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Biomedical subjects

C A Fuller

Publications and source records attributed to C A Fuller.

At least 55 records · Page 3Linked to original sources
PubMed1994

Group B streptococcal disease: a life-threatening infection in the newborn.

Group B streptococcal (GBS) disease, a life-threatening infection in newborns in the United States, causes considerable neonatal morbidity and mortality. GBS is also a major source of maternal infection. Screening during pregnancy leads to early identification. Intrapartal treatment of affected mothers can prevent harmful neonatal effects. Implementation of screening and treatment protocols is recommended for the protection of all obstetric and neonatal patients.

Clinical Protocols↗
PubMed1994

Changes in hypothalamic [correction of hypothalmic] staining for c-Fos following 2G exposure in rats.

The static gravitational field of the earth has been an important selective pressure that has shaped the evolution of biological organisms. This is illustrated by the evolution of tetrapods from a water environment where gravitational force was partially negated to a terrestrial environment where gravity is of greater consequence. Terrestrial invasion resulted in a series of new structural, physiological, and behavioral features. Therefore, it is not surprising that alterations in the gravitational field can cause widespread effects in many physiological systems and behaviors. Our previous studies have demonstrated that both exposure to hyperdynamic fields and the microgravity condition of space flight have significant effects on body temperature, heartrate, activity, feeding, drinking, and circadian rhythms. However, it has not been determined whether these physiological adaptations are associated with changes in neural activity within the hypothalamic nuclei that regulate these functions. This study examined the changes in body temperature, activity, body weight and food and water intake in rats caused by exposure to a hyperdynamic field. In addition, the immediate early gene activation marker, c-Fos, was used to examine potential protein synthesis changes in the hypothalamic nuclei that regulate these functions.

Animals↗
PubMed1993

Circadian rhythms of thermoregulation in the squirrel monkey (Saimiri sciureus).

Phase or amplitude differences between rhythms in heat production (HP) and heat loss (HL) have been suggested to account for the circadian rhythm in body temperature (Tb). To describe the relationships among these rhythms in a primate, five unrestrained squirrel monkeys (1.0-1.3 kg) were studied using combined direct and indirect calorimetry, with telemetry of Tb and activity, in a 24-h light-dark cycle (LD 12:12) at 25 +/- 0.5 degrees C. Dry (D; sensible) HL, evaporative (E) HL, HP (oxygen consumption and CO2 production), Tb, and activity were measured at 10-min intervals for a week. Tb, activity, HP, and HL displayed daily rhythms, peaking during the light period. Although the timing of peaks was not significantly different, the diurnal increase in Tb was seen to result from a delayed increase in DHL, and possibly, EHL, relative to increased HP. The nocturnal decrease in Tb was due to different time courses of decrease in HP and HL, with no clear lag in HL. The rhythm in Tb therefore resulted from both phase and time course differences in HP and HL rhythms.

Animals↗
PubMed1993

The regulation of rat activity following exposure to hyperdynamic fields.

The microgravity of spaceflight and the hyperdynamic fields produced via centrifugation have allowed researchers to examine the effect of altered gravitational environments on the regulation of physiological systems. In previous studies, we have discussed the importance of homeostatic and circadian mechanisms for the regulation of physiological systems such as body temperature and heart rate. Rats exposed to a chronic 2G field exhibited lower mean daily body temperature and heart rate. The homeostatic component of regulation for body temperature and heart rate adapts to a new steady state after 5-6 days. However, the circadian rhythm of body temperature and heart rate became severely depressed and did not recover for approximately 7-10 days. The measurements of body temperature and heart rate suggest an adaptation of homeostatic and circadian regulatory mechanisms following 10 days exposure to 2G. However, an important function of physiological homeostasis is to respond to environmental stressors. An important question thus becomes whether the regulation of body temperature and heart rate has sufficiently recovered to respond to an environmental challenge separate from that of the hyperdynamic field. In this study, a high frequency light/dark cycle (LD 3:3) was provided for 24 hours as an environmental challenge to assess the recovery of homeostatic and circadian regulation. Previous studies have demonstrated that high frequency light dark cycles are highly effective for testing homeostatic and circadian components of physiological regulation in monkeys and rats. For example, the nocturnal rat exhibited a homeostatic increase in body temperature during the dark periods and a decrease during the light periods. In addition, the magnitude of the body temperature response exhibits a time of day variation demonstrating the effect on circadian regulation.

