Adult Canines Research Articles

Comparison of concentric needle versus hooked-wire electrodes in the canine larynx

BACKGROUND: The use of a specific electrode type in laryngeal electromyography has not been standardized. Laryngeal electromyography is usually performed with hooked-wire electrodes or concentric needle electrodes. Hooked-wire electrodes have the advantage of allowing laryngeal movement with ease and comfort, whereas the concentric needle electrodes have benefits from a technical aspect and may be advanced, withdrawn, or redirected during attempts to appropriately place the electrode. OBJECTIVES: This study examines whether hooked-wire electrodes permit more stable recordings than standard concentric needle electrodes at rest and after large-scale movements of the larynx and surrounding structures. A histologic comparison of tissue injury resulting from placement and removal of the two electrode types is also made by evaluation of the vocal folds. METHODS: Electrodes were percutaneously placed into the thyroarytenoid muscles of 10 adult canines. Amplitude of electromyographic activity was measured and compared during vagal stimulation before and after large-scale laryngeal movements. Signal consistency over time was examined. Animals were killed and vocal fold injury was graded and compared histologically. RESULTS: Waveform morphology did not consistently differ between electrode types. The variability of electromyographic amplitude was greater for the hooked-wire electrode ( p < 0.05), whereas the mean amplitude measures before and after large-scale laryngeal movements did not differ ( p > 0.05). Inflammatory responses and hematoma formation were also similar. CONCLUSIONS: Waveform morphology of electromyographic signals registered from both electrode types show similar complex action potentials. There is no difference between the hooked-wire electrode and the concentric needle electrode in terms of electrode stability or vocal fold injury in the thyroarytenoid muscle after large-scale laryngeal movements. (Otolaryngol Head Neck Surg 1998;118:655-62.)

Protective Effects of Ischemic Preconditioning on Donor Lung in Canine Lung Transplantation

Myocardial ischemic preconditioning has been found to protect the myocardium. We hypothesized that lung ischemic preconditioning might enhance canine lung preservation and reduce allograft lung dysfunction after transplantation. Ten pairs of adult canines underwent left lung allotransplantation. Five donors were treated with ischemic preconditioning (their left hilus clamped for 10 min and released for 15 min [group IP]), and five donors were not treated with ischemic preconditioning (group C). The donor lungs were flushed with 4 degrees C Euro-Collins solution (ECS) and stored in the same solution for 2 1/2 h, then transplanted to the recipient canines. The animals were observed for 1 to 2 h after transplantation. The lung venous blood of the recipient and donor lung tissue was collected just after thoracotomy and 1 h after reperfusion of the transplanted lung in both groups. The numbers of polymorphonuclear leukocytes (PMNs) in the pulmonary venous blood after reperfusion were significantly higher in group IP than in group C (p<0.05). However, the numbers of PMNs in lung interstitium under microscopy were less in group IP than in group C. The thromboxane B2, malondialdehyde, and mean pulmonary artery pressure contents were significantly lower in group IP than in group C (p<0.05), and the superoxide dismutase and mixed venous oxygen tension values were significantly higher in group IP than in group C (p<0.05). Histologic findings show less damage in group IP than in group C. The protective effects of ischemic preconditioning in conjunction with ECS flush and storage were superior to using ECS alone. The possible mechanisms were that ischemic preconditioning inhibited the accumulation and activation of PMNs in lung tissue and reduced the production of oxygen-free radicals.

The maximum watts factor as a measure of detrusor contractility independent of outlet resistance.

