A system for measurements of micturition urethral cross-sectional areas and pressures

What Is the Future of Impedance Planimetry in Gastroenterology?

The gastrointestinal (GI) tract is efficient in transporting ingested material to the site of delivery in healthy subjects. A fine balance exists between peristaltic forces, the mixing and delivery of the contents, and sensory signaling. This fine balance is easily disturbed by diseases. It is mandatory to understand the pathophysiology to enhance our understanding of GI disorders. The inaccessibility and complex nervous innervation, geometry and mechanical function of the GI tract make mechanosensory evaluation difficult. Impedance planimetry is a distension technology that assesses luminal geometry, mechanical properties including muscle dynamics, and processing of nociceptive signals from the GI tract. Since standardized models do not exist for GI muscle function in vivo, models, concepts, and terminology must be borrowed from other medical fields such as cardiac mechanophysiology. The review highlights the impedance planimetric technology, muscle dynamics assessment, and 3 applied technologies of impedance planimetry. These technologies are the multimodal probes that assesses sensory function, the functional luminal imaging probe that dynamically measures the geometry of the lumen it distends, and Fecobionics that is a simulated feces providing high-resolution measurements during defecation. The advanced muscle analysis and 3 applied technologies can enhance the quality of future interdisciplinary research for gaining more knowledge about mechanical function, sensory-motor disorders, and symptoms. This is a step in the direction of individualized treatment for GI disorders based on diagnostic subtyping. There seems to be no better alternatives to impedance planimetry, but only the functional luminal imaging probe is currently commercially available. Wider use depends on commercialization of the multimodal probe and Fecobionics.

A new distensibility technique to measure sphincter of Oddi function

BACKGROUND

Evaluation of the biliary tract is important in physiological, pathophysiological, and clinical studies. Although the sphincter of Oddi (SO) can be evaluated with manometry, this technique has several limitations. This may explain the difficulties in identifying pathophysiological mechanisms for dysfunction of the SO and in identifying patients who may benefit from certain therapies. To encompass problems with manometry, methods such as the functional lumen imaging probe (FLIP) technique have been developed to study GI sphincters. This study set about miniaturising the FLIP probe and validating it for measurements in the SO. In order to get a better physiological understanding of the SO the aims were to show the sphincter profile in vivo and motility patterns of SO in pilot studies using volunteers that were experiencing biliary type pain but had normal SO manometry.

METHODS

The SO probe was constructed to measure eight cross-sectional areas (CSA) along a length of 25 mm inside a saline-filled bag. To validate the technique for profiling the SO, six perspex cylinders with different CSAs were measured nine times to assess reproducibility and accuracy.

KEY RESULTS

Reproducibility and accuracy for these measurements were good. The probe performed well in bench tests and was therefore tested in four humans. The data indicated that it was possible to make distensions in the human SO and that a geometric sphincter profile could be obtained.

CONCLUSIONS & INFERENCES

The probe will in future studies be tested for diagnostic purposes related to sphincter of Oddi diseases.

A new method for combined isometric and isobaric pharmacodynamic studies on porcine coronary arteries

1. The principal aim of the present study was to explore the isometric and isobaric capacity of a new intravascular technique, impedance planimetry, in basic pharmacodynamic investigations on porcine isolated epicardial coronary arteries. 2. The balloon-based catheter technique provides simultaneous measurements of luminal cross-sectional area and pressure. Sources of errors that may influence the accuracy of measurements were evaluated in detail. 3. Under isometric conditions, the stretch ratio-tension diagram showed typical developments of resting and active tensions of the smooth muscle when exposed to alternating maximal K+ depolarization and mechanical stretching. The mean (+/- SEM) maximum active tension was 28.43 +/- 1.72 mN/mm, which was reached at a stretch ratio of 1.26 +/- 0.02, corresponding to a resting tension of 10.50 +/- 0.53 mN/mm (n = 7). The concentration-response relationship to K+ at optimal basal tension was characterized by a mean (+/- SEM) pD2 value of 1.67 +/- 0.01 (n = 7). 4. Under isobaric conditions in the pressure range 40-140 mmHg, the method allowed the investigation of active vascular responses to partial K+ depolarization. The maximal active response to 25 mmol/L K+ was found at the transmural pressure of 60 mmHg (n = 7). To obtain full K+ concentration-response curves, a basal tension corresponding to a transmural pressure of 120 mmHg was required. The mean (+/- SEM) pD2 value for the concentration-response relationship to K+ was 1.53 +/- 0.01 (n = 10). 5. The vascular sensitivities to cumulatively added K+ and various agonists, such as acetylcholine, 5-hydroxytryptamine and noradrenaline, obtained from the same vessel segment at the same initial conditions corresponding to 120 mmHg were significantly higher with the isometric than with the isobaric approach. 6. The results of the present study suggest that impedance planimetry could be a useful tool in pharmacological and physiological investigations of medium-sized arteries, both under isometric and isobaric conditions.

