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Biomedical subjects

R M Hamilton

Publications and source records attributed to R M Hamilton.

At least 37 records · Page 2Linked to original sources
PubMed1997

Alveolar and dead space volume measured by oscillations of inspired oxygen in awake adults.

Forced sinusoidal oscillations in the inspired concentration of a low-solubility inert gas can be used to measure airways dead space and alveolar volume. When inspired oxygen is oscillated about its mean value in the same way, the ratio between the amplitudes of the resulting end-expired and inspired oxygen oscillations is the same as that of an inert gas such as argon. Thus, oxygen forcing oscillations can be used to measure lung volume. In nine healthy spontaneously breathing adults, the FIO2 (mean FIO2 = 0.26, mean minute volume = 8.5 L/min) was forced to sinusoidally oscillate with an amplitude of +/- 0.04. The mean airways dead space measured using FIO2 oscillations with a forcing period of 3 min was 0.17 +/- 0.04 L, and the airways dead space measured by a single-breath C02 technique was no different at 0.19 +/- 0.03 L. An oxygen oscillation of the same period measured the mean end-expired alveolar volume at 3.1 +/- 0.7 L. Adding together the airways dead space and end-expired alveolar volume, obtained by the oxygen oscillation technique, provided a measure of FRC that at 3.3 +/- 0.7 L matched the FRC of 3.3 +/- 0.8 L measured by whole-body plethysmography. A third measure of FRC using a multiple-breath nitrogen washout technique gave a smaller volume of 3.00 +/- 0.85 L. The advantage of using FIO2 oscillations is that accurate FRC measurements can be made continuously, without interfering with the subject's natural breathing rhythm.

Adult↗
PubMed1996

Five-year experience with implantable defibrillators in children.

Cardioverter-defibrillators were implanted in children aged 4 to 16 years over a 5-year period with no mortality and eventual clinically appropriate shocks in 6 of 11 patients. Both transvenous and epicardial implantable cardioverter-defibrillators were safe and effective in children resuscitated from sudden death or at high risk for sudden death.

Adolescent↗
PubMed1996

Clinical spectrum, therapeutic management, and follow-up of ventricular tachycardia in infants and young children.

We reviewed 40 infants and young children with VT. Median maximum VT rate was 214 beats/min (range 152 to 375 beats/min). A cause was defined in 20 (50%), the most common being cardiomyopathy or myocarditis in 8 (20%). There were six deaths (15%) related to VT, three of which occurred at diagnosis and in patients less than 1 week old. In 5 of 6 deaths related to VT, a cause was defined. At follow-up, 31 (91%) of 34 survivors did not have VT. The presence of symptoms was a predictor of death related to VT. The outlook for asymptomatic patients and those who survived more than 6 months after diagnosis and who do not have progressive myocardial disease appears good.

Actuarial Analysis↗
PubMed1996

Long-term outcome of mothers of children with complete congenital heart block.

OBJECTIVES: To determine the health of mothers of offspring with complete congenital heart block (CHB) both at the time of delivery of the affected child and in the long-term, and the percentage of mothers and children with CHB who had anti-SSA/Ro and/or SSB/La antibodies. PATIENTS AND METHODS: Sixty-four mothers of 64 children with CHB (seen between 1964 and 1993) were identified through the Cardiology database of The Hospital for Sick Children, Toronto, Canada. Medical information from these of children with CHB was evaluated. Data were obtained from the mothers by mailed questionnaire, telephone interview, and/or from the attending physicians. The presence of anti-Ro antibodies and anti-La antibodies were evaluated by ELISA assay. RESULTS: The mean age at the time of delivery of the first child with CHB was 28 +/- 6 years. At the time of delivery 42 (66%) mothers were healthy, 2 (3%) had systemic lupus erythematosus (SLE), 2 (3%) had linear scleroderma, 2 (3%) had rheumatoid arthritis; 3 (5%) had a history of rheumatic fever (but were otherwise well), 1 (2%) had Sjogren's syndrome (SS), and 12 (19%) had an undifferentiated autoimmune syndrome (UAS) (arthralgia, myalgia, photosensitivity, skin vasculitis, Raynaud's phenomenon). The mean time to follow-up from deliver to study was 121 +/- 88 months. The mean maternal age at study was 38 +/- 9 years. Three of 12 mothers who initially had a UAS progressed to SLE (average follow-up time of 80 months, median 96), and 2 developed SS (with average follow-up time 140 months, median 132) and 1 went into remission. The mean follow-up time for the other mothers who did not develop an autoimmune disease was 150 +/- 102 months. Thirty-six of the 42 initially healthy mothers remained well. One mother developed SLE; 1 developed hyperthyroidism; 1 developed anky-losing spondylitis; and 3 developed an UAS. The mean follow-up time of the 36 mothers who remained healthy was similar (123 +/- 97 months) to the 6 initial healthy mothers who developed an autoimmune disease (121 +/- 36 months). Anti-Ro and/or anti-La antibodies were positive in 32 of 53 (60%) mothers tested. Fourteen of the 53 mothers were symptomatic at the time of delivery and 39 were asymptomatic. Anti-Ro and/or anti-La antibodies were positive in 12 of 13 mothers tested at the time of delivery. CONCLUSIONS: The long-term maternal outcome in our cohort was very good as most of the initially healthy mothers remained well at follow-up. Twenty-five percent of the mothers with a UAS and only 2% of the initially healthy mothers developed SLE. The development of an autoimmune disease in an asymptomatic mother identified by the birth of a child with CHB was less common in our study than in previous studies. However, close follow-up of mothers with UAS is warranted.

