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Biomedical subjects

R F Albrecht

Publications and source records attributed to R F Albrecht.

138 records · Page 8Linked to original sources
PubMedDate not supplied

Nitroglycerin induced hypotension will maintain CBF in hypertensive rats.

Cerebrovascular effects of intravenous (iv) nitroglycerin (NTG) infusions were tested in four month old spontaneously hypertensive rats (SHR) and Wistar Kyoto controls (WKY). Cerebral blood flow (CBF) changes were measured during iv NTG infusion in ventilated, halothane anesthetized rats using radioactive microspheres. In control WKY rats given isotonic saline infusions instead of NTG, blood pressure and CBF did not change over 3 microsphere injections. When blood pressure was decreased to 65 and then 45 torr with iv NTG infusions, CBF was maintained or increased in both SHR and WKY. There was no difference in response between SHR and WKY. These results support other reports that NTG has direct cerebrovasodilating effects, and indicate that this action will maintain adequate CBF in hypertensive as well as normotensive subjects to pressures below 50 torr.

Anesthesia, Inhalation↗
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The influence of antihypertensive therapy on cerebral autoregulation in aged hypertensive rats.

Cerebrovascular responses to hemorrhage induced hypotension were tested in aged (24 month) spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) after ten weeks of antihypertensive drug or sham treatment. Antihypertensive drug treatment consisted of 1 mg/kg/day minoxidil, 4 mg/kg/day hydralazine and 4 mg/kg/day propranolol given in the drinking water. Antihypertensive therapy produced a 30% decrease in systolic blood pressure in aged SHR to levels not significantly different from sham treated WKY. Cerebral blood flow (CBF), measured under control conditions using ketamine anesthesia, was not significantly different between sham and drug treated SHR and WKY. Cerebral oxygen metabolic rate (CMRO2) was significantly decreased in drug treated SHR and WKY compared to sham treated rats. Lowering blood pressure to a level between 80 and 95 torr produced no significant change in CBF or CMRO2 in sham or drug treated WKY or antihypertensive treated SHR, but a produced a significant decrease it both CBF and CMRO2 in sham treated SHR. Decreasing mean blood pressure to 50-60 torr produced a significant decrease in CBF but not CMRO2 in both WKY treatment groups and in hypertensive treated SHR, but again in sham treated SHR both CBF ana CMRO2 were significantly decreased. These results indicate that aged hypertensive rats are unable to maintain CBF or CMRO2 under even moderate hypotensive test conditions, and that cerebral autoregulation can be improved with antihypertensive therapy.

Aging↗
PubMedDate not supplied

The role of adenosine in CBF increases during hypoxia in young vs aged rats.

The role of adenosine in the regional cerebral blood flow (rCBF) response to hypoxia was evaluated in young (6 month) and aged (26-28 month) F344 rats using theophylline, an adenosine antagonist. Regional CBF was measured with radioactive microspheres under control anesthetized conditions (70% N2O, 30% O2) and at two levels of hypoxia (CaO2 = 8.7-9.0 ml . 100ml-1 and 3.2-3.7 ml . 100ml-1). Without theophylline infusion, CBF increases were similar between young and aged rats during moderate hypoxia but were increased more in young during severe hypoxia. Intracerebrovascular theophylline infusion significantly attenuated the increase in CBF during both moderate and severe hypoxia and decreased the difference between young and aged rats. Theophylline infusion produced no significant effect on the increase in CBF produced by hypercapnia, indicating the specificity of the treatment for hypoxic induced CBF changes and adenosine release. Intracerebrovascular infusion of adenosine had no effect on CBF, presumably due to the presence of the blood brain barrier. The results suggest that adenosine plays a major role in CBF increases during both moderate and severe hypoxia and in the difference in response to hypoxia between young and aged rats.

Adenosine↗
PubMedDate not supplied

Cerebrovascular response to hypoxia in young vs aged rats.

