Pulmonary gas pressures videos and info

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

Location	pO₂ (Torr)	pCO₂ (Torr)
Outside air - dry air at sea level	160	0.3
Alveolar air	105	40
Arteriole blood	100	40
Venous blood	40	50
Cells	<< 40	50

The alveolar oxygen 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 factors that determine the values for alveolar PO₂ and PCO₂ are:

The alveolar pO₂ is not routinely measured but is calculated from blood gas measurements by the Alveolar gas equation.

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

Hyperventilation exists when the same ratio decreases.

v • d • e Respiratory system, physiology: respiratory physiology

Lung volumes	VC · FRC · Vt · dead space · CC calculations: respiratory minute volume · FEV1/FVC ratio devices: spirometry · body plethysmography · peak flow meter

Airways/ ventilation (V)	positive pressure ventilation · breath (inhalation, exhalation) · respiratory rate · respirometer · pulmonary surfactant · compliance · hysteresivity · airway resistance · bronchial hyperresponsiveness · bronchial challenge test · bronchoconstriction/bronchodilation

Blood/ perfusion (Q)	pulmonary circulation · hypoxic pulmonary vasoconstriction · pulmonary shunt

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

Control of respiration	pons (pneumotaxic center, apneustic center) · medulla (dorsal respiratory group, ventral respiratory group) · chemoreceptors (central, peripheral) · pulmonary stretch receptors (Hering-Breuer reflex)

Insufficiency	high altitude · oxygen toxicity · hypoxia

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