Chapter 103: Lung Flashcards
Name the muscles that cover the thoracic wall (6)?
Serratus dorsalis and ventralis
Scalenus
External abdominal oblique
Latissimus dorsi
Pectorals
Cutaneous trunci
Which ligament has to be transected in order to do a right caudal lung lobectomy?
Pulmonary ligament
Where are the pulmonary arteries and vein located in relation to the associated bronchus?
Artery: Craniodorsal
Vein: Caudoventral
What is Elastance?
What is Compliance?
Elastance: The degree to which the lung can return to its dimensions (recoil) after removal of distending forces of inspiration - measured as a pressure change required to elicit a unit volume change (ΔP/ ΔV).
Compliance: measurement of lung distensibility and is the reciprocal of elastance, measured as a change in volume per unit pressure change (ΔV/ ΔP) - equivalent to slope of pressure volume curve at any particular point
Surfactant is produced by which cells and what is its function?
Alveolar type 2 cells. Surfactant increases lung compliance by lowering surface tension and reduces the amount of work needed to inflate the lungs.
Ventilation is controlled in which part of the brain?
Medulla - generates breathing rhythm and regulates tidal volume.
The response to changes in CO2 is a result of stimulation of central chemoreceptors on the ventral surface of medulla:
CO2 (unlike HCO3 and H) can diffuse through BBB - when CO2 dissolves in the ECF it is converted to HCO3 and H+ which stimulates central receptors.
ECF has a lower pH than blood and less protein to buffer hydrogen ions, resulting increased sensitivity of central receptors to CO2 variations.
CO2 also stimulates peripheral receptors in the carotid and aortic bodies (response is smaller and less magnitude than that seen with stimulation of central receptors).
If PaO2 is below ______mmHg, ventilation increases - what is this specific reaction called?
Below 60mmHg - reaction is called hypoxic ventilation drive (will be an important reaction for maintaining ventilation if CO2 responsiveness has been altered by chronic lung disease or acid-base imbalance)
A normal cat or dog moves ____ml of air per kilogram per inspiration?
10ml - portion is alveolar, rest is dead space which is important for other functions such as thermoregulation - PaCO2 is only altered by alveolar ventilation (so panting is not considered hyperventilation)
(Dead space can increase if alveoli are ventilated but not perfused - PTE)
Which law does gas diffusion across blood-gas interface follow? What does that law state?
Fick’s law - rate of transfer of a gas through a sheet of tissue is proportional to surface area available for diffusion, diffusion coefficient of gas and difference in gas partial pressure between 2 sides and inversely proportional to tissue thickness (distance gas must travel)
At blood gas interface lungs have a surface area of 50-100m2 and 0.3um thickness which is ideal for diffusion.
The diffusion coefficient of CO2 is how many times greater than that of oxygen?
20 times - CO2 diffuses more rapidly
Most oxygen delivered to peripheral tissue is bound to hemoglobin (98.5%) - what is haemoglobin composed of?
Made of heme, an iron-porphyrin compound, joined to protein globin (4 polypeptide chains/hemes per molecule).
Adult hemoglobin is called A, which can have ferrous and ferric forms (ferric form is known as methemoglobin and is unable to carry oxygen).
Oxygen carrying capacity is the maximum amount of oxygen that can bind to hemoglobin.
1gram of hemoglobin can combine with xml of oxygen
1.34-1.39mL per 1g Hgb
Normal blood has 15g of HB/100ml - so oxygen carrying capacity is approximately 20.8ml oxygen/100ml of blood
Oxygen saturation of arterial blood with a PaO2 of 100mmHg is ?%
Saturation is 75% for venous blood with a PaO2 of ?mmHg
PaO2 of 100mmHg = O2 sat of 97.5%
75% O2 sat in venous blood = PaO2 of 40mmHg
Haemoglobin oxygen dissociation curve can be moved to the right by what?
Decreasing affinity
Increasing temp, PCO2, or 2-3- Diphosphoglycerate in RBCs
Decreased pH
BUT decreased pH can also shift it left.
The oxygen content of arterial blood (CaO2) is the sum of hemoglobin-bound and dissolved oxygen. It is reported in mL/dL
This is given by the formula CaO2 =
(1.36 × Hb × %O2Sat/100) + 0.003 PaO2
Where 1.36 is the mL of O2 per gram of Hb is hemoglobin in g/dL
Saturation of O2 is %sat/100
And the dissolved O2 in plasma is 0.003x the partial pressure of O2
How many ways is CO2 transported in blood?
