Biomedical subjects

R B Armstrong

Publications and source records attributed to R B Armstrong.

At least 55 records · Page 3Linked to original sources

PubMed1992

Effect of regular voluntary exercise on resting cardiovascular responses in SHR and WKY pregnant rats.

The purpose of this study was to assess the influence of regular voluntary exercise in pregnant normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats on 1) uteroplacental perfusion and mean arterial pressure in the resting conscious condition and 2) fetal number, fetal weight, and number of fetal resorptions. WKYs and SHRs were randomly assigned to standard cages [CWKY (n = 10); CSHR (n = 6)] or cages with activity wheels [EWKY (n = 7); ESHR (n = 8)]. EWKYs and ESHRs exercised for 12 wk, and then all rats were bred and experiments were conducted on gestational day 17. Resting blood flow (microspheres), heart rate (HR), and mean arterial pressure (Pa) were measured. No significant difference was found in Pa, HR, uterine blood flow (ESHRs 52 +/- 8 ml.min-1.100 g-1; CSHRs 28 +/- 6 ml.min-1.100 g-1), or maternal placental blood flow (ESHRs, 122 +/- 31 ml.min-1.100 g-1; CSHRs 78 +/- 21 ml.min-1.100 g-1) among the groups. Exercise altered the relationship between maternal placental and uterine blood flow and Pa in the SHR; SHRs with lower Pa maintained higher placental and uterine blood flow after training. Before gestation ESHRs ran on average more kilometers per week than EWKYs (43 +/- 3 vs. 34 +/- 4), but during gestation ESHRs averaged fewer kilometers per week than EWKYs (16 +/- 4 vs. 22 +/- 4). Succinate dehydrogenase activity was higher in the white vastus lateralis (1.02 +/- 0.2 mumol cytochrome c reduced.min-1.g wet wt-1) and vastus intermedius (3.1 +/- 0.5 mumol cytochrome c reduced.min-1.g wet wt-1) muscles of ESHRs.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1992

O2 delivery at VO2max and oxidative capacity in muscles of standardbred horses.

The purpose of this study was to describe the relationships between 16 physiological, biochemical, and morphological variables presumed to relate to the oxidative capacity in quadriceps muscles or muscle parts in Standardbred horses. The variables included O2 delivery (blood flow) and mean capillary transit time (MTT) during treadmill locomotion at whole animal maximal O2 consumption (VO2max, 134 +/- 2 ml.min-1 x kg-1), capillary density and capillary-to-fiber ratio, myoglobin concentration, oxidative enzyme activities, glycolytic enzyme activities, fiber type populations, and fiber size. These components of muscle metabolic capacity were found to be interrelated to varying degrees using correlation matrix analysis, with lactate dehydrogenase activity showing the most significant correlations (n = 14) with other variables. Most of the "oxidative" variables occurred in the highest quantities in the deepest muscle of the group (vastus intermedius) and in the deepest parts of the other quadriceps muscles where the highest proportions of type I fibers were localized. The highest blood flow measured with microspheres in the muscle group during exercise was in vastus intermedius muscle (145 ml.min-1 x 100 g-1), and the lowest was in the superficial part of rectus femoris muscle (32 ml.min-1 x 100 g-1). Average muscle blood flow during exercise at whole animal VO2max was 116 ml.min-1 x 100 g-1. Because skeletal muscle comprised 43% of total body mass (453 +/- 34 kg), total muscle blood flow was estimated at 226 l/min, which was approximately 78% of total cardiac output (288 l/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Clinical panel assessment of photodamaged skin treated with isotretinoin using photographs.

