Parameters influencing the accuracy of the point of force application determined with piezoelectric force plates.

Errors up to +/- 30 mm in determining the point of force application with piezoelectric force plates have been reported in the literature (Kistler, 1984. Multicomponent Measuring Force Plate for Biomechanics and Industry. Kistler, Switzerland; Bobbert and Schamhardt, 1990. Journal of Biomechanics 23, 705-710; Sommer et al., 1997. Proceedings of the XVI th I.S.B. Congress). To explain the main factors influencing the systematic errors the force plate system is modeled as a two-dimensional beam structure. By this model it is strongly indicated that the cause for the errors in determining the point of force application are bending moments in the measurement posts. The main parameters influencing the shape and magnitude of the error function are the ratios between the bending stiffness of the plate and the bending and compressive stiffnesses of the measurement posts. In the current design it is therefore not possible to eliminate the cause for the errors by changing the constructive parameters. By comparing the error functions derived with the beam model to the correction formulas given in the literature an improved algorithm is proposed. This paper shall help biomechanists in understanding the basic concepts of determining the point of force application with force plates and in constructing custom-made force plates for specific applications.     

Comparison of the effect of simvastatin, spironolactone and L-arginine on endothelial function of aorta in hereditary hypertriglyceridemic rats

Hereditary hypertriglyceridemic (hHTG) rats are characterized by increased blood pressure and impaired endothelium-dependent relaxation of conduit arteries. The aim of this study was to investigate the effect of long-term (4 weeks) treatment of hHTG rats with three drugs which, according to their mechanism of action, may be able to modify the endothelial function: simvastatin (an inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase), spironolactone (an antagonist of aldosterone receptors) and L-arginine (a precursor of nitric oxide formation). At the end of fourth week the systolic blood pressure in the control hHTG group was 148+/-2 mm Hg and in control normotensive Wistar group 117+/-3 mm Hg. L-arginine failed to reduce blood pressure, but simvastatin (118+/-1 mm Hg) and spironolactone (124+/-4 mm Hg) treatment significantly decreased the systolic blood pressure. In isolated phenylephrine-precontracted aortic rings from hHTG rats endothelium-dependent relaxation was diminished as compared to control Wistar rats. Of the three drugs used, only simvastatin improved acetylcholine-induced relaxation of the aorta. We conclude that both simvastatin and spironolactone reduced blood pressure but only simvastatin significantly improved endothelial dysfunction of aorta. Prominent increase in the expression of eNOS in large conduit arteries may be the pathophysiological mechanism underlying the protective effect of simvastatin in hHTG rats.     

Integrated stereological and biochemical studies on hepatocytic membranes. II. Correction of section thickness effect on volume and surface density estimates

The basic stereological formulas for estimating volume (Vv) and surface (Sv) densities are strictly valid only for true infinitely thin sections; the use of "ultrathin" sections of finite thickness T introduces systematic errors, mostly in the sense of overestimation of the parameters. These errors depend on the size and shape of the structural elements and on T. Correction factors for this effect of T are derived by considering model structures that simulate the shape and arrangement of subcellular organelles: (a) spherical vesicles, (b) disks as models for rough endoplasmic reticulum (RER) cisternae, (c) cylindrical tublules as models for smooth endoplasmic reticulum (SER) tubules, microvilli, etc. For vesicles, a model of discrete convex spherical particles is assumed; the correction factors consider loss of caps due to grazing sections and size distribution of the vesicles. The disk and tubule models are used in connection with the new integral geometric formulas of R.E. Miles which consider random aggregates of "inter-penetrating" particles so that the resultant structure is non- convex and thus approximates in nature the networks characteristic of endoplasmic reticulum (ER). Some practical examples relative to liver cells show that the errors due to section thickness may be of the order of 20-40% or more. Computation formulas as well as graphs are given for the determination of the correction factors for Vv and Sv.     

