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Biomedical subjects

M Eriksen

Publications and source records attributed to M Eriksen.

At least 19 recordsLinked to original sources
PubMed1997

Effect of ultrasound contrast medium in color Doppler and power Doppler visualization of blood flow in canine kidneys.

PURPOSE: To examine the effect of an ultrasound contrast medium (UCM) in the visualization of parenchymal blood flow by means of color Doppler and power Doppler sonography. MATERIAL AND METHODS: Nonenhanced and UCM-enhanced Doppler images of canine kidneys were obtained in a transversal plane during various states of flow reduction in the anterior branch of the renal artery. The UCM consisted of air-filled shell-stabilized microballoons (half-life approximately 2 min). The images were evaluated blindly by 4 observers who rated the amount of flow signal in the cortex and medulla, and categorized the flow state (normal, reduced or no flow) in the anterior part of the kidney. RESULTS: The UCM increased the area of Doppler signals in the cortex and outer medulla during normal or reduced blood flow. The border between nonperfused and normally perfused parenchyma was more distinct with the UCM. The categorization of the regional flow state was more correct with the UCM. Improvement with the UCM was greatest when the nonenhanced Doppler images had suboptimal intensity, but positive effects with the UCM were also seen in recordings with adequate precontrast intensity. Color blooming artifacts sometimes occurred on the side of the kidney facing away from the transducer. CONCLUSION: The UCM improved the color Doppler and power Doppler visualization of the parenchymal blood flow in the canine kidney, and allowed a more correct categorization to be made of the regional blood flow state.

Air↗
PubMed1996

Short-term control of cardiovascular function: estimation of control parameters in healthy humans.

In a previous study, we recorded short-term cardiovascular responses after a steep increase in arterial pressure in healthy humans [Am. J. Physiol. 266 (Heart Circ. Physiol. 35): H199-H211, 1994]. The aim of the present study was to develop a mathematical model of the baroreflex control of arterial pressure, to use this model with the previously recorded data to estimate unknown parameters in the reflex control loop, and then to analyze the overall open- and closed-loop performance of the system by model simulations with use of individual sets of optimal parameters. The mathematical model consists of a heart, a linear elastic arterial reservoir, and two parallel resistive vascular beds. The arterial baroreflex loop is modeled by two separate time domain processing objects, each with its own gain, time constant, and delay, to simulate the action of a sympathetic signal to the peripheral vascular bed and a parasympathetic signal to the heart. In repeated model simulations, the control parameters in the model were systematically adjusted by an automated algorithm that minimized the deviations between the time courses of the cardiovascular variables simulated by the model and the previously recorded responses in each individual. In all 10 subjects, the short-term cardiovascular responses were adequately simulated by using individual sets of parameters in the model. Open-loop transfer functions for arterial pressure control were obtained by using the individual sets of optimal model parameters in new simulation runs. Open-loop gain for arterial pressure control at nearly zero frequency (steady state) was between 0.9 and 4. Model simulations also indicated an underdampened response at 0.05-0.07 Hz in the closed-loop situation in four subjects, corresponding to peaks in the mean arterial pressor power spectra obtained from separate recordings of spontaneous variations in the resting situation.

Baroreflex↗
PubMed1995

A causal relationship between fluctuations in thermoregulatory skin perfusion and respiratory movements in man.

The relationship between regular respiration with normal tidal volume and spontaneous fluctuations in blood flow through skin arteriovenous anastomoses (AVAs) was investigated. Laser Doppler measurements from skin areas known to contain arteriovenous anastomoses, ultrasound Doppler measurements from the radial artery and respiratory movements were recorded simultaneously in 7 supine human subjects in a thermoneutral environment. The phase relationship between respiration and the onset of sudden arteriovenous anastomoses vasoconstrictions was calculated in each subject. A few seconds before a vasoconstriction, there was a clear tendency towards synchrony in the respiration recordings, indicating that some respiration-phase-dependent event precedes the vasoconstrictions. Since arteriovenous anastomoses constrictions are accompanied by specific changes in heart rate and blood pressure, our findings link respiration to low-frequency heart rate and blood-pressure variability in humans.

