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PubMed1998

Linear model of nitrogen balance and examination of the nature of true metabolisable energy and its nitrogen corrected form.

1. The nature of nitrogen (N) corrected true metabolisable energy (TMEN) was derived using a linear model of N balance, constructed from the relationship between excreted and ingested N. 2. TME was described in terms of a regression line, formed from 'fed' points relating energy voided to energy ingested (GE), as GE - (afed + bGE) + afast. On assignment of theoretical excreta and ingested energy components, a deviation from conceptual metabolisable energy (MEc), equal to the difference between afed and afast, was established and attributed to metabolic urinary energy (UmE). 3. The N balance model is based on the form of relationship between N excreted and N ingested (NI) that exhibits a linear deviation at 'initial' rates of N ingestion. The model postulates the following: The deviation is the result of a sparing effect of ingested N on the N component of UmE, viz. metabolic urinary N (UmN); The magnitude of UmN, through 'initial' values of fed N, is described by an intercept component, aNp, and a slope quantity, -(bNr - bNna) NI, where bNna and bNr are respectively the slopes of N excretion through 'initial' and 'subsequent' rates of ingested food N; The magnitude of the deviation from zero nitrogen balance (ZNB) through 'initial' and 'subsequent' rates of ingested N is the sum of the previous terms and aNm - (1 - bNr) NI, where aNm is the intercept component representing maintenance losses of N at fasting and (1-bNr) NI is the quantity of fed N retained to replace maintenance N loss. 4. Application of the appropriate energetic forms of UmN and aNm, viz. Et aNp - Et (bNr - bNna) NI and EuaNm, to the expression for obtaining TME, demonstrated that TME exceeded MEc by the quantities Et (bNr - bNna) NI and Et aNp, for test food intakes resulting in 'initial' and 'subsequent' rates of food N, respectively. 5. Application of appropriate energetic components of the model to simulate correction of TME to ZNB, demonstrated TMEZNB to be a biased quantity, deviating from MEc by the amount -Eu (1 - bNr) NI or expressed as an excreta energy slope component, [formula: see text] where Eu is an appropriate energy coefficient. An alternative perspective is that ZNB correction removes the energetic form of UmN as a source of bias, but introduces one related to EuaNm. Its nature may be perceived by regarding TME as a function of a regression line relating energy excreted (EE) to energy ingested that has been corrected for UmN energetic bias and is pivoting on a fulcrum vertically aligned with the position of ZNB on the GE (x) axis. The regression line rotates anti-clockwise in response to ZNB correction by an amount equal to the magnitude of EuaNm measured on the EE (y) axis from the point of interception. 6. The study identified processes that may be employed to remove bias and improve precision of TME.

Animals↗

PubMedDate not supplied

Sources of influence on rate of cognitive change over time in Swedish twins: an application of latent growth models.

The use of latent growth models to examine influence on individual differences on ability level versus rate of change were examined for measures of fluid ability, memory, and perceptual speed in a sample of twins from the Swedish Adoption/Twin Study of Aging. Results indicated a larger amount of individual variation for average ability level (i.e., intercept) than rate of change (i.e., slope) for all three traits: Block Design, Thurstone's Picture Memory, and Symbol Digit. Generally, genetic influences were of greater importance to individual variation in ability level whereas variation for rate of change exhibited a larger environmental component. These findings support theories of increasing environmental influences with age. When genetic and environmental sources of covariation between educational attainment and pulmonary function with latent growth parameters were considered, the sources of covariation between the latent cognitive growth model parameters (i.e., intercept and slope) and both covariates were primarily genetic for ability level (intercepts) but environmental for rate of change (slopes). Such findings suggest that the forces important to timing or entry into cognitive decline may reflect stochastic processes or external environmental factors, primarily nonshared, that may differentially hasten cognitive decline in twins. These same forces may overlap with those that influence higher or lower educational attainment or those leading to better or worse pulmonary functioning.

