Carbon monoxide disposition in the perfused rat liver

A simple method for determining carbon monoxide (CO) disposition in the rat liver perfused with erythrocyte-free buffer was developed. Wash-in experiments were performed with buffer containing tracer quantities of [14C]sucrose and 3H2O and equilibrated with CO. Outflow samples were collected into tubes containing human erythrocytes, which avidly bind CO. Outflow curves were analyzed using compartmental models. Fractional recovery of CO was 1.07 +/- 0. 17, and the apparent volume of distribution was 1.37 +/- 0.30 ml/g of liver (n = 8). A flow-limited model fitted the data most effectively, although estimates of the permeability-to-surface area product were attempted using a barrier-limited model. This technique will facilitate investigation of the effects of disease on gaseous substrate disposition in perfused organs.

Hepatic artery flow and propranolol metabolism in perfused cirrhotic rat liver

The oxygen limitation theory states that capillarization of the sinusoidal endothelium in cirrhosis impairs hepatocellular oxygen uptake manifesting as a reduction in oxygen-dependent enzyme activity including phase 1 drug metabolism. The hepatic artery supplies highly oxygenated blood to the liver. Therefore, we tested whether augmentation of hepatic arterial blood flow could improve hepatic oxygenation and function in cirrhosis. Rats were treated with carbon tetrachloride and phenobarbitone to induce hepatic cirrhosis or fibrosis. We used a bivascular rat liver perfusion model to examine the effects of increased hepatic artery flow on propranolol clearance and oxygen consumption. Each liver was perfused at three hepatic artery flow rates, 1 to 3, 4 to 6, and 7 to 9 ml/min with a constant portal venous flow of 7 to 9 ml/min. Increasing the hepatic artery flow led to improvement in propranolol clearance in control (n = 7, P <.001), fibrotic (n = 8, P <.001), and cirrhotic (n = 6, P <.001) livers. Intrinsic clearance of propranolol increased only in the cirrhotic livers (P =.01), indicating an improvement in enzyme activity. Regression analysis indicated that this improvement was mediated by change in oxygen delivery alone (P =.001). The results confirm that propranolol metabolizing enzyme activity in cirrhosis can be improved by increasing oxygen delivery by increasing hepatic arterial blood flow. These findings suggest that increasing hepatic arterial blood flow may be an important therapeutic strategy for improving global liver function in cirrhosis.

Pesticides and Parkinson's disease

Epidemiological studies and case reports provide evidence for an association between Parkinson's disease and past exposure to pesticides. Susceptibility to the effects of pesticides and other putative neurotoxins depends on variability in xenobiotic metabolism possibly generated by genetic polymorphisms, aging and variation in exposure to environmental agents including pesticides. The simplest mechanistic hypothesis for the association of pesticides with Parkinson's disease is that pesticides or their metabolites are directly toxic to mitochondria, although modulation of xenobiotic metabolism by pesticides provides an adjunct or alternative hypothesis.

Receptors involved in nerve-mediated vasoconstriction in small arteries of the rat hepatic mesentery

1. We have investigated the neurotransmitters and receptor subtypes involved in nerve-mediated vasoconstriction in small arteries of the rat hepatic mesentery. 2. A dense sympathetic innervation was demonstrated using catecholamine histochemistry and antibodies against the synaptic vesicle protein synaptophysin. 3. Reverse transcription-polymerase chain reaction (RT-PCR) demonstrated very strong expression of the alpha1A-adrenergic, neuropeptide Y (NPY) Y1, P2X1- and P2X4-purinergic receptors, moderate expression of the alpha2B-adrenergic receptor and the purinergic P2X5- and P2X7-receptors and weak expression of the alpha1B-, alpha1D-, alpha2A- and alpha2C-adrenergic receptors and the P2X2- and P2X3-purinergic receptors. NPY2 and P2X6 receptor expression was absent. 4. Electrical field stimulation (10 Hz, 10 s) produced contractions which were abolished by tetrodotoxin (10(-6) M) and/or guanethidine (GE, 5 x 10(-6) M) and a combination of benextramine (10(-5) M) and alpha,beta-methylene ATP, (alpha,beta-mATP, 3 x 10(-6) M) or PPADS (10(-5) M). Selective alpah1-adrenergic receptor antagonists showed the potency order of prazosin > WB-4101 > 5-methyl-urapidil > BMY 7378. Yohimbine (10(-8) M, 10(-7) M), alpha,beta-mATP (3 x 10(-6) M) and PPADS (10(-5) M) each enhanced the response to nerve stimulation. 5. Some experiments demonstrated a slow neurogenic contraction which was abolished by GE or the selective NPY1 receptor antagonist 1229U91 (6 x 10(-7) M). 6. We conclude that nerve-mediated vasoconstriction results from the activation of postsynaptic alpha,beta-adrenergic and P2X-purinergic receptors and under some conditions, NPY1 receptors. Neurotransmitter release is modulated by presynaptic alpha2-adrenergic receptors and possibly also P2X-purinoceptors. The major postsynaptic subtypes involved were well predicted by mRNA expression as measured by RT-PCR, suggesting that this technique may be a useful adjunct to studies aimed at identifying functional receptor subtypes.

