C&b 3 - Gaseous Exchange And Factors Affecting It

Front 1

7 layers of blood gas interface?

Back 1

1. Alveolar epithelia + surfactant

2. Interstitial space

3. Capillary endothelia

4. Plasma layer

5. RBC membrane

6. RBC cytoplasm

7. Haemoglobin

Front 2

Factors affecting gas exchange:

Back 2

- limited by diffusion

- decreased PO2 from inspired air

- Hypoventilated

- shunts

- VQ inequalities (ventilation perfusion)

Front 3

Pulmonary capillary transit time of an RBC

Back 3

0.25 s

Front 4

Use what to measure gas exchange? WHY?

Back 4

Carbon monoxide

because it binds strongly and irreversibly to Hb

Front 5

Fick's law eqn:

Back 5

V = [ A * D * ( P1 - P2 ) ] / T

 

V- diffusion rate

D- diffusion coeficient

P1 - P2 - partial p difference across blood gas interface

T- thickness of blood gas interface

Front 6

What is DLCO

Back 6

carbon monoxide transfer factor

DLCO measures amt of CO transported across alveolar capillary membrane each minute per unit of pressure gradient

Front 7

Effect of exercise on DLCO

Back 7

DLCO incr due to capillary distension

Front 8

Effect of recumbent posture on DLCO

Back 8

DLCO incr due to larger capillary volume

Front 9

Effect of disease on DLCO

Back 9

DLCO decr in emphysema/lung disease

Front 10

Whats KCO (carbon monoxide diffusion coefficient) ?

Back 10

KCO = DLCO / Alveolar volume

 

it measures amount of CO transferred into blood per unit alveolar volume

Front 11

Where is mixed venous blood found

Back 11

pulmonary artery

Front 12

Hypoventilation

Back 12

lower breathing rate than normal

Alveolar PO2 decr ; PCO2 incr

Front 13

Hyperventilation

Back 13

higher breathing rate than normal

Alveolar PO2 incr while PCO2 decr

Front 14

Hyperbaric oxygen therapy is ...

Back 14

- medically using higher conc. O2 than air

- to treat air embolism

- to treat decompression sickness

Front 15

Why is there danger of patient stopping breathing when given high conc. O2

Back 15

breathing usually hypercapnic driven so excess PO2 can suppress the drive

Front 16

Characteristics of pulmonary circulation:

Back 16

- Low pressure

- High flow

- Low volume

- Low resistance (despite high flow low pressure)

Front 17

How does the pulmonary circulation adapt its resistance to suit changes in blood flow?

Back 17

- Distension and recruitment of pulmonary capillaries both increased

Front 18

Pulmonary arteries compared to systemic

they are ....... than systemic ones in general

Back 18

shorter and thinner

less vascular smooth muscle

less elastin

 

Front 19

Pulmonary veins compared to systemic

they are ....... than systemic ones in general

Back 19

thinner

less vascular smooth muscle

Front 20

Pulmonary capillaries compared to systemic

Back 20

they are sandwiched between alveoli and blood flows through like a sheet - large SA

Front 21

effect on blood flow of:

Sympathetic

&

Parasympathetic

Back 21

Sympathetic ---> Vasoconstriction

 

Parasympathetic ---> Vasodilation 

Front 22

Pulmonary resistance

Back 22

Resistance to airflow during inhalation/exhalation

Front 23

Intra-alveolar capillary resistance

Back 23

?

Front 24

Extra-alveolar capillary resistance

Back 24

?

Front 25

Intrathoracic pressure

Back 25

Intrapleural pressure - pressure in pleural cavity

Front 26

Pressure variations throughout lung:

Top of lung

Back 26

intraalveolar capillary > artery entering alveolus > vein leaving alveolus

Front 27

Pressure variations throughout lung:

Lower region lung

Back 27

artery entering alveolus > intraalveolar capillary > vein leaving alveolus

Front 28

Pressure variations throughout lung:

Base of lung

Back 28

artery entering alveolus > vein leaving alveolus >  intraalveolar capillary 

Front 29

Pulmonary hypertension series of events:

Back 29

- chronic lung disease

- constriction of pulmonary arteries

- increased resistance due to constriction

- right heart pumps harder

- hypertrophy in right side

- pulmonary bp incr - hypertensioneV

Front 30

Ventilation V

Back 30

air entering lung

Front 31

Perfusion Q

Back 31

blood flowing through lung

Front 32

What causes arterial hypoxemia?

Back 32

VQ inequalities

Front 33

Whats an Ideal V/Q?

Back 33

V/Q = 1

Front 34

do different lung regions differ in V/Q?

Back 34

yes

Front 35

V/Q = 1 at...?

V = Q

Back 35

rib 3

Front 36

V/Q = 0.6 at...?
V < Q

Back 36

base of lung

Front 37

V/Q = 3.3 at...?

V > Q

Back 37

apex of lung

Front 38

Why is Ventilation higher in lung bases?

Back 38

- lower ribs more mobile so lower chest can expand more

- lower parts lung more compliant as upper parts attached to rigid bronchi

- basal alveoli more compliant

Front 39

Define shunts causing V/Q mismatches

Back 39

overperfusion - perfusion without ventilation

Front 40

Define deadspace causing V/Q mismatches

Back 40

overventilation - ventilation without perfusion

Front 41

Atelectais

Back 41

collapse of lungs and alveoli

Front 42

Pulmonary oedema

Back 42

1) left heart fails

2) blood backs into lungs

3) fluid diffuses into alveoli

4) blood gas interface now thicker

5) thus reduced gas exchange

Front 43

R to L shunt

Back 43

opening between septum allowing blood to bypass lungs

R ---> L direct

Front 44

Normal shunt

Back 44

deoxygenated blood from bronchial artery and coronary artery go through thesbesian veins back to left side heart

Front 45

Pulmonary embolism deadspace

Back 45

pulmonary arteries blocked by clots

Front 46

clots in PE pulmonary embolism from where?

Back 46

- fat from marrow of broken bones

- tumors

- air bubbles

Front 47

How does body adapt to shunts?

Back 47

Hypoxic pulmonary arteries vasoconstrict

so that blood is directed from poor ventilated to well ventilated areas

Front 48

How does body adapt to deadspace?

Back 48

hypocapnic bronchioles bronchoconstrict

so directs ventilation from poorly perfused to well perfused alveoli

Front 49

Hypoxia is ...?

Back 49

reduced PO2 in TISSUES

Front 50

Hypoxemia is ...? 

Back 50

reduced PO2 in BLOOD

Front 51

Causes of Hypoxia...

Back 51

"HASH"

Hypoxemia - low blood PO2

Anaemia - reduced O2 carrying capacity

Stagnant blood flow to tissues

Histotoxic - tissues poisoned,O2 usage impaired