Pulmonary gas pressures

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

Location	pO (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

Contents 1 Factors affecting alveolar gas pressures 2 Pathology 3 See also 4 External links

[edit] Factors affecting alveolar gas pressures

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 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

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

[edit] Pathology

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

Hyperventilation exists when the same ratio decreases.

[edit] See also

• Pulmonary alveolus

[edit] External links

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

Volumes: lung volumes - vital capacity - functional residual capacity - respiratory minute volume - dead space - spirometry - body plethysmography - peak flow meter ventilation (V) (positive pressure) breath (inhalation, exhalation) - respiratory rate - respirometer - pulmonary surfactant - compliance - hysteresivity - airway resistance pulmonary circulation - perfusion (Q) - hypoxic pulmonary vasoconstriction - pulmonary shunt ventilation/perfusion ratio (V/Q) and scan - zones of the lung - gas exchange - pulmonary gas pressures - alveolar gas equation - 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 high altitude - oxygen toxicity - hypoxia