Changes in MIC alter responses of Pseudomonas aeruginosa to tobramycin exposure

The pharmacokinetic parameters determining antibiotic efficacy are peak concentrations (Cmax), minimum (trough) concentrations (Cmin), and area under the concentration-time curve (AUC). There is general agreement about the importance of Cmax and AUC for aminoglycosides, but this is not so for maintenance of Cmin. With in vitro exposures modelling in vivo administration, Pseudomonas aeruginosa reference strain ATCC 27853 (MIC, 1 mg/liter) and a higher-MIC (relatively resistant) clinical isolate (MIC, 4 mg/liter) were used to explore bacteriostatic and bactericidal outcomes. With P. aeruginosa ATCC 27853, kill followed a complete bolus profile with a 30-min postdistribution peak (Cpeak30) of 10 mg/liter. The clinical isolate required a Cpeak30 bolus profile of 20 mg/liter for kill, and there was no difference between the efficacies of the bolus and infusion exposures. Bolus profiles that were truncated at 8.5 h and producing sublethal effects were then combined with a wide range of Cmins. With a Cpeak30 profile of 8 mg/liter, P. aeruginosa ATCC 27853 showed a graded bacteriostatic response until a Cmin of > or = 0.8 mg/liter, when complete kill resulted. In contrast, bactericidal effects on the clinical isolate required a Cpeak30 profile of 18 mg/liter with a Cmin of > or = 1.0 mg/liter. Therefore, Cmin also contributes to the bactericidal effect of tobramycin, with requirements showing minor variation with change in MIC. Dosing principles for relatively resistant (higher-MIC) organisms are suggested from the data. Relatively higher aminoglycoside doses via infusion regimens are likely to be needed to generate higher peak concentrations and higher AUC values necessary for bactericidal effect in resistant organisms. Maintenance of trough concentrations on the order of 1.0 mg/liter during the interdose interval will tend to guard against the possibility of inadequate peak and AUC exposures for kill.

The aging liver. Drug clearance and an oxygen diffusion barrier hypothesis

A change in drug clearance with age is considered an important factor in determining the high prevalence of adverse drug reactions associated with prescribing medications for the elderly. Despite this, no general principles have been available to guide drug administration in the elderly, although a substantial body of clearance and metabolism data has been generated in humans and experimental animals. A review of age-related change in drug clearances established that patterns of change are not simply explained in terms of hepatic blood flow, hepatic mass and protein binding changes. In particular, the maintained clearance of drugs subject to conjugation processes while oxygen-dependent metabolism declines, and all in vitro tests of enzyme function have been normal, requires new explanations. Reduction in hepatic oxygen diffusion as part of a general change in hepatocyte surface membrane permeability and conformation does provide one explanation for the paradoxical patterns of drug metabolism, and increased hepatocyte volume would also modify oxygen diffusion path lengths (the 'oxygen diffusion barrier' hypothesis). The reduction in clearances of high extraction drugs does correlate with observed reduction in hepatic perfusion. Dosage guidelines emerge from these considerations. The dosage of high clearance drugs should be reduced by approximately 40% in the elderly while the dosage of low clearance drugs should be reduced by approximately 30%, unless the compound is principally subject to conjugation mechanisms. If the hepatocyte diffusion barrier hypothesis is substantiated, this concept may lead to therapeutic (preventative and/or restorative) approaches to increased hepatocyte oxygenation in the elderly. This may lead to approaches for modification of the aging process in the liver.

