Mechanisms behind the postprandial increase in cardiac output: a clue obtained from transplanted hearts.

Consumption of a meal is followed by an increase in cardiac output (CO) which appears to be closely related to the concomitant increase in blood flow to the gastrointestinal organs. To gain information on the mechanism behind this increase in CO we have previously used Doppler ultrasound technique to record circulatory responses to a standardized meal in five patients with recently transplanted and thus denervated hearts. We obtained the surprising result that they reacted to the consumption of a meal with a greater increase in CO than did five matched normal controls.

Regulation of arterial blood pressure in humans during isometric muscle contraction and lower body negative pressure.

Previous studies have shown that the blood pressure response to isometric handgrip remains unchanged during reductions in preload induced by lower body negative pressure (LBNP). The purpose of the present study was to assess the beat-by-beat haemodynamic mechanisms allowing for precise control of mean arterial pressure (MAP). We have followed the cardiovascular variables involved in the regulation of MAP during isometric handgrip with and without additional application of LBNP during defined periods of the ongoing contraction.

Circulatory responses to a meal in patients with a newly transplanted heart.

It is well established that consumption of a meal releases a gradually developing and quite marked increase in blood flow to the gastrointestinal organs and a similar and simultaneous increase in cardiac output (CO). It is not known through which mechanism the pumping of the heart adjusts so accurately to the gastrointestinal flow increase. We have approached this problem by serving a standardized, mixed meal to five patients with recently transplanted and thus denervated hearts and to five sex- and age-matched controls.

[Distribution of left ventricular output].

Background: This survey focuses on distribution of cardiac output to various organs and on some dynamic changes occurring in cardiac output and its distribution.

Materials And Methods: Data presented are largely related to work carried out in our research group, where Doppler ultrasonography is widely used for measurement of cardiac output and arterial blood flow. Additional data are drawn from relevant literature, in part compiled through search in the PubMed database.

Involvement of the human splanchnic circulation in pressor response induced by handgrip contraction.

We have analysed the adjustment of blood flow and vascular conductance in the abundantly supplied splanchnic circulation to a generally released pressor reaction. Pressor responses were induced by 2-min periods of standardized, sustained handgrip in seven healthy students. The effects of handgrip tests were followed both in the fasting state and after the consumption of a substantial, mixed meal.

[Digestive system's large and changing needs of blood supply].

Doppler utrasonography has made it possible to record blood flow to the digestive tract (the superior mesenteric artery) directly and continuously in unanaesthetized, healthy humans. Several research groups have demonstrated how blood flow to the tract increases gradually and markedly after a meal, and more so after a big meal than after a small one. The increase in blood flow reaches its maximum after 20-40 minutes and lasts for 1.

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.

Post-prandial cardiovascular responses in man after ingestion of carbohydrate, protein or fat.

Changes in cardiac output and in superior mesenteric arterial flow were followed with Doppler ultrasound techniques in five young, healthy persons for 2 h after ingestion of medium-sized (4 MJ), fluid meals containing either carbohydrate, protein, fat or water only. Measurements were carried out before meals and at regular post-meal intervals, during which mean arterial blood pressure was also followed. All energy-containing meals caused marked and gradually developing post-prandial increases in cardiac output as well as in superior mesenteric arterial flow.

The effect of meal size on postprandial increase in cardiac output.

Heart rate, stroke volume, cardiac output and mean arterial blood pressure were followed from the resting pre-meal situation and for 2 hours after intake of standardized meals in four healthy individuals. Continuous records of stroke volume and cardiac output were achieved with an improved method of Doppler ultrasonography. A smallish meal and one 2 1/2 times larger were both given twice and in random order to each of the four test persons.

The effect of a meal on cardiac output in man at rest and during moderate exercise.

Cardiac output at rest increased by 11-63% in a group of healthy individuals after the consumption of a medium-sized, mixed meal. The maximum post-prandial levels of cardiac output were reached from 10 to 30 min after termination of the meal. Cardiac output values at rest fluctuate around a mean level, and this fluctuation was considerably more marked after a meal, when changes in cardiac output from one 15-s period to another could be of the order of 1-1.

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.

On the existence of stretchable pores in the exchange vessels of the isolated rabbit lung preparation.

In the present work our aim has been to seek evidence for or against the existence of stretchable pores in the exchange vessels of the lungs. In isolated rabbit lungs ventilated by positive pressure and perfused with homologous blood we performed repeated tests with fluid filtration from the exchange vessels. In these tests the outflow pressure was elevated to specific values for periods of 6 min.

Rabbit lung plasma and erythrocyte volumes. Lung hematocrit in relation to total body hematocrit.

The total body hematocrit has been reported to be 85--90% of packed cell volume (PCV) in several species. We have found similar values in rabbits. An "extra" plasma volume must exist somewhere in the vascular bed to explain this observation.

Aggregation fo blood platelets and increased hydraulic conductivity of pulmonary exchange vessels.

Pulmonary microembolization secondary to platelet aggregation has been suggested to be a pathogenetic component of the shock lung syndrome. In vitro experiments have also shown that platelets can release factors with a permeability-enhancing activity. We studied the effect of collagen-induced platelet aggregation on the hydraulic conductivity of thexchange vessels in isolated, blood-perfused rabbit lungs.

Interstitial fluid and transcapillary fluid balance in the lung.

Alterations in extravascular lung water content when capillary pressure or plasma colloid osmotic pressure is increased have been evaluated in isolated, continuously weighed, plasma-perfused pairs of rabbit lungs. After modest increases in left atrial pressure, most preparations rapidly reached a new stable weight, and thus a new transcapillary fluid balance, but no significant increase in extravascular lung water content could be detected. In preparations where there was still a steady, slow gain in weight and thus still some transvascular filtration of fluid 15 min after the increase in pressure, a moderate but significant increase in extravascular water could be detected.

Pulmonary vasomotor nerve responses in isolated perfused lungs of Macaca mulatta and Papio species.

1. Lung lobes of Macaca mulatta and Papio species were isolated from the body and perfused by a pump delivering a constant volume inflow. The left atrial pressure was kept constant and therefore any recorded change in pulmonary arterial pressure reflected a change in pulmonary vascular resistance.

Interrelations between pulmonary liquid volumes and lung compliance.

We have investigated the relative effects of lung edema and of increases in pulmonary blood volume (PBV) on lung compliance (CL), and also the effects of selective elevations of pulmonary arterial (Ppa) and left atrial (Pla) pressures on PBV and on CL, using an isolated, perfused, and ventilated rabbit lung preparation. Lung weight was continuously recorded. A step rise in Pla at constant flow caused a rapid rise in PBV accompanied by an immediate fall in CL.