Lecture 25 - Dynamic Mechanisms Of Breathing Flashcards
What does Poiseuilles law suggest
That the smallest tubes should have the greatest airway resistance, but since there is lots of them the cumulative resistance is lower
In resp physiology what is airway resistance
The resistance of the respiratory tract to airflow during inspiration and expiration
How is airway resistance measured
By body plethysmography
What happens during a traditional body plethysmograph
The test subject is in a sealed chamber with a single mouth piece. At the end of normal expiration the mouth piece is sealed off and the subject is asked to try to inhale
What occurs within the lungs during a body plethysmograph
When the subject tries to inhale, the lungs expand decreasing the pressure within the lungs and increasing the lung volume
What factors determine resistant in the lung
Lung volume and branching, bronchiolar smooth muscle tone, density and the viscosity of gas
What is laminar flow a function of
Gas viscosity
What does turbulent flow depend on
Gas density
Where does the bronchiolar smooth muscle line
The upper airway
What does bronchiolar smooth muscle allow for
Alterations in tone which alter the radius of the bronchiole
How is the tube radius decreased
By contraction
What factors causes the contraction of the tube
Parasympathetic activity, ACh, irritants and decreased alveolar Pco2
How is the tone radius increased
By muscular relaxation
What factors cause an increased tube radius
Sympathetic activity, pulmonary stretch, noradrenaline, adrenaline and salbutamol
What does bronchiolar smooth muscle have a major role in
Ventilation-perfusion matching and is also linked to lung diseases that are linked to increased resistance
In pressure-volume curve what direction is the inspiration and expiration curve
The inspiration curve is upwards and the expiration curve is downwards
What can pressure-volume curves be used is assess
Lung overdistension, airway obstruction, bronchiolar response and respiratory mechanics
What does the top part of the pressure-volume curve represent
Dynamic compliance
What occurs to the pressure-volume curve as airway resistance increases
The curve becomes wider
During inhalation what occurs to airway resistance, gas flow and lung volume
The airway resistance decreases as gas flow and lung volume increase
What is known as dynamic lowering of resistance during lung expansion
The airways being physically widened
During expiration what does the resistance of the upper airway help
To keep airway pressure high to maximise gas movement out of the alveoli
What does exhalation work against
Smooth muscle contraction and upper airway resistance
What does smooth muscle contraction cause
Dynamic compression
What is asthma caused by
An allergic inflammation which can be caused by dust mite fecal allergen or cat saliva allergen
What does asthma cause
Hyper-reactivity of the airway smooth muscle contraction which in turn causes bronchial smooth muscle thickening
What effect does asthma have on the convective gas flow of the lungs
For it to be much less efficient
When gas flow slows to the molecular diffusion rate in the upper airway what are the consequences
There is poor gas exchange in the respiratory acinus
When gas fails to reach the distal regions of the respiratory zone what happens
Alveolar Pco2 increases
What is the work of breathing used to overcome
The elastic and non-elastic resistances
What is work equal to
The force times the distance, which is equal to the pressure times the volume
In the quiet breathing cycle, during inspiration the energy input is required to overcome
The elastic component and the surface tension
During expiration the energy input is required to overcome
The airway and tissue resistance
During inspiration and expiration in panting what is the energy input required for
Inspiration - surface tension
Expiration - dynamic compression and upper airway resistance
In deep breathing during inhalation what is the energy input required for
Inhalation - elastic component
