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F A Brouwer

Publications and source records attributed to F A Brouwer.

11 recordsLinked to original sources
PubMed1995

Thoracic electrical bioimpedance: suitable for monitoring stroke volume during pregnancy?

To obtain normal values for maternal stroke volume and cardiac output during pregnancy, a non-invasive, accurate and reproducible method is required. The thoracic electrical bioimpedance (TEB) method may be suitable. However, this method is as yet only qualified for short-term trend recordings, since it assumes that body dimensions such as height, weight and thoracic circumference remain constant during the study. This may not be the case in long-term studies, especially during pregnancy. In this paper it is argued that changes in stroke volume (SV) during pregnancy are reflected most strongly when using the formula: SV = P VET (dZ/dt)max/Z0, where P is a personal factor to be determined at the beginning of pregnancy; VET the ventricular ejection time; (dZ/dt)max the maximum of the first derivative of the thoracic impedance during the cardiac cycle and Z0 the time average of this impedance during the cardiac cycle. Indexed parameters should not be used as this reduces sensitivity. Commercial equipment, based upon other algorithms, can be used by feeding the right parameters for each series of measurements. This enables calculation, trends in stroke volume and cardiac output for longitudinal studies for instance during pregnancy.

Algorithms↗
PubMed1993

Comparison of effects of dopamine hydrochloride and dopexamine hydrochloride on abdominal and femoral hemodynamics in anesthetized dogs.

The effects of dopamine and dopexamine administered in graded intravenous bolus injections (0.1-51.2 micrograms.kg-1) were compared in the renal and femoral, and in a number of splanchnic vessels at the organ level simultaneously in anesthetized dogs. Hemodynamic data are presented for each artery as conductance, which was obtained by dividing mean flow by mean arterial pressure. The data were analyzed in two different ways: 1) by responses at intervals of 3 sec to 12.8 micrograms dopamine or dopexamine during 1 min, and 2) by dose-response curves. Additionally, urine volume was measured during dopamine and dopexamine administration. During a period of 1 min after an injection of dopamine, early and late effects could be distinguished, while heart rate was unaltered. In the superior mesenteric, inferior mesenteric, splenic, common hepatic, renal, and femoral arteries, an early (at 18-21 sec) reduction in conductance was seen. The early reduction was often followed by an increase above the preinjection level. After dopexamine, the early reduction in conductance was not seen, except in the left gastric artery. In contrast to the effect of dopamine, dopexamine induced a more pronounced increase during the late phase. Contrary to dopamine, dopexamine increased the conductance in the common hepatic artery bed. It remains questionable whether dopaminergic receptors are present in this vascular bed. Dopamine raised blood pressure and urine production dose-dependently. Dopexamine decreased aortic pressure. Low dosages of dopexamine increased urine production, without raising renal blood flow. An advantage of dopexamine over dopamine could be that dopexamine does not stimulate alpha-adrenergic receptors.

Blood Flow Velocity↗
PubMed1980

Hemodynamic actions of pentagastrin.

Pentagastrin (Peptavlon, ICI 50123) is known as a powerful stimulator of gastric acid secretion. Several authors have demonstrated a close relationship between gastric acid secretion and gastric blood flow. In this study the general hemodynamic properties of pentagastrin were investigated qualitatively and quantitatively. The study was performed on anesthetized mongrel dogs. Blood flow was assessed with non-cannulating electromagnetic flow probes. Pentagastrin was injected intravenously at intervals of 2 min in amounts between 1 ng and 8192 ng/kg, following a logarithmic scale. Pentagastrin dose-dependently increased splanchnic blood flow in a reversed U-shaped manner. The major vasoactivity occurred in two organ areas--the gastric area and the pancreatico-duodenal area. Pentagastrin increased blood flow in these areas to 300% and 350% of initial value, respectively, at a dose of 2-4 microgram/kg. Since heart rate, cardiac output, and arterial pressure were not influenced, pentagastrin had no general hemodynamic effect. This was confirmed by blood flow measurements in the renal a., common carotid a., and femoral a. It was therefore concluded that the splanchnic blood flow increase was due to an extreme decrease of splanchnic vascular resistance.

Animals↗
PubMed1979

Time course and sensitivity of secretin-stimulated pancreatic secretion and blood flow in the anesthetized dog.

