GASTRIC EMPTYING OF SOLID RADIOPAQUE MARKERS IN HEALTHY DOGS

The gastric emptying of 1.5 mm diameter (small) and 5.0 mm diameter (large) radiopaque markers (BIPS) was assessed in 20 dogs. The markers were fed to the dogs in a test meal and abdominal radiographs were made hourly thereafter. Studies were repeated three times in each dog. The variation between two veterinarians interpreting the radiographs was low. The sex, age and day of the study did not have a significant effect on the lag phase or the time taken to empty 25%, 50% and 75% of the markers (T₂₅, T₅₀ and T₇₅ respectively). There was a weak but significant positive correlation between the body weight and T₅₀. There was no significant difference in gastric emptying parameters between the large and small markers.
The mean gastric emptying versus time curve of the small markers on day one was chosen to represent the reference curve for healthy dogs. The lag phase of the small markers on day one was 2.45 ± 2.04 hours, the T₂₅ was 4.85 ± 2.15 hours, the T₅₀ was 6.05 ± 2.99 hours and the T₇₅ was 8.32 ± 2.72 hours (mean ± SD).     

GASTRIC EMPTYING AND INTESTINAL TRANSIT TIMES OF RADIOPAQUE MARKERS IN CATS FED A HIGH-FIBER DIET WITH AND WITHOUT LOW-DOSE INTRAVENOUS DIAZEPAM

Reference ranges for gastric emptying time (GET), small intestinal transit time (SITT), and colonic transit time of 1.5-mm and 5-mm radiopaque markers in healthy cats fed a high-fiber meal were determined, and the influence of low-dose diazepam intravenous injection on the gastrointestinal transit of the markers was examined. The mean GETs and SITTs, and the mean residence times (MRTs) and geometric centers (GCs) of markers in the colon were determined. The effect of intravenous diazepam injection and marker size on these parameters was examined. Diazepam injection had no significant influence on gastrointestinal transit. The GETs of the 1.5-mm markers were significantly more rapid than those of the 5.0-mm markers. There were no significant differences between the SITTs or GCs of the 1.5-mm and 5.0-mm markers. Reference values were developed for GET, SITT, and colonic transit of radiopaque markers for cats fed a high-fiber meal. Diazepam injection had no effect on these parameters.     

Reference ranges for gastrointestinal transit of barium-impregnated polyethylene spheres in healthy cats

Commercial barium-Impregnated polyethylene spheres (BIPS) were administered to 12 healthy adult cats according to the manufacturer's Instructions (30 small BIPS and 10 large BIPS to each cat) together with 60 g of a canned food. Radiographs were taken at hourly Intervals until seven hours after feeding, and then at eight, 10,12,14,17,23 and 30 hours or until all the BIPS had left the stomach and at least 50 per cent had entered the colon. SIX cats were sedated Immediately after being fed the BIPS and six cats remained unsedated. For small BIPS (1–5 mm diameter), the gastric transit the (first exit of BIPS from the stomach) In the sedated cats had a median of 6 hours (range 3 to 8) and In the unsedated cats a median of 2–5 hours (range 2 to 6). Values for other transit times were not significantly different between the two groups, and the pooled data revealed a median 50 per cent gastric emptying time of 6-4 hours (range 2–5 to long), a complete gastric emptying time of 12 hours (range 6 to 27), an orocaecal transit time (first appearance of BIPS In the colon) of 6-5 hours (range 4-0 to 12-0) and a 50 per cent orocaecal transit time of 8-8 hours (range 4–6 to 12.8). The gastrolntestinal transit of large BIPS (5 mm diameter) was significantly correlated with the passage of small BIPS but, except for the complete gastric emptying the, was significantly slower.     

Gastric emptying as assessed by barium-impregnated polyethylene spheres in healthy dogs consuming a commercial kibble ration

Barium-impregnated polyethylene spheres (BIPS) were used to assess gastric emptying in medium-sized dogs consuming a commercial kibble ration. Two sizes of spheres were used: 1.5 mm and 5.0 mm in diameter. Ventrodorsal and right lateral recumbent radiographs were taken immediately before and after consumption of the test meal, and then hourly. The lag phase and the time to 25% (GET25), 50% (GET50), and 75% (GET75) gastric emptying of each sized marker were calculated. There was no significant difference between the lag phases of the small and large BIPS. There was a significant difference between the 1.5 and 5.0 markers at GET25, GET50, and GET75 in these medium-sized dogs. In a majority (70%) of the dogs in this study, GET25 of the 1.5-mm marker occurred at 4.73+/-1.44 hours; GET50 (1.5 mm) occurred at 8.29+/-1.62 hours, and GET75 (1.5 mm) occurred at 10.82+/-1.35 hours. The 5.0-mm markers tended to empty erratically and slowly. Four of the eight dogs retained some of the large markers in their stomachs at the end of the study period (24 hours).     

