Canine Thorax Research Articles

Parasternal thoracotomy via sternocostal disarticulation: a novel surgical approach to the canine thorax.

To describe the technique and outcomes of a modified paramedian thoracic approach in dogs involving a parasternal thoracotomy via rib disarticulation at the sternocostal joint. 93 client-owned dogs. Medical records of dogs that underwent parasternal thoracotomy at a private practice between the years 2015 and 2021 were reviewed. Signalment, weight, clinical presentation, surgical details, complications, and short-term outcomes were recorded. Cox proportional hazards regression models were utilized to analyze the impact of covariates on hazard events. Kaplan-Meier curves were employed to evaluate survival functions for select variables. Parasternal thoracotomy via sternocostal disarticulation was performed in 93 dogs. Eighty-eight dogs (94.6%) survived the procedure. Eighty-three dogs (89.2%) survived to discharge from the hospital. Age, weight, postoperative time to eating, postoperative ambulation, and surgical or anesthetic duration were not significantly associated with survival to discharge. Thoracostomy tube duration significantly decreased the likelihood for survival to discharge; for each additional hour of thoracostomy tube placement, the odds of survival to discharge diminished by 5.7% (hazard ratio, 0.94; 95% CI, 0.912 to 0.976). Parasternal thoracotomy via rib disarticulation at the sternocostal joints may be a viable alternative to median sternotomy that does not require specialized equipment for bilateral hemithoracic visualization. Postoperative complications and short-term outcomes are comparable to those reported for the traditional median sternotomy approach. Prolonged thoracostomy tube duration may impact survival to discharge.

Development of a Synthetic Training Model for Canine Thoracocentesis

Thoracocentesis, a procedure in which air or fluid is removed from the pleural space, is used to relieve respiratory distress, and as a diagnostic procedure in human and veterinary medicine. Veterinary students commonly learn and practice the procedure on canine cadavers which are in limited supply and are not amenable to long-term storage and use. Practicing thoracocentesis on a cadaveric model also provides limited feedback indicative of success and/or procedural complications. One commercial model for practicing canine thoracocentesis is available, but it costs over US$2000 and is excessively bulky. In order to improve the learning process for veterinary students, we have developed a reusable synthetic canine thorax model that accurately replicates the thoracocentesis procedure, provides immediate feedback to the students and reduces the need for canine cadavers. The low cost of our product provides an efficient alternative to cadavers for instruction in veterinary schools or hospitals.

Three-dimensional MRA Study of the Normal Canine Thorax: MIP Sections and Volume Rendering

The purpose of this study was to investigate the feasibility of three-dimensional contrast-enhanced magnetic resonance angiography (3D-CE-MRA) for the non-invasive anatomical evaluation of the thoracic vasculature in five normal Beagles. After intravenous gadolinium administration and a cardio-respiratory gating protocol, fast 3D gradient echo pulse sequence MRA was performed employing a 1.5 Tesla magnet and a human thorax coil. Three-dimensional vascular software was applied. Sagittal, transverse and dorsal maximum intensity projection (MIP) sections and volume rendering (VR) images were obtained and labelled. Anatomical literature, dissections and gross sections were employed to assist the identification of the vascular structures. With improvements in scanner technology, MIP sections and VR images are a promising, non-invasive and accurate method of evaluating the canine thoracic vasculature. Images provide a reference material for clinical studies of the canine thorax for radiologist-surgeon teamwork assessment and also encourage the development of this technique in veterinary medicine.