Osteochondral graft fixation using a bioresorbable bone cement

Multiple osteochondral grafts can be used to resurface large joint defects in both humans and horses. In humans, immediate postoperative weight bearing can be prevented, however in the equine, it is unavoidable. Early weight bearing can create detrimental graft micromotion. The aim of this study was to investigate the role of a bioresorbable cement in improving the initial stability of multiple osteochondral graft repairs of large subchondral cystic lesions in the horse. Configurations employed for filling a 20mm diameter cylindrical defect included: (A) twelve 4.5mm diameter grafts with cement, (B) five 6.5mm diameter grafts with cement, (C) four each of 4.5mm and 6.5mm grafts with cement and (D) cement only. Intact bone slices (E) were also tested. Push-out tests were used to quantify construct to host sidewall interface fixation. Configuration (A) proved clinically impractical (n=3). Configurations (B) (n=6), and (C) (n=4) had statistically similar interface stiffnesses and failure stresses (43+/-8 and 30+/-12 MPa and 0.96+/-0.1 and 1.2+/-0.3 Mpa, respectively) suggesting that they are equally susceptible to interface movement in the immediate postoperative period. By way of comparison, defects filled only with cement had an average stiffness of 53+/-7MPa and failure stress of 1.8+/-0.3 MPa (n=6) while the intact femoral condyle demonstrated a stiffness of 108+/-7 MPa and failure stress of 18+/-0.4 MPa (n=6). Cement augmentation improved immediate postoperative stability of multiple osteochondral graft constructs over uncemented constructs, although in all cases the observed moduli of elasticity and yield stress values were lower than those observed for cement only and intact bone test specimens. (all numbers are mean+/-SEM).     

Structural changes in rat aortic intima due to transmural pressure.

Huang et al. (1997) propose a new hypothesis and develop a mathematical model to explain rationally the in vitro and in situ measured changes (Tedgui and Lever, 1984; Baldwin and Wilson, 1993) in the hydraulic conductivity of the artery wall of rabbit aorta with transmural pressure. The model leads to the intriguing prediction that this hydraulic conductivity would decrease by one half if the thin intimal layer between the endothelium and the internal elastic lamina volume-compresses approximately fivefold. This paper presents the first measurements of the effect of transmural pressure on intimal layer thickness and shows that the intimal matrix is, indeed, surprisingly compressible. We perfusion-fixed rat thoracic aortas in situ with 2 percent glutaraldehyde solution at 0, 50, 100, or 150 mm Hg lumen pressure and sectioned for light and electron microscopic observations. Electron micrographs show a dramatic, nonlinear decrease in average intimal thickness, i.e., 0.62 +/- 0.26, 0.27 +/- 0.14, 0.15 +/- 0.10, and 0.12 +/- 0.07 (SD) micron for 0, 50, 100, and 150 mm Hg lumen pressure, respectively. The volume strain of the intima is more than 20 times greater than the radial strain of the artery wall due to hoop tension and two orders of magnitude greater than the consolidation of the artery wall as a whole assuming constant medial density (Chuong and Fung, 1984). Moreover, in both light and electron microscopic observations, it is easy to find numerous sites where the endothelium puckers into the fenestral pores at high lumen pressure, as predicted by the theory in Huang et al. (1997). In contrast, the average diameter of a fenestral pore increases only 10 percent as the lumen pressure is increased from 0 to 150 mm Hg. These results indicate that the thin intimal layer comprising less than 1 percent of the wall thickness can have a profound effect on the filtration properties of the wall due to the large change in Darcy permeability of the layer and the large reduction in the entrance area of the flow entering the fenestral pores, though the pores themselves experience only a minor enlargement due to hoop tension.     

Correction of the inertial effect resulting from a plate moving under low-friction conditions

The purpose of the present study was to develop a set of equations that can be employed to remove the inertial effect introduced by the movable platform upon which a person stands during a slip induced in gait; this allows the real ground reaction force (GRF) and its center of pressure (COP) to be determined. Analyses were also performed to determine how sensitive the COP offsets were to the changes of the parameters in the equation that affected the correction of the inertial effect. In addition, the results were verified empirically using a low friction movable platform together with a stationary object, a pendulum, and human subjects during a slip induced during gait. Our analyses revealed that the amount of correction required for the inertial effect due to the movable component is affected by its mass and its center of mass (COM) position, acceleration, the friction coefficient, and the landing position of the foot relative to the COM. The maximum error in the horizontal component of the GRF was close to 0.09 (body weight) during the recovery from a slip in walking. When uncorrected, the maximum error in the COP measurement could reach as much as 4 cm. Finally, these errors were magnified in the joint-moment computation and propagated proximally, ranging from 0.2 to 1.0 Nm/body mass from the ankle to the hip.     

