Lymph Propulsion Research Articles

Pathways of lymph flow from the intestine of the horse

The intestine of horses differs from that of most other domestic animals in having a huge ascending colon and cecum, which together act as a large fermentation vat. The lymph drainage from this intestine occurs through a complex network of lymph vessels and lymph nodes, of which there are several thousand. The pathways taken by lymph through these vessels and nodes were studied by tracing injections of dye, by examining Microfil casts, and with light and transmission electron microscopy. Lymph vessels transporting lymph from the intestinal wall generally terminate on a single node within a group of primary nodes. Efferent lymphatics form networks in the immediate vicinity of groups of nodes. In these networks, the vessels branch, anastomose, entwine amongst one another, and sometimes form recirculating loops. Usually 2-9 lymphatic vessels course away from these networks to secondary or higher-order nodes in both local and more central locations. Vessels reaching these nodes generally terminate on more than one node within each group. This pattern of lymph distribution is repeated as lymph passes through a succession of five or more nodes before flowing into the cisterna chyli. The complexity of the lymph pathways, it is suggested, would promote the mixing of lymph from different parts of the intestine and from different nodes, thus collating, integrating, and potentiating the immunological responses of these nodes. The walls of lymphatic vessels are well endowed with smooth muscle cells and elastic fibres, suggesting that intrinsic contractility of these vessels is a major mechanism in the propulsion of lymph from the intestine of the horse.

Rat intestinal lymph osmolarity during glucose and oleic acid absorption.

The two major purposes of this study were to determine 1) how glucose and oleic acid absorption by the intestinal villi influenced the osmotic composition of lymph as it exited the villus base and 2) what if any changes in lymph osmolarity occurred as the lymph traversed through the bowel wall. The rat jejunum was used in all studies and lymph was collected from individual lymphatics at 0.5-1 nl/min during control states and luminal exposure to 35-550 mg% glucose solutions (isotonic in saline) and 5 and 20 mM oleic acidtaurocholate solutions. Lymph collected from the base of villi during vigorous motility had an osmolarity of 403 +/- 15 mosM at rest and was only increased 30-50 mosM more except during exposure to 550 mg% glucose, where osmolarity increased over 100 mosM. Under comparable conditions, the submucosal lymph osmolarity at rest was 302 +/- 3.5 mosM and increased to 330-350 mosM during exposure to all of the solutions tested. When intestinal motility was virtually stopped, the submucosal lymph osmolarity was isotonic for all solutions tested. These observations indicate that absorption of glucose and oleic acid increased the osmolarity of lymph, leaving the villus only 30-50 mosM unless a glucose concentration of 550 mg% was present. Furthermore, the increased flow of villus lymph during absorption raised the osmolarity of the submucosal lymph when bowel motility assisted the lymph propulsion. This movement of materials from the villus to the submucosa by venular blood and lymph flow provides an opportunity for the villus tissue to influence the composition of the submucosal interstitial environment.

Lymphatic pathways and role of valves in lymph propulsion from small intestine.

The pathways through which lymph is propelled from the mucosal, submucosal, and muscle layer lymphatics of the small intestine, the interconnections between these layers, and the location of lymphatic valves within these layers were studied. Injections of fluid into a single lacteal or submucosal lymphatic of rats, rabbits, dogs, and cats spread in all directions through the submucosal lymphatics and into laceteals but did not enter the lymphatics of the muscle layer. Injections into muscle layer lymphatics also spread in all directions but in no case entered the submucosal lymphatics. The submucosal and muscle layer lymphatics join within the bowel wall near the mesenteric border to form collecting lymphatics characterized by valves and spontaneous contractions. These data indicate that lymphatics of the mucosa and submucosa form a syncytium independent of the muscle layer lymphatics and that few if any valves exist within these lymphatic networks. Cycling lacteal pressures were measured when intestinal motility was present but not when motility was abolished, suggesting that intestinal motility might have a role in lymph propulsion.

