Search PubMed⌕ Search

Biomedical subjects

J M Johnson

Publications and source records attributed to J M Johnson.

At least 199 records · Page 11Linked to original sources
PubMed1982

Effect of heat stress on cutaneous vascular responses to the initiation of exercise.

To explore further the competition between vasoconstrictor and vasodilator reflexes in the regulation of skin blood flow, responses in forearm blood flow (FBF) to the initiation of supine leg exercise were measured by plethysmography against a background of rising internal temperature. In 17 studies involving six men, skin temperature (Tsk) was controlled with water-perfused suits first at normothermic levels, followed by a 40- to 50-min period during which Tsk was held at 38-38.5 degrees C. Supine leg exercise at a moderate intensity (100-150 W) was performed for 5-6 min of each 15 min throughout, yielding one period of exercise performed during normothermic conditions and three periods of exercise performed during the period of elevated Tsk. On the average, FBF fell significantly with the beginning of each period of exercise (P less than 0.05). Furthermore, the amount by which FBF fell tended to increase with increasing levels of preexercise FBF. Thus the average fall in FBF associated with the onset of the last period of exercise, 2.45 ml X 100 ml-1 X min-1, significantly exceeded the 1.12 ml X 100 ml-1 X min-1 fall in FBF seen with onset of work in normothermic conditions. These responses were not due to changes in internal temperature as reflected by esophageal temperatures. However, individual studies occasionally revealed a reduction or abolition of the vasoconstrictor response with the last period of exercise. These findings are in agreement with earlier studies showing a cutaneous participation in the vasoconstrictor responses to exercise but also indicate that sufficient hyperthermia can attenuate or even abolish this response.

Adult↗
PubMed1981

Effect of upright exercise on threshold for cutaneous vasodilation and sweating.

To find whether exercise or upright posture affected the internal temperature threshold for cutaneous vasodilation or the relationship between skin blood flow (SkBF) and sweat rate (SR), the relationship of esophageal temperature (Tes) to forearm SkBF and SR was measured in four settings: supine rest, upright rest, supine exercise, and upright exercise. All studies were performed at an elevated skin temperature (38-38.5 degrees C). Compared with values from supine rest, upright exercise was associated with an increase in the internal temperature threshold for vasodilation of 0.39 +/- 0.07 degrees C (P less than 0.01), whereas there was no significant alteration in the threshold for the onset of sweating. Neither the ultimate slope of the SkBF-Tes relationship nor that of the SR-Tes relationship was altered by upright exercise. The upright posture and exercise each contributed to the elevation in the threshold for cutaneous vasodilation, with the average shifts being 0.11 +/- 0.05 degrees C (P less than 0.05) and 0.28 +/- 0.08 degrees C (P less than 0.01), respectively. The net effect of this shift in threshold was to reduce the level of SkBF at any level of Tes during exercise and to increase the difference in threshold between vasomotor and sudomotor responses.

Adult↗
PubMed1981

Needle aspiration biopsy of thyroid nodules.

Thin needle aspiration biopsies for cytology were performed upon 64 patients with hypofunctioning thyroid nodules. Surgical confirmation of the diagnoses was obtained in 41 of these patients. All 12 nodules with positive needle biopsies were found to be malignant at operation. Sixteen of 17 nodules with negative findings at biopsy were found to be benign; one was found to be malignant. Twelve nodules were in the questionable cytologic group, three were malignant and nine were benign. Twenty-three patients did not undergo operation after needle biopsy. Negative biopsy findings in these patients were instrumental in guiding decisions not to recommend operation. There was no morbidity after any of the 64 needle biopsies. An analysis of our results indicates that thin needle aspiration biopsy is a valuable diagnostic tool for the selection of thyroid nodules for surgical treatment. Its routine use on our service has increased the incidence of carcinoma in surgically explored cold thyroid nodules in the past year. The procedure was helpful not only in avoiding operation for some benign lesions but also in enabling the detection of a number of otherwise unsuspected malignant tumors. Objections which are usually raised to the large scale use of thin needle aspiration biopsies of thyroid nodules are not valid.

Biopsy, Needle↗
PubMed1980

Absorption and disposition of ampicillin in the elderly.

Ampicillin (500 mg) was administered intravenously (i. v.) and orally to a small panel of young and elderly subjects in a cross-over fashion. Plasma concentrations of ampicillin were measured by a fluorimetric technique for 8 h following dosage. A two compartment-open model was used to characterise the plasma concentration-time data for the intravenous study, and a one compartment-open model incorporating an absorption lag time and a first-order absorption rate constant for the oral data. Plasma clearance after i. v. ampicillin was found to be significantly decreased in the elderly (P < 0.05, 0.08 1 h-1kg-1 versus 0.18 1 h-1 kg-1), and half life and area under the plasma level-time curve were significantly increased (P < 0.05, 6.70 h versus 1.68 h, t1/2 beta; p < 0.01, 176.51 microgram.h ml-1 versus 37.88 microgram.h ml-1, AUCO infinity) as compared to the young. No significant differences were observed between the age groups for the volume of distribution terms and the changes in drug handling noted in the elderly were attributed to a decrease in the renal elimination of ampicillin. Following oral administration a significant increase in t1/2 beta, AUCO infinity and the maximum plasma concentration (Cpmax P < 0.01, 6.59 microgram ml-1 versus 3.42 microgram ml-1) of amplicillin was found in the elderly subjects. These findings were similarly attributed to a decrease in drug elimination in the aged, since no apparent age differences were noted in the pharmacokinetic parameters governing both rate and extent of ampicillin absorption.