Luminal cross-sectional area and tension-strain relation of the porcine bile duct

The bile duct is a distensible tube serving to transport bile from the liver and gallbladder to the duodenum. The purpose of this study was to characterize the luminal cross-sectional area (CSA) and tension-strain properties during distension of the normal isolated porcine common bile duct in vitro. An impedance planimetric system located inside a balloon was used. Eleven porcine bile ducts were examined in two locations, in the hepatic duct and in the common bile duct. The CSAs obtained in the common bile duct were significantly higher than those in the hepatic duct in the pressure range 0-8 kPa (P < 0.001). The circumferential wall tension (T)-strain (epsilon) relations for both locations fitted to the exponential equation T = a.eb. epsilon with determination coefficients of 0.97 +/- 0.01. The a and b constants were not statistically different between the two locations indicating that the elastic properties did not differ. In conclusion, the luminal CSAs were larger in the common bile duct when compared to the hepatic duct and the tension-strain relations did not differ between the two segments of the bile duct.

Regional differences exist in elastic wall properties in the ureter

According to classical mechanical theory, the passive elastic properties of a distensible tube are important for the resistance to flow. The aim was to study luminal dimensions under pressure loading and the tension-strain distribution of the ureter in anaesthetized pigs by means of impedance planimetry. Stepwise inflation of an intraluminal balloon in which the cross-sectional area (CSA) and pressure were measured provided the distension stimulus in the ureteropelvine junction, in the midureter and in the intramural part of the ureter at the ureterovesical junction. The circumferential tension-strain distributions were computed from steady state values of these measurements. The CSA always reached equilibrium within the two-minute distension period. The steady state pressure-CSA curves were nonlinear and differed between the three measuring points (p < 0.001). The most pronounced difference was found between the ureteropelvine junction and the two other measuring points. At the lowest applied pressure of 1 kPa the steady state CSA was 15.4 +/- 1.1, 16.6 +/- 1.1, and 19.9 +/- 19.9 mm2 in the intramural part, middle part and ureteropelvine junction, respectively. At the maximum pressure the figures were 41.9 +/- 2.9, 47.0 +/- 2.7, and 73.1 +/- 8.2 mm2 for the three locations, respectively. The circumferential tension-strain distributions were nonlinear with an exponential-like behaviour. The tension-strain curve obtained from the ureteropelvine junction was translated to the right compared to the curves obtained from the two other measuring points (p < 0.05) indicating that the ureteropelvine junction was more compliant than the two other locations.

Porcine coronary artery pharmacodynamics in vitro evaluated by a new intravascular technique: relation to axial stretch

A new intravascular balloon catheter-based technique, impedance planimetry and the wire-mounted isometric tension technique commonly employed to study vessel pharmacodynamics in vitro, were compared. Porcine left anterior descendent coronary artery reactivity to nifedipine was assessed and the influence of 20% axial stretch was investigated. There were no histological differences between segments where the impedance planimetry balloon had been inflated and untouched segments. EC50 values differed significantly between the three procedures applied: The isometric method (n = 7): 2.54 +/- 0.44.10(-9) M; nonstretched arteries by the impedance planimetric method (n = 7): 1.99 +/- 0.40.10(-8) M; arteries 20% axially stretched (n = 7): 2.00 +/- 1.36.10(-7)M (isometric and nonstretched: p < 0.05; isometric and stretched: p < 0.001; nonstretched and stretched: p < 0.05). Maximal relaxant responses to nifedipine were 91.8 +/- 2.1% (isometric method), 105.1 +/- 2.3% (nonstretched), and 104.9 +/- 7.7% (stretched) (ANOVA, p = 0.11). In stretched arteries, the initial 12-min response to an increased dose of nifedipine was more rapid than the response of nonstretched arteries at a concentration of 1.10(-7) M (p = 0.038) and had a nonsignificant tendency toward a more rapid response at other concentrations. Resting tone could not be demonstrated and time control experiments showed no change in the maximal vessel response to potassium with any of the three methods. A new method in the evaluation of artery pharmacodynamics in vitro was presented. The study demonstrated that axial stretching of an artery has impact on the pharmacodynamic reactivity to nifedipine in porcine coronary arteries. Further studies are needed to evaluate the impact of the method on endothelial function.