Changes in sound transmissibility through the canine thorax due to the experimental pleural effusion

The authors studied the effects of pleural effusion on sound transmissibility through the canine thorax. In the supine position, dogs received sound ranging from 100 to 1000 Hz at the tracheostoma. Using the microphones attached to the dorsal and ventral part of the chest wall, the relative level of the transmitted sound wave was determined in reference to the amplitude of the sound wave at a tracheostom. Measurements of sound transmissibility were performed before and after injecting saline into the bilateral pleural space which was intended to be experimental pleural effusion. In the dorsal part, the experimental pleural effusion decreased sound transmissibility in the frequency range between 100 and 300 Hz. At 100 Hz, the pleural effusion of 5, 10, and 15 ml/kg/hemithorax caused a decrease in sound transmissibility by 3.7 +/- 3.7, 6.6 +/- 4.9, and 10.0 +/- 5.7 dB, respectively. In the ventral part, the reduction in sound transmissibility in the low frequency range due to the pleural effusion was small. In contrast, introduction of pleural effusion caused an increase in sound transmissibility by 5 to 9 dB in the frequency range above 500 Hz. We consider that these changes in sound transmission are implicated in the physical findings such as "aegophony" and reduction in vocal fremitus or vocal ausculation.

Black and bright-blood sequences magnetic resonance angiography and gross sections of the canine thorax: An anatomical study

In this study, images of the canine thorax in transverse, dorsal and sagittal planes were obtained by black-blood T1 spin-echo pulse sequence and bright-blood gradient-echo sequence magnetic resonance imaging. The images were correlated with macroscopic cryosections and anatomical dissection of cadavers with blood vessels containing latex. Non-contrast-enhanced magnetic resonance angiography was obtained from two mature Beagle breed dogs. Macroscopic sections and dissections were performed in three dogs. Black and bright-blood angiography diagnostic methods are complementary and provide an accurate depiction of the vascular canine thorax.

The Clinical Usefulness of the Ventrodorsal Versus Dorsoventral Thoracic Radiograph in Dogs

Differences exist in the ventrodorsal (VD) and dorsoventral (DV) radiographic views of the canine thorax. One view may be preferred over another because of how it portrays different areas of interest or different disease conditions. The VD view is indicated for evaluation of the cranial and caudal mediastinum, the caudal vena cava, and the accessory lung lobe, and in cases of pleural effusion. Indications for the DV view include assessment of a consistent cardiac silhouette, evaluation of the pulmonary lobar vessels, and evaluation of the structures of the dorsal thorax, such as hilar lymph nodes, the caudal dorsal lungs, trachea, mainstem bronchi, and left atrium.

COMPARISON OF TWO‐ VS. THREE‐VIEW THORACIC RADIOGRAPHIC STUDIES ON CONSPICUITY OF STRUCTURED INTERSTITIAL PATTERNS IN DOGS

Three-view thoracic radiography is often used to evaluate patients for pulmonary metastatic disease. Although use of three views has been reported to be more sensitive than two views for focal lung disease, it also requires increased time, effort, and radiographic exposure of patients and personnel. This study was performed to evaluate the conspicuity of lesions on two-view vs. three-view radiographic procedures to determine the proportion of diagnoses that would change. One hundred three-view radiographic studies of the canine thorax were randomized, and four protocols were reviewed for each study: right lateral and ventrodorsal views, left lateral and ventrodorsal views, both lateral views, and all three views. Radiographs were interpreted as either positive or negative for structured interstitial pulmonary disease, and the certainty of the reading was recorded using a visual analog scale. There was 85-88% agreement between each two-view group and the three-view group, with the kapp statistic ranging from 0.698 to 0.758. There were no differences in certainty of diagnosis among the groups, though within each group there was more certainty for positive diagnoses than negative diagnoses. These findings indicate that three-view studies should be continued when evaluating for possible structured interstitial pulmonary disease, including metastatic disease, as eliminating one view from a three-view study would change the diagnosis in 12-15% of patients.

Normal Anatomical Imaging of the Thorax in Three Dogs: Computed Tomography and Macroscopic Cross Sections with Vascular Injection

The purpose of this study was to provide a new reference for interpretation of the normal anatomy of the canine thorax as imaged using computed tomography (CT). Three mature dogs, all mixed breed males, were used for this study. The dogs were sedated, anaesthetized and maintained in sternal recumbency. CT study from the first to the thirteen thoracic vertebra was performed with a TOSHIBA 600 HQ scanner (third generation equipment). Dogs were killed and vascular-injection technique was performed: red latex and blue latex filled vascular system. Injected dogs were frozen and sectioned with an electric bandsaw, the cuts matched as closely as possible to the CT images. The CT images from this study are intended as a reference for clinical CT imaging studies of the thoracic cavity of the dog and for interpreting lesions of the thorax and associated structures.