Adult↗

PubMed1999

Synthetic growth reference charts.

Distance standards of height (growth charts) tend to get out of date and must be actualized from time to time. The aim of the present meta-analysis was to investigate characteristics of the cross sectional incremental pattern of body stature, evaluating the possibility of generating distance standards of height without the need for extensive de novo measurements. In view of the differences in growth in early and late childhood, we divided the total period of child development into the period between birth and the age of 6y, and between 6 and early adulthood (15y in females, 18 y in males). With respect to birth length, we meta-analysed 50 European and US American growth studies; with respect to growth in early childhood, 14 studies were analysed; and with respect to growth in late childhood, we meta-analysed 40 male and 51 female growth studies, from 14 European countries and the USA. Variations in body stature were meta-analysed in very large data samples, including the 1992 German birth cohort with more than 500 000 measurements of newborns, 10 000 measurements of 2-y-old German children, more than 500 000 measurements of German school children, and 6 large growth surveys of Japan and Czechoslovakia, with altogether more than 24 000 000 measurements. We found a rigid pattern of cross sectional body stature increment between birth and early adulthood that could be expressed by age-specific linear regression coefficients. Body stature was found to be related between sexes. Male birth length correlated with female length (r = 0.933, p < 0.001, slope = 4.62, intercept = 0.89), stature of 6-y-old boys correlated with stature of 6-y-old girls (r = 0.96, p < 0.001, slope = 1.05, intercept= -6.75), and stature of 18-y-old boys correlated with stature of 15-y-old girls (r=0.96, p < 0.001, slope = 0.90, intercept = 2.85). The developmental pace was also strongly related in both sexes. In conclusion, age-specific linear regression coefficients can be utilized synthetically to generate distance standards for height (synthetic growth reference charts). Synthetic growth reference charts can help to actualize current growth charts without much additional effort, and they may also be used for populations for which autochthonous growth standards are not available.

Adolescent↗

PubMed2000

Contamination of in vivo bone-lead measurements.

This paper addresses one aspect of the calibration of a 109Cd based K-shell x-ray fluorescence measurement system, namely the treatment of the calibration line intercept. Under circumstances of contamination, the intercept may warrant statistical treatment different from that currently performed. This paper proposes refinements to the existing method of subtracting the phantom calibration line intercept from in vivo responses in the calculation of in vivo concentrations. These refinements are recommended because the existing method can underestimate in vivo concentrations by a small amount under normal operating conditions. Contamination of the calibration standard matrix of plaster of Paris by both lead and non-lead contaminants is addressed.

Bone and Bones↗

PubMed1986

Effects of left ventricular diastolic pressure on the pressure-flow relation of the coronary circulation during physiological vasodilatation.

A study to analyse the effects of left ventricular diastolic pressure on coronary pressure-flow relations during physiological vasodilatation was carried out in 14 anaesthetised dogs. The left circumflex artery was perfused at controlled pressures via an extracorporeal circuit and vasodilatation induced by 15 s occlusion of coronary flow. The relation between end diastolic coronary perfusion pressure and flow at peak hyperaemia was linear above 40 mmHg (group 1, n = 7) and became curvilinear at perfusion pressures below 40 mmHg (group 2, n = 7). At a mean left ventricular end diastolic pressure of 8.6(0.8) mmHg the mean zero flow intercept (Pint) in group 1 was 22.5(2.3) mmHg. Graded increases in left ventricular end diastolic pressure by infusion of blood resulted in a parallel rightward shift of the vasodilated pressure-flow relation (Pint = 1.06 X LVEDP + 13.8 mmHg, r = 0.87). The curvilinear relations at low perfusion pressures in group 2 had lower zero flow intercept pressures (Pint = 4.8(0.7) mmHg at left ventricular end diastolic pressure 6.6(1.5) mmHg). As with group 1, graded increases in left ventricular end diastolic pressure caused a rightward shift of the pressure-flow relation, with a direct relation between left ventricular end diastolic pressure and zero flow intercept (Pint = 0.93 X LVEDP + 3.9 mmHg, r = 0.89). Diastolic coronary pressure-flow relations during physiological vasodilatation are essentially linear at perfusion pressures greater than 40 mmHg but are appreciably curved at lower pressures. Increases in left ventricular end diastolic pressure cause a parallel rightward shift of the linear region of the pressure-flow relation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

End systolic pressure-length relations in halothane anaesthetised dogs: effects of regional ischaemia and inotropic agents.

