THE EFFECT OF DORSAL VERSUS VENTRAL RECUMBENCY ON THE RADIOGRAPHIC APPEARANCE OF THE CANINE THORAX

The thorax of nine dogs was radiographed with a vertical beam in both dorsal (VD) and ventral (DV) recumbency. The radiographs were evaluated subjectively and objectively for differences in appearance. To help explain appearance differences, lateral thoracic radiographs were made with the dogs in dorsal and ventral recumbency using a horizontally (laterally) directed x-ray beam. The appearance of thoracic viscera in VD and DV vertical beam radiographs differed. In VD vertical beam radiographs the craniocaudal axis of the heart appeared longer, the heart had a more consistent positional relationship to the thoracic spine, a larger area of the accessory lung lobe was visible, and a greater length of the caudal vena cava was visible. In DV radiographs the caudal lobar pulmonary arteries were more easily identified. The selection of dorsal versus ventral recumbency for thoracic radiography should be based on the clinical status of the patient and the reason(s) for which the radiograph is being made.     

PLEURAL FLUID MOVEMENT

The present study was an attempt to illustrate the differences between ventrodorsal (VD) and dorsoventral (DV) radiographs that result from the movement of free pleural fluid. A volume of 25 ml/kg of normal saline was introduced into the pleural space of a normal dog, and radiographs of the thorax were produced in ventral and dorsal recumbency using a vertical (overhead) x-ray beam and a laterally directed horizontal x-ray beam. On the DV projection (ventral recumbency) the heart, cranial mediastinum, cranial lung lobes, and the ventral aspect of the diaphragm were submersed in fluid, which resulted in the loss of radiographically detectable borders. On the VD projection (dorsal recumbency) radiographic visualization of these structures was improved due to movement of the free pleural fluid away from them, toward the dependent caudodorsal aspect of the thorax. Radiographs of three dogs with spontaneous pleural effusion are presented to illustrate the differences in radiographic appearance of the thorax with pleural effusion when radiographed in DV and VD projections. The movement of fluid to the dorsocaudal thoracic cavity in dorsal recumbency caused lesions that were obscured on the DV projection to be revealed on the VD projection. the authors therefore recommend the use of the VD projection of the thorax in patients with pleural fluid when clinical status permits.     

EFFECT OF DEPENDENCY VERSUS NONDEPENDENCY ON LUNG LESION VISUALIZATION

Paraffin blocks and mineral oil were used as a model to determine the effect of dependency versus nondependency on radiographic visualization of lung lesions in lateral thoracic radiographs. It was concluded that the increased opacity of the material surrounding the lesion, not contact between the heart and the lesion, was responsible for the inability to detect lung disease in the dependent lung. The results were tested in dogs with pneumonia in the right middle lung lobe. When the dog was in right lateral recumbency, the dependent right lung was increased in opacity and decreased in volume and the pulmonary lesion was difficult to detect. When the dog was in left lateral recumbency, the nondependent right lung was increased in volume and decreased in opacity and the pulmonary disease was clearly visible. A single recumbent lateral radiograph must not be used to assess a dog with suspected lung disease because lesions in the dependent lung lobes may not be detected.     

RADIOGRAPHIC HEART-VOLUME ESTIMATION IN NORMAL CATS

Heart volume mensuration was evaluated on conventional radiographs from eight normal cats in different body positions using computed tomography (CT). Heart volumes were calculated from orthogonal thoracic radiographs in ventral and dorsal recumbency and from radiographs exposed with a vertical X-ray beam in dorsal and lateral recumbency using the formula for an ellipsoid body. Heart volumes were also estimated with CT in ventral, dorsal, right lateral and left lateral recumbency. No differences between heart volumes from CT in ventral recumbency and those from CT in right and left lateral recumbency were seen. In dorsal recumbency, however, significantly lower heart volumes were obtained. Heart volumes from CT in ventral recumbency were similar to those from radiographs in ventral and dorsal recumbency and dorsal/left lateral recumbency. Close correlation was also demonstrated between heart volumes from radiographs in dorsal/ left lateral recumbency and body weights of the eight cats.     