The maximum watts factor (WFmax) is often used to characterize detrusor contractility. It was recently shown that the WFmax may increase in some patients with chronic outlet obstruction. It is, however, unclear whether this increase reflects a dependence of the WFmax on the degree of outlet obstruction or whether it represents a true increase in detrusor contractility secondary to chronic outlet obstruction. Therefore, this study was performed to investigate this issue using a canine model of acute outlet obstruction. Urodynamic studies were performed on adult canines with surgically exposed lower urinary tracts. Pressure transducers were used to measure the intravesical and the distal urethral pressures, whereas an ultrasonic flow meter was used to obtain a simultaneous measure of the urinary flow rate. Detrusor contractions were induced by electrically stimulating the pelvic nerves bilaterally. Varying degrees of outlet obstruction were created using an inflatable sphincter cuff secured around the bladder outlet. The WFmax, the detrusor pressure at voiding terminus (Pdet.clos), and the passive urethral resistance (R) were computed from measured pressure-flow rate data at each degree of outlet obstruction. The WFmax was not significantly correlated to either the sphincter cuff volume (r = 0.025, p = 0.871), the Pdet.clos (r = 0.286, p = 0.073) or the R (r = 0.110, p = 0.509). The WFmax was not significantly different among mild, moderate, and severe degrees of outlet obstruction (p = 0.176). Our results suggest that the WFmax is independent of the degree of acute outlet obstruction (defined in terms of the sphincter cuff volume, Pdet.clos and R). This validates the current practice of using the WFmax to evaluate detrusor function in patients with voiding dysfunction regardless of outlet resistance. Further, since the WFmax is independent of outlet obstruction acutely, it is reasonable that it would also be independent of outlet obstruction under chronic conditions. Our results, therefore, also imply that the increase in the WFmax with chronic outlet obstruction may represent a true increase in detrusor contractility and not a WFmax dependence on outlet resistance.

Inhibition of Wear Debris Mediated Osteolysis in a Canine Total Hip Arthroplasty Model

In this study the efficacy of an oral bisphosphonate therapy to inhibit wear debris mediated bone resorption was evaluated in a canine total hip replacement model. Adult canines were randomized to three groups (n = 8 each) with a right uncemented total hip replacement performed on each animal. Group I (control) received no particulate debris. In Groups II and III, a mixture of 1×109 particles were introduced into the proximal femoral gap intraoperatively. The particle mixture consisted of fabricated ultra high molecular weight polyethylene (mean 2.3 μm, 90% by number), titanium alloy (mean 3.1 μm, 5%), and cobalt chrome alloy (mean 0.8 μm, 5%). Group III canines additionally received oral drug therapy (5 mg once a day, alendronate sodium) which was begun on postoperative Day 7 and continued until the time of sacrifice. Post-operatively, all animals were allowed 24 weeks of full ambulation before euthanasia. Radiographs obtained preoperatively, postoperatively, and at time of sacrifice were evaluated for periprosthetic osteolysis. Interfacial tissues were examined histologically and placed in organ culture and the supernatants were assayed for prostaglandin E2 and interleukin-1. One animal receiving debris (Group II) suffered a periprosthetic fracture and was sacrificed from the study. Radiographically, one of eight Group I (control) and six of seven canines from Group II (debris) had periprosthetic radiolucencies with endosteal scalloping develop. In contrast, only one of eight animals from Group III (debris + alendronate) had periprosthetic radiolucencies develop. Whereas tissues from control animals were mostly fibrous and acellular, tissues from both experimental groups had significant macrophage infiltration. Levels of prostaglandin E2 and interleukin-1 were elevated significantly in periprosthetic tissues from both experimental groups compared with controls. Continuous administration of alendronate effectively inhibited bone lysis for the 24-week duration of the study. This is consistent with the literature indicating that alendronate is incorporated in the mineralizing matrix making it refractory to osteoclastic resorption. This report has significant clinical implications for controlling the most common cause of implant failure.

