Thorax 2 B Muscles of respiration B The diaphragm B The pleural cavities Rodrigo Carrasco, DVM, MSc
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Thorax 2
B Muscles of respirationB The diaphragmB The pleural cavities
Rodrigo Carrasco, DVM, MSc
Schnitzel the Schnauzer
B Midnight – 2 yr old male dog hit by car – no previous health problems
B Severely labored breathing, cyanotic mucous membranes, near collapse, no external lacerations
B No lung sounds on leftB Dx: diaphragmatic hernia
Fig 8.4. McGeady TA, et al. Veterinary Embryology. On reserve.
Pleural and Pericardial Cavities
Body wall folds (pleural pericardial folds) start folding medially - they subdivide the coelom into a pleural cavity (encloses lungs) and pericardial cavity (encloses pericardium).
Pleural cavity becomes larger as lung bud develops into each of the pleural cavities. The lung buds come off the pharynx. They develop from the endoderm and start as a tracheal groove at the bottom of the pharynx. Important to know because this is an area where developmental abnormalities occur. The trachea buds off the ventral aspect of the pharynx - and the trachea ends up ventral to the esophagus. The lung buds end up being successive branching of tubes. But they push themselves into the membrane. The pleural cavity has a thin serous membrane. The lung bud push into the serous membrane and grabs part of the visceral pleura. Outside of that there is parietal pleura. Between the visceral and parietal pleura are potential cavities that contain small amounts of serous pleural fluid - allows developing lung buds to slide along/into the pleural cavity. The fluid persists into adulthood- without it we couldnt breath, there’d be a lot of friction b/w lung and pleural cavity (painful). If we did a thoracocentesis - and we got back pleural fluid that was cloudy and coagulant and theres alot of it: difficulty/painful breathing, inappetant.
Formation of the Diaphragm
Fig 8.3. McGeady TA, et al. Veterinary Embryology. On reserve.
Pleuro-PericardialCavity
Lateral View of Embryo
Development of the Diaphragm
B Diaphragm separates pleuro-pericardial cavity from peritoneal cavity
B Pleuro-peritoneal folds from the lateral body wall fuse with septum transversum and mesoesophagus
B Congenital anomalies from incomplete fusion of components– Pleuro-peritoneal hernia– Pericardio-peritoneal hernia
Diaphragmatic HerniaB When fusion fails, there is a persistent opening
between the thoracic and abdominal cavities.
B When abdominal viscera pass through this opening into the thoracic cavity, this is referred to as congenital diaphragmatic herniation. Two types of congenital hernia are in domestic animals:– Pleuro-peritoneal herniation
• Failure of one or both pleuro-peritoneal folds to develop or fuse with mesoesophagus and septum transversum.
• Usually occurs on left side. Most common in humans resulting in viscera such as stomach and intestines being present in the pleural cavity.
foramen develops b/w pleural and peritoneal cavity
foramen develops b/w pleural and peritoneal cavity
• Domestic animals, particularly dogs and cats.• Result of defect in development of septum transversum
leading to improper communication between peritoneal and pericardial cavities.
• Herniation of viscera such as the liver, pyloric region of stomach and the intestines into the pericardial cavity.
Dorsally displacedtrachea
PPDH (congenital) –Radiographs
Very large cardiac silhouette (dorsal deviation of trachea and fills entire width of thorax (should only be about 65% of width)
Cardiac silhouette too wide Gas-filled loops of intestine superimposed with heart
Loss of border between heart and diaphragm
Relevant Clinical CaseB 2 year old female Australian shepherdB 1 month history of cough/gagging that started
after an episode of vomiting and possible trauma on the owner's farm. In the last 10 days the dyspnea worsened until she presented to the referring DVM. Greater than 750 ml of fluid with little cellularity was removed 2 days prior to the CT via thoracocentesis.
Diaphragmatic hernia (traumatic) -CT
Herniated liver
DiaphragmStomach
Spleen
Free fluidIn the thorax
Liver in normal position
Courtesy of Dr. James Montgomery (SACS)
A piece of liver is in the thoracic cavity
A piece of liver is in the thoracic cavity
Muscles of the thoracic wall
B ScalenusB Serratus ventralisB Serratus dorsalisB IntercostalsB Rectus thoracis
Triangular field of auscultation and line of pleural reflection
Samantha Bray
Is the place where you can hear the lung sounds. Cranial border just behind the forelimb. Dorsal border where you can feel the intercostal spaces. costal-chondral junction at rib 6, middle of the 8th rib and dorsal intercostal space at rib 11.