STUDY OBJECTIVE: The aim was to investigate the effects of regional myocardial ischaemia, calcium, and verapamil on (a) the hysteresis and (b) slope and length axis intercept of the left ventricular end systolic pressure-length relationship. DESIGN: Segment length in myocardium supplied by the left anterior descending coronary artery was measured in anaesthetised dogs using sonomicrometry. Three levels of regional myocardial ischaemia were produced by stenosis and occlusion of the left anterior descending artery (ischaemia 1, ischaemia 2, and occlusion). A snare placed around the descending thoracic aorta was used to obtain temporary aortic occlusions. SUBJECTS: Seven open chested mongrel dogs were used, weight 17 kg (range 16-20). MEASUREMENTS AND MAIN RESULTS: After abrupt release of temporary aortic occlusions, end systolic lengths were greater than before the occlusion in the normal myocardium. This hysteresis was abolished by regional myocardial ischaemia. However, hysteresis was insensitive to calcium and verapamil. The length axis intercept of the end systolic pressure-length relationship was increased during ischaemia 2, during coronary occlusion, and after administration of verapamil; its slope was increased after coronary occlusion. CONCLUSIONS: (1) Viscoelastic properties of the myocardium make a major contribution to hysteresis of the end systolic pressure-length relationship; and (2) the length axis intercept of this relationship is not constant and its slope does not appear to be a sensitive indicator of regional myocardial contractility during regional ischaemia.

Anesthesia↗

PubMed1994

Ischaemic preconditioning by partial occlusion without intermittent reperfusion.

OBJECTIVE: The aim was to investigate whether ischaemic preconditioning can be obtained by a partial coronary artery occlusion without intermittent reperfusion. METHODS: In seven anaesthetised open chest pigs, the flow in the proximal left anterior descending coronary artery was reduced to 30% of baseline during 30 min before the vessel was occluded completely for 60 min (60 min total coronary occlusion, TCO). After 2 h of reperfusion, the area at risk (AR) and infarct size (IS) were determined using standard procedures. Infarct sizes were compared to those observed in control animals (n = 12), which were subjected to 60 min TCO and 2 h reperfusion, and to infarct sizes determined in animals preconditioned by 10 min TCO with either 15 min (n = 10) or 60 min (n = 5) of reperfusion before the 60 min TCO and 2 h reperfusion. In the last three groups of animals, area at risk was varied by occluding the coronary artery or its branches at different sites. RESULTS: In the control animals infarct size was linearly related (r = 0.99, p < 0.001) to the area at risk with a positive intercept on the AR axis: IS/LVmass (x100%) = 0.88 AR/LVmass (x100%)-3.6. At comparable areas at risk, the infarct size of the animals preconditioned with a 10 min TCO was less than for the control animals. For the animals preconditioned with 10 min TCO and 15 min reperfusion, the relationship between infarct size and area at risk was again linear (r = 0.88) and also had a positive intercept on the AR axis: IS/LVmass (x100%) = 0.68 AR/LVmass (x100%)-4.8. All animals with the flow reduction to 30% of baseline immediately preceding the 60 min TCO had infarct sizes smaller (p < 0.05) than predicted from the regression equation for the control animals, but the infarct size limitation could not be simply related to variables such as changes in regional systolic and postsystolic segment length shortening, ATP, or ADP during the partial occlusion period. CONCLUSIONS: Myocardium can be preconditioned with a flow reduction to 30% of baseline for 30 min without intermittent reperfusion (two stage Harris model). The positive intercept on the AR axis of the IS-AR relationship warrants caution of the use of IS/AR as an index for infarct size limitation.