Mechanics of porcine coronary arteries ex vivo employing impedance planimetry: a new intravascular technique

Our objective was to evaluate methodological aspects of impedance planimetry, a new balloon catheter-based technique, for the investigation of coronary artery mechanical wall properties. We used a four ring-electrode electrical impedance measuring system that was located inside a balloon. Two of the electrodes were used for excitation and connected to a generator producing a constant alternating current of 250 mA at 5 kHz. The other two electrodes for detection were placed midway between the excitation electrodes. The balloon was distended with electrically conducting fluid through an infusion channel. The vessel cross-sectional area (CSA) was measured according to the field gradient principle by measuring the impedance of the fluid inside the balloon. Impedance planimetry was applied in the three major branches of the coronary arteries of seven extracted porcine hearts to assess luminal CSAs in response to internal pressurization. The biomechanical wall properties were evaluated by computing the strain [(r - r0) x r0(-1), where r is the vessels inner radius computed as (CSA x pi-1)1/2 and r0 is the radius of the vessel at a minimal distension pressure], the tension [(r x dP), where dP is the transmural pressure difference], and the pressure elastic modulus (delta P x r x delta r-1). We found that in vitro testing demonstrated that impedance planimetry was accurate and reproducible. The technique has controllable sources of error. Measurements were performed with consecutively increasing pressures in the range 1-25 kPa (8-188 mmHg, 0.01-0.25 atm). The CSAs increased nonlinearly and were significantly larger in the left anterior descendent coronary artery (LAD) (1 kPa, mean 5.0 mm2; 25 kPa, mean 21.8 mm2) than in both the left circumflex (Cx) (4.5-16.0 mm2) and the right coronary artery (RCA) (2.8-15.6 mm2) (analysis of variance, P < 0.001 for both). The circumferential wall tension-strain relation showed exponential behavior. For a given strain, tension values for LAD were significantly lower than those of Cx (P < 0.01). The pressure elastic modulus-strain relation also was exponential, and values for Cx were significantly lower than values for LAD (P < 0.001) and RCA (P < 0.05). Impedance planimetry was applied to the study of coronary artery biomechanics ex vivo. The LAD had the largest CSA, and the Cx was the least compliant. Methodological aspects of an in vivo introduction of the method require additional evaluation.

Measuring esophageal motility with a new intraluminal impedance device. First clinical results in reflux patients

BACKGROUND

The study was undertaken to determine the validity of intraluminal impedance measuring for the diagnosis of esophageal motility disorders in reflux patients.

METHODS

A new impedance device was used for the detection of esophageal motility patterns in a prospective study with 10 volunteers and 10 patients with reflux esophagitis grade II-III. Perfused manometry was correlated with the impedance tracings. Test meals were saline and curd in three different preparations with liquid to semisolid viscosity.

RESULTS

There was a marked delay in esophageal transport with increasing viscosity of the bolus (p < 0.01). A significant (p < 0.001) delay of the bolus transport in the inflamed esophageal areas was seen in reflux patients. A reduced contractility of the lower esophagus and the lower esophageal sphincter was detected by the impedance procedure in reflux patients, indicating that the pathologic motility patterns in reflux esophagitis are most likely secondary to the tissue inflammation.

CONCLUSION

We conclude that impedance procedures may give additional significant information about bolus transport and esophageal wall movements.

Elastic wall properties and collagen content in the ureter: an experimental study in pigs

We used an impedance planimetric method to look at elastic wall properties of ureter in ten anaesthetized pigs. A balloon was stepwise inflated and deflated in the ureteropelvine junction, in the mid-ureter, and in the intramural part of the ureter at the ureterovesical junction with pressures up to 70 cmH2O, while the pressure and balloon cross-sectional area (Bcsa) were measured simultaneously. The elastic wall parameters were calculated from these measurements. At sacrifice, tissue samples were collected for analysis of collagen content of the ureteral wall. A non-linear clockwise relation (hysteresis loops) between Bcsa and balloon pressure was demonstrated. At maximal inflation of the balloon, the Bcsa, wall tension, and compliance were 35.28 +/- 3.52, 38.44 +/- 3.23, and 61.36 +/- 8.09 mm2, 230.71 +/- 12.82, 242.38 +/- 10.49, and 302.17 +/- 20.03 cmH2O x m, and 0.167 +/- 0.047, 0.124 +/- 0.002, and 0.182 +/- 0.040 mm2 x cmH2O-1 in the intramural part of the ureter, middle part, and ureteropelvine junction, respectively. The collagen content was 0.3249 +/- 0.0077, 0.3301 +/- 0.0066, and 0.3457 +/- 0.0060 mg x mg-1 dry defatted weight in the intramural part, in the middle, and in the ureteropelvine junction, respectively. The collagen content of the ureteropelvine junction was significantly higher than that of the middle of ureter (P < 0.02) and than that of the intramural part (P < 0.05). No significant correlations were found between the elastic parameters at maximal inflation of the balloon and the collagen content (P < 0.10). In conclusion the elastic wall properties were significantly different in the three ureteral segments and the collagen content of the ureteropelvine junction differed from that of the two distal locations. However, no relationship between the wall properties and the collagen content was found.

