The normally closed clamp is installed on the drainage tube connecting the catheter to the bag or at any convenient location within the Foley assembly (catheter, drainage tube, and bag) where it can prevent backflow of urine when the clamp is closed in instances where the drainage bag or drainage tubing is placed above the bladder. According to a specific embodiment of the invention, a holding device for a Foley bag is provided (instead of the hook currently used in practice) that automatically opens a normally closed clamp. In one embodiment, the context-sensitive flow interrupter is used to address urine backflow occurrences in urinary catheter and drainage systems, and includes a holding device for a collection bag of the urinary catheter and drainage system. This high volume of undrained urine is likely a risk factor for urinary tract infections. As can be seen by the basal cystometrogram, a 20 cm H 2O backpressure on the bladder means that about 425 ml of urine is trapped in the bladder. The relationship between bladder pressure and volume of urine in the bladder can be understood by reference to the cystometrogram of FIG. ![]() In-vitro tests have shown that back-pressures of 20 cm H 2O can exist due to a urine-filled loop. The maximum difference in menisci elevation across the loop effectively sets the pressure and bladder volume thresholds before urine can crest over the downstream (distal) apex and flow into the collection bag. The pressure at airspace U equals the difference in elevation H between menisci U and D. Fluid will accumulate within the bladder until intravesical pressure exceeds the back-pressure caused by the air-lock obstruction of airspace U. ![]() Because the bladder is highly compliant, the bladder responds to backpressure by stretching and accommodating greater undrained urine volumes, while maintaining low intravesical (bladder) pressure.
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