Role of the Lymphatic Circulatory System in Shock

That the lymphatic vessel participates in the regulation of interstitial dynamics through its ability to contract and propel fluid and protein from the extravascular tissues back to the bloodstream has not been fully appreciated. The "lymph pump" appears to be regulated by local physiologic forces as well as neurogenic and humoral factors. We have assessed the effects of hemorrhage and endotoxin on the ability of the lymph vessel to propel fluid in sheep using a model system that permits the quantitation of lymphatic pumping in vivo without the complication of variable lymph inputs. A major blood loss was found to enhance lymphatic contractile activity and fluid pumping. Considering the large reservoir of fluid and protein in the interstitium and lymph, we speculate that stimulation of the "lymph pump" after hemorrhage might help to re-expand the vascular space. On the other hand, the intravenous administration of endotoxin inhibited lymphatic pumping, suggesting that impaired lymph propulsion in sepsis may contribute to edema by reducing the ability of the lymphatic vessel to remove extravasated protein from the tissues.

The role of external compression and movement in lymph propulsion in the sheep hind limb.

1. Pressure fluctuations and lymph flow were measured in metatarsal lymphatics in anaesthetized sheep. 2. Intermittent compression significantly increased lymph flow when this was applied over the hoof but did not increase flow significantly when applied over the metatarsal region. 3. In a second preparation a 15 cm length of metatarsal lymphatic was cannulated at both ends and measurements were made of the ability of the duct to pump saline from an inflow reservoir through an outflow at the same height. 4. In the absence of external forces fluid was propelled by the lymphatic's intrinsic contractions but when intermittent compression was applied over the metatarsal region flow increased almost fourfold. 5. When animals with the doubly cannulated duct were allowed to recover, the effect of normal limb movements on fluid propulsion was examined. Under these conditions flow only occurred in response to intrinsic lymphatic contractions and appeared to be unaffected by the animal moving round the cage. 6. These results suggest that the effects of external forces on lymph flow are more dependent on compression of tissues in the lymphatic drainage area than on compression of the main lymphatic ducts. External compression can increase fluid propulsion by these vessels but, since forces of adequate magnitude appear not to be encountered in normal hind-limb movements, lymph propulsion in this region must depend on intrinsic lymphatic pumping.

Distension pressure on subserosal and mesenteric lymph pressures of rat jejunum

Lymph pressure (Pl) in the subserosal lymphatics and mesenteric lymphatics was determined in the jejunum at various intraluminal distension pressures (DP). Pl in the subserosal lymphatics was approximately equal to DP, in the range of 3-100 mmHg, whether the intestine was in the basal state or during water absorption. At a DP of 0 mmHg, Pl was 1.5 +/- 0.1 mmHg. When DP was 3, 10, 20, 40, 70, or 100 mmHg, Pl was 2.9 +/- 0.2, 11 +/- 1, 23 +/- 1, 43 +/- 1, 71 +/- 2, or 102 +/- 2 mmHg, respectively. From these findings and other considerations it is inferred that Pl in the subserosal lymphatics could be similar to the tissue fluid pressure, which is apparently determined by DP due to compression of the intestinal wall. On the other hand, Pl in the mesenteric lymphatics was not affected by DP at all. When DP was in the range of 0-70 mmHg with free flow of lymph, mean Pl was 6-8 mmHg, and it was 23-28 mmHg during lymphatic obstruction. During pressure measurement, rhythmical contractions of these lymphatics occurred, which may be mainly responsible for the increase of Pl and propulsion of lymph as well.

Lymph pressure in rat intestinal lymph duct with lymphatic obstruction.