Influence of age and body size on gastrointestinal transit time of radiopaque markers in healthy dogs

OBJECTIVE: To compare gastric emptying time, small-intestinal transit time (SITT), and orocecal transit time (OCTT) of radiopaque markers in dogs varying in age and body size and to determine whether fecal variables (ie, consistency and moisture content) are related to gastrointestinal tract transit times in dogs. ANIMALS: 24 eight-week-old female puppies, including 6 Miniature Poodles, 6 Standard Schnauzers, 6 Giant Schnauzers, and 6 Great Danes. PROCEDURE: Gastrointestinal tract transit time experiments were performed at 12, 22, 36, and 60 weeks of age. Dogs were fed 30 small radiopaque markers mixed with a meal. Abdominal radiographs were taken. The time at which 50% of the markers had left the stomach (T50) and the time at which the first marker reached the colon were calculated. Fecal moisture content and scoring on the basis of fecal consistency were recorded during the same periods. RESULTS: Puppies had a shorter mean T50 than adults, and mean OCTT decreased significantly only during growth of large-breed dogs. However mean fecal moisture content significantly increased with age, except in Giant Schnauzers. No effect of body size on T50 was found regardless of age, and no difference was observed between OCTT of small- and large-breed adult dogs. The effect of age on the mean SITT was not significant for any breed. However, a strong positive correlation was recorded between body size and fecal moisture content (r2 = 0.77) or fecal scores (r2 = 0.69) in adult dogs. CONCLUSIONS AND CLINICAL RELEVANCE: Age affects T50 in small- and large-breed dogs and OCTT in large-breed dogs. However, body size does not affect T50 or OCTT. A relationship does not exist between gastrointestinal tract transit time and fecal variables in healthy dogs.     

PILOT STUDY TO ASSESS MEAL PROGRESSION THROUGH THE GASTROINTESTINAL TRACT OF HABITUATED DOGS DETERMINED BY FLUOROSCOPIC IMAGING WITHOUT SEDATION OR PHYSICAL RESTRAINT

A limiting factor of radiographic contrast studies is the requirement for restraint of the animal in order to reduce movement artifacts. To demonstrate that gastrointestinal transit can be analyzed by a barium meal in nonsedated and unrestrained dogs, a pilot study of six adult Labrador retriever dogs was undertaken. Study subjects were selected by convenience sampling from an available population of Labrador dogs and were trained to stand motionless during radiographic fluoroscopy. Following a meal containing 7% w/w powdered barium sulfate, radiographic images were generated using a digital fluoroscope C‐arm, at intervals of 5, 15, and 30 min, and at 1, 2, 3, 4, 5, 6, 7, and 8 h. A qualitative assessment of fill density using a 5‐point scale was made for the stomach, small intestine, and ascending, transverse, and descending regions of the colon at each timepoint. Gastric emptying half‐time occurred between 1 and 2 h postmeal. Mean fill density of the small intestine increased from 15 min postmeal and reached a peak at 3 h postmeal. Mean fill density of the proximal large intestine mirrored that of the small intestine. The distal large intestine remained empty for the first 2 h postmeal, then increased between hours 2 and 5 postmeal, and was subsequently at maximum fill density from hour 6 postmeal onwards. Fluoroscopic observation of a barium contrast meal provided an effective indication of the amount and progression of ingested food through the various regions of the gastrointestinal tract in habituated, fully conscious dogs.     

ULTRASONOGRAPHY OF THE NORMAL CANINE GASTROINTESTINAL TRACT

The normal sonographic appearance of stomach, small bowel, and colon was determined in normal dogs of small, medium, and large breeds. In all dogs studied, the stomach wall ranged from 3 mm to 5 mm in thickness, and the small and large bowel wall ranged from 2 mm to 3 mm in thickness. Peristalsis was routinely observed in the stomach and small bowel, but not in the colon. Ultrasonic identification of five gastrointestinal wall layers corresponding to the mucosal surface, mucosa, submucosa, muscularis propria, and subserosa/serosa was possible. Specific segments of the gastrointestinal (GI) tract were isolated and scanned in a water bath. In one dog, ultrasonic and histologic findings were compared and confirmed the anatomical identification found with ultrasound. Similarities and differences between the ultrasonic appearance of the GI tract of humans and small animals are discussed.     