Animals↗

PubMed2005

Passive cannabis smoke exposure and oral fluid testing. II. Two studies of extreme cannabis smoke exposure in a motor vehicle.

Two studies were conducted to determine if extreme passive exposure to cannabis smoke in a motor vehicle would produce positive results for delta-tetrahydrocannabinol (THC) in oral fluid. Passive exposure to cannabis smoke in an unventilated room has been shown to produce a transient appearance of THC in oral fluid for up to 30 min. However, it is well known that such factors as room size and extent of smoke exposure can affect results. Questions have also been raised concerning the effects of tobacco when mixed with marijuana and THC content. We conducted two passive cannabis studies under severe passive smoke exposure conditions in an unventilated eight-passenger van. Four passive subjects sat alongside four active cannabis smokers who each smoked a single cannabis cigarette containing either 5.4%, 39.5 mg THC (Study 1) or 10.4%, 83.2 mg THC (Study 2). The cigarettes in Study 1 contained tobacco mixed with cannabis; cigarettes in Study 2 contained only cannabis. Oral fluid specimens were collected from passive and active subjects with the Intercept Oral Specimen Collection Device for 1 h after smoking cessation while inside the van (Study 1) and up to 72 h (passive) or 8 h (active) outside the van. Additionally in Study 1, Intercept collectors were exposed to smoke in the van to assess environmental contamination during collection procedures. For Study 2, all oral fluid collections were outside the van following smoking cessation to minimize environmental contamination. Oral samples were analyzed with the Cannabinoids Intercept MICRO-PLATE EIA and quantitatively by gas chromatography-tandem mass spectrometry (GC-MS-MS). THC concentrations were adjusted for dilution (x 3). The screening and confirmation cutoff concentrations for THC in neat oral fluid were 3 ng/mL and 1.5 ng/mL, respectively. The limits of detection (LOD) and quantitation (LOQ) for THC in the GC-MS-MS assay were 0.3 and 0.75 ng/mL, respectively. Urine specimens were collected, screened (EMIT, 50 ng/mL cutoff), and analyzed by GC-MS-MS for THCCOOH (LOD/LOQ = 1.0 ng/mL). Peak oral fluid THC concentrations in passive subjects recorded at the end of cannabis smoke exposure were up to 7.5 ng/mL (Study 1) and 1.2 ng/mL (Study 2). Thereafter, THC concentrations quickly declined to negative levels within 30-45 min in Study 1. It was found that environmentally exposed Collectors contained 3-14 ng/mL in Study 1. When potential contamination during collection was eliminated in Study 2, all passive subjects were negative at screening/confirmation cutoff concentrations throughout the study. Oral fluid specimens from active smokers had peak concentrations of THC approximately 100-fold greater than passive subjects in both studies. Positive oral fluid results were observed for active smokers 0-8 h. Urine analysis confirmed oral fluid results. These studies clarify earlier findings on the effects of passive cannabis smoke on oral fluid results. Oral fluid specimens collected in the presence of cannabis smoke appear to have been contaminated, thereby falsely elevating THC concentrations in oral fluid. The risk of a positive test for THC was virtually eliminated when specimens were collected in the absence of THC smoke.

Adolescent↗

PubMed1993

Contraception for the year 2020.

