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Biomedical subjects

P E Petros

Publications and source records attributed to P E Petros.

At least 19 recordsLinked to original sources
PubMed2006

A pinch elastometer for soft tissue.

A prototype compression elastometer suited to the characterisation of soft tissue is analysed and tested by application to various elastomers. The test material is pinched between two rigid cylinders and the compression force and displacement interpreted to yield a measure of "effective" stiffness or to calibrate a simple non-linear-elastic material model (Neo-Hookean). This deformation suits the testing of bulk soft tissue since it effectively isolates the test material from boundary conditions such as other soft tissue, ligaments and bones. These can be highly variable in the body and can affect results greatly when employing other types of tests to determine the elastic nature of tissue. A simple linear-material analysis, based on established solutions to two-dimensional problems, is extended to take into account various geometrical complexities. This analysis permits immediate inversion of the readings from the device to yield the elastic properties of the material, without the need for complex numerical analysis. Finite element analysis is also employed to determine the range of reliable application of the linear-elastic model. In particular, this analysis permits the extension of the linear-elastic analysis to include simple forms of non-linear-material behaviour. The method is demonstrated using three elastomers having significantly different material properties. A viable range of application of the device is identified in which it yields results with reasonable precision and accuracy. The prototype device was able to measure the effective elastic modulus of the test materials with a maximum error of 13% for three material types (N=25). Repeatability error was less than 7% in all cases. Further refinement of the device and measuring system will reduce this uncertainty.

Biomechanical Phenomena↗
PubMed2001

Vault prolapse II: Restoration of dynamic vaginal supports by infracoccygeal sacropexy, an axial day-case vaginal procedure.

Our objective was to present and critically analyze the first 75 infracoccygeal sacropexy (ICS) operations for cure of vault prolapse. Level 1 reconstruction was achieved by the insertion of a tension-free vaginal tape (nylon) via the ischiorectal fossa into a transversely incised posterior vaginal fornix. Level 2 defects were repaired by cutting a central 'bridge' in the posterior vaginal wall and suturing the lateral flaps to the bridge. Level 3 repair reconstituted the perineal body. Postoperative pain was minimized by avoiding excessive tightening of tissues and avoiding surgery on the distal 1 cm of the vagina. Total operating time varied between 30 and 60 minutes. Mean blood loss was 120 ml. All patients were discharged within 24 hours of surgery, with minimal pain and without indwelling catheters. Almost all returned to normal activities within 7-10 days. Of the 75 patients (mean age 54 years), 71 were prospectively followed up between 1 and 4.5 years after surgery. Vault prolapse recurred in 6%. The main complication was tape erosion (5.3%). Infracoccygeal sacropexy is a promising day-case alternative to conventional methods. It has built-in safety, as it avoids pudendal nerves and vessels and surface rectal veins. Areas of future development are identified.

Adult↗
PubMed2001

Vault prolapse I: Dynamic supports of the vagina.

The relative contributions of muscle forces and vaginal suspensory ligaments to the anatomical support of the vagina have been long disputed. The aim of this study was to gain further insights into the role of striated muscle forces. Fifty consecutive patients presenting to a pelvic floor clinic were tested with perineal ultrasound, lateral X-rays at rest and on straining, 10 ml of radio-opaque dye having been injected into bladder, vagina, rectum and, in 12 patients, into the levator plate also. The relevance of muscle forces to the three anatomical levels of support, the cardinal/uterosacral ligament complex (level 1), the rectovaginal fascia (level 2) and the perineal body (level 3), was analyzed. Biopsies of the suspensory ligaments were performed per vaginam. During effort, the upper part of the vagina was stretched backwards and downwards against the perineal body. Compression of level 2 on standing lateral X-ray appeared to be related to the angle of the upper vagina to the horizontal at rest. In 23 patients in whom the angle was 45 degrees or more to the horizontal, only 2 demonstrated significant angulation of the upper vagina and therefore compression of level 2 on straining. In contast, all 27 patients with an angle less than 45 degrees to the horizontal demonstrated both vaginal angulation and compression. Histology demonstrated smooth muscle and nerves in the suspensory ligaments, indicating an active contractile role for these structures. Analysis of the directional forces suggests that inability ot angulate the vagina sufficiently may predispose to herniations of the walls of the vagina owing to the twin influences of gravity and downward muscle forces exerted by the levator muscles.

Adult↗
PubMed1998

The pubourethral ligaments--an anatomical and histological study in the live patient.

