Maintenance of Atrial Fibrillation in Anesthetized and Unanesthetized Sheep Using Cholinergic Drive

Atrial fibrillation (AF) was induced electrically and the duration of AF was measured in six isoflurane-anesthetized sheep (weight range 54.5–72.7 kg), and in five Unanesthetized sheep (weight range 60–75 kg). In the anesthetized sheep, AF was induced by direct electrical stimulation of the right atrium with a catheter electrode and the duration of AF was determined. Intravenous neostig- mine (10 fig/kg IV) was administered and the duration of AF was again measured. Then cholinergic drive was increased by bilateral electrical vagal stimulation; AF was induced and the duration of AF was measured. In the anesthetized animals with no neostigmine or vagal stimulation, 34% of the episodes of AF lasted 10 seconds, 11% lasted 20 seconds, and only 1 % lasted 200 seconds. However, in one anesthetized animal AF was sustained for 4,800 seconds with no drug or vagal support. The administration of neostigmine alone in 3 anesthetized animals more than doubled the average duration of AF. In the animals with vagal stimulation (after neostigmine), AF persisted throughout stimulation, but ceased shortly after vagal stimulation was terminated at 2,220, 4,500, and 3,840 seconds. The AF frequency ranged from 325–750/min. The Unanesthetized sheep were lightly sedated with a small dose (200 fig/kg IM) of xylazine to make them less sensitive to environmental noise; then AF was induced and its duration was timed. After these measurements, neostigmine was administered (30 μg/kg IM) and cholinergic drive was produced reflexly by intravenous injection of 60–2,000 fig of phenylephrine. AF was electrically induced at the time of maximum reflex slowing in heart rate. For the control (no drug! studies, 64% of the AF episodes lasted 10 seconds, 20% lasted 20 seconds, and only 2% of the episodes lasted as long as 140 seconds. When phenylephrine was injected after neostigmine to provide increased cholinergic drive, the duration of fibrillation depended on the dose of phenylephrine. In a 60-kg sheep, the duration of AF increased from 1 second with an intravenous dose of 60 μg to 700 seconds with an intravenous dose of 2,000 μg. However, there was a considerable range in responsiveness to the reflex cholinergic drive provided by the intravenous phenylephrine; for example a single intravenous 500-μg dose produced AF ranging from 190–540 seconds among the sheep. The duration of AF was most controllable in the anesthetized sheep, following neostigmine administration and with bilateral vagal stimulation. In the Unanesthetized sheep, AF could generally be sustained for more than the duration of the half-life (about 4 minutes) of phenylephrine following neostigmine. However, there was a large variation in the duration of AF among the animals for the same dose of phenylephrine. This study identifies two methods (direct vagal stimulation and reflex vagal stimulation) for providing the cholinergic drive needed to sustain AF in the adult sheep. The duration of AF is sufficiently long to enable the measurement of electrical atrial defibriilation threshold.     

Evaluation of direct and buffy coat films of peripheral blood for the early detection of bacteraemia

Abstract During an 8 month period, 298 evaluations of direct and buffy coat films of peripheral blood for the detection of bacteraemia were undertaken in 287 infants (243 less than 24 h of age and 55 aged between 2 days and 30 days). Bacteraemia was diagnosed by simultaneously drawn aerobic and anaerobic blood cultures. Intracellular organisms were observed in both the direct and buffy coat films of only four of 24 infants with bacteraemia, giving a sensitivity of 17%, specificity of 100% and positive and negative predictive values of 100% and 93%, respectively. Of 12 infants with bacteraemia on the first day of life, eight were asymptomatic when studied, and none of the 12 had positive smears. As two of four infants with positive smears died, it is concluded that in fulminating sepsis the tests seem to correlate with the degree of illness and may give useful information as to the causative organism and the choice of antibiotic. However, as a screening test, the present methodology lacks sensitivity and cost-effectiveness.     

PARANEOPLASTIC ENCEPHALOMYELITIS

Two patients with lung carcinoma exhibited pathologic features of meningoencephalitis, subacute cerebellar degeneration, myelitis, ganglioradiculitis and peripheral neuropathy with neurogenic atrophy of muscle. Their clinical and pathologic characteristics are described and compared with those of twenty-eight cases previously reported. This disorder tends to occur in the sixth and seventh decades of life, and is more common in males. The neoplasm is usually of bronchogenic origin. The clinical manifestations are variable, and the pathologic lesions may be more extensive than the clinical findings would suggest. The etiology of this syndrome remains unknown.