Search PubMed⌕ Search

Biomedical subjects

J Ludbrook

Publications and source records attributed to J Ludbrook.

At least 109 records · Page 6Linked to original sources
PubMed1980

A comparison of three blood tests for cancer.

Plasma carcinoembryonic antigen concentration, serum phosphohexose isomerase activity and the erythrocyte sedimentation rate were determined in patients with cancer, patients being treated for various benign conditions and healthy young persons. This was to make an intercomparison between the ability of these assays to distinguish patients who have cancer from those who do not and from normal persons. The upper boundaries of the assays were defined by the one-sided, distribution-free, upper tolerance limits of the reference populations. Only by means of the assay for carcinoembryonic antigen was it possible to distinguish patients who had cancer from those who did not. Twenty-two per cent of patients with cancer could be identified by this assay with a false-positive error rate of less than 5 per cent.

Adult↗
PubMed1979

A method for the analysis of sigmoid stimulus-response curves.

This paper describes a method, using an interactive computer programme, for fitting a curve to data which is expected to assume a sigmoid form. The programme is specifically designed to generate best estimates of the limits and maximum slope of stimulus-response curves for the carotid sinus baroreceptor reflex, but is applicable to curve-fitting tasks in other fields such as immunology, pharmacology, biochemistry and neurophysiology.

Animals↗
PubMed1978

Effect of isometric hand-grip exercise on the carotid sinus baroreceptor reflex in man.

1. The changes in R--R heart interval that result from step-increase and step-decrease in carotid sinus transmural pressure induced by a variable pressure neck chamber were measured in seven normal men. Observations were made at rest, and during isometric hand-grip exercise at 24%, 44% and 64% of maximal voluntary contraction. 2. The response of heart interval to increase in carotid sinus transmural pressure was progressively and markedly diminished according to the strength of hand-grip. This effect was fully developed from the moment of onset of the exertion. 3. The response of heart interval to decrease in carotid sinus transmural pressure was much less consistently affected by hand-grip exercise.

Adult↗
PubMed1978

Lack of effect of isometric handgrip exercise on the responses of the carotid sinus baroreceptor reflex in man.

1. The change in arterial pressure and heart rate resulting from alteration of carotid sinus transmural pressure by a median--34 mmHg and +33 mmHg by means of a variable-pressure neck chamber was tested in seven male volunteer subjects, at rest and during exertion of 35, 45 and 65% of maximum voluntary handgrip. 2. During 60 s of 35 and 45%, and during 30 s of 65%, of maximal voluntary handgrip there was virtually no alteration of the response of blood pressure to alteration carotid sinus transmural pressure. 3. The bradycardic response to increase in carotid sinus transmural pressure was reduced at various times after the commencement of handgrip at 45 and 65% of maximum voluntary contraction. 4. It is concluded that a reduction in arterial baroreceptor reflex sensitivy does not play an important role in the initiation of the increase in arterial blood pressure and heart rate caused by isometric exercise. 5. The hypothesis is advanced that some of the cardiovascular changes in exercise may result from elevation of the central 'set point' for blood pressure.

Adult↗
PubMed1978

Baroreceptor reflexes in human hypertension.

We studied the control of arterial pressure by the carotid sinus baroreceptors in 35 hypertensive humans, using a variable pressure neck chamber to alter carotid sinus transmural pressure in a graded fashion. The results were compared with those obtained from 11 normotensives. As in normotensives, reduction in carotid transmural pressure caused a linearly related pressor response and vice versa. However, whereas in normotensives the pressure response was greater than the depressor, the reverse was the case in hypertensives. Furthermore, the pressor response decreased and the depressor response increased progressively with an increase in severity of the hypertension. Thus while in normotensives the carotid baroreflex is more effective in protecting against hypotension, in hypertensives the antihypertensive function of the reflex is favored. Similar differences between hypertensives and normotensives were found with respect to the carotid baroreceptor control of heart rate. In eight hypertensives, reflex changes in heart rate also were studied by injection of phenylephrine and trinitroglycerine to vary not only carotid baroreceptor activity, but also activity of extracarotid baroreceptors. The results were compared with results of similar studies on eight normotensives. These comparisons suggest that, whereas the carotid baroreceptor reflex remains active in hypertension, reflexes stemming from extracarotid baroreceptor areas are much diminished.