Computed tomography and cross-sectional anatomy of the thorax in clinically normal dogs

To provide a detailed anatomic description of the thorax in clinically normal dogs by means of computed tomography. 4 clinically normal adult German Shepherd Dogs weighing 28 to 37 kg. Dogs were anesthetized and positioned in ventral recumbency for computed tomographic (CT) examination of the thorax. A CT image from the thoracic inlet to the diaphragm was made by use of a third-generation scanner with a slice thickness of 5 mm. Individual images were reviewed by use of soft tissue (window width, 250 Hounsfield units; window level, 35 Hounsfield units) and lung (window width, 1,000 Hounsfield units; window level, -690 Hounsfield units) settings. One dog, weighing 28 kg, was euthanatized, bound on a wooden frame in the same position as used for CT examination, and frozen at -14 degrees C until solid. By use of an electric band saw, the frozen thorax was sectioned at 10-mm-thick intervals. Slab sections were immediately cleaned, photographed, and compared with corresponding CT images. Anatomic sections were studied, and identified anatomic structures were matched with structures on corresponding CT images. Except for some blood vessels and details of the heart, most of the bony and soft tissue structures of the thorax discerned on anatomic slices could be found on matched CT images. Because CT images provide detailed information on most structures of the canine thorax, results of our study could be used as a guide for evaluation of CT images of the thorax of dogs with thoracic diseases.

Magnetically induced currents in the canine heart: a finite element study.

A moderately detailed three-dimensional (3-D) finite element model of the conductive anatomy of a canine thorax was used to determine the fields and currents induced by a time-varying magnetic field that has been shown to cause irregular heart beats in canines. The 3-D finite element model of the canine thorax was constructed from CT scans and includes seven isotropic tissue conductivities and the anisotropic conductivity of skeletal muscle. We use this model to estimate the stimulation threshold associated with stimulation of the heart by the time-varying magnetic field of a figure-eight coil. Variants of the thoracic model were also constructed to examine the sensitivity of model results to variations in model size, shape, and conductive inhomogeneity and anisotrophy. Our results show that myocardial fields were only midly sensitive to thoracic size. However, model shape and conductive inhomogeneity and anisotrophy substantially influenced the magnitude and distribution of myocardial fields and currents. Our results suggest that an induced peak field magnitude of approximately 1 V/cm is required to stimulate the heart with the magnetic excitation simulated in this study.

Finite element models of thoracic conductive anatomy: sensitivity to changes in inhomogeneity and anisotropy.

A moderately detailed 3-D finite element model of the conductive anatomy of a canine thorax was used to examine the sensitivity of the results obtained during simulated transthoracic defibrillation to variations in skeletal muscle anisotropy and differing degrees of model inhomogeneity. Our results suggest that the myocardial current density distribution is not particularly sensitive to the method used to model skeletal muscle anisotropy. However, anisotropy variations caused defibrillation parameters such as paddle to paddle impedance and threshold current to change by as much as 50%. We found a greater sensitivity in the myocardial current density and the defibrillation parameters to variations in model inhomogeneity. The changes observed in both depended substantially on paddle placement. This sensitivity to paddle placement highlights the difficulty in predicting how a reduction in anatomical detail will affect the myocardial current density distribution. In general, we found the defibrillation parameters to be more sensitive than the myocardial current density distribution to the variations in anatomical detail we examined.

