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Biomedical subjects

R H Cox

Publications and source records attributed to R H Cox.

At least 73 records · Page 4Linked to original sources
PubMed1988

Utilization of psychomotor screening for USAF pilot candidates: enhancing predictive validity.

Subjects for this research were 320 prospective pilots who were tested on computerized versions of the Two Hand Coordination (2HC) and Complex Coordination (CC) psychomotor tests. Independent variables included five basic error measures associated with the two tests, as well as seven new variables that had not previously been utilized. Results of MANOVA and multiple regression analyses revealed that performance on the two psychomotor tests were significantly related to Undergraduate Pilot Training (UPT) outcome. A trend was observed for a prediction model based on early and total trial data to yield higher simple and multiple correlations than a model based on late trials. Regressing the basic five independent variables on UPT outcome yielded R values of 0.334, 0.271, and 0.310 for early, late, and total trial data, respectively. The predictive validity of the basic five error scores was not incrementally increased by stepping in independent variables associated with the hypotenuse of horizontal and vertical error or stick movement. A stepwise multiple regression analysis revealed that the best two-variable prediction equation included the hypotenuse of horizontal and vertical error for both psychomotor tests (R = 0.329).

Aerospace Medicine↗
PubMed1987

Contribution of salt to arterial wall changes in DOCA hypertension in the rat.

The contribution of drinking fluid salt to the development of deoxycorticosterone (DOCA) hypertension and arterial wall changes was assessed in unilaterally nephrectomized rats. Half of the DOCA-treated animals received saline supplemented with 0.2% KCl and the other half received deionized water as drinking fluid. All animals were fed standard rat chow (Na content = 0.36%). After 8 weeks, arterial pressures were significantly elevated in both DOCA groups to values which were not significantly different. The heart weight to body weight ratio was also elevated in both DOCA groups with a larger response in the saline-treated ones. Body weight of saline-treated DOCA rats was significantly lower than untreated controls and water-treated DOCA rats. Arteries from both DOCA groups exhibited increased passive stiffness, larger maximum active stress, wall thickening, decreased collagen and elastin concentration, greater relative cell volume, and greater water and cation concentrations. Larger changes were generally found in the saline- than the water-treated group. These results show that saline administration is not necessary for the development of hypertension or hypertension-induced arterial wall changes in DOCA-treated, uninephrectomized rats. Hypertension developed more slowly and arterial wall changes were similar in magnitude in water-treated animals. These results suggest that the rate and/or time history of pressure elevation may be an important factor contributing to hypertension-related arterial changes.

Animals↗
PubMed1987

Connective tissue analysis of the canine circle of Willis in hypertension.

The collagen and elastin contents of the major arterial components of the canine circle of Willis (basilar artery, posterior cerebral artery, internal carotid artery, middle cerebral artery, and anterior cerebral artery) were determined as measures of the passive mechanical properties of these vessels. Studies were carried out in seven normotensive dogs and seven dogs in which experimental renal hypertension of 3 months duration had been induced. In the normotensive animals, the collagen content of the middle cerebral artery exceeded that of the other vessels considered. The elastin content and the total connective tissue were not significantly affected by arterial site. The middle cerebral artery collagen to elastin ratio was greater than corresponding values for the basilar, posterior cerebral, and internal carotid arteries. Connective tissue differences were less pronounced in the hypertensive animals. No component of the canine circle of Willis in the hypertensive dogs showed a significantly different collagen content, elastin content, total connective tissue content, or collagen to elastin ratio. In comparing cerebral vessels from normotensive and hypertensive dogs, total connective tissue values were greater in hypertension for all arterial sites considered. These acute physiological changes in connective tissue content over small distances in intracranial blood vessels from normotensive animals, together with unique connective tissue responses of these vessels to short term hypertension, may suggest additional possible factors important in the natural history of cerebrovascular pathological conditions.

Animals↗
PubMed1986

The effects of intracerebroventricular injection of clonidine on conditioned pressor and adrenergic responses in rats.