Adult↗
PubMed1977

Electrical bone-growth stimulation in an experimental model of delayed union.

An experimental model has been devised for the consistent production of delayed bone healing of the tibia in adult dogs. A double-blind trial, with bias eliminated, was used to evaluate the use of a commercially available direct-current bone-growth stimulator with this model. The stimulator produced a statistically significant acceleration of bone healing at four weeks in the experimental model. Osteogenesis was normal, and no dysplastic, inflammatory, or neoplastic changes were found. This research has shown that electrical stimulation of bone is safe and augments bone formation. The bone-growth stimulator unit remains on trial, but in future it may alter the management of many difficult orthopaedic problems.

Animals↗
PubMed1977

Comparison of whole plasma and perchloric acid-extracted plasma assays for carcinoembryonic antigen.

A direct, paired, comparison was made of two plasma radioimmunoassays for carcinoembryonic antigen (CEA), between a perchloric acid-extracted, ammonium sulphate precipitation method; and a whole-plasma, double-antibody method. For both assays the same preparations of standard CEA, 125I-labelled CEA, and anti-CEA serum were used. Plasma samples were taken from young healthy subjects (24), cancer-free hospital inpatients (44) and cancer-proven untreated patients (94). Within-batch and between-batch variation were both greater for the extracted-plasma method. Cancer discriminatory ability was assessed by probabilistic means. With cancer-free inpatients as the reference group, no difference between the assay methods was revealed. With young healthy subjects as the reference group the whole-plasma assay was superior.

Adult↗
PubMed1977

The variable-pressure neck-chamber method for studying the carotid baroreflex in man.

1. The variable-pressure neck-chamber method was analysed in ten healthy volunteer subjects to determine its suitability for the study of the carotid baroreceptor reflex in man. 2. Positive and negative pressures applied to the neck (range +/- 60 mmHg) were always transmitted linearly to a tissue catheter outside the carotid sinus, but only 86% of positive pressure, and 64% of negative pressure. Tissue pressures were confirmed by simultaneous measurement in the internal jugular vein adjacent to the carotid sinus. 3. Positive and negative pressure changes within the above range did not alter PO2 of internal jugular venous blood, suggesting that cerebral blood flow was unaltered. 4. Positive pressure changes induced reflex pressor responses of similar magnitude at arterial PO2 12-8 and 70-1 kPa (96 and 527 mmHg), suggesting that the carotid chemoreceptors were not involved. 5. It is concluded that the variable-pressure neck chamber is a valid method for selectively studying the carotid baroreceptor reflex in man. However, transmission of external pneumatic pressure to the carotid sinus is imperfect and greater for positive than for negative pressure. This must be recognized to avoid underestimation of gain and distortion of shape of the reflex.

Adult↗
PubMed1977

Circulatory reflexes from carotid and extracarotid baroreceptor areas in man.

The carotid sinus baroreceptor reflex was studied in 11 normotensive subjects, using a variable pressure neck chamber and correcting for imperfect pressure transmission to the carotid sinus. Decreased carotid baroreceptor stimulation caused a sustaineded rise in arterial pressure, and increased carotid baroreceptor stimulation caused a sustain fall. The responses were in linear relation to the stimulus, and, after reaching the steady state, greater for the reduced than for the increased baroreceptor stimulation. Thus the carotid sinus baroreceptor reflex of the normotensive man is an effective antihypotensive and antihypertensive feedback system, though the former function may have more sensitivity. The increased and decreased baroreceptor stimulation by the neck chamber also caused bradycardia and tachycardia which were modest in magnitude and often transient. In eight subjects the reflex changes in heart rate induced by the neck chamber were compared with those induced by altering transmural pressure not merely at the carotid sinus but throughout the arterial tree (injection of phenylephrine and trinitroglycerin). The slopes of these relations were 3 times as great in the latter circumstance. Thus the carotid baroreceptors play a lesser role in heart rate control than do extracarotid baroreceptors.