BACKGROUND AND DESIGN: Evaluation of the treatment of photodamaged skin requires adequate efficacy criteria. This study tested the ability of five independent dermatologists to distinguish the effect of topical treatment with isotretinoin cream (0.05% for 3 months, then 0.1% for 6 months) in 326 patients compared with vehicle for 9 months in 325 patients using high-quality, reproducible photographic slides. Panelists were blinded to the patient's identity, treatment group, and time of the photograph (baseline or end of treatment). A computer randomly projected the baseline photograph to one side of a split screen and the end-of-treatment photograph to the other. OBSERVATIONS: Isotretinoin was significantly better than vehicle for overall appearance, fine wrinkles, and discrete pigmentation by multivariate analysis of the combined results for all panelists. Univariate analysis for each panelist also indicated statistically significant superiority of isotretinoin over vehicle for overall appearance (four panelists), fine wrinkles (five panelists), and discrete pigmentation (three panelists). CONCLUSION: The clinical panel detected significantly better improvement in photodamaged-skin treated with isotretinoin than in such skin treated with vehicle. The panel provided an independent assessment of the effects of treatment uninfluenced by physical findings during treatment or information provided by the patients treated.

Humans↗

PubMed1991

Distribution of cardiac output during diurnal changes of activity in rats.

Rat locomotor and feeding behavior varies on a diurnal basis; at night the animals actively forage and eat, whereas during the day they are more inactive and somnolent. At night, cardiac output is higher, presumably for enhanced perfusion of the active muscles to support increased metabolism and for enhanced perfusion of the digestive organs to support increased digestion and nutrient absorption. Conversely, it is hypothesized that during the daytime, blood flow to these two tissues is relatively low. The purpose of this study was to test these hypotheses by measuring cardiac output and the distribution of cardiac output in rats at various times in the diurnal cycle (8:00 A.M., 4:00 P.M., and 8:00 P.M.). The radiolabeled microsphere technique was used to measure cardiac output and distribution of blood flow to the tissues. Distribution of the total cardiac output was accounted for by complete dissection, weighing, and counting of organs and carcass. Cardiac output at 8:00 P.M. (136 +/- 9 ml/min) was elevated 13% (P less than 0.05) over that at 4:00 P.M. The proportion of the cardiac output distributed to the skeletal muscles (4:00 P.M.: 25%; 8:00 P.M.: 27%) and to the digestive tract (4:00 P.M.: 14%; 8:00 P.M.: 14%) did not change between the two time periods. Thus total muscle blood flow increased (P less than 0.05) from 31 +/- 2 at 4:00 P.M. to 36 +/- 4 ml/min at 8:00 P.M.; the only digestive organ to show a significant increase in blood flow from 4:00 P.M. to 8:00 P.M. was the stomach (133 +/- 17 to 166 +/- 19 ml/min, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Mechanisms of exercise-induced muscle fibre injury.

Exercise for which a skeletal muscle is not adequately conditioned results in focal sites of injury distributed within and among the fibres. Exercise with eccentric contractions is particularly damaging. The injury process can be hypothesised to occur in several stages. First, an initial phase serves to inaugurate the sequence. Hypotheses for the initial event can be categorised as either physical or metabolic in nature. We argue that the initial event is physical, that stresses imposed on sarcolemma by sarcomere length inhomogeneities occurring during eccentric contractions cause disruption of the normal permeability barrier provided by the cell membrane and basal lamina. This structural disturbance allows Ca++ to enter the fibre down its electrochemical gradient, precipitating the Ca++ overload phase. If the breaks in the sarcolemma are relatively minor, the entering Ca++ may be adequately handled by ATPase pumps that sequester and extrude Ca++ from the cytoplasm ('reversible' injury). However, if the Ca++ influx overwhelms the Ca++ pumps and free cytosolic Ca++ concentration rises, the injury becomes 'irreversible'. Elevations in intracellular Ca++ levels activate a number of Ca(++)-dependent proteolytic and phospholipolytic pathways that are indigenous to the muscle fibres, which respectively degrade structural and contractile proteins and membrane phospholipids; for instance, it has been demonstrated that elevation of intracellular Ca++ levels with Ca++ ionophores results in loss of creatine kinase activity from the fibres through activation of phospholipase A2 and subsequent production of leukotrienes. This autogenetic phase occurs prior to arrival of phagocytic cells, and continues during the inflammatory period when macrophages and other phagocytic cells are active at the damage site. The phagocytic phase is in evidence by 2 to 6 hours after the injury, and proceeds for several days. The regenerative phase then restores the muscle fibre to its normal condition. Repair of the muscle fibres appears to be complete; the fibres adapt during this process so that future bouts of exercise of similar type, intensity, and duration cause less injury to the muscle.

