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At least 19 recordsLinked to original sources
PubMed1996

Transepithelial fluid shift generated by osmolarity gradients in unstimulated perfused rat submandibular glands.

The effects of osmotic gradients on transepithelial water movements were examined in unstimulated perfused submandibular glands of the rat. Osmotic gradients were applied transepithelially by adding sucrose to or removing it from the perfusate. An infusion of hypotonic perfusate shifted fluid from the interstitium to the lumen (luminal fluid shift) transiently, whereas an infusion of hypertonic perfusate shifted fluid from the lumen to the interstitium (interstitial fluid shift) transiently. The amount of fluid shifted from lumen to interstitium increased as the luminal fluid osmolarity was raised or as the perfusate osmolarity was reduced. Thus, fluid movements across the salivary epithelium were shown to be simply dependent on the osmolarity difference between lumen and interstitium. To estimate the effective pore radius of the epithelium, non-electrolyte solutions (urea, dimethylurea, diethylurea, mannitol, sucrose and maltotriose) were also used as luminal solutions. The results from non-electrolyte experiments showed that the effective pore radius of the passage for non-electrolytes was slightly larger than 0.38 nm. Solutes smaller than mannitol were less effective in opposing the interstitial fluid shift, and the value of effective pore radius in this report was similar to that of the secretory water pathway that has been measured in solvent drag studies (0.4 0.45 nm). These findings suggest that the passage for non-electrolytes may be water transport pathway in salivary epithelium.

Animals↗
PubMed2005

Volume turnover kinetics of fluid shifts after hemorrhage, fluid infusion, and the combination of hemorrhage and fluid infusion in sheep.

BACKGROUND: Hemorrhage is commonly treated with intravenous infusion of crystalloids. However, the dynamics of fluid shifts between body fluid spaces are not completely known, causing contradictory recommendations regarding timing and volume of fluid infusions. The authors have developed a turnover model that characterizes these fluid shifts. METHODS: Conscious, chronically instrumented sheep (n = 12) were randomly assigned to three protocol groups: infusion of 25 ml/kg of 0.9% saline over 20 min (infusion only), hemorrhage of 300 ml (7.8 +/- 1.1 ml/kg) over 5 min (hemorrhage only), and hemorrhage of 300 ml over 5 min followed by infusion as noted above (hemorrhage plus infusion). A two-compartment volume turnover kinetic model containing seven model parameters was fitted to data obtained by repeated sampling of hemoglobin concentration and urinary excretion. RESULTS: The volume turnover model successfully predicted fluid shifts. Mean baseline volumes of the central and tissue compartments were 1799 +/- 1276 ml and 7653 +/- 5478 ml, respectively. Immediate fluid infusion failed to prevent hemorrhage-induced depression of cardiac output and diuresis. The model suggested that volume recruitment to the central compartment after hemorrhage was primarily achieved by mechanisms other than volume equilibration between the two model compartments. CONCLUSION: Volume turnover kinetics is a promising tool for explaining fluid shifts between body compartments after perturbations such as hemorrhage and intravenous fluid infusions. The pronounced inhibition of renal output after hemorrhage prevailed regardless of fluid infusion and caused fluid retention, which expanded the tissue compartment.

Algorithms↗
PubMed1988

Effect of lower-body positive pressure on postural fluid shifts in men.