Isolation of interstitial fluid from skeletal muscle and subcutis in mice using a wick method

Until recent years, mice were sparsely used in physiological experiments, and therefore, data on the basic cardiovascular parameters of mice are lacking. Our aim was to gain access to interstitial fluid and thereby study transcapillary fluid dynamics in this species. Using a modified wick method, we were able to isolate interstitial fluid from subcutis and skeletal muscle in mice. Three-stranded, dry, nylon wicks were inserted post mortem in an attempt to avoid local inflammation and thus eliminate protein extravasation and wick contamination. Colloid osmotic pressure (COP) was measured with a colloid osmometer for submicroliter samples and averaged (means +/- SE) 18.7 +/- 0.4 in plasma, 9.1 +/- 0.4 in subcutis, and 12.3 +/- 0.5 mmHg in muscle. HPLC of plasma and wick fluid showed similar patterns except for some minor peaks eluting in the <40-kDa region. Plasma protein extravasation as determined by 125I-labeled human serum albumin showed that contamination of wick fluid by plasma proteins was negligible (<2%). Capillary hyperfiltration induced by intravenous infusion of saline (10% of body wt) was reflected in tissue fluid isolated by wicks as shown by the average postinfusion COP values of 14.5 +/- 0.6, 6.8 +/- 0.3, and 7.7 +/- 0.4 mmHg in plasma, subcutis, and muscle, respectively. We conclude that the wick technique can be easily adapted for use in mice and may represent a reliable method to isolate interstitial fluid and study transcapillary fluid flux in this species.     

Estimation of inspiratory pressure drop in neonatal and pediatric endotracheal tubes.

Endotracheal tubes (ETTs) constitute a resistive extra load for intubated patients. The ETT pressure drop (DeltaP(ETT)) is usually described by empirical equations that are specific to one ETT only. Our laboratory previously showed that, in adult ETTs, DeltaP(ETT) is given by the Blasius formula (F. Lofaso, B. Louis, L. Brochard, A. Harf, and D. Isabey. Am. Rev. Respir. Dis. 146: 974-979, 1992). Here, we also propose a general formulation for neonatal and pediatric ETTs on the basis of adimensional analysis of the pressure-flow relationship. Pressure and flow were directly measured in seven ETTs (internal diameter: 2.5-7.0 mm). The measured pressure drop was compared with the predicted drop given by general laws for a curved tube. In neonatal ETTs (2.5-3.5 mm) the flow regime is laminar. The DeltaP(ETT) can be estimated by the Ito formula, which replaces Poiseuille's law for curved tubes. For pediatric ETTs (4.0-7.0 mm), DeltaP(ETT) depends on the following flow regime: for laminar flow, it must be calculated by the Ito formula, and for turbulent flow, by the Blasius formula. Both formulas allow for ETT geometry and gas properties.     

On-line measurements of K+ activity in the tensile water of the xylem conduit of higher plants