Body Temperature↗

PubMed1991

Influence of type of enclosure on exercise fitness of dogs.

The effect of various confinement conditions on physical fitness in dogs was evaluated. Eighteen 9.5- to 10-month-old female purpose-bred Beagles were maintained individually for 3 months at a time in 1 of 6 confinement conditions: Condition A--an outdoor housing area with a conventional dog house and free access to a 6.1 x 9.1-m pen; condition B--outdoor kennel with a conventional dog house and free access to a 1.8 x 6.1-m run; condition C--indoor environmentally controlled 1.2 x 3.66-m run; condition D-0.9 x 1.2 x 0.84-m conventional laboratory cage in an indoor environmentally controlled room; condition E--0.9 x 1.2 x 0.84-m conventional laboratory cage in an indoor environmentally controlled room with treadmill exercise (7 km/h at a 10% grade) for 30 min/d, 5 d/wk; condition F--0.71 x 0.86 x 0.69-m conventional laboratory cage in an indoor environmentally controlled room. During the final week of each 3-month interval, muscle succinate dehydrogenase enzyme activities and submaximal exercise heart rates (during treadmill exercise) were determined to estimate physical fitness. Also, 5 days after being moved into a different housing condition, blood samples were collected for plasma cortisol determination. The type of confinement condition for dogs had little effect on muscle succinate dehydrogenase activity, but had a modest effect on submaximal exercise heart rates of dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Welfare↗

PubMed1990

Oxygen consumption and distribution of blood flow in rats climbing a laddermill.

The purpose of this study was threefold: 1) to determine whether untrained rats that refused to run on treadmill would climb on a laddermill (75 degrees incline); 2) to determine O2 consumption (VO2) in untrained rats as a function of laddermill climbing speed; and 3) to determine whether the circulatory response of untrained rats to laddermill climbing is similar to that previously reported for treadmill running at an equivalent VO2. Eighteen female Sprague-Dawley rats that would not perform on a treadmill as part of another study were used to measure VO2 as a function of laddermill speed (5-17 m/min). Data were obtained from all 18 rats; VO2 increased linearly as a function of laddermill speed (r = 0.83, y = 3.0 x + 63.2). Twenty-four female Sprague-Dawley rats that also refused to run on a treadmill were used to measure mean arterial pressure, heart rate, and blood flow distribution (with microspheres) during climbing at 5 and 10 m/min. These exercise intensities were metabolically equivalent to level treadmill running at 45 and 60 m/min (VO2 approximately 78 and 93 ml.min-1.kg-1, respectively). Of the 24 animals, 23 were willing to climb. Mean arterial pressures were higher (approximately 10%) during laddermill climbing than during equivalent treadmill running, but heart rates were the same. General blood flow distribution among muscles as a function of fiber type (with red muscles receiving higher flows) and between muscles and visceral tissues (muscle blood flow increased as a function of exercise intensity while visceral blood flows decreased) were similar to data for rats running on the level.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Rat skeletal muscle mitochondrial [Ca2+] and injury from downhill walking.

The purpose of this study was to evaluate the relationship between mitochondrial Ca2+ concentration (MCC) and the extent of muscle injury in rats that have performed prolonged downhill walking (eccentric exercise). MCC was used as an indicator of elevated [Ca2+] in the muscles, and injury was estimated from histochemical analysis of muscle cross sections by determining the numbers of intact fibers per unit area in the muscles. Elevations in MCC in the soleus and vastus intermedius muscles over time postexercise were inversely related (P less than 0.05) to the number of intact fibers per square millimeter in the respective muscles after downhill walking. Verapamil administration attenuated the elevation in MCC and injury in histochemical sections resulting from the downhill walking in soleus muscle, but intraperitoneal injection of the chelators EDTA or ethylene glycol-bis(beta-aminoethylether)-N,N,N',N'- tetraacetic acid significantly attenuated the increases in MCC and injury to both the vastus intermedius and soleus muscles in the downhill walkers. The chelators appear to exert their "protective" effects within the specific muscles that show the injury and do not significantly affect serum [Ca2+]. It is concluded that increases in MCC occur during exercise-induced fiber injury and that elevations in cellular Ca2+ may have a role in the etiology of the injury process.

