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Biomedical subjects

L Walløe

Publications and source records attributed to L Walløe.

13 recordsLinked to original sources
PubMed1991

Arm and leg blood pressures--are they really so different in newborns?

Controversy still exists over differences between upper and lower limb blood pressures (BP) in neonates. We measured upper arm and calf systolic (S) and diastolic (D) BP and heart rate (HR) using 2 Dinamap 847 instruments simultaneously every half minute for several measurement periods of 5-10 min. Nine healthy term newborns were studied in active (AS) and quite (QS) sleep on post-natal days 1 and 5. The results were examined using unbalanced analyses of variance. Arm SBP was 62.3 +/- 1.6 mmHg and DBP 35.5 +/- 1.0 mmHg on day 1 in AS and QS. Calf values were not significantly different but were slightly higher (by 2-3 mmHg) in AS. Arm SBP and DBP rose by 8.5 and 5 mmHg, respectively, between days 1 and 5 but calf pressures rose less. Calf SBP and DBP were significantly lower (by 4.6 and 3.4 mmHg, respectively) than the arm values in QS on day 5. Arm SBP and DBP were dependent on post-natal age but not on sleep state while calf SBP and DBP and HR were dependent on both. Mean HR rose with age from 114 to 117.6 bpm in QS and from 118.6 to 122.4 bpm in AS. Our non-invasive BP measurements were similar to available invasive data. We postulate that differences in arm and calf vasoreactivity account for the different dependence on sleep state and for the unequal changes in arm and calf BE from days 1 to 5.

Age Factors↗
PubMed1991

Cardiovascular responses to tilting in healthy newborn babies.

It has been suggested that newborn infants have immature baroreceptor responses and they are unable to maintain their blood pressure (BP) by appropriate reflex peripheral vasoactivity and heart rate (HR) changes in response to tilting. We have measured simultaneously upper arm and calf systolic and diastolic BP and HR every 30 s using an oscillometric method (Dinamap 847) in quiet and active sleep in 9 term babies. Measurements were performed continuously with 5-min periods in each of three positions; horizontal, 30 degrees head up and 30 degrees head down tilt. The results were analysed using unbalanced analyses of variance and multivariate regression. All responses were proportional to the angle of the tilt. The observed values were very close to those predicted from the model. HR increased and decreased by 3.25 beats/min (bpm) on 30 degrees up and down tilting respectively and by twice this amount when tilting through 60 degrees. Arm systolic and diastolic BP both decreased by 1.3 mmHg when tilting through 60 degrees from down to up and increased correspondingly with down-tilting. Calf systolic BP changed appropriately for the change in hydrostatic pressure (+7.37 mmHg with 30 degrees up tilting), but diastolic BP rose only by 60% of this value. The results showed no individual variation, were independent of day, sleep state, the number of tilts, the starting value of the BP and the direction of the previous tilt. This study shows that the healthy newborn has a well developed baroreceptor reflex.

Blood Pressure↗
PubMed1991

Sequential or fixed sample trial design? A case study by stochastic simulation.

The properties of Wilcoxon's rank sum test for fixed sample size and a Wilcoxon-type two-sample sequential test have been illustrated and compared by means of stochastic simulation. Data from a real fixed sample trial have been used, both for resampling from the original data, and for construction of an idealized theoretical distribution. The sequential and the fixed sample test obtain equal power, but the sequential test mostly includes considerably fewer patients to reach a conclusion, i.e. the mean and median number of patients included are both much lower than the fixed sample size. Under the hypotheses only a small fraction of the simulation runs exceed the fixed sample size. These findings exemplify results obtained in theoretical analyses and simulation studies covering a wide range of distributions. In our opinion sequential tests have obvious advantages and are in many cases better alternatives than fixed sample tests in clinical trials.

Clinical Trials as Topic↗
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↗
PubMed1979

Firing behaviour in a stochastic nerve membrane model based upon the Hodgkin-Huxley equations.

A nerve membrane model with a two-state pore system was investigated by computer simulation in the uniform (space-clamped) case. Both sodium and potassium conducting pores were modelled, each pore having four independent gates which switched randomly between the open and the closed position, governed by the assumed rate constants. Each pore conducted only when all the gates were open. The model was based upon the Hodgkin-Huxley equations for the giant axon in squid, and in the limit of an infinite number of pores it was identical to these. The firing behaviour of this model as a function of the number of pores and the injected current were investigated. The mean firing frequency and the distribution of interspike intervals were mainly used in the presentation of the results. It was found that for pore numbers less than about 20 000 the main effects due to a finite number of pores were a lowering of the current threshold for firing and a more linear frequency current relationship relative to that of the original H-H equations. For higher pore numbers an increase in the current threshold and a pronounced burst firing close to the threshold were found.

Animals↗
PubMedDate not supplied

Menarcheal age in Oslo during the last 140 years.

Data from maternity clinics have been used to study the trend in menarcheal age among girls born in Oslo after 1840. The investigation was based on recordings from approximately 50 women from each year. The women were divided into social categories according to their own or their husband's occupation. The results show a trend toward earlier maturation within the working class, which is characterized by two periods of rapid fall in menarcheal age. The first period covers women born between 1860 and 1880, and shows a fall in menarcheal age from about 15.6 to about 14.6 years. During the second period of rapid fall, which covers women born between 1905 and 1940, the menarcheal age was further reduced from about 14.6 to 13.3 years. The age at menarche has been stable at about 13.3 years for women born after 1940. These results contrast with those of some earlier studies of the menarcheal age in Norway. However, it is shown that the discrepancies between these investigations and our own disappear when the same computational methods and the same interpretation of the age recordings are used.

Adolescent↗