Disruption of the rhythmic activity of the medullary inspiratory neurons and phrenic nerve by fentanyl and reversal with nalbuphine

The effects of intravenous administration of fentanyl (50 and 100 micrograms/kg) on the discharge activity of the medullary inspiratory neurons and of the phrenic nerve were studied following vagotomy in nine decerebrate, paralyzed mechanically ventilated cats. In six cats, the inspiratory neurons explored were in the dorsal respiratory group (DRG) associated with the nucleus of the tractus solitarius (NTS), while in the remaining three, they were in the ventral respiratory group (VRG). In the former group, the rhythmic discharge of the inspiratory neurons was disrupted by fentanyl and replaced by a continuous discharge superimposed with irregularly occurring bursts. These changes were also reflected by the phrenic nerve discharge. Inspiratory neuronal activity increased significantly (P less than 0.05) at 1 and 5 min after completion of fentanyl injection. Disruption of the rhythmic activity of the inspiratory neurons and its replacement by a continuous and irregular discharge may lead to sustained contraction of inspiratory muscles and cessation of respiration. In the VRG, the activity of the inspiratory neurons was totally abolished by fentanyl. Thus, it appears that different groups of medullary inspiratory neurons have differential sensitivity to fentanyl. Nalbuphine, an opiate agonist-antagonist, restored the normal pattern and magnitude of the activity of the inspiratory neurons.

Comparison of cardiopulmonary variables with intermittent positive pressure ventilation and high-frequency jet ventilation during abdominal aortic operations

Cardiopulmonary variables with intermittent positive pressure ventilation (IPPV) and high-frequency jet ventilation (HFJV) were compared in 8 patients undergoing elective abdominal aortic operations under fentanyl-nitrous oxide anesthesia. Hemodynamics were stable under the two methods of ventilation, and most of the corresponding hemodynamic variables were statistically indifferent from each other. Alveolar gas exchange was also adequate with either method and most of the corresponding respiratory variables were not statistically different. The peak airway pressure was significantly less during HFJV than during IPPV (p less than 0.01). Diaphragmatic excursions are less during HFJV than during IPPV, resulting in a quieter surgical field. Therefore, hemodynamic stability and gas exchange adequacy coupled with less diaphragmatic excursions and lower peak airway pressure make HFJV an acceptable alternative to IPPV during abdominal aortic operations.

Serum creatine phosphokinase, lactic dehydrogenase, and their isoenzymes in the perioperative period

The purpose of the present investigation was to determine the normal perioperative variations in the serum concentration of creatine phosphokinase (CPK) and its isoenzymes MM, MB, and BB, and of lactic dehydrogenase (LDH) and its isoenzymes LDH1 to LDH5 to distinguish operation-induced changes in these enzymes from those due to acute myocardial infarction or malignant hyperthermia. In 30 patients, 52 to 75 years of age undergoing elective orthopedic operations, 10 serial blood samples were obtained in the perioperative period: two samples before skin incision and eight samples after the incision over a time span of 70 hours. The preinduction mean serum CPK level of 141 U/L increased gradually and significantly and reached a maximum mean concentration of 809 U/L 34 hours after incision (p less than 0.01). The CPK-MM percent increased after incision, whereas that of CPK-MB and CPK-BB decreased, although their absolute values in terms of U/L rose. The preinduction mean serum LDH value of 173 U/L increased gradually after incision and achieved peak levels at 34 hours (203 U/L) and 58 hours (210 U/L) after incision (p less than 0.05). The LDH1:LDH2 ratio did not change. The LDH5 percent increased and peaked 10 hours after incision (p less than 0.05). There was a significant correlation between severity of operation-induced tissue damage and the serum CPK concentration (p less than 0.001). The large increase in total CPK (primarily MM fraction) occurring after surgery may minimize the percentile effects caused by an increase in MB level due to myocardial infarction.