Adult↗
PubMed1995

The status of local smoking regulations in North Carolina following a state preemption bill.

OBJECTIVE: To determine the number and protectiveness of local smoking regulations adopted before the implementation of a preemptive statewide smoking control bill. METHOD: Review of local smoking control regulations from all 100 counties and 85 municipalities with populations greater than 5000 in North Carolina. MAIN OUTCOME MEASURES: Adoption of local smoking control regulations before and during the 3-month delay in enactment of the preemptive bill. Protectiveness of regulations was based on restrictions on smoking and requirements for separate ventilation systems at private work sites: none (smoking unrestricted); minimal (smoking restricted to designated areas); partial (smoking restricted to designated areas served by separate ventilation systems); and complete (smoking prohibited). Because some regulations would be phased in gradually over the next 5 years, we evaluated the requirements that will be in effect by January 1, 2000. RESULTS: Between July 15 and October 15, 1993, the number of local smoking regulations in North Carolina increased from 16 to 105. By the year 2000, 59% of private employees still will not be guaranteed any protection from work site environmental tobacco smoke; 19% will have minimal protection, 22% will have partial protection, and none will have complete protection. CONCLUSIONS: The 3-month delay in preemption created an unnatural time frame for communities to organize, debate, and adopt smoking restrictions. Despite the adoption of 89 new regulations, no private employees will be guaranteed complete protection from work site environmental tobacco smoke by the year 2000; new regulations can no longer be adopted. HB 957 has been a setback for public health in North Carolina.

Humans↗
PubMed1995

Spontaneous flow waves detected by laser Doppler in human skin.

The contribution of spontaneous variations in sympathetic nervous activity and perfusion pressure to the laser Doppler flux signal in human skin was studied in nine healthy subjects. Simultaneous recordings were made of laser Doppler flux, mean blood pressure, and blood flow in the radial artery. In the skin of the palm and sole, there was a significant and strong correlation between fluctuations in flux and radial artery velocity, which indicated a high degree of neural control of microcirculatory blood flow. This correlation decreased progressively toward the trunk and face. In the skin of the nose and at scattered sites on the face, trunk, and extremities, there was correlation between flux and mean blood pressure that indicated a predominantly "passive" vascular bed. At other sites, multivariate regression analysis revealed contributions of both blood pressure and sympathetic activity. In skin on the ear and forehead, a characteristic pattern of regular oscillations in flux, uncorrelated with blood pressure and sympathetic activity, was demonstrated. The laser Doppler signal from different skin sites thus contains varying contributions from variations in perfusion pressure, sympathetic nervous activity, and local, myogenic arteriolar vasomotion.

Adult↗
PubMed1995

Effect of local warming on hand and finger artery blood velocities.

The effect of local heating on blood velocities in arteries supplying the skin of hand and fingers was studied in subjects kept in their thermoneutral zone. The temperature of one hand was steadily raised from 35 to 43 degrees C in 15 min, whereas the control hand was kept in the air or immersed in a water bath at 35 degrees C. Simultaneous blood velocity recordings from the two hands were made continuously using ultrasound Doppler. In the heated hand, a general rise in blood velocity level was seen. However, the spontaneous fluctuations in blood velocity assumed to be caused by synchronous vasomotor activity of the arteriovenous anastomoses (AVAs) remained unchanged and closely correlated with those in the control hand throughout the experiment. Thus the central nervous control of AVA vasomotion seems to be unaffected by local heating. The elevation of blood velocity in the heated hand is probably due to dilatation of other parts of the vascular bed, e.g., ordinary arterioles in the skin. Earlier investigators, using venous occlusion plethysmography, have reported vasoconstriction in the locally heated human finger. No sign of such heat-induced vasoconstriction was found in this study.

