METHOD AND APPARATUS FOR MONITORING THE FLUID BALANCE OF THE BODY

Two high-frequency partial alternating currents of constant and equal size, 100 mu A, but with highly different frequencies, 1,5 and, respectively, 150 kHz, are delivered by means of a constant current source (K) to tape electrodes (E1 and, respectively, E2) about two places of peripherally remote relationship on the patient, for example one wrist and the diametrically opposed ankle. The voltage drop between two additional electrodes (E3 and, respectively, E4) located each near one the firstmentioned electrodes is measured by a detector (D) and divided into its two voltage components of different frequency, which components are proportional to the impedance of the body for the respective frequencies. The analogous component values are fed via an A/D-converter to a microprocessor (MD), which comprises a memory (M) for the measuring values received. To the microprocessor also information on the patient's weight and length are fed by setting devices (V, L). A first measurement is carried out and the result thereof is stored in the memory of the microprocessor. A second measurement is carried out, and a calculation of the change in the fluid balance relative to the first measurement now is carried out by the microprocessor according to an empirically constructed formula where DELTA V = change in fluid weight, k = a proportionality constant, S = body surface, based on patient's weight and length, Z1 and Z2 = impedance at 1,5 kHz and, respectively, 150 kHz at the second measuring occasion, Z1i< and Z>2i< = corresponding impedances at the first measuring occasion (initial values) and are shown on a digital indicator (R) connected to the microprocessor. Deux courants alternatifs partiels de haute fréquence ayant une intensité constante et identique, 100 muA, mais avec des fréquences très différentes, 1,5 et 150 kHz, respectivement, sont envoyés à l'aide d'une source à courant constant (K) à des électrodes en bandes (E1 et E2, respectivement) autour de deux endroits éloignés l'un de l'autre du patient, par exemple un poignet et la cheville diamétralement opposés. La chute de tension entre deux électrodes supplémentaires (E3 et E4, respectivement) chacune d'elles situées à proximité des électrodes mentionnées en premier lieu est mesurée par un détecteur (D) et est divisée en ses deux composantes de tension, de fréquences différentes, lesquelles composantes sont proportionnelles à l'impédance du corps pour les fréquences respectives. Les valeurs analogiques des compo