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Flashcards in Pulmonary: Physiology Review Deck (54)
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1
Q

Definition of Respiration

A
2
Q

Partial Pressure Abbreviations and Definitions

A
3
Q

Other Respiratory Definitions

A
4
Q

What are the funcitons of the upper respiratory tracts?

A

Air conditioning: humidification and warming (mouth, nose, nasal cavity, pharynx)

Filtration: nose, nasal cavity, pharynx

Olfaction

Phonation

5
Q

What are the functional characteristics of the lower respiratory system?

A

Cilia to move pathogens out

Mucus to entrap pathogens

Surfactant to maintain patency, opsonize pathogens, modify T-cells

Smooth muscle to regulate bronchomotor tone

Cartilage to keep trachea and bronchi open and to protect

NOTE: see attachment to see WHERE each begins and ends.

6
Q

What is the driving force for gas exchange in the lungs?

A

The difference in gas partial pressures

7
Q

How do we determine the partial pressure of a gas in the lungs?

A

Dalton’s Law of Partial Pressures

In dry gas (inspired air), the partial pressure of x is the barometric pressure times the fraction of the gas: Px = Pb * F

In humidified gas (bronchial air), the partial pressure of x is the difference between the barometric and water vapor pressures times the fraction of the gas:

Px=(PB - PH2)) * F

8
Q

What is the fraction of Oxygen in the air?

What is the barometric pressure?

A

The fraction of oxygen in the air 21% anywhere on earth.

The barometric pressure changes according to altitude. It s 760 mm Hg at sea level

9
Q

What is the point of measuring and calculating partial pressures?

A

When a patient is experiencing dyspnea,

knowing the partial pressures helps figure out where the problem is.

10
Q

What are the two ways air flows in the respiratory system and where do they happen?

A

Convection (bulk flow) in the airways

(May be turbulent or laminar/smooth)

Diffusion in the alveoli

11
Q

Since there is not mucus or cilia in the alveoli,

how are they protected from pathogens?

A

Macrophages phagocytize pathogens

Surfactant opsonizes them and modulates T-cells.

12
Q

What seven barriers must gases move through for gas exchange?

A

Alveolar fluid layer, epithelium, basement membrane

Interstitial space

Capillary basement membrane and endothelium

13
Q

What affects the concentration of gas in the body fluids?

A

The concentration of gas in the body fluids

is proportional to its partial pressure Px and its solubility

Henry’s Law:

Cx =Px * solubility

14
Q

Compare the solubility of oxygen versus carbon dioxide.

A

The solubility coefficient for carbon dioxide (.57) is WAY higher

than for other gases including oxygen (.024)

(CO2 likes fluids!)

Note: At equilibrium, the partial pressure of the gas in liquid phase

equals the partial pressure in the gas phase.

15
Q

What determines how easily a gas diffuses across cell membranes?

A

Rate of transfer is

proportional to the tissue area and the difference in partial pressure of the gas

and is inversely proportional to the tissue thickness.

Frick’s Law of Diffusion:

Flux = Area/thickness * pressure difference * diffusion coefficient

V = [A/Δx] · D · (P1 – P2)

16
Q

What are the limiting factors for gas movement in the body?

A

Diffusion through tissue water:

Thickness (inversely proportional)

Surfact area (proportional)

Note that both of these can be affected by disease states.

17
Q

What is the diffusion coefficient? (D)

A

The relative diffusion coefficient is based on oxygen (D=1).

Carbon Dioxide (D=20.3) likes to move through fluid

18
Q

How does surface area change as air moves down the airways?

A

While the surface area of individual airways

decreases as you go deeper into the lungs,

the total surface area increases dramatically.

19
Q

What is the total surface area available for gas exchange?

A

75.4 m2

However, this is the absolute maximum.

At rest we do not use this much, but during exercise we can recruit unopened alveoli.

In certain diseases, the alveoli are damaged or destroyed which limits the ability to recruit more when needed.

20
Q

What is the V/Q ratio?

A

The V/Q ratio is the ration of ventilation to perfussion

At equilibrium, gas exhange is perfusion limited and requires increased blood flow to increase gas exhange (give the patient some fluids or blood)

When equilibrium is not reached, gas exchange is diffusion-limited and requirees increased pressure gradient to increase gas exchange (give the patient some oxygen)

21
Q

What is the diffusing lung capacity?

