1. Causes of Disease
1. The characteristics of elderly female bladder and urethra are that the bladder function changes with age. The bladder capacity of elderly women decreases, the residual urine volume increases, and uncontrollable contractions occur. Alroms and Torrens conducted urinary tests on women around 50 years old, with a urine flow rate of 75ml/s, and those over 50 years old have a urine flow rate greater than 18ml/s. If the urine output per second is less than 15ml, it indicates the presence of urethral obstruction. Parviren conducted a bladder造影 study on 59 elderly women and found that many patients had trabecular diverticula and funnel-like prolapses, which were unrelated to urinary tract infections. After menopause, due to the decrease in estrogen levels, the vaginal and urethral mucosal epithelium becomes thin, the dense elastic fiber tissue around the bladder neck, and the glands and ducts surrounding the urethra and bladder neck become thin. Studies have confirmed that estrogen receptors exist on the cell membranes or nuclei of bladder trigone, bladder mucosa, and urethral mucosa cells in women, and the concentration of receptors in the urethra is significantly higher than that in the bladder. Therefore, post-menopausal women are prone to urinary incontinence. Studies have shown that estrogen replacement therapy for post-menopausal women can reduce nocturia, indirectly confirming that estrogen deficiency can reduce bladder stability. Animal studies have shown that hormone withdrawal can affect the density of receptors in the bladder and urethra and their sensitivity to hormones, and restoring normal estrogen levels can reverse these effects, increasing the number of receptors and their response to muscarinic and adrenergic agents. Moreover, the decrease in estrogen levels will promote the decrease in the responsiveness of smooth muscle to neural stimulation.
2. At the histological level, anatomical and ultrastructural research has found that the smooth muscle and striated muscle of the urinary tract in elderly women have obvious degenerative changes. In elderly women without obvious urogenital system lesions, abnormal changes may also be observed, which is the reason why elderly women are prone to functional disorders of the urogenital system.
3. The fibrosis of the bladder muscle in elderly women is the earliest confirmed cause of dysuria. The collagen fibers and elastic proteins in the bladder of elderly women have increased, and Levy and Wight focused on the submucosal layer accounting for 25% of the bladder wall thickness. They studied the bladder biopsy tissue under light and electron microscopes and found urinary dysfunction, mostly due to the separation and disarray of collagen, and almost no collagen tissue was found in patients with urgency. Elbadawi examined the bladder tissue, combined with urinary dynamics research, and the ultrastructure obtained confirmed that the histological changes were consistent with the clinical manifestations, with muscle cell and axon degeneration leading to a decrease in contractility, and the characteristic of urinary dysfunction is the instability of bladder detrusor function related to the dysfunction pattern and changes in ultrastructural muscle structure.
4. In recent years, the changes in the striated sphincter of the elderly bladder have accelerated cell apoptosis and programmed cell death, which are related to the reduction of muscle cells and may be a possible cause of urinary incontinence in elderly women.
5. The maintenance of urination in women relies not only on the urinary tract muscle tissue but also on the support of the pelvic floor. The pelvic floor muscles related to the female urinary tract are generally similar to those in men, with the urogenital diaphragm much thinner than in men. In addition to the urethra passing through it, the vagina also passes through the urogenital diaphragm. The free margin below the urogenital diaphragm has the superficial transverse perineal muscle, which originates from the ischial tuberosity and terminates at the central tendon. The ischiocavernosus muscle originates from the ischial tuberosity and terminates at the clitoris. The bulbocavernosus muscle originates from the central tendon, separates on either side of the vagina, passes through the vaginal orifice and urethra, and terminates at the clitoris. The pubococcygeus muscle originates from the lateral wall of the urethra and vagina, these muscles have a supporting effect on the pelvic floor and also play a role in suspending the urethra. The damage to these muscles can shorten the length of the urethra, reduce urethral resistance, and this is one of the reasons for stress urinary incontinence in elderly women.
6. Causes of stress urinary incontinence:
(1) Pregnancy and vaginal delivery are the main causes of stress urinary incontinence. During the process of pregnancy and delivery, excessive compression of the pelvic floor muscles by the presenting part of the fetus, the use of vacuum extraction and breech delivery by vaginal surgery, and increased abdominal pressure after delivery can all cause relaxation of the pelvic floor tissues. The multivariate regression analysis of a case-control study group by Van found that stress urinary incontinence is not related to the second stage of labor of the first child, but is significantly related to the use of forceps (Van, 2001). Persson found that the occurrence of stress urinary incontinence is significantly related to the age of first delivery, the number of deliveries, the birth weight of the fetus, and perineal anesthesia.