Studies from this laboratory have shown that the first filial offspring of female spontaneously-hypertensive rats and male Wistar-Kyoto (WKY) normotensive rats develop stress-induced hypertension. The present study sought to examine the effects of intracerebroventricular administration of clonidine (8 micrograms) on cardiovascular and sympathoadrenal responses to aversive classical conditioning in these borderline hypertensive rats (BHR) and in normotensive WKY control rats. Clonidine caused significant reductions in resting arterial pressure, vascular resistance, heart rate and concentrations of epinephrine (E) in plasma for both hypertensive and normotensive rats. Central administration of normal saline to control rats of each strain did not alter basal cardiovascular or sympathoadrenal function. The presentation of a conditioned stimulus (CS) elicited a significant increase in arterial pressure and total peripheral resistance in hypertensive rats treated with saline and clonidine and in normotensive rats treated with saline. In contrast, normotensive rats treated with clonidine showed no increases in arterial pressure or vascular resistance following the onset of the conditioned stimulus. The aversive conditioning session instigated significant increases in the concentrations of norepinephrine (NE) and E in plasma in saline-treated rats. Hypertensive and normotensive rats treated with clonidine-showed a blunted increase in plasma concentrations of NE and E during this period; however, concentrations of E in hypertensive rats increased significantly from the baseline period after injection. These data suggest that an abnormality in central alpha 2-adrenoceptor-mediated inhibition of sympathoadrenal discharge and sympathetic vasomotor tone may predispose the hypertensive rat to develop stress-induced hypertension.

Animals↗
PubMed1986

Effects of deoxycorticosterone on arterial wall properties in two-kidney rats.

The contribution of deoxycorticosterone acetate (DOCA) and salt to arterial pressure and hypertension-related arterial wall changes was assessed in Wistar rats. One group of two-kidney DOCA-treated animals was given a high salt diet and another group a low salt diet. After 16 weeks of treatment, the animals on low salt intake did not exhibit a significant increase in arterial pressure compared with untreated controls, while pressure was significantly elevated in the high-salt group. Values for the latter group were not as high as values in one-kidney, high salt DOCA-treated animals. Segments of the carotid and tail arteries were used for mechanical and chemical studies. Data obtained using arteries from the low salt two-kidney DOCA group were not significantly different from those of untreated controls. A number of significant differences were found in the two high salt groups compared with the low salt group and untreated controls; these included cardiac hypertrophy, increased passive arterial stiffness, decreased connective tissue concentration and increased maximum force development in response to high potassium plus norepinephrine activation. Larger changes were found in one-kidney compared to two-kidney DOCA animals. Thus DOCA administration to two-kidney rats on high salt intake produces moderate arterial hypertension and hypertension-related arterial wall changes. On the other hand DOCA administration to two-kidney rats on low salt intake does not produce an increase in arterial pressure nor altered arterial wall properties. These results suggest that DOCA in the absence of salt excess does not elevate arterial pressure or produce arterial wall changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Changes in cardiac output and vascular resistance during behavioral stress in the rat.

Normotensive Wistar-Kyoto (WKY) rats and borderline hypertensive rats (BHR) were exposed to aversive classical conditioning procedures and chronically instrumented with arterial catheters and electromagnetic flow probes around the ascending aorta. After postoperative recovery, hemodynamic measurements and blood samples were obtained from conscious animals at rest and during aversive conditioning. The cardiovascular response to the behavioral stress consisted of a significant increase in mean arterial blood pressure, total peripheral resistance index, cardiac index, heart rate, and aortic dP/dt for both strains. However, the elevated vascular resistance seen in the BHR resulted in a significantly greater increase in mean arterial blood pressure (21 mmHg) compared with the WKY rats (14 mmHg). In addition, the BHR showed a significantly (P less than 0.05) greater plasma norepinephrine concentration (760 +/- 99 pg/ml) in response to the stress than did the WKY rats (559 +/- 53 pg/ml). These data suggest that an increase in cardiac output, elevated vascular resistance, and increased sympathetic drive may contribute to the development of stress-induced hypertension in this animal model.

Animals↗
PubMed1986

Baroreceptor control of pressure-flow relationships during hypoxemia.

