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Nerve regeneration patterns after acute ischemic injury
763
CURRENTLITERATURE
fixed mid-dilated pupil. This led to the diagnosis of delayed retrobulbar hemorrhage with optic nerve compression. Intravenous treatment was started immediately and consisted of 100 g of mannitol, 500 mg of acetazolamide, and 200 mg of hydrocortisone. Within 10 minutes, his pain had diminished and he could see well enough to count fingers. Surgical decompression was planned but was postponed when his vision continued to improve. A 6-month follow-up revealed normal visual acuity. The author credits the osmotic agent mannitol for shrinking the vitreous, thus reducing tissue volume within the orbit. Acetazolamide reduces intraocular pressure by inhibiting carbonic anhydrase and reducing aqueous production. The author reports that as long as the patient has some perception of light or the vision is improving, then medical attention is worth pursuing. However, total loss of vision with no perception of light, or deterioration of vision in spite of medical therapy warrants immediate surgical decompression.-T.B. WELCH Reprint requests to Sunderland Eye Intirmary: Queen Alexandra Rd. Sunderland, Tyne and Wear, SR2 9HP, England.
Conversion of Induced Ventricular Tachycardia by Single and Serial Chest Thumps: A Study in Domestic Pigs One Week after Experimental Myocardial Infarction. Gertsch M, Hottinger S, Mettler D, et al. Am Heart J 118:248, 1989 This study compares the efficacy of a single chest thump (CT) with a series of chest thumps (XT) to convert an experimentally induced ventricular tachycardia (VT) in pigs. The authors review the history of a single CT in ventricular tachycardia and note that for it to be effective, it must occur in the nonrefractory period of the electric ventricular activity. The theoretical change of a single CT occurring at that time is 65%. Therefore, the use of XT may improve the chance of conversion. Domestic pigs were first prepared for this study by ligation of the left anterior descending coronary artery, creating an anterior infarction. One week later, VT was induced by electrical stimulation within the apex of the left ventricle. The experimental protocol involved a single CT after 20 seconds of sustained VT. If ineffective, a second single CT was applied 5 seconds later. If the second CT did not convert the rhythm, SCT (a series of five CT at short intervals) was performed, followed by a series of bimanual SCT if the VT persisted. Attempts were made to quantitate the force of the thumps delivered, with one investigator delivering a peak, single CT of 28 kg and SCT ranging from 10 to 15 kg. The other investigator produced forces of 35 kg and 14 to 20 kg, respectively. Results showed that 6 of 20 VTs were converted by the first CT, and none by the second CT (if VT still persisted). The successful CT all fell during the nonrefractory period. Of the 14 VT persisting, 7 were converted by the first series of SCT, and 6 by a second SCT series. Only 1 VT required electrical conversion. The rate of SCT is greater than the rate of the VT by 10% to 126%. The authors conclude that CT followed by SCT if needed may be effective in the treatment of new-onset sustained VT with preserved left ventricle function. However, at this time this is recommended only under hospital conditions with a standby defibrillator.-SE. LIEBLICH Reprint requests to Dr Gertsch: Department of Cardiology, Medical University Clinic, Anselspital, 3010 Bern, Switzerland.
Nerve Regeneration Patterns After Acute Ischemic Injury. Korthals JK, Gieron MA, Wisniewski HM. Neurology 39:932, 1989 In this study, ischemic injury to peripheral nerves was induced in cats. The method involved ligation of the distal aorta (above the external iliac arteries) and the right femoral arteries in cats. Clinical observations of the animals showed a mild to severe right foot drop in all the cats, and three of eight had a left foot drop as well. In those cats not sacrificed earlier, the foot drop resolved completely by 10 months. Nerve lesions were comprised of fiber loss predominantly in the centrofascicular regions at the proximal border of the infarcted nerves. The most severe changes were in the middle tibial and proximal superficial peroneal nerves. There were two patterns of nerve regeneration noted. In the first, the infarcts were partial or transfascicular, but did not involve the perineurium. These lesions allowed for nerve regeneration without major change of the fascicular architecture. In the second type, nerve fascicles were replaced by a collection of smaller fascicules. The minifascicules formed within the boundaries of the original perineurium. The original perineurium was noted to be replaced by collagen tissue. The mean myelinated fiber diameter was reduced in nerves that regenerated with this compartmentation pattern. Based on these findings, the authors concluded that compartmentation delays nerve restoration. The formation of minifascicules does not appear to be related to damage of the perineurium, but is probably due to simultaneous damage of the perineurium, endoneurium, and nerve fihers.-S.E. LIEBLICH Reprint requests to Dr Korthals: Department of Neurology, USF College of Medicine, 12901 Bruce B. Downs Blvd, Box 55.