The aim of the study was to analyze the structure, relations and insertions of the pubourethral ligament in the living female. Thirty-five women, mean age 44 years, were studied. The intravaginal slingplasty (IVS) procedure, as performed via two paraurethral incisions, allowed immediate access to the structures in this area, the urethra, vaginal hammock, pubourethral ligaments and anterior portion of the pubococcygeus muscle. Histological biopsies were performed from the structures identified as ligaments. The pubourethral ligament descends like a fan from the lower part of the pubic bone. It consists of vaginal and urethral parts, joined together by thin fibrous threads, giving the appearance of a continuous sheet of amorphous connective tissue. Each part generally varies between 5 and 7 mm in width and 3-4 mm in thickness. The urethral part is approximately 2 cm long and inserts into the midpart of the urethra. The vaginal part is approximately 3-4 cm long. It inserts into the vaginal hammock posterolaterally, approximately 1 cm short of the bladder neck. Histologically the ligaments consist of smooth muscle, elastin, collagen, nerves and, blood vessels. The dissections confirm that the pubourethral ligaments are strong finite structures. Allowing for differences between cadavers and live patients, relationships and insertions are much as described by Robert Zacharin.

Adolescent↗
PubMed1998

Symptoms of defective emptying and raised residual urine may arise from ligamentous laxity in the posterior vaginal fornix.

OBJECTIVES: To prospectively test the hypothesis that laxity in the posterior ligaments of the vagina may cause raised residual urine and abnormal emptying symptoms. METHODS: Eighteen patients, 16 multiparous, and 2 nulliparous, were referred with symptoms of abnormal bladder emptying. All were assessed with standard cystometry and standing resting and straining lateral X-ray films, with the bladder containing a Foley balloon catheter containing 10 ml of radio-opaque dye. Three patients were also assessed with videocystourethrograms, and these were compared to 4 normal controls. A posterior fornix repair was performed. A full thickness horizontal vaginal incision was made using a scalpel. The incision was stretched antero-posteriorly, and the utero-sacral and cardinal ligaments tightened by suturing them side to side. RESULTS: Specific symptoms of defective opening were reduced from a total of 43 pre-operatively to 9 post-operatively. Mean residual urine was reduced from 98.7 to 31.7 ml (p < OR = 0.028). Peak flow increased from 29.7 to 34.2 ml/s, p < OR = 0.08. Mean flow pre-operative was 8.18 ml/s, and post-operative flow 8.6 ml/s (p < OR = 0.88). Mean emptying time decreased from 65.3 to 60.4 s. CONCLUSIONS: Reference to radiographs in normal patients demonstrates that bladder funnelling is associated with a powerful downward force transmitted to the coccyx via the utero-sacral ligaments. Correction of laxity in the utero-sacral ligaments, the effective insertion points of the downward force, improved bladder emptying. This appears to sustain the hypothesis that abnormal bladder emptying in the female may be at least partly caused by ineffectiveness of the opening muscles, because of laxity in their insertion points.

Adult↗
PubMed1997

Role of the pelvic floor in bladder neck opening and closure I: muscle forces.

The aim of the study was to identify the striated muscle forces hypothesized to assist bladder neck opening and closure in females. Cadaveric dissection was used to identify the levator plate (LP), the anterior portion of pubococcygeus muscle (PCM), the longitudinal muscle of the anus (LMA), and their relation to the bladder, vagina and rectum. X-ray video recordings were made during coughing, straining, squeezing and micturition in a group of 20 incontinent patients and 4 controls, along with surface EMG, urethral pressure and digital palpation studies. During effort, urethral closure appeared to be activated by a forward muscle force corresponding to PCM, and bladder neck closure by backward muscle forces corresponding to LP and LMA. During micturition the PCM force appeared to relax, allowing LP and LMA to pull open the outflow tract. The data appear to support the hypothesis of specific directional muscle forces stretching the vagina to assist bladder neck opening and closure.

Adult↗
PubMed1997

New ambulatory surgical methods using an anatomical classification of urinary dysfunction improve stress, urge and abnormal emptying.

The aim of the study was to introduce an anatomical classification for the management of urinary dysfunction based on the Integral Theory, a new connective tissue theory for female incontinence. Eighty-five unselected patients, aged 27-83 years, 12 with pure stress symptoms and 73 with mixed incontinence symptoms, were classified as having laxity in the anterior, middle or posterior zones of the vagina, using specific symptoms, signs and urodynamic parameters summarized in a pictorial algorithm. Special ambulatory surgical techniques, which included the creation of neoligaments, repaired specific connective tissue defects in the anterior (intravaginal slingplasty (IVS), n = 85), middle (cystocele repair, n = 6), or posterior zones (uterine prolapse repair, n = 31, or infracoccygeal sacropexy, n = 33). Almost all patients were discharged within 24 hours of surgery, without postoperative catheterization, returning to fairly normal activities within 7-14 days. At (mean) 21-month follow-up cure rates were: stress incontinence 88% (n = 85), frequency 85% (n = 42), nocturia 80% (n = 30), urge incontinence 86% (n = 74), emptying symptoms 50% (n = 65). Mean objective urine loss (cough stress test) was reduced from 8.9 g preoperatively to 0.3 g postoperatively, and mean residual urine >50 ml from 110 ml to 63 ml, P = <0.02. Pre- and postoperative urodynamics indicated that detrusor instability was not associated with surgical failure. Two new directions, based on the Integral Theory, are presented for the management of female urinary dysfunction, an anatomical classification which delineates three zones of vaginal damage, and a series of ambulatory surgical operations which repair these defects. The operations are fairly simple, safe, effective and easily learnt by any practising gynecologist.