Effect of paddle placement and size on defibrillation current distribution: a three-dimensional finite element model

A realistic three-dimensional finite element model of the conductive anatomy of a canine thorax was constructed for use in the study of transthoracic electrical defibrillation. The model was constructed from a series of 21 cross-sectional CT scans of a 14.5 kg beagle, each separated by 0.82 cm. The electrical conductive properties of 8 distinct tissues were incorporated, including the anisotropic properties of skeletal muscle. Current density distributions were obtained for six paddle pairings and two paddle sizes. A quantitative basis for comparing the resulting distributions was formulated. Our results suggest that placing one or both of the paddles near the heart delivers a higher fraction of current to the heart. However, such paddle placements also produce a less uniform myocardial current density distribution and thus have a higher potential for causing damage. We found that some paddle positions can produce myocardial current densities close to the threshold for damage in successful defibrillations. Results obtained for 8 and 12 cm paddles indicate that 12 cm paddles may offer modest advantages over 8 cm paddles in clinical defibrillation. Comparison of our results to available in vivo experimental data confirm the validity of the finite element method for examining continuum field variables pertinent to electrical defibrillation.

SPECT quantification of technetium-99m microspheres within the canine lung.

Attenuation compensated single photon emission CT (SPECT) count rates of 99mTc microsphere activities from 151 selected small regions of interest (ROIs) in an intact canine thorax were compared with the count rates obtained from scintillation camera images of similar ROIs from frozen slices of the thorax. A first-order method was used to compensate the SPECT and scintillation camera images for the effect of Compton scattering. The SPECT and scintillation camera count rates correlated well: r = 0.95 (RMS error 4.8 counts/s) for 19 X 19 X 13 mm thick ROIs. We conclude that regional quantification of 99mTc microspheres within the dog thorax is possible using camera-based SPECT systems.

Computerized tomographic imaging is insensitive to density variation during scanning

It is claimed and demonstrated by example, that boundaries of regions, whose densities vary considerably during the scan time, are usually readily recognizable in comput(eriz)ed (computer-assisted) tomographic images, even when the number of measured (or given) projections is few enough that the images are strongly contaminated with ‘streak’ artefacts. Several illustrative examples are presented. The data was obtained from computer-generated phantoms, from physical phantoms measured with a low resolution computerized tomography (CT) scanner, and from high resolution CT measurement of a canine thorax.

Biplane videoroentgenographic analysis of dynamic regional lung strains in dogs.

A method is described for determining the spatial distribution of pulmonary parenchymal strains in the intact canine thorax, using measurements of displacement of metallic (1-mm-diam)) markers percutaneously implanted throughout the parenchyma of the right lung. Dogs are supported head up or head down in a water-immersion respirator with the animal's airway connected to ambient air. Tracking of the parenchymal markers is accomplished by stereo biplane videoroentgenographic recordings, which allow high temporal (60/S) and spatial (+/- 1.5 mm) resolution measurements of the "tagged" lungs during various respiratory maneuvers. After transferring the video information to a stop-action video disc, an operator-interactive computer program is used to input the geometric coordinates of the markers into the computer. The true spatial coordinates are then determined after correction for pincushion and magnification distortions. Spatial and temporal distributions of regional parenchymal strains are obtained by determining the distance between markers on a frame-by-frame basis over the extent of the respiratory cycle. Data indicate nonuniformity in regional lung parenchymal strains.

Three-dimensional visualization of the intact thorax and contents: A technique for cross-sectional reconstruction from multiplanar X-ray views

A method is described for obtaining the three-dimensional spatial distribution of roentgen opacity within the intact canine thorax. Video recordings of multiple roentgenographic projections are digitized during rotation of the dog in the X-ray field to provide the data required for the reconstruction of a sequence of parallel spatially adjacent cross-sectional images of the thorax or heart over their entire anatomic extent at 1 60 second intervals in time. The accuracy of the technique is demonstrated with test objects and excised canine hearts, and the capability for high temporal resolution is illustrated by the cross-sectional reconstruction of a metabolically supported, isolated working canine left ventricle at different phases of the cardiac cycle. These data, along with simultaneous measurement of intracardiac and transmural pressures, provide the determinants required for estimations of dynamic myocardial length/tension relationships that are necessary for the quantitative assessment of cardiac contractility and reserve.