How is it used?

A

Diffusing Lung Capacity DL combines the factors that affect diffusion: the diffusion coefficient (D), the surface area (A) and the membrane thickness (Δx).

DL = D · A/Δx

So Fick’s Law becomes:

V (flux) = DL · (P1 – P2)

This accounts for the time it takes for gas (oxygen)

to combine with blood proteins (Hb)

22
Q

How do we measure lung diffusion capacity and what affects it?

A

We use carbon monoxide to measure it: DLCO

It is limited in patients with thickened respiratory membranes like the edema in heart failure and the firbrosis in sarcoidosis.

It is limited in patients with decreased surface area for gas change like emphysema

23
Q

How is oxygen transported in the blood?

A
  1. 5% dissolved in plasma
  2. 5% bound to Hb (improving carrying capacity by 70 fold)

Oxygen content in the blood = dissolved oxygen + oxygen bound to Hb

Oxygen bound to Hb = binding capacity * %Hb saturation

24
Q

What factors decrease Hb saturation?

(What causes the Hb to unload Oxygen?)

A

Increased temperature

Increased PCO2

Increased 2,3 DPG

Increased acidity (decreased pH)

25
Q

How is Carbon Dioxide transported in the blood?

A

7% dissolved in plasma

23% bound to Hb in the RBCs

70% in bicarb buffer system in RBCs

26
Q

What muscles assist with ventilation during rest?

During exerise or disease?

A

Inspiration: Diaphram and external intercostals at rest

Accessory muscles added during exercise/disease.

Expiration: passive at rest (recoil)

Abdominal and internal intercostals used during exercise or disease.

27
Q

What is the net driving pressure for air movement during ventilation?

A

Driving pressure for ventilation:

The force of muscle contraction

Lung compliance (ΔP/ΔV)

Airway resistance

28
Q

What is the general gas law and how does it apply to ventilation?

A

PV=nRT

At constant temperature, P*V is constant so:

P1V1 = P2V2

Eg: increased volume in the lungs during inspiration

leads to decreased pressure in the lungs, pulling air inside.

29
Q

Which volumes and capacities cannot be measured by spirometry?

A

You cannot measure Residual Volume (RV)

Therefore you also cannot measure Functional Residual Capacity (FRC)

or Total Lung Capacity (TLC) because these are calculated using RV.

Know and understand the attached graph!!!

30
Q

What happens to the pressure in the lungs when the volune in the lungs increases?

A

It decreases. See attached.

31
Q

What is physiologic dead space?

A

Physiological dead space is the volume of lungs that

does not participate in gas exchange.

Physiologic dead space = anatomic dead space (150 mL) + functional dead space

Functional dead space increases due to disease,

thereby increasing physiological dead space.

32
Q

What is the difference between pulmonary ventilation (breathing)

and alveolar ventilation?

Minute ventilation (amount of air expired in a minute) = Tidal Volume * Respiratory Rate

(VE) = VT (mL) x Resp Rate (breaths/min)

Alveolar ventilation is the amount of air entering/leaving the alveoli in a minute, accounting for the physiologic dead space

(VA) = (VT –VD) x RR

A
33
Q

What is happening to the volume of air when the lungs are at rest?

A

The lungs are at rest at the Functional Residual Capacity,

when the elastic recoils of the lung and chest wall are equal but opposite.

See attached.

34
Q

What are compliance and elastance and how are they related?

A

Compliance is lung stretchability: change in volume over change in pressure

Compliance = Δ volume /Δ pressure

Elastance is tendencey to recoil: change in pressure over change in volume

Elastance = Δ pressure/ Δ volume

Compliance is inversely proportional to elastance.

35
Q

What affects compliance and elastance?

A

Collagen and elastin fibers

Surface tension of small airways and alveoli

Elastic recoil is the pressure difference required

to inflate the lung to a specific volume

36
Q

What role does Surfactant play in pulmonary compliance?

A

Surfactant reduces surface tension in the alveoli, thereby increasing compliance.

Without surfactant, the attractive forces of fluid would collapse the alveoli.

Since each alveoli has the same amount of surfactant,

smaller alveoli have a higher concentration,

thereby balancing the volume difference

so that there is no pressure gradient

(gases do not move from one alveoli to another).

