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Biomedical subjects

M Manohar

Publications and source records attributed to M Manohar.

At least 73 records · Page 4Linked to original sources
PubMed1987

Regional distribution of brain blood flow during maximal exertion in splenectomized ponies.

It has been reported in exercising ponies that O2 supply to all regions of the brain increased primarily due to a large increment in CaO2 and it was implied that this may reflect a generalized increase in brain metabolism during strenuous exercise. Splenectomy ameliorates the rise in CaO2 observed with exercise in ponies. Thus, the objective of the present study was to examine changes in regional brain blood flow and O2 supply of splenectomized ponies with sub-maximal and maximal exercise and to compare these data with previous observations in normal ponies. It was reasoned that in the absence of a marked rise in CaO2, the brain blood flow of splenectomized ponies would have to increase markedly if brain metabolism also increased with severe exercise. Regional brain blood flow was studied using 15 micron diameter radionuclide labeled microspheres injected into the left atrium during rest (control) and sub-maximal as well as maximal exertion on a treadmill. It was observed that despite marked arterial hypocapnia and acute systemic hypertension which developed during exercise, blood flow as well as O2 supply in the cerebral cortex, caudate nuclei, cerebral white matter, cerebellar white matter, thalamus-hypothalamus, mid-brain, pons and medulla were not different from control values. In the cerebrellar cortex, however, blood flow and O2 supply increased with both work intensities. Thus, it was concluded that in exercising ponies, metabolic O2 requirement increased in the cerebellar cortex but was most likely not different from control (rest) in other regions of the brain.

Animals↗
PubMed1987

Transmural coronary vasodilator reserve and flow distribution during maximal exercise in normal and splenectomized ponies.

1. Transmural distribution of myocardial blood flow was studied using 15 micron diameter radionuclide-labelled microspheres in six normal ponies and nine splenectomized ponies at rest, and during maximal exercise performed without as well as with adenosine infusion (3 microM kg-1 min-1). The splenectomized ponies were also studied during submaximal exercise performed at 75% of the workload. 2. Maximal exertion in normal ponies increased heart rate (348%), mean arterial blood pressure (40.9%), rate-pressure product (563%), arterial O2 content (43.2%), and mean pulmonary artery pressure (247%). Accompanying these changes, the left ventricular, septal and right ventricular myocardial blood flows increased 419, 500, and 921% above control values, respectively, and the perfusion in all regions became nearly homogeneous. 3. Adenosine infusion during maximal exercise in normal ponies caused further significant increments in transmural myocardial blood flow in all regions as coronary vascular resistance decreased, thereby demonstrating considerable unutilized coronary vasodilator capacity. 4. In splenectomized ponies, with maximal exercise heart rate rose to a similar value as in normal ponies but mean aortic pressure, rate pressure product, pulmonary artery pressure and arterial O2 content were significantly less than in normal ponies (P less than 0.01). 5. Transmural myocardial perfusion in the splenectomized ponies also increased markedly with both exercise intensities and no significant differences were observed. 6. In the left ventricle and the septum of splenectomized ponies, transmural blood flow levels during maximal exertion were significantly higher (P less than 0.05) than in normal ponies. Adenosine infusion during maximal exercise in splenectomized ponies failed to cause further increments in blood flow to the inner layers of the left ventricle and the septum. 7. It is concluded that marked augmentation of arterial O2 content in normal ponies helped limit the increment in left ventricular myocardial perfusion required during maximal exertion, and thereby helped preservation of considerable unutilized coronary vasodilator capacity.

Animals↗
PubMed1987

Blood flow in respiratory muscles during maximal exertion in ponies with laryngeal hemiplegia.