Absorption↗
PubMed1980

Evaluation of an immobilized-enzyme analyzer for measuring galactose in serum.

Reportedly, galactose provides an alternative carbohydrate source and improved homeostatic regulation of glucose in the premature infant. Because of its potentially toxic effects, sensitive methods are needed for monitoring its concentration during therapy. We evaluated an immobilized galactose oxidase/hydrogen peroxide electrode system and a modified homogeneous enzymic method. Both methods are suitable for measuring galactose in a small sample and are comparably precise. The latter method gives superior analytical recoveries below 100 mg/L, but is linear in absorbance response to only 300 mg/L. We find the immobilized-enzyme method superior for monitoring treatment of neonates with galactose, because it requires only a few minutes and 25 microL of serum, and the analytical procedure is simpler.

Enzymes, Immobilized↗
PubMed1979

Vertebral arteriovenous fistulas.

Vertebral arteriovenous fistulas are rare. A report of two cases is presented with problems related to diagnosis and therapy. An alternative approach to surgical management is given.

Adult↗
PubMed1979

Responses of forearm blood flow to graded leg exercise in man.

To test whether the cutaneous vascular responses to exercise are influenced by the level of work, three strategies were followed. In each, forearm blood flow and esophageal temperature were measured throughout. In part I, the forearm blood flow-internal temperature relationships from separate sessions of steady-state exercise at different loads were compared. In part II, work load was varied between 50 and 150 W. Work load was raised or lowered 50 W every 5 min over 60-75 min. The third strategy was to examine the immediate change in forearm blood flow accompanying rapid, large increments or decrements in work load. The results do not support a graded response of the cutaneous circulation to exercise. In both the first and second protocols above, the relationship of forearm blood flow to internal temperature was not measurably altered by work load. Multiple linear regression analysis failed to reveal a consistent role for work load in part II. In the third protocol, there was no consistent or sustained response to an abrupt change in work load. Thus over the range of work loads used in this study there appears to be no major role for the level of work in the regulation of forearm skin blood flow other than through the effect on internal temperature.

Adult↗
PubMed1979

Electrocardiographic verification of esophageal temperature probe position.

Esophageal temperature (Tes) varies with depth of insertion. Characteristic features of the esophageal electrocardiogram (ECG) can be used to place probes in the region where the esophagus is between the aorta and the left atrium. This describes a suitable catheter for recording of Tes and ECG and how features of the electrical activity of the atria may be used to place the probe tip. Records of Tes versus depth obtained during heating of four human subjects are included. The technique eliminates the need for radiographic verification of probe position. It could readily be employed in clinical situations with the advantage of having both a central temperature and an electrocardiogram available from a simple, readily inserted, and readily tolerated catheter.

Body Temperature↗
PubMed1979

Reflex control of skin blood flow by skin temperature: role of core temperature.

Two protocols were used to discover whether the reflex response in skin blood flow (SkBF) to rising skin temperature (Tsk) was dependent on the level of internal temperature. Part I. In five subjects, Tsk (controlled with water-perfused suits) was raised to 37 degrees C prior to, between 2 and 5 min, or between 10 and 17 min of exercise. The associated SkBF elevation per degree rise in Tsk averaged 0.20, 1.28, and 1.75 ml/100 ml . min, respectively. When Tsk was raised during the first 5 min of exercise, esophageal temperature (Tes) rose markedly (0.39 degrees C), but transiently fell if Tsk was raised after 10 min of exercise. Part II. In six subjects, different work loads were used to develop different levels of internal temperature. Tsk was elevated to 37 degrees C after 10--15 min at light (50--75 W) or moderate (100--150 W) work loads. At the heavier work load (and higher Tes), the rise in forearm SkBF per degree rise in Tsk averaged 2.33 +/- 0.38 (SE) times that observed at the light work load. These data strongly suggest that the reflex response of SkBF to rising Tsk is dependent on the level of internal temperature.

Adult↗
PubMed1978

Arteriovenous fistula secondary to rupture of atherosclerotic abdominal aortic aneurysm. Report of five cases.

Five patients with an acute spontaneous arteriovenous fistula as a result of rupture of abdominal aortic aneurysms into the inferior vena cava of iliac vein are presented. A high mortality usually accompanies this rather infrequent complication of abdominal aortic aneurysms. The pathologic and physiologic aspects of this catastrophic event are discussed with emphasis on the variation of operative management necessary for a successful outcome.

Acute Disease↗