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Biomedical subjects

K Hamilton

Publications and source records attributed to K Hamilton.

At least 73 records · Page 4Linked to original sources
PubMed1991

Transesophageal echocardiographic evaluation for mural thrombus following radiofrequency catheter ablation of accessory pathways.

BACKGROUND: Catheter ablation of accessory pathways (APs) provides a definitive therapy for patients with Wolff-Parkinson-White Syndrome. The reported incidence of thrombus formation on ablation-induced injuries with direct current shock varies from 0%-20% in animal studies. The purpose of this study was to determine the prevalence of mural thrombus following catheter ablation with radiofrequency current of accessory pathways in humans. METHODS AND RESULTS: Radiofrequency current (30-35 watts) was applied through a catheter electrode placed against the mitral or tricuspid annulus guided by catheter recordings of AP potentials. Transthoracic (TTE) and transesophageal echocardiography (TEE) were performed in 95 of 111 patients, at 18 +/- 6 hours following catheter ablation. After ablation, no thrombus was identified at or near the ablation site in any patient. Two out of 95 patients had a mural thrombus at a remote site that was detected by TEE but not by TTE. No new wall motion abnormality was detected in any patient. No significant regurgitant valvular lesion was found in any patient. CONCLUSION: Intracardiac thrombus was not identified at the site of catheter ablation, possibly owing to the small lesions produced by radiofrequency energy and high blood flow normally present in those areas. However, patients may be at small risk for mural thrombus at a remote site from prolonged placement of catheters.

Adult↗
PubMed1989

The effects of hyperbaric air in combination with ethyl alcohol and dextroamphetamine on serial choice-reaction time.

The effects of ethyl alcohol (1.5 ml/kg body weight) and dextroamphetamine (15 mg) on nitrogen narcosis were investigated in two experiments using a 2-, 3- and 4-choice serial reaction time (RT) task with accuracy held constant. Narcosis was induced with air at 6.4 atmospheres absolute (ATA) and a heliox mixture was used as a control. Heliox at 6.4 ATA did not affect RT. Alcohol alone and air at 6.4 ATA increased the intercept of the Hick-Hyman function whereas amphetamine alone decreased it. The increased intercept with air at 6.4 ATA was exacerbated additively by alcohol and ameliorated antagonistically by amphetamine. The slope of the Hick-Hyman function was unaffected. Frequency distributions were shifted as a whole and their shapes were unaltered. It is concluded that these data are consistent with the slowed processing model which proposes that the effects of narcosis on performance are due to a decrease in arousal in conjunction with secondary changes in task strategy.

Adult↗
PubMed1989

Nitrogen narcosis and ethyl alcohol increase the gain of the vestibular ocular reflex.

The effects of air, helium-oxygen (6.4 ATA), and ethyl alcohol (40% by volume at a dose of 1.5 ml/kg body weight) were examined on the gain, number of beats, and phase lag of the vestibular ocular reflex (VOR) by means of electronystagmography (n = 7). It was found that hyperbaric air and alcohol, both alone and in combination, produced approximately the same increase in the velocity of the slow phase component of the nystagmus, thereby elevating the gain of the system to unity. Hyperbaric helium-oxygen did not influence the gain. These findings suggest that nitrogen nacrosis differentially impairs the system controlling the VOR. It is proposed that this impairment may help to explain the disorientation sometimes associated with nitrogen narcosis.

Adult↗
PubMed1987

Function of the Y optic nerve fibres in the cat: do they contribute to acuity and ability to discriminate fast motion?