To quantify the effect of 60 mm Hg lower-body positive pressure (LBPP) on orthostatic blood-volume shifts, the mass densities (+/- 0.1 g.1-1) of antecubital venous blood and plasma were measured in five men (27-42 years) during combined tilt table/antigravity suit inflation and deflation experiments. The densities of erythrocytes, whole-body blood, and of the shifted fluid were computed and the magnitude of fluid and protein shifts were calculated during head-up tilt (60 degrees) with and without application of LBPP. During 30-min head-up tilt with LBPP, blood density (BD) and plasma density (PD) increased by 1.6 +/- 0.3 g.1-1, and by 0.8 +/- 0.2 g.1-1 (+/- SD) (N = 9), respectively. In the subsequent period of tilt without LBPP, BD and PD increased further to + 3.6 +/- 0.9 g.1-1, and to + 2.0 +/- 0.7 g.1-1 (N = 7), compared to supine control. The density increases in both periods were significant (p less than 0.05). Erythrocyte density remained unaltered with changes in body position and pressure suit inflation/deflation. Calculated shifted-fluid densities (FD) during tilt with LBPP (1006.0 +/- 1.1 g.1-1, N = 9), and for subsequent tilt after deflation (1002.8 +/- 4.1 g.1-1, N = 7) were different from each other (p less than 0.03). The plasma volume decreased by 6.0 +/- 1.2% in the tilt-LBPP period, and by an additional 6.4 +/- 2.7% of the supine control level in the subsequent postdeflation tilt period. The corresponding blood volume changes were 3.7 +/- 0.7% (p less than 0.01), and 3.5 +/- 2.1% (p less than 0.05), respectively. Thus, about half of the postural hemo-concentration occurring during passive head-up tilt was prevented by application of 60 mm Hg LBPP.

Adult↗
PubMed1983

Prediction of postdialysis serum sodium concentration and transcellular fluid shift without measuring body fluid volumes.

The postdialysis levels of serum sodium concentration, urea concentration, and osmolality, as well as the magnitude of both transcellular fluid shifts and sodium removal, were predicted based on computer modeling without measuring body fluid volumes. A 4-h hemodialysis was performed in five patients at a constant ultrafiltration rate of 0.5 L/h using dialysate with normal (141 mEq/L) or high (150 mEq/L) Na+ concentration. The serum sodium concentration, urea concentration, and osmolality, as well as intracellular and extracellular fluid volumes, were determined before and after hemodialysis. The model predictions without measurement of body fluid volumes were in excellent agreement with measured values, suggesting clinical validity. The model may be useful in clinical practice to control the postdialysis levels of sodium and water content by computerized hemodialysis.

Adult↗
PubMed2000

Effects of aging on cardiovascular responses to gravity-related fluid shift in humans.

BACKGROUND: Fluid shift induced by postural change causes autonomic neural responses of the cardiovascular system that buffer blood pressure fluctuation. The aim of the study was to clarify the effects of aging on cardiovascular autonomic functions in response to gravity-related fluid shift that unloads or loads the baroreceptors in human subjects. METHODS: A chest electrocardiogram, blood pressure by Finapres, and stroke volume by impedance method were measured in healthy young men (23-31 years old) and healthy elderly men (74-80 years old) during supine rest, at 90 degrees head-up tilt and thermoneutral head-out water immersion. Spectral analysis was applied to the time series data of the R-R intervals (heart rate variability [HRV]) and systolic blood pressure (blood pressure variability [BPV]). The arterial baroreflex gain for heart rate was estimated using frequency transfer function analysis. RESULTS: The young subjects had stable blood pressure, despite the larger amount of fluid shift induced by both tilt and immersion, and had marked changes in HRV and BPV. The elderly subjects failed to maintain stable blood pressure during these perturbations, despite less fluid shift and no significant changes in HRV and BPV. The arterial baroreflex gain for heart rate was not changed in the elderly subjects, whereas the gain decreased with upright in the young subjects and showed an increasing tendency during immersion compared with upright posture. CONCLUSIONS: These findings suggest that the adaptivity of the autonomic nervous system to gravity-related fluid shift is reduced in elderly people, and this may cause blood pressure instability.

Adult↗
PubMed1983

Physiological and behavioral effects of tilt-induced body fluid shifts.

