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G R Nadzam

Publications and source records attributed to G R Nadzam.

13 recordsLinked to original sources
PubMed2000

Vasopressin deficiency provides evidence for separate circadian oscillators of activity and temperature.

Vasopressin-containing Long-Evans and vasopressin-deficient Brattleboro rats were maintained in individual cages while telemetered activity (AC) and body temperature (BT) data were collected. Rats were initially exposed to a 12 h/12-h light/dark cycle (photic zeitgeber) and were allowed ad-libitum access to food and water. Daily feeding, care, and handling (nonphotic zeitgebers) occurred at the beginning of the second hour of the dark cycle. After a 14-day habituation period, rats were subjected to continuous light (LL) or dark (DD) and nonphotic cues were presented irregularly. During the habituation period, both strains exhibited clear 24-h circadian rhythms of AC and BT. In LL or DD, photic cues were removed and nonphotic cues were presented irregularly. There was a shift in the rhythm for Long-Evans animals to 26 h for both AC and BT in LL and 24.6 h in DD. Feeding, care, and handling were seen as minor artifact. In Brattleboro rats, although there were robust 26-h and 24.6-h circadian rhythms of AC in the LL and DD, respectively, BT data were inconsistent and showed sporadic fluctuations. In the BT rhythm of Brattleboro animals, strong peaks were associated with feeding, care, and handling times and trough periods were characterized by a dramatic drop in temperature. This experiment demonstrates that AC and BT are controlled by separate oscillators. In addition, the importance of vasopressinergic fibers in the control of circadian rhythms of BT is evidenced by the loss of circadian rhythms in animals lacking these functional fibers when exposed to free-running paradigms where there is no entrainment of photic or nonphotic oscillators.

Animals↗
PubMed1999

Higher energy synchronized external direct current cardioversion for refractory atrial fibrillation.

OBJECTIVES: We sought to evaluate the safety and efficacy of higher energy synchronized cardioversion in patients with atrial fibrillation refractory to standard energy direct current (DC) cardioversion. BACKGROUND: Standard external electrical cardioversion fails to restore sinus rhythm in 5% to 30% of patients with atrial fibrillation. METHODS: Patients with atrial fibrillation who failed to achieve sinus rhythm after at least two attempts at standard external cardioversion with 360 J were included in the study. Two external defibrillators, each connected to its own pair of R-2 patches in the anteroposterior position, were used to deliver a synchronized total of 720 J. RESULTS: Fifty-five patients underwent cardioversion with 720 J. Mean weight was 117 +/- 23 kg (body mass index 48.3 +/- 4.1 kg/m2). Structural heart disease was present in 76% of patients. Mean left ventricular ejection fraction was 45 +/- 12%. Atrial fibrillation was present for over three months in 55% of the patients. Sinus rhythm was achieved in 46 (84%) of the 55 patients. No major complications were observed. No patient developed hemodynamic compromise and no documented cerebrovascular accident occurred within one month after cardioversion. Of the 46 successful cardioversions, 18 patients (39%) remained in sinus rhythm over a mean follow-up of 2.1 months. CONCLUSIONS: External higher energy cardioversion is effective in restoring sinus rhythm in patients with atrial fibrillation refractory to standard energy DC cardioversion. This method is safe and does not result in clinical evidence of myocardial impairment. It may be a useful alternative to internal cardioversion because it could be done within the same setting of the failed standard cardioversion and obviates the need to withhold protective anticoagulation for internal cardioversion.

Adult↗
PubMed1998

The role of vasopressin in modulating circadian rhythm responses to phase shifts.