Vehicle travel speeds and the incidence of fatal pedestrian crashes

The aim of this study was to estimate the likely effect of reduced travel speeds on the incidence of pedestrian fatalities in Adelaide, Australia. The study was based on the results of detailed investigations of 176 fatal pedestrian crashes in the Adelaide area between 1983 and 1991. The method developed to estimate the effect of reduced travelling speed is described and supported by references to the published literature. A reduction in the speed limit from 60 to 50 km/h was one of four speed reduction scenarios considered. The smallest estimated reduction in fatal pedestrian collisions in the selection presented was 13%, for a scenario in which all drivers obeyed the existing speed limit. The largest estimated reduction was 48% for a scenario in which all drivers were travelling 10 km/h slower. The estimated reductions in fatalities obtained in this study are compared with those observed in places where the urban area speed limit has been lowered.

Dosing implications of a clinical interaction between grapefruit juice and cyclosporine and metabolite concentrations in patients with autoimmune diseases

OBJECTIVE

To determine the effect of chronic grapefruit juice administration on steady state blood concentrations of cyclosporine and metabolites in patients with autoimmune diseases.

METHODS

9 patients stabilized on administration of cyclosporine (range 0.7-6.7 mg/kg/day) were given either grapefruit juice or water using randomized crossover design. Whole blood samples were collected before the morning cyclosporine dose and during the 12 h interdose interval. Cyclosporine concentrations were measured using a relatively specific assay (Emit) and total metabolite concentrations were estimated using a nonspecific assay (polyclonal Abbott-TDx).

RESULTS

Exposure to grapefruit juice produced significant increases in predose cyclosporine concentrations (p < 0.01) and total metabolite concentrations (p = 0.03) and the area under the cyclosporine and metabolite blood concentration-time curves (p = 0.005, p = 0.001, respectively). One patient developed significant neurological side effects associated with a 68.9 and 214% increase in predose cyclosporine and metabolite concentrations, respectively, during grapefruit juice co-administration.

CONCLUSION

Grapefruit juice causes an increase in both parent and metabolite profiles, indicating an alteration in the disposition of cyclosporine and metabolites. This interaction is of potential clinical importance in terms of mechanism, side effects, and dosing.

Increased sensitivity of propranolol clearance to reduced oxygen delivery in the isolated perfused cirrhotic rat liver

BACKGROUND & AIMS

Capillarization of the sinusoids in cirrhosis is proposed to reduce oxygen availability to the hepatocyte, resulting in the patterns of altered drug metabolism observed in cirrhosis. If this were true, drug metabolism in cirrhotic livers would be expected to be more sensitive to reduced oxygen delivery than in noncirrhotic livers. The aim of this study was to compare the sensitivity of propranolol clearance with reduced oxygen delivery in isolated perfused livers from healthy and cirrhotic rats.

METHODS

Propranolol clearance was measured at steady state in 5 normal and 5 cirrhotic weight-matched perfused rat livers under single-pass conditions with normal oxygen delivery (mean, 71.5 mumol/min) and with graded reductions in oxygen delivery (range, 58.1-18.8 mumol/min).

RESULTS

In noncirrhotic livers, propranolol clearance was independent of oxygen supply for the oxygen delivery range of 73-45 mumol/min but decreased with further reductions in oxygen supply. In cirrhotic livers, propranolol clearance decreased linearly (r2 = 0.92; P < 0.005) for the entire oxygen delivery range (73.4-18.8 mumol/min).

CONCLUSIONS

The increased sensitivity of propranolol clearance in perfused cirrhotic livers to reductions in oxygen delivery is consistent with impaired oxygen delivery to hepatocytes in cirrhosis. These novel findings potentially hold implications for clinical management of patients with cirrhosis.