Effects of halothane on medullary inspiratory neurons of the cat

The effect of halothane on the electrical activity of inspiratory neurons of the nucleus tractus solitarius (NTS) was studied in decerebrate, paralyzed, mechanically ventilated cats. Simultaneous recording of the activity of the neurons of the NTS and the phrenic nerve was done to identify the inspiratory neurons. Cells whose firing activity was synchronous with that of the phrenic nerve were considered inspiratory neurons. Administration of 1% and 1.5% halothane in oxygen induced a dose-dependent depression of the cell activity (spikes/s) with the cervical vagi intact or severed. Five and ten minutes after inhalation of 1% halothane, the cell activity (mean +/- SE) expressed as per cent of the control was 55.3 +/- 9 and 27 +/- 7, respectively (P less than 0.001), before bilateral cervical vagotomy. The corresponding values for 1.5% halothane were 25 +/- 10.1 and 5.6 +/- 3, respectively. Upon termination of halothane administration, the cell activity gradually returned toward the control level. The cell response to halothane was not affected by bilateral cervical vagotomy. Hypercapnia produced by inhalation of 5% CO2 increased the cell activity, but halothane caused profound depression of the cells even in the presence of hypercapnia. Based on these results, it may be concluded that: halothane has inhibitory effects on the activity of the inspiratory neurons of the NTS; and halothane-induced respiratory depression has a central component and that the NTS may serve as a site of action of halothane for its respiratory depressant effect.

Persistence of polymicrobial abscesses in the poorly controlled diabetic host

Polymicrobial infections are frequently found in soft tissue infections of the lower extremities in diabetic patients. The relative susceptibility to and persistence of soft tissue polymicrobial infections of diabetic and nondiabetic mice using bacteria commonly found in clinical foot infections were studied. Subcutaneous abscesses were induced in three groups of diabetic and nondiabetic mice using: (1) E. coli and enterococcus, (2) enterococcus and Bacteroides fragilis (B. fragilis), and (3) E. coli and B. fragilis. Abscesses were removed at 1 and 2 wk for total colony counts. At 1 wk, there was a significantly greater bacterial growth in the abscesses of the diabetic mice compared with the nondiabetic mice only in the group injected with enterococcus and B. fragilis. There were significantly higher colony counts in the diabetic compared with the nondiabetic mice in all three groups at 2 wk after injection of the bacteria. Two weeks after injection of inocula containing B. fragilis, both in combination with E. coli or enterococcus, all nondiabetic mice had eradicated B. fragilis from the abscesses, but significant numbers of B. fragilis persisted in the abscesses of the diabetic mice. In the diabetic mice, the presence of enterococci was more synergistic for growth of B. fragilis than was the presence of E. coli. These studies demonstrate that the bacteria of polymicrobial soft tissue infections persist for a longer period of time in the diabetic compared with the nondiabetic host. In addition, B. fragilis has increased pathogenicity in the diabetic compared with the nondiabetic host, particularly in the presence of enterococci.

Fentanyl and alfentanil suppress brainstem pain transmission

The effects of intravenously administered fentanyl (25 micrograms/kg, n = 9; 50 micrograms/kg, n = 5) and alfentanil (12.5 micrograms/kg, n = 5; 25 micrograms/kg, n = 7) on the noxiously evoked, single-unit activity of cells in the nucleus reticularis gigantocellularis (NRGC) were studied in decerebrate cats. Only cells of the NRGC excited exclusively by supramaximal electrical stimulation of A delta fibers (noxious stimulation) of the superficial radial nerve were studied. The noxiously evoked activity of all cells in the NRGC was suppressed by the administration of opioids (by 58 and 88% for fentanyl, 25 micrograms/kg and 50 micrograms/kg, respectively; by 35 and 78% for alfentanil 12.5 micrograms/kg and 25 micrograms/kg, respectively). Fentanyl and alfentanil effects were antagonized by the intravenous administration of naloxone. These results indicate that opioid suppression of noxiously evoked activity is seen in neurons located in the brainstem, and thus suppression of brainstem neurons may be important in the production of fentanyl and alfentanil analgesia.

Effect of administration of estrogen to pregnant rabbits on the lipid content and composition of the fetal brain

Intramuscular injection of 17 beta-estradiol to pregnant rabbits did not produce any significant change in the phospholipid, neutral lipid and cholesterol content of the fetal brains, nor did it cause any significant difference in their wet and dry weights. It may be inferred that use of estrogen in the gestational period to enhance surfactant production and lung maturation in the fetus would not produce adverse effects on the fetal brain lipids.

