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PubMed1985

[Modelling in hemodialysis. Why? How?].

It is an imperative necessity to adapt dialysis therapy patient to patient. This adaptation of dialysis procedure requires appropriate representation of water and solute exchanges. Kinetic modelling of hemodialysis was investigated in this respect. The goal of kinetic modelling is either to estimate one or several biologic parameters which are not easily measurable or to reach a prerequisite optimal physiologic state for a given patient. Constructing a model implies a physiological conception of solute and water exchanges that allows a definition of biologic parameters concerned. Mathematic equations only translate quantitatively water and solute transfers. A suitable model is in agreement with experimental data, and the best is the simplest. Therefore the capital point resides in the choice of assumptions which determine the model's precision and complexity. This review also outlined the limits of kinetic modelling which allows neither the determination of the best target nor the "a posteriori" justification of assumptions.

Body Fluid Compartments↗
PubMed1995

Modulation of water diffusion during gonadotropin-induced ovulation: NMR microscopy of the ovarian follicle.

The preovulatory rat follicle reaches a diameter of 1 mm with no internal blood vessels. Nutrient supply to the enclosed oocyte depends solely on passive diffusion across the follicular wall and the follicular fluid. Spin-echo and stimulated-echo NMR microscopy experiments were applied here for studying modulations in water diffusion during gonadotropin-induced maturation of perfused rat ovarian follicles (32 degrees C). Two diffusion compartments were observed for the follicular wall. The intracellular water diffusion coefficient, measured at a short diffusion time (9 ms) was 0.28 x 10(-5) cm2/s. Diffusion at long diffusion times was restricted to 16 microns, the size of cells in the follicular wall, and did not change during maturation. In the follicular fluid a transient 26% decrease in the diffusion coefficient was observed 4-7 h after gonadotropin stimulation, a change that is bound to affect the metabolic balance of the oocyte before ovulation.

Animals↗
PubMed1998

Role of urinary and cloacal bladders in chelonian water economy: historical and comparative perspectives.

The Parisian comparative anatomist Claude Perrault, dissecting an Indian giant tortoise in 1676, was the first to observe that the urinary bladder is of an extraordinary size in terrestrial tortoises. In 1799, the English comparative physiologist Robert Townson suggested that the bladder functioned as a water reservoir, as he had shown previously for frogs and toads. However, these observations went unnoticed in subsequent reports on tortoise water economy that were made by travellers and naturalists visiting the Galapagos Archipelago and marvelling over the huge numbers of giant tortoises that inhabited these desert-like islands. The first such report was by an American naval officer, David Porter, who was a privateer in the 1812-15 war with England. In his journal he referred to the constant supply of water which the Galapagos tortoises carried with them. References to the location in the body, as well as the amounts and quality of the water stored, were, however, contradictory. The confusion concerning the anatomical identity of the water reservoir in the Galapagos tortoise, Geochelone elephantopus, persisted throughout the nineteenth century, and continued when studies of tortoise water economy and drinking behaviour in arid environments were taken up independently in the desert tortoise, Gopherus agassizii, which inhabits the desert regions in the south-western United States. In 1881 Cox found large sacs filled with clear water under the carapace, but it was half a century later that these sacs were identified as the large bilobed bladder; references to specific water sacs continued to appear in the literature until the 1960s. Since 1970, information on the water economy of desert tortoises has been obtained from extensive field studies. Rates of disappearance of tritiated water injected into the body have shown that during the drought periods of the summer, water turnover (intake) rates do not differ from the rates of metabolic water production. Under these conditions urine is not voided, but is stored in the large bladder. During a drought period the bladder urine increases from initially low osmolality finally to reach isosmolality with the blood plasma. Soluble K+ is the major cation of the urine, but large amounts of K+ are also present as precipitated urates. During a drought period the body is in negative water balance, but despite substantial losses of total body water, the plasma concentrations of Na+ and Cl- can remain constant for many months, indicating regulation of the extracellular fluid and water content of the body tissues by reabsorption of water from the urinary bladder. The bladder thus acts both as a store for nitrogenous waste and K+ and as a water reservoir during droughts. Following rain showers, there is a sharp decline in tritium activity correlated with copious drinking from temporary pools of rain water. The old bladder urine is voided and most of the water drunk is stored as a highly dilute urine. In 1676 Perrault observed that in a freshwater turtle, Emys orbicularis, but not in the giant tortoise, two other bladders opened into the cloaca. By the mid-twentieth century it had been established that these cloacal bladders typically were restricted to species of chelonians that led a semi-terrestrial or semi-aquatic life. The function of the bladders has been debated since Townson observed in 1799 that dehydrated freshwater turtles took up water by anal drinking, suggesting that anal drinking served in the water economy of semi-terrestrial turtles. Since then, the bladders have been ascribed hydrostatic and respiratory functions, but the recent literature mostly argues for a respiratory function. The possible role of the cloacal bladders as a water reservoir in amphibious turtles is still open. Terrestrial amphibians and tortoises are unique among vertebrates in possessing large urinary bladders that may function as water reservoirs in dry environments. (ABSTRACT TRUNCATED)

Animals↗
PubMed2005

Intravenous fluid-associated morbidity in postoperative patients.

