Understanding the mechanics of the bladder through experiments and theoretical models: Where we started and where we are heading

Abstract

Bladder control problems affect both men and women and range from an overactive bladder, to urinary incontinence, to bladder obstruction and cancer. These disorders affect more than 200 million people worldwide. Loss of bladder function significantly affects the quality of life, both physically and psychologically, and also has a large impact on the healthcare system, i.e., the incurring costs related to diagnosis, treatment and medical/nursing care. Improvements in diagnostic capabilities and disease management are essential to improve patient care and quality of life and reduce the economic burden associated with bladder disorders. This paper summarizes some of the key contributions to understanding the mechanics of the bladder ranging from work conducted in the 1970s through the present time with a focus on material testing and theoretical modeling. Advancements have been made in these areas and a significant contribution to these changes was related to technological improvements.

Stretch‐ and carbachol‐induced ATP release from bladder wall preparations of young and aged mice

“…Thus, ATP release was significantly associated with the tissue elastic modulus, an index of tissue stiffness, with a constant change of strain. The elastic modulus itself is a positive function of strain, when these strains are over ranges near to and above the resting length of the tissue 12 ; these experiments used smaller proportional strain changes (20% of resting length) which reflect changes in the intact bladder during filling. 13 A striking feature of the data is the wide range of elastic modulus values in the cohort of young animals, similar to that observed in aged animals.…”

Pre-clinical Research on Bladder Toxicity After Radiotherapy for Pelvic Cancers: State-of-the Art and Challenges

“…Most of their membrane apical surface (almost 80%) is covered with protein plaque whose precise composition is unclear, but a main component seems to be protein called Uroplakin (9). Together with the glycosaminoglycan (GAG) layer over the urothelium and the tight junctions between umbrella cells, the protein plaque creates the urine-plasma barrier and probably hampers bacterial adherence (9,11). Another function of urothelial cells seems the detection of bladder volumes and strain, through a direct signaling on afferent nerves or indirect communication with interstitial cells (9).…”

“…Laplace's law, assuming spherical shape, incompressible wall and an isotropic homogeneous stretch, accurately describes the bladder mechanics during filling: wall tension, intravesical pressure and bladder size are directly related (8,9). During bladder filling, intravesical pressure is relatively constant, avoiding urine outflow to the upper urinary tract, and bladder is slowly stretched while volume increases (8,9,11,12). A small increase in bladder pressure during filling is caused by a small increase in bladder wall tension, due to the viscoelastic response of the extracellular matrix when collagen fibers, initially folded, begin to stretch (12,13).…”

“…In addition, cellular framework and membrane attachments are provided by other cytoskeletal proteins, such as non-muscle β-and γ -actins, filamin, calponin and intermediate filaments (8,9,11).…”

A non-invasive ultrasound imaging method to measure acute radiation-induced bladder wall thickening in rats

“…The progression of the radiationinduced bladder damage in humans consists of three main steps: an acute phase with recovery usually within a few weeks, a symptom-free period whose duration depends on the radiation dose, and, lastly, a chronic, irreversible late response, in general arising within a year [2][3][4]. The modeling of radiation-induced urinary toxicity represents a complex topic [5,6] which is attracting increasing interest in radiotherapy [7,8].…”