(2) Urethra and vagina surgery The repair of the anterior and posterior walls of the vagina, radical hysterectomy for cervical cancer, resection of urethral diverticula, and other surgeries can destroy the normal anatomical support of the urethra and bladder.
(3) Dysfunction Congenital insufficient support of bladder and urethra surrounding tissues or incomplete neural支配, is the pathogenic cause of young women and nulliparous women. Postmenopausal women due to the decrease of estrogen, while causing the submucosal veins of the urethra and bladder triangle to become thinner, blood supply is reduced and mucosal epithelium degenerates, the superficial epithelial tissue of the urethra and bladder becomes loose, the urethra and surrounding pelvic floor muscles atrophy, and thus urinary incontinence. Salinas also found that although the menopausal state is related to the occurrence of stress urinary incontinence, the risk of occurrence does not increase with age, and the risk of stress urinary incontinence after 52 years old disappears. The onset before menopause is often due to malnutrition, physical weakness, leading to atrophy of the muscle and fascia of the urethra and bladder neck, and urinary incontinence.
(4) Pelvic mass When there is a large mass in the pelvic cavity, such as uterine fibroids, ovarian cysts, it can increase abdominal pressure, lower the position of the bladder and urethra junction, and cause urinary incontinence.
(5) Body weight Many literature reports indicate that the occurrence of stress urinary incontinence is related to the increase of the patient's body mass index (BWI).
(6) The symptoms of stress urinary incontinence in the second half of the menstrual period are more obvious in patients with cyclic stress urinary incontinence, which may be related to the relaxation of the urethra caused by progesterone.
2. Pathogenesis
1. General pathogenesis
(1) Characteristics of the female pelvis: The anterior part of the female pelvic outlet is wide, and the pelvic floor muscles are relatively flat, unlike males, which are not inclined. Therefore, the support for the organs in the anterior pelvis and the support are weaker than males, and the external urethral sphincter is not as strong as males. When these supporting tissues are damaged, the bladder bottom can droop, causing the upper urethra to descend into the peritoneal cavity. Therefore, stress urinary incontinence is more common in elderly women.
(2) Decreased urethral resistance: The urethra can prevent the outward flow of urine, which is related to the length and tension of the urethra. If the urethra is shorter than 3 cm, it cannot prevent the outward flow of urine. The higher the tension of the urethral wall, the greater the urethral resistance. The length of the urethra is proportional to the tension of the urethral wall and inversely proportional to the diameter of the urethral lumen. The Laplace law can express P = T/r (P - urethral wall tension, T - urethral length, r - urethral diameter).
(3) Under normal circumstances, due to the contraction of the anal muscle, the external urethral sphincter, and the pelvic floor muscles, the urethra elongates, the lumen becomes finer, and the tension increases significantly, preventing the urine in the bladder from flowing out due to increased pressure because the urethra has a certain length and tension. The urine can reach the proximal 1/3 of the urethra at most under the influence of abdominal pressure and then returns to the bladder. Urinary incontinence occurs due to dysfunction of the sphincter system, damage to the above muscles, or decreased tension of the smooth muscle. The muscle contraction force is not enough to elongate the urethra. When abdominal pressure increases, the urethral resistance is insufficient, that is, the urethral pressure is less than the bladder pressure. As a result, the urine does not flow back into the bladder as normally after entering the urethra, and thus it is involuntarily discharged.
(3) Dysfunction of the surrounding supporting tissues of the urethra: Under normal circumstances, the bladder urethra junction during the storage phase is above the middle third of the pubic symphysis, the posterior angle of the bladder urethra is 90° to 100°, and the anterior tilt angle of the urethra is 30° to 45°. The position and angle change little with changes in body position and increased abdominal pressure, making the bladder neck and the proximal urethra become intra-abdominal organs. When abdominal pressure increases and bladder pressure increases, this part of the urethra also receives the same pressure effect, known as the pressure transmission effect. It makes the bladder neck and urethra flat instead of funnel-shaped, and the surrounding supporting tissues of the female urethra play a very important role in urine control. The relaxed and prolapsed pelvic floor and urogenital diaphragm are not conducive to the function of the external urethral sphincter. During stress urinary incontinence, the posterior angle of the bladder urethra disappears, and the tilt angle of the urethra increases. Congenital pelvic floor weakness, multiple childbirth, insufficient estrogen, hysterectomy, pelvic surgery, and trauma can all weaken the surrounding supporting tissues of the urethra and be replaced by fat and other connective tissues. The result is:
① The bladder neck and urethra descend, and the proximal urethra shortens.
② Relaxation of the bladder neck and the proximal urethra.
③ When abdominal pressure increases, the closing force of the bladder neck and the proximal urethra is insufficient, and the bladder and the proximal urethra are opened due to the sudden increase in bladder pressure.
