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Biomedical subjects

I D McCarthy

Publications and source records attributed to I D McCarthy.

At least 37 records · Page 2Linked to original sources
PubMed1995

The acute vascular response to intramedullary reaming. Microsphere estimation of blood flow in the intact ovine tibia.

The tibial nutrient artery supplies 62% of cortical blood flow in the diaphysis and normal blood flow is centrifugal (Willans 1987). Intramedullary reaming destroys the nutrient artery and injures the endosteal surface of the cortex. Trueta (1974) suggested that the direction of blood flow can reverse from centrifugal to centripetal after loss of the endosteal supply. We examined this hypothesis by measuring cortical and periosteal blood flow after intramedullary reaming of the tibia in eight sheep, using 57Co radiolabelled microspheres. The unreamed contralateral tibiae served as a control group. Thirty minutes after reaming there was no significant change in cortical blood flow, but a sixfold increase in the periosteal flow. Our study confirms Trueta's hypothesis; after trauma or in other pathological states, flow can become centripetal.

Animals↗
PubMed1994

Humoral regulation of blood flow in the vertebral endplate.

STUDY DESIGN: Blood flow in the sheep lumbar spine was measured. OBJECTIVES: The effect of vasoactive agents, noradrenaline and acetylcholine, on blood flow adjacent to the disc--bone interface was determined. SUMMARY OF BACKGROUND DATA: The main route for disc nutrition is through the vertebral endplate. Although the vascular anatomy in this region has been well described, its response to neurohumoral influences has not been quantified. METHODS: Blood flow in bone adjacent to the lumbar intervertebral discs was measured using the microsphere technique before and after infusions of noradrenaline and acetylcholine in two groups of five female sheep. Systemic arterial pressure was measured during each infusion. RESULTS: Vertebral bone blood flow was unchanged during noradrenaline infusion, but increased by 60% during acetylcholine infusion. This was associated with a significant decrease in systemic arterial pressure. CONCLUSIONS: These data are consistent with the existence of muscarinic receptors in vessels of the vertebral endplate, which suggests that the vasculature may influence disc nutrition.

Acetylcholine↗
PubMed1994

The vascular response to fracture micromovement.

Micromovement has been shown to promote the healing of experimental fractures, but its role in the clinical management of fractures with soft-tissue injury is less certain. In a 2-mm transverse osteotomy of the ovine tibia held in an instrumented external fixator, axial interfragmentary displacement was quantified in vivo for six weeks after osteotomy. Group I (n = 11) had an axial fixation stiffness of 460 N/mm and Group II (n = 12) had a stiffness of 238 N/mm. With a 25% difference in micromovement, a fourfold change in corticomedullary blood flow was observed at two weeks after osteotomy (p < 0.01). Although by six weeks mechanical properties in torsion were similar, there were marked differences in the periosteal cross-sectional perimeter, area, and intracortical porosity that complemented the hemodynamic changes. The early vascular response is very sensitive to the initial mechanical environment, and appears to precede and determine the organization of osteogenesis. Further understanding of this relationship may prove to be of direct clinical relevance in the augmentation of healing of devascularized diaphyseal fractures.

Animals↗
PubMed1992

A distributed model of exchange processes within the osteon.

In order to understand various exchange processes within the osteon, a mathematical model to describe the system has been developed which allows for concentration gradients in the axial and radial directions as well as cellular consumption and binding to bone surface. The normal values for the model parameter are discussed and the effects of the model parameters on the behaviour of the model are investigated. This model supports the idea that diffusion alone may be an inefficient mechanism in transport between blood and osteocytes.

Biological Transport↗
PubMed1992

What should a pharmacy manager do when a serious medication error occurs? A panel discussion.

Questions related to medication errors were discussed by a panel of hospital department managers. When a serious medication error occurs, the manager has a responsibility to help the employee, the patient, and the patient's family cope with its effects, as well as a responsibility to prevent such errors from recurring. The difficulty of dealing with medication errors may be compounded when the legal system and the news media get involved. Therefore, a system for handling a serious error should be in place before that error occurs. It is also necessary to decide whether to use medication error reports in the employee evaluation process; this could make employees reluctant to report their errors. Ultimately, pharmacy managers are responsible for medication errors that occur, and repercussions have varied from nothing to reprimands to termination. Past errors, if they are reported, can be used to improve the system in which they occurred and to educate other health-care professionals. Therefore, pharmacists need to cooperate with other health-care professionals in documenting medication error reports. A national reporting system is needed so that medication error information can be shared on a large scale without placing the people involved in legal jeopardy. Sharing information about medication errors is necessary to prevent future occurrences; mechanisms are needed to facilitate such sharing.