Telemetered body temperature (BT), heart rate (HR), and motor activity (AC) data were collected in vasopressin-containing, Long-Evans (LE) and vasopressin-deficient, Brattleboro (DI) rats. In Experiment 1, the rats were initially exposed to a 12 h/12 h light/dark cycle under ad-libitum feeding and were then subjected to either a phase-advance or phase-delay shift of 6 h. After the phase-advance shift, neither strain adapted; however, after the phase-delay shift, both strains adapted rapidly. In Experiment 2, the animals were subjected to either a nocturnal or a diurnal restricted-feeding paradigm and were then exposed to either a phase-advance or phase-delay shift with synchronized feeding. In the nocturnal restricted-feeding paradigms, both strains rapidly adapted to both shifts. Concerning diurnal restricted-feeding, DI animals readily entrained to the presentation of food in both shifts; whereas, LE animals exhibited a confused rhythmicity. In Experiment 3, animals were subjected to a phase-advance shift, while the time of feeding was held constant. Following the shift, LE animals responded to the onset of the dark at the new time; yet, were still influenced by the presentation of food. The DI animals maintained the preshift circadian pattern and continued to be dominated by the presentation of food. These experiments indicate that circadian rhythms of LE animals are dominated by the light entrainable oscillator (LEO) in ad-libitum feeding and by both the LEO and food entrainable oscillator (FEO) in restricted-feeding. On the other hand, the circadian rhythms of DI animals are dominated by the FEO unless food is provided ad-libitum. The demonstrated role of vasopressin in synchronizing circadian rhythms to the LEO may be of significance in understanding human circadian rhythm disturbances, such as jet lag.

Animals↗
PubMed1997

Effects of polarity on defibrillation thresholds using a biphasic waveform in a hot can electrode system.

The polarity of a monophasic and biphasic shocks have been reported to influence DFTs in some studies. The purpose of this study was to evaluate the effect of the first phase polarity on the DFT of a biphasic shock utilizing a nonthoracotomy "hot can" electrode configuration which had a 90-microF capacitance. We tested the hypothesis that anodal first phase was more effective than cathodal ones for defibrillation using biphasic shocks in ten anesthetized pigs weighing 38.9 +/- 3.9 kg. The lead system consisted of a right ventricular catheter electrode with a surface area of 2.7 cm2 and a left pectoral "hot can" electrode with 92.9 cm2 surface area. DFT was determined using a repeated "down-up" technique. A shock was tested 10 seconds after initiation of ventricular fibrillation. The mean delivered energy at DFT was 11.2 +/- 1.7 J when using the right ventricular apex electrode as the cathode and 11.3 +/- 1.2 J (P = NS) when using it as the anode. The peak voltage at DFT was also not significantly different (529.0 +/- 41.3 and 531.8 +/- 28.6 V, respectively). We concluded that the first phase polarity of a biphasic shock used with a nonthroracotomy "hot can" electrode configuration did not affect DFT.

Animals↗
PubMed1996

Large change in voltage at phase reversal improves biphasic defibrillation thresholds. Parallel-series mode switching.

BACKGROUND: Multiple factors contribute to an improved defibrillation threshold of biphasic shocks. The leading-edge voltage of the second phase may be an important factor in reducing the defibrillation threshold. METHODS AND RESULTS: We tested two experimental biphasic waveforms with large voltage changes at phase reversal. The phase 2 leading-edge voltage was twice the phase 1 trailing-edge voltage. This large voltage change was achieved by switching two capacitors from parallel to series mode at phase reversal. Two capacitors were tested (60/15 microfarads [microF] and 90/22.5 microF) and compared with two control biphasic waveforms for which the phase 1 trailing-edge voltage equaled the phase 2 leading-edge voltage. The control waveforms were incorporated into clinical (135/135 microF) or investigational devices (90/90 microF). Defibrillation threshold parameters were evaluated in eight anesthetized pigs by use of a nonthoracotomy transvenous lead to a can electrode system. The stored energy at the defibrillation threshold (ion joules) was 8.2 +/- 1.5 for 60/15 microF (P < .01 versus 135/135 microF and 90/90 microF), 8.8 +/- 2.4 for 90/22.5 microF (P < .01 versus 135/135 microF and 90/90 microF), 12.5 +/- 3.4 for 135/135 microF, and 12.6 +/- 2.6 for 90/90 microF. CONCLUSIONS: The biphasic waveform with large voltage changes at phase reversal caused by parallel-series mode switching appeared to improve the ventricular defibrillation threshold in a pig model compared with a currently available biphasic waveform. The 60/15-microF capacitor performed as well as the 90/ 22.5-microF capacitor in the experimental waveform. Thus, smaller capacitors may allow reduction in device size without sacrificing defibrillation threshold energy requirements.

