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Biomedical subjects

L Walløe

Publications and source records attributed to L Walløe.

At least 37 records · Page 2Linked to original sources
PubMed1990

Improved method for cardiac output determination in man using ultrasound Doppler technique.

An existing ultrasound Doppler method for measuring cardiac output has been improved and refined, partly by locating the sampling volume higher up in the aorta while still using the aortic ring size as the effective transverse flow area. The basis for using this technique is the approximately rectangular systolic velocity profile in the aortic orifice in physiologically and anatomically normal subjects, and the fact that this profile velocity is conserved as the maximum velocity in the ascending aorta for some 3 to 4 cm above the valves. This higher location of the sampling volume improves Doppler signal quality, and does not reduce the accuracy of the method, as can be confirmed in each experimental subject. Together with automatic computer-based online signal analysis, the technique employed enables us to make continuous long-term beat-to-beat measurements of cardiac output in subjects without aortic valve disease or grossly deforming disease of the aortic root.

Aorta↗
PubMed1990

Dynamics and dimensions of cardiac output changes in humans at the onset and at the end of moderate rhythmic exercise.

1. An improved Doppler ultrasound technique was used to measure stroke volume (SV) and cardiac output (CO) on a beat-to-beat basis in a group of supine humans before, during and after periods of standardized, rhythmic exercise, involving the quadriceps muscle groups on both sides. The development of CO on such bouts of exercise was compared to Doppler ultrasound records of the simultaneous femoral arterial flow (FF) response. 2. Records of CO at rest revealed spontaneous fluctuations around a mean level, with differences between the minimal and maximal values of the order of 1 l min-1. The mean CO level at rest again varied considerably from one day to another and from test run to test run. 3. Upon start of exercise an immediate and rapid increase in heart rate (HR) and CO took place. The entire increase, the size of which varied appreciably from test run to test run, was completed within 10-15 s. No or only minor changes were seen in the mean SV level during the exercise periods. 4. The time course of the increase in FF was indistinguishable from that of the increase in CO, which occurred without any detectable delay relative to the changes in FF. These closely parallel developments indicate a tight regulatory coupling between the two types of flow changes. 5. In the majority of tests the total and two-sided increase in FF seen in the steady-state situation in the last part of an exercise period was significantly larger than the recorded increase in CO. This discrepancy implies that some redistribution of flow from tissues other than the working muscles might take place, even at this moderate level of work. 6. Upon the end of exercise a striking but transient increase in CO occurred, resulting from an increase in SV concomitant with a maintained HR. In the course of five to eight post-exercise cardiac cycles about 100 extra milliliters of blood were expelled from the heart. This cardiac outflow overshoot was found to occur during a post-exercise fall in mean arterial blood pressure (MAP).

Adult↗
PubMed1989

Temporal relationship between blood flow changes and release of ions and metabolites from muscles upon single weak contractions.

The temporal changes in muscular blood flow and in the release of ions and metabolites have been studied during and after short-lasting isometric contractions. Blood velocities in the human femoral artery were measured using pulsed bidirectional Doppler ultrasound equipment during single contractions of the quadriceps muscle group. Contractions of 5 s and 30 s duration and at a tension of 10% MVC (maximal voluntary contraction) were investigated. Even the contractions of 5 s duration caused conspicuous post-contraction increases in femoral arterial flow. The following substances were analysed in the femoral vein during and following the contractions: potassium, lactate, inorganic phosphate, calcium, sodium, oxygen and haemoglobin. Following contractions of 5 s duration, an increase in the venous potassium concentration (by 0.9 mM) was found, but there was no change in concentration of any of the other substances analysed. Following contractions of 30 s duration a more marked increase in the venous potassium concentration (by 1.5 mM) was found, and in addition substantial changes in venous lactate concentration and oxygen saturation. There were small but statistically significant changes in the concentrations of inorganic phosphate and calcium, but no change in the sodium concentration. The time-course and magnitude of the changes in venous potassium concentration fit well with the idea that potassium is important in the initiation and regulation of the functional hyperaemia in contracting muscles.