A head impact model of early axonal injury in the sheep

Axonal injury (AI), one of the principal determinants of clinical outcome after head injury, may evolve over several hours after injury, raising the future possibility of therapeutic intervention during this period. A new head impact model of AI in sheep was developed to examine pathological and physiological changes in the brain resulting from a graded traumatic insult. In this preliminary study 10 anesthetized and ventilated Merino ewes were used. Head injury was produced by impact from a humane stunner to the temporal region of an unrestrained head. Eight sheep were studied for 1, 2, 4, or 6 h after impact. Two sham animals (no impact, 6 h survival) were also examined. Arterial blood pressure, intracranial pressure, and cerebral blood flow were monitored continuously. A physiological index of injury severity was calculated by weighting the percentage shift from preinjury values for each monitored parameter over the first hour after injury. Immunostaining with amyloid precursor protein (APP) was used as a marker of axonal damage and the distribution of APP positive axons was recorded according to a sector scoring method (APPS). Widespread AI was identified in 7 of the 8 impacted animals, around cerebral contusions and in hemispheric white matter, central gray matter, brain stem, and cerebellum, and was detected as early as 1 h after injury. The degree of axonal injury (APPS) correlated well with an index of physiological response to injury (r = 0.83, p = 0.005).

Kill kinetics and regrowth patterns of Pseudomonas aeruginosa exposed to concentration-time profiles of tobramycin simulating in vivo infusion and bolus dosing

Pseudomonas aeruginosa ATCC 27853 was exposed to tobramycin concentration-time profiles modelling in vivo bolus and infusion dosing. Dependence of bactericidal and bacteriostatic activity on the initial profile of peak concentration (bolus effect > infusion) and area under the antibiotic concentration-time curve was observed at peak concentration/MIC ratios of 10 or below.

Minimisation of aminoglycoside toxicity in patients with cystic fibrosis

BACKGROUND

There is evidence that administration of higher doses of aminoglycosides given less frequently improves the bactericidal effect and reduces the potential to cause side effects. To investigate this, a prospectively randomised open label therapeutic trial was undertaken in stratified groups of patients with cystic fibrosis to examine the efficacy and toxic potential of an aminoglycoside dosing regimen designed to generate high peak drug concentrations at 12 hourly intervals compared with conventional dosing at eight hourly intervals.

METHODS

Patients in group A received tobramycin eight hourly using a dose aimed at generating a peak concentration of 10 mg/l with trough concentrations below 2 mg/l, and those in group B received the total daily dose required to achieve eight hourly target concentrations administered as two equal 12 hourly doses. Clinical outcomes measured and assessed included vestibular symptoms, hearing and renal function, length of hospital stay, readmission rate, and mortality.

RESULTS

Twenty nine patients were recruited during a six month period, 20 to group A and nine to group B. The average peak tobramycin level was higher in group B (12.5 (2.2) mg/l) than in group A (7.9 (1.9) mg/l), whilst the average trough level was higher in group A (0.8 (0.3) mg/l) than in group B (0.5 (0.2) mg/l). There was a difference in the number of ototoxic events between patients in group A (seven of 18, 38.9%) and group B (none of eight), but no difference was found in other outcome measures assessed.

CONCLUSIONS

These results suggest that 12 hourly high peak aminoglycoside dosing may be less toxic than equivalent eight hourly dosing, without any apparent difference in efficacy.

Aminoglycoside dosing: one, two or three times a day?

The safety and efficacy of conventional aminoglycoside dosing regimens have been proven in clinical trials. Higher doses at longer intervals may be more effective if they result in higher peak serum levels of the drug, but few trials of "once-a-day" dosing have shown improved clinical outcome. The clinical safety of allowing trough serum levels to fall below the minimum inhibitory concentration is not established. Literal "once-a-day" dosing will result in drug accumulation and toxicity in patients with reduced renal clearance, and in potential lack of efficacy and the emergence of antibiotic-resistant organisms in those with increased renal clearance. However, modified "once-a-day" dosing, with the interval determined by the individual's renal clearance rate (hence avoiding subtherapeutic trough levels), will avoid these problems.

Extended hospital stays with increasing age: the impact of an acute geriatric unit

OBJECTIVES

To examine the association between increasing age and extended length of hospitalisation, and the impact of an acute geriatric unit on this association.

DESIGN

Retrospective analysis of concurrently collected data of patients admitted to three general medical units, one of which was an acute geriatric unit.