A COMPARISON OF NORMAL FELINE THORACIC RADIOGRAPHS MADE IN DORSAL VERSUS VENTRAL RECUMBENCY

Thoracic radiographs of 11 normal cats were made in dorsal (VD) and ventral (DV) recumbency with a vertically directed x-ray beam. These radiographs were compared subjectively and objectively with each other and with an additional pair of radiographs made with the cats in dorsal and ventral recumbency using a horizontally directed x-ray beam. Differences were found between VD and DV thoracic radiographs but they were minimal. In VD radiographs the caudal mediastinum and accessory lobe regïon of the lung were more clearly seen but cardiac shape varied somewhat. In DV radiographs, the appearance of the heart was more constant and caudal lobar pulmonary arteries more clearly seen. The results of this study indicated that both VD and DV radiographs are satisfactory for radiographic examination of the feline thorax     

Effect of body position on ultrasonographic estimations of bladder volume

A study was undertaken to determine the effect of body position on ultrasonographic bladder measurements and volume estimations. Of the 42 dogs studied, 15 were fresh canine cadavers without urological disease and the remaining 27 were undergoing investigations for disorders of the lower urinary tract. Bladder volume was estimated using a formula described previously. Irrespective of whether all dogs were considered together or only live animals were included, measurements made in dorsal recumbency tended to underestimate bladder volume while those made in right lateral recumbency resulted in overestimation. This was due to significant differences in all linear measurements, apart from width, between body positions. Measurements in right lateral recumbency were higher than those in dorsal recumbency. In all animals and in living dogs alone, bladder measurements in dorsal recumbency appeared to give a more accurate estimation of actual bladder volume.     

THE CANINE LATERAL THORACIC RADIOGRAPH

Selected structures seen on right and left lateral thoracic radiographs of 12 dogs were evaluated for differences in position, size, and shape. The size and position of the cardiac silhouette were different when thoracic radiographs made in left and right lateral recumbency were compared. These changes were, however, considered insignificant. The position of the right cranial lobe bronchus relative to the left varied in right lateral recumbency and left lateral recumbency. The right cranial lung lobe was better aerated when dogs were positioned in left lateral recumbency.
Lesions seen in the caudal portion of the left cranial lung lobe or the right middle lobe were masked when the affected lobe was dependent, and enhanced when the affected lung lobe was non-dependent. It is believed that this difference occurred due to compression of the dependent lung with greater aeration of the non-dependent lung.     

Effect of body position on oesophageal and gastric pressures in the anaesthetised dog

The effect of body position on lower oesophageal sphincter pressure (LOSP), gastric pressure and barrier pressure (BrP) was investigated in 40 dogs anaesthetised for neutering procedures. The dogs were placed in lateral recumbency followed by dorsal recumbency (group 1) or vice versa (group 2). LOSP decreased significantly in the animals which were positioned initially in lateral recumbency, when they were then placed in dorsal recumbency, while those initially positioned in dorsal recumbency showed no significant change in their LOSP or BrP when their position was altered to lateral recumbency. When the data from both groups were pooled, LOSP and BrP were significantly lower when the dogs were in dorsal compared to lateral recumbency (P<0–05).     

Effect of body position on cranial migration of epidurally injected methylene blue in recumbent dogs

OBJECTIVE: To determine the relationship between different body positions during recumbency on the cranial migration of epidurally injected methylene blue in canine cadavers. SAMPLE POPULATION: 21 fresh cadavers of clinically normal adult female mixed-breed dogs. PROCEDURE: Dogs were randomly assigned to the following 3 groups: dogs remaining in right lateral recumbency (n = 7), dogs rotated from left to right lateral recumbency (7), and dogs rotated from dorsal to right lateral recumbency (7). Each dog received an epidural injection of 0.05% methylene blue (0.1 mL/kg) at the lumbosacral space. A dorsal laminectomy of the vertebral column was made, and cranial extent of methylene blue in 4 quadrants (right lateral, left lateral, ventral, and dorsal) was determined by examining dura mater staining. RESULTS: No significant difference was found among groups in regard to body weight or body condition score. Epidural cranial migration of methylene blue in the right lateral quadrant was significantly greater in dogs that remained in right lateral recumbency than in dogs that were rotated from left to right lateral recumbency. No significant difference was found within groups for epidural cranial migration of methylene blue between each quadrant. No significant relationship was found between body weight or body condition score and epidural cranial migration of methylene blue. CONCLUSIONS AND CLINICAL RELEVANCE: Body positioning and amount of recumbency time influence cranial migration of epidurally injected methylene blue. If greater cranial migration of an epidurally administered drug is desired, placing the patient in lateral recumbency with the surgical site on the dependent side may precede surgery.     