Adult↗
PubMed1995

Acute effects of indometacin on cerebral blood flow in man.

Blood velocity changes in the internal carotid artery were estimated using Doppler ultrasound before, during and after injection of indometacin or placebo in 7 healthy adults. Upon injection of the active substance there was a rapid reduction in blood velocities in the internal carotid artery, increasing with increasing doses of indometacin. A fall in end-expiratory PCO2 was also observed, indicating a state of hyperventilation. The observed relative reduction in cerebral blood flow was much higher in all subjects than the expected reduction due to the accompanying drop in PCO2. Experiments in which arterial PCO2 was kept constant showed that indometacin also causes a reduction in blood velocity independent of changes in PCO2. We suggest that indometacin has both a direct effect on the cerebral microcirculation, and an additional effect mediated through induction of hyperventilation. The drug probably affects the respiratory center through an increase in intracerebral PCO2 due to reduced perfusion.

Adult↗
PubMed1994

Connection between skin arteriovenous shunt flow fluctuations and heart rate variability in infants.

Large, spontaneous fluctuations in blood flow to acral skin, caused by synchronous opening and closing of arteriovenous anastomoses (AVAs), have been demonstrated in adults in a thermoneutral environment. Individual AVA constrictions were accompanied by a diphasic heart rate (HR) response, indicating the presence of an autonomic rhythm which affected both skin AVA activity and heart rate variability. In the present study, 24 neonates were examined on day 2 (range 1-3 days) and re-examined at 14 weeks (11-17 weeks). The presence of rhythmic, synchronous fluctuations in laser Doppler flux in the palm of the hand and sole of the foot in 20 of 24 neonates strongly indicated the presence of functional skin AVA at birth. Both neonates and 3-month-old infants showed a diphasic HR response in association with cutaneous AVA constrictions. The infant response differed from the adult response mainly by the longer duration of the secondary bradycardia. This may reflect different properties of the baroreceptor reflex in infants and adults.

Arteriovenous Anastomosis↗
PubMed1994

Results of the Dutch community project "Healthy Bergeyk".

BACKGROUND: This article reports on the results of a community health project that was implemented in the Dutch municipality of Bergeyk. The major goal was to reduce four cancer-related risk behaviors: smoking, high fat consumption, excessive alcohol use, and exposure to artificial sunlight. A control community received no new intervention. Intervention methods included mass media messages, self-help materials, small group activities, lectures, and structural activities. Community organization principles such as a social network approach, community participation, and intersectoral cooperation were applied in the project. METHODS: Data were collected from both communities among cohort research samples on three occasions using telephone interviews. RESULTS: The results indicate a significant reduction in fat intake in the experimental community. No other significant behavioral effects were found. Further analysis among respondents in the experimental condition showed that those personally exposed to the project as indicated by familiarity with and discussion about the project, had a greater decrease in fat consumption between baseline survey and second post-test than those who were not. Also, the percentage of smokers who quit between baseline survey and second post-test was greater among those who knew about the project than among those who did not. Finally, discriminant analysis was used to further examine the determinants of project exposure. Community involvement, marital status, education, and sex were related to project exposure. CONCLUSIONS: It is concluded that with the time limitations of the project in mind, the findings are encouraging.

Adult↗
PubMed1994

Thermoregulatory fluctuations in heart rate and blood pressure in humans: effect of cooling and parasympathetic blockade.