INTRODUCTION: There is marked variation in postoperative fluid prescribing which may contribute to postoperative morbidity. However, there are few data regarding the overall incidence of fluid associated morbidity in postoperative patients. PATIENTS AND METHODS: Data regarding fluid and electrolyte prescription, fluid balance and intravenous fluid associated morbidity were prospectively collected from 71 patients representing 173 patient days of intravenous fluid therapy. RESULTS: There was no correlation between fluid and electrolytes prescription and pre-operative weight, serum electrolyte levels or ongoing fluid losses. 17% of patients developed significant fluid associated morbidity. 7 patients developed a tachyarrhythmia, which was associated with the prescription of inadequate maintenance potassium. 5 patients developed fluid overload, associated with excessive fluid volume and sodium administration. CONCLUSIONS: Surgical house-staff do not appear to use the available fluid balance information when prescribing. The introduction of fluid prescribing protocols may improve practice. This study provides an accurate measure of fluid-associated morbidity in order to measure the efficacy of such protocols.

Aged↗
PubMed1999

Thermoregulation as a switchboard of autonomic nervous and endocrine control.

Analyzing the multiple effectors of autonomic temperature regulation has, sometimes unexpectedly, provided insights into the characteristics according to which the non-thermoregulatory functions of these effectors are controlled. This article reviews the sympathetic control of cardiovascular and immune functions, hormonal control of energy balance and neurohormonal control of salt and fluid balance inasmuch as they are challenged by competing demands of thermoregulatory requirements. These interactions are taken as examples for the analytical power of the experimental conception to challenge non-thermoregulatory control systems with thermoregulatory activation, and vice versa. Animal models carrying spontaneous or intentionally produced gene defects and molecular and histochemical techniques of gene identification and neuronal tracing are becoming increasingly important. They are applied, in connection with physiological studies exploiting mutual interactions of autonomic control systems, with the aim to elucidate the cytoarchitecture of neuronal circuits by which specific autonomic regulatory activities are controlled.

Animals↗
PubMed2006

Pathophysiology of water and sodium retention: edematous states with normal kidney function.

Body fluid volume regulation by the kidney relies upon the complex interaction of numerous factors. However, in edematous disorders, extrarenal factors can override the 'innate wisdom' of the kidney. For example, in patients with cardiac failure or liver disease and in pregnant women, the normal kidney continues to retain sodium and water despite expanded blood, plasma and extracellular fluid volumes. Such fluid retention can ultimately lead to pulmonary congestion, ascites or peripheral edema. Understanding the kidney's modulation of total body sodium and water in these patients has been perplexing. Cardiac output cannot provide the sole afferent signal for the kidney to regulate sodium and water balance, as the normal kidney can retain excessive amounts of sodium and water when cardiac output is low (e.g. in low output cardiac failure) or high (e.g. cirrhosis or pregnancy). Therefore the integrity of the arterial circulation, which can be impaired either by a low cardiac output or arterial vasodilation, is an important factor in body fluid composition and volume regulation in health and disease.

Atrial Natriuretic Factor↗
PubMed1995

Body fluid alterations and organ hypertrophy in age-dependent salt hypertension of Dahl rats.

The relationship between possible alterations in the volume or distribution of extracellular fluid and the development of salt hypertension was studied in inbred salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) Dahl rats. Blood pressure, cardiac and renal hypertrophy as well as body fluid volumes were determined in young and adult SS/Jr and SR/Jr rats of both sexes that were subjected to low, normal or high salt intake for various periods of time. Salt hypertension in young salt-sensitive rats fed a 4% NaCl diet was not accompanied by any substantial intravascular or interstitial expansion as compared to salt-resistant rats that remained normotensive. There was no sex difference in the response of blood pressure or body fluids to high salt intake. Major expansion of plasma and blood volume, which was elicited by 8% NaCl diet feeding from prepuberty, was not accompanied by a further blood pressure rise (compared to salt hypertensive SS/Jr rats fed 4% NaCl diet). In conclusions, salt hypertension can occur in Dahl salt-sensitive rats without major salt and water retention. The degree of intravascular expansion is not directly related to blood pressure levels in salt-loaded Dahl rats. A high salt intake seems to exert its hypertensive effects in Dahl rats preferentially by influencing the balance of vasoconstrictor and vasodilator systems rather than by increasing the haemodynamically active intravascular volume.

Aging↗
PubMed1997

[Continuous veno-venous hemofiltration in acute renal insufficiency and heart failure].

The application of intermittent renal replacement therapies in critically ill patients with both acute renal failure and heart failure is often associated with circulatory instability and refractory hypotension. We have evaluated the efficacy and safety of a continuous technique (continuous veno-venous hemofiltration-CVVH) in 7 patients (1 male, 6 females, mean age 77 +/- 4 years) referred to our intermediate care unit for oliguria, acute renal failure and NYHA functional class IV, CVVH was performed by a peristaltic pump with blood flow at 200 ml/min, controlled ultrafiltration production rate (25 ml/min), minute to minute microprocessor controlled fluid balance system, biocompatible filters, low-dose prostacyclin for the extracorporeal circuit maintenance. Non invasive evaluation of cardiac function was performed by Doppler echocardiography. A total of 673 hours of CVVH were performed, with a mean extracorporeal circuit duration of 96 +/- 26 hours/patient (range 15-134). Daily urea clearance was 32 +/- 21. A mean body weight decrease of 10% was obtained (body weight before-CVVH 64.5 +/- 6 kg vs end-CVVH 58.5 +/- 5 kg, p < 0.01, paired data Student's test) without any hemodynamic worsening; metabolic control was adequate (urea before-CVVH 251 +/- 73 mg% vs end-CVVH 117 +/- 18 mg%, p < 0.01). Hospital survival was 42% (3/7 patients). In patients with acute renal failure and severe heart failure, CVVH allows an easy control of both fluid balance and acid-base equilibrium, along with the maintenance of acceptable hemodynamic stability.

Acid-Base Equilibrium↗