Legislation, Medical↗
PubMed1991

Heterogeneity of blood flow in tibial cortical bone: an experimental investigation using microspheres.

The distribution of tibial blood flow was measured by injecting approximately (600-1000) x 10(3) 15 mu microspheres, labelled with either tin-113 (113Sn) or cobalt-57 (57Co) into femoral arteries of five mature greyhounds. The diaphyseal cortex, stripped of periosteum and devoid of marrow, was sawn into 40 pieces (10 transverse sections x 4 anatomical quarters/section). Relative deposition densities of the 113Sn microspheres in 40 pieces of cortex were found. These values, together with their associated masses, proved, from a statistical point of view, that flow rate heterogeneity was substantial in the diaphysis. In particular, for the diaphyseal cortex, distribution of relative deposition densities (flow rates) in six bones was found to be positively-skewed with a relative dispersion ((SD/mean) x 100) of approximately 40%.

Animals↗
PubMed1991

The effect of devascularisation upon early bone healing in dynamic external fixation.

We examined the effect of periosteal devascularisation upon the early healing of osteotomies of sheep tibiae held in an instrumented external fixation system with an axial stiffness of 240 N/mm. At 14 days, cortical blood flow measured by the microsphere technique was 19.3 ml/min/100g in the well-vascularised osteotomies, but only 1.7 ml/min/100g in the devascularised osteotomies, despite an increase in medullary flow (p less than 0.0005). Delay in healing of the devascularised osteotomies was suggested by an in vivo monitoring system and confirmed by post-mortem mechanical testing. We suggest that the osteogenic stimulus of dynamic external fixation is dependent on the early restoration of cortical blood flow in devascularised fractures.

Animals↗
PubMed1991

Rapid effects of parathyroid hormone(1-34) and prostaglandin E2 on bone blood flow and strontium clearance in the rat in vivo.

The vascular effects of noradrenaline, ATP, parathyroid hormone (PTH) and prostaglandin E2 (PGE2) were investigated in the rat. Additionally, the exchange of mineral ions between bone and blood was assessed by measuring strontium clearance, with the aim of investigating whether the vascular effects of these agents altered uptake of mineral ions or if this exchange could be changed independently of blood flow. Radioactive microspheres and 85Sr were used to establish bone blood flow and mineral clearance. Measurements of bone blood flow and arterial pressure were made in each animal and used to calculate vascular resistance. A measurement of 85Sr clearance was also obtained. Arterial blood pressure was significantly affected by noradrenaline (P less than or equal to 0.003) and ATP (P less than or equal to 0.015). Additionally, noradrenaline significantly (P less than or equal to 0.03) reduced bone blood flow. This decrease was related to a significant increase in vascular resistance. Arterial blood pressure and bone blood flow were significantly reduced by both bovine PTH(1-34) (P less than or equal to 0.001, P less than or equal to 0.02) and PGE2 (P less than or equal to 0.005, P less than or equal to 0.001). Vascular resistance to bone was increased by both agents but this was only statistically significant in the case of PGE2 (P less than or equal to 0.01). A significant (P less than or equal to 0.001) reduction in strontium was also produced by PGE2. In each group the relationship between bone blood flow and strontium clearance was then analysed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1989

Multiple tracer studies of bone uptake of 99mTc-MDP and 85Sr.

Multiple tracer outflow dilution studies were performed on the normal canine tibia. In all cases 125I-labeled albumin was used as a vascular tracer. In one series of experiments 99mTc-labeled methylene diphosphonate and [14C]sucrose were used as test tracers, and in a second series 85Sr and 22Na were used. A bolus of three tracers was injected into the tibial nutrient artery, and fractional concentrations appearing in the ipsilateral femoral vein were measured for a period of 5 min. A distributed model, containing parameters for capillary and bone permeability and apparent volumes of distribution of interstitial fluid, was fitted to these data. It was found that there was no discrimination between movement of 85Sr or 22Na from interstitial fluid space into bone. Transcapillary exchange does not appear to be a significant barrier to exchange between blood and bone surfaces.

Animals↗
PubMed1987

Bone blood flow measured with microspheres: the problem of non-entrapment.

