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Biomedical subjects

J M Johnson

Publications and source records attributed to J M Johnson.

At least 109 records · Page 6Linked to original sources
PubMed1993

Postmarketing surveillance: curriculum for the clinical pharmacologist. Part II: Clinical and regulatory considerations.

This is the second of a two-part series that develops a curriculum on postmarketing surveillance. With the ongoing emphasis on drug safety and possible earlier marketing of drugs, this becomes an essential element of clinical pharmacology training. The usual educational focus on drug safety is a pharmacokinetic or pharmacodynamic perspective on a specific drug or drug class, perhaps in the context of clinical trial study design and analysis. This curriculum complements this approach and provides an overview of drug safety surveillance from regulatory and epidemiologic perspectives.

Adverse Drug Reaction Reporting Systems↗
PubMed1993

Prenatal diagnosis of neonatal alloimmune thrombocytopenia using an allele-specific oligonucleotide probe.

The prediction of neonatal alloimmune thrombocytopenia (NAIT) in affected families is usually based on information about gene frequencies of the antigen systems involved, parental phenotyping, and fetal platelet counts. Recently the use of allele-specific oligonucleotide probe typing for PlA (HPA-1) antigens has been described to determine the risk of second or subsequent fetuses in families where one infant had the diagnosis of anti-PlA1 (HPA-1a)-mediated NAIT (McFarland et al., 1991a). This paper describes the first case in which the prenatal diagnosis of PlA (HPA-1) antigen status was accomplished using this technology on genomic DNA derived from chorionic villus tissue in the first trimester, and presents the implications of these findings for the clinical management of this disorder.

Adult↗
PubMed1993

Cranial cruciate ligament rupture. Pathogenesis, diagnosis, and postoperative rehabilitation.

Rupture of the cranial cruciate ligament is the most common cause of stifle lameness in the adult dog. An understanding of the pathogenesis of cranial cruciate ligament rupture and the resulting degenerative joint disease is crucial in establishing an accurate diagnosis and implementing appropriate treatment. Early diagnosis of the cruciate-deficient stifle with appropriate therapeutic intervention may minimize degenerative joint disease but does not prevent it in all cases. Rehabilitation of the surgically corrected cruciate-deficient stifle may influence the success of the surgical outcome.

Animals↗
PubMed1993

Changes in photosynthesis and water status of developing leaves of Brachystegia spiciformis Benth.

Changes in net carbon assimilation and water status were studied during leaf development in the deciduous, tropical species Brachystegia spiciformis Benth. In this upland savanna African tree, bud-burst and leaf development occur approximately two months before the rainy season. The newly formed leaves synthesize anthocyanin until the fully expanded leaves of the whole canopy are red. This foliage is referred to as "spring flush" foliage. Subsequently, the anthocyanins are metabolized and the pre-rain leaves become green. Carbon dioxide assimilation exhibited a bimodal diurnal pattern and was similar for pre-rain green leaves and fully expanded flushing leaves, although pre-rain green leaves showed a net uptake of carbon throughout the daylight period, whereas flushing leaves exhibited only brief periods of net photosynthesis in the morning and early afternoon. Measurements of leaf water potential and relative water content showed a diurnal pattern with considerable variation throughout the day. Leaf water potential and relative water content values decreased soon after sunrise reaching a minimum at a time corresponding to the afternoon peak in CO(2) assimilation. Stomatal conductance was closely related to transpiration rate in both flushing and pre-rain green leaves, although flushing leaves had lower stomatal conductances than pre-rain green leaves. Pre-rain green leaves exhibited a compensation irradiance of approximately 180 micro mol m(-2) s(-1), whereas flushing leaves had positive net photosynthesis only at PPFDs greater than 300 micro mol m(-2) s(-1). Rate of photosynthesis (expressed per leaf area or chlorophyll unit) increased as anthocyanin concentration decreased, although the photosynthetic rate continued to increase long after the leaf anthocyanins had been degraded to low, visually undetectable amounts. Post-rain green leaves had chlorophyll concentrations, transpiration rates and stomatal conductances similar to those of pre-rain green leaves; however, photosynthetic rates in post-rain leaves were more than three times higher. Thus, during the early stages of the spring flush, carbon asimilation rates of the flushing leaves were inversely related to leaf anthocyanin concentrations. In pre-rain green leaves, photosynthesis was limited by other non-stomatal factors.