This paper addresses the "fluid shift theory" of space motion sickness. The primary purpose of our research was the development of procedures to assess individual differences in response to rostral body fluid shifts on earth. Experiment I examined inner ear fluid pressure changes during head-down tilt in intact human beings. Tilt produced reliable changes. Differences among subjects and between ears within the same subject were observed. Experiment II examined auditory threshold changes during tilt. Tilt elicited increased auditory thresholds, suggesting that sensory depression may result from increased inner ear fluid pressure. Additional observations on rotation magnitude estimation during head-down tilt, which indicate that rostral fluid shifts may depress semicircular canal activity, are briefly described. The results of this research suggest that the inner ear pressure and auditory threshold shift procedures could be used to assess individual differences among astronauts prior to space flight. Results from the terrestrial observations could be related to reported incidence/severity of motion sickness in space and used to evaluate the fluid shift theory of space motion sickness.

Adolescent↗
PubMed1986

Continuous blood densitometry: fluid shifts after graded hemorrhage in animals.

To evaluate rapid fluid shifts after graded hemorrhage in splenectomized animals, four pigs and two dogs were bled 15-23 ml/kg body wt in steps of 2.2-6.0 ml/kg. Arterial blood density (BD), mean arterial pressure (MAP), and central venous pressure (CVP) were recorded continuously, and arterial plasma density (PD) and hematocrit (Hct) were determined from blood samples. Erythrocyte density was computed from PD, BD, and Hct. Starting with stable control conditions, MAP, CVP, and BD fell from the beginning of hemorrhage. Each blood withdrawal was followed by an immediate and rapid decrease in BD, even at the lowest (less than 3 ml/kg) initial blood losses. The time course of BD change mirrored that of the volume replacement, with time constants of 3.0-9.6 min and amplitudes depending on the magnitude of the relative volume loss. The PD decrease was significant (P less than 0.01) after 5.4 +/- 0.7 ml/kg hemorrhage. At 15 ml/kg blood loss the mean PD and BD had dropped by 0.99 +/- 0.15 and 2.42 +/- 0.26 g/l, respectively, and Hct had dropped by 2.40 +/- 0.47 units. Calculations suggest that either the inward-shifted fluid has a higher density than normal ultrafiltrate and/or there is a rise of the whole-body-to-large vessel Hct (F cell ratio). The rapid fluid replacement ranged from 5.8 +/- 0.8 to 10.6 +/- 2.0% of the initial plasma volume, or one-fifth to one-third of the lost volume with a 20% hemorrhage. Transvascular fluid shifts can be monitored with continuous high-precision blood densitometry.

Animals↗
PubMed1984

A- and B-scan characteristics of shifting fluid level.

A shifting fluid level (SFL) was detected by A- and B-scans in 155 eyes. All eyes had a hemorrhage into the vitreous. In 129 of the 155 eyes (83%) the vitreous hemorrhage resulted from proliferative diabetic retinopathy. In 11 (7%) and seven eyes (5%), respectively, the hemorrhage was a complication of closed vitrectomy and scleral buckling procedures. In eight eyes (5%), the hemorrhage resulted from severe penetrating ocular trauma. The SFL was characterized by a high-amplitude echo on A-scan, and straight horizontal or vertical linear echo on horizontal or vertical B-scan, respectively. It showed a typical shift toward the most posterior portion of the globe when the eye was moved in the different positions of gaze. The SFL was overlying the retina in 150 eyes (97%) and was suspected to be subretinal in five eyes (3%). SFL represented a layer of sedimented red blood cells on the surface of the retina or choroid.

Adolescent↗
PubMed1987

Fluid shifts and hydration state: effects of long-term exercise.

