PubMed Health⌕ Search

Biomedical subjects

S K Powers

Publications and source records attributed to S K Powers.

At least 19 recordsLinked to original sources
PubMed1992

Relation between polyporphyrin distribution and blood brain barrier changes in the rat glioma model.

Photofrin (a polyporphyrin mixture) distribution in a rat glioma model was studied in relation to changes in the blood brain barrier (BBB). At selected intervals after intraperitoneal injection of Photofrin, the concentration of polyporphyrins (PP) and Evans Blue Dye, an indicator of BBB permeability, were determined for tumor, brain adjacent to tumor (BAT), and normal brain tissue. Contrary to earlier reports of maximal accumulation at 4-24 hours, tumor levels of PP increased throughout the 96 hour measurement period. During the early stages of tumor development, PP uptake by tumor appeared to be less correlated to BBB disruption. We conclude that passive diffusion through an incompetent BBB does not completely explain PP accumulation in tumor tissue.

Animals↗
PubMed1992

Interstitial photoradiation injury of normal brain.

The effect on normal brain of continuous interstitial laser irradiation at 630 nm through an implanted cylindrical-shape, diffusion-tipped optical fiber was studied in the rat. Brain water content in the laser irradiation area (LIA) and Evans blue (EB) dye content in selected areas of the brain were measured for different laser power outputs from 0 to 250 mW after 5 minutes of photoradiation. The degree and nature of tissue damage was examined histologically and correlated with the laser power level. There is significant brain damage, blood brain barrier (BBB) disruption, and brain edema in LIA for laser power outputs in excess of 100 mW from the diffusion tip (p less than 0.001). Brain edema in the LIA is strongly correlated with BBB disruption indicated by the presence of EB. Histologically, the cortical surface was more susceptible than deeper white matter regions to interstitial laser irradiation. Possible indirect mechanisms of brain injury from interstitial laser irradiation are discussed.

Animals↗
PubMed1992

Fenestration of intraventricular cysts using a flexible, steerable endoscope.

Multiloculated hydrocephalus with multiple intraventricular septae due to meningitis associated with ventriculitis and other CSF containing intraventricular cysts can be treated by endoscopic fenestration. Seven patients with various CSF containing intraventricular cysts were treated using a flexible steerable endoscope and the argon laser. The experience using several currently available steerable endoscopes for treatment of this neurosurgical problem is reviewed. Emphasis is placed on the use of the laser for cyst fenestration. Successful decompression of the ventricular cyst(s) was accomplished in five cases with the endoscope alone. Craniotomy was required in two patients in order to complete cyst fenestration. It is the author's impression that laser assisted ventriculoscopy with steerable flexible endoscopes is an alternative and oftentimes superior method of treating CSF containing cysts within the lateral ventricles of hydrocephalic patients. Steerable flexible endoscopes designed specifically for neurosurgical use are needed.

Adolescent↗
PubMed1992

Fluid replacement beverages and maintenance of plasma volume during exercise: role of aldosterone and vasopressin.

Previous experiments have demonstrated that consumption of a glucose polymer-electrolyte (GP-E) beverage is superior to water in minimizing exercise-induced decreases in plasma volume (PV). We tested the hypothesis that elevated plasma concentrations of vasopressin and/or aldosterone above that seen with water ingestion may explain this observation. Six trained cyclists performed 115 min of constant-load exercise (approximately 65% of maximal oxygen consumption) on a cycle ergometer on two occasions with 7 days separating experiments. Ambient conditions were maintained relatively constant for both exercise tests (29-30 degrees C; 58-66% relative humidity). During each experiment, subjects consumed 400 ml of one of the following beverages 20 min prior to exercise and 275 ml immediately prior to and every 15 min during exercise: (1) distilled water or (2) GP-E drink contents = 7% carbohydrate (glucose polymers and fructose; 9 mmol.l-1 sodium; 5 mmol.l-1 potassium; osmolality 250 mosmol.l-1). No significant difference (P > 0.05) existed in mean skin temperature, rectal temperature, oxygen consumption, carbon dioxide production or the respiratory exchange ratio between treatments. Further, no significant differences existed in plasma osmolality and plasma concentrations of sodium, potassium, chloride or magnesium between treatments. Plasma volume was better maintained (P < 0.05) in the GP-E trial at 90 and 120 min of exercise when compared to the water treatment. No differences existed in plasma levels of vasopressin or aldosterone between treatments at any measurement period. Further, the correlation coefficients between plasma concentrations of vasopressin and aldosterone and change in PV during exercise were 0.42 (P < 0.05) and 0.16 (P > 0.05), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Exercise-induced hypoxemia in athletes: role of inadequate hyperventilation.