Digestive sensitivity varies according to size of dogs: a review

Field observations on food tolerance have repeatedly shown that when fed an identical diet, large breed (>25 kg) dogs present softer and moister faeces than small breed ones (<15 kg). The purpose of this review is to highlight the findings of four PhD theses, carried out between 1998 and 2013, whose objectives were to investigate the anatomical and physiological peculiarities that would explain, at least in part, this observation, as well as their nutritional implication. This work showed that large breed dogs, in contrast with smaller breeds, present a highly developed caecum and colon, which could explain the relatively longer colonic transit time. A prolonged colonic transit time could explain higher colonic fermentative activity, as supported by higher faecal concentrations of fermentative by‐products. This effect would be reinforced by increased intestinal permeability and reduced sodium net‐absorption. Taken together, these elements could be a possible cause of higher digestive sensitivity in large breed dogs. When prescribing a diet to a small or large breed dog, several aspects of the formulation must be taken into account. For a large breed dog, the general goal is to limit any ingredient that could increase the level of fermentable undigested residues and, in fine, exacerbate colonic fermentation. Highly digestible sources of proteins and starches are therefore strongly recommended to maintain an optimal digestive tolerance. Fermentable fibre sources (i.e. beet pulp and FOS) must also be used in limited quantity in their diet. Conversely, the incorporation of non‐fermentable fibre (i.e. cellulose) appears useful to increase their stool quality. For a small breed dog, the general objective is to minimize any ingredient that could excessively limit colonic fermentation and induce in fine constipation. Purified starches and cellulose are therefore not really suitable for them. In contrast, cereals flours as well as non‐fermentable fibre provided by cereals are recommended.     

Fatigue microdamage in the radial predilection site for osteosarcoma in dogs

OBJECTIVE: To evaluate whether body size and anatomic site influence the quantity of bone microdamage in dogs without osteosarcoma (OS). SAMPLE POPULATION: Pairs of radii were collected from 10 small dogs (< 15 kg) and 10 large dogs (> 25 kg). PROCEDURE: Specimens were stained in basic fuchsin for bone microdamage. Transverse sections were cut from each proximal and distal radial metaphysis at 15 and 85% of bone length. The following variables were determined for each region: mean microcrack length (CrLe, microM), microcrack density (CrDn, microcracks/mm2), microcrack surface density (CrSDn, microm/mm2), and estimated activation frequency (Acf, microcracks/mm2/y). RESULTS: Metaphyseal region did not significantly influence CrDn, CrLe, and CrSDn. The CrDn and CrSDn were influenced by body size, with microdamage being increased in large dogs, compared with small dogs. However, mean CrLe was not significantly influenced by body size. Acf significantly decreased with age and was significantly decreased in large dogs and in the distal radial metaphysis, compared with small dogs and the proximal radial metaphysis, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Our data did not reveal an increase in microdamage or remodeling at the OS predilection site (ie, the distal metaphysis of the radius), suggesting that induction of microdamage and an associated increase in bone remodeling are unlikely to be an important risk factor for induction of OS.     

Intramedullary pressure in canine long bones

Intramedullary pressure was measured bilaterally in 36 dogs: in the diaphysis and distal metaphysis of the femur, in the proximal metaphysis of the tibia and humerus, and in the diaphysis of the radius. Pressure measurements were repeated in 5 dogs, 14 days after the initial recordings. Mean (+/- SD) pressures in the femoral diaphysis and distal metaphysis were 27.6 (+/- 15.4) mm of Hg and 17.6 (+/- 10.5) mm of Hg, respectively. Mean (+/- SD) pressures in the tibial diaphysis and proximal metaphysis were 26.4 (+/- 13.0) mm of Hg and 17.9 (+/- 11.8) mm of Hg, respectively. Mean (+/- SD) pressures in the humeral diaphysis and proximal metaphysis were 26.2 (+/- 15.8) mm of Hg and 13.4 (+/- 7.7) mm of Hg, respectively. The mean (+/- SD) pressure in the radial diaphysis was 15.4 (+/- 18.9) mm of Hg. Metaphyseal pressure was significantly (P less than 0.05) lower than diaphyseal pressure. Repeated pressure measurements in 5 dogs did not vary significantly from initial values, suggesting that the wide range of pressure was real not artifactual.     

