Lung Mechanics Flashcards
Define compliance.
The change in lung volume per unit change in distending pressure.
- obstructive - compliance increased
- restrictive - compliance reduced
Give 4 examples of procedures used for measuring static lung volumes.
- body plethysmography
- nitrogen washout
- helium dilution
- radio graphic imaging
Define total lung capacity.
The volume of gas in the lungs and airways at position of full inspiration.
Define residual volume.
The volume of gas remaining in the lungs and airways at the position of full expiration.
Define tidal volume.
The volume of gas expired or inspired during one breathing cycle.
Define functional residual capacity.
The volume of gas in the lungs at the end of tidal respiration.
Define expiratory reserve volume.
The maximum volume of gas which can be expired from a position of functional residual capacity.
Define inspiratory capacity.
The maximum volume of gas which can be inspired from a position of full reserve volume.
Define thoracic gas volume.
The volume of gas in the thorax.
Define vital capacity.
The maximum volume of air that can be exhaled from a position of full inspiration, or inhaled from a position of full expiration.
Describe the nitrogen washout technique.
Nitrogen washout is a technique used for calculating static lung volumes. He patient breathes 100% oxygen in order to ‘washout’ nitrogen within the lung. The initial alveolar nitrogen concentration and the amount of nitrogen ‘washed out’ can be used to calculate the lung volume at the start of the washout. The washout is considered complete when the nitrogen concentration is
Explain the helium dilution technique as a method of measuring static lung volumes.
Helium is an inert, poorly soluble gas. The patient breathes in a known concentration of helium which is then diluted by the helium-free gas within the lungs. If the expired helium concentration is monitored, the volume of gas within the lungs can be calculated from the dilution effect. Soda lime is used to prevent the patient from rebreathing carbon dioxide and the test ends when equilibrium is reached (no more than 0.02% in 30 seconds).
Describe whole boy plethysmography.
Based on Boyle’s Law that pressure and volume remain constant in a constant temperature. The patient sits inside a box of known volume. When the patient breathes against a closed shutter, pressure changes occur within the thoracic cavity which results in compression and rarefaction of the air within the cavity. By measuring pressure changes at the mouth (equivalent to alveolar pressure when breathing against a closed shutter), and changes in the box volume (thoracic volume) the volume of gas in the thorax can be measured.
Describe the use of radiographic imaging as a technique for static lung volumes.
Chest X-Ray used to outline the lungs in both anteroposterior and lateral views. A given geometry is assumed or planimeters are used to derive the confined volume. In the determination of TLC 6-25% of subjects differed by >10% from TLC measured by plethysmography.
What is transfer factor?
Transfer factor of the lung to carbon monoxide in a single breath.