Adult↗
PubMed1977

Experimental delayed union of the dog tibia and its use in assessing the effect of an electrical bone growth stimulator.

A technique has been described for the consistent production of delayed bone healing of the tibia in an animal model. A controlled double blind trial, where independent observors did not know the coding of the stimulators and did not collaborate with each other, has evaluated the use of a direct current bone growth stimulator in such an animal model. The conclusion of the experiment is that this commercially available direct current stimulator does produce a significant acceleration of bone healing at 4 weeks in the experimental model used. There is no evidence of inflammatory or neoplastic changes. The eventual clinical role of electrical bone stimulation remains uncertain and many questions remain unanswered, but are promising enough to encourage a controlled clinical trial in situations of disturbed bone healing. Electrical stimulation is apparently safe and appears to significantly augment bone formation. A controlled clinical trial is now being carried out in major medical centers in Australia.

Animals↗
PubMed1976

Effects of the sympathetic nervous system and the adrenal medullary hormones on dog hind limb blood flow after haemorrhage.

The contributions of the sympathetic nervous system and the adrenal medullary catecholamines to the response of dog hind limb resistance vessels to haemorrhage were examined. Anaesthetized dogs were bled either 30% or 45% of blood volume. There was little difference between the vascular conductance response in untreated hind limbs and sympathectomized limbs. Conductance in limbs that had been both sympathectomized and alpha-adrenergically blocked with phenoxybenzamine was markedly above that of untreated limbs. Blood flow in both the untreated limbs and the sympathectomized limbs was closely similar to that predicted from the pressure-flow curve for the hind limbs obtained in non-bled dogs. Flow was higher than predicted in the limbs with combined sympathectomy and alpha-adrenergic blockade. It is concluded that the sympathetic nervous system exerted little vasoconstrictive influence after haemorrhage, but that circulatory catecholamines exerted a strong vasoconstrictive influence that was opposed in the normal limbs by an almost equally powerful vasodilatory force of undetermined origin.

Animals↗
PubMed1976

Carotid baroreceptor reflex in normotensive and hypertensive subjects.

1. A graded decrease and increase in carotid baroreceptor activity (induced by a varying pressure in a neck chamber) caused a linearly related increase and decrease in arterial blood pressure. This occurred in both normotensive and hypertensive subjects. 2. Decrease of carotid baroreceptor activity caused a greater increase of blood pressure in normotensive than in hypertensive subjects. Increasing the activity caused changes of similar magnitude in the two groups. 3. Decrease of baroreceptor activity also caused an increase in heart rate although increasing the activity of the reflex had little effect on heart rate, particularly in normotensive subjects. Thus the carotid baroreceptor effect on blood pressure does not always reflect that on heart rate and inference of one reflex response from measurement of the other may be in error.

Blood Pressure↗
PubMed1976

Factors influencing the carotid baroreceptor response to pressure changes in a neck chamber.

1. Transmission of pneumatic pressure from a neck chamber to the region of the carotid sinus is imperfect and asymmetric (86% of positive pressure, 64% of negative pressure). This has to be taken into account in the correct analysis of the carotid baroreceptor reflex. 2. There is no evidence for a reduction in cerebral blood flow nor of carotid chemoreceptor stimulation in response to an increase in neck chamber pressure of about 45 mmHg. Thus it is likely that the pressor response to this manoeuvre is in fact due to reduction in carotid baroreceptor activity.

Carotid Sinus↗