Laryngeal hemiplegia increases the respiratory effort required during exercise. By use of 15-micron-diam radionuclide-labeled microspheres, respiratory muscle blood flows were studied at rest, submaximal exercise (SE), maximal exercise (ME), and ME + adenosine (3 mumol X kg-1 X min-1) in nine healthy laryngeal hemiplegic (LH) ponies to ascertain whether vasodilator reserve in these tissues may be exhausted during SE, which caused maximal respiratory frequency (f) to be reached. Blood flows were also studied in the limb muscles, and data were compared with normal ponies (M. Manohar, J. Appl. Physiol. 60: 1571-1577, 1986). The heart rate, f, and change in pleural pressure in LH ponies during SE were 205 +/- 5 beats/min, 91 +/- 10 breaths/min, and 61.2 +/- 8.7 cmH2O. Corresponding values for ME were 223 +/- 2 beats/min, 90 +/- 7 breaths/min, and 75.1 +/- 5.2 cmH2O. The treadmill speed for SE was set at 75% of that for ME. Mean aortic pressure (161 +/- 9 mmHg), diaphragmatic (206 +/- 27 ml X min-1 X 100 g-1), and intercostal muscle (124 +/- 12 ml X min-1 X 100 g-1) blood flows in LH ponies increased markedly with SE and these values were not different from ME (170 +/- 5 mmHg, 293 +/- 40 ml X min-1 X 100 g-1, 167 +/- 15 ml X min-1 X 100 g-1, respectively). This suggested that maximal vasodilation in the respiratory muscles was achieved during SE. Vascular resistance in the diaphragm and intercostal muscles of LH ponies also remained similar for SE, ME, and ME + adenosine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1987

Skeletal muscle perfusion during prolonged 2.03% end-tidal isoflurane-O2 anesthesia in isocapnic ponies.

Effects of 1.55 minimum alveolar concentration isoflurane O2 anesthesia (2.03% end-tidal isoflurane) on blood flow in the up-(nondependent) and down-(dependent) positioned skeletal muscles were studied at 60, 120, and 180 minutes in 6 healthy isocapnic ponies in right lateral recumbency on a nonpadded hardwood floor. Measurements were made, using 15-micron diameter radionuclide-labeled microspheres injected into the left ventricle, and comparisons were made with data obtained from ponies in the conscious state. Isoflurane administration caused a sharp reduction in cardiac output and systemic pressure (P less than 0.01), but total peripheral resistance did not change significantly. In the triceps brachii, gluteus medius, biceps femoris, and vastus lateralis of both sides, blood flow decreased significantly during 1.55 minimum alveolar concentration isoflurane anesthesia (P less than 0.01), and fluctuations did not occur with increasing duration of anesthesia. In masseter muscles, perfusion values during the 3 hours of anesthesia were not significantly different from values in awake ponies. Despite the fact that 4 ponies developed marked edema of the dependent masseter muscle, 1 pony without masseter edema developed postanesthetic forelimb lameness and 2 of the 4 ponies with masseter edema had generalized hind limb weakness after anesthesia; significant differences in blood flow between up- and down-positioned muscles were not observed. During isoflurane-O2 anesthesia in ponies, a sharp significant decrease in skeletal muscle blood flow was observed (P less than 0.01). Decreased equine skeletal muscle perfusion during isoflurane anesthesia also may be accompanied by accentuated O2 loss from the arterial blood via the countercurrent O2 exchange between large arterioles and venules.

Adrenal Glands↗
PubMed1987

Systemic distribution of blood flow in ponies during 1.45%, 1.96%, and 2.39% end-tidal isoflurane-O2 anesthesia.