The spontaneous fluctuations in acral skin blood flow, mean blood pressure (MAP), and heart rate (HR) were studied in 9 healthy supine volunteers in a thermoneutral and in a cool environment, and after parasympathetic blockade by atropine. In skin areas with a high density of arteriovenous anastomoses (AVAs), there were large, spontaneous fluctuations in blood flow in a thermoneutral environment. The fluctuations were nearly abolished in a cool environment, while they seemed unaffected by atropine administration. Power spectral analysis demonstrated a reduction in HR and MAP variability in the low- and mid-frequency (LF) (< 0.15 Hz) band after cooling, and a prominent reduction in HR variability in both the LF and the high-frequency (HF) (< 0.15 Hz) band after atropine administration. A sudden drop in skin vascular conductance was accompanied by diphasic HR changes and an increase in MAP. After atropine administration, the initial HR acceleration was delayed and reduced in magnitude. The secondary HR deceleration, which probably represents baroreceptor modulation, was abolished. Atropine administration caused a delayed, but augmented increase in MAP, which was probably related to the loss of baroreceptor control of HR. The presence of an autonomic rhythm, consisting of sympathetic vasoconstrictor impulses to skin AVAs, connected with reciprocal sympathetic and vagal impulses to the heart, is indicated. The HR changes were mainly determined by vagal activity. The rhythmic changes in skin blood flow, HR and MAP were suppressed in a cool environment.

Adult↗
PubMed1994

Priority of blood flow to splanchnic organs in humans during pre- and post-meal exercise.

Cardiac output and superior mesenteric arterial flow in five healthy young men were followed using Doppler ultrasound techniques at rest and during 4 min bouts of bicycle exercise in both a pre- and a post-meal situation. The meal given was mixed and heavy, with an energy content (related to body size) of about 1400-1600 kcal (5.9-6.9 MJ). Two levels of exercise, 50-65 W and 150-200 W (about 75% of VO2max), were tested, with the subjects cycling in a reclining position. Superior mesenteric arterial flow increased threefold, to about 1.1 l min-1, after the meal. During exercise in the fasting situation there were only modest changes in splanchnic vascular conductance, and moderate increases in superior mesenteric arterial flow were actually recorded. Exercise in the post-prandial state caused appreciable reductions in splanchnic vascular conductance, and a 38% reduction was observed during the most heavy exercise. However, not even such a decrease in conductance resulted in any definite reduction in superior mesenteric arterial blood flow, which was maintained at the pre-exercise level. Cardiac output increased by about 1.3 l min-1 after the meal. The exercise-induced increases in cardiac output were of the same order in the fasting and in the post-prandial state. Variance analyses showed the high cardiac output levels reached during post-prandial exercise to be no different from levels that would be reached by pure summation of the changes caused by eating alone and by exercise alone. It is concluded that blood flow to the splanchnic organs in reclining man retains its high pre- and post-prandial priority during short exercise bouts of up to 75% of VO2max.

Adult↗
PubMed1994

Short-term cardiovascular responses to a step decrease in peripheral conductance in humans.

A step decrease in total peripheral conductance (TPC) was introduced in 10 healthy volunteers by rapid inflation to suprasystolic pressure of bilateral thigh cuffs. This provoked a sudden statistically significant increase in mean arterial blood pressure (MAP) of 5 mmHg during supine rest and of 8 mmHg during moderate supine exercise by the quadriceps muscles. Central venous pressure was not changed by cuff inflation. The increase in MAP was blunted by a rapid but transient decrease in both heart rate (HR) and cardiac stroke volume. At rest, a gradual increase in TPC, starting after 4 s, nearly fully restored MAP to its original value at 10 s. During exercise, MAP was halfway corrected at 10 s but then started to increase again, probably as a result of an ischaemic muscle pressor response. After cholinergic blockade by atropine, the immediate HR response was eliminated, but HR decreased gradually after a delay of 3 s. The time development of the slow increase in TPC was not changed by atropine. In conclusion, the regulatory correction of a sudden increase in arterial pressure in supine unanesthetized healthy humans is achieved through an immediate transient parasympathetic bradycardia during the first few seconds and a more gradual sympathetic peripheral vasodilation after 4 s. After cholinergic blockade, a slow presumably sympathetic HR response was observed.

Adult↗
PubMed1994

Peripheral vasoconstriction shortly after onset of moderate exercise in humans.

