Term
|
Definition
47 mmHg. Used in calculations of partial pressure in "wet" air inside trachea.
Px = PB x F (dry gas/atmospheric)
PB, barometric pressure, 760 mmHg at sea level
F, fractional concentration of gas
Px = (PB – PH2O) x F (humidified gas)
PH2O, water vapor pressure, 47 mmHg at 370
Obligatory and influenced ONLY by temperature |
|
|
Term
|
Definition
Deals with gases dissolved in solution (blood)—O2 & CO2 en route to/from lung
Converts the partial pressure of a gas in the liquid phase to the concentration of gas in the liquid phase:
Relates gas phase in alveolus to liquid phase in capillary
At equilibrium, P (gas) = P (liquid)
Cx = Px X Solubility
Only applies to concentration of gas in solution, not bound (ie to Hb) |
|
|
Term
|
Definition
Found in Fick's law.
D(diffusion coef)= Solubility/ sq. root of molecular weight |
|
|
Term
|
Definition
| Is totally dissolved in blood, no carrier. |
|
|
Term
| Forms of Gases in Solution |
|
Definition
Dissolved gas:
Henry’s Law (again & again)
ONLY dissolved gas contributes to partial pressure
N2 is only inspired gas that is only dissolved
Bound gas:
O2 bound to Hb, CO2 in Hb and bound to proteins
Chemically modified:
Conversion of CO2 to HCO3- in RBC, Most CO2 is carried in this way!!!(Not bound or dissolved) |
|
|
Term
| Method of measuring diffusion |
|
Definition
CO transfer across pul/cap barrier is exclusively limited only by diffusion
Single-breath of a low [CO], measure rate of disappearance of CO from mixture, this proportional to diffusion rate. Diffusion rate modified in various disease processes or in strenuous activity.
Emphysema- ↓ surface area
Fibrosis or pulmonary edema- ↑ thickness
Anemia- ↓ Hb to bind CO
Exercise- ↑ blood flow, “recruit”, ↑ surface area
Possible artifacts
1. Hb, low hemoglobin can affect CO diffusion, lowers diffusion capacity. Principle assumes there is enough Hb for Co to attach to.
2. Capillary blood volume, determines blood flow |
|
|
Term
| Spatial and temporal qualities of PO2 |
|
Definition
Temporal- Greatest at end-inspiration
Spatial – Greatest at apex, diffusion greatest at beginning of capillary
Fick’s Law applies well for a single point in the respiratory cycle and single point in the lung
But, there are temporal (point in the respiratory cycle) and spatial (different alveoli/gravity) changes in “real life” |
|
|
Term
| Spatial and temporal qualities of PCO2 |
|
Definition
Temporal- Least at end-inspiration
Spatial – Least at apex, diffusion greatest at beginning of capillary
Fick’s Law applies well for a single point in the respiratory cycle and single point in the lung
But, there are temporal (point in the respiratory cycle) and spatial (different alveoli/gravity) changes in “real life” |
|
|
Term
|
Definition
| CO x (Arterial O2 content-venous O2 content) |
|
|
Term
| Gas exchange during exercise |
|
Definition
| In exercise, CO increases, increases rate of O2 transfer. Can also offload more O2 to tissues and come back slightly more desaturated (less preloading). |
|
|
Term
| Diffusion-Limited Gas Exchange |
|
Definition
Total amount of gas transported across the alveolar-capillary barrier is limited by diffusion
As long as there is a partial pressure gradient diffusion continues along the capillary
Example gas: CO, tightly bound and never dissolved in blood=constant pressure gradient, alveolar content of CO always greater than the dissolved capillary content. |
|
|
Term
| Perfusion-Limited Gas Exchange |
|
Definition
Total amount of gas transported across the alveolar-capillary barrier is limited by blood flow (perfusion)
The partial pressure gradient is not maintained, and the only way to increase the amount of gas transported is by increasing blood flow.
Example gas: CO2 and O2
Reaches equilibrium and new blood must be brought in to regain gas exchange. |
|
|
Term
| Fibrosis effects on O2 diffusion |
|
Definition
| Creates a thicker alveolar wall that inhibits gas exchange. O2 exchange goes from perfusion limited to diffusion limited. |
|
|
Term
| High altitude effects on diffusion |
|
Definition
Lowers PO2.
Because of this, there is reduced diffusion and gas exchange takes longer to equilibriate due to less pressure difference in alveoli and capillaries. |
|
|
Term
| Causes of decreased diffusion (measured by diffusion of CO) |
|
Definition
1. Thickening of alveolar-blood gas interface
Pulmonary fibrosis
Pulmonary edema, fluid in alveoli limits diffusion
2. Decrease in capillary surface area
Emphysema (COPD) due to destruction of alveoli and decreased surface area
3. Decrease in Hb
Anemia |
|
|
