Biomedical subjects

H J Duncan

Publications and source records attributed to H J Duncan.

34 records · Page 2Linked to original sources

PubMed1985

Martorell's hypertensive ischemic leg ulcers are secondary to an increase in the local vascular resistance.

In 1945 Martorell described ischemic leg ulcers in patients with hypertension and suggested that the ischemic necrosis was secondary to hypertensive arteriolar disease. The aim of the study was to examine the minimum vascular resistance in the skin of patients with these ulcers. Twelve control subjects (median age 52 years), eight patients with peripheral vascular disease (PVD) (median age 73 years), and six patients with hypertensive ulcers (median age 74 years) were studied. The minimum vascular resistance (MVR) and skin perfusion pressure (SPP) were determined by an isotope clearance method. Presence and severity of PVD were assessed by ankle/arm pressure ratios. The ulcer patients had a higher ankle/arm pressure ratio than the PVD group (p = 0.026) but had similar SPP (p = 0.47). When compared with the control group they had a similar pressure ratio (p = 0.09) but lower SPP (p = 0.001). The MVR was higher in the ulcer patients than the control subjects (p = 0.005) and the PVD group (p = 0.01). The study shows that patients with hypertensive ulcers have a high vascular resistance. This increase in resistance may interfere with the compensatory relaxation that normally occurs distal to an arterial narrowing, resulting in poor tissue perfusion and subsequent ulcer development.

Adult↗

PubMed1985

The effectiveness of local injections of vasodilating agents to produce vasodilation in subcutaneous tissue in rabbits.

The isotope washout method has been widely used to study characteristics of the microcirculation in localized vascular beds. Some of these studies have used local injections of vasodilating agents to maximally dilate the vascular bed. This study was undertaken to determine the agent most effective in producing this critical vasodilation. A rabbit model was constructed that allowed the study of the subcutaneous blood flow by either 133Xe and 131I-antipyrine washout. Dose-response curves were constructed for five agents. The agents used and the doses that produced the maximum washout rate, were histamine (100 micrograms), verapamil (0.5 mg), prostaglandin E1 (6 micrograms), papaverine (5 mg) and nitroprusside (60 micrograms). The five agents at these doses were compared with each other, and nitroprusside produced a greater washout rate than papaverine (P less than 0.005), histamine (P less than 0.001) and verapamil (P less than 0.005). There was no difference between nitroprusside and prostaglandin E1 (P greater than 0.01). The effect of three of the agents in producing tissue oedema was examined by comparing the washout rates values obtained with the two isotopes. Both nitroprusside and papaverine produced large oedema whereas histamine resulted in little oedema formation. Nitroprusside, therefore, appears to be the most suitable vasodilating agent for use in studies which require maximum vasodilation of localized vascular beds.

Alprostadil↗

PubMed1983

Paraplegia following abdominal aortic surgery. Case reports.

Well-known complications of abdominal aortic aneurysm surgery include haemorrhage, arterial occlusion, infection and aortoduodenal fistula. Less well known is the occurrence of paraplegia. At present there is no estimate of its incidence, and only isolated cases have been reported. We report 2 cases of paraplegia following elective aortic surgery and 2 others following acute occlusion of the abdominal aorta.

Aged↗

PubMed1982

The effects of concurrent responding and reinforcement on behavioral output.

Four birds key pecked on concurrent variable-interval one-minute variable-interval four-minute schedules with a two-second changeover delay. Response rates to the variable-interval one-minute key were then reduced by signaling its reinforcer availability and later by providing its reinforcers independently of responding. Each manipulation increased response rates to the variable-interval four-minute key even though relative reinforcement rates were unchanged. In a final phase, eliminating the variable-interval one-minute key and its schedule produced the highest rates of all to the variable-interval four-minute key. These results show that both reinforcement and response rates to one schedule influence response rates to another schedule. These results join those of Guilkey, Shull, & Brownstein (1975) in failing to replicate Catania (1963). Moreover, they violate the predictions of the equation for simple action (de Villiers & Herrnstein, 1976). In terms of a median-rate measure (reciprocal of the median interresponse time), rates to the variable-interval four-minute key were high when responding was not reduced to the variable-interval one-minute key and were low when it was reduced. This rate difference suggests a process difference between concurrent-schedule procedures that maintain high concurrent response rates versus those that do not. This process difference jeopardizes attempts to integrate single- and concurrent-operant performances within a single formulation.

Journal Article↗

PubMed1980

Chronic intestinal ischaemia: A report of 3 cases.

Chronic intestinal ischaemia should always be considered in the differential diagnosis of dyspepsia. Three cases are described to illustrate the variable presentation of the condition, its diagnosis and the satisfactory result of surgical reconstruction which may avert the potentially fatal complication of acute mesenteric thrombosis.

Adult↗

PubMed1980

The role of endorphins in animal learning and behavior.

The present review examined the influence of endorphins in animal learning and behavior. It was suggested that in learning paradigms involving stress, the stressor elicits the release of endorphins. Given the evidence on endorphin-mediated, stress-induced analgesia, it was further suggested that the stress-induced release of endorphins modulates the aversiveness of the stressor, and as such, affects the learning based on this stressor. A number of learning paradigms, e.g., the conditioned emotional response, preference for signaled shock, conditioned taste aversions, and learned helplessness, were presented in support of this mediation of learning by the endorphins. A possible interaction between the endorphins and adrenocorticotropic hormone was offered as a physiological basis for this mediation.

Adrenocorticotropic Hormone↗

PubMed1979

Atmospheric levels of trace elements in Glasgow.

Explore the source record for details and available documents.

Air Pollutants↗

PubMed1977

Stimulus generalization from feeder to response key in the acquisition of autoshaped pecking.

During autoshaping, a 6-second presentation of one stimulus and a variable time 30-second presentation of a second stimulus alternated in appearance on a pigeon key. Grain always was delivered for 3 seconds at the end of the first stimulus interval. In the first experiment, autoshaped pecking of the stimulus preceding grain delivery began much sooner when that stimulus was a black vertical line on a white background and the other stimulus was green than when the opposite stimulus arrangement was used. Because these two stimuli differed in form, hue, brightness, and similarity in hue and brightness to the illumination of the raised feeder, three subsequent experiments examined whether the differential speed of autoshaping in the two groups was due to a feature-positive, feature-negative effect, a preference for brighter over darker stimuli, a simple preference for white over green, or stimulus generalization from the brightness or hue of the illuminated, raised feeder to the stimulus on the key preceding grain delivery. The data from these experiments showed that the first autoshaped key peck was most likely to be made to the stimulus of the same hue as that illuminating the feeder, regardless of whether that stimulus was positively or negatively associated with grain delivery. At least under some conditions, therefore, stimulus-generalization mediated response transfer of pecking grain in the presence of the hue illuminating the feeder to pecking the key illuminated by a similar hue appears to account for the occurrence of autoshaped key pecking.

Journal Article↗

PubMed1974