Analysis of all possible combinations of four measurements determining true propagation in arteries.

All possible combinations of four measurements of blood pressure, blood flow and vascular diameter are examined by transmission-line theory. It is found that only nine measurement combinations can give the attenuation coefficient gamma, reflection coefficient R and characteristic impedance Z0 simultaneously. At least one pressure measurement must be included.

Capillary transit times and kinetics of oxygenation in the primary respiratory organ of early chick embryo.

In early avian embryos respiratory gas exchange between environment and blood takes place via the blood vessels of the yolk sac. To investigate the principles governing oxygen transfer we determined the RBC velocity, the length of the a-v channels, and the RBC transit time in the vitelline capillary network of 4-day-old chick embryos. Measurements were carried out using a digital video analyzing system for on-line velocity measurements (modified dual video window technique) and morphometric determinations.

[Design of a tibial intramedullary nail based on anatomic studies of intraosseous vessels].

The design of the tibial medullary nail can be improved in order to preserve intraosseus vessels by osteosynthesis of the tibia. The nutrient artery of the human tibia enters the compacta in an average height of 33% dorsally and is leaving it in a height of 50% of the tibial length. In the medullary cavity the vessel splits up.

Detecting right ventricular volume changes using the conductance catheter.

The purpose of this study was to assess the role of conductance catheter position within the right ventricle in obtaining adequate indications of phasic changes in ventricular volume. Possible applications of this technology are in rate responsive pacemakers and implantable defibrilators. The conductance catheter was placed in the right ventricle by cannulation of a jugular or femoral vein or a branch of the pulmonary artery.

Autoradiographic studies of rat astroglial cell proliferation in vitro with and without treatment with basic fibroblast growth factor.

Using specific autoradiographic methods, cell cycle parameters of untreated and basic fibroblast growth factor (bFGF)-treated astroglial cells from newborn rats grown in primary culture were directly measured. The mode of proliferation was also analysed. In untreated cultures, S phase duration (Ts = 6.

Possible sources of discrepancy between sphygmomanometer cuff pressure and blood pressure quantified in a collapsible-tube analogue.

This paper examines the assumption that the audible events detected as Korotkov sounds in sphygmomanometry occur when blood pressure equals arm-cuff pressure. Several effects that contribute to discrepancy between these pressures are quantified using an idealised arm-and-cuff system consisting of a thick-walled collapsible tube subject to external compression along a central part of its length. The effects studied are (1) transverse pressure difference, resulting from tissues sustaining a part of the external compression through (a) circumferential bending stiffness and (b) longitudinal curvature of the tensed localised neck at the site of initial collapse, (2) longitudinal pressure difference between upstream pressure and pressure at the collapse point due to both (a) viscous and (b) inertial pressure drop.

A general method of determining the frequency-dependent propagation coefficient and characteristic impedance of an artery in the presence of reflections.

An iterative method of calculating propagation parameters at harmonics of heart rate for a uniform vascular segment from a combination of four arterial waveform measurements is presented. Measurements of blood pressure, vascular diameter, and blood flow-rate may be combined arbitrarily provided only that at least one measurement of pressure and one of flow-rate be included; the requirement of four measurements implies at least two measurement sites along the vessel. The analysis is thus a generalization of those associated with previous methods of determining propagation parameters, allowing for instance relaxation of the requirement of equal spacing in the three-point method.

Sectorial angioarchitecture of the human tibia.

The blood supply of the periosteum of the human tibia was investigated by anatomical dissection of 12 lower extremities which were filled with injection mass. By division of the tibia into 4 segments (proximal and distal fifths; proximal and distal diaphysis) a general supplying system of the periosteum was found. The proximal fifth of the tibial periosteum is nourished by branches of the arteriae recurrentes tibiales anterior et posterior and the aa.

Characterization of astroglial cell proliferation in vitro and in vivo.

On the basis of experimental set-ups in vitro and in vivo and by making use of specific autoradiographical techniques, the following data on the proliferation of astrocytes from newborn rats in vitro and unpretreated rats and mice in vivo could be obtained: (i) The commonly employed immunohistochemical staining techniques in vitro are not applicable in tissue sections. (ii) In vivo, astrocytes show increasing durations of cell cycle (tc) as well as S phase (ts) prenatally until about birth. A similar trend can be observed in vitro.

[The arterial blood supply of the tibial and practical consequences].

In the periosteum of the human tibia, the arterial blood supply shows a general sectorial angioarchitecture. There are 4 segments: proximal and distal 1/5, proximal and distal diaphysis. The proximal 1/5 of the tibial periosteum is supplied with blood by the aa.

Measurements of wave speed and compliance in a collapsible tube during self-excited oscillations: a test of the choking hypothesis.