Effect of traditional acupuncture on proximal colonic motility in conscious dogs

Acupoints on the Large Intestine Meridian and specific acupoints related with large intestine have been empirically used to treat large intestinal disease. However, the relationship between acupoints related with large intestine and their functions has not been investigated fully. We investigated whether large intestine-related acupoints affect colonic motility in conscious dogs implanted with electrodes at the proximal colon. Manual acupuncture was applied at the following acupoints: 7 main points on the Large Intestine Meridian (LI1, LI2, LI3, LI4, LI5, LI6, and LI11), ST25, BL25 or GV1. Acupuncture at the Large Intestine Meridian acupoints, ST25 and BL25 had no significant effects on the proximal colonic motility. However, acupuncture at GV1 depressed the proximal colonic motility by decreasing the total duration and the frequency of contractile states, which may contribute to the therapeutic effects of GV1. This study also revealed that there was no clear correlation between Large Intestine Meridian and the proximal colonic motility in conscious dogs.     

MICRONODULAR ULTRASOUND LESIONS IN THE COLONIC SUBMUCOSA OF 42 DOGS AND 14 CATS

Micronodular ultrasound lesions have been detected in the colonic submucosa of dogs and cats at our hospital. The lesions had rounded/oval shapes, measured 1–3 mm in size, and exhibited a hypo/anechoic ultrasonographic pattern. To our knowledge, these lesions have not been previously reported in human or veterinary patients. The purpose of this retrospective study was to determine whether micronodular lesions were associated with other abdominal ultrasound abnormalities or clinical findings. Medical records of dogs and cats with sonographic reports describing micronodular lesions within the colonic submucosa were reviewed. Concurrent ultrasonographic abnormalities were recorded and compared with clinical sidgns and follow‐up data. A total of 42 dogs and 14 cats met inclusion criteria. Concurrent sonographic abnormalities included the following: increased colon wall thickness (12.5%); small bowel wall thickening, altered layering, and/or hyperechoic mucosa (45%); abdominal effusion (29%); caudal mesenteric lymphadenopathy (46%); mesenteric lymphadenopathy (27%); and pericolic peritoneal fat reactivity (9%). Fifty of 56 animals presented with diarrhea. Twenty‐seven cases had clinical signs of colitis and ultrasonographic lesions were limited to the colonic submucosa. In nine cases, follow‐up examination at 6–8 weeks showed resolution of clinical and ultrasonographic signs. Ultrasonographic and clinical examinations in 17 patients at 12–18 months and in 20 patients at 18–30 months from initial diagnosis showed resolution of submucosal lesions and clinical signs of enteropathy. The authors propose that micronodular submucosal ultrasound lesions may represent reactive intraparietal lymphoid follicles and may be indicators of colonic inflammatory diseases in dogs and cats.     

Effects of carprofen on the integrity and barrier function of canine colonic mucosa

OBJECTIVE: To measure effects of carprofen on conductance and permeability to mannitol and histologic appearance in canine colonic mucosa. SAMPLE POPULATION: Colonic mucosa from 13 mature mixed-breed dogs. Procedures-Sections of mucosa from the transverse colon and proximal and distal portions of the descending colon were obtained immediately after dogs were euthanized. Sections were mounted in Ussing chambers. Carprofen (400 microg/mL) was added to the bathing solution for treated sections. Conductance was calculated at 15-minute intervals for 240 minutes. Flux of mannitol was calculated for three 1-hour periods. Histologic examination of sections was performed after experiments concluded. Conductance was graphed against time for each chamber, and area under each curve was calculated. Conductance X time, flux of mannitol, and frequency distribution of histologic findings were analyzed for an effect of region and carprofen. RESULTS: Carprofen significantly increased mean conductance X time, compared with values for control (untreated) sections for all regions of colon. Carprofen significantly increased mean flux of mannitol from period 1 to period 2 and from period 2 to period 3 for all regions of colon. Carprofen caused a significant proportion of sections to have severe sloughing of cells and erosions involving >or= 10% of the epithelium, compared with control sections. CONCLUSIONS AND CLINICAL RELEVANCE: Carprofen increased in vitro conductance and permeability to mannitol in canine colonic mucosa. Carprofen resulted in sloughing of cells and erosion of the colonic mucosa. These findings suggested that carprofen can compromise the integrity and barrier function of the colonic mucosa of dogs.     

