Some bronchial capillaries & veins anastamose with Pulmonary capillaries & veins bypassing the right ventricle. Measurement of Total dead space is by Bohr’s equation: Total dead space calculated by Pco2 of expired air, Pco2 of arterial blood and the tidal volume.Īlveolar CO2% - Expired air CO2% Dead space air = Expired air x Alveolar CO2 % Expired air 500ml Expired air CO2= 4.0ml% Alveolar CO2 =5.5 ml% ( ) Dead space air=550x = 150 ml 5.5ġ0 Physiological shunt: Shunt is the volume of blood that passes from the venous to the arterial side, without passing through ventilated alveoli 1. The volume of gas in nonperfused alveoli and any volume of air in the alveoli in excess of that necessary to arterialize the blood in the alveolar capillaries is part of the dead space (nonequilibrating) gas volume.Ĩ Measurement of anatomic dead space: single-breath N2 curves. In healthy individuals, the two dead spaces are identical In disease states, there may be no exchange between the gas in some of the alveoli and the blood, and some of the alveoli may be overventilated. Total (Physiologic) dead space = (volume of gas not equilibrating with blood, ie, wasted ventilation) + anatomical dead space. Anatomical dead space Functional unit for Gas exchangeħ Anatomic dead space = Volume of air in the conducting zone which is not available for exchange

2 Learning objectives Differences in ventilation & perfusion in different parts of the lungs Dead space(DS), anatomical DS, Physiological DS (Total DS) Bohr’s equation to estimate total DS Meaning of shunt Alveolar gas equation Diffusion and flow limited exchange Diffusion capacity for oxygen, carbon dioxide & carbon monoxideģ Learning objectives At the of the lecture students should be able to Įxplain the differences in ventilation & perfusion in different parts (zones)of lung Explain the term dead space and describe the distinction between anatomic & physiologic (total)dead space Determine total dead space by Bohr’s equationĤ Explain the meaning of shunt alveolar gas equation, diffusion limited & flow limited exchangeĮxplain the diffusing capacity of the lung for oxygen, carbon dioxide, carbon monoxide Describe the structure of respiratory membrane & factors affecting diffusion of gases Describe the diffusion of oxygen from lungs to pulmonary capillaryĥ Pressure gradients for gas transfer in the body at restĬonducting pathway for the passage of air.

Apex physiological dead space