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Biomedical subjects

T Riggs

Publications and source records attributed to T Riggs.

At least 19 recordsLinked to original sources
PubMed2005

Maximizing statistical power in group-randomized vaccine trials.

Statistical power in group-randomized vaccine trials is complex: group randomization may increase power by capturing more transmission effects but may decrease power as more individuals are affected by a common source of variance. The former effect dominates when most infections arise from within the group and the latter when most arise outside. This process is complicated further when individuals possess partial natural immunity. Vaccine trials typically compare infection frequency (as measured by agent or antibody detection) in vaccinated vs. unvaccinated groups. To assess the relative contributions to statistical power by direct agent detection vs. serological detection of recent infection, we constructed stochastic compartmental models using differential equations describing all possible discrete states of the group. We contrasted models where natural immunity was absent, altered only the susceptible state, or altered both the susceptible and infected states. We observed the effects of endemic infection levels, the fraction of infection arising from outside the group, infectiousness vs. susceptibility vaccine effects and waning rates. There was significant enhancement of statistical power when serological testing separated infected and susceptible classes into subsets by natural immunity status.

Haemophilus Infections↗
PubMed2000

An outbreak of Campylobacter jejuni infections associated with food handler contamination: the use of pulsed-field gel electrophoresis.

In 1998, an outbreak of Campylobacter jejuni infections occurred in Kansas among persons attending a school luncheon; community cases were also reported. In a cohort study of luncheon attendees, 27 (17%) of 161 persons reported illness. Consuming gravy (relative risk [RR], 4.2; 95% confidence interval [CI], 1.5-11.7) or pineapple (RR, 2.4; 95% CI, 1.0-5.7) was associated with illness. Both foods were prepared in a kitchen that served 6 other schools where no illness was reported. A cafeteria worker at the luncheon had a diarrheal illness and was the likely source of the outbreak. The pulsed-field gel electrophoresis (PFGE) patterns of the isolates from the food handler and those of 8 lunch attendees were indistinguishable. Isolates from 4 community patients differed. This was the first use of PFGE in a Campylobacter outbreak in the United States; its use was critical in determining that community cases were not linked.

Adolescent↗
PubMed1999

Double-outlet right ventricle: an antenatal diagnostic dilemma.

OBJECTIVE: The purpose of this study was to describe the antenatal ultrasonographic findings of fetuses with double-outlet right ventricle (DORV). DESIGN: The records were reviewed of all fetuses scanned in our ultrasound unit which were suspected of having DORV during a 6-year period ending in April 1996. A medical record search for all infants with a postnatal diagnosis of DORV was also undertaken to identify cases that were not detected antenatally. Records were examined to determine the accuracy of antenatal diagnosis and the reasons for diagnostic errors. Fetuses without follow-up were excluded. RESULTS: There were 20 fetuses with antenatally detected conotruncal defects that had DORV included in the differential diagnosis. Three fetuses were excluded, seven did not have DORV and ten were confirmed postnatally as having DORV. Two additional infants were found to have DORV from the medical record search, producing a total of 12 cases. Antenatal sonographic cardiac findings included malpositioned (overriding or transposed) great arteries (n = 11), ventricular septal defect (n = 11) and small pulmonary artery suggesting stenosis (n = 4). Confirmed postnatal cardiac findings that were missed antenatally included aortic coarctation (n = 2), right-sided aortic arch (n = 2) and pulmonary stenosis (n = 1). Seven of the 12 fetuses had extracardiac findings. Nine of the 12 fetuses tested had a normal karyotype. Eleven of the 12 infants were liveborn. Nine of these 11 survived the neonatal period and underwent surgical repair within the first year of life; two subsequently died. In total, seven fetuses survived and five did not. CONCLUSIONS: Most fetuses with DORV can be identified antenatally as having an abnormal heart. However, it is very difficult to distinguish this particular defect from other conotruncal abnormalities.

Diagnosis, Differential↗
PubMed1999

Doppler velocity and flow through the aortic isthmus in normal term neonates.

Our hypothesis was that the relationship between the internal aortic diameter and the Doppler flow velocity across the aortic isthmus could be modeled by applying the principle of conservation of mass flow. The aortic diameter decreased at the isthmus by a mean of 18% (t = 11.02, p < 0.0001), while the flow velocity increased by a mean of 44% (t = 10.09, p < 0.0001). The mean peak mass flow rate was 34. 5 ml/s preisthmus and 32.9 ml/s at the isthmus with excellent correlation (r = 0.830). We conclude that the increase in Doppler velocity observed in the descending aorta can be explained by the normal narrowing observed at the aortic isthmus and application of the continuity equation for conservation of mass flow.

Aorta, Thoracic↗
PubMed1995

Tetralogy of Fallot: prenatal diagnosis and postnatal survival.

