Gas Exchange Flashcards
External Respiration
Pulmonary ventilation (Breathing) Pulmonary Gas Exchange
Components of Respiration
External Respiration
Internal Respiration
Transport of Gases through blood
Internal Respiration
Systemic tissue gas exchange
Cellular Respiration
Respiratory Cycle-Inspiration
During inspiration, the diaphragm contracts, increasing the volume of the thoracic cavity. This increase in volume results in a decrease in pressure, which causes air to rush into the lungs.
Respiratory Cycle-Expiration
During expiration, the diaphragm returns to an upward position, reducing the volume in the thoracic cavity. Air pressure thus increases, forcing air out of the lungs.
Partial Pressure of Gases
Partial Pressure of gases is the pressure exerted by a gas in a mixture of gases or liquids
Law of Partial Pressure
Dalton’s Law
The partial pressure of a gas in a mixture will equal the total pressure if that gas
Arterial Blood
PO2 and PCO2 equal alveolar PO2 and PCO2
Due to continuous ventilation PO2 and PCO2 should remain relatively constant
Factors that Determine Diffuse of O2 into blood
1) O2 pressure gradient between alveolar air and blood
2) Total functional surface are
3) Respiratory minute ventilation
4) Alveolar ventilation versus deadspace ventilation
Structural Factors that Facilitate Oxygen Diffusion from the Alveolar Air to the Blood
The walls of the alveoli and capillaries form only a very thin barrier for gases to cross. As little as half a micron.
The alveolar and capillary surfaces are large
The blood is distributed through the capillaries in a thin layer so that each red blood cell comes close to alveolar air.
Bohr Effect
Increased PCO2 at the tissue level will decrease the affinity between oxygen and Hb (dumping of O2 at the tissue level)
Haldane Effect
Increased CO2 loading caused by a decrease in PO2 (increase loading of CO2) at the tissue level
Rate of Diffusion
〖Diffusion 〗_gas= [(A x Cs)/T ] x ∆P According to Fick’s Law the membrane diffusion rate is affected by Surface Area (A) Solubility of Gas (Cs) Membrane Thickness (T) Partial Pressure (∆P)
Diffusion Rate and Surface Area
As surface area increases there will be a greater diffusion rate
Diffusion Rate and solubility coefficient
As solubility coefficient increased there will be an increase in diffusion rate
Diffusion Rate and Partial Pressure Gradient
As the partial pressure gradient increases there is an increase in diffusion rate
CO2 Diffusion versus O2
CO2 will diffuse 20 times faster than O2 due to the fact that it has a higher solubility (heavier molecule)
Graham’s Law
Gas diffusion rate is inversely proportional to the square root of the gram molecular weight (density)
the lighter the gas the faster the diffusion rate
Henry’s Law
Gas diffusion is directly proportional to the partial pressure
Basis of O2 therapy
Greater pressure=greater diffusion
Capillary Blood Transit
Capillary Transit Time=0.75 sec
Alveolar-Capillary Equilibrium-Within the first 0.25
Perfusion and Diffusion Limitations to O2 transfers
Decreased or increased blood flow
Thickened alveolar blood flow
CO Diffusion
Limited diffusion due to a strong affinity to Hgb
PP doesn’t rise easily
N2O Perfusion
Perfusion is limited
Equilibrium pressure is reached quickly, therefore more blood is needed to accept more N2O
Oxygen Diffusion Path Length
From alveolar gas to red blood cells
The path is less than 1/2 micron
Pathologies that increase O2 Diffusion
Pulmonary Fibrosis
Interstitial Edema
Alveolar Fluid
Interstital Fibrosis
Measuring Diffusion Capacity
Done through the Single-Breath CO Diffusion Test (DLCOsb)
DLCO=mL CO transferred to the blood/min
Mean PACO=Mean PCCO
Normal Values in Diffusion Capacity
20-30mL/min/mmHg
DLO2=DLCO x 1.23=~32mL/min/mmHg
Unit of diffusion is opposite of resistance
Conductance
Flow/pressure
Factors that Affect DLCO
Body Size Age Lung Volume Exercise Body Position (will be 15-20% higher in supine) Alveolar PO2 and PCO2 Alveolar PCO Hemoglobin Concentration Pulmonary Diseases (decrease total AC Membrane)
Water Balance in Lungs
The Pulmonary capillary is a semi-permeable membrane
Due to the net outward pressure there will always be movement of fluids out of the capillaries
Lymphatic vessels will immediately drain the fluid coming out of the interstitial , which is important to make sure that fluid does not enter the alveoli
Due to the fact that the alveolar wall is so thin any increase in interstitial pressure will rupture the alveoli
Oncotic Pressure
Influence of proteins on osmotic pressure
the effect of of filtration on protein concentration will also serve as a mechanism to limit capillary filtration
Normal tissue oncotic pressure is ~5mmHg
Tissue (Interstitial) Oncotic Pressure (Πi)
The oncotic pressure of interstitial fluid will interstitial protein concentration and reflection coefficient of the capillary wall
The more permeable the capillary barrier is to protein the higher interstitial oncotic pressure
Pressure is also determined by amount of fluid filtration into interstitum (increase filtration will decrease interstitial protein concentration and reduce osmotic pressure)
Water Imbalance-Pulmonary Edema
Increased hydrostatic pressure (fluid pushed out of capillaries) which can be cause by: Left ventricular failure, fluid overload,
Increased Capillary Permeability which can be caused by: non cardiac pulmonary deem
Decreased Plasma Oncotic Pressure: starvation, hemodilation, proteinuria
Lymphatic Insufficiency: Tumour, compression, trauma
