Pulmonary gas pressures

Pathophysiology sample values
BMP/ELECTROLYTES:
Na⁺ = 140	Cl⁻ = 100	BUN = 20	/
			Glu = 150
K⁺ = 4	CO₂ = 22	PCr = 1.0	\
ARTERIAL BLOOD GAS:
HCO₃⁻ = 24	p_aCO₂ = 40	p_aO₂ = 95	pH = 7.40
ALVEOLAR GAS:
	p_ACO₂ = 36	p_AO₂ = 105	A-a g = 10
OTHER:
Ca = 9.5	Mg²⁺ = 2.0	PO₄ = 1
CK = 55	BE = −0.36	AG = 16
SERUM OSMOLARITY/RENAL:
PMO = 300	PCO = 295	POG = 5	BUN:Cr = 20
URINALYSIS:
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:
CSF alb = 30	CSF glu = 60	CSF/S alb = 7.5	CSF/S glu = 0.4

The factors that determine the values for alveolar pO₂ and pCO₂ are:

Following is a list of average partial pressures (in torr) for a human at rest:

Partial pressure of oxygen (at sea level)

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 150 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.

Location	pCO₂ (Torr)
Outside air - dry air at sea level	0.3
Alveolar air	35
Arteriole blood	40
Venous blood	50
Cells	50

Hypoventilation exists when the ratio of carbon dioxide production to alveolar ventilation increases above normal values.

Hyperventilation exists when the same ratio decreases.

Respiratory physiology

Respiration	breath inhalation exhalation respiratory rate respirometer pulmonary surfactant compliance elastic recoil hysteresivity airway resistance bronchial hyperresponsiveness constriction dilatation mechanical ventilation

Control	pons pneumotaxic center apneustic center medulla dorsal respiratory group ventral respiratory group chemoreceptors central peripheral pulmonary stretch receptors Hering–Breuer reflex

Lung volumes	VC FRC Vt dead space CC PEF calculations respiratory minute volume FEV1/FVC ratio Lung function tests spirometry body plethysmography peak flow meter nitrogen washout

Circulation	pulmonary circulation hypoxic pulmonary vasoconstriction pulmonary shunt

Interactions	Perfusion (V) ventilation (Q) ventilation/perfusion scan zones of the lung gas exchange pulmonary gas pressures alveolar gas equation alveolar–arterial gradient hemoglobin oxygen–haemoglobin dissociation curve (Oxygen saturation 2,3-BPG Bohr effect Haldane effect) carbonic anhydrase (chloride shift) oxyhemoglobin respiratory quotient arterial blood gas diffusion capacity (DLCO)

Insufficiency	high altitude oxygen toxicity hypoxia

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