Tampa, FL 33612. Cardiovascular Influences of Nitrous Oxide in Spontaneously Hypertensive Rats. Henry RJ, Quack RM. Anesth Prog 36:88, 1989 The cardiovascular effects of nitrous oxide are still controversial, and some feel that nitrous oxide is contraindicated for hypertensive patients. The authors evaluated the effects of oxygen with 20%, 40%, or 60% N,O (experimental group) or nitrogen (control group) on blood pressure (BP) and heart rate (HR) in spontaneously hypertensive rats and normotensive rats. Pressure and pulse were determined from plethysmography of the animal’s tail. Hypertensive rats exposed to nitrous oxide showed a concentration-dependent decrease in BP and HR, and no change when exposed to nitrogen. Normotensive rats showed a decrease in BP and HR with either nitrous oxide or nitrogen. The authors state that it is unclear why the two groups responded differently to nitrogen, and they question how much of the apparent effects are due to an increased oxygen concentration, rather than the nitrous oxide effects. However, they do emphasize that BP and HR were not increased in either group and hypertension was not worsened in hypertensive rats. They conclude that previous recommendations contraindicating nitrous oxide in hypertensive patients appear to be unfounded, although the definitive human study has yet to be performed.-J. DEMBO Reprint requests to Dr Henry: Department of Pediatric Dentistry, University of Florida College of Dentistry, Box J-426, J. Hillis Miller Health Center, Gainesville, FL 32610
CURRENTLITERATURE
fixed mid-dilated pupil. This led to the diagnosis of delayed retrobulbar hemorrhage with optic nerve compression. Intravenous treatment was started immediately and consisted of 100 g of mannitol, 500 mg of acetazolamide, and 200 mg of hydrocortisone. Within 10 minutes, his pain had diminished and he could see well enough to count fingers. Surgical decompression was planned but was postponed when his vision continued to improve. A 6-month follow-up revealed normal visual acuity. The author credits the osmotic agent mannitol for shrinking the vitreous, thus reducing tissue volume within the orbit. Acetazolamide reduces intraocular pressure by inhibiting carbonic anhydrase and reducing aqueous production. The author reports that as long as the patient has some perception of light or the vision is improving, then medical attention is worth pursuing. However, total loss of vision with no perception of light, or deterioration of vision in spite of medical therapy warrants immediate surgical decompression.-T.B. WELCH Reprint requests to Sunderland Eye Intirmary: Queen Alexandra Rd. Sunderland, Tyne and Wear, SR2 9HP, England.