During exercise, increased capillary hydrostatic pressure caused by elevation of arterial pressure produces plasma volume shifts from the vascular space to the interstitial fluids. Following a rapid efflux of vascular fluid within minutes of exercise, there is very little further reduction in plasma volume during long-term exercise, suggesting protective mechanisms against loss of circulating blood volume. These mechanisms probably include increasing plasma protein oncotic pressure, differences in peripheral vasoconstriction in active muscles and inactive tissues, and elevated lymph flow. The interaction of these factors provides optimal thermoregulatory and cardiovascular stability. The dynamics of fluids shifts during long-term exercise are altered by hydration state. The hypovolemia caused by dehydration acts to conserve blood volume by reducing the amount of plasma shift and sweat loss during exercise. The consequence is less heat dissipation and greater cardiovascular stability. In contrast, the hypervolemia produced by hyperhydration promotes greater shifts of fluid and sweat loss, resulting in lower body temperature and heart rate during prolonged work. The beneficial effects of hyperdydration and subsequent hypervolemia are manifest in the adaptation of body fluids and electrolytes to exercise training. Thus, with regard to fluid shifts during long-term exercise, training is an effective way to become hyperhydrated and to reduce the limiting effects of working in 'hostile' environments.

Adaptation, Physiological↗
PubMed2002

Third-space fluid shift in elderly patients undergoing gastrointestinal surgery: Part 1: Pathophysiological mechanisms.

Third-space fluid shift, the movement of body fluid to a non-functional space, is a frequently occurring and potentially fatal clinical phenomenon. Little published research exists however in medical or nursing journals concerning its incidence, significance and ramifications in elderly patients undergoing major gastrointestinal surgery. This initial article, part I, explores fluid movement between fluid compartments and uses these principles to discuss the pathophysiology of the two distinct phases of third-space fluid shift. Part II will examine the criteria nurses could use in the clinical assessment of patients in both first and second phases third-space fluid shift and discuss the clinical reliability of these criteria.

Age Factors↗
PubMed1983

Fluid shifts in vascular and extravascular spaces during and after simulated weightlessness.

To simulate weightlessness in a normal-gravity environment, eight male subjects were tilted 5 degrees head-down for 8 h to determine vascular and extravascular shifts of fluid. Most of the initial loss of leg volume during head-down tilt represented a passive shift of venous blood toward the head. Facial edema, headache, nasal congestion, and a pronounced diuresis were associated with this redistribution of blood volume. As measured by the wick-catheter technique during head-down tilt, interstitial fluid pressure in lower-leg muscle and overlying subcutaneous tissues decreased by 7.4 and 4.4 mmHg, respectively. Interstitial fluid was shifted from the lower legs at a rate of 12 ml X h-1. Dehydration of lower-leg tissues probably resulted from decreased capillary blood pressure within these tissues during tilt. Other transcapillary pressures were unchanged. The abrupt alterations in local blood pressure upon changes in body posture were probably sufficient to explain all shifts of vascular and extravascular fluid. In this regard, countermeasures may be necessary to maintain precapillary-muscle tone during long space flights in order to prevent swelling of lower-leg tissues upon readjustment to Earth's gravity.

Airway Obstruction↗
PubMed1981

Transvascular fluid shift after blood volume modification in relation to compliances of the total vascular bed and interstitial fluid space.

The transvascular fluid shift after blood volume modification was analyzed by means of continuous blood volume determination and stimulation analysis. On splenectomized dogs, 15% of the circulating blood was withdrawn and retransfused, while the circulating blood volume, hematocrit and colloid osmotic pressure were continuously monitored. Based on the results, the transvascular fluid shift was stimulated by a two-compartment model. The compliance of the intravascular and interstitial fluid spaces as well as the transvascular filtration coefficient was determined on the whole body, simultaneously. No statistically significant differences were found between any of the values for blood withdrawal and retransfusion. The compliance of the vascular space, 4.62 +/- 0.82 ml/mmHg . kg of body weight, was almost identical with that of the interstitial fluid space, 4.75 +/- 1.52 ml/mmHg . kg of body weight. The whole body capillary filtration coefficient was 0.74 +/- 0.39 ml/min . mmHg . kg of body weight, which is within the range of the reported values of the capillary filtration coefficient for muscle and intestine. It is suggested that the rapid transvascular fluid shift after blood volume modification is provided with the fact that the compliances of intravascular and interstitial fluid spaces are almost identical.