In higher plants the xylem is the main pathway for anti-gravitational, long-distance transport of nutrients and water from the root through the shoot to the upper leaves. In the xylem conduit water is in a metastable state if tension larger than 0.1 MPa (i.e. negative pressure) is developed. While diurnal changes in negative pressure of individual xylem vessels can quite accurately be recorded by the minimal-invasive xylem pressure probe technique and water flow by non-invasive NMR techniques, the problem of continuous monitoring of solute flow remains a hitherto unresolved challenge. As shown here, integration of a K+ selective and a potential measuring microelectrode into the xylem pressure probe allowed on-line measurements of the K+ activity in individual xylem vessels of maize roots together with pressure and trans-root potential, the potential difference between the xylem and the external medium (i.e. the overall driving force of ions through the root tissue). When light irradiation was increased from 10 micro mol m(-2) s(-1) to 300 micro mol m(-2) s(-1) and negative pressure developed in the vessel, xylem K+ activity dropped from 3.6 +/- 2.6 mm to 0.9 +/- 0.7 mm (n = 16), whereas the trans-root potential depolarized from -2 +/- 11 mV to + 12 +/- 11 mV (n = 11), i.e. by + 14 +/- 7 mV. The effect of light on all three parameters was reversible. Exposure of the root to various K+ activities in the bath ranging from 0.1 to 43 mm revealed that the K+ activity of the xylem sap was shielded against short-term fluctuations in K+ supply to a large extent. In contrast, control experiments in which the root was cut 1 cm below the probe insertion point, allowing direct entry of external K+ into the xylem vessels, demonstrated that the xylem equilibrated rapidly with external K+. This was taken simultaneously as a proof for the correct reading of the probe.     

Analytical study of the effects of soft tissue artefacts on functional techniques to define axes of rotation

The accurate location of the main axes of rotation (AoR) is a crucial step in many applications of human movement analysis. There are different formal methods to determine the direction and position of the AoR, whose performance varies across studies, depending on the pose and the source of errors. Most methods are based on minimizing squared differences between observed and modelled marker positions or rigid motion parameters, implicitly assuming independent and uncorrelated errors, but the largest error usually results from soft tissue artefacts (STA), which do not have such statistical properties and are not effectively cancelled out by such methods. However, with adequate methods it is possible to assume that STA only account for a small fraction of the observed motion and to obtain explicit formulas through differential analysis that relate STA components to the resulting errors in AoR parameters. In this paper such formulas are derived for three different functional calibration techniques (Geometric Fitting, mean Finite Helical Axis, and SARA), to explain why each technique behaves differently from the others, and to propose strategies to compensate for those errors. These techniques were tested with published data from a sit-to-stand activity, where the true axis was defined using bi-planar fluoroscopy. All the methods were able to estimate the direction of the AoR with an error of less than 5°, whereas there were errors in the location of the axis of 30–40 mm. Such location errors could be reduced to less than 17 mm by the methods based on equations that use rigid motion parameters (mean Finite Helical Axis, SARA) when the translation component was calculated using the three markers nearest to the axis.     

Calibration of measured center of pressure of a new stairway design for kinetic analysis of stair climbing

A stairway that allows the collection of kinetic data is essential for biomechanical studies on stair climbing. There is a need to validate the measured center of pressure (COP) on the surface of a stair in order to verify the accuracy of the calculation of joint kinetics. The purpose of this study was to validate a new stairway design for kinetic analysis of stair climbing through a calibration and error analysis of the COP obtained from this system. The new stairway design allows the collection of kinetic data for multiple steps without any constraint to foot placement. Known vertical forces were applied to known locations on the surface of each stair and each force plate. Multiple regression analyses were conduced to determine the distribution pattern of the error in the measured COP. It was found that the error in the COP was a function of location on the stair or force plate. The magnitude of the vertical force had no significant effect on the error in the measured COP. The distribution pattern of the error in the measured COP on the force plates used in this study matched the results in the literature. A healthy female subject was used as the subject in a stair climbing test. The error in the measured COP had a significant effect on the calculated joint resultant moments, especially the abduction-adduction and internal-external rotation moments. The correction of these errors should make the kinetic calculation in stair climbing more accurate.     

Effects of crystalloid and colloid fluids on extravascular lung water in hypoproteinemic dogs