Lymph pressure (PL) in the main intestinal lymph duct with obstruction of lymph flow was determined. Under various conditions, the rate of lymph flow (JL) was essentially the same in either A rats (with communications between hepatic and intestinal lymphatics) or B rats (without such communications), but PL of A rats was significantly lower (P less than 0.01) than that of B rats. When the intestine was in the basal state, JL of A and B rats was 0.2-0.3 ml/h per rat, and PL was 1.5 +/- 0.2 and 3.3 +/- 0.2 mm/Hg, respectively. During fluid absorption, JL of A and B rats increased to 0.8-0.9 ml/h, and PL was 2.1 +/- 0.4 and 6.4 +/- 0.7 mmHg, respectively. During intravenous saline infusion, JL of A and B rats increased greatly to approximately 14 ml/h, and PL was 3.1 +/- 0.3 and 10.4 +/- 1.1 mmHg, respectively. The lower PL in A rats is apparently due to the possibility that during lymphatic obstruction most lymph could be drained off by the hepatic lymphatics. In A rats, luminal distension pressure had no effect on PL but in B rats PL decreased when distension pressure was 20 mmHg or higher. Furthermore, lymph pressure waves indicate the occurrence of rhythmical contractions of the lymph duct or its surrounding tissues, which may play a role in the propulsion of lymph.

High frequency ventilation and the accumulation of extravascular lung water.

INTRODUCTION Pulmonary edema, or increased lung water, adversely affects gas exchange and pulmonary compliance. Numerous safety factors exist to protect against pulmonary edema and alveolar flooding. The most important of these safety factors is thought to be the lymphatic system, which removes water and protein that filters out of the pulmonary capillaries into the interstitium of the lung [ 131. Controversy has existed with regard to how lymph is propelled through the lymphatic system and cleared from the lungs. Essentially, the question centers on whether extrinsic forces caused by movement of surrounding structures (such as muscles, arteries, heart, or lungs) propels the lymph or whether intrinsic forces (rhythmic contractions of smooth muscle in the lymph vessels) were involved. Hall et al. cannulated lymph vessels throughout the body and discovered that extrinsic forces were minor and superimposed on the major intrinsic pressure waves. This applied everywhere except in the central lymphatic system, where the pressures generated by lung expansion and contraction seemed to be the major force [4]. Respiratory movement has been felt by many to be of primary importance for pulmonary or central lymph flow [7, 11, 12, 151. However, Staub and others have felt that intrinsic forces are the most important [ 12, 141. A relatively recent ventilatory technique, high frequency ventilation (HFV), offers an opportunity to examine the importance of extrinsic respiratory tidal motion on the propulsion of lymph in the pulmonary system [2,3]. High frequency ventilation differs from conventional ventilation by using a much smaller tidal volume (often less than dead space) and higher frequencies. This technique involves minimal bulk flow of air and almost no chest wall motion. High frequency ventilation provides a way to maintain normal blood gases for extended periods of time, while maintaining a decreased or absent tidal movement. We asked the question, does marked reduction of tidal expansion and contraction of the lungs have an effect on the accumulation of EVLW in normal dogs over 48 hr?

Variegated effects of prostaglandins on spontaneous activity in bovine mesenteric lymphatics

The effects of PGs (PGA 2, PGB 2, PGE 2, PGF 2α, PGI 2, and 6-keto PGF 1α) were investigated quantitatively in insolated bovine mesenteric lymphatics for elucidating the possible significance of PGs in lymph propulsion. 10 −8 M PGF 2α, PGA 2, and PGB 2 produced recognizable increases of frequency and amplitude of spontaneous contractions. The positive chrono-and inotropic responses were enhanced with increasing concentration of the PGs from 10 −8 to 10 −6 M. Both PGE 2 and PGI 2 in a concentration range from 10 −8 to 10 −6 M caused dose-related reductions in the amplitude of spontaneous contractions. No decrease in contraction rhythm was observed by the administration of PGI 2 and PGE 2 at concentrations lower than 5 × 10 −7 M. All of the above-mentioned responses induced by PGF 2α, PGA 2, PGB 2, PGI 2, and PGE 2 were not inhibited by pretreatment with α- and β-adrenergic blocking agents, muscarinic antagonist, antihistamics, and serotonic antagonist. These findings suggest that PGF 2α, PGA 2, and PGB 2 in a low concentration may facilitate lymph flow of bovine mesenteric lymphatics in the living body, since the spontaneous contractions of lymphatic smooth muscle may drive lymph centripetally in the presence of direction valves. On the other hand, PGI 2 and PGE 2 may cause an inhibition of lymph transport.