These experiments examined the exercise-induced changes in pulmonary gas exchange in elite endurance athletes and tested the hypothesis that an inadequate hyperventilatory response might explain the large intersubject variability in arterial partial pressure of oxygen (PaO2) during heavy exercise in this population. Twelve highly trained endurance cyclists [maximum oxygen consumption (VO2max) range = 65-77 ml.kg-1.min-1] performed a normoxic graded exercise test on a cycle ergometer to VO2max at sea level. During incremental exercise at VO2max, 5 of the 12 subjects had ideal alveolar to arterial PO2 gradients (PA-aO2) of above 5 kPa (range 5-5.7) and a decline from resting PaO2 (delta PaO2) 2.4 kPa or above (range 2.4-2.7). In contrast, 4 subjects had a maximal exercise PA-aO2 of 4.0-4.3 kPa with delta PaO2 of 0.4-1.3 kPa while the remaining 3 subjects had PA-aO2 of 4.3-5 kPa with delta PaO2 between 1.7 and 2.0 kPa. The correlation between PAO2 and PaO2 at VO2max was 0.17. Further, the correlation between the ratio of ventilation to oxygen consumption vs PaO2 and arterial partial pressure of carbon dioxide vs PaO2 at VO2max was 0.17 and 0.34, respectively. These experiments demonstrate that heavy exercise results in significantly compromised pulmonary gas exchange in approximately 40% of the elite endurance athletes studied. These data do not support the hypothesis that the principal mechanism to explain this gas exchange failure is an inadequate hyperventilatory response.

Adult↗
PubMed1992

High intensity exercise training-induced metabolic alterations in respiratory muscles.

Limited information exists concerning the effects of high intensity interval exercise training (HIET) on metabolic alterations in both inspiratory and expiratory muscles. To test the hypothesis that HIET will improve the oxidative capacity of the diaphragm and major expiratory muscles, we examined Krebs cycle and beta oxidation enzyme activities in the diaphragm and three groups of expiratory (abdominal) muscles in rats subjected to 12 weeks (5 days.wk-1) of treadmill exercise. Two groups of female Sprague-Dawley rats (age ca 120 days) were studied: (1) HIET group (n = 10; animals performed 6 x ca 5-min running intervals.day-1 at ca 90-95% VO2max); (2) sedentary control group (n = 7). When compared to controls, HIET resulted in significantly elevated (P less than 0.05) activities of 3-hydroxy-acyl-Co-A dehydrogenase (HADH) and citrate synthase (CS) in the costal diaphragm, rectus abdominus, external obliques, and the plantaris muscles. In contrast, training did not increase (P greater than 0.05) the activities of CS or HADH in the crural diaphragm or the internal obliques/transversus abdominus muscles. By comparison, the training-induced increases in oxidative capacity (e.g., CS activity) in the costal diaphragm, rectus abdominus, and external obliques were relatively small (ca 23, 10, 12%, respectively) when contrasted to the exercise-induced increase in CS activity in the plantaris muscle (ca 47%). We conclude that HIET results in small but significant improvements in the oxidative and beta oxidation capacities of the costal diaphragm and at least two abdominal expiratory muscles.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1992

Diaphragmatic fiber type specific adaptation to endurance exercise.

Recent evidence suggests that exercise training results in a significant improvement in the oxidative capacity of the mammalian diaphragm; however, limited data exist concerning which diaphragmatic fiber types are metabolically altered due to training. To test the hypothesis that exercise training increases the oxidative capacity of diaphragmatic type I and IIa fibers only, we examined the effects of endurance training on the fiber type specific changes in oxidative capacity, cross-sectional area, and capillarity of the costal diaphragm. Female Fischer-344 rats (age ca 180 days) were divided into either sedentary control group (n = 6) or an exercise training group (n = 6). The trained animals exercised for 10 wks on a motor-driven treadmill (60 min.day-1; 5 days.wk-1) at a work rate equal to ca 55-65% VO2max. Capillaries were identified histologically and fiber types determined using ATPase histochemistry. Fiber cross-sectional area (CSA) and succinate dehydrogenase (SDH) activity in individual fibers were measured using a computerized image analysis system. Compared to control animals, training did not increase the capillary to fiber ratio in any diaphragm fiber type (P greater than 0.05); however, training increased capillary density (capillary No./CSA) in type IIa fibers due to a reduction in cell CSA (P less than 0.05). Further, training resulted in significant (P less than 0.05) increases in total diaphragmatic SDH activity (delta increase = 17.5%) and an increase in SDH activity in both type I (delta increase = 14%) and IIa fibers (delta increase = 17.4%). In contrast, training did not alter (P greater than 0.05) SDH activity in type IIb fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1992

Improved survival from intracavitary photodynamic therapy of rat glioma.