Adult↗
PubMed1997

On the flow through the human female urethra.

The flow characteristic for a human female urethra is determined by direct measurement of flow rate and pressure difference data. The measurements are made on a full-scale physical model of a urethra in its open state, which was created using dimensional information taken from video cystograms. The measured data therefore include viscous dissipation effects associated with developing flow, changes in cross-sectional area and changes in flow direction. These effects are often ignored in mathematical models of this system. The data may therefore assist in the development and testing of more realistic models for urine flow. The measured characteristic is compared with a mathematical model of the flow based on a straight tube of uniform diameter carrying fully developed turbulent flow. When the diameter of the model tube is chosen to be equal to the distal diameter of the urethra, it is observed that the predicted flow characteristic provides a good first approximation to the measured characteristic, despite the substantial differences in geometry and flow regime between the mathematical model and the actual system.

Female↗
PubMed1995

Urethral pressure increase on effort originates from within the urethra, and continence from musculovaginal closure.

The aim of the study was to determine the contribution of intra-abdominal pressure transmission to urinary continence in the female. Five patients with genuine stress incontinence (GSI) were studied. Pressure transmission was measured in equivalent positions inside and outside the urethra and bladder during the Intravaginal Slingplasty procedure, a surgical operation used for treatment of urinary incontinence, and performed under local anaesthesia. A 6 mm diameter channel was created alongside the urethra. Two separate microtransducer catheters appropriately marked for length were inserted, one inside the urethra, and the other inside the described channel. With the vaginal hammock intact, an average of 10 simultaneous pressure measurements were made intraoperatively in response to coughing and straining in equivalent positions inside the urethra, and directly outside. Significantly higher pressure readings were found inside the urethra (P = 0.0025), indicating that an active component within the urethra may have created this pressure rise. After opening out two suburethral vaginal flaps, large quantities of urine were lost on coughing in all patients. Continence was achieved on tightening the suburethral vagina, indicating that an adequately tight vaginal hammock is a critical element in the continence process. The findings of this study question intraabdominal pressure as a mechanism contributing to continence, but support an alternative mechanism, musculovaginal closure of the urethra.

Aged↗
PubMed1993

Bladder instability in women: a premature activation of the micturition reflex.

Urethrocystometry was performed during a provocative handwashing test in 163 patients, 115 of whom had a prior history of urge incontinence. Almost invariably, a rise in detrusor pressure, when present, followed a fall in urethral pressure, and both were preceded by urge symptoms. This pattern appears to conform to the concept of "urethral instability", "detrusor instability" and urge incontinence being different manifestations of a prematurely activated micturition reflex.

Adult↗
PubMed1993

Natural volume handwashing urethrocystometry: a physiological technique for the objective diagnosis of the unstable detrusor.

A group of 163 patients attending with a naturally full bladder had urethrocystometric assessment during provocation with a handwashing test. The results were compared with those from a similar group of 169 patients who were subjected to a handwashing test following the infusion of 500 ml of saline with fast-fill cystometry. The latter group was found to have an unacceptably high number of false-positive results. Also, the results appear to indicate that urine loss due to uncontrolled detrusor contraction may be mainly due to premature activation of the micturition reflex. A fall in the intraurethral pressure was found in 79% and a rise in detrusor pressure in 49% of the patients presenting with a prior history of an unstable bladder. Natural urethrocystometry appears to be a useful and informative technique for objectively assessing patients with a prior history of bladder instability.

False Positive Reactions↗
PubMed1993

Tests for 'detrusor instability' in women. These mainly measure the urethral resistance created by pelvic floor contraction acting against a premature activation of the micturition reflex.

The principal aim of this study was to analyse the simultaneous pressure readings derived from bladder and urethra during a handwashing test. A total of 163 patients with urinary incontinence were studied. It was demonstrated that contraction of the pelvic floor stretches the vagina. In many patients, this appeared to inhibit the micturition reflex, possibly by supporting the nerve endings at bladder neck, thereby inhibiting their premature activation. There was also evidence that this stretching activated reflex contraction of the urethra, the vagina-urethral (coital) reflex, thereby increasing the urethral resistance. On further analysis, it was concluded that urodynamic testing does not detect 'detrusor instability' per se. It detects the urethra's attempts at closure.

Adult↗