Adult↗
PubMed1988

Time course and magnitude of blood flow changes in the human quadriceps muscles during and following rhythmic exercise.

1. Pulsed bidirectional Doppler-ultrasound equipment was used to measure changes in blood velocities in the femoral artery on a beat to beat basis for consecutive contraction and relaxation phases during voluntary rhythmic exercise of the quadriceps muscle group in man. 2. Rapid and large fluctuations of blood velocities were found, being high during relaxation and low during contraction phases. At the onset of contraction phase, negative velocities were present, indicating retrograde flow. During the rest of the contraction phase, forward flow occurred comparable to the resting flow level even at high loads. 3. Estimated maximal flow to the whole leg during relaxation phase, calculated from these blood velocity measurements and vessel diameter (measured with echo-ultrasound equipment with high resolution) was in two of the subjects 3.32 l min-1 (female) and 5.97 l min-1 (male). When using computer tomography to estimate the volume of the quadriceps muscle group, the calculated maximum flow to this muscle group was 243 (female) and 257 (male) ml min-1 100 ml muscle-1. The time-averaged flow during exercise to the whole leg was 1.51 l min-1 (female) and 2.47 l min-1 (male). The calculated time-averaged flow to the quadriceps muscle group was 101 (female) and 98 (male) ml min-1 100 ml muscle-1. 4. The duration of post-contraction hyperaemia following such rhythmic exercise of up to 6 min duration and up to 75% maximum voluntary contraction was never in excess of 150 s.

Adult↗
PubMed1987

Changes in human cerebral blood flow due to step changes in PAO2 and PACO2.

The effect of moderate hypoxia on cerebral blood flow (CBF) in man has not been well described, and little is known about the interaction of changes in arterial PO2 and PCO2 as regards CBF. Using a non-invasive doppler ultrasound method we have measured the instantaneous mean blood velocity (which is proportional to CBF as long as the cross-section of the vessel is constant) in the carotid artery in four healthy unanaesthetized subjects. We found in all subjects that a reduction in alveolar PO2 from about 13 to about 8.7 kPa with maintained constant alveolar PCO2 (PA, CO2) caused CBF to increase gradually over 10 min (half-time about 4 min) to about 125% of control. The CBF decreased quickly (half-time about 45 s) towards control when alveolar PO2 was reset to 13 kPa. As measured 5 min after a step-change in PA, O2, the change in CBF was independent of PA, CO2 within the range 3.3-6.7 kPa. An increase in PA, O2 to about 33 kPa reduced CBF only if PA, CO2 was in the hypercapnic range. Unexpectedly we found that the CBF response showed 'adaptation' during both maintained increase and decrease in PA, CO2. The CBF started to return towards control level within 10 min after induction of hypo- or hypercapnia. We conclude that also moderate hypoxia causes increased CBF in unanaesthetized man within a wide range of PA, CO2.

Adult↗
PubMed1986

Localization of atheromatous lesions in normal and hypercholesterolaemic pigeons.

Computerised morphometry was used to define the distribution of aortic atheroma in 10 normal White Carneau pigeons (age 42 months) and in groups of 10 weanling or mature birds given a cholesterol coated diet for 24 weeks. Mean serum total and HDL-cholesterol was substantially higher in cholesterol fed animals (15 v 8 mmol/l). The spatial distribution of disease was identical in each group. Lesions developed just proximal to the first major abdominal branch and were more plentiful on the right hand side. The major histological component of the lesions was fibrous intimal thickening and when studied separately its distribution closely matched that of the overall lesion. Foam cell aggregates were more plentiful on the right. This distribution pattern is very similar to that seen in early human atheroma and supports the hypothesis that lesions form in regions of low flow velocities.

Animals↗
PubMed1985

Distribution pattern of sudanophilic plaques in the descending thoracic and proximal abdominal human aorta.