The effectiveness of intratumoral photoradiation in photodynamic therapy (PDT) using a polyporphyrin photosensitizer was studied in the RT-2 rat glioma model. One week after intracerebral implantation of RT-2 cells, experimental rats received a single i.p. injection of 2 mg/kg of Photofrin. After administration of the photosensitizer (48 h), the tumors were partially resected and the exposed cavity was irradiated with 15 J of laser light at a wavelength of 630 nm. Further treatment with a large craniectomy significantly enhanced rat survival. Control rats which received no photosensitizer but were treated with surgery, alone or in combination with laser irradiation, succumbed from early tumor recurrence. Photodynamic therapy without decompressive surgery resulted in hemorrhagic infarction of residual tumor and adjacent brain with focal cerebral edema which resulted in cerebral herniation and early death. Our results indicate that photodynamic therapy is effective in treating residual brain tumor but at the expense of brain tissue surrounding the tumor. Unless relieved, intracranial pressure from photodynamic therapy-associated cerebral edema in this animal model resulted in shortened survival.

Animals↗
PubMed1992

Exercise-induced cellular alterations in the diaphragm.

Limited data exist concerning the effects of exercise training on cellular oxidative capacity in the diaphragm of senescent animals. In this study we examined the changes in cellular oxidative capacity, muscle cell cross-sectional area (CSA), and capillarity within the costal diaphragm of senescent animals after a 10-wk endurance-training program. Twelve 24-mo-old female Fischer 344 rats were divided into either a sedentary control group (n = 6) or exercise training group (n = 6). The trained animals exercised on a motor-driven treadmill (60 min/day, 5 days/wk) at a work rate equal to approximately 55-65% VO2max. Capillaries were identified histologically and fiber types determined using adenosinetriphosphatase (ATPase) histochemistry. Succinate dehydrogenase (SDH) activity and CSA in individual fibers were measured using a computerized image analysis system. Exercise training did not increase (P > 0.05) the capillary-to-fiber ratio for any fiber type. However, training significantly decreased CSA (P < 0.05) and increased capillary density (capillary number/CSA) (P < 0.05) in type I, type IIa, and type IIb fibers. Furthermore, exercise training resulted in small but significant increase in SDH activity (P < 0.05) in type I and IIa fibers, whereas training did not alter SDH activity (P > 0.05) in type IIb fibers. These data demonstrate that endurance training in senescent animals results in small relative improvements in both oxidative capacity and capillary density in costal diaphragmatic type I and IIa muscle fibers. The increase in both capillary density and fiber SDH activity was largely due to a reduction in fiber CSA.

Aging↗
PubMed1992

Aging and respiratory muscle metabolic plasticity: effects of endurance training.

We examined the oxidative and antioxidant enzyme activities in respiratory and locomotor muscles in response to endurance training in young and aging rats. Young adult (4-mo-old) and old (24-mo-old) female Fischer 344 rats were divided into four groups: 1) young trained (n = 12), 2) young untrained (n = 12), 3) old trained (n = 10), and 4) old untrained (n = 6). Both young and old endurance-trained animals performed the same training protocol during 10 wk of continuous treadmill exercise (60 min/day, 5 days/wk). Compared with young untrained animals, the young trained group had significantly elevated (P less than 0.05) activities of 3-hydroxyacyl-CoA dehydrogenase (HADH), glutathione peroxidase (GPX), and citrate synthase (CS) in both the costal diaphragm and the plantaris muscle. In contrast, training had no influence (P greater than 0.05) on the activity of lactate dehydrogenase within the costal diaphragm in young animals. In the aging animals, training did not alter (P greater than 0.05) activities of CS, HADH, GPX, or lactate dehydrogenase in the costal diaphragm but significantly (P less than 0.05) increased CS, HADH, and GPX activities in the plantaris muscle. Furthermore, training resulted in higher activities of CS and HADH in the intercostal muscles in the old trained than in the old untrained animals. Finally, activities of CS, HADH, and GPX were significantly (P less than 0.05) lower in the plantaris in the old untrained than in the young untrained animals; however, CS, HADH, and GPX activities were greater (P less than 0.05) in the costal diaphragm in the old sedentary than in the young untrained animals.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1992

Alterations in diaphragmatic oxidative and antioxidant enzymes in the senescent Fischer 344 rat.