ASSESSMENT OF BARIUM IMPREGNATED POLYETHYLENE SPHERES (BIPS®) AS A MEASURE OF SOLID-PHASE GASTRIC EMPTYING IN NORMAL DOGS-COMPARISON TO SCINTIGRAPHY

Barium impregnated polyethylene spheres (BIPS) are radiopaque markers used for investigation of a variety of gastrointestinal disorders. One proposed use of the small (1.5 mm) marker is quantitative assessment of solid-phase gastric emptying, which may offer a simple, inexpensive alternative to nuclear medicine studies. In this study the rate and pattern of gastric emptying of a radiolabeled meal containing 30 small BIPS was evaluated in normal dogs by simultaneous comparison of the radiopaque marker method and a scintigraphic method. Serial scintigraphic images and radiographs were obtained for 8 hours or until 95% of the markers had left the stomach. Emptying curves were constructed and statistical analyses performed. There were significant differences in gastric emptying times and lag phase characteristics between the BIPS and scintigraphic studies. These results indicate that in normal dogs there are differences in both the rate and the pattern of solid-phase gastric emptying of a radiolabeled meal as assessed by scintigraphy and the gastric emptying of small BIPS.     

THE NORMAL UPPER GASTROINTESTINAL EXAMINATION IN THE FERRET

Upper gastrointestinal examinations were performed in 11 unsedated ferrets and 4 ferrets sedated with ketamine and diazepam. Each animal received a 8-13 mL/kg body weight dosage of barium liquid (30% weight:volume). Radiographs were made immediately and at 5, 10, 20, 40, 60, 90, 120 and 150 min (mins) after the barium was administered. Gastric emptying began immediately. Mean total gastric emptying was longer in sedated ferrets (130 +/- 40 min versus 75 +/- 54 min); however, this difference was not statistically significant (p = 0.18). Small intestinal transit time was less than 2 h in all ferrets. The barium-filled small bowel was best visualized on the 20- and 40-min radiographs and did not exceed 5-7 mm in width. Flocculation of barium in the small intestine and adherence of barium to the stomach mucosa was seen in almost all animals. The longitudinal colonic mucosal folds in the colon were well visualized in the normal upper gastrointestinal study and aided in distinguishing small intestine from large intestine. The use of ketamine and diazepam sedation did not significantly affect the parameters evaluated in the upper gastrointestinal study series.     

Radiographic findings and clinical factors in dogs with surgically confirmed or presumed colonic torsion

Colonic torsion is a life‐threatening condition in dogs and radiographic findings for this condition have not been well described. The purpose of this retrospective case series was to describe radiographic findings and clinical signs in a group of dogs with colonic torsion. Inclusion criteria were dogs presenting during the period of 2006 and 2016, and that had abdominal radiography and a surgically confirmed or presumed diagnosis of colonic torsion. For each dog, clinical data were recorded from medical records and imaging findings were recorded from retrieved plain radiographs and positive contrast radiographs in which barium enema was performed. Fourteen dogs met inclusion criteria. Of these, nine dogs had colonic torsion confirmed at surgery, with five dogs having surgical confirmation of colonic congestion or mesenteric torsion. Radiographic findings included segmental distention of the colon (14/14), focal narrowing of the colon (11/14), displacement of cecum (11/14), displacement of descending colon (14/14), and mild to no small intestinal distention (14/14). In cases where barium enema was performed, focal narrowing of the colon and longitudinal striations that course in a helical pattern were identified, termed the “torsion sign.” Vomiting was the most common clinical sign observed (12/14), followed by abdominal pain in a small majority of cases (8/14). Severe abdominal pain and hypovolemic shock were uncommon in the patients reported (3/14). Colonic torsion should be considered as a differential diagnosis for dogs with radiographic segmental colonic distention with displacement of the descending colon and cecum. Barium enema is recommended for more definitive diagnosis.     