3 ways:
- Dissolved form: 5% of transported CO2
- In chemical combination as carbamino compounds: 20% of excreted CO2
- Majority is transported in the form of bicarbonate
The _____ effect is the increased capacity of blood to carry CO2 under conditions of decreased haemoglobin oxygen saturation?
Haldane effect (named for a dude named Haldane, not a chemical)
More CO2 binds to haemoglobin at lower oxygen saturation, which facilitates the removal of CO2 from the tissues.
Describe the V/Q ratio:
What conditions cause a high V/Q ratio? A low V/Q ratio?
The V stands for ventilation, which is the air the patient breathes in.
The Q stands for perfusion, which is blood flow.
Essentially, the V/Q ratio is the amount of air that reaches the lungs divided by the amount of blood flow in the capillaries in the lungs.
When lungs are functioning properly, a V/Q ratio is around 1. A number that’s higher or lower is called a V/Q mismatch.
High V/Q (vent > perfusion): PTE
Low V/Q (vent < perfusion): atelectasis, pneumonia, severe pulmonary edema
(IMPORTANT)
Hypoxemia is caused by (5)?
- Hypoventilation
- Low fraction of inspired oxygen
- Diffusion impairment (increased thickness or decreased surface area of alveolar membrane)
- V/Q mismatch
- Shunting
Which side should a patient who has had an intercostal thoracotomy be recovered on?
Side of thoracotomy down, and reposition regularly in postop period.
An A-a gradient of greater than what means that oxygen supplementation needed?
What is a normal A-a gradient?
The Alveolar-arteriolar gradient, or P(A-a)O2 is measured in mmHg. The formula is P(A-a)O2 = PAO2 – PaO2
A gradient above 20mmHg indicates need for O2 supplementation.
Normal is less than 10mmHg
As a general rule an intercostal thoracotomy allows access to approx. how much of the ipsilateral thoracic cavity and mediastinal structures
one third
The hilus is located between which rib spaces?
Cranial, Right middle, and caudal lung lobectomies generally performed through which intercostal spaces?
Hilus is between 4th and 5th
Cranial lobe through 4th or 5th
Right middle - Right 5th
Caudal lobe through 5th or 6th
Define bullae and define bleb
Bullae: large air spaces develop within lung parenchyma
Blebs: small accumulations of air between parenchyma and visceral pleura
which vein drains the first intercostal veins?
What drains the others?
First intercostals = costocervical vein
Azygous for the rest
List the contributors to airway resistance and their percentages for
- Inspiratory resistance?
-Expiratory resistance?
Contributors to inspiratory airway resistance: nares 79% of total resistance, larynx 6%, small airways 15%
Expiratory resistance: nasal 74%, laryngeal 3% and 23% small airways
How many sternebrae does a dog have?
9
List the lung lobes:
Left:
- Left cranial (subdivided into cranial and caudal)
- Left caudal
Right:
- Cranial
- Middle
- Caudal
- Accessory
What muscles can be engaged to aid inspiration and expiration?
Inspiration:
- external intercostal
- sternocleidomastoid
- scalenus
- serratus ventralis
Expiration:
- Internal intercostals
- Abdominal rectus
What can alter lung compliance?
Fibrosis or edema
What is the maximum volume of lung which can be acutely removed?
50%
What % volume is within the left and right lungs?
- Left lung 42%
- Right lung 58%
A rightward shift of the O2/Hg dissociation curve results in better or worse unloading of O2 in peripheral tissues?
Better.
(IMPORTANT)
Hypoxemia is an arterial oxygen saturation of less than what %?
90%
After thoracotomy, what 4 things must be corrected to help restore normal pulmonary and cardiac physiology?
Hypoxemia, residual pneumothorax, pleural effusion, pain.
If a patient is hypoxemic post thoracotomy, you should evacuate the pleural space and repeat blood gas analysis in how many minutes?
10 minutes
How does pain affect physiology after thoracotomy?
Prevents full thoracic wall excursion -> reduced ventilation
Catecholamine release -> vasoconstriction, reduced perfusion, arrhythmias
What are three causes of diffusion impairment?
chronic emphysema
pulmonary interstitial fibrosis
early pulmonary edema
At rest, how does ventilation occur?
Diaphragm contracts, bringing caudal lung surface with (active) expiration is passive with recoil of the lungs to resting state.
During exercise, how does respiration occur?
The external intercostals, sternocleidomastoid, scalenus and serratus ventralis pull rostral and outward to increase ventilation and the internal intercostals and rectus help with expiration.
What is Fick’s law?
Rate of transfer of a gas through a sheet of tissue is proportional to surface area available for diffusion diffusion coefficient of gas, and difference in partial pressure.
It is inversely proportional to tissue thickness.
