[Venous hemodynamics. Base equations].

C Ribreau

Home/Archive/PubMed

PubMed · 2584884

[Venous hemodynamics. Base equations].

C Ribreau

View original source ↗Export metadata ↓

Abstract

The hydrodynamics in tubes with inert walls collapsed by a negative transmural pressure (inside pressure minus outside pressure) set up a fundamental and original approach in venous hemodynamics. Mechanisms of flow regulation and flow limitation can occur especially when the upstream pressure is held constant or when the average flow speed in a cross-section equals the local pressure waves speed. The three baseline equations on mechanics are required to demonstrate these properties: --the tube law, --the equation of motion, --the equation of continuity. It is shown that the behaviour of the tube varies with the nature of the flow (subcritical, critical or supercritical, subsonic, sonic or supersonic, according to the aerodynamics). Though this study does not take all the physiological and biological data into account, it includes indeed the three fundamental aspects on mechanics of the veins. The rheologic equation on the state of the venous wall, normal or pathologic, plays a major and determinant role.

Explore related subjects

Biomechanical Phenomena Biophysical Phenomena Biophysics Hemodynamics Mathematics Models, Biological Veins Venous Pressure English Abstract Journal Article

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

C Ribreau. 1989. [Venous hemodynamics. Base equations].. https://pubmed.ncbi.nlm.nih.gov/2584884/

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2007

The effect of excessive tibial torsion on the capacity of muscles to extend the hip and knee during single-limb stance.

Excessive tibial torsion, a rotational deformity about the long axis of the tibia, is common in patients with cerebral palsy who walk with a crouch gait. Previous research suggests that this deformity may contribute to crouch gait by reducing the capacity of soleus to extend the knee; however, the effects of excess external torsion on the capacity of other muscles to extend the stance limb during walking are unknown. A computer model of the musculoskeletal system was developed to simulate a range of tibial torsion deformities. A dynamic analysis was then performed to determine the effect of these deformities on the capacity of lower limb muscles to extend the hip and knee at body positions corresponding to the single-limb stance phase of a normal gait cycle. Analysis of the model confirmed that excessive external torsion reduces the extension capacity of soleus. In addition, our analysis revealed that several important muscles crossing the hip and knee are also adversely affected by excessive tibial torsion. With a tibial torsion deformity of 30 degrees , the capacities of soleus, posterior gluteus medius, and gluteus maximus to extend both the hip and knee were all reduced by over 10%. Since a tibial torsion deformity reduces the capacity of muscles to extend the hip and knee, it may be a significant contributor to crouch gait, especially when greater than 30 degrees from normal, and thus should be considered by clinicians when making treatment decisions.

Biomechanical Phenomena↗

PubMed2007

Predicting the subject-specific primary stability of cementless implants during pre-operative planning: preliminary validation of subject-specific finite-element models.

Pre-operative planning help the surgeon in taking the proper clinical decision. The ultimate goal of this work is to develop numerical models that allow the surgeon to estimate the primary stability during the pre-operative planning session. The present study was aimed to validate finite-element (FE) models accounting for patient and prosthetic size and position as planned by the surgeon. For this purpose, the FE model of a cadaveric femur was generated starting from the CT scan and the anatomical position of a cementless stem derived by a skilled surgeon using a pre-operative CT-based planning simulation software. In-vitro experimental measurements were used as benchmark problem to validate the bone-implant relative micromotions predicted by the patient-specific FE model. A maximum torque in internal rotation of 11.4 Nm was applied to the proximal part of the hip stem. The error on the maximum predicted micromotion was 12% of the peak micromotion measured experimentally. The average error over the entire range of applied torques was only 7% of peak measurement. Hence, the present study confirms that it is possible to accurately predict the level of primary stability achieved for cementless stems using numerical models that account for patient specificity and surgical variability.

Biomechanical Phenomena↗

PubMed2007

Experimental validation of intact and implanted distal femur finite element models.

Four finite element (FE) models of intact and distal femur of knee replacements were validated relative to measured bone strains. FE models of linear tetrahedrons were used. Femoral replacements with cemented stemless, cemented and noncemented femoral stems of the PFC Sigma Modular Knee System were analyzed. Bone strains were recorded at ten locations on the cortex. The magnitude of the FE bone strains corresponded to the mean measured strains, with an overall agreement of 10%. Linear regression between the FE and mean experimental strains produced slopes between 0.94 and 1.06 and R(2) values between 0.92 and 0.99. RSME values were less than 12%. The FE models were able to adequately replicate the mechanical behavior of distal femur reconstructions.

Biomechanical Phenomena↗