PubMed Health⌕ Search

Biomedical subjects

I B Faris

Publications and source records attributed to I B Faris.

35 records · Page 2Linked to original sources
PubMed1982

Effect of exercise on gain of the carotid-sinus reflex in rabbits.

1. Blood pressure, heart rate and cardiac output were measured in six rabbits before, during and immediately after treadmill exercise. During the same periods the dynamic gain of the carotid-sinus baroreceptor reflex was estimated by creating a sinusoidal oscillation of carotid-distending pressure. 2. The average blood pressure did not change significantly during or after exercise, but heart rate and cardiac output rose markedly and there was a concomitant fall in systemic vascular resistance. 3. The reflex gain for blood pressure decreased by one-fifth during exercise, and the gains for heart rate and vascular resistance by two-fifths. Immediately after exercise the gains for all three variables decreased further, to between one-half and one-third of the resting values. 4. Our results indicate that during and after dynamic exercise the correction of a potential disturbance of blood pressure by the carotid-sinus baroreceptor reflex is decreased in magnitude or in speed.

Animals↗
PubMed1982

Increased vascular resistance in vasodilated skin an indicator of diabetic microangiopathy?

The method of isotope clearance has been used to investigate the vascular resistance in skin in severely atherosclerotic patients with and without diabetes. Dilatation of the skin vessels was achieved by the injection of histamine with a radioactive tracer (99mTc). The perfusion pressure of the skin was varied by applying graded external counter pressure over the injected area. The blood flow at any given perfusion pressure was lower (and thus the resistance higher) in the diabetic subjects (P = 0.01). These results could be explained if there was microangiopathy affecting the skin vessels.

Aged↗
PubMed1981

The carotid sinus-blood pressure reflex in conscious rabbits: the relative importance of changes in cardiac output and peripheral resistance.

This paper reports experiments to determine the relative roles of changes in cardiac output and systemic vascular resistance in determining the blood pressure response to intermittent step-changes and continuous sinusoidal changes in carotid sinus transmural pressure. Conscious rabbits with a variable-pressure capsule implanted around an innervated carotid sinus were used. After step-change in capsule pressure the approximate proportions of the changes in blood pressure attributable to changes in cardiac output were, during the pressor response, 7% after 2.5 s, 22% after 10 s and 27% at plateau, and during the depressor response 100%, 8% and 17%, respectively. During sinusoidal change in capsule pressure a mean 7% of the change in blood pressure over the full cycle was attributable to change in cardiac output.

Animals↗
PubMed1981

Blood volume and the carotid baroreceptor reflex in conscious rabbits.

1. The effects of acute blood volume change in conscious rabbits on a.c. gain of the carotid baroreceptor reflex with respect to heart rate, blood pressure, cardiac output and systemic vascular resistance were studied. 2. With acute, isohaemic increase in blood volume by 20% and 40% the only consistent trend was a decrease in gain for systemic vascular resistance. 3. With acute reduction in blood volume there was a consistent tendency for gain for heart rate to fall. With 20% reduction in blood volume, gain for cardiac output fell but gain for systemic vascular resistance rose and its phage-lag became shorter, so that gain for blood pressure was unaltered. The enhanced gain for systemic vascular resistance was not sustained with 35% reduction in blood volume, so that gain for blood pressure fell. 4. Thus control of blood pressure by the carotid sinus reflex is remarkably unaffected by acute change in blood volume, and is impaired only when there is depression of gain for cardiac output without a concomitant rise in gain for systemic vascular resistance.

Animals↗
PubMed1980

The carotid sinus baroreceptor reflex in conscious rabbits.

1. A method is described for altering the pressure across the wall of the carotid sinus in conscious rabbits by enclosing the carotid bifurcation in a rigid, fluid-filled capsule. The extracapsular arterial baroreceptors were denervated. 2. The baroreceptor--heart rate reflex, elicited by injecting vasoactive drugs or inflating aortic and vena caval cuffs, was used to test the new method. The function of the carotid sinus was shown to be unaffected by enclosure in the capsule. Denervation of the extracapsular baroreceptors reduced the gain of the baroreceptor--heart rate reflex two- to threefold. 3. The characteristics of the carotid baroreceptor reflex were studied in sixteen animals by the capsule method. Median estimates of maximum gain, and the range over which blood pressure changed, were 1.1 mmHg/mmHg and 57 mmHg respectively. There was good agreement between duplicate estimates made 1--20 days apart. 4. There was only a weak association between the effects on blood pressure and heart rate of altering carotid sinus transmural pressure. Autonomic blockade of the heart, so that its rate was fixed, did not reduce the gain or range of blood pressure change.