Novel methods for the regulation of human fertility in the post-HIV era are discussed, based on the control of regulatory peptides and their respective genes. Three mechanisms are examined, each representing a step-wise increase in target or functional specificity. These centre on the selective control of the genes encoding the gonadotrophins and/or the interception of circulating gonadotrophins by receptor antagonists or binding proteins, the selective neutralisation of hCG and other signals involved in the maternal recognition of pregnancy by receptor antagonists and antibodies, and the interception of the putative disintegrin-integrin recognition events involved in sperm-oocyte recognition and fusion. A brief consideration is given to the use of vaccination procedures and somatic gene therapy for the long term regulation of fertility. By 2020, it is predicted that contraception, abortion and unplanned pregnancy could be replaced by reversible sterilisation based on the molecular interception of events involved in sperm-oocyte recognition and fusion. Contraceptive-like steroids will still be available but their use will be targeted to the provision of positive health care, with particular regard to breast cancer, osteoporosis and well-being.

Contraception↗

PubMed1992

Effects of varying crop load on photosynthesis, dry matter production and partitioning of Crispin/M.27 apple trees.

Fruit load was altered by flower thinning on three- and four-year-old, field-grown apple trees. Increasing fruit load led to increases in dry matter production per unit leaf area and partitioning to fruit and to decreases in fruit size, percentage fruit dry matter, dry matter partitioning to new shoot growth, thickening of existing woody tissue and root growth. Flower bud production for the following spring was also negatively affected by an increase in fruit load. Leaf photosynthesis was increased in cropping trees in July and August at the time of maximum fruit dry weight increase. Calculated light interception was linearly related to leaf area. The efficiency of conversion of intercepted photosynthetic active radiation to dry matter energy equivalents was 3.3% in heavily cropping trees and 1.8% in non-cropping trees. Total dry matter production was linearly related to both leaf area and light interception, but the variance accounted for by the regression was more than doubled if fruit dry matter or fruit number was included in the regression.

Journal Article↗

PubMed2000

Light spectral composition in a tropical forest: measurements and model.

I present a simple model that simulates vertical variations in the light spectrum within a forest canopy. The model considers only the vertical, downward transmission of light. The light in each canopy level was assumed to consist of non-intercepted radiation and radiation intercepted within the level and transmitted. The spectrum of non-intercepted light in each canopy level is the same as that of incident light above the canopy (input parameter), whereas the spectrum of transmitted light depends on leaf area index (LAI) and the mean transmission spectrum of leaves. The model was tested in a forest and provided adequate predictions of measured values. Stronger deviations were produced in the near infrared (NIR) waveband in lower canopy levels. Multiple regression between LAI, as the dependent variable, and spectral characteristics (Blue, Green, Red and NIR intensities) had an r(2) of 0.926. As a complement to other methods, I suggest light spectrum analysis as a non-destructive technique for estimating LAI in forest canopies.

Journal Article↗

PubMed2003

Influence of leaf angle on photosynthesis and the xanthophyll cycle in the tropical tree species Acacia crassicarpa.

We examined the effects of artificially altering leaf angle of the tropical tree species Acacia crassicarpa (A. Cunn. ex Benth., Fabaceae) on light interception, leaf temperature and photosynthesis in the wet and dry seasons of tropical Australia. Reducing leaf angle from the natural near-vertical angle (90 degrees ) to 67.5, 45, 22.5 and 0 degrees greatly increased light interception and leaf temperature, and decreased photosynthetic activity. Compared with the 90 degrees phyllodes, net photosynthetic rates in the horizontal phyllodes decreased by 18 and 42% by the second day of leaf angle change in the wet and dry seasons, respectively. The corresponding values for Day 7 were 46 and 66%. Leaf angle reduction also altered the diurnal pattern of photosynthesis (from two peaks to one peak) and reduced daily CO2 fixation by 23-50% by Day 2 and by 50-75% by Day 7 in the dry season. In contrast, the xanthophyll cycle pool size in the phyllodes increased with leaf angle reduction. Thus, there are at least five major advantages to maintaining high leaf angle orientation in tropical tree species. First, it reduces excessive light interception. Second, it lowers leaf temperature. Third, it protects the photosynthetic apparatus against photodamage by excessive light. Fourth, it minimizes xanthophyll cycle activity and reduces the cost for xanthophyll biosynthesis. Finally, it enhances photosynthetic activity and helps to sustain high plant productivity.