SETTING

Alfred Hospital, Melbourne (a tertiary referral teaching hospital), between 1 July 1993 to 30 June 1994.

PATIENTS

Those classified into the same diagnosis-related groups (DRGs) as the 15 most common DRGs of the acute geriatric unit.

OUTCOME MEASURE

Incidence of patients with extended lengths of stay ("high outliers"), analysed by age, medical unit and DRG.

RESULTS

Of 3499 patients discharged from the hospital with the 15 study DRGs, 303 patients (8.6%) were from the acute geriatric unit, and 274 and 300 patients (7.8% and 8.5%) were from the two other general medical units, respectively. Patients in the acute geriatric unit were significantly older (median age group, 75-79; age range, 18-98) than patients in all other hospital units (median age group, 60-64; age range, 18-97) (P < 0.0001). Analysis of patients with respiratory and cardiovascular DRGs admitted to all general medical units compared with specialty units showed this age discrepancy was even more marked for patients aged over 85. There was an increased likelihood (P < 0.001) of an extended length of stay for patients aged over 55. The incidence of high outliers for comparable DRGs was lower for patients cared for by the acute geriatric unit, compared with general medical units. In the acute geriatric unit, unlike the overall trend, the proportion of high outliers did not increase with age.

CONCLUSIONS

The specialised management of acute geriatric medical units can counteract the trend towards increased incidence of high outliers with increasing age, despite significantly older patients.

Clinical pharmacokinetic and pharmacodynamic considerations in patients with liver disease. An update

The effects of liver disease on pharmacokinetics and pharmacodynamics are highly variable, and difficult to predict as the mechanisms of these effects are not well understood. Since the majority of the published literature is concerned with cirrhotic liver disease, this review also focuses mainly on this area. Four different theories have been proposed to account for the effects of chronic liver disease with cirrhosis on hepatic drug elimination: the sick cell theory; the intact hepatocyte theory; the impaired drug uptake theory; and the oxygen limitation theory. While some data in support of each of the first 2 theories have been published recently, a large amount of clinical data would appear to refute both of these theories. These clinical data are substantially consistent with the latter 2 theories, which regard the decreased permeability of the capillarised sinusoid as the critical feature in cirrhosis. Further work is required to determine the applicability of each of these theories. In cirrhosis, drug glucuronidation is spared relative to oxidative drug metabolism; however, in advanced cirrhosis this pathway may also be impaired substantially. There is evidence that in cirrhosis other conjugation pathways may also be impaired to variable degrees. Growing evidence suggests that biliary drug excretion is impaired in cirrhosis. Recent studies with several racemic drugs indicate that the disease can have different effects on the hepatic elimination of individual enantiomers, which may lead to a change in the concentration-response relationships of racemic drugs in cirrhosis. A major finding which has emerged in recent years is that, even with moderate degrees of hepatic impairment, there is a decrease in clearance of drugs or active metabolites normally cleared by the kidney. The effect on renal clearance of unbound drug may be masked if there is a concomitant decrease in plasma protein binding of the drug. Neither serum creatinine levels nor creatinine clearance are useful markers of the renal dysfunction associated with cirrhosis. Both may greatly overestimate renal function in patients with cirrhosis due to increased fractional renal tubular secretion of creatinine. Altered receptor sensitivity has been observed with some drugs in cirrhosis, while for other drugs there is no change in pharmacodynamics. Precise determination of drug dosage in cirrhosis requires information on changes in pharmacodynamics and plasma protein binding in addition to changes in drug elimination. Pharmacokinetic investigations in a variety of chronic liver diseases without cirrhosis (e.g. carcinoma, schistosomiasis and viral hepatitis) suggest that in the absence of cirrhosis, impairment of drug elimination is not sufficient to warrant reduction of drug dosage. However, if cirrhosis is present, 'safe' drug use requires an awareness of the possibility of multiple interactions between changes in hepatic and renal disposition and pharmacodynamics. In chronic liver disease with cirrhosis, dosage reduction is the general rule regardless of the route of elimination of drug or metabolite.

