Chapter 103: Lung

Question 1

Name the muscles that cover the thoracic wall (6)?

Answer 1

Serratus dorsalis and ventralis
Scalenus
External abdominal oblique
Latissimus dorsi
Pectorals
Cutaneous trunci

Question 2

Which ligament has to be transected in order to do a right caudal lung lobectomy?

Answer 2

Pulmonary ligament

Question 3

Where are the pulmonary arteries and vein located in relation to the associated bronchus?

Answer 3

Artery: Craniodorsal
Vein: Caudoventral

Question 4

What is Elastance?

What is Compliance?

Answer 4

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

Question 5

Surfactant is produced by which cells and what is its function?

Answer 5

Alveolar type 2 cells. Surfactant increases lung compliance by lowering surface tension and reduces the amount of work needed to inflate the lungs.

Question 6

Ventilation is controlled in which part of the brain?

Answer 6

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).

Question 7

If PaO2 is below ______mmHg, ventilation increases - what is this specific reaction called?

Answer 7

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)

Question 8

A normal cat or dog moves ____ml of air per kilogram per inspiration?

Answer 8

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)

Question 9

Which law does gas diffusion across blood-gas interface follow? What does that law state?

Answer 9

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)

Question 10

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?

Answer 10

20 times - CO2 diffuses more rapidly

Question 11

Most oxygen delivered to peripheral tissue is bound to hemoglobin (98.5%) - what is haemoglobin composed of?

Answer 11

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).

Question 12

Oxygen carrying capacity is the maximum amount of oxygen that can bind to hemoglobin.

1gram of hemoglobin can combine with xml of oxygen

Answer 12

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

Question 13

Oxygen saturation of arterial blood with a PaO2 of 100mmHg is ?%

Saturation is 75% for venous blood with a PaO2 of ?mmHg

Answer 13

PaO2 of 100mmHg = O2 sat of 97.5%

75% O2 sat in venous blood = PaO2 of 40mmHg

Question 14

Haemoglobin oxygen dissociation curve can be moved to the right by what?

Answer 14

Decreasing affinity
Increasing temp, PCO2, or 2-3- Diphosphoglycerate in RBCs

Decreased pH
BUT decreased pH can also shift it left.

Question 15

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 =

Answer 15

(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

Question 16

How many ways is CO2 transported in blood?

Answer 16

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

Question 17

The _____ effect is the increased capacity of blood to carry CO2 under conditions of decreased haemoglobin oxygen saturation?

Answer 17

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.

Question 18

Describe the V/Q ratio:

What conditions cause a high V/Q ratio? A low V/Q ratio?

Answer 18

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)

Question 19

Hypoxemia is caused by (5)?

Answer 19

• Hypoventilation
• Low fraction of inspired oxygen
• Diffusion impairment (increased thickness or decreased surface area of alveolar membrane)
• V/Q mismatch
• Shunting

Question 20

Which side should a patient who has had an intercostal thoracotomy be recovered on?

Answer 20

Side of thoracotomy down, and reposition regularly in postop period.

Question 21

An A-a gradient of greater than what means that oxygen supplementation needed?

What is a normal A-a gradient?

Answer 21

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

Question 22

As a general rule an intercostal thoracotomy allows access to approx. how much of the ipsilateral thoracic cavity and mediastinal structures

Answer 22

one third

Question 23

The hilus is located between which rib spaces?

Cranial, Right middle, and caudal lung lobectomies generally performed through which intercostal spaces?

Answer 23

Hilus is between 4th and 5th

Cranial lobe through 4th or 5th
Right middle - Right 5th
Caudal lobe through 5th or 6th

Question 24

Define bullae and define bleb

Answer 24

Bullae: large air spaces develop within lung parenchyma
Blebs: small accumulations of air between parenchyma and visceral pleura

Question 25

which vein drains the first intercostal veins?
What drains the others?

Answer 25

First intercostals = costocervical vein
Azygous for the rest

Question 26

List the contributors to airway resistance and their percentages for
- Inspiratory resistance?

-Expiratory resistance?

Answer 26

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

Question 27

How many sternebrae does a dog have?

Answer 27

9

Question 28

List the lung lobes:

Answer 28

Left:
- Left cranial (subdivided into cranial and caudal)
- Left caudal

Right:
- Cranial
- Middle
- Caudal
- Accessory

Question 29

What muscles can be engaged to aid inspiration and expiration?

Answer 29

Inspiration:
- external intercostal
- sternocleidomastoid
- scalenus
- serratus ventralis

Expiration:
- Internal intercostals
- Abdominal rectus

Question 30

What can alter lung compliance?

Answer 30

Fibrosis or edema

Question 31

What is the maximum volume of lung which can be acutely removed?

Answer 31

50%

Question 32

What % volume is within the left and right lungs?

Answer 32

• Left lung 42%
• Right lung 58%

Question 33

A rightward shift of the O2/Hg dissociation curve results in better or worse unloading of O2 in peripheral tissues?

Answer 33

Better.
(IMPORTANT)

Question 34

Hypoxemia is an arterial oxygen saturation of less than what %?

Answer 34

90%

Question 35

After thoracotomy, what 4 things must be corrected to help restore normal pulmonary and cardiac physiology?

Answer 35

Hypoxemia, residual pneumothorax, pleural effusion, pain.

Question 36

If a patient is hypoxemic post thoracotomy, you should evacuate the pleural space and repeat blood gas analysis in how many minutes?

Answer 36

10 minutes

Question 37

How does pain affect physiology after thoracotomy?

Answer 37

Prevents full thoracic wall excursion -> reduced ventilation

Catecholamine release -> vasoconstriction, reduced perfusion, arrhythmias

Question 38

What are three causes of diffusion impairment?

Answer 38

chronic emphysema
pulmonary interstitial fibrosis
early pulmonary edema

Question 39

At rest, how does ventilation occur?

Answer 39

Diaphragm contracts, bringing caudal lung surface with (active) expiration is passive with recoil of the lungs to resting state.

Question 40

During exercise, how does respiration occur?

Answer 40

The external intercostals, sternocleidomastoid, scalenus and serratus ventralis pull rostral and outward to increase ventilation and the internal intercostals and rectus help with expiration.

Question 41

What is Fick’s law?

Answer 41

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.