Effects of 1.1, 1.5, and 1.8 minimal alveolar concentration (MAC) isoflurane-O2 (1.45%, 1.96%, and 2.39% end-tidal isoflurane, respectively) anesthesia on cardiac output, blood pressure, and blood flow to the brain, thyroid glands, adrenal glands, kidneys, and splanchnic organs were examined in 9 healthy isocapnic adult ponies. Tissue blood flows were studied using 15-micron diameter radionuclide-labeled microspheres that were injected into the left ventricle, and comparisons were made with data obtained from ponies in the conscious state. Isoflurane anesthesia caused dose-related reduction in cardiac output and arterial blood pressure, but total peripheral resistance was not significantly altered (P greater than 0.05). In the brain, vasodilation occurred with exposure to isoflurane that peaked at 1.5 MAC. Vasodilation was more pronounced in the cerebellum, pons, and medulla, compared with that in the cerebrum. Perfusion increased in cerebellar gray, as well as white, matter. However, in the cerebrum, blood flow increased in the white matter, whereas it decreased in caudate nuclei and was similar to value in the cortex of awake ponies. In thyroid glands and pancreas, intense vasoconstriction occurred during isoflurane anesthesia which caused precipitous reduction in blood flow in these organs. By contrast, adrenal gland blood flow was not affected during the 3 levels of isoflurane anesthesia because vasodilation occurred. The renal blood flow registered dose-dependent reductions during isoflurane-O2 anesthesia, but renal vasoconstriction occurred only during the deepest level (1.8 MAC) of anesthesia. Although the small intestine and and colon blood flow decreased with each concentration of isoflurane, the splenic blood flow remained unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Regional brain blood flow and O2 delivery during severe exertion in the pony.

Regional distribution of brain blood flow (radionuclide labelled 15 microns diameter microspheres) and O2 supply were studied in 11 healthy adult grade ponies at rest and during severe exercise (SE) performed on a treadmill (heart rate = 220 +/- 4 beats X min-1; VO2 = 126 +/- 9 ml X min-1 X kg-1). During SE, the mean aortic pressure increased to 169 +/- 4 mm Hg and the pHa, PaCO2 and PaO2 were 7.213 +/- 0.010, 30 +/- 1 mm Hg and 85 +/- 4 mm Hg, respectively. The hemoglobin concentration increased by 59.6% with SE. Whereas blood flow increased in the cerebellar gray matter (96%), pons (39.5%) and medulla (55.6%), in none of the other brain regions blood flow was different from rest. However, vascular resistance decreased only in the cerebellar cortex. Due to a 58% increment in arterial O2 content with SE, the O2 supply to all regions of the brain increased (P less than 0.01). The latter may be suggestive of an overall increase in brain metabolism during heavy exertion in ponies.

Animals↗
PubMed1986

Blood flow to the respiratory and limb muscles and to abdominal organs during maximal exertion in ponies.

Using radionuclide-labelled microspheres, 15 micron in diameter, we studied blood flow in the respiratory muscles (diaphragm and intercostal muscles), abdominal organs (adrenal glands, kidneys, pancreas, spleen and the small and large intestines), muscles of propulsion (gluteus medius and biceps femoris), and other working (triceps brachii and longissimus dorsi lumborum) and non-working (temporal and masseter) muscles of ponies at rest and during maximal exercise performed on a treadmill. During maximal exercise heart rate, whole body O2 consumption, cardiac output and mean aortic pressure increased 4.4-fold, 38-fold, 8-fold and 1.5-fold of their resting values, respectively. During maximal exertion arterial CO2 tension and arterial pH decreased while arterial O2 content increased by 58% due to a 59.6% rise in haemoglobin concentration. Arterial O2 tension decreased somewhat and the calculated alveolar to arterial O2 tension gradient widened during exertion. During maximal exertion blood flow in the adrenal glands increased while that in the kidneys, spleen, pancreas, small intestine and colon decreased precipitously. Thus ponies exhibited intense vasoconstriction in the renal and splanchnic vascular beds, similar to that reported in man but not in exercising dogs. During maximal exertion stride (and hence respiratory) frequency of galloping ponies was 138 +/- 3 min-1, and the blood flow and O2 delivery in the diaphragm were not different from those in other strenuously working muscles, namely gluteus medius, biceps femoris (muscles of propulsion) and triceps brachii. Blood flow in the intercostal muscles was only 54% of that in the diaphragm at rest, but with maximal exercise it registered a marked increment and the perfusion became similar to that in the longissimus dorsi lumborum, a powerful extensor of the back and loins.