Animals↗
PubMed1993

Effect of SCN lesions on sleep in squirrel monkeys: evidence for opponent processes in sleep-wake regulation.

Sleep and wakefulness are governed by both the suprachiasmatic nuclei of the hypothalamus (SCN), and a sleep homeostatic process; however, the interaction of these control systems is not well understood. From rodent studies it has been assumed that the SCN promote neither wake nor sleep but gate the homeostatic sleep-promoting process. Yet in humans sleep tendency is lowest during the later waking hours of the day, and sleep duration can be predicted because of the precise circadian timing of waking. Thus in primates, the SCN could assure sleep-wake cycle consolidation by actively promoting or facilitating wakefulness. To evaluate this hypothesis, we examined the sleep-wake and sleep-stage patterns of intact and SCN-lesioned (SCNx) squirrel monkeys maintained in constant light. This diurnal primate has consolidated sleep and wake patterns more similar to man than rodents. Sleep-wake, sleep stages, brain temperature, and drinking circadian rhythms were eliminated, and total sleep time was significantly increased (4.0 hr, P < 0.01) in SCNx monkeys. However, total times in deeper stages of non-rapid eye movement (non-REM; e.g., delta sleep) and REM sleep were not significantly affected by SCN lesions. Increased total sleep time was associated with a reduction in subjective day wake consolidation, as evidenced by substantially shorter wake bout lengths in SCNx monkeys (15 +/- 6 min) as compared to intact monkeys (223 +/- 10 min; P < 0.0001, ANOVA). These findings show that the SCN influence the regulation of daily total wake and sleep times, and implicate an alternative sleep-wake regulatory model in which an SCN-dependent process actively facilitates the initiation and maintenance of wakefulness and opposes homeostatic sleep tendency during the subjective day in diurnal primates.

Analysis of Variance↗
PubMed1992

Thermoregulatory responses of rhesus monkeys during spaceflight.

This study examines the activity, axillary temperature (T(ax)), and ankle skin temperature (Tsk) of two male Rhesus monkeys exposed to microgravity in space. The animals were flown on a Soviet biosatellite mission (COSMOS 1514). Measurements on the flight animals, as well as synchronous flight controls, were performed in the Soviet Union. Additional control studies were performed in the United States to examine the possible role of metabolic heat production in the T(ax) response observed during the spaceflight. All monkeys were exposed to a 24-h light-dark cycle (LD 16:8) throughout these studies. During weightlessness, T(ax) in both flight animals was lower than on earth. The largest difference (0.75 degree C) occurred during the night. There was a reduction in mean heart rate and Tsk during flight. This suggests a reduction in both heat loss and metabolic rate during spaceflight. Although the circadian rhythms in all variables were present during flight, some differences were noted. For example, the amplitude of the rhythms in Tsk and activity were attenuated. Furthermore, the T(ax) and activity rhythms did not have precise 24.0 hour periods and may have been externally desynchronized from the 24-h LD cycle. These data suggest a weakening of the coupling between the internal circadian pacemaker and the external LD synchronizer.

Animals↗
PubMed1992

Conservative surgery of the mitral valve: a report of the first 100 cases from one unit and one surgeon.