Cerebrovascular responses of young and aged rats were tested to graded levels of hypoxia using a modification of the Levine ischemic-hypoxic rat model in which one carotid artery was ligated. Rats were anesthetized with 70% N2O, 30% O2 and cortical and subcortical cerebral blood flow (CBF) were measured with radioactive microspheres. CBF and cerebral cortical oxygen consumption (CMRO2) were measured under control conditions and during hypoxia with arterial oxygen content maintained at approximately 9, 5 and 3 ml . dl-1. CBF responses in cortical and subcortical tissues were similar between young and aged under control conditions and during moderate hypoxia (CaO2 = 9 ml . dl-1). Maximum cerebrovascular responses to severe hypoxia were greater in young than in aged rats and these trends were significant in both ligated and unligated cortical tissue (p less than 0.05). CMRO2 was maintained at control levels during moderate hypoxia but decreased significantly more in aged than in young rats when CaO2 was decreased to 3 ml . dl-1. These results suggest that baseline CBF and the sensitivity of cerebrovascular receptors to moderate hypoxia are similar in young vs aged rats but that maximum reactivity severe hypoxia is attenuated in aged subjects. CBF measured after one minute of hypoxia, before the induction of brain tissue acidosis, produced no significant change in the CBF response to hypoxia or in the difference between young and aged rats. Brain tissue pH changes do not appear to be the major factor for mediating CBF increases during hypoxia in young or aged rats, although it may interact with other mediators of the response.

Aging↗
PubMedDate not supplied

Brain metabolic changes in young vs aged rats during hypoxia.

Brain energy state and glycolytic metabolites were measured in young (6 month) and aged (28 month) male rats under normoxic (70% nitrous oxide, 30% oxygen) or hypoxic (PaO2 = 25 mm Hg) test conditions. Hypoxic ischemia was induced in one cerebral hemisphere by ligation of one carotid artery. Under normoxic test conditions brain energy metabolite concentrations were similar between young and aged rats. Brain tissue glucose, glycogen, glucose-6-phosphate and critic acid cycle intermediate concentrations were decreased in aged rats during normoxia while fructose-6-phosphate and pyruvate were increased. Decreases in brain energy state and increases in lactate/pyruvate ratios were significant in both young and aged rats during hypoxia and were greater in aged animals in hypoxic-ischemic tissues. These results indicate that brain energy state is normal in aged rats under normoxic conditions but that hypoxic-ischemia produces a greater degree of brain energy failure compared to younger animals.

Aging↗
PubMedDate not supplied

Cerebral effects of extended hyperventilation in unanesthetized goats.

Thirty-six adult, male unanesthetized goats were hyperventilated to a PaCO2 level of 16-18 mm Hg for 6 hours. Arterial and sagittal sinus blood and cerebrospinal fluid were analyzed for pH, blood gases, bicarbonate, lactate, and pyruvate before hyperventilation, during hyperventilation, and after the termination of hyperventilation. Total cerebral blood flow, regional brain blood flows, and cerebral metabolic rate for oxygen were calculated from the distribution of radioactive microspheres. Intracranial pressure was measured in either the right or left cerebral ventricle. With the initiation of hyperventilation, cerebral blood flow and cerebral metabolic rate for oxygen fell significantly (64 +/- 5 ml/100 g/min to 41 +/- 3; 4.6 +/- 0.3 ml O2/100 g/min to 3.6 +/- 0.2), but both returned to prehyperventilation values within 6 hours of hyperventilation. With termination of hyperventilation, cerebral blood flow and cerebral metabolic rate for oxygen increased significantly above control levels (64 +/- 5 vs. 105 +/- 9; 4.6 +/- 0.3 vs. 5.4 +/- 0.4). Intracranial pressure was unaffected by hyperventilation or its termination. Arterial and sagittal sinus blood and cerebrospinal fluid pH increased with hyperventilation but returned to control values by 6 hours. However, pH was still significantly elevated at 6 hours. Lactate and pyruvate followed a similar pattern except in the cerebrospinal fluid, where both increased throughout the course of hyperventilation. There were no significant differences in the lactate:pyruvate ratio. On termination of hyperventilation, pH of the arterial and sagittal sinus blood and cerebrospinal fluid fell below control levels. Bicarbonate values decreased in all fluid compartments and were still below control values 2 hours after the cessation of hyperventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
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Absence of autoregulation of cerebral blood flow during halothane and enflurane anesthesia.