The localization of sudanophilic plaques around the intercostal ostia and the origin of the superior mesenteric and coeliac artery was examined in 38 human aortae. The perimeter of the opened aorta and the outline of each sudanophilic plaque were digitized and computerized. By means of a special program the results were displayed as progressive contour lines connecting points with an equal frequency of plaques. This study shows that the sudanophilic plaques have a distinct spatial distribution both in the thoracic and abdominal aorta. Around the intercostal ostia peak frequency of plaques is found just proximal to the lower lip of the ostia. In the bifurcation of both the superior mesenteric and coeliac artery the plaques are present on the outer walls while the inner walls and the apex itself are free of plaques.

Adolescent↗
PubMed1983

Localization of atherosclerotic lesions in the bifurcation of the main left coronary artery.

The detailed distribution of atherosclerotic lesions in the branching region of the left main coronary artery in man was studied. Tissue cubes of the hearts, containing the left coronary arteries, were removed, and 1.5-mm-thick parallel and consecutive slices were cut perpendicular to the main coronary artery. Histological sections of the slices were stained and photographed. Drawings of the cross-sections of the arteries, including information about thickness of the intima and borders of the atherosclerotic lesions, were fed into a computer, scaled and analyzed. Casts were made of the left main coronary bifurcation from additional hearts. The curvature of the arteries and the angles of the bifurcation were measured. Atherosclerotic lesions have a distinct pattern with a high frequency on the outer walls of the bifurcation and at the inner curvature downstream from the bifurcation. The extent of intimal thickening and the occurrence of atherosclerotic lesions were mostly in agreement.

Adult↗
PubMed1983

Localization of early atherosclerotic lesions in the right carotid bifurcation in humans.

The detailed localization of early atherosclerotic lesions in the right carotid bifurcation was studied in 37 carotid arteries obtained from autopsies of young persons who had suffered a violent and sudden death. Drawings of the sudanophilic lesions in the vessel wall were fed to a computer, scaled to a standardized size and shape, and added together. The results are presented as contour lines connecting points with equal frequency of early lesions. The distribution of early lesions reveals a distinct pattern: The early lesions start to develop on the outer walls of the bifurcation, while the inner walls downstream from the flow divider are left free, as are also the lateral walls. In the carotid sinus the distribution of the lesions has a U-formed pattern.

Adolescent↗
PubMed1981

Pulsatile pressure and flow in arterial stenoses simulated in a mathematical model.

This paper presents the detailed pulsatile pressure and flow velocity patterns inside an axis symmetric stenosis model with 75% constriction. The pressure and velocities have been calculated by solving the Navier-Stokes equations by the finite element method, the velocity profile in a straight tube caused by a pulsating driving pressure has been calculated first and then used as a boundary condition for the stenosis calculations. The results of the mathematical simulations of the stenosis model have been obtained in terms of velocity vectors, streamlines and isobars at 16 different instances in time, each 15 degrees apart during a cardiac cycle. The calculated velocity field shows that a vortex is developed at the wall distal to the stenosis as the velocity decreases from the peak systolic value. At the site of the vortex, a local pressure minimum is found due to the conversion of pressure to kinetic energy. when the flow is reversed, the reversal occurs first along the wall, thus forcing the vortex toward the centre of the tube. As the reverse flow velocity increases, a vortex is also developed at the proximal site of the stenosis.

Arterial Occlusive Diseases↗
PubMed1981

Localization of early atherosclerotic lesions in an arterial bifurcation in humans.

The detailed localization of early atherosclerotic lesions in arterial bifurcations was studied in 33 brachiocephalic arteries obtained from autopsies of young persons who had suffered a violent and sudden death. Drawings of the sudanophilic lesions in the vessel wall were fed to a computer, scaled to a standardized size and shape, and added together. The results are presented as contour lines connecting points with equal frequency of early lesions. The distribution of the early lesions reveals a distinct pattern: The early lesions start to develop on the outer walls of the bifurcation, while the inner walls downstream from the flow divider are kept free as are also the lateral walls. These results are clearly in conflict with Fry's shear stress hypothesis, while they seem to support Caro's hypothesis of inhibition of local diffusionsal transport. The results are also at variance with results obtained in most animal models, suggesting that the process which takes place in the vessel wall in these animals may be different from human atherosclerosis.