OBJECTIVE: To report the first 100 mitral valve repairs performed in a unit with an aggressive approach to conservative mitral valve surgery. DESIGN: Case notes were reviewed retrospectively and patients invited for clinical examination and cross sectional and Doppler echocardiography. SETTING: Tertiary cardiothoracic referral centre. PATIENTS: Between December 1985 and April 1991 mitral valve repair was carried out on 100 patients (66 males). Patients with pure mitral stenosis were excluded. Sixty seven had degenerative and 15 rheumatic mitral valve disease. Median age was 66 (range 12 to 79) years, with an interquartile range of 59 to 71 years. INTERVENTIONS: Operative procedures included annuloplasty ring in 97, resection of the posterior leaflet in 67, resection of endocarditic portion of posterior leaflet in four, commissurotomy in six, and correction of anterior leaflet abnormalities in seven. Thirty nine concomitant cardiac procedures were performed in 32 patients. Six operations were emergencies, and three of these required concomitant procedures. MAIN OUTCOME MEASURES: Mortality, operative failure rate, patients' functional state and degree of residual mitral regurgitation, incidence of thromboembolism, and endocarditis. RESULTS: Follow up ranged from one to 59 months, median 14 months, and an interquartile range of four to 23.5 months. Early mortality was 1%, late mortality 5%, and there was a 2% reoperation rate. Eighty four patients had moderate to severe mitral regurgitation preoperatively. At follow up mitral regurgitation was absent or mild in 78. Eighty six patients were in New York Heart Association (NYHA) class I-II at follow up compared with 80 in NYHA class III-IV preoperatively. There were no thromboembolic events. CONCLUSION: This study shows that satisfactory results can be obtained with mitral valve repair in a fairly elderly population with a high incidence of concomitant cardiac disorders. We suggest that these encouraging results will lead to earlier mitral valve repair in mitral regurgitation.

Adolescent↗
PubMed1992

Isoperiodic neuronal activity in suprachiasmatic nucleus of the rat.

A subpopulation of neurons in the suprachiasmatic nucleus (SCN) is shown here to exhibit isoperiodic bursting activity. The period of discharge in these cells may be lengthened or the periodicity may be transiently disrupted by photic stimulation. It is suggested that many, if not all, of these cells are vasoactive intestinal polypeptide (VIP) neurons. It is shown that the ultradian periodicity of these cells, estimates of the VIP neuron population size in the SCN, effects of partial lesions on tau (period), and estimates of the phase stability of SCN-driven circadian rhythms are consistent with a strongly coupled, multioscillator model of circadian rhythmicity, in which the oscillator population constitutes a restricted subset of the SCN neuronal population.

Animals↗
PubMed1992

Hemodynamic evaluation of the Monostrut and spherical disc Björk-Shiley aortic valve prosthesis with Doppler echocardiography.

A Doppler echocardiographic study was performed to assess whether the Monostrut model of the Björk-Shiley valve (Shiley, Inc., Irvine, Calif.) had an improved hemodynamic performance in comparison with the spherical disc model in the aortic position. Twenty retrospectively randomly selected patients were studied, 10 with each valve type. Within each valve type two sizes of valve were studied, 21 and 23 mm. The two groups were comparable with respect to age, postoperative time, fractional shortening, New York Heart Association functional class preoperatively, and body surface area. Pulsed and continuous wave Doppler measurements were recorded at rest. Continuous wave Doppler recordings were performed every 2 minutes after exercise with supine bicycle ergometry until 10 minutes after exercise. Peak and mean gradients across the aortic valve prostheses were estimated. Both groups achieved a significant and comparable rise in heart rate with exercise. The mean gradients +/- standard error of the mean at rest and 2 minutes after exercise were 19.7 +/- 1.9 mm Hg and 30.9 +/- 2.2 mm Hg, respectively in the spherical disc group compared with 14.9 +/- 1.1 mm Hg and 23.6 +/- 1.7 mm Hg in the Monostrut group (p < 0.05 and p < 0.025, respectively). Peak transvalvular gradient at rest was 30.7 +/- 2.7 mm Hg in the spherical group compared with 23.9 +/- 1.9 mm Hg in the Monostrut group (p < 0.05). We conclude that the Monostrut Björk-Shiley valve prosthesis has better hemodynamic performance than the spherical disc model in the aortic position.

Aortic Valve↗
PubMed1991

Histopathological validation of high frequency epicardial echocardiography of the coronary arteries in vitro.