Animals↗
PubMed1996

The interaction of vasopressin and the photic oscillator in circadian rhythms.

Telemetered body temperature (BT), heart rate (HR), and activity (AC) data were collected in vasopressin-containing Long-Evans (LE) and vasopressin-deficient Brattleboro (DI) rats. The rats were exposed to a 12/12 h light/dark cycle under three conditions: 1) ad lib feeding throughout the 24-h cycle, 2) two scheduled-feeding periods during the diurnal component of the light/dark cycle, and 3) two scheduled-feeding periods during the nocturnal component of the light/dark cycle. With ad lib feeding, natural nocturnal cycles of BT, HR, and AC were maintained in both strains. Marked changes were observed under the condition of scheduled feeding during the diurnal component of the light/dark cycle. In DI animals the influence of the photic oscillator was lost and BT, HR, and AC shifted from nocturnal to diurnal patterns. Circadian rhythms in DI animals were now synchronized by the nonphotic zeitgeber of scheduled food presentation. On the other hand, LE animals lost a well-defined circadian rhythmicity resulting from adherence to the photic oscillator, while at the same time being influenced by the nonphotic oscillator. Under the condition of scheduled feeding during the nocturnal component of the light/dark cycle, the circadian rhythms were similar in DI and LE rats. Results show that vasopressin has a significant interaction with the photic oscillator, which is obvious only when the photic and nonphotic oscillators are uncoupled. In addition, the results demonstrate that the strength of the photic oscillator is decreased or that the effect of this oscillator is masked or lost in DI rats compared to LE rats.

Animal Nutritional Physiological Phenomena↗
PubMed1976

Ventricular performance after onset of renal hypertension.

1. In renal hypertensive dogs, the slope of the relation between either stroke volume or cardiac output and end-diastolic pressure is shifted to the right of the normal curves. 2. The maximum to which stroke volume or cardiac output can be raised during loading is significantly less. These changes in cardiac performance appear to be unrelated to the severity of hypertension.

Animals↗
PubMed1976

Method for chronic recording of electroencephalographic activity in conscious dogs.

The difficulties involved in recording high-quality electroencephalograms chronically from conscious dogs have been resolved by devising an implantable pure silver electrode assembly that can be screwed permanently into the skull. The assembly eliminates electromyographic artifacts and provides high-fidelity tracings. Construction is simple and commercially available, inexpensive parts are used. Highly satisfactory records can be obtained over periods of months.

Animals↗
PubMedDate not supplied

Vasopressin deficiency and circadian rhythms during food-restriction stress.

Vasopressin-containing, Long-Evans (LE) rats and vasopressin-deficient, Brattleboro (DI) rats were monitored for activity and core body temperature via telemetry. Rats were exposed to a 12-12 light-dark cycle and allowed to habituate with ad lib access to food and water. The habituation period was followed by an experimental period of 23 h of food-restriction stress in which a 1-h feeding period was provided during the light cycle. Although both strains of animals showed nocturnal activity and temperature rhythms during the habituation period, DI rats were more active than LE rats. The DI rats also had a lower body temperature in the dark. During the experimental period, both strains exhibited a phase shift of activity and body temperature correlating with the presentation of food. The DI rats developed a diurnal shift more rapidly than LE rats. The DI animals showed a dramatic increase in activity during the light phase and a marked decrease in body temperature during the dark phase. The LE animals showed a significant attenuation of activity, but maintained both nocturnal and diurnal temperature peaks throughout the food-restricted condition.

Animals↗