Indirect evidence links self-excited oscillation of flow through collapsed tubes with choking, defined by the cross-sectionally averaged fluid speed u reaching the local speed of small pressure waves c. This was tested by measuring both c-u and c as functions of tube cross-sectional area during self-excited oscillation, using small superimposed high-frequency wave packets. The wavespeed c was derived from the local slope of the pressure/area relationship, measured at both high and low frequency, while c-u was taken as the upstream propagation rate of the pressure disturbances.

Morphometric evaluation of chondrocyte cavities in normal and prearthrotic human femoral heads.

In 25 human femoral heads, the structural changes in the chondrocyte cavities of prearthrotic cartilage were determined in three different layers by detailed morphometric evaluation. As examination parameters, the area, perimeter, diameter, and the form deviation from a circle (form PE) were chosen. In addition, we calculated the numeric cell density and the mean distance between two chondrocyte cavities.

Oscillations in a collapsed-tube analog of the brachial artery under a sphygmomanometer cuff.

To determine whether self-excited oscillations in a Starling resistor are relevant to physiological situations, a collapsible tube conveying an aqueous flow was externally pressurized along only a central segment of its unsupported length. This was achieved by passing the tube through a shorter and wider collapsible sleeve which was mounted in Starling resistor fashion in a pressure chamber. The tube size and material, and all other experimental parameters, were as used in our previous Starling resistor studies.

Cross-sectional area measurement in collapsed tubes using the transformer principle.

To avoid the necessity for intraluminal catheters as used with the axial impedance method of measuring the cross-sectional area of flexible tubes independently of their shape, while retaining the advantage of an immediate electrical output, an electromagnetic method was tested. The method uses a single-turn sensing coil attached to or embedded in the tube wall at the site of interest as the secondary winding of a transformer. One or more primary coils coaxial with the tube provide an alternating magnetic field parallel to the tube axis, and the resulting secondary voltage, after amplification and demodulation, is directly proportional to tube cross-sectional area.

Effect of radial position on volume measurements using the conductance catheter.

A finite-difference computer model has been used to determine the potential distributions arising from a dipole current source aligned parallel to the axis of bounding cylinders. The radial position of this source had large and nonlinear influence on the potentials along the dipole axis. The accuracy of the computer simulation was established from comparison with an analytic solution of a simple geometry.

Right ventricular volumetry by catheter measurement of conductance.

The electrical conductivity of blood is sufficiently higher than that of myocardium to make feasible the detection of cardiac volume changes by measurement of intraventricular fluid conductance. An eight-electrode catheter was used to inject an alternating current (100 microA or less, at 1500 Hz) via the two electrodes nearest the ventricular base and apex, then the resulting five voltage differences between adjacent pairs of the six intervening electrodes were measured. When current amplitude was held constant, the cross-sectional area of the ventricular cavity slice defined by planes perpendicular to the catheter through the relevant pair of electrodes was inversely proportional (to the first order) to the voltage difference.

The effects of wall thickness, axial strain and end proximity on the pressure-area relation of collapsible tubes.

Segments of silicone rubber tube were suspended between rigid pipes and subjected to slowly varying transmural pressure covering a range from slight distension to collapse with osculation. The local inside cross-sectional area at a chosen axial site was simultaneously measured via catheter by an electrical impedance method. Pressure-area relations were recorded thus at various axial sites, under varying conditions of axial tube wall tension, in tubes of two different wall thickness (0.

Unstable equilibrium behaviour in collapsible tubes.

Thick-walled silicone rubber tube connected to rigid pipes upstream and downstream was externally pressurised (pe) to cause collapse while aqueous fluid flowed through propelled by a constant upstream head. Three types of equilibrium were found: stable equilibria (steady flow) at high downstream flow resistance R2, self-excited oscillations at low R2, and 'unattainable' (by varying external pressure) or exponentially unstable equilibria at intermediate R2. The self-excited oscillations were highly non-linear and appeared in four, apparently discrete, frequency bands: 2.

Real time detection of significant blood pressure events in ambulant subjects.

A typical twenty-four hour continuous ambulatory blood pressure (BP) record demonstrates many marked, apparently spontaneous blood pressure spikes. Awareness of such BP fluctuations may help determine their causative mechanisms and lead to improved applications of conscious learned control of BP (Biofeedback). A microprocessor device has been constructed to monitor direct arterial blood pressure in real time and to compile a profile history of the BP and heart rate (HR).

A mathematical model of unsteady collapsible tube behaviour.

A simple, third-order lumped parameter model is presented to describe unsteady flow in a short segment of collapsible tube held between two rigid segments and contained in a pressurised chamber. Equilibrium states and their stability are analysed in detail, as is fully non-linear time dependent behaviour, including in particular the excitation and sustenance of limit--cycle oscillations. The model explicitly neglects both wave propagation (and hence the possibility of choking) and the influence on the elastic properties of the tube of longitudinal tension, but it is otherwise firmly based on fluid mechanical principles.