Lecture 7 Flashcards
When does ventilation of the lungs occur?
When the difference in the pressure between the airway opening and the alveoli is sufficient to overcome tissue (lung and chest wall) elastance and resistance to the flow of the air in the airways.
How do you get air into the lungs?
Expand the volume (increase) and to overcome the elastane and overcome the resistance to airflow.
What is the equation of motion known as?
It is where ventilation can not occur unless change in pressure is large enough to overcome:
- Tissue elastance.
- Air-flow resistance.
What is intra-pleural pressure equal to?
The oesophageal pressure.
What is the length of one breath?
4 seconds. For inspiration (2sec) and expiration (2sec). Roughly 15 breaths a minute.
Describe air-flow?
Draw in vastly for 1 second then at a diminishing rate for another 1 sec. Then when you expire it is the same.
Where does peak airflow coincide with?
With the steepest part of the volume (flow is rate of change of volume in time). Both with expiratory and inspiratory.
What does air-flow resistance introduce?
Phase-shift (time lag) between pressure and flow.
What happens when we inspire on the graph?
The oesophageal pressure decreases so the pressure becomes more positive overall; allowing the volume to increase.
What is the dotted line in the middle?
Have to overcome the elastance and air-flow resistance.
What happens when you have a larger loop?
It means that ventilation must be faster as you have dropped Pip even more. As you have put Pip into positive range, by exhaling very rapidly.
What happens when you have a small loop?
Almost no air-flow resistance.
How is ventilation achieved?
Active contraction of skeletal muscles against a (variable pressure) load. This produces external work (W) at the expense of metabolic energy expenditure (em).
What needs to be done?
Work needs to be done to overcome lung (and tissue) elastance (E = C-1) as well as resistance to airflow (and tissue movement) R.
What do patients with COPD reduce?
Breathing frequency, which reduces work against viscous resistance to air flow which reduces total amount of work.