A New Biologic Membrane in Cardiovascular Surgery

Reconstruction techniques for major vessels and intracardiac defect repair use synthetic grafts or autogenic pericardium. Here, autologous abdominal parietal peritoneum with the overlying posterior rectus sheath as a biologic membrane are evaluated. Twelve adult canines were used. Via a midline subumbilical incision, the parietal peritoneum and overlying posterior rectus sheath were harvested. In the first group of six, the membrane was used to repair the right ventricular infundibulum and perform pulmonary artery annuloplasty. In the second group of six, under cardiopulmonary bypass and moderate hypothermia, the right atrium was opened and a secundum type defect was created. Autopsies performed 90 days after surgery revealed mild intrapericardial adhesions and moderate pericardial reaction over the cardiotomy incisions. The right ventricular outflow tract patch was nonaneurysmal. The interatrial patch was intact without thrombi. Histologic examination revealed intact membrane morphology, fibroblasts, smooth muscle cells, and endothelialization. Proline C14 uptake and autoradiography detected cellular viability of implanted membranes. These findings suggest that the peritoneum with overlying sheath repaired vascular and intracardiac defects and substituted for pericardium. Future studies are needed before clinical use.

Premorbid determinants of left ventricular dysfunction in a novel model of gradually induced pressure overload in the adult canine.

When a pressure overload is placed on the left ventricle, some patients develop relatively modest hypertrophy whereas others develop extensive hypertrophy. Likewise, the occurrence of contractile dysfunction also is variable. The cause of this heterogeneity is not well understood. We recently developed a model of gradual proximal aortic constriction in the adult canine that mimicked the heterogeneity of the hypertrophic response seen in humans. We hypothesized that differences in outcome were related to differences present before banding. Fifteen animals were studied initially. Ten developed left ventricular dysfunction (dys group). Five dogs maintained normal function (nl group). At baseline, the nl group had a lower mean systolic wall stress (96 +/- 9 kdyne/cm2; dys group, 156 +/- 7 kdyne/cm2; P < .0002) and greater relative left ventricular mass (left ventricular weight [g]/body wt [kg], 5.1 +/- 0.36; dys group, 3.9 +/- 0.26; P < .02). On the basis of differences in mean systolic wall stress at baseline, we predicted outcome in the next 28 dogs by using a cutoff of 115 kdyne/cm2. Eighteen of 20 dogs with baseline mean systolic stress > 115 kdyne/cm2 developed dysfunction whereas 6 of 8 dogs with resting stress < or = 115 kdyne/cm2 maintained normal function. We conclude that this canine model mimicked the heterogeneous hypertrophic response seen in humans. In the group that eventually developed dysfunction there was less cardiac mass despite 60% higher wall stress at baseline, suggesting a different set point for regulating myocardial growth in the two groups.

Thermal effects of neutralization therapy and water dilution for acute alkali exposure in canines.

To evaluate the change in temperature of the gastric mucosa and lumen contents when a weak acid or water is used to manage acute alkali exposure. A prospective in-vivo canine model was used in a university-based animal laboratory setting. Eighteen adult canines weighing 20-25 kg were placed under a surgical plane of anesthesia and a laparotomy was performed. A gastrotomy was then made later ligation of the distal esophagus and proximal duodenum. Separate mucosa and lumen temperature probes were placed. Then 25 mL of room-temperature (24-26 degrees C) 50% sodium hydroxide (NaOH) was instilled in the gastric lumen. After 5 minutes, each canine was given treatment. Group 1 (n = 10) was treated with 75 mL of room-temperature orange juice. Group 2 (n = 8) was treated with 75 mL of room-temperature water. Continuous mucosa and lumen temperatures were observed and recorded at baseline and at specified intervals for 35 minutes after the alkali insult. Repeated-measures analysis of variance was used to evaluate the overall temperature profile. Signed-rank tests were used to compare the changes in temperature immediately following neutralization treatment. Significant temperature decreases of 1.1 degrees C and 2.1 degrees C were observed for both mucosa (p = 0.002) and lumen (p < 0.001) temperature, respectively, following neutralization therapy with room-temperature orange juice. In the group treated with room-temperature water, significant temperature decreases of 2.1 degrees C for mucosa (p = 0.01) and 2.4 degrees C for lumen (p = 0.01) were observed. Posttreatment temperatures did not exceed baseline for the entire observation period. Neutralization therapy with room-temperature orange juice or water dilution for acute gastric injuries by liquid alkali does not cause a rise in mucosal or intraluminal temperatures in an in-vivo canine model.