Animals↗

PubMed1990

Distribution of blood flow during exercise after blood volume expansion in swine.

To study the distribution of blood flow after blood volume expansion, seven miniature swine ran at high speed (17.6-20 km/h, estimated to require 115% of maximal O2 uptake) on a motor-driven treadmill on two occasions: once during normovolemia and once after an acute 15% blood volume expansion (homologous whole blood). O2 uptake, cardiac output, heart rate, mean arterial pressure, and distribution of blood flow (with radiolabeled microspheres) were measured at the same time during each of the exercise bouts. Maximal heart rate was identical between conditions (mean 266); mean arterial pressure was elevated during the hypovolemic exercise (149 +/- 5 vs. 137 +/- 6 mmHg). Although cardiac output was higher and arterial O2 saturation was maintained during the hypervolemic condition (10.5 +/- 0.7 vs. 9.3 +/- 0.6 l/min), O2 uptake was not different (1.74 +/- 0.08 vs. 1.74 +/- 0.09 l/min). Mean blood flows to cardiac (+12.9%), locomotory (+9.8%), and respiratory (+7.5%) muscles were all elevated during hypervolemic exercise, while visceral and brain blood flows were unchanged. Calculated resistances to flow in skeletal and cardiac muscle were not different between conditions. Under the experimental conditions of this study, O2 uptake in the miniature swine was limited at the level of the muscles during hypervolemic exercise. The results also indicate that neither intrinsic contractile properties of the heart nor coronary blood flow limits myocardial performance during normovolemic exercise, because both the pumping capacity of the heart and the coronary blood flow were elevated in the hypervolemic condition.

Animals↗

PubMed1990

Hemodynamic responses during exercise at and above VO2max in swine.

Mean arterial pressure (Pa), heart rate, cardiac output (Q), and Q distribution (with radiolabeled microspheres) were measured in miniature swine as they ran at high levels on a motor-driven treadmill. Each animal ran on two occasions: once during exercise at maximal O2 uptake (VO2max) and once at an intensity estimated to require approximately 115% VO2max. The purpose was to assess these cardiovascular variables to determine whether the calculated resistance to blood flow during supramaximal exercise was different from that during maximal exercise. A total of 114 tissues/organs were dissected for blood flow analysis. Pa and Q were unaltered between the two exercise conditions. Blood flow to all but one of the 62 skeletal muscles sampled was unchanged between conditions as were the blood flows to the visceral organs and brain. The results demonstrate that vascular resistance was constant in all these tissues between maximal and supramaximal exercise intensities. Elevated blood flows were measured in 7 of the 11 coronary sites sampled. Calculated resistance to blood flow indicated that a decrease in resistance occurred in most of the samples having elevated blood flow. Because heart rate was elevated during the supramaximal exercise, the increase in blood flow was probably in response to the greater myocardial work and concomitant elevation in O2 demand. In summary, it was shown that Pa, Q, and Q distribution in most tissues remained unchanged during exercise at intensities above VO2max. Thus a precise matching occurs between the increasingly powerful vasoconstrictor drive initiated by the sympathetic nervous system and the elevated local vasodilatory drive responding to the greater O2 demand during the supramaximal exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Effects of training on reproductive tissue blood flow in exercising pregnant rats.

The purpose of this study were to investigate 1) whether treadmill training would attenuate the reduction in reproductive (RBF) and visceral tissue blood flow (VBF) that occurs during an acute bout of submaximal exercise (EX) in pregnant rats and 2) whether fetal number of fetal weight would be affected by training. One group (T) of female rats trained on a treadmill (10 degrees incline, 30 m/min) for 1 h/day 5 days/wk for 10 wk before becoming pregnant. A second group (UT) was run at the same speed and incline for 10 min/day 5 days/wk for 2 wk. T and UT rats were bred until pregnant. Skeletal muscle blood flow, RBF, and VBF were measured at pre-EX and at 1 and 10 min of EX (10 degrees incline, 30 m/min). No differences were observed before or during exercise between the two groups in RBF and VBF, heart rate, or mean arterial pressure. Both groups experienced decreases in VBF (except liver) and RBF from pre-EX to EX. In most muscles skeletal muscle blood flow increased for both groups from pre-EX to EX. Neither group experienced a change in mean arterial pressure from pre-EX to EX, but heart rate increased significantly for both groups. No differences were observed between groups in fetal number, fetal weight, or fetal resorptions. It was concluded that training does not significantly attenuate the reduction in RBF and VBF in pregnant rats that occurs during an acute bout of submaximal EX and that training does not affect fetal weight or fetal number.