Adult↗
PubMed1996

Normal values for the childhood signal-averaged ECG.

To obtain normative data for the childhood signal-averaged ECG (SAECG), we obtained SAECGs in 155 volunteers, aged 5-15 years, using Frank leads and a Fourier transform filter. Unfiltered QRS duration (QRSDU) and filtered QRS duration (QRSDF) were significantly longer in males, and the root mean square of the terminal 40 ms (RMS40) was significantly higher in females. There were no gender differences in the duration of high frequency low amplitude signals < 40 microV (DHFLA). All SAECG variables were significantly related to body surface area (BSA). Regression models were established for SAECG variables. For males, the predicted mean + 1.96 standard deviations (SD) for QRSDF (97.5th centile) ranged from 114 ms at BSA 0.70 m2 to 123 ms at 1.90 m2. For females, the predicted mean + 1.96 SD for QRSDF ranged from 110 ms at BSA 0.70 m2 to 119 ms at 1.90 m2. For males and females, the predicted mean + 1.96 SD for DHFLA ranged from 34 ms at 0.70 m2 to 38 ms at 1.90 m2. For males, the predicted mean - 1.96 SD (2.5th centile) for RMS40 (based on natural logarithm model) ranged from 30 microV at 0.70 m2 to 15 microV at 1.90 m2. For females, the predicted mean -1.96 SD for RMS40 ranged from 42 microV at 0.70 m2 to 20 microV at 1.90 m2. In children 5-15 years of age, both gender and BSA need to be taken into account when interpreting the SAECG.

Adolescent↗
PubMed1996

Torsade de pointes, acquired complete heart block and inappropriately long QT in childhood.

After spontaneously acquiring complete heart block, two children presented with torsade de pointes as a result of inappropriate prolongation of the QT interval. Although both remain well following pacemaker insertion, their cases illustrate the importance of QT interval assessment in patients with atrioventricular block, and demonstrate that syncopal episodes, and possibly sudden death, in children with acquired heart block can be due to bradycardia-induced ventricular tachyarrhythmias, rather than extreme bradycardia per se.

Child, Preschool↗
PubMed1995

Chaotic atrial rhythm in children.

Chaotic atrial rhythm (CAR) usually occurs as a sequela of chronic obstructive lung disease in adults. We report the clinical manifestations and response to therapy in nine children with CAR treated predominantly with propafenone or amiodarone. Age at presentation ranged from 1 day to 30 months; six patients were < or = 2 weeks old. Six patients had tachycardia, and three had congestive heart failure. The atrial rate was 200 to 500 (mean 369 +/- 71) beats/min and the ventricular rate 150 to 300 (mean 251 +/- 37) beats/min. Eight patients had cardiac abnormalities. Intravenous drug therapy was not successful in converting CAR to sinus rhythm in any patient. A mean of four (range three to five) drugs was used in each patient; amiodarone and propafenone, alone or in combination, proved most successful. Seven patients were discharged from the hospital: full control was achieved in three (digoxin and amiodarone in two and digoxin, amiodarone, and procainamide in one), good control in three (digoxin, amiodarone, and propafenone in two and digoxin and propafenone in one), and ventricular rate control in one (digoxin, amiodarone, and propafenone). Two neonates with hypertrophic cardiomyopathy died. Long-term follow-up showed that CAR had resolved in five patients but persisted in two. We conclude that CAR remains difficult to control despite the use of newer antiarrhythmic agents but may resolve during long-term follow-up.