The accuracy and reliability of measurement of coronary artery dimensions and detection of atherosclerotic lesions by high frequency epicardial echocardiography were compared with histopathological results. Ten pressure perfused human hearts were examined in vitro with a 10 MHz (Diasonics) transducer and a 7.5 MHz (Vingmed/Sonotron) transducer. There was close agreement between ultrasound and pathological measurements of coronary artery luminal diameter. Qualitative changes in wall structure such as diffuse wall thickening and calcification were readily identified; however, the resolution of the transducers was not high enough accurately to measure wall dimensions in normal coronary arteries. Coefficient of variation measurements for intra and inter observer variability (5.2% and 6.9% respectively) showed excellent reproducibility. The technique was accurate in identifying atherosclerotic lesions, imaging arteries distal to an occlusion, locating deeply sited arteries, and identifying complete obliteration of an artery. Intraoperative video playback and transducer miniaturisation may minimise problems caused by cardiac movement and restricted access. With these developments intraoperative assessment of coronary artery disease may become a real possibility.

Coronary Artery Disease↗
PubMed1991

Diurnal responses of mammals to acute exposure to a hyperdynamic environment.

Acute exposure to hyperdynamic environments elicits significant depressions in core temperature in both diurnal squirrel monkeys and nocturnal rats. This study describes time of day variations in core temperature responses in squirrel monkeys and rats exposed for 70 min to a hyperdynamic environment (2 g) produced via centrifugation. Experiments were performed during the middle of the light or dark phase. After a 70-min control period, squirrel monkey resting core temperature was 38.6 +/- 0.2 (SE) and 36.8 +/- 0.2 degrees C during the day and night, respectively. At the end of a 7-min exposure to 2 g, squirrel monkey core temperature decreased 1.3 +/- 0.2 degree C during the day but remained a constant 36.8 +/- 0.4 degrees C at night. Core temperature of rats exposed to an identical 70-min 2 g profile decreased 1.5 +/- 0.4 degree C from a resting 37.1 +/- 0.6 degrees C during the day and 2.3 +/- 0.2 degrees C from a resting 37.8 +/- 0.3 degrees C at night. Thus, in both species, there were clear day-night differences in response to hyperdynamic environments, with the greatest fall in core temperature occurring during the animal's active period.

Adipose Tissue, Brown↗
PubMed1990

The response of suprachiasmatic neurons of the rat hypothalamus to photic and serotonergic stimulation.

Single-unit activity of the rat suprachiasmatic nucleus and surrounding regions was recorded in vivo. Photically responsive neurons were typically inhibited by low intravenous doses of the serotonin (5-HT) agonist quipazine. The 5-HT antagonist, metergoline, administered in a low intravenous dose, reversed the effects of quipazine. The subsequent response to photic stimulation was essentially identical to the initial photic response. Thus the photic response of neurons in the suprachiasmatic nucleus (SCN) and adjacent regions is relatively uninfluenced by 5-HT blockade.

Action Potentials↗
PubMed1990

Light suppression of melatonin in the squirrel monkey (Saimiri sciureus).

This study examined plasma melatonin levels and the suppressant effect of light on melatonin production in the squirrel monkey. Monkeys were maintained on a 12:12 light-dark cycle (LD 12:12) with lights on from 07:00 to 19:00. Plasma levels of melatonin were determined by gas chromatography negative chemical ionization mass spectrometry. Melatonin levels at 00:00 (99.5 +/- 18.9 pg/ml) were significantly higher than at 02:00 (57.21 +/- 7.7 pg/ml; Student's t = 2.859; P less than or equal to 0.021). Baseline values at 02:00 were compared with levels at the same time of day after exposure to 2 hours of 200 lux of light (30.6 +/- 13.1 pg/ml), which caused an average suppression of 54.8% in melatonin levels. One animal did not show light suppression. Results indicated that the squirrel monkey suppressant response to light, as well as baseline values of melatonin, varied between animals.

Animals↗