Stimulus of respiratory rate

Blood (central) 

·       PaCO2

·       PaO2

·       pH

Lung

·       J

·       Stretch

·       Irritant

Cortical 

·       Emotional stuff

Hormonal

·       Pregnancy (progesterone)

Exercise

Causes of increase Aa gradiant

V/Q

Shunt

Diffusion

·       Membrane

·       PAO2 (FIO2)

·       Transit time

Causes of low PaO2

·       FiO2

·       V/Q

·       Shunt

·       Hypoventilation

·       Diffusion

Causes of Hypercapnoea

PaCO2 = CO2 production/alveolar ventilation

CO2 production

·       Metabolic

·       Substrate

·       CO2 rebreathing

Ventilation

·       UMN

·       LMN

·       NMJ

·       Chest wall

·       V/Q dead space

·       Diffusion

·       Shunt

CO2 elimination – linear curves and tightly controlled via chemoreceptors

CO2 carriage in blood

HCO3                         90             60

Carbamino               5                30

Dissolved                  5                10

2,3 DPG

O2

·       COAD

·       Altitude

·       Exercise

·       Pregnancy

·       Alkalosis

CVS

·       Anemia

Other

·       Stored blood

Venous Admixture

True shunt

·       phys

o    bronchial veins

o   thebesian veins (The Thebesian vessels or veins are embedded in the walls of the heart itself. They serve to drain the myocardium and are present in all four heart chambers)

·       patho

o    atelectasis

o    consolidation

o    AV malformation

o    R-L shunt

o    Malignancy

o    Eisenmengers

VQ mismatch

Airways Resistance 

Laminar 

·       Radius 

o    Drugs, histamine, disease (asthma, inflammation, infection, neoplasm)

o    Dynamic airway compression,, neural, 

o    CO2 dilates

o    FB

·       Length

·       Viscosity

Turbulent

·       Flow/resp rate

·       Density

·       Radius

Lung Volume

ETT

Compliance

Lung

·       Volume 

o    Body size

o    Disease – atelectasis, oedema, consolidation, lobectomy, pneumonectomy

o    Gravity

o    Age 

·       Elastic

o    Emphysema

o    Disease – fibrosis, oedema, ARDS

·       Surfactant

o    Decrease (IRDS, PE)

Chest Wall

·       Kyphoscoliosis

·       Ank spond

·       Diaphragm – supine, pregnancy, obesity

Dynamic Compliance

·       Increase AWR – bronchoconstriction

·       Time constant

FRC

Chest wall

·       Diaphragm (pregnancy, abdo mass, posture, aanesthesia)

·       Burns

·        Kyphosis

Lung

·       Emphysema

·       Pulm oedema, ARDS

AWR

·       Dynamic hyperinflation

PEEP

Dead Space

ANATOMIC

Individual

·       Age

·       Size

·       sex

Positional

·       supine head

·       flexion

Drugs

·       bronchodilator, anaesthetic gas

ETT and Attachments

ALVEOLAR

West zone 1

·       hypotension

·       IPPV

·       Erect

PE

Work of Breathing

ELASTIC

Compliance factors

·       Lung – surfactant, elastic, lung volume

·       Chest wall – KP, AS, diaphragm

NON ELASTIC

Airways resistance

·       Laminar, turbulence, lung vol, ETT

Tissue Resistance

·       Friction associated with viscoelastic deformation at pleural/CW/Abdo interface

Pulmonary Vascular Resistance

Pulm artery pressure 

– incr Cardiac output, gravity, Wests Zones.

Lung volume

 - FRC

Hypoxic pulm vasoconstriction

Drugs

– NO, GTN< Milrinone, Volatile

Disease 

- COAD

Neural – Alpha 1 increases, B2 decreases

Humoral – eicosanoid, 5HT, catecholamine increases

Viscosity - anemia