Effects of medetomidine on intestinal and colonic motility in the dog

The motor responses of the jejunum and colon to stimulation of α₂-adrenoceptors by medetomidine and clonidine were investigated in four dogs. In fasting dogs, medetomidine, at a dose rate of 30 μg/kg i.v., disrupted the migrating myoelectric complex (MMC) pattern of the small intestine for about 2 h. Similar, but shorter-lasting effects were also induced by clonidine (30 μg/kg i.v.) on the jejunum. The administration of α₂-agonists inhibited colonic motility in fasting dogs, although medetomidine-induced inhibition was preceded by a short period of increased muscle tone. All these effects were reversed by the α₂-antagonists atipamezole (0.15 mg/kg i.v.) and yohimbine (0.20 mg/kg i.v.). In fed dogs, medetomidine (30 μg/kg i.v.) induced a strong increase of the tone on the proximal colon, while the activity of the medium and distal colon was completely suppressed. Yohimbine (0.50 mg/kg i.v.) immediately restored the activity of the colon and induced a propagated giant contraction and defaecation by the animal. These data confirm the importance of a₂-adrenergic receptors in the control of intestinal and colonic motility in the dog.     

CT findings in five dogs with surgically confirmed colonic torsion

Colonic torsion is a life‐threatening condition that results in colonic ischemia, necrosis, perforation, sepsis, and eventual death. The aim of this multicenter, retrospective case series study was to describe the CT findings in dogs with surgically confirmed colonic torsion. Medical records were searched for dogs with surgically confirmed colonic torsion following abdominal CT. Five dogs met the inclusion criteria. Three had a history of chronic intermittent diarrhea prior to presentation. Two dogs presented with acute vomiting, diarrhea, and abdominal pain and one dog presented with acute vomiting and lethargy. Computed tomographic findings in all dogs with surgically confirmed colonic torsion include: “whirl sign,” displacement and distension of the cecum and colon, focal narrowing of the colon, and distension of the mesenteric vasculature in all dogs (5/5); streaky peritoneal fat and peritoneal effusion (4/5), pneumatosis coli (2/5), small intestinal distension (2/5), portal vein thrombosis (1/5), and reduced colonic wall contrast enhancement (1/5). In all dogs (5/5), the torsion site was the descending colon and demonstrated an anticlockwise rotation. At surgery, three of the five dogs had a partial colonic torsion with hyperemia at the site of obstruction and two of the five dogs had a complete torsion with marked necrosis of the colonic wall. Displacement of the colon and cecum, segmental distension and focal narrowing of the colon, the presence of a “whirl sign” and distension of the mesenteric vasculature are CT findings highly suggestive of colonic torsion.     

QUANTITATIVE ASSESSMENT OF SURGICALLY INDUCED MITRAL REGURGITATION USING RADIONUCLIDE VENTRICULOGRAPHY AND FIRST PASS RADIONUCLIDE ANGIOGRAPHY

Radionuclide ventriculography has been used in humans to evaluate valvular incompetency. The stroke volume ratio, derived from the radionuclide ventriculogram, is used to quantify the severity of mitral regurgitation (MR). Previous studies conducted in humans have shown that left to right stroke volume ratio increases as the severity of MR increases. In this study, we evaluated radionuclide ventriculography as a noninvasive method to detect MR in dogs with surgically created mitral insufficiency. Six male and three female adult, conditioned mongrel dogs were used. Scintigraphic studies were performed prior to and 4 weeks after surgically created MR. Because of the overlap of the left and right ventricles when viewed from a left lateral position, we combined data from a first-pass radionuclide angiocardiogram with the radionuclide ventriculogram to obtain a corrected stroke volume ratio. Blood flow transit parameters were also derived from the first-pass radionuclide angiocardiogram. Standard left ventricular functional indices were also measured from the radionuclide ventriculogram. On the left lateral view of the heart, 25 to 30% of the right ventricular volume overlaps the left ventricle. After correcting for the overlap, the stroke volume ratio of normal dogs was 1.17±0.178 (mean±SD), which increased to 2.06±0.41 (mean±SD) (p<.001) 4 weeks after creation of MR. The was no significant change in left ventricular ejection fraction or peak rate of ejection following MR. The transit times of blood through the left ventricle were measured from the first-pass radionuclide angiocardiogram and were expressed as half-time clearance, peak clearance rate, and time to peak clearance rate. The baseline half-time clearance was 2.07±0.71 s (mean±SD), which increased to 6.70±4.89 s (mean±SD) (p=.02) after creation of MR. The baseline peak clearance rate was 49.75±8.96 cts/s (mean±SD), which decreased to 23.12±6.84 cts/s (mean±SD) (p<.001) after creation of MR. Stroke volume ratios significantly increased following creation of MR. Blood flow transit through the left ventricle slowed following creation of MR. The variability of these parameters were small in the baseline studies, suggesting these techniques may be clinically useful to gauge the severity of MR in dogs.