Biomedical subjects

S F Ibrahim

Publications and source records attributed to S F Ibrahim.

4 recordsLinked to original sources

PubMed1998

Measurement of the time course of peripheral vasoactivity: results in cigarette smokers.

The brachial artery response to flow was assessed non-invasively by ultrasonic measurement of arterial diameter before and 1 min after 5 min of cuff-induced ischemia. It was hypothesized that continuous measurement of arterial diameter and flow velocity would provide a more complete and accurate evaluation of the response to change in blood flow. Therefore, a system to provide this data was developed and its utility in exploring the acute and chronic effects of smoking on arterial function was demonstrated. Brachial artery diameter and flow velocity were measured before, during and for at least 3 min after 5-min of forearm cuff occlusion. Measurements were acquired from 12 habitual smokers (mean 18.3 pack years), after at least 2 h (mean 6.5 h) without smoking ('pre-cigarette') and immediately after smoking one cigarette ('post-cigarette'), as well as from 12 age- and sex-matched lifelong non-smokers. The slope of brachial artery diameter versus time during the occlusion period and the maximum dilation after cuff release relative to the pre-occlusion diameter were significantly decreased in pre-cigarette smokers compared with non-smokers (P < 0.0001 for both comparisons). Importantly, the absolute arterial dilation during the period of increased flow (i.e. reactive hyperemia) was equal for the pre-cigarette smokers and non-smokers (0.31 +/- 0.03 vs. 0.32 +/- 0.04 mm, respectively). Immediately after smoking, the flow response parameters in chronic smokers changed toward non-smoker values (P < 0.001 for post-cigarette vs. pre-cigarette comparisons of the diameter slope during occlusion and the maximum dilation after cuff release relative to pre-occlusion diameter). Thus, continuous diameter measurements in smokers who refrained from smoking demonstrated abnormal constriction of the brachial artery during the low flow period of cuff occlusion, but normal absolute dilation during the period of increased flow. Immediately after smoking, the artery no longer constricted during occlusion. These findings demonstrate the potential value of continuous monitoring of arterial diameter and flow velocity before, during and after application of a vasoactive stimulus.

Adult↗

PubMed1997

Peripheral vasoactivity in familial hypercholesterolemic subjects treated with heparin-induced extracorporeal LDL precipitation (HELP).

Hypercholesterolemia is associated with abnormalities in arterial vasoactivity which can be reversed with cholesterol-reducing therapies. Heparin-induced extracorporeal LDL precipitation (HELP), an invasive method for treating refractory hypercholesterolemia, causes regression of both xanthomas and atherosclerosis, but its effect on vasoactivity has not been investigated. We tested the effects of HELP on vasoactivity with an ultrasound system for continuous measurement of arterial flow velocity and end-diastolic diameter. We measured brachial artery vasoactivity before, during, and after a 5 min forearm vascular occlusion. Vasoactivity measurements were acquired from 6 subjects with familial hypercholesterolemia (FH) who had been treated chronically with HELP, immediately before and after each of 4 treatments, and from 12 age- and sex-matched normocholesterolemic subjects (2 matched with each HELP subject). Peak arterial dilation after cuff release, relative to the pre-occlusion diameter, was similar for the pre-treatment, post-treatment, and normocholesterolemic groups (0.29 mm pre-treatment, 0.30 mm post-treatment and 0.33 mm normocholesterolemic, P = NS). The slope of arterial diameter during occlusion was also similar for the three groups (-0.10 microm/s pre-treatment, 0.02 microm/s post-treatment, and 0.06 microm/s normocholesterolemic, P = NS). These two parameters are known to be decreased in hypercholesterolemic subjects to an extent which could be readily detected by the power of this study. Interestingly, one homozygous FH subject consistently demonstrated significant improvement in these two parameters immediately after HELP, suggesting an individual difference in arterial physiology. On average, FH patients treated chronically with HELP have similar vasoactivity to age- and sex-matched subjects with low risk for atherosclerosis. This result, in light of the many studies that have associated hypercholesterolemia with abnormal vasoactivity, suggests that chronic HELP therapy improves vasoactivity in patients with severe hypercholesterolemia.

Adult↗

PubMed1996

Treatment of hypercholesterolemia with heparin-induced extracorporeal low-density lipoprotein precipitation (HELP).

Familial hypercholesterolemia (FH) can cause early disability and death from premature atherosclerotic cardiovascular disease. Patients homozygous for the disease have very high plasma cholesterol, extensive xanthomatosis, and die from atherosclerosis in childhood or early adulthood. Past attempts to improve the prognosis included removal of cholesterol from the circulation by ileal bypass or biliary diversion. Neither treatment was successful. Direct removal by plasmapheresis of low-density lipoprotein (LDL), the primary carrier of cholesterol in plasma, was first performed on an FH homozygous patient in 1966. The treatment was well tolerated and led to rapid diminution of xanthomas. Other experimental treatments included selective LDL apheresis with monoclonal or polyclonal antibody affinity columns. A method for selective LDL apheresis was developed in 1983 by Armstrong, Seidel, and colleagues based on heparin precipitation of LDL at low pH. This method, called HELP, removes all apolipoprotein B-containing lipoproteins including LDL and lipoprotein (a), as well as some fibrinogen. LDL apheresis by HELP is well tolerated; the incidence of side effects is low, and the treatment has been associated with regression of cardiovascular disease. LDL apheresis, rather than liver transplantation, is the treatment of choice for patients with severe, life-threatening hypercholesterolemia which does not respond to diet and drug therapy.

Adult↗

PubMed1992

Does limb proprioception drift?

The hypothesis that proprioceptively perceived limb position drifts during visual occlusion was re-examined by combining some of the protocols used in previous experiments. Sixteen adult subjects made judgements of static limb position during visual occlusion lasting up to 2 min. In addition, the effect of brief 250 ms "glimpses" of the limb, occasional proprioceptive stimulation and directed attention were examined. Despite, conflicting evidence from earlier experiments, there was clear evidence of a drift in perceived limb position, towards the body, during visual occlusion. This drift was halted if brief glimpses of the limb were provided, or minor re-positioning (without vision) was allowed. In neither case, however, did the supplementary cues reset limb position to its originally perceived position. Drift was amplified when subjects attempted to attend to limb position rather than perform a secondary tracking task. The results are not easily accounted for if drift is considered purely as an effect of peripheral sensor adaptation. A notion of central-drift between visual and proprioceptive maps is suggested as an alternative hypothesis.

Cues↗