In the absence of peripheral chemoreceptors, the effects of graded hypoxemia on the carotid sinus control of central and regional hemodynamics were studied in anesthetized mongrel dogs. Baroreceptor stimulation was effected by carotid sinus isolation and perfusion under controlled pressure. Blood flows were measured in the aorta and the celiac, mesenteric, left renal, and right iliac arteries. Carotid sinus reflex set-point pressures were well maintained until hypoxemia was severe. Carotid sinus reflex set-point gain was maximal during mild hypoxemia. Reflex operating point regional flows were unaffected by hypoxemia. A factorial analysis of overall reflex increases in mean aortic pressure, flow, and power during reduced baroreceptor stimulation showed potentiation by increasing hypoxemia. Corresponding effects of baroreceptor stimulation and hypoxemia on aortic resistance and heart rate were additive. Celiac, renal, and iliac blood flows increased during both hypoxemia and reduced baroreceptor stimulation. Only in the celiac bed were blood flow changes independent of concomitant changes in cardiac output. Thus, at maximum sympathetic stimulation (low carotid sinus pressure) during hypoxemia, the cardiovascular system maintained both central and regional blood flows at high systemic blood pressures independent of the peripheral chemoreceptors.

Animals↗
PubMed1986

Alterations in canine coronary arteries produced by chronic cigarette smoking.

Segments of left circumflex coronary artery were obtained from beagles that had been exposed to cigarette smoke for 2 years and from nonsmoking controls. A ring sample from each was used to determine passive (0-Ca2+ and 2 mM EGTA) and active (75 mM K+) force-length relations. Other contiguous samples were used to determine collagen and elastin content, water content and distribution, and total electrolyte content. No significant differences were found in passive mechanical properties or the collagen and elastin content of arteries from the two groups of animals. Maximum values of active force development were found to be increased in arteries from smoking dogs as were values on the ascending part of the active force-length curve. Total water content and the distribution space of an extracellular marker (60Co-EDTA) were not significantly different among arteries from the two groups. This along with the similarity of total electrolyte contents suggests that values of cell volume were not different between the two groups and that the above differences in active force development represent alterations in smooth muscle cells at the subcellular level. These results suggest that the contribution of chronic smoking as one of a group of cardiac risk factors may be due to an effect of augmenting coronary artery smooth muscle contractility.

Animals↗
PubMed1986

Aortic connective tissue content in White Leghorn females.

The aortae of adult female chickens were analyzed for their connective tissue content. Collagen increased primarily in the distal aorta; elastin decreased between the proximal and middle aorta; the collagen to elastin ratio increased progressively along the aorta. These changes in connective tissue contribute to nonuniform mechanical properties and related hemodynamic phenomena of the avian aorta.

Animals↗
PubMed1986

Effects of norepinephrine on 86Rb-uptake by arteries from spontaneously hypertensive and Wistar-Kyoto rats.

The effects of norepinephrine on Na+ -pump activity and cell Na+ were determined using carotid and tail arteries from Wister-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Maximum and control Na+ -pump activities were elevated in SHR versus WKY arteries. Cell Na+ was only elevated in Na+ -loaded SHR tail arteries. Norepinephrine increased control Na+ -pump activity in both SHR and WKY, and also increased control cell Na+ levels, but only in carotid arteries, of both groups. The increased control Na+ -pump activity produced by norepinephrine may be secondary to increased cell Na+ in carotid arteries, but not in tail arteries. The elevated Na+ -pump activity in SHR arteries does not appear to be caused by elevated cell Na+.

Animals↗
PubMed1986

Optimal pedalling rate in prolonged bouts of cycle ergometry.

This study was designed to investigate the variables which contribute to the determination of optimal pedalling rate in cycling. Five trained bicycle racers were used as subjects for the study. The experiment consisted of five 20- to 30-min tests at about 85% of each subject's pre-determined VO2max. Pedal rates of 40, 60, 80, 100, and 120 rpm were used. In the experiment, efficiency, heart rate, and perceived exertion measures were obtained at 10 and 20 min of exercise. Blood lactate concentration and plasma levels of epinephrine and norepinephrine were measured at rest, during the exercise sampling periods, and at 5 min of recovery following the exercise bout. When compared across pedal rates, gross efficiency, heart rate, and perceived exertion all were minimal at 60 or 80 rpm for each sampling period. Blood lactate showed the same relationship to pedal rate as the preceding variables at 10 min of exercise but not late in the test. The catecholamine values appeared to follow a similar trend but not significantly. The experiment showed that for this group of cyclists an optimal pedal rate existed for a prolonged period of exercise and was evident in measures of both efficiency and perceived exertion. The experiment indicates that, for researchers and for cyclists who use high power outputs, the choice of pedal rate is an important one.