Amiodarone↗
PubMed1995

Treatment of atrial ectopic tachycardia in infants < 6 months old.

Nineteen infants < 6 months old who had atrial ectopic tachycardia (AET) were treated with antiarrhythmic drugs. AET was controlled with digoxin in 1 patient, propafenone in 2, digoxin with propafenone in 9, digoxin with amiodarone in 4, and digoxin with propafenone and amiodarone in 2; radiofrequency ablation was performed in 1 drug-resistant case. AET resolved in 14 of 15 infants within 1 year. Drug side effects occurred in 5 patients. We conclude that AET in infants < 6 months old can be successfully treated with antiarrhythmic drugs, and we recommend a three-step approach with digoxin, a class 1C antiarrhythmic drug, and a class 3 drug. Resolution of AET in infants is frequent.

Amiodarone↗
PubMed1994

Clinical efficacy and safety of intravenous Amiodarone in infants and children.

The effectiveness and safety of intravenous amiodarone in children are not well established. This study reviewed its use in 30 infants and children for life-threatening tachyarrhythmias: 18 patients (19 episodes) with supraventricular tachycardia, and 12 with ventricular tachycardia. Eighteen patients had structural heart defects with arrhythmias that occurred after surgery. The mean loading dose was 5 mg/kg infused over 1 hour, with a starting maintenance dose of 5 micrograms/kg/min. In 18 treatment episodes, amiodarone was used alone or in combination with digoxin. Thirteen patients received amiodarone combined with other antiarrhythmic agents. Intravenous amiodarone was effective or partially effective in 94% of patients, achieving a therapeutic effect in a median time of 1 day (range 1 hour to 5 days). The mean effective maintenance dose was 9.5 micrograms/kg/min (13.7 mg/kg/day), and median treatment duration was 5 days (range 1 to 30). Adverse effects occurred in 18 patients (58%), however none necessitated termination of amiodarone therapy. Potentially significant electrocardiographic abnormalities occurred in 5 patients during combination antiarrhythmic therapy with propafenone. Sinus bradycardia requiring temporary postoperative pacing occurred in 3 patients treated with amiodarone alone. Intravenous amiodarone used alone or in combination therapy is an effective treatment for resistant, life-threatening arrhythmias in infants and children. Combination drug therapy with propafenone must be used cautiously. Potential bradycardia pacing may be necessary during administration of amiodarone after surgery.

Adolescent↗
PubMed1994

Risk factors for atrial tachyarrhythmias after the Fontan operation.

OBJECTIVES: The purpose of this study was to define the incidence and risk factors for atrial tachyarrhythmias after the Fontan operation. BACKGROUND: Atrial tachyarrhythmias cause morbidity after the Fontan operation. Causative factors may be affected by the type of systemic to pulmonary connection. METHODS: The Fontan operation was performed in 270 consecutive patients between 1982 and 1992. The mean age at operation was 7.0 +/- 4.3 years. Direct atriopulmonary connection was used in 138 patients (51%), total cavopulmonary connection in 94 (35%) and right atrial to right ventricular connection in 38 (14%). RESULTS: Atrial tachyarrhythmias were seen early postoperatively in 55 patients (20%), preoperative atrial tachyarrhythmia being the only risk factor. Follow-up was achieved for 228 early survivors (97%) at a mean interval of 4.4 years. There were 20 late deaths. Late atrial tachyarrhythmias were noted in 29% of patients who received an atriopulmonary connection, 14% of those who received a total cavopulmonary connection and 18% of those who received a right ventricular connection (p < 0.02). Significant risk factors as determined by univariate and multiple logistic regression analysis were atriopulmonary connection type (odds ratio 0.40 for total cavopulmonary relative to atriopulmonary connection [p < 0.05] and 0.37 for right ventricular relative to atriopulmonary connection [p = 0.08]), longer follow-up interval (odds ratio 1.32 for each consecutive year [p < 0.002]) and atrial tachyarrhythmia in the operative period (odds ratio 6.31 [p < 0.0001]). CONCLUSIONS: Early postoperative atrial tachyarrhythmias, length of follow-up and atriopulmonary connection are significant independent risk factors for the presence of late atrial tachyarrhythmias.