37
Q

How does airway resistance affect the flow of air?

A

Flow (Q) = pressure gradient (ΔP)/resistance (R)

The pressure gradient can be the difference between inside and outside pressure in ventilation or between alveoli and blood in gas exchange.

38
Q

What is the key factor that affects airway resistance?

A

According to Poiseuille’s Law: Resistance (R) = 8ηl / πr4

Most of these variables are constant in the body, so they key factor is the

radius of the airway

Resistance is inversely proportional to r4

so a tiny change in radius will have a huge impact on resistance.

Eg: if you cut the radius in half, you increase the resistance 16-fold!

39
Q

How does lung volume affect resistance?

A

Increased volume decreases resistance

(Inversely proportional)

40
Q

How does the automomic system regulate airway resistance?

A

Sympathetic: bronchodilation decreases resistance

(via circulating catecholamines on bronchial smooth muscle)

Parasympathetic: bronchoconstriction increases resistance

(via Ach from vagus nerve on bronchial smooth muscle)

41
Q

How do we estimate physiologic dead space?

A

It is the tidal volume times the proportion of air

that does not participate in gas exchange:

VD = VT x (PaCO2 – PECO2 )/ PaCO2

42
Q

How do we measure PaCO2?

(alveolar partial pressure of CO2)

A

We cannot meausure it directly

so we used PACO2 (arterial partial pressure of CO2)(via blood gas)

as a surrogate because they are closely related.

43
Q

How are PACO2 and PAO2 related?

A

They are inversely proportional.

So when one increases, the other decreases.

44
Q

What are the regional differences in the V/Q ratio?

A

At the apex of the lung, the alveoli are full but the capillaries are thin so the Ventilation to Perfusion (V/Q) ration is high (3.0)

At the base of the lungs, the alveoli are compressed by gravity but the capillaries are more full (gravity causes the blood to pool there), so the V/Q ratio is low (.6)

45
Q

What is shunt

and what types of shunts are there?

A

A shunt is when the blood bypasses the respiratory membrane

and therefore does not participate in gas exchange.

Examples:

Physiologic shunts: Bronchial perfusion and thebesian channels

Nonphysiologic shunts: developmental anomalies such as foramen ovale

Local shunts: when blood is diverted away from a faulty alveolus

46
Q

What are two causes of a V/Q mismatch?

A

Airway obstruction, such as a blockage or a shunt,

Q is normal, but V is zero: V/Q =0

Perfused but not ventilated

Pulmonary embolus or dead space

V is normal but Q is zero

V/Q is infinite

Ventilated but not perfused

47
Q

What parts of the brain control ventilation?

A

Medulla: rhythm generation

Pons: regulates medulla

Cortex: conscious and emotional response

See attached for details.

48
Q

How does respiratory information from the periphery get to the brain?

A

Chemoreceptors sense CO2 and O2

Mechanoreceptors in lung and muscle sense stretch and joint movement

Irritant receptors in the airway epithelial cells sense toxins/irritants

J receptors in the alveolar walls capillaries sense engorged capillaries during edema

See attached.

49
Q

How do central chemoreceptors communicate with the brain?

A

Directly sense decreased pH in the CSF

Indirectly sense increased PaCO2 in the blood

50
Q

Which chemoreceptor is the most important during normal breathing?

A

The central chemoreceptor.

51
Q

How do we assess respiratory function in a patient with dyspnea?

(What tests can we use?)

A

Spirometry to assess lung volumes, capacities re obstructive/restrictive disease

Pulse oximetry to indirectly assess PaCO2

Arterial blood gas (ABG) to assess gas exchange

52
Q

What is the alveolar-arterial gradient?

(A-a gradient)

A

The A-a gradient tells us how much inspired oxygen

is actually getting into the blood stream.

A-a gradient = [PIO2 - (PACO2 / R)] - PaO2

Normal A-a gradient: Age/4 + 4

If the gradient is high then O2 in the alveolus is not getting into the arterial blood effectively.

53
Q

What affects the A-a gradient?

A

A-a gradient = [PIO2 - (PACO2 / R)] - PaO2

Alveolar PCO2 is affected by: respiratory rate, tidal volume and dead space

Arterial PO2 is affected by changes in inspired oxygen, poor diffusion across the respiratory membrane, R-L shunting and V/Q defects.

54
Q
A