Abdomen↗
PubMed1986

Right heart pressures and blood-gas tensions in ponies during exercise and laryngeal hemiplegia.

Right atrial, right ventricular, and pulmonary artery pressures, along with change in pleural pressure, were determined with catheter-tipped micromanometers in two groups of ponies at rest, as well as during moderate (trot; heart rate = 180 beats . min-1) and severe (gallop; heart rate = 220 beats . min-1) exercise performed on a treadmill. Group A (n = 8) ponies served as controls, and group B ponies (n = 6) had laryngeal hemiplegia (LH) induced by sectioning the left recurrent laryngeal nerve 20-29 days before the study. It was observed that LH ponies could not gallop for more than 45-90 s. With both levels of exertion, pressures in the right atrium, right ventricle, and pulmonary artery increased very significantly in normal ponies. The change in pleural pressure of galloping ponies was 30.4 +/- 2.9 cmH2O, and the respiratory (and stride) frequency was 138 +/- 4 breaths . min-1. During severe exercise in normal ponies, the systolic, mean, and diastolic pressures in the pulmonary artery were 107 +/- 7, 63.5 +/- 4.2, and 46 +/- 4 mmHg, despite the fact that no alveolar hypoxia could be detected. In LH ponies pulmonary artery pressures rose to levels observed in normal ponies, but during galloping, the change in pleural pressure (delta Ppl) (92 +/- 6 cmH2O) was three times that in normal ponies, and there was no synchronization of respiratory (86 +/- 6 breaths . min-1) frequency to stride frequency (142 +/- 3 strides . min-1). Despite these respiratory adjustments (decreased frequency and increased delta Ppl), arterial PO2 decreased and arterial PCO2 increased in galloping LH ponies.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Vasodilator reserve in respiratory muscles during maximal exertion in ponies.

Eight healthy adult grade ponies were studied at rest as well as during maximal exertion carried out with and without adenosine infusion (3 microM X kg-1 X min-1 into the pulmonary artery) on a treadmill to compare levels of blood flow in respiratory muscles with those in other vigorously working muscles and to ascertain whether there remained any unutilized vasodilator reserve in respiratory muscles of maximally exercising ponies. Radionuclide-labeled 15-micron-diam microspheres, injected into the left ventricle, were used to study tissue blood flows. During maximal exertion, there were increases above base-line values in heart rate (336%), mean aortic pressure (41%), cardiac output (722%), and arterial O2 content (56%). The whole-body O2 consumption was 123 +/- 11 ml X min-1 X kg-1, and the stride/respiratory frequency of the galloping ponies was 138 +/- 4/min. With adenosine infusion during maximal exertion, mean aortic pressure decreased (P less than 0.05), but none of the above variables was different from maximal exercise alone. During maximal exertion, blood flow in the adrenal glands, myocardium, respiratory, and limb muscles increased, whereas that in the kidneys decreased and the cerebral perfusion remained unaltered. With adenosine infusion during maximal exercise, renal vasoconstriction intensified, whereas adrenal and coronary beds exhibited further vasodilatation. During maximal exertion, blood flow in the equine diaphragm (265 +/- 36 ml X min-1 X 100 g-1) was not different from that in the gluteus medius (253 +/- 36) and biceps femoris (233 +/- 29); both are principal muscles of propulsion in the equine subjects) or the triceps brachii (227 +/- 26) muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1986

Effect of furosemide administration on systemic circulation of ponies during severe exercise.