Journal Article↗
PubMed1993

Mechanisms of control of skin blood flow during prolonged exercise in humans.

Exercise in a warm environment raises internal temperature and leads to a rapid increase in skin blood flow (SkBF). As exercise continues, and internal temperature approaches 38 degrees C, the rate of rise of SkBF is markedly attenuated despite further significant increases in internal temperature. To find whether this attenuation is mediated by increased cutaneous active vasoconstrictor activity or by a reduced rate of rise of active vasodilator activity, each of 12 male subjects had 0.64 cm2 forearm skin sites iontophoretically treated with bretylium tosylate for selective local blockade of noradrenergic vasoconstrictor nerves. SkBF was monitored there and at adjacent untreated control sites by laser-Doppler blood flowmetry (LDF). Whole body skin temperature (Tsk) was controlled by water-perfused suits, and esophageal temperature (Tes) was monitored as an index of internal temperature. Mean arterial pressure (MAP) was monitored and cutaneous vascular conductance was calculated as LDF/MAP. Sweat rate was also monitored by dew point hygrometry in 11 subjects. Tsk was raised to 38 degrees C, after which subjects began 20-30 min of exercise on a bicycle ergometer. The rate of the initial rapid increase in SkBF with increasing Tes was not altered by bretylium treatment (P > 0.05 between sites). The attenuation of the rate of rise during the latter phase of exercise was not abolished by bretylium treatment (P > 0.05 between sites); instead, there was a trend for the attenuation to be enhanced at those sites. We conclude that the attenuated rate of rise of SkBF is due to limitation of active vasodilator activity and not due to increased vasoconstrictor tone.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Role of sympathetic nerves in the vascular effects of local temperature in human forearm skin.

The role of adrenergic nerve function in the cutaneous vascular response to changes in local skin temperature in the human forearm was examined using three protocols: 1) blocking release of norepinephrine presynaptically by local iontophoresis of bretylium (BT), 2) altering background adrenergic tone by changing whole body skin temperature, and 3) blocking cutaneous nerves by proximal infiltration of local anesthetic. Forearm skin blood flow was measured by laser-Doppler flowmetry (LDF) and cutaneous vascular conductance (CVC) was calculated as LDF/blood pressure. In protocol 1, local cooling (29 degrees C) elicited a rapid and sustained fall in CVC at control sites (-43 +/- 8%) in contrast to a biphasic response at BT-treated sites, consisting of an initial vasodilation followed by a vasoconstriction (percent change CVC = 28 +/- 13 and -34 +/- 18, respectively). Local warming (39 degrees C) increased CVC at control and at BT-treated sites by 331 +/- 46 and 139 +/- 31%, respectively. In protocol 2, at a neutral, cool, or warm whole body skin temperature, local cooling (29 degrees C) elicited similar reductions in CVC (-34 +/- 8, -29 +/- 5, and -30 +/- 4%, respectively), and local warming (38 degrees C) produced similar increases in CVC (89 +/- 15, 85 +/- 21, and 74 +/- 22%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Hydrolyzable tannins: potent inhibitors of hydroperoxide production and tumor promotion in mouse skin treated with 12-O-tetradecanoylphorbol-13-acetate in vivo.

The anti-oxidant and the anti-tumor-promotion activities of several hydrolyzable tannins (HTs), including a commercial tannic-acid (TA) mixture, were examined in mouse skin treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) in vivo. A single application of TPA gradually increases the hydroperoxide (HPx)-producing activity of the epidermis, which is maximally stimulated at 3 days and returns to control levels at 9 days. Pre-treatments with TA and ellagic acid (EA) strongly inhibit, in a dose-dependent manner, this HPx response to TPA. Total inhibition by TA lasts for about 16 hr, beyond which it is substantially reduced but not completely lost. TA can also reduce the level of epidermal HPx when it is applied 36 hr after the tumor promoter. EA is an antioxidant 10 times more potent than TA and n-propyl gallate (PG), which are equally effective against TPA-induced HPx production. Gallic acid is the least effective of the HTs in inhibiting HPx formation. TA also inhibits the production of HPx induced by several structurally different tumor promoters and the greater HPx responses produced by repeated TPA treatments. When applied 20 min before each promotion treatment, twice a week for 45 weeks, several HTs inhibit the incidence and yield of papillomas and carcinomas promoted by TPA in initiated skin. Overall, TA is more effective than EA and PG in inhibiting skin-tumor promotion by TPA, suggesting that the anti-oxidant effects of HTs are essential but not sufficient for their anti-tumor-promotion activity.