Ureteral motility in sheep

Ureteral motility was studied in twenty-five sodium pentobarbital-anaesthetized sheep. Mean frequency of the peristaltic waves was 15 per min and the range was 11-19. Frequency was the same throughout the length of the ureter. Mean contraction pressure (cm H2O) was 40 in the upper ureter, 35 in the middle ureter and 31 in the lower ureter. Mean concentration time was 1 sec and range was 0.6-1.5. Mean relaxation time was 1.1 sec and range was 0.7-1.5. Diuresis induced by rapid intravenous administration of physiologic sodium chloride solution abolished the peristaltic activity.

Effects of saline extract of ovine hydatid cyst scoleces in sheep. Blockade of responses by compound 48/80

The effects of intravenous administration of the saline extract of the ovine hydatid cyst scoleces on the cardiovascular and respiratory systems were studied in sodium pentobarbital-anesthesized sheep. Scoleces were obtained from the lung hydatid cysts of freshly slaughtered sheep, sonicated in physiologic saline and centrifuged to recover the extract in the supernatant fluid. Administration of 1-4 ml of the saline extract resulted in hypotension, shallow rapid respiration, slight elevation of the central venous pressure and transient electrocardiographic changes. Pretreatment of the animals with atropine, 1 mg/kg S.C., or with the antihistamine antazoline, 5 mg/kg I.V., did not block the responses to the saline extract of hydatid cyst scoleces. Pretreatment with compound 48/80, a histamine releaser, abolished the reactions to the administration of the scoleces extract. It is concluded that ovine hydatid scoleces extract has profound cardiovascular and respiratory effects, and that histamine release seems to be involved in the induction of responses to the extract.

Effects of ovine hydatid cyst fluid in sheep before and after treatment with hydrocortisone, antihistamines and atropine

The cardiovascular and respiratory responses to scolex-free ovine hydatid cyst fluid were studied in 65 sodium pentobarbital-anesthetized sheep. The arterial blood pressure (ABP), central venous pressure (CVP), stethogram and electrocardiogram were recorded. Intra-venous administration of 10 ml or less hydatid fluid brought about moderate to severe fall in ABP and rapid respiration or permanent respiratory cessation in majority of the animals. Forty six percent of the sheep died of circulatory and respiratory failure after the first injection or the hydatid fluid. Boiled hydatid fluid did not lose its potency to evoke the above responses. Hydrocortisone, given 200 mg daily for seven days, failed to prevent the reactions to hydatid fluid. Intravenous administration of the antihistamines chlorpheniramine, 4 mg/kg, and antazoline, 5 mg/kg, caused only partial prevention of the responses in 8 out of 15 responsive sheep. Pretreatment of the animals with atropine, 0.5--1 mg/kg subcutaneously, did not block the reactions. The cardiovascular and respiratory responses to ovine hydatid fluid may be due to antigen-antibody reactions or some toxic component of the fluid.

Effect of electrical stimulation of the medullary respiratory neurons on respiratory air flow in cats. New findings on expiratory neurons

Respiratory air flow during electrical stimulation of the medullary respiratory neurons was measured in 25 sodium pentobarbital-anesthetized cats. The effect of variation of stimulus parameters on the air flow was studied too. The medullary respiratory neurons were localized by exploring the medulla with microelectrodes. The inspiratory neurons were found hetween 2 and 4 mm lateral to the midline, and from the level of the obex to 4 mm rostrally in the ventral reticular formation. The expiratory cells were between 2 and 3 mm lateral to the midline, extending from the level of the obex to 3 mm caudally, slightly less ventral than the inspiratory neurons. The maximal inspiratory and expiratory flow rates were 56 and 44 liters per minute respectively when the respiratory neurons were stimulated with a stimulus of 4 volts and 200 Hz/sec., while duration of the stimulating pulse was 0.5 millisecond. In general, the increase in air flow was proportional to the magnitude of the stimulus strength, stimulus frequency and duration of the stimulating pulse.

Effect of electrolytic lesions of the medullary inspiratory region in rats

The medulla oblongatas of 48 anesthetized rats were explored by electrical stimulation. The pneumotachogram and in some, the arterial blood pressure as well, were recorded. The inspiratory area was located in the ventral reticular formation from the obex to 1.8 mm rostral to the obex. It occupied about 2.2 mm3 on each side of the midline. The expiratory reactive points were scattered in a region which was dorsal and caudal to the inspiratory area. Unilateral and midline lesions produced by 3, 5 and 8 ma direct current did not stop rhythmic respiration. There was an initial increase in the respiratory rate followed by diminution to below that of the prelesion time. The respiratory air flow was decreased. The changes in respiratory rate and air flow were not statistically significant in majority of the above groups. Bilateral lesions produced by 3 or 5 ma stopped breathing. Continuation of thythmic respiration after destruction of a number of inspiratory neurons and/or fibers in the midline or one side of the medulla indicates that all the inspiratory neurons and fibers are not essential for the maintenance of respiration. Cessation of thythmic respiration after destruction of all or most of inspiratory neurons on both sides of the midline indicates the essential role of the medulla-oblongata for genesis or maintenance of rhythmic respiration.

