Complete High Yield Cardio-Pulmonary Physiology Summary (MBBS)

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Physio-CVP
Topic: Airway Resistance and Pulmonary Flow

Airway Resistance Factors: Obstructive Restrictive
↑ Sympathetic Innervation TLC Increases Decreases
↑ Bronchodilation RV Increases Decreases
↑ Agents ↑ Resistance FEV1/FVC ratio Decreases Increases

↓Density/Viscosity ↓
Resistance

↓ PCO2 ↑ Resistance

↑ Lung Volume ↓
Resistance

we can use a Flow-Volume curve to find
the:

Residual Volume

Total Lung Capacity

Forced Vital Capacity

Formula → FVC = TLC - RV



Topic: Hypoxia and VQ mismatch

Tissue Hypoxia: Hypoxia = low O2 in
Tissues
Stagnant ( ↓ Blood Flow)
Hypoxemia = low O2 in
Anemic ( ↓ O2 carrying ability
Blood
of the blood)
Hypoxia can cause
Histoxic (↓ ATP production in
Cyanosis
cellular level)
A-a difference is seen in
VQ mismatch and Right/eft
shunts



Arterial Hypoxemia: The Higher Va the Lower Q and Higher alveolar PO2
and Low PCO2
Low PIO2 ( ↑ altitudes ↓PI02 ↓ PAO2 ↓ PaO2
↓Oxygen) ↑ Va ↓ Q ↑ PO2 (Hyperventilation)

Hyperventilation ( ↑ PACO2 ↓PAO2) ↓ Va ↑ Q ↑ PO2 (Hypoventilation)

Diffusion Limitation ↑AaDO2 ↑V/Q mismatch ↓PO2 ↑Hypoxia

VQ mismatch V/Q increases at the Apex of the lung

Right/Left Shunts




Physio-CVP 1

, Topic: Alveolar Ventilation

Alveolar Volume Va = Vt - Vd

Ventilation V = Vol x Freq

Physiological Dead Space Vt.F = (Vt-Vd).F + Vd.F

Respiratory quotient (RQ) is in TISSUE

Respiratory exchange ratio (R) is in LUNGS

R = RQ = VCO2/VO2

Dalton Law Ptotal = P1 + P2 +P3

Partial Pressure PIO2 = FIO2 (0.21) x (PB – PH2O)

PH20 = 47 and FIO2 = 0.21 (constants)

↑ altitudes ↓ Pb ↓PI02 (O2 conc is the same)

Alveolar PO2 = PIO2 - PACO2/R (when R<1)

Alveolar PCO2 = VCO2/Va x 863

PACO2 depends upon Alveolar Ventilation (Va) and CO2 Production (VCO2)

We can find Alveolar Ventilation thru:

Va = VCO2/PCO2 x 863

Va = (Vt - Vd) . Freq

Increase Va Increase PACO2 Decrease PaCO2

Hyperventilation when ↑ Va ↓ PCO2

Hypoventilation when ↓ Va ↑ PCO2

Hypercapnia: when we exercise the ↑ Va but PCO2 will Not change (as PCO2 doubles Va will also double, thus this
isn’t Hyperventilation)

During Strenuous Exercise the PaO2, PaCO2, and pH will be CONSTANT but only Ventilation will Increase



Topic: Pulmonary Gas Exchange

a Driving force of partial pressure is used so gases can diffuse btw the Alveolar-Capillary layer Df = P1 - P2

Fricks Law V = DL x (P1-P2)

DL (Diffusion Capacity) of CO2 is GREATER than DL of O2 thus diffusion problems occur for O2 (and Not for CO2)

to measure DLO2 we use DLCO instead as CO has higher affinity for Hb

DLCO = VCO / PACO

Factors affecting Diffusing Capacity (DL):




Physio-CVP 2

, ↑ Exercise ↑ DL ( ↑ Recruitment and Distension of capillaries)

↑ Lung Size ↑ DL

↑ Supine ↑ DL

↑ Thickness ↓ DL




Mixed Venous blood will go to the alveoli and O2 will diffuse

the Driving pressure will be the Highest at the beginning, and
will slowly decrease towards the end of the capillary (as
PAO2=PaO2)

No Diffusion Limitation




However when there is a incomplete equilibration of O2 partial
pressure btw alveolar gas and capillary blood, there is
DIFFUSION LIMITATION, as the PaO2 and PAO2 is
unequal thus creating a (A-a) PO2 gradient

There will be NO Diffusion Limitation for CO2 as it has Higher
Diffusion Capacity than O2

Factors affecting Diffusion Limitation:

Rigorous Exercise will cause low time for diffusion to
occur to increase CO thus leads to Arterial Hypoxemia

Low Diffusion Capacity due to Increase in Thickness and
Low SA

Low Alveolar PO2 at High Altitude leads to Hypoxia

Perfusion Limitation will occur when O2 uptake is completed
EARLY (at 0.25) and so PAO2=PaO2 but way early

Hence the only way to Increase O2 transfer would be to add
More Blood

Nitrous Oxide is Perfusion Limited

Carbon Monoxide is Diffusion Limited

There will be NO Diffusion Limitation




Physio-CVP 3