Animals↗
PubMed1992

Antitumor-promoting activities of hydrolyzable tannins in mouse skin.

Ellagic acid and gallic acid and its derivatives, applied topically to female CF-1 mice 20 min before each 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment inhibit the inductions of epidermal ornithine decarboxylase activity, hydroperoxide production and DNA synthesis caused by this potent tumor promoter in relation with their abilities to inhibit the promotion of skin papillomas and carcinomas in the two-step initiation-promotion protocol. Because of its potency against TPA promotion, tannic acid, which is already known to inhibit tumor initiation, may inhibit the multistage process of carcinogenesis.

Animals↗
PubMed1992

Resting and maximal forearm skin blood flows are reduced in hypertension.

To find whether the vasodilator capacity of nonacral skin is reduced in hypertension, we measured forearm blood flow by venous occlusion plethysmography in 10 seated normotensive (mean +/- SD mean arterial pressure, 94 +/- 5 mm Hg) and 10 hypertensive (112 +/- 9 mm Hg) men at rest for 39 minutes while the forearm was heated with water at 42 degrees C, a maneuver known to selectively and maximally vasodilate skin. Blood pressure, measured every 5 minutes, did not change with heating. We found that in the normotensive group resting forearm blood flow was higher (3.64 +/- 1.12 versus 2.48 +/- 0.58 ml/100 ml tissue per minute, p less than 0.001; normotensive group versus hypertensive group) and resting forearm vascular resistance lower (30.17 +/- 10.99 versus 48.88 +/- 17.37 mm Hg.min.100 ml tissue per minute, p less than 0.05; normotensive group versus hypertensive group), and maximal forearm blood flow with local heating was higher (29.32 +/- 11.99 versus 18.19 +/- 4.50 ml/100 tissue per minute, p less than 0.018; normotensive group versus hypertensive group and vascular resistance lower (4.07 +/- 1.04 versus 6.54 +/- 1.17 mm Hg.min.100 ml tissue per minute, p less than 0.005; normotensive group versus hypertensive group). To find whether this degree and duration of local warming maximally vasodilated the skin in hypertensive subjects (as it does in normotensive subjects), we measured forearm skin blood flow before and during local heating plus 10 minutes of ischemia using a laser Doppler flowmeter.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Zinc and iron utilization in young women consuming a beef-based diet.

The purpose of this study was to determine the utilization of zinc in young adult women fed diets containing varying amounts of lean ground beef. A secondary objective was to determine the utilization of iron. The 28-day study was divided into one 7-day preexperimental period, during which a vegetarian diet was fed, and three randomly arranged 7-day experimental periods. During the experimental periods, the diets contained 3, 6, or 9 oz of beef, supplying varying levels of zinc and iron. Complete collections of urine and fecal samples were obtained from each subject. All the diets resulted in positive zinc balance; however, mean zinc balances were significantly higher when subjects consumed the experimental diets containing beef. When data for all diets containing beef were combined, mean values for apparent zinc absorption and zinc retention were not significantly higher than values that resulted from the vegetarian diet. Consumption of all diets resulted in a positive iron balance; however, mean iron balances were significantly higher for diets containing beef. As the amount of beef in the diet increased, the bioavailability of iron increased. We found that zinc and iron utilization was enhanced after consumption of a diet including lean ground beef. Results of this study also suggest that little increase in zinc and iron utilization is realized by including more than 3 oz beef per day in the diet.

Adult↗
PubMed1992

The tendency for temperament to be "temperamental": conceptual and methodological considerations.