Localization of the medullary respiratory neurons in rats by microelectrode recording

Neuronal activity has been recorded extracellularly from the medulla of anesthetized rats. Units whose discharge frequency varied in phase with respiratory airflow were located bilaterally between 1.5 and 2 mm lateral to midline, extending from 1 mm caudal to 1.5 mm rostral to the obex, in the ventral two-thirds of the medulla. Expiratory units predominated and were intermingled with inspiratory units. Ten different patterns of discharge were distinguished, varying from a short burst at the beginning of expiration to a resting discharge which increased in frequency during either inspiration or expiration. Evidence was also obtained that fiber tracts from other areas of the brain cross midline just caudally to the obex and pass to the respiratory centers on which they apparently exert and excitatory action.

Ureterometrographic studies on human subjects with normal urinary tract system

Ureteral motility was studied in 40 subjects with normal urinary tract systems. Although the contraction waves were often monophasic in shape some were characterised by the presence of a notch on the contraction or relaxation limb of the peristaltic complex, indicating that notched complexes do not necessarily signify obstructive uropathy. Retrograde filling of the bladder to within its physiologic limits with isotonic saline solution markedly changed the pattern of the ureteral activity.

Effect of ovine hydatid cyst fluid on the cardiovascular and respiratory systems in sheep

Rupture of the hydatid cyst in man brings about mild to severe toxic reactions including death. The present study was undertaken to investigate some of the responses resulting from administration of the ovine hydatid fluid to the sheep, which, like man, is an intermediate host of the Echinococcus granulosus. In 50 sodium pentobarbital-anesthetized sheep, the arterial blood pressure (A.B.P.), central venous pressure (C.V.P.), respiration and electrocardiogram were recorded. Intraveonus administration of 5-10 ml hydatid fluid brought about moderate to severe fall in A.B.P. and rapid respiration with or without transient apnea or permanent repiratory cessation in 80 percent of the animals. Fifty percent of the sheep died of circulatory and respiratory failure after the first injection of the hydatid fluid. Boiled hydatid fluid did not lose its potency to evoke the above responses. Pretreatment of the aminals with atropine sulfate, 0,5 mg/kg subcutaneously, did not block the reactions. Administration of the antihistamine chlorpheniramine, 4 mg/kg intravenously, caused partial prevention of the reactions in 6 out of 10 responsive sheep. The cardiovascular and respiratory responses to ovine hydatid fluid may be due to antigen-antibody reactions or some toxic component of the fluid.

Pathophysiological changes resulting from intravenous injection of ovine hydatid cyst fluid to sheep

The pathophysiological changes produced by intravenous administration of ovine hydatid fluid were studied in 40 sodium pentobarbitone-anaesthetized sheep. Hydatid fluid was obtained from the lung and liver cysts of freshly-slaughtered sheep.

Fifty per cent of the animals died following intravenous injection of 5-10 ml hydatid fluid. In the latter group, postmortem examination revealed a great amount of mucus in the lower airway, intra-alveolar oedema and haemorrhage, congestion of the pulmonary capillaries and peribronchiolar vessels and of the central sinusoids of the liver.

Eighty per cent of the animals (including those which died) developed hypotension and respiratory alterations such as transient apnoea and/or rapid respiration to hydatid fluid administration. The 20% non-reactive animals manifested low blood pressure and respiratory changes when they were reinjected hydatid fluid 48 hours or more after the first test.

Pretreatment with the antihistamine chlorpheniramine substantially reduced the fall in blood pressure in 3 out of 8 reactive sheep. Atropine pretreatment failed to block the reactions to hydatid fluid.

The responses brought about in sheep by hydatid fluid administration may be due to antigen-antibody reactions or due to pharmacological properties of the cyst fluid.