④ Decreased closing ability of the external urethral sphincter, if the bladder pressure is sufficient to overcome the pressure of the insufficiently closed urethral segment of the external urethral sphincter, stress urinary incontinence will occur.
(4) Atrophy of urethral mucosa: The soft and皱褶的urethral mucosa can seal the urethral space left after the contraction of the sphincter, preventing urinary incontinence. The urethral mucosal pad plays a relatively important role in female urine control. Before the age of 45, the urethral mucosa and its submucosal tissues and blood vessels are rich, and with the decrease in estrogen levels, the above tissues atrophy, the sealing effect of the urethral mucosal pad decreases, and urinary incontinence is more likely to occur.
2. Pathogenesis of Stress Urinary Incontinence Stress urinary incontinence is classified into high mobility of the bladder neck type and urethral sphincter dysfunction type. The former accounts for more than 90%, and the latter for less than 10%. The pathogenesis of stress urinary incontinence is not yet clear. No hypothesis has been widely accepted, but possible mechanisms include the following:
(1) Decreased urethral resistance: To maintain an effective urinary control mechanism, two factors are required: complete urethral internal structure and sufficient anatomical support. The integrity of the urethral internal structure depends on the resistance produced by the combination of the urethral mucosa and the urethral closure pressure. The combination of the urethral mucosa is formed by mucosal folds, surface tension of secretions, and submucosal venous plexus, and the combination can prevent leakage. The urethral closure pressure comes from the tension of the submucosal blood vessels and muscles. An increased urethral closure pressure results in greater resistance and can control urination. The relaxation and injury of the pelvic floor tissues lead to reduced urethral resistance. Some studies have found that the nerve-muscle conduction disorder cannot reflexively cause an increase in urethral pressure when the intra-abdominal pressure increases. This type of stress urinary incontinence is characterized by urethral sphincter dysfunction.
(2) The pressure relationship between the urethra and bladder: In those with good urinary control mechanisms, the pressure of the proximal urethra is equal to or higher than the intravesical pressure. When the intra-abdominal pressure increases, due to the average transmission of intra-abdominal pressure to the bladder and 2/3 of the proximal urethra (located in the abdominal cavity), the urethral pressure is still maintained equal to or higher than the intravesical pressure, so urinary incontinence does not occur. Conversely, due to the relaxation of the pelvic floor in patients with stress urinary incontinence, 2/3 of the proximal urethra moves outside the abdominal cavity, at rest the urethral pressure is reduced (still higher than the intravesical pressure), but when the intra-abdominal pressure increases, the pressure can only be transmitted to the bladder and cannot be transmitted to the urethra, so the urethral resistance is not enough to resist the pressure of the bladder, leading to urinary leakage. This explains the pathogenesis of the high mobility of the bladder neck in stress urinary incontinence.
(3) The anatomical relationship between the urethra and bladder: The posterior angle of the normal urethra with the bladder bottom should be 90° to 100°, the axis of the upper urethra is perpendicular to the vertical line of standing, and the urethral inclination angle is about 30°. In patients with stress urinary incontinence, due to the relaxation of the pelvic floor tissues, the bladder bottom moves downward and backward, gradually making the posterior angle of the urethra and bladder disappear and the urethra shorten. This change is like the initial stage of urination, once the intra-abdominal pressure increases, it can induce involuntary urination. In addition to the disappearance of the posterior angle of the urethra and bladder, the urethral axis also rotates, making it increase from the normal 30° to more than 90°, as shown in Figure 1. This also explains the pathogenesis of the high mobility of the bladder neck in stress urinary incontinence from one side.
(4) Petros elaborated on the pathogenesis of stress urinary incontinence from the hypothesis of the normal urethra and bladder neck closure mechanism: The closure of the urethra is caused by the contraction of the anterior part of the pubococcygeus muscle to form what is called a ' hammock '. The formation of the ' hammock ' is transmitted by the posterior part of the vagina behind the pubourethral ligament. The closure of the bladder neck, known as 'knotting', is mediated by the posterior part of the vagina behind the pubourethra, and is completed by the common contraction of the 'lifting support structure'. The 'lifting support structure' refers to the transverse muscles of the rectum and the longitudinal muscles around the anus. The measurement of the vaginal fornix muscle electrogram confirmed this hypothesis. In women without urinary incontinence, the contraction of the 'lifting support structure' makes the vagina reach the X point, the contraction of the pubococcygeus muscle pulls the vagina forward to form a ' hammock ' and close the urethral cavity. If there is vaginal wall relaxation, the contraction of the pubococcygeus muscle exceeds the fixed distance and cannot reach the transition point Ⅺ, then the urethra cannot be closed and urinary incontinence occurs.