Acacia↗

PubMed1990

Assessing seasonal leaf area dynamics and vertical leaf area distribution in eastern white pine (Pinus strobus L.) with a portable light meter.

We evaluated the ability of a portable light meter (Sunfleck Ceptometer, Decagon Devices, Pullman, WA, USA) to quantify seasonal photosynthetically active radiation (PAR, 400-700 nm) interception, projected stand leaf area index (LAI), and vertical LAI distribution in a 32-year-old eastern white pine (Pinus strobus L.) plantation. Canopy PAR transmittance measured with the ceptometer was converted to LAI with the Beer-Lambert Equation. The ceptometer was sensitive to changes in PAR transmittance resulting from foliage growth. Predicted stand LAI ranged from 3.5 in the dormant season to a maximum of 5.3 in late July. Predicted LAI values were within 9% of values determined from destructive sampling. Published canopy extinction coefficients (k) were inadequate for converting PAR transmittance data to stand LAI because a significant amount of PAR was intercepted by dead branches and stems below the forest canopy. Because of interception by dead branches and stems, we estimated k = 0.84, which is substantially higher than previously reported values. The ceptometer was also sensitive to seasonal changes in PAR transmittance within the canopy. However, in contrast to predictions based on the Beer-Lambert Law, the relationship between proportional PAR transmittance (Q(i)/Q(o)) and cumulative LAI within the canopy was linear. Thus, vertical LAI distribution was best estimated with a linear model, as opposed to the non-linear model assumed in the Beer-Lambert Equation. We hypothesize that the linear relationship was a result of a gap in the canopy which was not represented by the cumulative leaf area distribution estimation procedure.

Journal Article↗

PubMed1989

Effect of epostane, ZK 98299, and ZK 98734 on the interruption of pregnancy in the rat.

The objective of these studies was to determine whether treatment of 10-day pregnant rats with a combination of epostane (a progesterone biosynthesis inhibitor) and either ZK 98299 or ZK 98734 (progesterone receptor antagonists) would result in additive or synergistic effects on the interruption of pregnancy. When these compounds were tested individually, the order of potency in interrupting pregnancy was ZK 98734 greater than ZK 98299 greater than epostane (50% effective doses 1.3, 4.0, and 35 mg/kg, respectively). Epostane and ZK 98299 were then tested in combination. When epostane was given either 4 h prior to or concurrently with ZK 98299, the combined drug treatment resulted in a significant additive increase in interceptive activity compared to when ZK 98299 was administered alone. In vitro binding studies showed that ZK 98299 and ZK 98734 bound to the rat uterine progesterone receptor in vitro with approximately equal affinity. ZK 98734 bound to the rat thymus glucocorticoid receptor and to the rat ventral prostate androgen receptor with a greater affinity than ZK 98299. The affinity of ZK 98299 for the rat uterine estrogen receptor was weak while the binding of ZK 98734 was not detectable. Thus, the in vitro receptor binding profiles observed were consistent with the known progesterone and glucocorticoid antagonist activities of ZK 98299 and ZK 98734. Overall these findings show that the interceptive activity of epostane and ZK 98299, agents that exert their interceptive activity via different molecular mechanisms, is additive in the 10-day pregnant rat.

Abortion, Veterinary↗

PubMed1990

Comparison of end-systolic pressure-length relations and preload recruitable stroke work as indices of myocardial contractility in the conscious and anesthetized, chronically instrumented dog.