We compared the effect of crystalloid to colloid fluid infusion on extravascular lung water (EVLW) in hypoproteinemic dogs. Plasmapheresis was used to decrease plasma colloid osmotic pressure (COP) to less than 40% of its base-line level. Five animals were then infused with 0.9% sodium chloride (saline), five with 5% human serum albumin (albumin), and five with 6% hydroxyethyl starch (hetastarch) to increase the pulmonary arterial occlusive pressure by 10 Torr in comparison to the postplasmapheresis level for a 5-h study interval. On completion of the procedure, the lungs were harvested and EVLW measured by the blood-free gravimetric technique. Three to six times the volume of saline compared with albumin or hetastarch (P less than 0.001) was infused. In the saline animals, COP was decreased to 3.3 +/- 1.3 Torr, whereas COP was increased to 18.1 +/- 1.4 Torr in albumin animals (P less than 0.001) and 20.1 +/- 1.6 Torr in the hetastarch group (P less than 0.001). The saline-treated dogs developed gross signs of systemic edema. The EVLW was 8.1 +/- 0.9 ml/kg in saline animals compared with 5.3 +/- 2.1 ml/kg in the albumin (P less than 0.05) and 4.1 +/- 1.4 ml/kg in the hetastarch (P less than 0.01) groups. These data indicate that crystalloid fluid infusion during hypoproteinemia is associated with the development of both systemic and pulmonary edema.     

Evaluation of a new algorithm to determine the hip joint center

Accurately locating the hip joint center is a challenging and important step in many biomechanical investigations. The purpose of this study was to test the accuracy and robustness of a "pivoting" algorithm used to locate the hip center. We tested the performance of this algorithm with data acquired by manipulating a ball and socket model of the hip through several motion patterns. The smallest mean errors of 2.2+/-0.2 mm occurred with a circumduction motion pattern, while the largest errors of 4.2+/-1.3 mm occurred with single-plane motion (e.g., flexion/extension). Introducing random noise with an amplitude of 30 mm increased the errors by only 1.3+/-0.5 mm with a circumduction motion pattern. The pivoting algorithm performs well in the laboratory, and further work is warranted to evaluate its performance in a clinical setting.     

Soft-tissue artefact assessment during step-up using fluoroscopy and skin-mounted markers

When measuring knee kinematics with skin-mounted markers, soft tissue and structures surrounding the knee hide the actual underlying segment kinematics. Soft-tissue artefacts can be reduced when plate-mounted markers or marker trees are used instead of individual unconstrained mounted markers. The purpose of this study was to accurately quantify the soft-tissue artefacts and to compare two marker cluster fixation methods by using fluoroscopy of knee motion after total knee arthroplasty during a step-up task. Ten subjects participated 6 months after their total knee arthroplasty. The patients were randomised into (1) a plate-mounted marker group and (2) a strap-mounted marker group. Fluoroscopic data were collected during a step-up motion. A three-dimensional model fitting technique was used to reconstruct the in vivo 3-D positions of the markers and the implants representing the bones. The measurement errors associated with the thigh were generally larger (maximum translational error: 17mm; maximum rotational error 12 degrees ) than the measurement errors for the lower leg (maximum translational error: 11mm; maximum rotational error 10 degrees ). The strap-mounted group showed significant more translational errors than the plate-mounted group for both the shank (respectively, 3+/-2.2 and 0+/-2.0mm, p = 0.025) and the thigh (2+/-2.0 and 0+/-5.9mm, p = 0.031). The qualitative conclusions based on interpretation of the calculated estimates of effects within the longitudinal mixed-effects modelling evaluation of the data for the two groups (separately) were effectively identical. The soft-tissue artefacts across knee flexion angle could not be distinguished from zero for both groups. For all cases, recorded soft-tissue artefacts were less variable within subjects than between subjects. The large soft-tissue artefacts, when using clustered skin markers, irrespective of the fixation method, question the usefulness of parameters found with external movement registration and clinical interpretation of stair data in small patient groups.     

Spacing of fetuses and local competition in strains of mice with large, medium and small litters.

The tendency for fetuses to be evenly spaced along the uterine horn and the relationship of this to local competition between fetuses was examined in three strains of mice which characteristically produce large, medium and small litters. Local competition was assessed by correlating, within each uterine horn, the weight of each fetus or placenta with the mean distance to its immediate neighbours. Weights and distances were measured on day 19 of gestation, on the day before expected parturition and distances only on day 7. Average litter sizes (live fetuses) were 16.3 +/- 0.9, 11.7 +/- 0.6 and 7.2 +/- 0.5 (mean +/- SEM) in the large, medium and small litter strains, respectively (n = 7, 7 and 10, respectively). On day 19, the mean distance between fetuses was significantly less (P < 0.05) in the large strain (10.1 +/- 1.0 mm) than in the medium (14.0 +/- 1.2 mm) or small (13.5 +/- 1.0 mm) strains. Evenness of spacing, expressed as the standard deviation of distances between fetuses divided by the mean distance, improved from day 7 to day 19 of gestation in all three strains and effectively prevented local competition between fetuses in the medium litter (r = 0.04) and small litter strains (r = 0.17), but not in the large litter strain (r = 0.45, P < 0.01). Thus, local crowding does not seem to be detrimental to fetal growth in mice, except in strains specifically bred for large litters.     