Animals↗
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↗
PubMed1976

The neuropathic factor in the aetiology of diabetic foot ulcers.

The nature and severity of changes due to peripheral neuropathy has been assessed clinically and electrophysiologically in 39 diabetic patients, 23 of whom had penetrating ulcers on the sole of the foot. Patients suffering from diabetic foot ulcers were found to have sensory loss to pin prick in the feet more frequently than "controls". The electrophysiological measurements confirmed the severity of the neuropathy with absent sural nerve action potentials in 95% of the ulcer patients and inexcitability of small foot muscles in 40%. Weakness of small foot muscles due to neuropathy is thought to underlie the foot deformity that leads to maldistribution of weight bearing, and subsequent pressure necrosis of analgesic skin.

Action Potentials↗
PubMed1975

The neuropathic ulcer and loads on the foot in diabetic patients.

Normal subjects and diabetic patients with and without food ulcers have been studied using an apparatus which measures the loads on the foot during walking. Diabetic patients have alterations in loading which show as a lateral shift of the highest maximum load on the forefoot and a decrease in the load carried by the toes. There is a significant progression of these changes between normal subjects, diabetic patients with deformity of the foot but no ulcer, and diabetic patients with foot ulcers. All the patients with ulcers exerted maximum loads at the site of the ulcer.

Adolescent↗
PubMedDate not supplied

Static versus dynamic techniques for characterizing the carotid sinus baroreceptor reflex in conscious rabbits.

1. We have studied in conscious rabbits the dynamic (AC) characteristics of the carotid sinus baroreceptor reflex by effecting sinusoidal pressure changes across the all of the carotid sinus of 28, 55 and 103 mmHg amplitude at frequencies of 0.005, 0.01 and 0.01 Hz. 2. The amplitudes of the reflex oscillations of blood pressure and heart rate were dependent on both input frequency and amplitude. The output amplitude for blood pressure was maximal at 0.005 Hz, for heart rate at 0.02 Hz: i.e. blood pressure output exhibited frequency attenuation, heart rate output frequency amplification. 3. AC gain was similarly dependent on input frequency, and was inversely associated, for both blood pressure and heart rate, with input amplitude. 4. Phase lag for heart rate behind carotid transmural pressure was small (3-4 degrees), suggesting that vagal efferent mechanisms predominated. For blood pressure it was positively associated with input frequency, and was much larger (30 degrees, 19 degrees and 12 degrees). 5. The reflex was also elicited by intermittent static (DC) input. The AC and DC output amplitudes were similar at high input amplitudes, but DC gain was always greater than AC except for the case of heart rate at high input frequency and low input amplitude. 6. The AC characteristics of the reflex were satisfactorily reproducible over 2-15 days. AC output amplitude provides a measure of the performance limits of the reflex, AC gain of its capacity to buffer rapidly changing disturbances, while phase lag reflects the inertia of the reflex.

Animals↗
PubMedDate not supplied

The diagnosis of aorto-iliac stenosis: a comparison of thigh pressure measurement and femoral artery flow velocity profile.

Patients with vascular disease of the legs were studied by indirectly measuring thigh and ankle systolic pressures and recording the femoral artery flow profile before and after exercise with the aim of identifying those patients in whom significant aortoiliac stenosis may not have been diagnosed by angiography. A group of patients with aortoiliac stenosis or occlusion has been compared with a group with superficial femoral artery (SFA) occlusion and apparently normal controls. Resting thigh pressures were reduced in the group of patients with aortoiliac disease and with SFA occlusion. There was no significant change in thigh pressure with exercise in any group but ankle pressure fell with exercise in the patients with aortoiliac disease and with SFA occlusion. Femoral artery flow profiles provided better discrimination between the groups but six of the forty-two patients with SFA occlusions had abnormal tracings and a low thigh pressure suggesting they may have significant proximal disease.

Aorta, Abdominal↗