Development of an index of myocardial contractility that is both load independent and easily quantified in vivo has been a difficult task. Recently, three measures of contractile state have been advocated that appear to fulfill these requirements: the end-systolic pressure-length relationship (ESPLR), the ESPLR area, and regional preload recruitable stroke work (PRSW). Because the effects of halothane and isoflurane on these indices of contractility have yet to be studied, the purpose of this investigation was to compare the effects of these volatile anesthetics on contractile function as evaluated via these techniques in chronically instrumented dogs. Because autonomic nervous system tone substantially influences systemic hemodynamics in vivo, experiments were performed in the presence of pharmacologic blockade of the autonomic nervous system. Four groups comprised the 36 experiments that were performed with nine dogs. Following inhalational induction, the dogs were maintained on 1.5 MAC and 2 MAC of halothane or isoflurane. Pressure-length loops were generated after 1 h of equilibration using preload reduction via partial inferior vena caval occlusion or afterload augmentation by a phenylephrine infusion. The PRSW and ESPLR were then calculated, respectively. Slope and length intercept variables obtained from the ESPLR failed to significantly change from control with increasing levels of anesthetic depth despite substantial decreases in other indices of contractility. However, combination of slope and length intercept parameters into the ESPLR area model proved to be a sensitive and easily calculable measure of depressed myocardial function. Similarly, regional PRSW slope precisely reflected changes in contractile state when halothane (62 +/- 10 for control to 30 +/- 6 erg.cm-2.10(-3).mm-1 at 2 MAC) or isoflurane (83 +/- 14 for control to 55 +/- 8 erg.cm-2.10(-3).mm-1 at 2 MAC) were administered. The PRSW slope also demonstrated a significant difference in depressed contractility when equianesthetic concentrations of halothane and isoflurane were compared (63 +/- 7% of control with halothane versus 86 +/- 4% of control with isoflurane at 1.5 MAC; 50 +/- 5% of control with halothane versus 70 +/- 6% of control with isoflurane at 2 MAC). The ESPLR area also accurately demonstrated the differential depression in contractile function suggested by recent in vitro studies when equianesthetic doses of halothane and isoflurane were compared in vivo. Therefore, while ESPLR slope and length intercept variables fail as indices of myocardial contractility, ESPLR area and regional PRSW slope were shown to be useful indicators of contractile state in the conscious and anesthetized dog.

Analysis of Variance↗

PubMed1998

Validation of a hand-held lactate device in determination of blood lactate in critically injured patients.

OBJECTIVES: Admission blood lactate is an accurate predictor of injury severity and mortality in trauma patients. The purpose of this study was to evaluate a portable lactate analyzer in a clinical setting by patient care staff. DESIGN: A prospective, single-operator control solution and patient sample study, using two test devices and a reference device. SETTING: An urban Level I trauma center. PATIENTS: A convenience sample of 47 trauma patients. INTERVENTIONS: Intra-assay precision was demonstrated by performance of consecutive analyses of two lactate control solutions (high and low lactate control concentrations) by medical students and physicians. Split sample, simultaneous testing of the portable lactate analyzer was then performed on 66 whole blood specimens from a convenience sample of 47 trauma patients admitted to an urban Level 1 trauma center over 4 mos. Samples were tested simultaneously tested on two portable lactate analyzers and a reference instrument. MEASUREMENTS AND MAIN RESULTS: Acceptable intra-assay precision was achieved. Regression analysis for two test instruments demonstrated a slope of 0.920, an intercept of 0.323, an r2 of .982, and an SEM of 0.496. Regression analysis for test instrument "A" vs. the reference instrument showed a slope of 0.861, an intercept of 0.209, an r2 of .977, and an SEM of 0.598. Regression analysis for test instrument "B" vs. the reference instrument demonstrated a slope of 0.929, an intercept of -0.095, an r2 of .983, and an SEM of 0.506. CONCLUSIONS: Good correlation with a low SEM was obtained over a wide range of clinically relevant lactate values. Use of point of care lactate analysis will decrease analytic time, making an important diagnostic parameter immediately available in the critical care setting.

Adolescent↗

PubMed2000

Short-term and long-term outcome prediction with the Acute Physiology and Chronic Health Evaluation II system after orthotopic liver transplantation.