Animals↗

PubMed1990

Acne: therapeutic perspectives with an emphasis on the role of isotretinoin.

This article provides nurses with information about drug therapy for acne. Various therapeutic modalities are discussed with an emphasis on the use of isotretinoin. The risks associated with pregnancy during isotretinoin therapy are discussed to help nurses work effectively with physicians and patients in the treatment of severe acne in women of childbearing potential.

Acne Vulgaris↗

PubMed1990

Initial events in exercise-induced muscular injury.

Immediately following unaccustomed exercise, particularly that with eccentric contractions, there is evidence of injury to skeletal muscle fibers: a) disruption of the normal myofilament structures in some sarcomeres, observable with both light and electron microscope and b) loss of intramuscular proteins (e.g., creatine kinase enzymes) into the plasma, indicating damage to sarcolemma. This pathology is probably responsible for the temporary reductions in muscle force and delayed-onset soreness that can occur following eccentric exercise. The mechanisms underlying this injury are not known, although loss of intracellular Ca2+ homeostasis could play a primary role. In other experimental muscle injury models, elevated [Ca2+]i appears to cause release of muscle enzymes through activation of phospholipase A2, which in turn could induce injury to sarcolemma through production of leukotrienes and prostaglandins, through free O2 radical formation (in the subsequent lipoxygenase and cyclooxygenase reactions), and/or through release of detergent lysophospholipids. On the other hand, the mechanism responsible for the rapid damage to myofibrils caused by increased [Ca2+]i is unknown. Regardless of the cause(s), the initial and early events in the injury process are autogenetic; i.e., they are indigenous to the muscle cells and occur before phagocytic cells enter the injury site.

Calcium↗

PubMed1990

Verapamil-induced creatine kinase loss from rat slow and fast muscles.

The purpose of this study was to determine the dose-response relationship between verapamil HCl and creatine kinase (CK) release from isolated rat slow (soleus, S) and fast (flexor digitorum profundus, F) skeletal muscles. Total CK activity in F muscle was approximately 2x greater than in S muscle. For both S and F muscles, CK release as a function of verapamil concentration in the incubation medium was linear (r = 0.94); the slope of the line for F muscle was 4.5x that of the S muscle. S and F muscles lost up to 38-44% of their total CK activity during the 2 hr incubation. The CK activity lost to the medium was 100% of the MM isoform. The mechanism of the enzyme release is not known.

Animals↗

PubMed1989

Effects of dipyridamole on muscle blood flow in exercising miniature swine.

The purpose of this study was to determine whether a vasodilator reserve exists in respiratory muscles and forelimb skeletal muscles in miniature swine during treadmill exercise. Blood flow (BF) was measured with radiolabeled microspheres during preexercise and before and after dipyridamole (DYP; 1 mg/kg iv) at 2 min of treadmill exercise at 11.2 (70% Vo2 max) and 17.6 km/h (Vo2 max). Muscle BFs were increased during exercise, and the relationship between exercise intensity and BF varied among the muscles. The high-oxidative extensor muscles and the flexor muscles attained peak BFs at 11.2 km/h, whereas the more superficial, lower oxidative extensor muscles showed increases in BF up to maximal exercise. During running at 11.2 km/h, DYP produced increases in BF only in cardiac muscle, respiratory muscle and the medial head of the triceps muscle (MHT), which is composed of 91% slow-twitch oxidative (SO) fibers. During maximal exercise (17.6 km/h), DYP produced a 31-mmHg decrease in mean arterial pressure (MAP) and increases in vascular conductance in all muscles studied. BF was only increased in MHT and cardiac muscle. We conclude that vasodilator reserve remains in skeletal muscle and respiratory muscle even during maximal exercise in swine. If it is assumed that DYP-induced vasodilation in a muscle sample is indicative of adenosine production, these results suggest that SO skeletal muscle (MHT) and respiratory muscle are similar to cardiac muscle in that they produce adenosine even when adequately perfused. Furthermore, during maximal exercise, all skeletal muscle appears to produce adenosine, suggesting that muscle BF is restricted under these conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Blood flow distribution in rat muscles during preexercise anticipatory response.