Adolescent↗
PubMed1980

Summation of excitation and inhibition in a second order sensory neuron investigated by computer simulation.

Dorsal spinocerebellar tract (DSCT) neurones adequately activated by primary afferents from the muscle spindles in one muscle in the hindleg of the cat, is regularly inhibited by primary afferents from other muscles. The inhibitory input causes a constant reduction in firing frequency independent of the excitatory drive of the cell. In a simple model the effects of presynaptic inhibition and of postsynaptic inhibition with different time course of the inhibitory action, have been explored. Within the scope of this model, only postsynaptic inhibition with a very long time-constant could explain the experimental results. It is suggested that the inhibitory action is transmitted to the DSCT-cell through a number of synapses distributed over the dendrites.

Animals↗
PubMed1980

Blood flow in arteries determined transcutaneously by an ultrasonic doppler velocitymeter as compared to electromagnetic measurements on the exposed vesels.

We have compared the instantaneous mean blood velocity measured transcutaneously from total cross-sections of arteries in dogs by the use of a new pulsed heterodyne ultrasound doppler equipment, with instantaneous blood flow as measured simultaneously by an electromagnetic flowmeter applied on the exposed vessels. The experiments were performed on the common carotid and the femoral arteries in a variety of flow situations, always with a close fit between the two curves. The results show that the output from the ultrasound equipment is proportional to flow.

Animals↗
PubMed1980

Skin blood flow in humans as a function of environmental temperature measured by ultrasound.

We have measured the blood velocities in arteries supplying the skin in humans both in areas with arteriovenous anastomoses (AVA) and in skin areas without AVA in different temperature situations by means of a pulsed, bidirectional doppler ultrasound instrument. The instrument measures the time average of the instantaneous mean of the blood velocities present in a cross-section of a vessel. So long as the cross-sectional area of the vessel is constant, this average velocity is proportional to volume flow. We observe rapid and large fluctuations in blood velocities in arteries supplying skin areas with AVA in a comfortably warm environment. These fluctuations are substantially larger and more rapid than described by previous authors who have used plethysmograph methods. The blood velocities are more constant both at higher and lower environmental temperatures. There are no similar fluctuations in blood velocity in arteries supplying skin areas without AVA.

Adult↗
PubMed1980

Transfer properties of the slowly adapting stretch receptor of the crayfish abdomen.

The slowly adapting stretch receptor in the abdomen of freshwater crayfish (Astacus fluviatilis) was investigated to determine its properties under dynamic conditions. An in situ preparation was used; the necessary dissection did not involve the receptor organ or its immediate surroundings. Sinusoidal variations in the angle of flexion in the joint to which the receptor organ was connected, were generated by a feed-back controlled stretcher. Nerve spiked recorded from the axon of the receptor neurone and information about angle of flexion in the joint obtained by position transducers, were fed into a computer. Fourier transforms were performed on both input and output data to determine the amplitude of the 0. and 1. harmonic together with the phase of the 1. harmonic. The receptor organ was investigated for linearity up to 1.5 degrees input amplitude, and proved to be surprisingly linear within this range. In addition, the transfer function of the receptor organ was determined by stimulating it with small-amplitude sinusoidals with different frequencies. With a steady flexion of 35-40 degrees in the joint, the gain of the receptor organ increased 5-6 times when the modulation frequency of the input signal was increased from 0.1 to 5 cycles/s. A maximum in gain was constantly found at about 5 cycles/s, with a rapid fall towards 0 when the modulation frequency was increased further. A change in phase lead from positive (leading output) to negative with change in sign about 1 cycle/s was also found. These results resemble the results found by investigators of isolated preparations. A "hold" property is probably a part of the overall property of the receptor organ together with an element of Maxwell type. An element of the form h(s) = ksn with n approximately 0.45 is also a part of the transfer function of the receptor organ, although the physiological parallel to this element is uncertain.

Abdomen↗