Experimental Study of Extraaortic Balloon Counterpulsation as a Bridge to Other Mechanical Assists

A special extraaortic balloon was developed that can be placed around the ascending aorta. This balloon can easily support the heart temporarily in a median sternotomy field, especially in cases in which it is difficult to use intraaortic balloon pumping because of peripheral arterial disease. The goal of this study was to judge the applicability of this extraaortic balloon counterpulsation. An extraaortic balloon was placed around the ascending aorta of eight adult canines. Two heart failure models were used in this study: group A-moderate heart failure; group B-severe heart failure. In group A, the aortic systolic pressure was significantly reduced (9.3%, p < 0.01), but in group B, there was no significant change. In group A, there was a significant increase in cardiac output (12.0%, p < 0.01), but in group B, there was no significant change. The endocardial viability ratio in both groups significantly increased (group A: 11.3%, p < 0.01; group B: 11.9%, p < 0.05). An extraaortic balloon around the ascending aorta is easily applicable through a median sternotomy, and can be used as a bridge to more powerful mechanical assists when intraaortic balloon pumping cannot be used.

Dosimetry using the right angle firing neodymium: YAG laser fiber for treating canine prostate

For assessment of the dosimetric and optimal efficacy of Visual Laser Ablation of the Prostate (VLAP), depth, surface area and volume of thermal penetration of the prostate were determined in 14 adult canines. All prostates were irradiated using the right angle laser fiber (Urolase, Bard, USA) with neodymlum (Nd): YAG laser application. In Group 1 animals, treatment was conducted at 40 watts for 60 seconds (2400 jules) and in Group 2, at 60 watts for 60 seconds (3600 jules). Each prostate was dissected out and examined macro and microscopically at 3 days and 1, 2, 4, 8 and 12 weeks after surgery. Mean depth of prostatic penetration, surface area and volume of prostatic tissue ablation in each treatment were 4.75 +/- 1.25 mm, 4.13 +/- 1.13 cm2, 3.39 +/- 1.58 cm3 in Group 1 and 5.75 +/- 1.25 mm, 4.80 +/- 1.95 cm2, 4.36 +/- 1.99 cm3 in Group 2, respectively. Histologically, coagulation necrosis and chronic inflammatory changes of the prostatic stroma became evident in 1 to 4 weeks, and reepithelization in the cavity could be observed at 8 to 12 weeks following the treatment. From these result, it would appear that photoirradiation of canine prostate by the right angle laser fiber brings about cavity formation and that more effective dosimetry with maximum penetration in the canine prostate is possible at 60 watts for 60 seconds of pulse duration. Based on these findings, Nd:YAG laser therapy should find a broader scope of clinical application in the management of benign prostatic hyperplasia.

An Improved Technique for Measuring In Vivo Intervertebral Motion in the Canine

An experimental animal study using an established technique for measuring in vivo motion in canines was designed to improve measurement techniques and to eliminate the effects of the instrument mounting technique on the tissue and subsequently on the motion being measured. The purpose of this study was to improve a technique for measuring in vivo intervertebral motion in canines, so that the measuring technique did not affect the motion being measured. Biplanar radiography has been used to measure in vivo intervertebral motion, but involves radiation exposure and expensive equipment. Electromechanical devices have been used more recently but have had significant effects on the motion over extended time periods. Intervertebral motion was measured using an instrumented spatial linkage in eight adult canines divided into two groups that differed regarding the method of "mounting pin" placement. Group I had open surgical placement of the pins and Group II had pins placed into the spinous processes. After pin implantation, the instrumented spatial linkage was attached and motion data were recorded during walking. This testing sequence was repeated 3 weeks later. Animals were killed and intervertebral and facet motion were calculated from the experimental data and compared statistically. Facet motion decreased 1 to 3 weeks after pin implantation for animals of group I (3.4 +/- 0.2 mm to 1.1 +/- 0.3 mm), whereas the facet excursion of animals in Group II showed no change (3.0 +/- 0.2 mm and 3.1 +/- 0.3 mm). A new method of measuring in vivo intervertebral motion in canines has been developed and shown to have no significant affect on the segment mechanics.

