunteers. CSF TYR concentrations were reduced (p < .05) in the OCD patients compared to the healthy subjects. CSF NE in TS patients was 55% higher than in healthy controls (p < .001) and 35% higher than in OCD patients (p < .001). After covarying for height, CSF HVA levels were reduced (p < .05) in the OCD group compared to TS patients but not compared to the normal volunteers. No mean differences in CSF MHPG, TRP, and 5-HIAA were observed in this study across the three groups. The CSF NE data support the hypothesis that noradrenergic mechanisms are involved in the pathobiology of TS. Alterations in the balance of noradrenergic, dopaminergic, and serotonergic systems are likely involved in the pathobiology of OCD.

Preliminary study of eating disorders among French female adolescents and young adults

We have performed an exploratory study of eating disorders among female adolescents (N = 38) and young adult (N = 38) students living in Paris, France. A high percentage of the subjects in the adolescent (68.4%) and young adult (50%) groups displayed one or more atypical eating behaviors with grazing being prominent (60.5% and 42.1%, respectively) in both groups. Bulimia nervosa (DSM-III-R) was found only in the older group (3/38 vs. 0/38). Binge eating was significantly more frequent among the older subjects (12/38 vs. 1/38). Nicotine dependence and daily grazing with a history of grazing during childhood were reported in all subjects with bulimia nervosa (DSM-III-R). These data, while requiring replication in larger samples, indicate that atypical eating behaviors are common in the populations sampled. Furthermore, daily grazing (especially with a history of grazing during childhood) and nicotine dependence may be strongly associated with the development of bulimia nervosa.

Elevated cerebrospinal fluid levels of oxytocin in obsessive-compulsive disorder. Comparison with Tourette's syndrome and healthy controls

BACKGROUND

Limited neurobiological data have implicated central arginine vasopressin in the pathobiology of obsessive-compulsive disorder (OCD). Based on twin, family genetic, and pharmacological studies, some forms of OCD are etiologically related to Tourette's syndrome. The role of arginine vasopressin and related compounds such as oxytocin in Tourette's syndrome has not been previously explored.

METHODS

To compare cerebrospinal fluid (CSF) levels of arginine vasopressin and oxytocin, we collected CSF at midday in a standardized fashion from a total of 83 individuals (29 patients with OCD, 23 patients with Tourette's syndrome, and 31 normal controls). We also collected family study data on each subject to determine which subjects had a family history positive for Tourette's syndrome, OCD, or related syndromes.

RESULTS

In contrast to previous reports, we report similar concentrations of arginine vasopressin for all three groups but increased oxytocin levels in patients with OCD. Remarkably, this increase was observed only in a subset of patients with OCD (n = 22) independently identified as being without a personal or family history of tic disorders (P = .0003). In this subgroup of patients, the CSF oxytocin level was correlated with current severity of OCD (n = 19, r = .47, P < .05).

CONCLUSIONS

A possible role for oxytocin in the neurobiology of a subtype of OCD is suggested by the elevated CSF levels of oxytocin and by the correlation between CSF oxytocin levels and OCD severity. These findings reinforce the value of family genetic data in identifying biologically homogeneous (and perhaps more etiologically homogeneous) groups of patients with OCD. Together with emerging pharmacological data showing differential responsiveness to treatment of tic-related OCD vs non-tic-related OCD, these data also argue strongly for the incorporation of tic-relatedness as a variable in biological and behavioral studies of patients with OCD.

Comparison of the appropriateness of coronary angiography and coronary artery bypass graft surgery between Canada and New York State

OBJECTIVE

To compare the appropriateness of coronary angiography and coronary artery bypass graft (CABG) use between the United States and Canada.

DESIGN

Retrospective randomized medical record review.

SETTING

All hospitals performing coronary angiography and/or CABG surgery in two Canadian provinces (Ontario and British Columbia); in New York State, 15 randomly selected hospitals that provide coronary angiography and 15 randomly selected hospitals that provide CABG surgery.

PATIENTS

All patients were randomly selected. For coronary angiography, 533 patients in Canada and 1333 patients in New York were selected; for CABG, 556 patients in Canada and 1336 patients in New York were selected.

MAIN OUTCOME MEASURES

Percentage of patients in each country who had coronary angiography or CABG for necessary, appropriate, uncertain, or inappropriate indications as rated by criteria developed separately in each country and the complications of those procedures.

