1. Gas exchange
Airway
no gas exchange
CO2 O2
flow

2. Anatomical dead space VD Anat = 1 ml/lb body wt. airway
room air
start insp
end insp
end exp
CO2 O2
No gas exchange (white) in anatomical dead space
flow

3. Minute Ventilation: Correction for VD Anat:
VE = breathing frequency (f) x tidal volume (VT)
5 L/min = 10/min x ml
Correction for VD Anat:
VE = f x (VT – VD anat)
3.5 L/min = 10/min x (500 – 150) ml

4. Estimating anatomical dead space
Volume x Fraction = Mass of Gas
Mass of Gas of VT = sum of gas masses
of VA and VD
end exp VD VT
VT x FECO2 = VA x FACO2 + VD X FDCO2 VA
Since FDCO2 = 0
VA = (VT x FECO2) / ( FACO2)
Since VA = VT - VD
VD =
(FACO2 - FECO2)
FACO2 VT

5. Partial pressure of a gas
Dalton’s Law: in a mixture of gases, partial pressure (Pgas) of each gas contributes additively to total pressure (PB) in proportion to the gas’s fractional volume (Fgas)
Pgas = PB x Fgas

6. Alveolar PO2 is < Inspired PO2
21%
H2O
14%
CO2
dry room air inspired air alveolar gas PO
PCO
PH2O (37oC) PN
Total (mmHg)

7. Henry’s Law: at equilibrium, gas pressure above a liquid equals gas pressure in the liquid
PO2, gas = 100 mmHg
PO2, blood = 100

8. Alveolar gas partial pressures determine blood gas tensions
flow
CO2 O2
PCO2, blood =40
PCO2, alv =40
PO2, alv =100
PO2, blood =100
alveolus

9. Blood gas tension determines blood gas content
Concentration of gas dissolved per liter of blood (C) depends on gas solubility (a) and Pgas in blood
CO2 = a x PO2, blood
a, Solubility coefficient (ml O2/[liter.mmHg])
CO2 = x = 3 ml O2/liter of blood
= 0.3 ml O2/100ml of blood
Dissolved gas

10. The oxyhemoglobin dissociation curve
100
HbO2 saturation
(%) 50
PO2, blood

11. The O2 carrying capacity of blood = Hgb-bound O2 + dissolved O2
PO2, alv
dissolved O2 in blood
PO2, blood
HgbO2 saturation
= 1.34 ml at 100%
O2 content in 1 liter of blood at PO2, blood of 100 mmHg = (HgbO2 sat [%] x 1.34 x [Hgb]) + (.03 x PO2, blood)
= (0.98 x 1.34 x 150 [g/l]) + 3 = 200 ml O2/liter of blood

12. How tissues get O2 O2 O2 alveolus alveolus tissue tissue PO2, alv =100
100 50
~30%
PO2, blood
HgbO2 saturation
(%) O2
flow
PO2, blood =100
tissue
PO2, tissue 10 O2 40 40 50
100
PO2, blood

13. Low pH unloads O2 better O2 O2 alveolus pH alveolus tissue tissue pH
PO2, alv =100
alveolus
100 50
~50%
tissue
PO2, blood
HbO2 saturation
(%) pH O2
flow
PO2, blood =100
tissue
PO2, tissue 10 O2 pH 40 40 50
100
PO2, blood

14. The oxyhemoglobin dissociation curve
100
HbO2 saturation
(%) pH pH 50
PO2, blood

15. The pulmonary circulation
CO2
Pulmonary
capillaries
Pulmonary
artery
Pulmonary
vein LA RV
tissue

16. PVR is <<< SVR
= (Ppa – Pla) / CO
= 2 units O2
CO2
Pulmonary
capillaries
Ppa = 20
Pla = 10 LA
Pao = 200 RV
Pra = 0
CO = 5
SVR
= (Pao – Pra) / CO
= 40 units
tissue
Note: pressures are ‘mean’
and in cmH2O. CO is 5 L/min.

17. The lung has low vascular resistance

18. The lung has low vascular tone
pressure
lung
flow
kidney
flow autoregulation
time

19. Systemic capillaries

20. Lung capillaries
Alveolar wall

21. Lung capillaries
Alveolus

22. The lung’s low vascular resistance is due to
Low vascular tone
Large capillary compliance

23. PA enters mid lung height
30 cm PA

24. Gravity determines highest blood flow at lung base
End expiration
Ppa Pla
(cmH2O)
-10 cm
Palv = 0
10 5
0 cm
20 10
30 20
+10 cm

25. Hypoxic pulmonary vasoconstriction
PO2 = 100 mmHg
hypoxia
100 40
100 40
100 40 40
PO2

26. Capillary filtration determines lung water content
alveolus
lymphatic
capillary

27. The Starling equation describes capillary filtration
alveolus Pc Pi
FR = Lp x S [ (Pc – Pi) – s (Pc – Pi) ]
FR filtration rate
S capillary surface area
Pc capillary pressure
Pi interstitial pressure
s reflection coefficient
Pc plasma colloid osmotic pressure
Pi interstitial colloid osmotic pressure

28. Keeping the alveoli “dry”: Large capillary pressure drop20
Pressure
(cmH2O) 15
s (Pc – Pi) 10 PA
Capillary bed LA
s (Pc – Pi) = .8 (30 – 12)

29. Keeping the alveoli “dry”: Perivascular cuff formation
alveolus
vascular cuffing

30. Perivascular cuffs in early pulmonary edema
Normal lung
Early pulmonary edema

31. The ultimate insult: alveolar flooding
alveolus

32. active liquid transport
Keeping the alveoli “dry”: active transport removes alveolar liquid
NaCl
alveolar space
NaCl transporter
active liquid transport
Na-K pump Na K Cl
interstitium

33. SUMMARY
Features of the pulmonary circulation designed for efficient gas exchange:
1. Accommodate the cardiac output * low vascular tone * high capillary compliance

34. SUMMARY
Features of the pulmonary circulation designed for efficient gas exchange:
2. Keep filtration low near alveoli * low Pc * vascular interstitial sump

35. SUMMARY
Features of the pulmonary circulation designed for efficient gas exchange:
3. Keep liquid out of the alveoli * active transport * high resistance epithelium

36. Control of Breathing
Central neurons determine minute ventilation (VE) by regulating tidal volume (VT) and breathing frequency (f).
VE = VT x f

37. Neural Control of Breathing – Respiratory neurons
VRG
pons
medulla
DRG

38. Neural Control of Breathing – The efferent pathway
muscle supply
autonomic
Phrenic n.

39. Central chemoreceptors
Control of Breathing by
Central chemoreceptors
Central chemoreceptors
CO2, H+
major regulators of
breathing
CO2, H+
Central chemoreceptors
Resp neurons VE

40. Chemical Control of Breathing –
Peripheral
chemoreceptors
IXth n.
Carotid body O2
~10% contribution
to breathing
CO2 pH

41. CO2 drives ventilation VE 50 5 35 40 45 CO2 tension in blood (L/min)
hypercapnia VE
(L/min)
quiet breathing 5
CO2 tension in blood
(mm Hg)

42. Hypoxia is a weak ventilatory stimulus
blood pO2 = 50 mmHg 50
blood pO2 = 100 mmHg VE
(L/min) 5
CO2 tension in blood
(mm Hg)

43. Reflex Control of Breathing – Neural receptors
Airway Receptors:
Slowly adapting (stretch - ends inspiration)
Rapidly adapting (irritants - cough)
Bronchial c-fiber (vascular congestion - bronchoconstriction)
Xth n.
afferents
Parenchymal c-fiber (irritants - bronchoconstriction)