The immediate cardiovascular responses at the onset of supine dynamic leg exercise were studied by noninvasive methods in healthy humans. Total peripheral conductance (TPC), heart rate, and cardiac output increased very rapidly at the onset of exercise. Mean arterial pressure (MAP) showed a moderate anticipatory increase during a 10-s countdown to exercise and then decreased (but not below resting level) during the first 10 s of exercise. The TPC response was biphasic, and TPC started to fall from its peak value approximately 12 s after onset of exercise. This peripheral vasoconstriction increased MAP. After 25 s, the cardiovascular variables were stable for the rest of the 2-min exercise period. In the same subjects, cholinergic blockade was induced by atropine sulfate (0.035 mg/kg) and resting cardiac output, MAP, and TPC increased considerably. The exercise protocol was repeated after atropine, and the increase in heart rate at onset of exercise was slower and smaller. MAP decreased and remained depressed throughout the exercise period. A monophasic increase in TPC was seen. We suggest that, in the normal situation, the biphasic response in TPC reflects a baroreflex sympathetic vasoconstriction very shortly after onset of exercise and that this response is due to a rapid increase in set point for arterial pressure control at the onset of exercise. After cholinergic blockade, MAP was probably continuously well above the set point for arterial pressure control both before and during exercise and no reflex vasoconstriction was observed in this situation.

Adult↗
PubMed1993

Fluctuations in blood flow to acral skin in humans: connection with heart rate and blood pressure variability.

1. Spontaneous fluctuations in blood flow in arteries supplying acral skin were investigated with Doppler ultrasound in human subjects. Finger blood pressure, heart rate (HR) and cardiac output were measured simultaneously and noninvasively. 2. Synchronous fluctuations in flow were found in arteries supplying the hands and feet. The fluctuations were larger and more rapid than the flow variations which have been demonstrated with other methods. The magnitude of the total flow fluctuations in the hands and feet was estimated to be 5-10% of cardiac output in resting subjects. This range of flow fluctuations is made possible by spontaneous opening and closing of skin arteriovenous anastomoses (AVAs). 3. The fluctuations in skin blood flow were accompanied by inverse fluctuations in mean blood pressure (MAP). The power spectra of skin vascular conductance and MAP both contained maximum intensity at low frequencies, below 0.15 Hz, with high coherence. 4. The central circulatory events connected with the skin blood flow fluctuations were calculated from the experimental data with the use of transfer function analysis. There was a rise in HR, cardiac output and MAP starting 1-4 s before a cutaneous vasoconstriction. This indicates that the HR and MAP responses are not only passive effects of changes in peripheral resistance, but are the result of a simultaneous activation of the peripheral vascular and cardiac efferent branches of the autonomic nervous system. The HR and MAP responses are then modified, probably by baroreceptor activation.

Adult↗
PubMed1993

Respiration-synchronous fluctuations in stroke volume, heart rate and arterial pressure in humans.

1. Simultaneous recordings of beat-to-beat left cardiac stroke volume (SV, pulsed ultrasound Doppler), mean arterial pressure (MAP) and heart rate (HR) were obtained in ten healthy young adults during spontaneous respiration at supine rest, before and after cholinergic blockade by atropine (0.035 mg kg-1). 2. Respiration-synchronous fluctuations in SV, HR, cardiac output (CO) and MAP were quantified by spectral analysis of the recordings of each of these variables. 3. Before atropine administration, respiration-synchronous fluctuations in HR and SV were prominent. The changes in HR and SV were inversely related and variation in SV was the main source of respiratory variability in CO. Respiration-synchronous fluctuations in MAP were mainly caused by variations in CO. 4. After cholinergic blockade, respiratory HR variations were eliminated, whereas the respiratory fluctuations in SV persisted. The fluctuations in CO and MAP increased. In this situation, mechanically induced variations in SV were not counteracted by inverse HR fluctuations and the influence on CO thus increased. 5. The main source of respiratory fluctuations in MAP in supine humans is thus variation in SV, while inverse, vagally mediated HR variations tend to reduce the fluctuations in CO and MAP.

Adult↗