The effects of halothane and enflurane anesthesia under conditions of normo-, hyper-, and hypocarbia on the autoregulation of cerebral blood flow (CBF) in the goat were evaluated. The goat was selected because of its unique arterial blood supply to the head and the development of a method by which CBF may be continuously measured. The study revealed that 1 MAC of halothane or enflurane anesthesia at normocarbia abolished cerebral autoregulation, CBF increasing or decreasing with increasing or decreasing peripheral blood pressure. Reduction of anesthesia to 0.5 MAC partially restored cerebral autoregulatory capability. The effect of 1 MAC and 0.5 MAC anesthesia on cerebral autoregulation of blood flow was potentiated by hypercarbia and antagonized by hypocarbia, indicating that the vascular response to blood CO2 fluctuations remained intact.

Anesthesia↗
PubMedDate not supplied

The effects of doxapram on cerebral blood flow and peripheral hemodynamics in the anesthetized and unanesthetized goat.

The effects of doxapram on cerebral blood flow (CBF) and peripheral hemodynamics were evaluated in the goat after direct injection into the cerebral circulation and after peripheral IV administration. Doxapram injected centrally via the temporal artery, in doses too small to affect peripheral circulation, produced an immediate and prolonged decrease in CBF in both anesthetized and unanesthetized gohanges in blood CO2 concentration, since blood flow decreased immediately after injection and as reduction in CBF occurred in the absence of changes in blood CO2. Pheripheral IV administration of doxapram in clinical doses to anesthetized and unanesthetized goats produced a biphasic cardiovascular response. Cerebral blood flow, cardiac output, blood pressure, and heart rate decreased abruptly, but with the exception of CBF, these parameters returned to or exceeded preinjection values within 30 seconds. Cerebral blood flow slowly returned to preinjection values (within 10 minutes) and, in the case of unanesthetized animals and anesthetized animals ventilated with room air, rose substantially above preinjection levels, reaching a peak 20 minutes after injection. The latter observation is thought to be a compensatory reaction to the reduction in CBF; it was not evident in anesthetized animals ventilated with 100% O2.

Anesthesia↗
PubMedDate not supplied

The effect of enflurane, isoflurane, fluroxene, methoxyflurane and diethyl ether anesthesia on ouabain tolerance in the dog.

Digitalis tolerance in dogs anesthetized with enflurane, isoflurane, fluroxene, methoxyflurane, and diethyl ether was compared with that in dogs anesthetized with pentobarbital. Ouabain dosage needed to cause ventricular tachycardia was significantly higher than that of pentobarbital with all agents except fluroxene, as was the LD50. The relative potency of these anesthetics in converting ouabain-induced ventricular tachycardia to sinus rhythm, in order of descending effectiveness, was: diethyl ether, methoxyflurane, enflurane, fluroxene, isoflurane, pentobarbital.

Anesthesia, Inhalation↗
PubMedDate not supplied

Enflurane anesthesia for surgical removal of pheochromocytoma.

Four cases describing the use of enflurane as the main anesthetic during surgical removal of pheochromocytoma (PCC) are presented and the preoperative preparation and intraoperative management of the patients are discussed. Serum levels of epinephrine and norepinephrine were measured in 3 of the reported cases. Intraoperative values were extremely elevated during tumor manipulation, but there was only 1 minor episode of arrhythmias. Criteria for choosing anesthetic agents for surgical removal of PCC are outlined. The authors conclude from their experience and that of others that enflurane is as safe and effective an anesthetic as any now available for PCC excision.

Adult↗
PubMedDate not supplied

Arrhythmic doses of epinephrine and dopamine during halothane, enflurane, methoxyflurane, and fluroxene anesthesia in goats.

The cardiac arrhythmicity of epinephrine and dopamine was compared in awake goats and during approximate equivalent levels of halothane, enflurane, methoxyflurane, and fluroxene anesthesia. The arrhythmic threshold dose for epinephrine and dopamine was significantly (p less than 0.05) reduced during halothane anesthesia when compared to values determined in awake animals. Enflurane anesthesia had no significant affect on the arrhythmic threshold dose for either catecholamine. However, methoxyflurane and fluroxene anesthesia significantly (p less than 0.05) elevated the arrhythmic threshold dose for dopamine. Epinephrine produced greater elevations in mean arterial pressure than dopamine with all anesthetics except enflurane, and dopamine produced significantly (p less than 0.05) higher heart rates in the awake animals and those anesthetized with halothane and enflurane. The authors conclude that, in terms of arrhythmic potential, there is no advantage in the use of dopamine rather than epinephrine for the reversal of halothane-induced myocardial depression during halothane or enflurane anesthesia.

Anesthesia, Inhalation↗