OBJECTIVES: To correlate prenatal echocardiographic findings with infant outcome in a large screening population affected by tetralogy of Fallot. METHODS: Inclusion criteria required confirmed postnatal cardiac diagnosis, at least one fetal ultrasound examination with satisfactory heart visualization, and infant delivery at our institution. Aortic and pulmonary artery diameters were measured from real-time ultrasound or videotaped scans and compared against published nomograms. The pulmonary artery to aorta ratio was also evaluated in a similar manner. Infant survival was assessed 1 year after delivery. RESULTS: Seventeen fetuses were confirmed to have a ventricular septal defect and an overriding aorta with varying degrees of right ventricular outflow obstruction after delivery. All karyotypes were normal. Ultrasound screening identified 12 of 17 abnormal hearts at a mean gestational age of 22.9 +/- 5.1 weeks; two of these fetuses were thought to have only ventricular septal defect before delivery. Five fetuses had enlarged aortic roots during the initial scan. Only two of the ten fetuses with a measurable pulmonary artery had initial sonographic evidence for valve stenosis. Six other pulmonary arteries became abnormally small with advancing pregnancy. The pulmonary artery to aorta ratio was decreased in six of the ten fetuses with a measurable pulmonary artery. Sixteen infants survived at least 1 year after birth and successfully completed either corrective or palliative cardiac surgery. CONCLUSION: Fetuses with tetralogy of Fallot may present with only a ventricular septal defect and aortic septal override by prenatal ultrasound examination. Pulmonary artery stenosis is not always present at initial ultrasound examination, but this finding can develop or worsen during pregnancy. Furthermore, a normal aortic diameter does not exclude tetralogy of Fallot. Infant survival appears to be favorable in the absence of other major structural or chromosomal anomalies.

Female↗
PubMed1992

Cerebral blood flow velocity in normal, full-term newborns is not related to ductal closure.

OBJECTIVE: To correlate changes in blood flow velocity in the anterior and middle cerebral arteries with closure of the ductus arteriosus in normal, full-term newborns during the first 2 days following delivery. DESIGN: Survey. SETTING: Large community hospital. PARTICIPANTS: Twenty-three normal, full-term neonates. SELECTION PROCEDURES: Volunteer sample. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: We measured blood flow velocity in the anterior and middle cerebral arteries, cardiac output, and patency of the ductus arteriosus using pulsed Doppler, M-mode, and real-time ultrasound. The initial examination was performed at (mean +/- SD) 7.6 +/- 2 hours and the second examination was performed at 30 +/- 3 hours. The systolic, diastolic, and mean blood flow velocity in the anterior and middle cerebral arteries increased significantly from day 1 to day 2. Cardiac output did not change significantly (252 +/- 49 vs 279 +/- 69 cm3/kg per minute). Thirteen newborns on day 1, but only two newborns on day 2, had echocardiographic evidence of a patent ductus arteriosus. Newborns whose ductus was already closed on day 1 had similar increases in blood flow velocity in the anterior and middle cerebral arteries from day 1 to day 2 compared with newborns whose ductus had closed from day 1 to day 2. CONCLUSION: The normal increase in blood flow velocity in the anterior and middle cerebral arteries in the first 2 days following delivery is not related to changes in cardiac output or ductal closure.

Aorta↗
PubMed1991

Pulmonary-to-aorta diameter ratio in the normal and abnormal fetal heart.

In an attempt to establish the normal ratio of pulmonary artery to aorta diameters at varying gestational ages, the pulmonary artery and aorta diameters of 316 normally grown fetuses between 14 and 39 weeks' gestational age were measured. The ratios for each fetus were derived, and regression analysis was used to evaluate the relationship between gestational age and each diameter. We conclude that the diameters of the pulmonary artery and aorta are closely related to fetal age but that the ratio is independent of age (mean, 1.09; SD, 0.17). The diameters of the pulmonary artery and aorta in 21 fetuses with proved congenital heart disease were then compared with those of this normal population. The pulmonary artery/aorta ratio was abnormal in 13 of 21 fetuses with congenital heart disease. Actual measurements of the great vessels can be difficult and may be misleading, but a quick comparison of relative size by inspection is feasible.

Aorta↗
PubMed1986

Biliary tract injuries following routine cholecystectomy.