RESULTS

For coronary angiography, 9% of Canadian cases and 10% of New York cases were rated inappropriate using Canadian criteria compared with 5% and 4%, respectively, using US criteria. For CABG, 4% of Canadian cases and 6% of New York cases were rated inappropriate by Canadian criteria compared with 3% and 2%, respectively, using US criteria. A lower proportion of procedures were performed on persons aged 75 years or older in Canada than in New York for both coronary angiography (5% vs 11%; P < .001) and CABG (6% vs 14%; P < .001). Women were also represented in lower proportions among angiography cases in Canada than in New York (28% vs 35%; P = .023). Canadian patients with left main coronary disease waited significantly longer between angiography and CABG than did New York patients (P < .0001).

CONCLUSIONS

Rates of inappropriate use of cardiac procedures were low in Canada and New York, which suggests that the regionalization of cardiac procedures that characterizes both health care systems contributes to better clinical decision making. Differences in the use of cardiac procedures among the elderly in the two countries merits further comparative examination.

Noradrenergic and adrenergic functioning in autism

A neurochemical assessment of noradrenergic and adrenergic functioning was carried out with autistic patients and normal control individuals. Norepinephrine and related compounds were measured in autistic (n = 17 unmedicated, 23 medicated; age range 9-29 years old) and normal controls (n = 27; age range 9-36 years old). Plasma levels and urinary excretion of 3-methoxy-4-hydroxy-phenylglycol (MHPG) were measured, as were urinary excretion rates of norepinephrine (NE), epinephrine (EPI), and vanillylmandelic acid (VMA). No significant group mean differences were seen between the autistic and control groups. In both the autistic and control groups urinary excretion rates of norepinephrine and epinephrine were substantially higher in the afternoon-evening (5-11 PM) compared to the overnight (11 PM-7 AM) collection period. Based on our neurochemical assessment, marked abnormalities in basal noradrenergic functioning do not appear to be present in autism.

Advanced glycation end products (AGEs) on the surface of diabetic erythrocytes bind to the vessel wall via a specific receptor inducing oxidant stress in the vasculature: a link between surface-associated AGEs and diabetic complications

Vascular complications are an important cause of morbidity and mortality in patients with diabetes. The extent of vascular complications has been linked statistically to enhanced adherence of diabetic erythrocytes to endothelial cells (ECs) and to the accumulation of a class of glycated proteins termed advanced glycation end products (AGEs). We hypothesized that formation of AGEs on the surface of diabetic erythrocytes could mediate their interaction with ECs leading to binding and induction of vascular dysfunction. Enhanced binding of diabetic erythrocytes to ECs was blocked by preincubation of erythrocytes with anti-AGE IgG or preincubation of ECs with antibodies to the receptor for AGE (RAGE). Immunoblotting of cultured human ECs and immunostaining of normal/diabetic human tissue confirmed the presence of RAGE in the vessel wall. Binding of diabetic erythrocytes to endothelium generated an oxidant stress, as measured by production of thiobarbituric acid-reactive substances (TBARS) and activation of the transcription factor NF-kappa B, both of which were blocked by probucol or anti-RAGE IgG. Erythrocytes from diabetic rats infused into normal rats had an accelerated, early phase of clearance that was prevented, in part, by antibody to RAGE. Liver tissue from rats infused with diabetic erythrocytes showed elevated levels of TBARS, which was prevented by pretreatment with anti-RAGE IgG or probucol. Thus, erythrocyte surface AGEs can function as ligands that interact with RAGE on endothelium. The extensive contact of diabetic erythrocytes bearing surface-associated AGEs with vessel wall RAGE could be important in the development of vascular complications.

Case-based reasoning and imaging procedure selection

RATIONALE AND OBJECTIVES

Case-based reasoning, an artificial intelligence technique for learning and reasoning from experience, has shown great potential for use in decision support systems. The authors developed and tested a prototype case-based decision support system to explore the applicability of this technique to the selection of diagnostic imaging procedures.

METHODS

A case-based system, ProtoISIS, was developed based on the Protos learning apprentice. ProtoISIS learned the domain of ultrasonography and body computed tomography by reviewing 200 consecutive cases of actual requests for imaging procedures. ProtoISIS was tested by using it to classify four sets of 25 cases of actual imaging procedure requests.

RESULTS

ProtoISIS correctly classified 72% of the imaging-procedure requests. Its performance improved as it gained experience: in the last two test series, it correctly classified 84% of the cases presented.

CONCLUSIONS

Case-based reasoning can be applied successfully to the selection of diagnostic imaging procedures and holds potential for use in clinical decision support aids. Further work is necessary to realize a clinically useful system.