OBJECTIVE: To evaluate the relationship between the postoperative Acute Physiology and Chronic Health Evaluation (APACHE) II score and mortality at hospital discharge and at 1 yr in liver transplant recipients. POPULATION: Adult orthotopic liver transplant (OLTX) recipients (n = 599) admitted to the intensive care unit postoperatively at a university hospital. METHODS: The cohort was split randomly into development and validation sets. Three models were compared for each end point: a) the original APACHE II slope with the original APACHE II postgastrointestinal surgery intercept; b) the original APACHE II slope with an OLTX-specific intercept generated from the development set; and c) an OLTX-specific slope and intercept generated from the development set. Goodness-of-fit and calibration were assessed by the Hosmer-Lemeshow C statistic (where p>.05 suggests good fit) and standardized mortality ratios. Discrimination was assessed by receiver operator characteristic area under the curve analysis. MEASUREMENTS AND MAIN RESULTS: Hospital and 1-yr mortality rates were 9.9% and 15.9%, respectively. The APACHE II score was strongly associated with mortality (chi-square, p<.0001), but when used with the original equation, it significantly overestimated hospital mortality (standardized mortality ratio, 0.73 [confidence interval, 0.58-0.99]). Using the OLTX-specific approaches, goodness-of-fit for both hospital and 1-yr mortality was good (p = .2-.57) but discrimination was only moderate (receiver operator characteristic area under the curve, 0.675-0.723). CONCLUSIONS: APACHE II is a good predictor of short- and long-term mortality after liver transplantation, especially when using OLTX-specific coefficients. Because fit and calibration were better than discrimination, APACHE II will be most useful in the prediction of risk for groups of patients (e.g., in clinical trials or institutional comparisons) rather than for individuals. This study raises the possibility that APACHE II may be useful for long-term mortality prediction in other critically ill populations. The overestimation of mortality using the original equation suggests that orthotopic liver transplantation, by reversing the underlying pathophysiology, may modify risk.

APACHE↗

PubMed2000

Evaluation of a new transcardiac conductance method for continuous on-line measurement of left ventricular volume.

OBJECTIVE: To evaluate a new, less invasive, conductance method to measure continuous on-line left ventricular volume. End-systolic and end-diastolic volumes obtained with this transcardiac conductance method were compared with simultaneous measurements using the conventional intracardiac conductance catheter. DESIGN: Controlled animal study. SETTING: Research laboratory in a university hospital. SUBJECTS: Six sheep. INTERVENTIONS: Anesthetized sheep were instrumented and inotropic condition was varied by beta-receptor stimulation (5 microg/kg/min of dobutamine) and beta-receptor blockade (1 mg/kg of propranolol). In each condition (control, dobutamine, repeat control, propranolol), ventricular volume was varied over a wide range by gradual preload reduction using a vena caval balloon catheter. MEASUREMENTS AND MAIN RESULTS: We compared the two methods by performing linear regression analysis on simultaneous end-systolic and end-diastolic volumes obtained during gradual caval occlusions. We statistically analyzed the intercepts, slopes, and correlation coefficients of the regression equations relating the transcardiac and conductance catheter measurements to determine the effects of interanimal variability, inotropic condition, and cardiac phase on the relationship between the two methods. The results show an excellent linear correlation between the two methods (mean intercept, -1.82+/-1.24 mL; mean slope, 0.787+/-0.024 and r2 = .94). Both slope and intercept of the relationship between the two methods show a significant interanimal and cardiac phase related variability but no significant dependence on inotropic condition. CONCLUSIONS: The significant interanimal variability indicates that the new method requires individual calibration in each subject. However, the small variability of the regression coefficients with changes in condition indicates that after initial calibration, end-systolic and end-diastolic volume can be followed accurately even in the presence of large changes in volume and inotropic state. This new method may facilitate quantitative continuous assessment of cardiac function in clinical practice, for example, in the intensive care unit.

Animals↗