Animals↗
PubMed1994

Enhanced slow caudad fluid shifts in orthostatic intolerance after 24-h bed-rest.

To evaluate mechanisms of late orthostatic intolerance, slow fluid shifts along the body axis were studied during deconditioning by 24-h bed-rest and during 13-min upright tilts before and after this manoeuvre. In 11 healthy male subjects the fluid volumes of a thorax and a calf segment (impedance plethysmography) as well as tissue thickness at the forehead and the tibia (miniature ultrasonic plethysmograph) were recorded. Cardiovascular performance was monitored by recording heart rate (electrocardiogram), brachial and finger arterial pressure (by the Riva Rocci method and by the Finapres technique) as well as stroke volume (by impedance cardiography). Bed-rest led to a cephalad fluid shift with a mean interstitial leg dehydration of 2.2 ml.100 ml-1 with no changes in body mass and plasma volume. No syncope during the tilt occurred before bed-rest, while after bed-rest 8 subjects fainted between min 2.1 and 9.0 of the tilt. Bed-rest resulted in an augmented initial heart rate response to tilting which was similar in all subjects. In later orthostasis, bed-rest caused two- to threefold faster caudad fluid shifts with higher calf filtration rates in fainters (prior to hypotension) than in nonfainters. Through bed-rest the estimated extravasation within 10 min into general lower body tissue spaces increased by 192 ml in (late) fainters as opposed to only 23 ml in nonfainters. It was concluded that contributing factors to orthostatic intolerance may be slow transcapillary fluid shifts which are easily underestimated and whose quantity and time course call for further investigation after various deconditioning manoeuvres. In particular, the postflight fluid shifts in astronauts who will have markedly dehydrated legs, may impose a circulatory stress which needs to be evaluated. In general, the filtration rate in relevant areas appears to be an integrative and easily determined parameter, reflecting hormonal and neurogenic vascular as well as local interstitial control of the Starling forces.

Adult↗
PubMed2002

Third-space fluid shift in elderly patients undergoing gastrointestinal surgery: Part II: nursing assessment.

Third-space fluid shift is the mobilisation of body fluid to a non-contributory space rendering it unavailable to the circulatory system. It is a recurrent clinical phenomenon requiring swift identification to minimise deleterious effects. Nurses experience difficulties however in its early identification, diagnosis and subsequent treatment because of the lack of consensual and consistent information regarding third-spacing. This article, part II, building on the previous article, explores the clinical validly and reliability of signs and symptoms of both phases of third-space fluid shift. In addition it reinforces the use multiple patient assessment cues if nurses are to differentiate between, and accurately respond to, the various causes of both hypovolaemia and hypervolaemia. It assists nurses to increase their knowledge and uderstanding of third-space fluid shift in patients undergoing gastrointestinal surgery.

Aged↗
PubMed1987

Space shuttle inflight and postflight fluid shifts measured by leg volume changes.

This is a study of the inflight and postflight leg volume changes associated with spaceflight on Space Shuttle missions. The results of this study show an inflight volume loss of 2 L from lower extremities, 1 L from each leg, representing an 11.6% volume change. The vast majority of this change appears to be a shift in body fluids, both intravascular and extravascular. The fluid shift occurs rapidly on Mission Day 1 (MD-1), with it being essentially complete by 6 to 10 h. The regional origin of shift and leg volume change shows a far greater absolute volume (708 ml vs. 318 ml) and percentage (69% vs. 31%) of the total change coming from the thigh as compared to the lower leg. Postflight, the return of fluid to the lower extremities occurs rapidly with the majority of volume return complete within 1.5 h postlanding. At 1 week postflight there is a residual leg volume decrement of 283 ml or 3.2% that is probably due to tissue loss secondary to atrophic deconditioning and weight loss.

Body Fluids↗
PubMed1983

Intercompartmental fluid shifts after dextran infusion in rabbits.