We investigated age-related changes in antioxidant, glycolytic, beta-oxidation, and tricarboxylic acid cycle enzyme activity in the diaphragm and plantaris muscle of female Fischer 344 rats. Tissue samples from the costal and crural diaphragm and plantaris muscle were obtained from 30 animals in the following age groups: 1) 6 mo old (n = 10), 2) 26 mo old (n = 10), and 3) 30 mo old (n = 10). Aging had no effect (P greater than 0.05) on the activities of citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase (HADH) in the costal or crural diaphragm. Similarly, no age-related differences existed (P greater than 0.05) in the crural diaphragm in lactate dehydrogenase (LDH) or glutathione peroxidase (GPX) activity. In contrast, the activities of LDH and GPX were significantly (P less than 0.05) higher in the costal diaphragm in the 30- than in the 6-mo old animals. In addition, the ratio of LDH to CS activity increased (P less than 0.05) as a function of age in the costal diaphragm. Conversely, the ratio of CS to GPX activity in the costal diaphragm was lower (P less than 0.05) in the 30- than in the 6-mo old animals. No significant (P greater than 0.05) age-related differences existed in LDH-to-CS or CS-to-GPX activity ratios in the crural diaphragm. Finally, aging resulted in a significant decrease (P less than 0.05) in the activities of LDH, CS, and HADH in the plantaris muscle. These data demonstrate that, unlike many hindlimb locomotor muscles, the oxidative capacity of the Fischer 344 rat diaphragm does not decrease in old age.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1992

Endurance training-induced increases in expiratory muscle oxidative capacity.

Recent evidence demonstrates that endurance exercise training improves the oxidative capacity of the major mammalian inspiratory muscle (e.g., costal diaphragm). In contrast, no data exist concerning the effects of exercise training on abdominal expiratory muscles. We tested the hypothesis that 12 wk of endurance exercise training would significantly increase the activity of selected beta oxidation and Krebs cycle enzymes of abdominal expiratory muscles of the rat. To test this hypothesis two groups of female Sprague-Dawley rats were studied: group 1, continuous exercise training (n = 13); and group 2, sedentary control (n = 6). Exercise trained animals ran 5 d.wk-1 on a motorized treadmill for 45 min.d-1 at approximately 75-80% VO2max. When compared with controls, exercise training resulted in elevated (P less than 0.05) activities of 3-hydroxy-acyl-Co-A dehydrogenase (HADH) and citrate synthase (CS) in two abdominal expiratory muscles (rectus abdominus and external obliques). In contrast, training did not alter (P greater than 0.05) CS or HADH activity in the internal obliques/transversus abdominus muscles. In general, the training-induced increases in expiratory muscles CS activity were relatively small (approximately 10-13%) when compared with the training-induced increase in CS activity in the plantaris muscle (approximately 44%). These data demonstrate that continuous exercise training results in small but statistically significant improvements in the oxidative and beta oxidation capacities of expiratory muscles.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1991

The effects of caffeine on graded exercise performance in caffeine naive versus habituated subjects.

The physiological effects of caffeine on subjects habituated to caffeine is relatively unstudied compared to those of caffeine naive subjects during graded exercise. Thus, the purpose of this investigation was to determine the effects of caffeine on maximal oxygen consumption (VO2max) and the anaerobic threshold in these two populations. Seventeen moderately trained males were classified according to caffeine usage: (1) caffeine consumption 25 mg.day-1 or less (CN) (n = 8) or (2) caffeine consumption above 300 mg.day-1 (CH) (n = 9). The subjects were tested post-absorptive on the same cycle ergometer on three occasions with 7 days separating the tests. One hour before each test the subject ingested either a gelatin capsule (C); 3 mg.kg-1 body weight of caffeine (C3); or 5 mg.kg-1 body weight of caffeine (C5). The subject then performed an incremental VO2max test beginning at 50 W and the work rate was increased 30 W every 2 min until the subject could not maintain the power output. Serial venous blood samples were drawn over 30 s at the end of each stage. The CN group significantly increased resting heart rate (fc) and expired ventilation volume (VE) after C3 and C5 and VO2 after C5. No significant differences were found for exercise VE, VO2, respiratory exchange ratio, fc or time to exhaustion. There were no significant differences (P less than 0.05) in the lactate threshold or the ventilatory threshold between treatment in either group. The CH subjects showed a significant increase (P less than 0.05) in resting plasma free fatty acid (FFA) concentration only during the C3 and C5 treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Age-related changes in enzyme activity in the rat diaphragm.