Time-effect relationship and sensitivity of pancreatic exocrine secretion and pancreatic blood flow were established, to test the supposition that blood flow to the pancreas is controlled by the secretory process. Pancreatic exocrine secretion rate was stimulated by incremental iv doses of secretin (Karolinska, 0.001--4 U/kg) in pentobarbital anesthetized dogs. Arterial pancreatic blood flow was measured by electromagnetic flowmeters; secretion rate was determined by measurement of frequency of consecutive secretory drops. Exocrine secretion rate and blood flow increased markedly. Secretion responded at a dose level 3-7 times lower than blood flow did. So at low secretory performance, the pancreas seemed to be well provided with basal blood supply. At moderate and high secretory levels blood flow did increase, but the flow increase was seen 16-22 sec before the secretion increase. So the additional support of blood flow in the secretory process occurred during the cellular preparation and during the start of the secretion increase. This suggests that secretion increase and blood flow increase are mediated by independent processes or receptors, but these processes seem to cooperate in processing the pancreatic juice.

Animals↗
PubMed1979

The effect of secretin on peripheral arterial blood flow.

Arterial blood flow was measured in 18 arteries leading to nearly all major organs in the anesthetized dog, to obtain information about the specificity of the blood flow effects caused by secretin. This gastro-intestinal hormone was administered intravenously in a sequence of bolus injections (0.001--4 U/kg). Blood flow increase in the pancreatico-duodenal arteries was highest of all arteries observed. This flow increase in the superior pancreatico-duodenal artery was also found in its truncal artery (gastroduodenal a.), but to a less extend: the effect was diluted by the other--less reacting--branch (right gastro-epiploic a.) of the same truncal artery. We conclude that secretin preferentially increased blood flow in the pancreatico-duodenal arteries. Since secretin effects on heart rate and arterial pressure were but small, the flow increase in the pancreatico-duodenal area were caused by a lowering of the resistance of the pancreatico-duodenal vasculature. Comparison between the flow responses, elicited by secretin (Boots) and secretin (Karolinska), is discussed.

Animals↗
PubMed1978

Motor effects of graded doses of pentagastrin on the gut of the anesthetized dog.

Gastrointestinal motor activity of the anesthetized dog was assessed by strain gage force transducers on longitudinal and transverse muscle of the gastric body and antrum, duodenum, jejunum, ileum, and colon. Dose-dependent effects of pentagastrin (1-8192 ng/kg, i.v.) were only seen on the stomach: increases in gastric body tone, antral contractile force and contractile frequency of the gastric phasic activity. Body tone and antral force were more sensitive to pentagastrin than was contractile frequency. Supra-maximal doses and repetition of the dose-response protocol gave smaller increments for body tone and antral force, while the increase in contractile frequency remained unaffected. The different responses to pentagastrin of force and frequency indicate that pentagastrin acts on 2 different receptor-effector systems.

Animals↗
PubMed1976

Norepinephrine and isoprenaline induced changes of peripheral blood flow acceleration caused by changes of cardiac inotropy.

In anesthetized dogs the norepinephrine (NE) and isoprenaline (ISO) (1--1024 ng/kg i.v.)--induced increase of maximum peripheral flow acceleration (celiac artery, cranial mesenteric artery, renal artery; and femoral artery) and the changes of the maximum first derivative of arterial pressure were compared with the increases of maximum ascending aortic flow acceleration and maximum first derivative of left ventricle pressure (LV dP/dt max). The maximum effect of each dose on maximum acceleration of flows (dF/dt max) and maximum first derivative of pressures (dP/dt max) occurred simultaneously for all v56--512 ng/kg) and for ISO (D50:128--256) ng/kg). We demonstrated that other varure) played only a minor role in the increases of LV dP/dt max in our studies. In contrast with the uniform response of dF/dt max and dP/dt max, the reaction of peripheral vascular resistance varied. In particular in the gastrointestinal tract the resistance could either be increased (NE, D50:115 ng/kg) or decreases (ISO, D50:15 ng/kg). Gastrointestinal resistance was a more sensitive variable for catecholamine stimulation than dF/dt max and dP/dt max. The data show that under the present experimental conditions induced by NE and ISO is due to increase of cardiac inotropy.

Animals↗