Systemic distribution of blood flow was studied in 11 healthy adult grade ponies, using radionuclide-labeled microspheres (15 micron diameter) that were injected into the left ventricle. Measurements were made at rest, during severe exercise (SE) without furosemide, as well as during SE at 10 minutes and 120 minutes after furosemide administration (1.0 mg/kg, IV). During SE, heart rate, cardiac output, mean aortic pressure, and whole body O2 consumption were 220 +/- 4 beats/min, 720 +/- 44 ml/min/kg, 169 +/- 4 mm of Hg, and 126 +/- 9 ml of O2/min/kg, respectively. With SE performed after furosemide administration, mean aortic pressure decreased from prefurosemide SE value (P less than 0.05), but heart rate, cardiac output, and whole body O2 consumption remained similar to values during SE without furosemide. During SE, blood flow to cerebellar gray matter, pons, and medulla oblongata increased despite marked hypocapnia, but in other regions of the brain, blood flow was unchanged. As arterial O2 content increased by 58% with SE, O2 delivery to all brain regions increased. With SE, adrenal gland blood flow increased, but intense vasoconstriction in the kidneys, spleen, pancreas, small intestine, and colon caused blood flow to plummet. During SE, blood flow in the diaphragm, gluteus medius, biceps femoris (muscles of propulsion), and triceps brachii muscles increased to a similar level, indicating that metabolic requirements of the diaphragm during exercise may not be less than those of other vigorously contracting muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1986

Pressures in the right side of the heart and esophagus (pleura) in ponies during exercise before and after furosemide administration.

Pressures in the right side of the heart and esophagus (pleural) have not been determined in the exercising equine subjects. In the present study, 8 healthy ponies were examined to determine the changes in these variables caused by 2 degrees of exercise done on a treadmill (heart rate:183 +/- 5 beats/min [trot] and 220 +/- 6 beats/min [canter]). Measurements were also made during both degrees of exertion 10 minutes and 120 minutes after furosemide (1.0 mg/kg) administration. It was observed that both gaits resulted in significant increases in pulmonary artery, right ventricular, and right atrial pressures. The pulmonary artery systolic, mean, and diastolic pressures during strenuous exertion were 306%, 252%, and 242% of the respective resting values. At canter, when respiratory frequency (138 +/- 4 breaths/min) is synchronized with stride frequency, the delta esophageal pressure approached 30.4 +/- 2.86 cm of water. During exercise 10 minutes after furosemide administration, the increment in right atrial pressure was markedly attenuated. During strenuous exertion 120 minutes after furosemide administration, the right atrial and pulmonary arterial pressures increased, but to a significantly lower level than did the prefurosemide values. However, the mean pulmonary artery pressure was still 240% of the resting value. It is concluded that marked pulmonary hypertension is a consistent feature of moderate, as well as strenuous, exertion in the pony. Although furosemide administration attenuated the pulmonary hypertension somewhat, the significance remains unclear.

Animals↗
PubMed1985

Transmural coronary vasodilator reserve and flow distribution in unanesthetized calves sojourning at 3500 m.

Regional myocardial blood flow (MBF; 15-micron-diam radionuclide-labeled microspheres) was studied in six unanesthetized calves sojourning at 3500 m (PB = 500 mm Hg) for 53 +/- 2 days. These high-altitude (HA)-exposed calves were studied during chronic hypoxemia (PaO2 = 48 +/- 1 mm Hg), maximal coronary vasodilation, and during acute normoxemia (PaO2 = 91 +/- 1 mm Hg). Nine calves born and raised at sea level (SL) were also studied at matched PaO2 during chronic normoxemia, maximal coronary vasodilation, and acute hypoxemia to serve as control. Marked pulmonary hypertension and right ventricular (RV) hypertrophy were present in HA calves. Left ventricular (LV) MBF of HA calves during chronic hypoxemia (1.05 +/- 0.11 ml X min-1 X g-1) was similar to that of normoxemic SL calves (1.11 +/- 0.06 ml X min-1 X g-1) but MBF in their hypertrophied RV (1.65 +/- 0.21 ml X min-1 X g-1) exceeded that in normoxemic SL calves (0.47 +/- 0.06 ml X min-1 X g-1). More interesting was the finding that RV and LV MBF of HA calves did not change between chronic hypoxemia and acute normoxemia. By contrast, acute hypoxemia of a similar degree caused a dramatic increase in RV as well as LV MBF of SL calves. Minimal LV coronary vascular resistance was similar in the two groups of calves. This meant that functional cross-sectional area of LV coronary vascular bed was not altered in response to sojourn at HA. Minimal RV coronary vascular resistance of HA calves was also not different from that of SL calves. This means that functional cross-sectional area of the RV coronary vascular bed in HA calves increased proportionately with the increase in their RV mass.

