The dead space is increased by following factors: general anesthesia, artificial airway, emphysema, age, neck extension, positive pressure ventilation, pulmonary embolus, pulmonary artery thrombus, hemorrhage, hypotension, emphysema. Reversible airway obstruction can be studied by deter- mining the. The anatomic dead space is the sum of volume exhaled during the first phase and half of volume exhaled during the second phase. Alveolar ventilation can be calculated on the basis of an assumed physiologic dead space. The first phase has no nitrogen, the second phase nitrogen concentration increases and third phase is plateau phase. The subject breathes out and deeply inhales from 0% nitrogen gas mixture and exhales into the equipment that measures nitrogen and gas volume. Physiological dead space is calculated as follows:Īlveolar dead space is calculated as follows: Slowly the expirate is switched to Douglas bag once the respiration became steady. The rate of respiration and minute volume are recorded. The expirate is passed through the dry gas meter and into the atmosphere via two-way tap. The latter is firmly supported in the mouth by the standard mouth piece. A nose clip is applied and the subject is asked to breathe in and out through Ruben non-return valve. The examination is carried out by subject lying on the bed supported by pillow. The anatomic dead space is measured by Fowler’s method.
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