This retrospective study was done to review the epidemiology, etiology, method of treatment, and results of repairs of biliary tract injuries following routine cholecystectomy. Fourteen patients have been treated at our hospital for biliary tract injuries during a 10-year period (January 1974-December 1983). One injury occurred at our institution. During this same time span, 941 cholecystectomies were performed at our hospital giving an incidence of 0.11 per cent for the injury. Trained surgeons were responsible for nine injuries, family practitioners for two injuries, and a surgery resident for one injury. Two injuries were caused by individuals whose level of training could not be determined. In only one case was massive hemorrhage associated with the injury. Four patients had their injuries diagnosed and treated at the time of their original surgery. Two had successful initial repairs. The other two required further reconstructive surgery with good results. Ten patients had a delay in diagnosis, and nine required biliary tract reconstruction. Four of these had good results. Combining both groups, 13 patients required 20 procedures. Stents were used in 14 procedures with good results in 43 per cent. Stents were left in place 6.9 months. Five procedures were done without stents and four resulted in failure. Biliary tract injuries are devastating problems caused by trained surgeons through lack of attention. Better results can be obtained if the injury is recognized early and treated. The overall success rate was 62 per cent. The use of stents improved the success rate.

Adult↗
PubMed1981

Two dimensional echocardiography in evaluation of right atrial masses: five cases in pediatric patients.

Five unusual cases of a right atrial mass in children are described to illustrate the very valuable contribution that two dimensional echocardiographic examinations can bring to both the initial diagnosis and the subsequent management of patients with these findings. One patient had a large benign hemangioendothelioma of the right atrium. Two infants had extension of a Wilms' tumor from the kidney by way of the inferior vena cava to the right atrium. A fourth patient, an 8 year old girl, had no cardiac disease, and manifested Staphylococcus aureus endocarditis of the tricuspid valve with a large pedunculated mass and subsequent pulmonary embolus. A fifth patient, a premature infant with a central hyperalimentation catheter in the right atrium, had a large thrombus on the catheter that was successfully eradicated with urokinase-induced thrombolysis. Two dimensional echocardiography provides real time imaging of the entire right atrium, interatrial septum, inferior and superior venae cavae and tricuspid orifice and hence is valuable in the diagnosis and management of these clinical problems.

Child↗
PubMed1981

Respiratory variation in Frank vectorcardiography and echocardiography in children.

Forty pediatric patients underwent echocardiographic and Frank vectorcardiographic studies during normal respiration. The right ventricular minor axis (RVEDD) increased significantly with inspiration (p less than 0.005), while the left ventricular minor axis did not significantly change. The distance from the anterior chest wall to the center of the left ventricle did significantly increase with inspiration (p less than 0.005). Some vectorcardiographic parameters changed with inspiration, also. Both the maximal spatial vector to the left (MSVL) and the X to the left (X-L) significantly decreased with inspiration. Although the average magnitude of these changes was small (10-15%), there was wide variation. Five of twenty-one patients with left ventricular hypertrophy during expiration had a clearly normal Frank VCG during inspiration. It is suggested that phases of respiration should be monitored when evaluating the Frank VCG in pediatric patients.

Adolescent↗
PubMed1981

Determination of alkaline phosphatase in casein: collaborative study.

A collaborative study was made to determine alkaline phosphatase in casein samples by the rapid colorimetric test. Six to eight collaborators tested 10 unknown casein samples containing various amounts of residual phosphatase with and without the addition of magnesium acetate. Results indicated that magnesium acetate significantly increased phosphatase activity. The collaborators correctly analyzed 95% of the samples with the added magnesium acetate. The method has been adopted official first action.

Alkaline Phosphatase↗
PubMed1980

The pediatric spectrum of dynamic left ventricular obstruction.

Twenty-one pediatric patients with echocardiographic and/or hemodynamic evidence of dynamic left ventricular obstruction are presented in order to examine the pathophysiologic mechanisms of this disorder. Neonates commonly had transient hypertrophic cardiomyopathy related to hypertension or to being infants of diabetic mothers. Infants with D-transposition of the great arteries sometimes developed signs of subpulmonic dynamic obstruction. Older children and adolescents had either classic findings of IHSS or concentric left ventricular hypertrophy. The spectrum of hypertrophic cardiomyopathy appears to be broader in pediatric patients than in adults.

Adolescent↗
PubMed1979

Echocardiographic assessment of the adequacy of pulmonary arterial banding.

Thirty-one echocardiograms of 21 patients who had pumonary arterial banding were analyzed to assess the aequacy of surgery. In 5 patients the echocardiograms were obtained before and after banding and in 16 patients only after surgery. Right and left ventricular systolic time intervals were measured echographically. The ratios of the right ventricular preejection period to right ventricular ejection time (RPEP/RVET) were correlated with both diastolic (r = 0.94) and systolic (r = 0.86) pulmonary arterial pressures distal to the band. The analysis of right ventriclar systolic time intervals, especially the RPEP/RVET ratio, clearly differentiated patients with an adequate band (distal pulmonary arterial diastolic pressure less than 15 mm Hg) from patients with an inadequate band (distal pulmonary arterial diastolic pressure equal to or greater than 30 mm Hg). The results indicate that echocardiography is a useful noninvasive tool in evaluating the adequacy of the pulmonary arterial band and facilitates the follow-up of patients after banding.

Blood Pressure↗