Adenosine↗
PubMed1985

Transmural coronary vasodilator reserve, and flow distribution during tachycardia in conscious young swine with right ventricular hypertrophy.

Regional distribution of myocardial blood flow (MBF) was examined in eight normal and nine pulmonary artery banded (PAB) pigs before and during pacing induced tachycardia (heart rates: 175, 225 and 275 beats X min-1) as well as during iv adenosine infusion (1.5 mg X kg-1 X min-1; maximal coronary vasodilatation) using radionuclide labelled 15 micron diameter microspheres that were injected into the left atrium. It was observed that MBF per unit myocardial mass in the hypertrophied right ventricle (RV) of PAB pigs was similar to that in the RV of normal pigs. Also, minimal coronary vascular resistance per unit myocardial mass was similar between the two groups of pigs for RV as well as left ventricle (LV). This suggests that the increase in RV myocardial mass of young PAB swine was attended by appropriate adjustments in functional cross-sectional area of the RV coronary vascular bed. Despite similarity of maximal coronary vasodilator capacity in the two groups of swine, during pacing induced tachycardia MBF in the hypertrophied RV subendocardium as well as the right and middle layers of the interventricular septum in PAB pigs increased to a significantly lower level than in normal pigs and the RV endo:epi perfusion ratio, unlike in normal pigs, decreased to near unity. Increments in transmural LV MBF of PAB pigs were also attenuated during pacing at 225 and 275 beats X min-1 but the LV endo:epi perfusion ratio for the two groups of pigs remained similar. These findings suggest a possible overall depression of myocardial function in PAB swine.

Adenosine↗
PubMed1985

Regional blood flow changes in response to near maximal exercise in ponies: a review.

In recent years, increasing attention has been focused on the physiological responses of the horse to maximal exercise. Cardiovascular response in near maximally exercised galloping ponies (heart rate 225 +/- 7 beats/min; whole body oxygen consumption 122 +/- 12 ml/min/kg) comprised a marked increase in blood flow to the cerebellum, myocardium, diaphragm and the working muscles, while renal blood flow decreased precipitously. Cerebral and brainstem perfusion did not vary from resting values. Transmural homogeneity of myocardial blood flow persisted during near maximal exercise. It was reported that tachycardia of exercise contributed about one-third of the total increment in left ventricular coronary blood flow. Considerable unutilised coronary vasodilator capacity was also demonstrated in near maximally exercised ponies and it was suggested that maximally exercising ponies were not limited from further exertion because of the coronary circulation.

Animals↗
PubMed1985

Regional distribution of porcine brain blood flow during 50% nitrous oxide administration.

Regional distribution of brain blood flow was examined in 6 healthy nonmedicated swine during inhalation of 50% O2 (+ 50% N2) and at 45 minutes of 50% end-tidal nitrous oxide administration. All animals were surgically prepared 10 to 12 days before the hemodynamic study. Catheters were implanted in the left atrium, ascending aorta, descending aorta, and pulmonary artery. Brain blood flow was determined, using 15-micron diameter radionuclide-labeled microspheres injected into the left atrium. Administration of 50% nitrous oxide markedly increased blood flow in all regions of the brain (except corpus callosum), even though the animals were not excited and the arterial blood pressure, arterial blood-gas tensions, pHa, and cardiac output were not different from respective control values. At 45 minutes of 50% nitrous oxide administration, cerebral, cerebellar, and brain-stem blood flows were 144%, 137%, and 137% of respective control values. It is concluded that 50% nitrous oxide administration caused marked vasodilatation in all regions of the porcine brain.

