Clarence N. Peiss

Effects of Sodium Pentobarbital on Electrical and Reflex Activation of the Cardiovascular System

The effects of small doses of sodium pentobarbital (5 mg/kg) on the cardiovascular responses to stimulation of the medulla, hypothalamus, stellate ganglia and sciatic nerve, and to bilateral occlusion of the carotid arteries were studied. It was concluded that: 1) this drug depressed cardiovascular responses to all of these procedures except stimulation of the stellate ganglia; 2) the effects of the anesthetic in this dose are referable to some part(s) of the central nervous system; 3) cardiovascular responses to hypothalamic stimulation were depressed more than those elicited by stimulation of the dorsal medullary reticular formation.

Rhythmic phrenic nerve activity and respiratory activity in spinal dogs.

The possibility of respiratory activity in adult spinal dogs was reinvestigasted with emphasis placed on the contribution of the phrenic nerves and diaphragm. Under chloroform anesthesia, the spinal cord was transected at either the C1 or C2 level. After spinal transection and occlusion of the blood flow to the head, anesthesia was discontinued. In 6 dogs spinal rhythmic respiratory activity was induced by administration of doxapram HCl, 3-5 mg/kg i.m., while in 2 dogs such activity occurred spontaneously. The observed cyclic changes in intrapleural pressure correlated with unilateral phrenic neurogram. The bursts frequency of the phrenic nerve activity was altered by the artificial positive-pressure respiration synchronizing the phrenic activity with the respirator. This suggests that afferent reflexes can modulate this spinal, cyclic phrenic nerve activity. This study demonstrates that the phrenic nerve and the diaphragm play a major role in spinal respiratory activity.

Pentobarbital-induced apneusis in intact, vagotomized, and pneumotaxic-lesioned cats.

While recording several respiratory parameters, sodium pentobarbital (PB) was infused into the inferior vena cava of spontaneously breathing, PB anesthetized cats. Three cat groups were investigated: intact control (group A); vagotomized (group B); pneumotaxic center-lesioned (group C). With a few exceptions, all cats developed PB-induced inspiratory apneusis. Groups B and C exhibited 10-sec inspiratory hold pattern at significantly lower PB levels than group A cats. All groups developed apnea at different PB levels. Ventilation was consistently depressed, predominantly by breathing frequently attenuation. Tidal volume remained comparable to control, but decreased in vagotomized cats at high PB levels. These results are interpreted to signify that (1) inspiratory inhibitory inputs are more susceptible to depression by PB than inspiratory drive mechanisms; (2) the breathing pattern of apneusis results when summed inspiratory inhibition is reduced below a critical minimum level; (3) vagal and pneumotaxic center inhibitions on inspiration are equally weighted at apneusis, but not at apnea. These results are further discussed in terms of the inspiratory off-switch model. A possible model of Biot respiration is also introduced.

Hypothalamic Temperatures and Blood Flow.

Summary Simultaneous temperature measurements in the hypothalamus and arterial blood reveal that the thermosensitive elements in the hypothalamus are normally cooled by the blood perfusing it. Posterior hypothalamic temperatures are consistently higher than those in the anterior hypothalamus. Occlusion of the common carotid arteries elicited a marked elevation in hypothalamic temperatures. Small i.v. doses (2.5 to 10 mg/kg) of sodium pentobarbital resulted in a prompt and sustained decline. The fall in temperature after pentobarbital appears to be due to a significant increase in hypothalamic blood flow.

Evaporation of small water drops maintained at constant volume

An apparatus was devised which permits measurement of the evaporative rate of small water drops maintained at constant volume. The surface temperature of the drop was measured with a small thermocouple. Evaporative rates were measured at drop radii ranging from 0.023 to 0.18 cm, with a total of 128 measurements. Mathematical analysis was performed using a multiple curve fitting program for 19 different curves. It was found that a plot of radius against evaporative rate (g/s/mm Hg) is best fit by a parabola with a correlation coefficient of 0.998.

Comparative Study of Effect of Epinephrine and Norepinephrine on Cardiovascular System of Turtle, Alligator, Chicken and Opossum.∗

Summary Turtles, alligators, opossums and chickens were given epinephrine and norepinephrine intravenously and their cardiovascular responses compared. The cardiovascular system of all species seems to be more reactive to epinephrine than to norepinephrine, but to various degrees. A tentative hypothesis, that epinephrine is the neurotransmitter in the opossum and norepinephrine is the neurotransmitter in the chicken, is considered.