Intercompartmental fluid shifts were studied in New Zealand White rabbits after infusion of hyperoncotic dextran solution with a mean molecular weight of 64,200 and osmolality of 220 mosmol/kg H2O. In comparison with the control period, it was found that 1) plasma volume increased by a net volume of 83 +/- 12 ml; 2) systemic blood pressure increased slightly but significantly and central venous pressure increased markedly (this was accompanied by a reduction of interstitial fluid pressure from a control of -1 to -8 cmH2O after dextran); 3) plasma volume expansion was not accompanied by plasma sodium and chloride dilution when they were expressed in meq/kg of plasma water; and 4) plasma osmolality did not change after dextran infusions. The increase in plasma volume unaccompanied by any change in plasma sodium, chloride, or osmolality may be explained by a transcapillary fluid shift from the interstitial space to the bloodstream caused by an increase in plasma oncotic pressure. Because the more negative interstitial fluid pressure did not seem to attract any appreciable amount of fluid from the cells, we concluded that the interstitial space did not hydrodynamically couple the intravascular space to the cellular compartment.

Animals↗
PubMed1994

A comprehensive Guyton model analysis of physiologic responses to preadapting the blood volume as a countermeasure to fluid shifts.

The Guyton model of fluid, electrolyte, and circulatory regulation is an extensive mathematical model capable of simulating a variety of experimental conditions. It has been modified for use at NASA to simulate head-down tilt, a frequently used analog of weightlessness. Weightlessness causes a headward shift of body fluids that is believed to expand central blood volume, triggering a series of physiologic responses resulting in large losses of body fluids. We used the modified Guyton model to test the hypothesis that preadaptation of the blood volume before weightless exposure could counteract the central volume expansion caused by fluid shifts, and thereby attenuate the circulatory and renal responses that result in body fluid losses. Simulation results show that circulatory preadaptation, by a procedure resembling blood donation immediately before head-down bedrest, is effective in damping the physiologic responses to fluid shifts and reducing body fluid losses. After 10 hours of head-down tilt, preadaptation also produces higher blood volume, extracellular volume, and total body water for 20 to 30 days of bedrest, compared with non-preadapted control. These results indicate that circulatory preadaptation before current Space Shuttle missions may be beneficial for the maintenance of reentry and postflight orthostatic tolerance in astronauts. This paper presents a comprehensive examination of the simulation results pertaining to changes in relevant physiologic variables produced by blood volume reduction before a prolonged head-down tilt. The objectives were to study and develop the countermeasure theoretically, to aid in planning experimental studies of the countermeasure, and to identify potentially disadvantageous physiologic responses that may be caused by the countermeasure.

Adaptation, Physiological↗
PubMed1983

Intercompartmental fluid shifts due to glucose release during hemorrhage in rabbits.

Intercompartmental fluid shifts were studied in 18 anesthetized New Zealand White rabbits after hemorrhage. During graded hemorrhage the plasma volume spontaneously replaced was proportional both in time and amount to the hyperosmolar response. This, in turn, was mainly due to hyperglycemia. In 5 fed rabbits and 5 rabbits unfed for 40 h, all subjected to 16 ml/kg of hemorrhage, plasma volume replacement was closely correlated with the hyperglycemic response. Plasma glucose concentration gradually increased in fed animals throughout a 2-h posthemorrhagic period, whereas the hyperglycemic response ceased 15 min after hemorrhage in unfed animals, and further fluid shift also stopped. During the first 30 min after hemorrhage most of the fluid that shifted into the bloodstream came from the interstitial space, as judged by a lack of change in plasma sodium and chloride concentrations. However, during the second hour of the posthemorrhagic period of well-fed rabbits, plasma sodium and chloride concentrations decreased, suggesting that dilute fluid had shifted from the cells to the interstitial space and bloodstream. We concluded that the hyperglycemic response during and after hemorrhage played a significant role in plasma volume replacement, but this was less after a period of food deprivation.

Animals↗