Vascular supply to thoracic
wall
DSW 7-36
E & DeL 3-4
Aorta takes blood caudally. At level of 3/4th there are dorsal intercostal arteries - has a dorsal branch (goes to vertebrae) and continues along thoracic wall and produces lateral cutaneous branches. They continue ventrally and produce internal thoracic artery.
Aorta takes blood caudally. At level of 3/4th there are dorsal intercostal arteries - has a dorsal branch (goes to vertebrae) and continues along thoracic wall and produces lateral cutaneous branches. They continue ventrally and produce internal thoracic artery.
Lateral foramen (intervertebral foramen) where nerves come out - then branch several times - lateral branch and ventral branch. Ventral branch travels with intercostal arteries in the intercostalspace.
Lateral foramen (intervertebral foramen) where nerves come out - then branch several times - lateral branch and ventral branch. Ventral branch travels with intercostal arteries in the intercostalspace.
1. Cephalic vein2. proximal humerus3. triceps4. Right lung5. Liver6. Stomach7. Right atrium8. Aortic arch9. Cranial vena cava10. pulmonary valve11. left AV valve12. Left lung13. caudal mediastinum14. Diaphragm
thoracic limb
1. Cephalic vein2. proximal humerus3. triceps4. Right lung5. Liver6. Stomach7. Right atrium8. Aortic arch9. Cranial vena cava10. pulmonary valve11. left AV valve12. Left lung13. caudal mediastinum14. Diaphragm
Dog thorax - dorsal view
Cavity smaller than outward appearance:
B Extrinsic muscles of forelimb
B diaphragm
Diaphragm
B Peripheral muscle– 2 crura from L1 - L3
• Right larger than left– Costal arch and sternum
B Central tendon– Trefoil
B 3 openings– Aortic hiatus– Esophageal hiatus– Caval foramen
Samantha Bray
Caudal most attachment of diaphragm = crus (there are 2).
7
4
Caudal most attachment of diaphragm = crus (there are 2).
7
4
1. left crus2. right crus3. aorta4. esophagus5. attachment of caudal mediastinum to diaphragm6. sternal and costal parts of diaphragm7. tendinous center8. attachment of plica venae cavae9. caudal vena cavae.
Functional ConsiderationsB Construction = locomotion +
respiration (e.g. biped vs quadriped)B Diaphragmatic mode
– Accounts for ~70% of air flow– Contraction & flattening of diaphragm– Caudal displacement of abdominal viscera– Thoracic pressure < atmospheric pressure
Contraction - moves diaphragm caudally - gives more space for air. Inspiration - creates a negative pressure.
Contraction - moves diaphragm caudally - gives more space for air. Inspiration - creates a negative pressure.
Functional ConsiderationsB Costal mode
– Muscle involvement controversial– Rib like a “bucket handle”– Muscles widen & shorten rib cage
B Inspiration: – serratus ventralis & dorsalis (cranial), scalenus,
B Phrenic nerve (C5 - C7) - voluntary somatic– Effect of denervation?
Rib movement during breathing
In exercise expiration can be an active process.
Phrenic Nerve - innervates diaphragm
slight decrease in inspiration
Rib movement during breathing
In exercise expiration can be an active process.
Phrenic Nerve - innervates diaphragm
slight decrease in inspiration
Visceral piston
Art and Bayly, 2014
During inspiration (running) - inspiration is coordinated with elevating the anterior end of the body. It helps move the viscera caudally - pulls ribcage forward/outward. When expiration is coordinated with the forelimb down (weightbearing) cranial displacement of viscera - diaphragm contracts - air moves out.
During inspiration (running) - inspiration is coordinated with elevating the anterior end of the body. It helps move the viscera caudally - pulls ribcage forward/outward. When expiration is coordinated with the forelimb down (weightbearing) cranial displacement of viscera - diaphragm contracts - air moves out.
Pleural Cavities - dorsal
Pleura:B Parietal
– Costal– Diaphragmatic– Mediastinal
B Visceral– Pulmonary
Serous membrane: Lines body cavities; flat mesothelialcells with underlying CT; serous fluid