Effects of sensory (teasing) exposure to food on oral propranolol bioavailability

In order to further examine the mechanism of the increase in the plasma propranolol concentration versus time curve (AUC) caused by ingestion of propranolol with food, we administered R, S-propranolol tablets (0.5 mg kg-1) orally to healthy human volunteers and dogs in the presence and absence of sensory exposure to food without ingestion (teasing). Six healthy human volunteers were fasted on one occasion and on the other they were presented with an appetising meal, without eating it (teasing protocol). There was a strong trend to a greater propranolol AUC in the teasing protocol (139 +/- 54 mg mL-1 h-1 fasting, 178 +/- 105 mg mL-1 h-1 teasing; p = 0.1), and time of peak concentration (tmax) was significantly prolonged (80 +/- 22 min and 120 +/- 32 min, respectively; p < 0.03). Further studies were carried out in dogs who received R-propranolol (2 mg kg-1) as an oral solution by gavage tube on four different occasions: fasting, following intragastric administration of a high-value liquid meal, following teasing with food in the animal house at normal feeding time (high-intensity teasing). There were no significant differences in pharmacokinetic parameters between the fasting and intragastric food protocols. Low-intensity teasing resulted in significantly lower AUC and peak concentrations (Cmax) compared with fasting (p < 0.05), confirming food effect patterns known to occur in dogs. High-intensity teasing resulted in significantly greater AUC and Cmax compared with fasting (p < 0.05), reproducing in dogs the increase in propranolol AUC known to occur with food ingestion in humans. These findings suggest that the mechanism of the 'food effect' may involve physiological responses to the sight and smell of food additional to mechanisms activated by ingestion.

A prospective audit of total parenteral nutrition at a major teaching hospital

OBJECTIVE

To examine patterns of use and clinical outcomes of total parenteral nutrition (TPN).

DESIGN

A prospective six-month audit (December 1992-June 1993).

PATIENTS AND SETTING

All inpatients administered TPN at a metropolitan teaching hospital during the audit period.

MAIN STUDY MEASURES

Process measures included data about TPN initiation (bodyweight, period not receiving oral/nasogastric feeding, serum albumin level, compliance with hospital guidelines), TPN delivery data (kilojoules, and nutrient and electrolyte content), and bases for cessation or changes of TPN (biochemistry data, gastric and intestinal function). Outcome measures included body mass change, infection rate, detection of biochemical abnormalities, and death.

RESULTS

During the audit 168 consecutive patients received 175 TPN courses. These patients were followed until discharge or death; 49 patients (29%) died. Intensive care units accounted for 57.7% of TPN use. Deviations from approved hospital guidelines for initiation of TPN were common. Only a minority of patients were malnourished on objective audit criteria; 18% of men and 13% of women were underweight by body mass index criteria and 36% were malnourished when serum albumin level (< 30 g/L) was considered. Early initiation of TPN outside accepted guidelines was common. Complications included bacteraemia (9.1% of patients tested) and catheter-tip sepsis (55.2% of 87 catheters tested). Four patients died; line sepsis caused one death and probably a further two. The incidence of glucose intolerance was 36.5%, and 25% had markers of abnormal liver function.

CONCLUSIONS

TPN use is associated with a high risk of morbidity, and a 1.7% mortality. We recommend better patient selection for TPN, more appropriate use of enteral feeding, better infection control procedures, avoidance of substrate overload (particularly glucose), and earlier change to enteral nutrition.

Demographic characteristics, drinking patterns and drink-driving behavior of injured male drivers and motorcycle riders

OBJECTIVE

The demographic characteristics, usual drinking and drink-driving patterns, incidence of problem drinking, precrash drinking behavior and attitudes towards drink-driving of crash-involved male drivers and riders are described and related to blood alcohol concentration (BAC) on admission to hospital. A better understanding of these issues will enable drink-driving countermeasures to target more specifically those individuals who are most at risk of being killed or injured in alcohol-related road crashes.

METHOD

Between June 1985 and April 1987 interviews were conducted with a sample of 302 male drivers and motorcycle riders admitted to the Royal Adelaide Hospital in Adelaide, South Australia.