Radioactive microspheres were injected into the tibial nutrient arteries of dogs. The validity of their use to measure bone blood flow was tested by examining their concentration in femoral venous blood. Non-entrapment in the tibia was considerable in two animals following rather prolonged alternate periods of perfusion and ischaemia. When such treatment was minimised, non-entrapment was small, showing that in this respect microspheres provide a valid means of measuring bone blood flow.

Animals↗
PubMed1987

The pattern of distribution of blood flow in dog limb bones measured using microspheres.

The distribution of blood flow to segments of the leg bones of anaesthetised dogs was studied using radioactive microspheres injected into the heart or the tibial nutrient artery. Following central injection, repeated measurements after an interval showed no change of pattern of distribution. The effects of ligation of the tibial nutrient artery during this interval suggested that 30% of the blood flow to the tibia is normally via this vessel, which predominantly supplies the diaphysis. This deduction differed from that derived from the injection of microspheres during perfusion through a tibial nutrient artery cannula, when half the flow reached the epiphyses. This proportion decreased and the flow to the diaphyseal marrow increased after alternate periods of perfusion and ischaemia, demonstrating the labile nature of bone blood flow distribution.

Animals↗
PubMed1986

Inhibition of bone cell metabolism increases strontium-85 uptake.

Experiments have been performed on the canine tibia to investigate whether perturbation of the energy metabolism of bone cells can influence the short-term exchange of bone mineral. Simultaneous injection of three radioactive tracers, 125I-albumin, 85Sr, and 86Rb, into the tibial nutrient artery was followed immediately by measurement of the concentration of these tracers in the venous outflow from the bone for a period of 5 minutes. This procedure was performed before and after the injection of potassium cyanide into the bone. From the measured concentrations, extraction ratios for 85Sr and 86Rb with respect to 125I-albumin were calculated. It was found that net extraction after 5 minutes of 85Sr was significantly increased. This result indicates that efflux of ions from exchangeable mineral is dependent to a significant extent on the metabolic activity of bone cells.

Albumins↗
PubMed1986

In vitro measurement and computer modelling of the diffusion of antibiotic in bone cement.

The diffusion coefficient for a particular antibiotic (benzyl penicillin) in various types of bone cement has been calculated from direct measurement of the passage of radio-labelled penicillin through thin sections of cement at intervals over a period of 90 days, assuming the transport processes to be Fickian. Since the concentration gradient across the test sample is not uniform in the earlier stages of the experiment, a finite-difference approximation to the diffusion equation was used to take account of the transient behaviour in determining the coefficient. This method of analysis may also be used to predict the release, as a function of time, from the surface of antibiotic-loaded bone cement and from implanted pre-loaded PMMA beads used to provide antibiotic cover following bone or joint surgery. Our computer-generated predictions appear to agree very well with previously published figures arising from in vivo and in vitro studies and we conclude therefore, that Fick's Law accurately describes the process, even when the cement mix is inhomogeneous. We have by this means a reliable method by which the diffusion coefficients for various combinations of cement, antibiotic and other additives may be retrospectively determined and compared.

Anti-Bacterial Agents↗
PubMed1986

Distributed model of blood-bone exchange.

An understanding of bone physiology obtained from a knowledge of fluid spaces and their associated barriers may lead to better management of bone pathologies. Such information can be obtained by mathematically modelling the results of multiple tracer outflow dilution techniques, which in our case were performed on the canine tibia. Hence, a computer model was developed to describe the exchange processes of tracers between blood and bone. Capillary permeability, bone binding and the vascular, interstitial fluid and bone volumes of distribution were used as parameters in the equations describing the system, which also used published morphometric bone data. Parameter estimates were then derived by the use of optimization procedures.

Animals↗
PubMed1986

The volume of distribution of ceftazidime and albumin in normal, immature and infected bone.

The penetration of ceftazidime into bone was determined by measuring the volume of distribution of 14C-ceftazidime in infected and non-infected bone of adult mongrel dogs. The volume of distribution in non-infected cortical bone was 0.114 +/- 0.011 l/kg (mean +/- S.E.M.) and increased significantly in non-infected immature callus to 0.484 +/- 0.13 l/kg (P less than 0.05). In the presence of infection, the volume of distribution in non-infected cortical bone was 0.144 +/- 0.05 l/kg, and significantly higher in infected reactive cortical bone, 0.453 +/- 0.07 (P less than 0.05). We conclude that ceftazidime penetrates infected and non-infected bone and that this penetration is greater into immature bone.

Animals↗