Limited data exist concerning the effect of growth and aging on the metabolic properties of the diaphragm. Therefore, we investigated age-related changes in protein concentration and glycolytic and Krebs cycle enzyme activity in the diaphragm as well as the plantaris muscle of female Sprague-Dawley rats ranging in age from 1 to 12 months. Samples from the costal and crural diaphragm and the plantaris muscle were obtained from 38 animals in the following age groups: (1) 1 month old (N = 7); (2) 4 month old (N = 6) (3) 6 month old (N = 13); and (4) 12-month-old (N = 12). Body weight and diaphragm weight increased rapidly by a factor of 6 and in parallel during 1-4 months postpartum before reaching a plateau at 6 months of age. No significant difference (P greater than 0.05) existed in the ratio of diaphragm weight to body weight among age groups. Protein concentration was significantly higher (P less than 0.05) in the costal diaphragm and plantaris at 4 and 6 months when compared to 1 and 12 months of age. In the crural diaphragm, protein concentration was significantly lower (P less than 0.05) at 1 month postpartum when compared to all other age groups. Succinate dehydrogenase (SDH) activity was significantly higher (P less than 0.05) at 1 month of age in the plantaris, the costal diaphragm and the crural diaphragm when compared to older animals. In contrast, the activity of lactate dehydrogenase (LDH) in the plantaris, the costal diaphragm and the crural diaphragm was significantly lower (P less than 0.05) in the 1-month-old animals when compared to all other ages.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1991

Evidence for an alveolar-arterial PO2 gradient threshold during incremental exercise.

Examination of the alveolar-to-arterial O2 tension (A-a PO2 difference) provides a method of examining the efficiency of pulmonary gas exchange during exercise. At present, considerable confusion exists as to the exact pattern of the A-a PO2 difference during incremental exercise. We tested the hypothesis that the A-a PO2 difference during incremental exercise is alinear with respect to metabolic rate. Measurements of the A-a PO2 difference were made on six healthy male subjects during incremental exercise under sea level conditions (PIO2 = 149 torr). An alinear model best described the relationship between the A-a PO2 difference and metabolic rate; only small increases in the A-a PO2 difference occurred at low work rates followed by a rapid increase at higher work rates. The existence of a "A-a PO2 difference threshold" was mathematically confirmed by the use of a computer algorithm to define inflection points. These data provide evidence that the relationship between the A-a PO2 difference and metabolic rate is alinear and that a metabolic threshold exists for a rapid increase in the A-a PO2 difference. We conclude that the efficiency of pulmonary gas exchange during exercise is unaltered from rest during low-to-moderate power outputs, however, high intensity exercise compromises pulmonary gas exchange efficiency as evidenced by a significant widening of the A-a PO2 difference.

Adult↗
PubMed1991

Stereotactic intratumoral photodynamic therapy for recurrent malignant brain tumors.

Photodynamic therapy (PDT) using purified hematoporphyrin derivative and stereotactic intratumorally implanted optical laser fiber(s) was used to treat patients with recurrent malignant gliomas and metastatic melanoma of the brain. Tumor response to PDT was evaluated by recording changes in the volume and pattern of tumor enhancement between computed tomographic and magnetic resonance imaging scans done before and after PDT, metabolic changes in tumor tissue by 31P magnetic resonance spectroscopy, and patient outcome. Toxicity of PDT to brain was evaluated on the basis of changes in the patients' neurological examinations and correlated with changes in brain adjacent to tumor seen on postoperative imaging studies. Dramatic tumor responses to PDT were seen in all gliomas, but no response of tumor to treatment was seen with melanoma. Transient signs and symptoms of increased peritumoral cerebral edema caused by PDT were seen in all patients. Two patients suffered permanent neurological sequelae, monocular blindness and a partial visual field defect, as a result of treatment. Two patients with recurrent anaplastic astrocytomas remain in remission at 45 and 35 weeks after PDT. We conclude that intratumoral photoradiation therapy of hematoporphyrin derivative-photosensitized malignant gliomas effectively produces necrosis of the solid component of malignant gliomas; however, intratumoral photoradiation may not reach the portion of tumor that invades normal brain.

Adult↗
PubMed1991

Deformity correction and long-term survival in an infant with iniencephaly. Case report.

The authors describe the case of a male infant who was diagnosed prenatally as having iniencephaly. Since birth, the child has grown, thrived, and undergone two successful operations to correct his cervical deformity. This case demonstrates that the iniencephaly defect is not uniformly fatal and that neurosurgical intervention may offer significant improvement in the cervical deformity.

Abnormalities, Multiple↗