RESULTS

With one exception, the likelihood of having a high BAC (i.e., 80 mg/dl or above) did not differ with demographic profile. As BAC increased, there was a significant increase in: various indices of quantity and frequency of drinking; beer being the preferred beverage; percentages drinking alone, in a hotel, in a vehicle and for various less socially acceptable reasons; frequency of drink-driving; likelihood of previous drink-driving suspension; and, more liberal attitudes towards drink-driving. About 25% of those with a BAC of at least 150 mg/dl were probably experiencing alcohol-related problems prior to the crash, compared with only a very small proportion of those with lower BACs. Precrash drinking most commonly involved drinking in a hotel, drinking with friends and drinking beer, with no significant differences between BAC groups.

CONCLUSIONS

The results suggest that usual drinking and drink-driving patterns, as well as attitudes to drink-driving, become more extreme as the BAC of male crash-involved drivers and riders increases.

Brain injury without head impact?

The proposition that acceleration of the brain without direct impact to the head can result in brain injury is examined by reviewing a series of 414 road users who were fatally injured in the vicinity of Adelaide, South Australia. The series comprises 170 pedestrians, 10 pedal cyclists, 143 motorcyclists, and 91 vehicle occupants. In each case a member of the research team attended the autopsy to look for evidence of impact on the body, particularly to the head or face. The brain was examined by a neuropathologist and the type and pattern of injury was recorded. The circumstances of the crash were investigated, including an examination of the crash site and the vehicles involved and, where relevant, interviews with witnesses. In cases involving a motorcyclist the helmet worn was retrieved by the police and assigned to the research unit for examination. Particular attention was paid to the identification of objects causing injury to the head or face and also to objects impacted by a helmet. Brain injury was recorded as a cause of death in 55% of the 403 cases for which there was a clear classification of cause of death. Brain injury, at any level of severity, was identified by a neuropathologist in 86 percent of the 414 fatally injured road users in the sample, including 24 cases that were examined microscopically. There were no cases in which there was an injury to the brain in the absence of evidence of an impact to the head.

Topography of axonal injury as defined by amyloid precursor protein and the sector scoring method in mild and severe closed head injury

Axonal injury (AI), as defined by amyloid precursor protein (APP) positive axonal swellings, was recorded on a series of line diagrams of standard brain sections divided into 116 sectors to provide an Axonal Injury Sector Score (AISS) ranging from 0 to 116. This sector scoring method of recording axonal damage and providing a topographic overview of AI was applied to a series of 6 mild head injury cases [Glasgow Coma Scale (GCS) 13-15] and six severe head injury cases (GCS 3-8). The AISS ranged from 4 to 107 overall and varied from 4 to 88 in the mildly injured group and 76 to 107 in the severe head injury group, supporting the concept that there is a spectrum of AI in traumatic head injury and that the AISS is a measure of the extent of AI. APP immunostaining demonstrated positive axonal swellings 1.75 h after head injury and analysis of the pattern of AI in the mild and severe head injury groups showed that axons were more vulnerable than blood vessels and that the axons in the corpus callosum and fornices were the most vulnerable of all.

Oxygen supplementation restores theophylline clearance to normal in cirrhotic rats

BACKGROUND/AIMS

Capillarization associated with hepatic fibrosis may present a functional barrier to oxygen diffusion into the hepatocyte, and restriction on cellular oxygen supply may represent the rate-limiting constraint on hepatic oxidative drug metabolism. The aim of this study was to test this hypothesis by examining the effect of oxygen supplementation on plasma theophylline clearance in 10 control and 10 cirrhotic rats.

METHODS

Theophylline (3 mg/kg) was administered intravenously on two separate occasions, 24 hours apart, during which time the rats breathed either room air or oxygen (95%) from 1 hour before dosing until the end of plasma sampling with a randomized order of gas exposure.

RESULTS

Theophylline clearance was significantly reduced by a mean of 37% (n = 10; P = 0.003) in cirrhotic rats compared with controls. Oxygen supplementation significantly improved plasma theophylline clearance in cirrhotic rats by a mean of 40% (n = 10; P = 0.007), whereas clearance remained unchanged in healthy rats. Clearance in oxygen-supplemented cirrhotic rats was not significantly different from that in controls (P > 0.05).

CONCLUSIONS

These novel findings indicate an important role for hepatic oxygenation in improving drug disposition in cirrhosis, which may have potentially important clinical implications for the management of this disease.