1. A controlled pressure block has been applied to the optic nerve of the cat, sufficient to bring about degeneration of the axons of the large (Y) nerve fibres caudal to the block site. This degeneration has been monitored by means of implanted electrodes in optic nerve and tract which have shown a loss of the short-latency (t1) response 4-6 days after the block, and also by histological examination of the optic nerve. 2. Cats with one optic nerve blocked in this way have been used in behavioural experiments, one or other eye being covered during the tests. Tested via the blocked nerve, all cats with loss of only Y fibres could perform certain tests: the visual placing reaction, the blink reflex, the pupillary (light) reflex and simple manoeuvres such as walking a plank and jumping from table to floor. 3. When acuity was tested by means of the Mitchell jumping apparatus, cats with loss of only Y fibres showed the same acuity using either eye. This was true also of one cat in which many X fibres had also degenerated, as evidenced by a 55% loss of the medium-latency (t2) response, but in another cat with 90% loss of the t2 response acuity was reduced to about half-normal. 4. Ability to discriminate fast motion was tested by a modification of the Mitchell apparatus. All cats were able to discriminate the motion of an 11.5 deg spot up to a velocity of 6260 deg/s, whether using their normal eye or their affected eye. However, the loss of the Y fibres reduced the ability to discriminate fast motion, so that for any given level of contrast the velocity which could be discriminated was about two-thirds of the velocity discriminated using the normal eye. The ability of the cat to discriminate fast motion seems to be similar to that of the human. 5. These results suggest that there is no sharp restriction of function between the Y and X systems but instead considerable overlap. However, each system possesses specialized features giving it superiority in certain conditions.

Animals↗
PubMed1986

Physiologic changes induced by endotracheal instillation and suctioning in critically ill preterm infants with and without sedation.

Endotracheal instillation and subsequent suctioning produces fluctuations of intracranial pressure (ICP), mean arterial pressure (MAP), and cerebral perfusion pressure (CPP) in sick preterm infants. In an attempt to observe if these fluctuations could be minimized using sedation, we studied a group of seven sick mechanically ventilated preterm infants with and without sedation. Continuous monitoring of ICP, MAP, heart rate, CPP, and arterial oxygen tension (PaO2) were obtained. The statistical analysis of the data revealed significant blunting of fluctuations of MAP, ICP, and CPP with sedation.

Blood Pressure↗
PubMed1986

Effects of ethanol and amphetamine on inert gas narcosis in humans.

The effects of ethyl alcohol (1 ml/kg body weight), dextroamphetamine (15 mg), and nitrous oxide (20%) on reaction time were investigated in 6 subjects with a 2-, 3-, and 4-choice serial reaction time task. Each drug was assessed separately and in combination with nitrous oxide. The error rate was held constant. Neither ethanol and nitrous oxide nor amphetamine and nitrous oxide influenced the slope of the Hick-Hyman function, but the former combination increased the intercept while the latter decreased it. The drugs, either alone or in combination, shifted the frequency distributions of the reaction times as a whole, rather than modifying either their shapes or the pattern of the response latencies around an error. These results indicate that the drugs have a common pattern of effects on reaction time and that alcohol exacerbates narcosis while amphetamine ameliorates it. This is interpreted as support for the view that narcosis causes a nonspecific slowing of information processing by decreasing arousal.

Adult↗
PubMed1986

Effects of inert gas narcosis on the vestibular ocular reflex.

A study was conducted to examine the vestibular ocular reflex (VOR) during narcosis. The slow phase velocity of the nystagmus was measured in six subjects by means of electronystagmography during the inhalation of 25% nitrous oxide. It was found that nitrous oxide increased the velocity of the slow phase component of the VOR by approximately 50%. This result indicates that the gain of the VOR is effectively increased during nitrous oxide induced narcosis. It appears that the vestibular end organs and/or the central pathways controlling nystagmus are affected by nitrous oxide and this may be a reason for the disruption in balance associated with inert gas narcosis.

Adult↗
PubMed1985

Ultrasound diagnosis of pseudoaneurysm and contiguous ventricular septal defect complicating inferior myocardial infarction.

Two patients with recent inferior myocardial infarction were found by two-dimensional and Doppler echocardiography to have both an inferior wall pseudoaneurysm and a contiguous rupture of the posterior ventricular septum. The pseudoaneurysm was not suspected clinically in either patient. In one patient, a complex or dissecting septal rupture was visualized in detail. To our knowledge, the combined defect has not previously been diagnosed during life by noninvasive methods.

Aged↗
PubMed1984

The use of left ventricular end-ejection pressure and peak pressure in the estimation of the end-systolic pressure-volume relationship.