Temperament seems to be a concept that stimulates a great deal of enthusiasm among nurses and professionals who "discover" it. Yet "knowing" that you have captured something of value does not necessarily imply full knowledge and understanding of the object. On the contrary temperament enthusiasts guarantee no consensus of opinion about what it is or how to best measure it. And so the conceptual and methodological issues for debate and discussion continue spilling over into both its research and clinical use. Sorting out the issues and the implications for use when there has been so much discussion and debate can be difficult. This article attempts to identify the main issues surrounding temperament, where we stand on some of the issues, and the practical implications for nurses who are interested in incorporating the measurement of temperament into clinical practice and research.

Child, Preschool↗
PubMed1992

Control of skin blood flow during exercise.

When body temperature rises, skin blood flow (SkBF) increases to effect transfer of metabolic heat from the core to the skin. This convective heat transfer is never more important than during dynamic exercise. Control of SkBF involves a complex interaction of regulatory systems (body temperature, blood pressure, metabolism, etc.) and efferent mechanisms (passive withdrawal of constrictor tone, reflex vasoconstriction, active vasodilation). The purpose of this paper is to provide an updated review of this complex control system--control that allows for maintenance of blood pressure and perfusion of active muscle without adverse impact on thermoregulation. Also discussed are vasomotor mechanisms, various components of exercise that are important in the control of SkBF (e.g., intensity, posture, and duration of exercise), and the influences of such factors as blood volume and tonicity, aerobic fitness and heat acclimation, and age.

Age Factors↗
PubMed1992

A comprehensive analysis of preoperative patient education.

1. One of the most important responsibilities of a nurse is preoperative preparation of the patient for surgery. Preoperative teaching helps to relieve some of the emotional stress patients have when facing surgery. 2. By providing a structured preoperative teaching class, the nurse can inform, support, and collaborate with adult surgical patients about the planned care. The nurse can also involve patients as partners in making the best possible decisions about their care. 3. Patient evaluations about the preoperative education class revealed a high level of satisfaction. The classes were believed to be an important contribution to patient education.

Humans↗
PubMed1992

Exercise and the cutaneous circulation.

Our understanding of the control of the cutaneous circulation has increased over the past decade, but is still far from complete. There is a cutaneous vasoconstriction at the beginning of exercise that usually effectively competes with concurrent thermoregulatory drives for vasodilation. This cutaneous vasoconstrictor response, however, requires dynamic activity by a significant muscle mass as small muscle groups or isometric exercise are ineffective or nearly so. Also, exercise causes the threshold internal temperature relative to rest such that SKBF is lower during exercise than in resting conditions for a given thermal stimulus. A further influence by exercise on the cutaneous circulation is to limit the degree of cutaneous vasodilation when heat stress and exercise are combined. These three roles for exercise compete with the thermogenic role that promotes vasodilation. The previously described effects act through the adrenergic vasoconstrictor system and the separate active vasodilator system. The increase in SKBF with heat stress represents the combination of withdrawal of vasoconstrictor activity and elevation of active vasodilator activity. The vasoconstrictor effect of the initiation of exercise is accomplished strictly through enhanced vasoconstrictor activity; vasodilator withdrawal does not participate [72]. However, both the exercise-induced elevation in thermoregulatory threshold for raising SKBF and the limitation to cutaneous vasodilation during exercise are strictly functions of the active vasodilator system [69, 73, 78]. In the first case, active vasodilation is delayed until a higher (relative to rest) level of internal temperature is reached. In the second case, the plateau in SKBF during exercise in the heat is due to a similar plateau in active vasodilator activity. Exercise has also served as a tool for the study of other influences on the cutaneous circulation. The influences of alterations in body fluid volumes, osmolarity, acclimatization, hypertension, time of day, menstrual phase, and others on the control of SKBF have been assessed by using exercise as a calorigenic source. The question as to whether the nonthermoregulatory influences of exercise interact with these other influences to give a modification of the pattern of control different from what might be observed at rest is largely unanswered. Future directions for research are numerous, but several fundamental questions are outstanding. The mechanism of active cutaneous vasodilation has been elusive since its discovery and remains an exceptionally important question. Second, the sensory elements associated with exercise giving rise to the alterations in the pattern of control are unclear. This problem is made challenging by the fact that the efferent control by exercise differs between its initiation and events later in exercise.(ABSTRACT TRUNCATED AT 400 WORDS)

Acclimatization↗