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Computer simulation of thirst and water balance

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Abstract

The body water, alimentary exchange, renal control, and drinking sub-systems involved in water regulation in the rat were simulated using a digital computer. For each subsystem, coefficients and time constants were fitted to published data, and the calculations closely followed a physiological understanding of the mechanisms in question. Experimental data were then obtained for the drinking and renal response to injections and continuous infusions of hypertonic saline in rats, and the overall performance of the model was tested by comparing its response to these experimental results. Agreement was good for these and other results, indicating that the model adquately takes account of the major variables in the regulation of body water. Manipulations of the model and comparisons with rats indicate the necessity for short term oral and gastric feedback, and for a thirst threshold.

Sommaire

L'eau du corps, les échanges alimentaires, la régulation rénale et les sous-systèmes de boire impliqués dans la régulation de l'eau chez le rat, ont été simulés en utilisant un ordinateur digital. Pour chaque sous-système les constantes des coefficients et du temps furent ajustés aux données publiées et les calculations suivirent de près la compréhension physiologique des mécanismes en question. Puis, des données expérimentales furent obtenues pour le boire et la réaction rénale aux injections et aux infusions continuelles de sérum hypertonique chez les rats et aussi l'action globale du modèle furent vérifiées, en comparant sa réaction avec les résultats expérimentaux. La comparaison pour ces résultats et autres a été bonne, en indiquant que le modèle tient compte en juste proportion de variables majeures dans la régulation de l'eau du corps. Les manipulations du modèle et les comparaisons avec les rats indiquent la nécessité pour des rétro-actions orales et gastriques à court terme et pour un seuil de la soif.

Zusammenfassung

Es wurden der Wasserbestand im Körper von Ratten, die Nahrungsumwandlung, Nierenkontrolle und die Nebensysteme in der Flüssigkeitsaufnahme, die mit der Wasserregulierung zusammenhängen, unter Verwendung eines Digitalrechners simuliert. Für jedes Nebensystem wurden Koeffizienten und Zeitkonstanten in die veröffentlichten Unterlagen eingepasst und die Berechnungen folgten aufs Genaueste einem physiologischen Verständnis des in Frage kommenden Mechanismuses. Dadurch wurden experimentelle Unterlage über die Flüssigkeitsaufnahme- und Nierenreaktion nach Injektionen und fortlaufenden Infusionen mit hypertonischem Salz in Ratten gewonnen. Die Gesamtleistung des Musterbeispiels wurde durch Vergleich seiner Reaktion mit experimentell erzielten Reaktions-resultaten überprüft. Die Übereinstimmung dieses sowie auch anderer Befunde war zufriedenstellend, was darauf hindeutet, dass das Musterbeispiel die hauptsächlichen Varianten in der Regulierung der Körperflüssigkeit hinreichend berücksichtigt. Manipulation mit dem Musterbeispiel und Vergleich mit Ratten weist auf die Notwendigkeit eines kurzfristigen, oralen und gastrischen Feedbacks und einer Durstgrenze hin.

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Abbreviations

ADH:

total ADH

ADH c :

ADH concentration

ADH E :

effective ADH concentration

ALD:

total aldosterone

ALD c :

aldosterone concentration

C c :

cellular concentration of sodium in milli-equivalents per ml (m-equiv./ml)

C W :

cellular water (ml)

D C :

drinking fluid concentration of sodium (m-equiv./ml)

D I :

drinking inhibition factor (ml/100 g body wt)

D Na :

rate of drinking sodium (m-equiv./min)

D W :

rate of drinking water (ml/min)

τ C :

cellular error (ml/100 g body wt)

τ E :

extracellular error (ml/100 g body wt)

ECF:

extracellular fluid

E C :

extracellular concentration of sodium (m-equiv./ml)

E W :

extracellular water (ml)

GFRN :

glomerular filtration rate of sodium (m-equiv./min)

GFR W :

glomerular filtration rate of water (ml/min)

ICF:

intracellular fluid

I.C.:

initial conditions

INF:

infusion of sodium (m-equiv./min)

I C :

intestine concentration of sodium (m-equiv./ml)

I Na :

intestine sodium (m-equiv.)

I W :

intestine water (ml)

I-E ANa :

active flow of sodium from intestine to ECF (m-equiv./min)

I-E AW :

water carried by active sodium from intestine to ECF (ml/min)

I-E PNa :

passive flow of sodium between intestine and ECF (m-equiv./min)

I-E PW :

passive flow of water between intestine and ECF (ml/min)

K :

potassium (m-equiv.)

L :

insensible water loss (ml/min)

OS W :

osmotic flow of water between ECF and cells (ml/min)

S C :

stomach concentration of sodium (m-equiv./ml)

S H :

signal completely inhibiting stomach discharge (value 0 or 1)

S I :

stomach inhibition factor (ml/100 g body wt)

S Na :

stomach sodium (m-equiv.)

S W :

stomach water (ml)

S-E W :

flow of water between stomach and ECF (ml/min)

S-I Na :

flow of sodium from stomach to intestine (m-equiv./min)

S-I W :

flow of water from stomach to intestine (ml/min)

T :

total thirst signal (ml/100 g body wt)

T FNa :

tubular rejection factor of sodium

T FW :

tubular rejection factor of water

TRF Na :

tubular reabsorbtion factor of sodium

TRF W :

tubular reabsorbtion factor of water

U C :

urine concentration (m-equiv./ml)

U Na :

urine sodium (m-equiv./min)

U′ Na :

urine sodium for concentration check (m-equiv./min)

U W :

urine water (ml/min)

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Authors and Affiliations

  1. Laboratory of Experimental Psychology, University of Sussex, Brighton, Sussex

    F. M. Toates & K. Oatley

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  1. F. M. Toates
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  2. K. Oatley
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Requests for reprints should be addressed to Dr. K. Oatley, Laboratory of Experimental Psychology, University of Sussex, Brighton, BN1 9QY. Copies of the simulation program in Elliott Algol are also available.

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Toates, F.M., Oatley, K. Computer simulation of thirst and water balance. Med. & biol. Engng. 8, 71–87 (1970). https://doi.org/10.1007/BF02551751

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