Intrinsic propulsive activity of thoracic duct perfused in anesthetized dogs

We have investigated the regulation of the intrinsic smooth muscle propulsive activity of the thoracic duct in the anesthetized, ventilated dog. We cannulated both ends of the duct and, with the chest open and ventilation constant, perfused it with Krebs-Henselite buffer at constant inflow and outflow pressures. With inflow and outflow pressures equal (no net driving pressure) flow through the duct must be due to intrinsic smooth muscle contractions. When we increased transmural distending pressure of the thoracic duct, flow increased as distending pressure increased to 5 cm H 2O, then declined. Although there was no evidence of any basal neural stimulation of the duct, intravenous infusion of catecholamines increased flow. Their effects were blocked by phentolamine (α-blocker). 5-Hydroxytryptamine caused flow to increase, then decrease. The decrease appeared to be due to duct spasm, not inhibition. Constant intravenous infusions of histamine, prostaglandin E 1, and bradykinin either had no effect or inhibited flow. Intrinsic myogenic activity of the thoracic duct in the living animal may be a significant factor in lymph propulsion.

Mechanisms of decubitus ulcer formation--an hypothesis.

Understanding of the etiology of decubitus ulcer formation is fragmentary and the existing literature contains much experimental data that are inconsistent with the idea that pressure sore formation is due extensively to depriving a tissue region of blood. In fact, there is substantial data that illustrate that tissue can remain viable for very extended lengths of time, up to 13 hours, when subjected to externally applied pressures that collapse the blood microvasculature in a region. Based on these observations and on studies done in this laboratory on lymph propulsion and pressure sore prevention, an hypothesis has been formulated that is consistent with the published data and with clinical observations. The hypothesis states that a major contributing factor to pressure sores is the tissue necrosis that is caused by the accumulation of anaerobic metabolic waste products due to occlusion of the lymph vessels.

The significance of respiration for thoracic duct flow in relation to other driving forces of lymph flow.

Experiments were performed to study the effect of respiratory intrathoracic pressure changes upon thoracic duct lymph propulsion as compared to other forces driving lymph flow in anaesthetized and artificially ventilated dogs. The effect of an open bilateral pneumothorax upon thoracic duct flow and protein composition was determined at rest, with passive limb movement and during saline infusion. The effect of hyperventilation was also tested.

A computer model of the lymphatic system

A mathematical model of the whole body lymphatic network, which simulates the lymph propulsion along the network from the periphery through the thoracic duct into the venous system, is developed using the fundamental conservation laws and current notions of lymphology. Only the major lymphatic vessels are considered. The set of mathematical equations are then translated into a series of FORTRAN statements for the purpose of digital computer simulation of the pressure and flow patterns along the network. The model analysis revealed interesting characteristics of lymphatic contractility at various points along the network.

Vasa vasorum within the media of bovine mesenteric lymphatics.

SummarySmooth muscles in bovine mesenteric lymphatics were well-developed and arranged in three layers, i.e., the internal longitudinal, intermediate circumferential, and external longitudinal. The outermost one was much thicker than the other two. Blood capillaries were found within the smooth muscle layers as well as in the ad-ventitia. These blood capillaries may be essential for maintaining vigorous rhythmic contractions of the lymphatic smooth muscles which act as a driving force for the propulsion of lymph. The presence of numerous mitochondria and glycogen granules seemed to reflect a high metabolic activity of the smooth muscle cells.The authors are indebted to Dr. T. Suganuma and Mr. R. Ichikawa for their technical advice and assistance.

Biomechanics of a lymphatic vessel.

The principles of mechanics and the current notions of lymphatic physiology are integrated into a simple mathematical model of a lymphatic vessel which establishes a theoretical base for lymph propulsion in the lymphatic system. The model specifically considers the active and passive contractilities of the lymphatics. The model is simulated on a digital computer. The pressure and flow patterns derived from the model are consistent with the currently available experimental data.