An Improved Technique for Measuring In Vivo Intervertebral Motion in the Canine

Study Design An experimental animal study using an established technique for measuring in vivo motion in canines was designed to improve measurement techniques and to eliminate the effects of the instrument mounting technique on the tissue and subsequently on the motion being measured. Objectives The purpose of this study was to improve a technique for measuring in vivo intervertebral motion in canines, so that the measuring technique did not affect the motion being measured. Summary of Background Data Biplanar radiography has been used to measure in vivo intervertebral motion, but involves radiation exposure and expensive equipment. Electromechanical devices have been used more recently but have had significant effects on the motion over extended time periods. Methods Intervertebral motion was measured using an instrumented spatial linkage in eight adult canines divided into two groups that differed regarding the method of “mounting pin” placement. Group I had open surgical placement of the pins and Group II had pins placed into the spinous processes. After pin implantation, the instrumented spatial linkage was attached and motion data were recorded during walking. This testing sequence was repeated 3 weeks later. Animals were killed and intervertabral and facet motion were calculated from the experimental data and compared statistically. Results Facet motion decreased 1 to 3 weeks after pin implantation for animals of group 1 (3.4 ± 0.2 mm to 1.1 ± 0.3 mm), whereas the facet excursion of animals in Group II showed no change (3.0 ± 0.2 mm and 3.1 ± 0.3 mm). Conclusions A new method of measuring in vivo intervertebral motion in canines has been developed and shown to have no significant affect on the segment mechanics.

The ability of recombinant tissue plasminogen activator to inhibit post-radical pelvic surgery adhesions in the dog model

We investigated the ability of recombinant tissue plasminogen activator to inhibit post-radical pelvic surgery adhesions formation in 40 adult female canines undergoing radical hysterectomy, bilateral salpingo-oophorectomy, omentectomy, resection of pelvic and abdominal peritoneum, and placement of a peritoneal access catheter. Immediately after operation one half of animals received either recombinant tissue plasminogen activator, 1 mg/kg weight, diluted in 9 ml sterile normal saline solution per milligram of the plasminogen activator or 10 ml vehicle per kilogram intraperitoneally every 12 hours for a total of 10 doses. A single control animal died postoperatively of complications of intestinal obstruction. No bleeding abnormalities were noted in either group of animals. Four weeks after surgery, animals underwent reexploration and adhesions were quantified. Adhesion scores for the animals treated with recombinant tissue plasminogen activator (n = 20; mean score, 1.29 +/- 1.97; median, 0.6) were significantly less than for control animals (n = 19; mean score, 4.64 +/- 3.71; median, 3.86; p = 0.03). Whereas recombinant tissue plasminogen activator appears to effectively prevent post-radical pelvic surgery adhesions in this canine model, phase I and II trials in humans will be required to determine safety and clinical benefit.

Elevated Intravesical Pressure Causes Arterial Hypoperfusion in Canine Colocystoplasty: A Fluorometric Assessment

Since 1988 there have been 15 reported cases of late, spontaneously ruptured intestinal cystoplasties at bowel sites remote from the anastomosis. Ischemic necrosis has been suggested as a possible etiology. We examined this hypothesis by quantifying the uptake of intravascular fluorescein in the augmented bowel of adult mongrel canines. There was a statistically significant decrease in fluorescein uptake at high intravesical pressures, which appeared to be most pronounced at the antimesenteric border. This laboratory study supports a recent clinical report of histological changes pathognomonic for chronic ischemia in the augmented bowel of patients with spontaneous rupture.

