Pulmonary gas pressures
- The pressure of outside air
- The partial pressures of inspired oxygen and carbon dioxide
- The rates of total body oxygen consumption and carbon dioxide production
- The rates of alveolar ventilation and perfusion
|Na+ = 140||Cl− = 100||BUN = 20||/|
|Glu = 150|
|K+ = 4||CO2 = 22||PCr = 1.0||\|
|ARTERIAL BLOOD GAS:|
|HCO3− = 24||paCO2 = 40||paO2 = 95||pH = 7.40|
|pACO2 = 36||pAO2 = 105||A-a g = 10|
|Ca = 9.5||Mg2+ = 2.0||PO4 = 1|
|CK = 55||BE = −0.36||AG = 16|
|PMO = 300||PCO = 295||POG = 5||BUN:Cr = 20|
|UNa+ = 80||UCl− = 100||UAG = 5||FENa = 0.95|
|UK+ = 25||USG = 1.01||UCr = 60||UO = 800|
|PROTEIN/GI/LIVER FUNCTION TESTS:|
|LDH = 100||TP = 7.6||AST = 25||TBIL = 0.7|
|ALP = 71||Alb = 4.0||ALT = 40||BC = 0.5|
|AST/ALT = 0.6||BU = 0.2|
|AF alb = 3.0||SAAG = 1.0||SOG = 60|
|CSF alb = 30||CSF glu = 60||CSF/S alb = 7.5||CSF/S glu = 0.4|
The partial pressures (in torr) for a human at rest:
Partial pressure of oxygen (at sea level)
(Torr or mmHg)
|Arterial blood||95-100 (PaO2)|
The alveolar oxygen partial pressure is lower than the atmospheric O2 partial pressure for two reasons.
- Firstly, as the air enters the lungs, it is humidified by the upper airway and thus the partial pressure of water vapour (47 mmHg) reduces the oxygen partial pressure to about 100 mmHg.
- The rest of the difference is due to the continual uptake of oxygen by the pulmonary capillaries, and the continual diffusion of CO2 out of the capillaries into the alveoli.
The alveolar pO2 is not routinely measured but is calculated from blood gas measurements by the alveolar gas equation.
Partial pressure of carbon dioxide
(Torr or mmHg)
|Outside air - dry air at sea level||0.3|
Hypoventilation exists when the ratio of carbon dioxide production to alveolar ventilation increases above normal values – greater than 45mmHg. If pH is also less than 7.35 this is respiratory acidosis.