Evaluation of six-lead electrocardiograms obtained from dogs in a sitting position or sternal recumbency

OBJECTIVE: To compare 6-lead ECG traces in clinically normal conscious dogs in a sitting position and sternal recumbency to that of right lateral recumbency. ANIMALS: 31 healthy dogs with no history of cardiac disease. PROCEDURE: Six-lead ECGs were recorded for dogs in right lateral recumbency, a sitting position, and sternal recumbency. Q-, R-, and S-wave amplitudes as well as QRS-complex duration were measured in all leads. Additionally, P-wave amplitude and duration, PR interval, ST-segment elevation or depression, and OT interval were measured in lead II. RESULTS: Compared with measurements in right lateral recumbency, the sitting position resulted in increased Q-wave amplitude (lead III), increased R-wave amplitude (leads I and aVL), decreased R-wave amplitude (leads III and aVF), increased S-wave amplitude (lead aVR), decreased S-wave amplitude (lead aVL), increased P-wave amplitude (lead II), and a leftward shift in the mean electrical axis. Compared with measurements in right lateral recumbency, sternal recumbency resulted in decreased Q-wave amplitude (leads I, II, and aVF), increased R-wave amplitude (leads 11, III, and aVF), decreased R-wave amplitude (lead aVR), increased S-wave amplitude (lead aVR), increased P-wave amplitude (lead II), and decreased ST-segment depression (lead II). Compared with right lateral recumbency, the sitting position or sternal recumbency did not result in significant differences in PR interval, QT interval, or QRS-complex duration. CONCLUSIONS AND CLINICAL RELEVANCE: Significant changes are found in ECG measurements in the sitting position and sternal recumbency, compared with right lateral recumbency. In dogs, many ECG reference range values for right lateral recumbency are not valid for ECGs obtained in the sitting position or sternal recumbency.     

Influence of patient positioning on sensitivity of mesenteric portography for detecting an anomalous portosystemic blood vessel in dogs: 34 cases (1997-2000).

OBJECTIVE: To determine whether sensitivity of detecting an anomalous portosystemic blood vessel during operative mesenteric portography varied with patient positioning. DESIGN: Retrospective study. ANIMALS: 34 dogs with a portosystemic shunt diagnosed via scintigraphy or surgery. PROCEDURE: Portograms were evaluated for a portosystemic blood vessel. Sensitivity was calculated from results obtained with dogs in left lateral, right lateral, and dorsal recumbency and from results obtained with dogs in 2 or 3 positions. Differences in sensitivity among positions and between 2 examiners were evaluated. RESULTS: Sensitivity was 85, 91, and 100% in dorsal, right lateral, and left lateral recumbency, respectively. Sensitivity was lower in dorsal recumbency than in left lateral recumbency, although differences were not significant. There was no significant difference between sensitivity of results obtained in dorsal and right lateral recumbency or right lateral and left lateral recumbency. Sensitivity for combined right lateral and dorsal positions was 97%, which was better than that in dorsal recumbency alone, although the difference was not significant. Because sensitivity in left lateral recumbency was 100%, there was no need to evaluate the improvement obtained by combining the result of this position with the results of other positions. CONCLUSION AND CLINICAL RELEVANCE: Results of mesenteric portography varied with patient positioning. The optimal position varied among patients but left lateral recumbency may be better and dorsal recumbency worse. Sensitivity may be improved by performing the test with the patient in orthogonal recumbent positions.     

ASSESSMENT OF RESPIRATION‐INDUCED DISPLACEMENT OF CANINE ABDOMINAL ORGANS IN DORSAL AND VENTRAL RECUMBENCY USING MULTISLICE COMPUTED TOMOGRAPHY