Previous work has suggested that preexercise "anticipatory" blood flow distribution in the muscles of rats is influenced by the intensity of the preceding conditioning or training program. The purpose of this study was to carefully control the conditioning programs for control, low-speed conditioned, and high-speed conditioned rats to determine the respective effects on preexercise mean arterial pressure (Pa), heart rate (HR), and blood flow distribution in muscles and other organs. Control (daily placement on treadmill, no exercise), low-speed conditioned (daily treadmill walking up a 12 degree incline at 15 m/min), and high-speed conditioned (daily treadmill galloping up a 12 degree incline at 50 m/min) rats were conditioned for 2-4 wk in their respective programs. On the experimental day, the circulatory variables were measured immediately before exercise by using the same preexercise regimen as during the conditioning sessions. Pa, HR, and blood flow distribution were the same in control and low-speed conditioned rats (P greater than 0.05). However, in high-speed conditioned rats, HR (+9%), Pa (+7%), and white gastrocnemius muscle (+46%) blood flow were higher than in controls (P less than 0.05). The higher white muscle flow was the result of the higher Pa and lower resistance to flow. These data demonstrate that specific changes in preexercise anticipatory blood flow distribution among muscles occur during exercise conditioning programs and that the changes are dependent on the intensity of the conditioning regimen. The mechanisms responsible for the adaptations are not known.

Animals↗

PubMed1989

No relationship between progressive muscle hyperaemia and temperature in exercising rats.

During prolonged submaximal exercise muscle blood flow has been shown to increase progressively in rats and miniature swine. This study was designed to test the hypothesis that the increases in muscle blood flow are associated with progressive elevations in body temperature in rats. Colonic temperature and muscle blood flow (determined using radioactive microspheres) were measured after 15, 30 and 45 min of exercise in rats exercising on a treadmill at 15 m min-1 on a 0 degree incline. Total hindlimb muscle blood flow increased from 79 +/- 8 ml min-1 100 g-1 at 15 min to 95 +/- 10 ml min-1 100 g-1 at 30 min (P less than 0.05). The greatest increases in blood flow occurred in the deep extensor muscles of the hindlimb. For example, in the red portion of the gastrocnemius muscle, blood flow increased from 197 +/- 15 ml min-1 100 g-1 at 15 min to 285 +/- 17 ml min-1 100 g-1 at 30 min (P less than 0.05). Colonic temperature, however, remained stable at 38.5 degrees C over this period. These data indicate that the progressive hyperaemia in muscle was unrelated to body temperature.

Animals↗

PubMed1989

A comparison of methods used to determine VO2 of exercising humans and animals.

The purpose of these experiments was to compare two systems for measuring oxygen uptake (VO2): the open circuit method of indirect calorimetry (Rv), which is commonly used in human studies, and the open flow method, which has been adopted in a variety of animal studies. VO2 measured using the Rv system (procedure 1) was accepted as the criterion value. Two procedures were used to calculate VO2 in the open flow system: MCO2 (where O2 and CO2 were measured in mixed expired gas) and MO2 (O2 measured only). VO2 was measured in ten human subjects during three continuous incremental cycling tests to peak power output administered on three separate occasions--once using each of the three procedures. The results indicated a relatively small difference in VO2 between the Rv and MCO2 procedures (6.2 +/- 4.5%) and between the Rv and MO2 procedures (3.7 +/- 1.7%), across a broad range of power outputs (40-100% VO2 peak). The difference between the Rv and MCO2 procedures decreased as power output increased, while that between the Rv and MO2 procedures remained relatively constant. Therefore, the open flow method is shown to be a valid and reproducible technique for assessment of the metabolic activity of humans and animals.

Adult↗