Lamina Repair and Replacement to Control Laminectomy Membrane Formation in Dogs

This study examined the efficacy of lamina repair by the use of various techniques to prevent postlaminectomy scar formation in a canine system. Five-level noncontiguous laminectomies were performed on six adult canines. The most caudal (Site 1) was left uncovered and served as the control. Exposed dura at each of the remaining four levels was covered with one of the following: Site 2, free autogenous laminar bone graft; Site 3, polymethylmethacrylate; Site 4, Teflon-Proplast composite; Site 5, collagen gel. The dogs used in the study were killed 16 weeks after surgery. Three specimens were examined by plain roentgenography and computerized tomography, two specimens were examined histologically, and the remaining four specimens were graded according to scar volume and scar adherence, as detected during gross dissection of the postlaminectomy scar. No repair technique interfered with roentgenography evaluation. The least scar and fewest adhesions were present under the free bone graft repair site. The Teflon-Proplast composite and polymethylmethacrylate both limited the amount and adherence of scar. Collagen gel and control sites were indistinguishable in this study. It is concluded that lamina repair with a solid material covering exposed dura significantly reduces the formation of postlaminectomy membrane and scar.

Experimental determination of the force required for insertion of a thermoseed into deep brain tissues

Our laboratories are developing a new technique for delivering localized hyperthermia to deep-seated brain tumors. In this technique, a spherical thermoseed is stereotactically navigated through the brain and tumour tissues via the noncontact application of an external magnetic force. The force required to produce motion of a 3 mm diameter sphere through in vitro brain tissues was measured to be 0.07 +/- 0.03 N. This result was obtained from a series of experiments performed on whole brain specimens extracted from adult canines. Data were also taken with a 3 mm x 3 mm cylinder and a 5 mm sphere. An experimental procedure simulating physiological conditions was developed prior to testing. Evaluations of systematic effects included determinations of the calibration uncertainties, tests of the dependence of the measured force on temperature, and studies of the effects of method of storage of the tissue specimens. The results obtained are compared with (and confirmed by) two different series of experiments performed in vivo on adult canines and with another series of experiments using brain phantom gelatin.

Transalveolar transplantation of maxillary canines. A follow-up study

This follow-up study on transalveolar transplantation includes 56 maxillary impacted canines in 47 patients, with a post-operative control period of 2-10 years (mean 4.7 years). The prognosis of the transplanted teeth is still very good; only two canines have been lost, due to poor oral hygiene or fracture of the tooth. These positive follow-up results indicate that transalveolar transplantation will offer greater flexibility in the treatment of impacted maxillary canines in adults.

Nonlinear magnetic stereotaxis: Three‐dimensional, invivo remote magnetic manipulation of a small object in canine brain

In a series of in vivo experiments on five adult canines, a small cylindrical permanent magnet (approximately 5-mm diameter x 5 mm long) was magnetically moved under fluoroscopic guidance from an occipital-lobe burr hole to a predetermined destination within the brain and then removed. On three of the animals, dorsal and temporal skull markers were used to establish a coordinate system against which the motions of the seed were referenced. These procedures were sufficiently accurate to permit the guided motion of the seed along nonlinear paths within the brain, including traversal of the midline through the corpus callosum. For removal, the seed could be steered either to a frontal lobe location for extraction through an auxiliary burr hole, or back to the same burr hole through which it had been inserted. This article discusses the way in which stereotactic motions were obtained, the performance limits of the instrumentation and the precision of motion achieved.

Effects of Surgical Treatment and Immobilization on the Healing of the Medial Collateral Ligament: A Long-Term Multidisciplinary Study

The long-term effects of surgical repair and immobilization on the healing of the transected medial collateral ligament (MCL) were studied biomechanically, biochemically and histologically in a canine model. Twelve adult canines were divided into two experimental groups and studied at 48 weeks postoperatively. For Group I, the transected MCL of the left knee was not repaired, and the joint was not immobilized. For Group II, the MCL was repaired and the joint was immobilized for six weeks. The right knee of each canine was sham-operated and served as the control. Histologically, the collagen fibers were less aligned in both of the experimental groups than in the controls. Furthermore, there were minimal differences in collagen and fibroblast alignment between the groups, although poorer alignment was observed for Group I at 12 weeks. Biochemically, the levels of types I and III collagen, reducible collagen cross-links and total collagen concentration for both groups returned to normal levels. Biomechanically, Group I achieved better results than Group II in terms of varus-valgus (V-V) knee rotation and ultimate load of the femur-MCL-tibia complex (FMTC), as these values returned to the level of controls. However, the mechanical properties of the healing MCLs did not compare well with the controls; the tensile strength was only 62% and 45% of controls for Groups I and II, respectively, at 48 weeks. These results suggest that conservative treatment (i.e., no surgical intervention) with early mobilization is better than surgical treatment with immobilization for an isolated Grade III MCL injury.