The cervical lymphatic ducts of the dog: Structure and function of the endothelial lining

In addition to the usual organelles, the endothelial cells of the cervical lymphatic ducts contain numerous fine filaments throughout the central portion of their cytoplasm. The histochemical localization of a myoid fibril stain within the endothelial cells suggests that these filaments are myofilaments which might make the cell capable of some degree of contraction. Fine “anchoring filaments” previously described by others in lymphatic capillaries are observed beneath the endothelium of the cervical collecting ducts. There are two kinds of filament: small filaments and larger filaments that resemble tubules. The abluminal surfaces of the endothelial cells are marked by depressions which could be either pockets or grooves. These depressions are formed by processes of adjacent endothelial cells at some of their junctions and are populated by numerous tubular filaments which have been renamed “junctional filaments.” Although these ducts are among the larger lymph ducts of the dog's body, the smooth muscle cell component is sparse. The paucity of contractile cells and the complete absence of grossly observable spontaneous contractions would indicate that in the cervical ducts of the dog instrinsic lymphatic contraction is not a prime mechanism in the propulsion of lymph. The endothelial lining with its specialized junctions, anchoring filaments and possible presence of myofilaments may, however, play a role in the regulation of lymph flow in this otherwise passive system.

Intrinsic contractility of lymphatics in sheep and in dogs.

Intralymphatic pressures were monitored from plastic cannulas implanted in the thoracic, lumbar trunk and mesenteric lymphatics of conscious and anesthetized sheep, and in the thoracic duct of anaesthetized dogs. Extrinsic factors appeared to be important in the propulsion of lymph only in the thoracic duct of the dog. Intrinsic pulsatile pressure patterns were recorded from all lymphatics studied in sheep, and from the thoracic duct in one out of three dogs. The pulses ranged from about 1–15 mm Hg in amplitude and from about 2–20 pulses/min in frequency. A parameter of contractility was defined and used to establish the existence in sheep of a linear relationship between contractility and flow rate. This relationship was demonstrated when flow was increased by infusion into the lymphatic or into a vein, or, in the case of mesenteric lymphatics, by feeding fat. It was concluded that the intrinsic contractility is myogenic in origin and is the major factor responsible for lymph propulsion at least in sheep; the relationship between contractility and flow enables the rate of lymph flow to keep pace with the rate of lymph production.

STRUCTURE AND FUNCTION OF LYMPHATIC VESSELS OF THE BAT'S WING

The lymphatics of the bat's wing could be separated in vivo into two morphologically and functionally distinct types. Vessels selected for subsequent electron microscopy were labelled in vivo with Berlin blue which could be readily identified in the electron microscope. The terminal bulbs which are responsible for absorption of fluid and particles from the tissues have walls composed of a single layer of endothelium lined on its abluminal surface by a generally tenuous condensation of fibrillar material. Absorption is considered to occur through large gaps present in the endothelial lining. Although the endothelial junctions have no specialized attachment zones, no evidence was obtained for any flap‐valve action in these regions. No gaps were found in the endothelial layers of the collecting and transport channels. The transport channels which are contractile and are responsible for the propulsion of lymph in vivo contain smooth muscle cells in their walls. These cells are not innervated. The cusps of the lymphatic valves are simply two layers of endothelium separated by a narrow zone containing fine fibrillar material. The endothelial cells are phagocytic to the marker particles.

Energy equivalent pressure.

THE OBJECT of this paper is to describe, quantitatively, differences in steady and pulsatile blood flow in terms of an energy equivalent pressure , which is obtained by calculation from phasic flow and pressure measurements. Any project to develop an artificial heart or to aid the failing heart by surgical methods involves consideration of the nature of blood flow in the arterial system. The pulsatile properties of arterial flow and pressure have been thought by some investigators to be important and by others unimportant. It has been suggested that these properties influence the exchange rate between interstitial fluid and lymph, help maintain normal capillary flow and normal kidney function, and have an effect on cellular metabolism by aiding in the propulsion of lymph and in the exchange of cerebrospinal fluid. 1 The arterial pressure pulse has been found by numerous investigators to undergo characteristic changes in vascular disease. Its quantitative measurement,

Intrinsic rhythmic propulsion of lymph in the unanaesthetized sheep.

Intrinsic rhythmic propulsion of lymph in the unanaesthetized sheep.