The end-systolic pressure-volume relationship (ESPVR) as derived from left ventricular pressure-volume loops has gained increasing acceptance as an index of ventricular contractile function. In animal experiments the ESPVR has been defined as a line connecting the upper left corners of several differently loaded pressure-volume (P-V) loops with a slope parameter Ees and a volume axis intercept parameter Vo. In the clinical setting, several variants of the ESPVR have been determined with use of peak left ventricular pressure, end-ejection pressure, and end-ejection volume. The maximum P-V ratio has also frequently been measured. We attempted to determine which of these alternatives resulted in good approximations of the reference ESPVR in eight isolated canine ventricles that ejected into a simulated arterial impedance system with resistance, compliance, and characteristic impedance. We determined various versions of the ESPVR from the same set of beats quickly obtained with little change in inotropic background. To vary ventricular pressure wave forms, each of the arterial impedance parameters was independently controlled at 50%, 100%, and 200% of normal. Against each of the nine combinations of the impedance parameters four P-V loops were obtained under four preloads and from each of the sets of four P-V loops, the reference ESPVR, linear regression of the peak pressure on end-ejection volume (ESPVRPP-EEV), and linear regression of end-ejection pressure on end-ejection volume (ESPVREEPV) were determined. In addition, the maximum P-V ratio (MPVR) was calculated for each P-V loop.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Synthesis of prostanoids with bicyclo[2.2.1]heptane, bicyclo[3.1.1]heptane, and bicyclo[2.2.2]octane ring systems. Activities of 15-hydroxy epimers on human platelets.

A number of prostanoids with bicyclo[2.2.1]heptane, bicyclo[3.1.1]heptane, and bicyclo[2.2.2]octane ring systems have been prepared by routes which allow the introduction of the omega chain after the alpha chain. The introduction of a 16-p-halophenoxy substituent confers platelet aggregation activity on both 15 alpha- and 15 beta-hydroxy epimers. In the case of the pinane thromboxane ring system, the natural omega-chain compound is an inhibitor of aggregation, whereas the 16-p-fluorophenoxy analogue is a potent aggregation agent.

Bridged Bicyclo Compounds↗
PubMed1978

Treatment of obesity: cost-benefit assessment of behavioral therapy, placebo, and two anorectic drugs.

Mazindol, diethylpropion, and a placebo were compared with behavioral therapy for effectiveness in producing weight reduction in an outpatient obesity clinic. Each method was also compared in cost and harmful side effects. The patients were recruited from the middle and lower socioeconomic groups. Of the 120 patients beginning treatment, only 33 completed the entire 14-week study. There was no statistically significant difference in the weight loss among the treatment groups. The program of behavioral therapy was administered by a dietitian who as experienced in the techniques of behavior modification; the drug treatment groups were seen by physicians. We conclude that behavioral therapy may be the treatment of choice in an outpatient obese population since it requires little physician time, is less expensive, and avoids the side effects of anorectic drugs.

Appetite Depressants↗
PubMed1977

Treatment of obesity: comparison of physician and nonphysician therapists using placebo and anorectic drugs in a double-blind trial.

In a randomized double-blind trial, 60 obese patients were assigned in groups of 12 to five therapists. The patients for each therapist were then randomly assigned in groups of four to placebo or one of two preparations of mazindol. Ninety-three percent of the patients completed the nine weeks of treatment. Weight loss averaged 1.1 lb per week and there was no advantage to pharmacological agents over placebo. However, there were significant differences between therapists. Weight loss by the patients assigned to physicians was no better than for those assigned to nonphysician personnel, but there were significant differences between individual nonphysician personnel. These findings support the concept that nonphysician personnel may be effective in treating many obese patients. In addition, we could not find a significant effect of either form of mazindol when compared to placebo.

Adolescent↗
PubMed1977

Predictors of successful weight loss in an outpatient obesity clinic.

Patients attending weight reduction clinics were tested at the beginning of the program to assess a variety of background variables which might influence successful weight loss. These included measures of self-esteem, social acceptance, locus of control, responsiveness to external stimuli, attitudes toward weight loss, and knowledge about nutrition. Success was related to social conformity and desire for social acceptance but not to self esteem or locus of control. Individuals who believed that poor eating habits caused their obesity and those who were less responsive to environmental cues which may trigger feeding, were also more successful.

Adolescent↗