Analysis of Variance↗
PubMed1989

Transmission of residues to eggs following long-term administration of 14C-labelled deoxynivalenol to laying hens.

The transmission of radioactive residues of 14C-labelled deoxynivalenol (DON; vomitoxin) to eggs was investigated during prolonged administration of low levels of DON-contaminated feed to White Leghorn chickens. Laying hens were provided with a 5.5 ppm 14C-DON-spiked diet (.55 mg DON; .8.25 microCi bird/day) for a 65-day period, after which they received a clean, unadulterated diet for 21 days. Total residues (based on specific radioactivity) increased daily until the 8th day of 14C-DON exposure, when levels reached a plateau for several days, then decreased slowly thereafter. Maximum radioactivity measured was equivalent to 1.7 micrograms DON or metabolites per 60-g egg; the yolk, albumen, and shell membrane contributed 70, 29, and 1% of the total amount, respectively. By Day 30, levels had declined to 25% of peak levels (.40-micrograms DON equivalents/egg) and remained relatively constant until the spiked feed was removed at Day 65, at which time residues quickly declined to negligible values. These findings indicate that although very low concentrations of DON can be found in eggs under these feeding conditions, levels are so low that a potential health hazard to humans would likely be minimal.

Animal Feed↗
PubMed1987

Body weight, blood pressure, and electrolyte excretion of young adults from six ethnic groups in Hawaii.

There is positive correlation between high dietary intake of sodium and prevalence of hypertensive disease. Dietary potassium shows a negative correlation with this prevalence. Racial background of subjects may affect such relationships. This is a study of the relationships between ethnicity and blood pressure in young adults of six ethnic groups in Hawaii. Body weight, electrolyte excretion, which may reflect intake, and blood pressure of the subjects are reported here. Caucasians and Hawaiians and part-Hawaiian young adults tended to be taller and heavier than the Chinese, Filipinos, Japanese, and Koreans. Both systolic and diastolic pressures were significantly higher in males than in females (all races combined). No significant differences between sexes or races were found in urinary excretion of sodium and potassium or in urinary sodium:potassium ratios. Body weight and Quetelet's Index but not sodium:potassium ratio correlated significantly with diastolic pressure.

Adult↗
PubMed1986

Tissue distribution and excretion of radioactivity following administration of 14C-labeled deoxynivalenol to White Leghorn hens.

The disposition of [14C]deoxynivalenol ([14C]DON) administered to hens as either a single oral dose or consumed in spiked feed over a 6-day period was determined by tracing the specific radioactivity of tissues and excreta. Following a single intubated dose (2.2 mg [14C]DON; 2.4 microCi/bird), the toxin was found to be poorly absorbed; peak plasma levels (2-2.5 hr post-treatment) accounted for less than 1% of the administered dose. Maximum tissue residues were measured at 3 hr in all tissues (liver, kidney, brain, heart, spleen, proventriculus, gizzard, small intestine) except for fat, muscle, and oviduct which occurred at 6 hr postdosing. Among the organs, the highest activities were measured in kidney, liver, and spleen; however, these levels were equal to less than 500 ng DON equivalents/g tissue, and declined quickly. Clearance of radioactivity from tissue had an average half-life of 16.83 +/- 8.2 hr (range 7.7-33.3 hr, depending on the tissue). Elimination of the labeled toxin in excreta occurred rapidly; recovery of radioactivity accounted for 78.6, 92.1, and 98.5% of the dose by 24, 48, and 72 hr, respectively. In continuously dosed birds fed 2.2 mg unlabeled DON for 6 days followed by 2.2 mg (1.5 microCi) [14C]DON for 6 days, accumulation of radioactivity in tissues did not occur. Maximum residual levels, which occurred in the kidneys, were only 60 ng DON equivalents/g. Estimated level of residues contained in the edible tissues amounted to only 13-16 micrograms DON/1.5 kg hen.