Conversion of Induced Ventricular Tachycardia by Single and Serial Chest Thumps: A Study in Domestic Pigs One Week after Experimental Myocardial Infarction. Gertsch M, Hottinger S, Mettler D, et al. Am Heart J 118:248, 1989 This study compares the efficacy of a single chest thump (CT) with a series of chest thumps (XT) to convert an experimentally induced ventricular tachycardia (VT) in pigs. The authors review the history of a single CT in ventricular tachycardia and note that for it to be effective, it must occur in the nonrefractory period of the electric ventricular activity. The theoretical change of a single CT occurring at that time is 65%. Therefore, the use of XT may improve the chance of conversion. Domestic pigs were first prepared for this study by ligation of the left anterior descending coronary artery, creating an anterior infarction. One week later, VT was induced by electrical stimulation within the apex of the left ventricle. The experimental protocol involved a single CT after 20 seconds of sustained VT. If ineffective, a second single CT was applied 5 seconds later. If the second CT did not convert the rhythm, SCT (a series of five CT at short intervals) was performed, followed by a series of bimanual SCT if the VT persisted. Attempts were made to quantitate the force of the thumps delivered, with one investigator delivering a peak, single CT of 28 kg and SCT ranging from 10 to 15 kg. The other investigator produced forces of 35 kg and 14 to 20 kg, respectively. Results showed that 6 of 20 VTs were converted by the first CT, and none by the second CT (if VT still persisted). The successful CT all fell during the nonrefractory period. Of the 14 VT persisting, 7 were converted by the first series of SCT, and 6 by a second SCT series. Only 1 VT required electrical conversion. The rate of SCT is greater than the rate of the VT by 10% to 126%. The authors conclude that CT followed by SCT if needed may be effective in the treatment of new-onset sustained VT with preserved left ventricle function. However, at this time this is recommended only under hospital conditions with a standby defibrillator.-SE. LIEBLICH Reprint requests to Dr Gertsch: Department of Cardiology, Medical University Clinic, Anselspital, 3010 Bern, Switzerland.
Nerve Regeneration Patterns After Acute Ischemic Injury. Korthals JK, Gieron MA, Wisniewski HM. Neurology 39:932, 1989 In this study, ischemic injury to peripheral nerves was induced in cats. The method involved ligation of the distal aorta (above the external iliac arteries) and the right femoral arteries in cats. Clinical observations of the animals showed a mild to severe right foot drop in all the cats, and three of eight had a left foot drop as well. In those cats not sacrificed earlier, the foot drop resolved completely by 10 months. Nerve lesions were comprised of fiber loss predominantly in the centrofascicular regions at the proximal border of the infarcted nerves. The most severe changes were in the middle tibial and proximal superficial peroneal nerves. There were two patterns of nerve regeneration noted. In the first, the infarcts were partial or transfascicular, but did not involve the perineurium. These lesions allowed for nerve regeneration without major change of the fascicular architecture. In the second type, nerve fascicles were replaced by a collection of smaller fascicules. The minifascicules formed within the boundaries of the original perineurium. The original perineurium was noted to be replaced by collagen tissue. The mean myelinated fiber diameter was reduced in nerves that regenerated with this compartmentation pattern. Based on these findings, the authors concluded that compartmentation delays nerve restoration. The formation of minifascicules does not appear to be related to damage of the perineurium, but is probably due to simultaneous damage of the perineurium, endoneurium, and nerve fihers.-S.E. LIEBLICH Reprint requests to Dr Korthals: Department of Neurology, USF College of Medicine, 12901 Bruce B. Downs Blvd, Box 55.
Tampa, FL 33612. Cardiovascular Influences of Nitrous Oxide in Spontaneously Hypertensive Rats. Henry RJ, Quack RM. Anesth Prog 36:88, 1989 The cardiovascular effects of nitrous oxide are still controversial, and some feel that nitrous oxide is contraindicated for hypertensive patients. The authors evaluated the effects of oxygen with 20%, 40%, or 60% N,O (experimental group) or nitrogen (control group) on blood pressure (BP) and heart rate (HR) in spontaneously hypertensive rats and normotensive rats. Pressure and pulse were determined from plethysmography of the animal’s tail. Hypertensive rats exposed to nitrous oxide showed a concentration-dependent decrease in BP and HR, and no change when exposed to nitrogen. Normotensive rats showed a decrease in BP and HR with either nitrous oxide or nitrogen. The authors state that it is unclear why the two groups responded differently to nitrogen, and they question how much of the apparent effects are due to an increased oxygen concentration, rather than the nitrous oxide effects. However, they do emphasize that BP and HR were not increased in either group and hypertension was not worsened in hypertensive rats. They conclude that previous recommendations contraindicating nitrous oxide in hypertensive patients appear to be unfounded, although the definitive human study has yet to be performed.-J. DEMBO Reprint requests to Dr Henry: Department of Pediatric Dentistry, University of Florida College of Dentistry, Box J-426, J. Hillis Miller Health Center, Gainesville, FL 32610