Adult↗
PubMed1986

Baroreceptor control of heart rate in chickens (Gallus domesticus).

The baroreceptor control of heart rate was examined in nonanesthetized, nonrestrained, White Leghorn chickens (n = 10) by measuring the heart period response to modest increases in systolic blood pressure induced by IV boluses of phenylephrine (0.04 micrograms/g). In each animal, a sciatic artery and a femoral vein were chronically instrumented for the measurement of blood pressure and heart rate, together with venous access. Sustained and consistent cardiac slowing was seen in all chickens in response to small increases in systolic pressure. The mean slope of the regression equation between heart period and systolic pressure was 13.9 +/- 0.8 s X 10(-4)/mm of Hg. This sensitivity was reduced to 2.1 +/- 1.5 s X 10(-4)/mm of Hg by anesthetizing the chickens with isoflurane (inspired concentrations of 1%).

Animals↗
PubMed1985

Chloride ion nuclear magnetic resonance spectroscopy probe studies of copper and nickel binding to serum albumins.

The binding of Cu2+ and Ni2+ to bovine, dog, and human serum albumin has been studied by the 35Cl NMR probe technique. The number of primary copper sites were estimated to be 1.3 for human serum albumin, 3.1 for bovine serum albumin, and 6.6 for dog serum albumin. A similar number of primary nickel sites was determined for each of these albumins. On the basis of the chloride probe experiments, it appears that both copper and nickel have the same binding sites on albumin.

Animals↗
PubMed1985

Blood pressure and heart rate responses to environmental stress in the spontaneously hypertensive rat.

Blood pressure and heart rate responses of the spontaneously hypertensive rat (SHR) and the Wistar-Kyoto rat (WKY) to mild restraint and tone-shock pairings were compared during a pre-stress, aversive conditioning and post-stress period, after five previous days of exposure to the paradigm. Although SHR and WKY showed similar responses to the onset of the pre-stress period, SHR showed significantly larger blood pressure responses following the onset of the conditioning than WKY. Furthermore, WKY showed a significant blood pressure and heart rate reduction during the conditioning session which was absent in the SHR. During the post-stress period, the blood pressure of SHR remained significantly elevated compared to their home cage rest values, but the blood pressure of WKY returned to basal levels. It is concluded that while the SHR is more reactive than the WKY to stimulus onset, the major source of between-strain differences after 20 min relates to differences in adaptation to continued environmental stimulation. This can lead to exaggerated estimates of physiological reactivity of the SHR, and is supportive of Folkow's view that SHR are both hyperreactive and show more prolonged defense reactions.

Animals↗
PubMed1985

Pregnancy-induced changes in sheep uterine and carotid arteries.

To characterize the effects of pregnancy on vascular tissue, intact segments of the uterine and carotid arteries were removed from nonpregnant and near-term pregnant sheep. Pressure-diameter relations were measured on isolated segments under activated (122 mM K+, 10(-4) M phenylephrine) and passive (0.1 mM Ca2+, 10(-5) M iodoacetic acid) conditions. DNA and RNA were determined spectrophotometrically. Collagen, elastin, and water contents were also measured. Pregnancy had no effect on either the mechanics or the biochemical properties of the carotid artery. However, there was a marked increase in internal radius in the uterine artery with pregnancy (0.060 +/- 0.016 vs. 0.198 +/- 0.019 cm). Active tangential stress increased, as did passive stiffness of the uterine artery. The collagen fraction decreased during pregnancy (57.2 +/- 2.4 vs. 45.7 +/- 2.2%), while elastin and RNA remained unchanged. A small decrease in DNA produced a significant increase in the RNA-to-DNA ratio. These data suggest that, in pregnancy, the uterine artery selectively undergoes a characteristic hypertrophy of its vascular smooth muscle.

Animals↗