Effect of environment on blood pressure: home versus hospital.

The effect of environment on blood pressure was studied by recording intra-arterial pressure continuously in nine patients with essential hypertension during controlled periods of activity and rest at home and in hospital. Mean systolic pressure was higher at home (152 +/- 16 mm Hg) than in hospital (138 +/- 11 mm Hg, p less than 0.01), the difference being greatest during the period of activity (165 +/- 21 v 142 +/- 13 mm Hg, p less than 0.001); heart rates and diastolic pressures did not differ significantly at these times. Systolic pressure recorded by conventional sphygmomanometry was also higher at home (173 +/- 23 v 159 +/- 23 mm Hg, p less than 0.01), as was diastolic pressure (98 +/- 10 v 89 +/- 11 mm Hg, p less than 0.02). Systolic pressure was consistently higher at home, and this effect was independent of the pressure of an observer. This must be taken into consideration when assessing blood pressure and efficacy of treatment in hospital.     

Roentgen stereophotogrammetric analysis methods for determining ten causes of lengthening of a soft-tissue anterior cruciate ligament graft construct

There are many causes of lengthening of an anterior cruciate ligament soft-tissue graft construct (i.e., graft+fixation devices+bone), which can lead to an increase in anterior laxity. These causes can be due to plastic deformation andor an increase in elastic deformation. The purposes of this in vitro study were (1) to develop the methods to quantify eight causes (four elastic and four plastic) associated with the tibial and femoral fixations using Roentgen stereophotogrammetric analysis (RSA) and to demonstrate the usefulness of these methods, (2) to assess how well an empirical relationship between an increase in length of the graft construct and an increase in anterior laxity predicts two causes (one elastic and one plastic) associated with the graft midsubstance, and (3) to determine the increase in anterior tare laxity (i.e., laxity under the application of a 30 N anterior tare force) before the graft force reaches zero. Markers were injected into the tibia, femur, and graft in six cadaveric legs whose knees were reconstructed with single-loop tibialis grafts. To satisfy the first objective, legs were subjected to 1500 cycles at 14 Hz of 150 N anterior force transmitted at the knee. Based on marker 3D coordinates, equations were developed for determining eight causes associated with the fixations. After 1500 load cycles, plastic deformation between the graft and WasherLoc tibial fixation was the greatest cause with an average of 0.8+/-0.5 mm followed by plastic deformation between the graft and cross-pin-type femoral fixation with an average of 0.5+/-0.1 mm. The elastic deformations between the graft and tibial fixation and between the graft and femoral fixation decreased averages of 0.3+/-0.3 mm and 0.2+/-0.1 mm, respectively. The remaining four causes associated with the fixations were close to 0. To satisfy the remaining two objectives, after cyclic loading, the graft was lengthened incrementally while the 30 N anterior tare laxity, 150 N anterior laxity, and graft tension were measured. The one plastic cause and one elastic cause associated with the graft midsubstance were predicted by the empirical relationships with random errors (i.e., precision) of 0.9 mm and 0.5 mm, respectively. The minimum increase in 30 N anterior tare laxity before the graft force reached zero was 5 mm. Hence, each of the eight causes of an increase in the 150 N anterior laxity associated with the fixations can be determined with RSA as long as the overall increase in the 30 N anterior tare laxity does not exceed 5 mm. However, predicting the two causes associated with the graft using empirical relationships is prone to large errors.     