Animals↗
PubMed1986

A pneumatic device for attaching wing bands to day-old chicks.

A device for attaching aluminum bands to the wings of day-old chicks is described and illustrated. It is powered with compressed air and utilizes both hand and foot operated controls. Using this device, an operator can apply wing bands without an assistant at rates up to 300 chicks/hour.

Animal Identification Systems↗
PubMed1985

The tolerance of White Leghorn and broiler chicks, and turkey poults to diets that contained deoxynivalenol (vomitoxin)-contaminated wheat.

Three experiments were done to determine the effects of giving White Leghorn chickens, broiler chickens, and turkey poults diets that contained white winter or spring wheat contaminated with 4-deoxynivalenol (DON). Diets that contained .35 and .7 mg DON/kg from winter wheat did not (P greater than .05) influence feed intake, body weight gain, feed/gain ratio, and organ weight/body weight ratios of Leghorn and broiler chickens, and poults when fed between 7 and 21 days in Experiment 1. Dietary DON levels up to 4.6 mg/kg increased the feed intakes (P less than .01) and daily body weight gains (P less than .05) of Leghorn chickens between 7 and 35 days of age in Experiment 2 but had little effect (P greater than .05) on these variables for broiler chickens between 7 and 52 days of age in Experiment 3. Within Experiments 2 and 3, feed/gain ratios and organ weight/body weight ratios were similar among the Leghorn and broiler chickens, respectively. The dressing percent and chilled carcass weights of eviscerated broiler chickens were not affected (P greater than .05) by DON in the diets of Experiment 3. Mortality was low (less than 3.3%) for the three experiments and necropsy examination indicated that the birds died from several causes unrelated to the dietary treatment. There was no evidence of emesis during the experiments or of overt changes in the appearance of the oral cavity, heart, liver, spleen, kidney, proventriculus, gizzard, and intestines of a random sample of birds killed by carbon dioxide asphyxiation and necropsied. Differences occurred between the analyzed and calculated DON contents of the experimental diets; possible reasons for these differences are discussed. The results of these experiments indicate that young chickens and turkey poults can tolerate diets that contain DON up to at least 5 mg/kg from white winter or spring wheat.

Animal Feed↗
PubMed1985

Effects of feeding white Leghorn hens diets that contain deoxynivalenol (vomitoxin)-contaminated wheat.

A short-term (10 weeks, Experiment 1) and a long-term experiment (24 weeks, Experiment 2) were done to determine effects of incorporating either white winter wheat, naturally contaminated with 1 mg deoxynivalenol (DON)/kg, or spring wheats, containing up to 6.5 mg DON/kg, into the diets of White Leghorn hens. Based on chemical analysis, the diets in Experiment 1 contained less than .05 to .7 mg DON/kg, while those in Experiment 2 contained from .2 to 4.9 mg/kg. Incorporation of winter or spring wheat in the experimental diets had no effect (P greater than .05) on feed intake and efficiency, egg production and yield, the number of soft shell and cracked eggs observed in the laying house, body weight at the completion of the experimental period, fertility, hatchability of fertile eggs, and the proportion of malformed embryos and pips. In addition, presence of DON-contaminated wheat did not influence (P greater than .05) the organ weight to body weight ratio for a randomly selected sample of hens necropsied at the completion of each experiment. There was little evidence of lesions in the oral cavity, esophagus, proventriculus and gizzard, hemorrhaging in the viscera or skeletal muscles, or of changes in the appearance of spleen, heart, and kidney. However, the livers from DON hens were fatty in appearance. Furthermore, vomiting (emesis), diarrhea, or changes in behaviour were not apparent and mortality, normally very low, was not increased during either experiment. Inverse linear relationships were obtained in Experiment 1 between dietary DON concentrations and egg weight (P less than .05), shell weight and thickness (P less than .01), and percent shell (P less than .05). Although egg and shell variables measured in Experiment 2 were not significantly influenced (P greater than .05) by DON treatment, trends towards lower values with higher dietary DON levels were evident. Egg specific gravity, nondestructive deformation, and quasistatic compression fracture strength of the egg's shell were not influenced (P greater than .05) by dietary DON levels. The results from these experiments indicate that laying hens can tolerate diets containing up to 5 mg DON/kg from white winter or spring wheat for extended periods of time without serious adverse effects on health and productivity.

Animal Feed↗