Anesthesia, Inhalation↗
PubMed1985

Cerebral, renal, adrenal, intestinal, and pancreatic circulation in conscious ponies and during 1.0, 1.5, and 2.0 minimal alveolar concentrations of halothane-O2 anesthesia.

Blood flow to the brain, kidneys, adrenal glands, pancreas, and small intestine was studied in 8 healthy ponies while awake (control) and during 1.0, 1.5, and 2.0 minimal alveolar concentrations (MAC) of anesthesia produced, using halothane vaporized in oxygen. During the anesthesia steps, intermittent positive-pressure ventilation was used to ensure isocapnia. Organ blood flow was determined with 15-micron (diameter) radionuclide-labeled microspheres, after allowing 30 minutes of equilibration at each of the 3 preestablished end-tidal halothane concentrations. The sequence of 1.0, 1.5, and 2.0 MAC levels of anesthesia (0.90, 1.35, and 1.80% end-tidal halothane) was randomized for every animal. In the awake ponies, cerebral blood flow in the cortical (106 +/- 15 ml/min/100 g) and deep gray (103 +/- 12 ml/min/100 g) matter was approximately 5-fold of that in the white matter (22 +/- 3 ml/min/100 g). In the brain stem, there was a decreasing gradient of blood flow from the cranial (thalamohypothalamus: 65 +/- 8 ml/min/100 g) to caudal regions (medulla: 34 +/- 5 ml/min/100 g). Vasodilatation occurred in all regions of the brain with halothane-O2 anesthesia; the decrease in vascular resistance reached its nadir at 1.5 MAC. In the medulla and pons, blood flow increased above control values, with each of the 3 concentrations of halothane, but in the midbrain and thalamohypothalamus, it remained similar to the control value. In the cerebral white matter and cerebellum, blood flow increased with 1.0 and 1.5 MAC of halothane anesthesia, whereas mean aortic pressure decreased to 91% and 74% of the control value. Blood flow in the cerebral cortex was not different from the control value, even at 2.0 MAC of halothane, despite a 49% reduction in perfusion pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1984

Bovine regional brain blood flow during sojourn at a simulated altitude of 3500 m.

Regional distribution of brain blood flow (15 micron diameter radionuclide labelled microspheres injected into the left atrium) was studied in 6 unanesthetized calves during the 7th-8th weeks of exposure to a simulated altitude of 3500 m (PB = 500 mm Hg). Measurements were made during chronic hypoxemia (PaO2 = 48 +/- 1 mm Hg) and acute normoxemia (PaO2 = 91 +/- 1 mm Hg). Five calves, born and raised at sea level, were also studied in a similar manner during normoxemia (PaO2 = 86 +/- 2 mm Hg) and at 12 and 22 min of acute hypoxemia (PaO2 = 49 +/- 1 mm Hg) to serve as controls. Acute hypoxemia in sea level calves resulted in a marked uniform increase in blood flow to all regions of the brain and the brain O2 delivery remained similar to its normoxemic value. By comparison, however, blood flow in all regions of the brain in calves sojourning at 3500 m remained unchanged between hypoxemia and normoxemia. In these calves brain O2 delivery decreased during hypoxemia. These experiments demonstrated that blood flow in the bovine brain-stem and cerebellum behaved in the same manner as in the cerebrum during exposure to acute as well as chronic hypoxia. It is suggested that there are likely to be differences in adaptation of bovine cerebral circulation to acute vs chronic hypoxia.

Acute Disease↗