Biomechanical wall properties of the human rectum. A study with impedance planimetry

Biomechanical properties of the rectal wall were studied in 17 healthy adult volunteers (nine men and eight women). With impedance planimetry it is possible to obtain simultaneous measurements of pressure and rectal cross sectional area (CSA) during balloon inflations. Rectal distensions were done with an intraluminal balloon using specified pressures up to 40 cmH2O above baseline rectal pressure. Balloon inflation elicited a phase of rapid increase in rectal CSA followed by a phase of slow increase until a steady state was reached. Steady state occurred within 67 to 140 seconds with the shortest period at the highest distension pressures. Steady state rectal CSA values had a non-linear relation to increasing distension pressure. Rectal CSA values in women showed a tendency of being slightly higher than male values at all pressure steps with a significant difference at 3 and 5 cm H2O. Biomechanical parameters were calculated from rectal CSA pressure relations. Circumferential wall tension increased in a linear way. Rectal compliance decreased in a non-linear way with no further decline between 30 and 40 cmH2O. The pressure elastic modulus increased steeply until a distension pressure of 35 cmH2O with no further increase to 40 cmH2O. This suggests that rectal tone is reduced as the muscle fails to resist further distension at 35 cmH2O and higher pressures. Impedance planimetry offers new possibilities for investigation of anorectal physiology through the study of segmental biomechanical wall properties of the human rectum.

A technique for measurement of related values of pressure and cross-sectional area in the male urethra

A probe for measurement of related values of cross-sectional area and pressure in the male urethra was constructed. The probe allows induction of variable pressures or fluid volumes in a distensible balloon located in the urethra and simultaneous recording of related values of cross-sectional area and pressure. Cross-sectional area is measured in the range of 11-102 mm2 using the field-gradient principle. Pressure is measured in the range of 0-250 cmH2O using tip transducers. The time constant for cross-sectional area measurement is 0.02 s and that for pressure measurement, 0.007 s. The pressures required to reach the maximal and minimal cross-sectional areas of the balloon are 2.8 and -2.4 cmH2O, respectively. The shape of the probe after its placement in the urethra was studied by transrectal ultrasound in five volunteers. The results showed that the measurement error caused by the slope of the balloon walls or the forced bending of the catheter did not exceed 5%. The method enables a description of the biomechanical properties of the male urethra at rest in terms of estimated pressure at zero cross-sectional area, elastance, and stress-relaxation and at voluntary contraction in terms of work and power as evaluated at well-defined anatomical locations.

Urodynamics in benign prostatic hyperplasia: a survey

Urodynamic investigations have been used in the diagnosis of prostatic obstruction for the last 30 years. The methods have changed, and the emphasis is now more on diagnosing borderline cases and ruling out obstruction than actually demonstrating the obstruction. The philosophy surrounding the clinical management of benign prostatic hyperplasia (BPH) is changing. Three concepts are useful in this context: the presence of actual prostatic enlargement, the symptomatology, and the presence of urodynamic obstruction. These items are not always present together. It is of extreme importance for our understanding of BPH to realize the way these concepts interrelate. The paper stresses the importance of detrusor-related phenomena in the symptomatology and urodynamics.

The four-electrode impedance technique: a method for investigation of compliance in luminal organs

A probe for measurement of related values of cross-sectional area (CA) and pressure has been developed to record characteristics of the walls in luminal organs. The aim of this study was to test the probe in vitro. CA was measured in the range 0.17 to 7.07 cm2 by means of the field gradient principle. Pressure was measured in the range 0 to 20 kPa (150 mmHg) by external transducers. After calibration both the pressure and the CA measuring system did measure the parameters adequately. The CA measuring system was dependent on the temperature and electrolyte concentration of the fluid, but was not affected by the size and form outside the excitation electrodes. The upper frequency limits for recordings of CA and pressure were 15.7 and 0.44 Hz, respectively. These in vitro results indicate that the tube assembly has characteristics sufficient for simultaneous measurement of CA and pressure in sphincter regions. These two variables can be used to describe mechanical wall properties such as compliance, hysteresis and creep.

Rigidity of the resting female urethra. Part I. Static measurements

A new probe was used to examine 16 female volunteers. The probe makes possible recording of related values of induced increasing and decreasing urethral pressures, and cross-sectional area in the resting female urethra. From diagrams showing these relationships urethral rigidity, defined as the change in urethral pressure divided by the change in cross-sectional area, and urethral hysteresis can be calculated. The study demonstrates the quantities and the significance of urethral rigidity and hysteresis during pressure measurements in the urethra.