Functional and Pharmacological Effects of Ureteral Diversion

Urinary diversion is the final therapeutic approach in several bladder pathologies including selected cases of bladder cancer, neurogenic bladder, and painful bladder syndrome. While there have been a few experimental studies on the effects of urinary diversion and subsequent undiversion on bladder capacity, the pharmacological changes occurring with diversion and undiversion have not yet been investigated. Our primary objectives were to determine the functional and pharmacological alterations in the defunctionalized bladder and the effects of refunctionalization on these changes. Thirty-two male adult canines weighing 15 to 20lb. were used for this study. Three groups of dogs were urine diverted for one, three, and six month durations (four dogs per group). Another three groups of dogs were urine diverted for one, three, and six months (four dogs per group); these dogs were then undiverted for three months. Six control animals received either one or two sham operations at one, three, and six months.In all groups the functional and contractile characteristics of the bladders were assessed by urodynamics and in vitro contractile studies; bladder weight and muscarinic receptor density were also measured. Intravesical capacities determined by in vivo cystometry were reduced significantly to 74%, 63%, and 47% of control values at one, three, and six months respectively after urinary diversion. Bladder capacity returned to above normal levels in bladders diverted and then subsequently undiverted. Similarly, the compliance and bladder weight of the diverted bladders were significantly less than control, while diverted bladders subsequently undiverted were similar to controls. Maximal bladder contractility in response to bethanechol stimulation was less in diverted bladders compared to control. This decrease in contractility was accompanied by a decrease in muscarinic receptor density. After undiversion maximal bladder contractility to bethanechol reached control levels; this was accompanied by a parallel increase in muscarinic receptor density to control values. There was no effect of diversion or undiversion on the maximal response of bladder strips to methoxamine stimulation. Thus, a bladder that has been diverted (defunctionalized) for a period of time showed decreases in capacity, compliance, and contractility to muscarinic stimulation along with a decrease in muscarinic receptor density. All of these parameters were restored after refunctionalization of the bladder.

The Influence of Opening the Thorax on Defibrillation Threshold in Canines

To determine if intraoperative testing is predictive of implantable defibrillator performance postoperatively, we measured sequential pulse defibrillation thresholds (DFTs) in 16 adult canines (28.0 +/- 3.5 kg, mean +/- SD body weight) at the time of epicardial defibrillation electrode implantation. Three epicardial defibrillation electrodes were sutured directly to the anterior, posterior, and left lateral epicardial surfaces of the heart through a left fifth intercostal thoracotomy. The pericardium was sutured closed over the electrodes and DFT was measured first with the thorax open and again after closing all surgical wounds, evacuating the thorax, and reinflating the lungs. Mean +/- SD DFT voltage, current, and impedance (pulse 1), and total delivered energy (both pulses) for the open chest measurements were 321 +/- 87 volts, 4.2 +/- 1.9 amps, 80 +/- 14 ohms and 5.3 +/- 3.7 joules, respectively. The corresponding DFT values for the closed chest measurements were 321 +/- 92 volts, 5.1 +/- 1.9 amps, 64 +/- 10 ohms and 6.1 +/- 3.9 joules, respectively. Paired Student's t-test comparison of open versus closed chest DFT values indicated that there were no significant differences in voltage (P greater than 0.80) or energy (P greater than 0.20), but there were significant differences in both current (P less than 0.01) and impedance (P less than 0.001). It is concluded that despite alterations in impedance and current flow, voltage and energy DFT are not significantly different between open and closed chest animals. This suggests that intraoperative testing of implantable defibrillators is predictive of postoperative performance.