Respiratory‐induced organ displacement during image acquisition can produce motion artifacts and variation in spatial localization of an organ in diagnostic computed tomography (CT) examinations. The purpose of this prospective study was to quantify respiratory‐induced abdominal organ displacement in dorsal and ventral recumbency using five normal dogs. All dogs underwent CT examinations using 64 multidetector row CT (64‐MDCT). A “3‐dimensional (3D) apneic CT exam” of the abdomen was acquired followed by a “4‐dimensional (4D) ventilated CT exam.” The liver, pancreas, both kidneys, both medial iliac lymph nodes, and urinary bladder were delineated on the 3D‐apneic examination and the organ outlines were compared to the maximum alteration in organ position in the 4D‐ventilated examination. Displacement was measured in dorsal‐to‐ventral (DV), right‐to‐left (RL), and cranial‐to‐caudal (CC) directions. Respiratory‐induced displacement of canine abdominal organs was not predictable and showed large variability in the three directions evaluated. For most canine abdominal organs, dorsal recumbency provided overall the least amount of displacement among all directions evaluated except for liver and urinary bladder. For liver, a large variability was found for all directions and a statistically significant difference was found only in the RL direction with ventral recumbency exhibiting less displacement (P = 0.0099). For the urinary bladder, ventral recumbency also provided less displacement but this was statistically significant only in the RL direction (P < 0.0001). Findings from this study indicated that dorsal recumbency may be preferred for minimizing respiratory motion artifacts in whole abdomen studies, but ventral recumbency may be preferred for liver and urinary bladder studies when respiration cannot be controlled.     

DUPLEX-ULTRASONOGRAPHIC EVALUATION OF THE COMMON CAROTID ARTERY IN THE RESTING, SEDATED AND ANESTHETIZED HORSE

The aim of this study was to determine the blood flow in the carotid artery during halothane anaesthesia by means of duplex-sonography. Seventeen warm blood horses were evaluated in dorsal and lateral recumbency and the results were compared with the values of the same horses resting and under sedation. The cross sectional area of the vessels, the time-averaged maximal blood velocity, time-averaged maximal blood flow and the resistance index were determined and the flow profile was evaluated. During halothane anesthesia the total blood flow shows a significant increase which is not dependent on the positioning of the horse. Mean blood velocity is decreased by sedation and significantly increased during anesthesia. Reduced peripheral resistance is expressed by a decline of the resistance index. After sedation and during recumbency there is an increase in diameter of the carotid artery.     

Effects of posture and intraruminal pressure on the bronchial calibre of cattle during xylazine/halothane anaesthesia

The effects of changes in body position and intraruminal pressure on the bronchial calibre of anaesthetised, paralysed adult cattle were investigated using a computer-aided forced airflow oscillation technique which enabled the measurement of specific lower airways conductance (sGlaw), expiratory reserve volume (ERV) and residual resistance (RA). sGlaw and RA were highest in dorsal and lowest in sternal recumbency, but ERV was very much greater in sternal recumbency than in other positions. Turning the animals from right to left lateral recumbency resulted in a marked reduction in sGlaw and increase in ERV, providing further evidence of functional impairment of the dependent areas of the lungs of large animals. Changes in intraruminal pressure had little effect on bronchial calibre, suggesting that the respiratory dysfunction resulting from ruminal tympany is primarily caused by a reduction in compliance rather than an increase in airway resistance.     

Atelectasis causes gas exchange impairment in the anaesthetised horse

The anatomical basis of gas exchange impairment in the anaesthetised horse was studied by computerised tomography (CT; three shetland ponies) and morphological analysis (one pony and three horses). By means of CT, densities were seen in dependent lung regions early during anaesthesia, both with spontaneous breathing and with mechanical ventilation. The densities remained for some time where they had initially been created when the animal was turned from dorsal to sternal recumbency. Deep insufflation of the lungs reduced the dense area. Gas exchange was impaired roughly in proportion to the dense area. On histological analysis, the densities were atelectatic and congested with blood. Gravimetry showed no more extravascular water per unit lung tissue in the atelectatic than in the 'normal' regions, and the blood content was increased only slightly. It is concluded that the horse develops atelectasis in dependent lung regions early during anaesthesia in dorsal recumbency, and that atelectasis is the most likely explanation for the large shunt and impaired arterial oxygenation regularly seen during anaesthesia.     

POSITIVE-CONTRAST ARTHROGRAPHY

Normal colony Beagle dogs were used to evaluate the effect of concentration, volume, and limb positioning on positive-contrast arthrography in the humeral joint. An 8.4% w/v (33.3 mg/ml ± volume) concentration of analytic grade metrizamide (33 mg/ml of iodine) was thought to provide arthrograms of the highest diagnostic quality. Optimal volume of contrast medium was 2–4 ml in dogs with weight of 7.0–15.6 kg (mean, 10.3 kg). Radiographs thought to be of greatest diagnostic value were those made with the dog in lateral recumbency and the limb positioned for neutral, traction, flexion, supination, and pronation views, plus a caudocranial radiograph made with the dog in dorsal recumbency and the limb in traction.     

