During plethesmography, which of the following occurs as patient expires with closed glottis in the box? (AIPG 2011)
|A||The pressure increases in both|
|B||The pressure decreases in both|
|C||The pressure in lungs increases and in the box decreases|
|D||The pressure in box increases and in the lungs decreases|
1. It is the most common method of meauring lung volumes.
2. Pressure in the box chnages in an opposite direction to that of the thorax.
3. The thorax expands on inspiration, thereby compressing gas in the box.
4. The opposite occurs on expiration.
I. It is commonly used alterative method of measuring lung volume that takes advantage of the principle of Boyle's law, which states that the volume of gas at a constant temperature varies inversely with the pressure applied to it.
II. The primary advantage of body plethysmography is that it can measure the total volume of air in the chest, including gas trapped in bullae. Another advantage is that this test can be performed quickly.
III. Drawbacks include the complexity of the equipment as well as the need for a patient to sit in a small enclosed space. A patient is placed in a sitting position in a closed body box with a known volume.
IV. From the FRC, the patient pants with an open glottis against a closed shutter to produce changes in the box pressure proportionate to the volume of air in the chest.
V. The volume measured by this technique is referred to as thoracic gas volume (TGV) and represents the lung volume at which the shutter was closed, typically FRC.