Effect of prolonged renal dysfunction on intravascular and extravascular pulmonary fluid volumes during left atrial hypertension

To examine the development of pulmonary edema during experimental renal dysfunction, left atrial pressure was altered in 14 mongrel dogs divided into two groups. Group 1 was composed of seven control animals, and Group 2 was composed of seven animals with surgically induced renal failure (1 week of bilateral ureteral ligation). Data were obtained at two levels of matched transmural pulmonary vascular pressure (defined as mean left atrial pressure less serum protein osmotic pressure). In the animals with renal dysfunction, extravascular lung water (EVLW) (thermal-green dye technique) was higher at moderately (-1 to -2 mm Hg) and severely elevated (11 to 12 mm Hg) vascular driving pressures (11.5 +/- 1.2 cc/kg vs 10.6 +/- 0.8 cc/kg and 14.8 +/- 1.3 cc/kg vs 13.0 +/- 1.9 cc/kg, respectively, both P less than 0.05 vs control). Because protein osmotic pressure was lower in the renal failure group (15.0 +/- 1.8 mm Hg vs 18.4 +/- 1.4 mm Hg, P less than 0.05), greater accumulations of extravascular lung water occurred at lower levels of left atrial pressure (14.2 +/- 1.4 mm Hg vs 17.1 +/- 1.2 mm Hg, P less than 0.05; 26.8 +/- 2.6 mm Hg vs 29.5 +/- 2.3 mm Hg, P less than 0.01). In addition, when the ratio of EVLW/PBV (pulmonary blood volume) was examined in both groups at each stage of the experiment, the ratio was greater in the Group 2 animals at each elevated pressure, suggesting increased permeability with renal dysfunction. In conclusion, pulmonary edema formation occurs at lower left atrial pressures in the setting of sustained renal dysfunction, this phenomenon can be partially explained by lower protein osmotic pressure though altered pulmonary microvascular permeability may contribute to edema formation.     

Intraocular pressure and tear production in captive eland and fallow deer

Applanation tonometry was used to estimate intraocular pressure (IOP) and Schirmer tear test (STT) I was used to estimate tear production in both eyes of 12 juvenile elands (Taurotragus oryx) and one eye each of 15 Asian fallow deer (Dama mesopotamica). Mean (+/- standard deviation) IOP was 14.6 +/- 4.0 mm Hg in the eland and 11.9 +/- 3.3 mm Hg in the deer. Mean tear production was 18.7 +/- 5.9 mm/min in the eland and 10.5 +/- 6.5 mm/min in the deer. The large variation in IOP between two members of the family Bovidae, the elands reported here and the Thomson gazelle (Gazella thomsoni) for which we previously reported a mean pressure of 7.6 mm Hg, illustrates the need to establish reference values for each species. Tear production may be influenced by the species' natural habitat.     

Influence of age, body mass index, and blood pressure on the carotid intima-media thickness in normotensive and hypertensive patients.

We investigated whether body mass index and blood pressure have an additive influence on the carotid intima-media thickness (IMT). In 27 patients treated for hypertension (47.2+/-8.7 years) and 23 normotensive subjects (44.1+/-8.1 years), 24-h recording of blood pressure was performed. The carotid IMT was determined by ultrasonography and baroreflex sensitivity by a spectral method from 5-min recordings of blood pressure. Significant differences between hypertensive and normotensive subjects were observed for carotid IMT (0.60+/-0.08 vs. 0.51+/-0.07 mm; p<0.001) and baroreflex sensitivity (3.5+/-1.8 vs. 5.6+/-2.1 ms/mm Hg; p<0.001). Hierarchical multiple regression analysis (p<0.01) showed that carotid IMT was positively correlated with age (p<0.001) and body mass index (p<0.05) in normotensive subjects. The increased carotid IMT in hypertensive patients was not additively influenced by either age or body mass index. Baroreflex sensitivity decreased with age (p<0.01) and with carotid IMT (p<0.05) in normotensive subjects only. Multiregression analysis showed that an additive influence of age and body mass index on the development of carotid IMT is essential only in normotensive subjects. In hypertensive subjects the influence of blood pressure predominates, as documented by a comparison of the carotid IMT between hypertensive and normotensive subjects.