Nunn's Chapter 6 Flashcards
- What prevents airway narrowing as we change from upright to supine position and in what situations can these mechanisms fail?
In changing from upright to supine position, there is no change in normal subjects. Genioglossus EMG activity increases 34%. Other muscles are activated as well (tensor palatini, palatoglossus, palatopharyngeus). These mechanisms can be altered by sleep, hypoxia and anesthesia.
How is the larynx involved in control of airway resistance during quiet breathing, during inspiration and during expiration?
During quiet breathing, movement of the vocal cords allows fine control of resistance. During inspiration, abduction of the vocal cords (posterior cricoarytenoids) decreases resistance. During expiration, adduction of the vocal cords by the thyroadenoids increases resistance (this may help prevent collapse of lower airways).
- What is the surface area of the diaphragm?
900 cm^2
What is the innervation of the diaphragm?
C3-4-5.
What are the two portions of the diaphragm and what are their origins anatomically?
The crural diaphragm begins at the lumbar vertebra and the arcuate ligaments. The costal diaphragm begins at the lower ribs and the xiphisternum. Both the crural and the costal diaphragm insert into the central tendon.
What is the zone of diaphragm opposition and how much of the diaphragm is involved in this zone?
The diaphragm zone of opposition is the portion of the diaphragm that is in direct contact with the rib cage. At FRC in the standing position this is about 55% of the diaphragm.
Name the three behaviors by which diaphragm contraction increases lung volume?
a. Piston-like behavior (the zone of opposition shrinks). This is mechanically efficient.
b. Non piston-like behavior (contraction of diaphragm fibers reduces the curvature of the diaphragmatic dome). This is less efficient.
c. Combination of both piston and non-piston-like behavior.
How are respiratory muscle subtypes classified?
Respiratory muscle subtypes are classified based on the amount of myosin heavy chains (MHC) expressed. The type and proportion of myosin heavy chains determines the velocity of contraction.
What are the respiratory muscle fiber types?
Type 1 fibers – contract and relax slowly and use aerobic pathway. They are fatigue resistant.
Type 2B fibers – are glycolytic, contract quickly and fatigue quickly.
Type 2A fibers – are intermediate between type 1 and type 2B.
Proportions of fiber types in the human diaphragm and what are they used for?
45% of fibers in the human diaphragm are type 1. Type 1 can manage all ventilator levels. Type 2 fibers are probably only needed for expulsive efforts and for active movement such as running and jumping.
What percentage of maximum load can the diaphragm manage chronically?
The diaphragm can handle up to 40% of its maximum load indefinitely. Beyond this point, fatigue develops
What is the importance of blood flow to the diaphragm during diaphragm fatigue?
Augmenting cardiac output and therefore diaphragm blood flow increases the contractility of a fatigued diaphragm.
What is the implication of blood flow to the diaphragm during weaning from mechanical ventilation?
Diaphragm function can become supply-dependent during weaning.
What is the time course and severity of diaphragm atrophy during mechanical ventilation?
In animals, after 18 hours of mechanical ventilation with or without paralysis, 10% of mass is lost. Fiber types can change within 24 hours. Decreases in type 1 and increases in type 2A fibers are seen within 24 hours of mechanical ventilation.
During quiet breathing, where is the work of breathing done and how is this energy expended?
During quiet breathing, all work of breathing is done by the inspiratory muscles. 50% is lost as heat during inspiration to overcome frictional resistance. 50% is stored as potential energy by deformed tissues. This is used during expiration and is lost as heat during expiration to overcome resistance.
