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Abstract
A tetrapolar 75-kHz,
0.2-mA constant-current electrical impedance measuring system was used to
monitor urinary volume change over 12 four-hour sessions in 20 male and 20
female normal human subjects. Two spot voltage electrodes (E) and two spot
current electrodes (1) were applied 5 cm above the symphysis pubis at 15 cm interelectrode
distances, 7.5 cm
bilaterally from the midline. Five measurements of impedance and skin
temperature were made at 15-minute intervals over 4 hours. Specific gravity,
impedance change, and volume were recorded with each voided specimen.
Suprailiac and infrascapular skinfolds, and circumference at iliac crests
were measured. The subjects drank 175 ml of fluids per hour during the
testing session. Subjects remained in the supine position during
measurements. They walked to the lavatory to void. Bladder fullness is defined
as the urge to void. Results include: (1) a poor negative correlation between
specific gravity of urine and impedance  (2) baseline impedance was dependent upon individual
subject characteristics: in males skin area, skinfold thickness, and
suprailiac circumference; in females skinfold thicknesses and time since last
menstrual period; (3) impedance decreased with urinary bladder filling and
increased upon voiding  ; (4) the cumulative sum test (CUSUM) predicted time to
void in 78.9% of voids  and no void (when
voiding did not occur) in 66.8% of no voids . Overall accuracy
of the CUSUM test was 74.6% .
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