Thoracoscopic pericardectomy performed without pulmonary exclusion in 9 dogs

OBJECTIVE: To show the feasibility of thoracoscopic pericardectomy without pulmonary exclusion in dogs. STUDY DESIGN: Prospective clinical study. SAMPLE POPULATION: Nine client-owned dogs. METHODS: Dogs referred for the treatment of pericardial effusion by thoracoscopic pericardectomy were intubated with a standard endotracheal tube, mechanically ventilated, and placed in dorsal recumbency. The thoracoscope was introduced into the thorax lateral to the xyphoid process. The operating instruments were inserted at the level of the ventral third of each sixth intercostal space. The pericardium was cut and retrieved through 1 instrument portal. RESULTS: Lung inflation did not interfere with the surgical dissection. A subphrenic pericardectomy was performed in all dogs without iatrogenic trauma. Operative time, from portal placement to skin closure, ranged from 60 to 100 minutes for the first 2 dogs and decreased to 30 to 45 minutes for the latter 7 dogs. CONCLUSIONS: The reported technique avoids the need for selected intubation which requires special tubes, can be technically difficult to perform, and is not recommended in compromised animals in which bilateral lung ventilation is necessary to ensure adequate tissue oxygenation. CLINICAL RELEVANCE: Thoracoscopic pericardectomy offers several advantages over open techniques, including less postoperative pain and morbidity, shorter hospital stay, and improved cosmetic appearance. It can be performed without pulmonary exclusion.     

COMPUTED TOMOGRAPHY OF BALL PYTHONS (Python regius) IN CURLED RECUMBENCY

Anesthesia and tube restraint methods are often required for computed tomography (CT) of snakes due to their natural tendency to curl up. However, these restraint methods may cause animal stress. The aim of this study was to determine whether the CT appearance of the lungs differs for ball pythons in a curled position vs. tube restraint. Whole body CT was performed on ten clinically healthy ball pythons, first in curled and then in straight positions restrained in a tube. Curved multiplanar reformatted (MPR) lung images from curled position scans were compared with standard MPR lung images from straight position scans. Lung attenuation and thickness were measured at three locations for each scan. Time for positioning and scanning was 12 ± 5 min shorter for curled snakes compared to tube restraint. Lung parenchyma thickness and attenuation declined from cranial to caudal on both straight and curled position images. Mean lung parenchyma thickness was greater in curled images at locations 1 (P = 0.048) and 3 (P = 0.044). Mean lung parenchyma thickness decreased between location 1 and 2 by 86–87% (straight: curled) and between location 1 and 3 by 51‐50% (straight: curled). Mean lung attenuation at location 1 was significantly greater on curled position images than tube restraint images (P = 0.043). Findings indicated that CT evaluation of the lungs is feasible for ball pythons positioned in curled recumbency if curved MPR is available. However, lung parenchyma thickness and attenuation in some locations may vary from those acquired using tube restraint.     

Radiographic and computed tomographic evaluation of experimentally induced lung aspiration sites in dogs

This study was performed to radiographically examine the prevalence of aspiration sites and to evaluate their atomical correlation with the bronchial pattens. Ten healthy beagle dogs were repeatedly radiographed, at weekly intervals, in the left and right lateral, ventrodorsal (VD) and dorsoventral (DV) positions. Three mililiters of iohexol distilled with same volume of saline was infused into the tracheal inlet. Which lung lobe was aspirated was decided upon by the presence of a significant alveolar pattern due to the contrast medium. Alveolar patterns were identified at the left (100%) and right cranial lung lobes (77%) with the dogs in dependant lateral recumbency, at the right caudal lung lobe (71%) with the dogs in VD recumbency and at the right middle lung lobe (59%) with the dogs in DV recumbency, respectively. The anatomical correlation was evaluated by performing computed tomography. The right principal bronchus (165.8 ± 1.6°) was more straightly bifurcated than was the left principal bronchus (142.7 ± 1.8°, p < 0.01). In VD position, the right side lung had a greater opertunity to become aspirated. The ventrally positioned right middle lobar bronchial origin was more easily to be aspirated the other laterally positioned ones. We think that these anatomical characteristics can be one of the causes for aspiration pneumonia to occur more frequently in the right side lung.