Muscles of Inspiration
Diaphragm (pulls down abdomen) External intercostals (raise ribs) Scalene (raise 1st and 2nd ribs) Sternomastoids (raise sternum) Additional muscles of head and neck
Why skeletal muscles?
Because we want to be able to control them, and to change respiratory rate when we need more air
-Allows rapid, uniform action and ability to respond to changes
Why is skeletal muscle not great always?
- if you injure the brain/SC they can stop working
- length-tension curve (you can have increased lung size–> stretched muscles)
Under normal conditions, the lungs and muscle/ribs are…
NOT physically connected to one another
-separated by pleural cavity, which is filled with fluid
What is on either side of the intrapleural space?
Visceral plura (by the lungs) and parietal pleura (by the muscle) -they have fluid in-between them
Intrapleural Pressure
- at rest: -5cmH2O (negative because of the lung’s elastic coil–the lungs want to be smaller, and the ribs want to pull away/be bigger)
- with inspiration: decreases (-8; reached at end of inspiration)
Alveolar Pressure
- as the lungs increase in size, the AP decreases
- rest: 0 cm H2O (matches atm pressure)
- inspiration: -1 cm H2O (below atm pressure, so air flows in)
- end of inspiration: returns to 0, and air stops coming in
Tidal Volume
amount of air inhaled in a given breath (Vt)
-in a typical breath, Vt is about 500mL
Muscles of Expiration
- abdominal muscles (push diaphragm upwards)
- intercostal muscles (decrease AP diameter of the thorax)
- accessory muscles (indicated difficulty breathing)
When do we use muscles of expiration?
in pathology–>typically we do not use them in a normal breath because expiration is passive because the lungs have elastic recoil (want to be smaller)
-basically, once the inspiratory muscles relax, air flows out and we reset
As expiration continues, the volume of air ____ and the alveolar pressure ___.
- decreases
2. increases (back to 0)
Peak negative value at inspiration of Intrapleural vs. alveolar
- End of inspiration
2. Mid inspiration
Minute Ventilation
how much air is inhaled every minute
Vdot=Vt x frequency
Anatomic Dead Space
no alveoli; cannot participate in gas exchange
-typically equals the same number as their weight
Minute Alveolar Ventilation
Valv=Vt - Vds
VdotA=Valv x f
When does air flow reach maximum L/sec?
halfway because as alveolar pressure starts to return back to 0 cmH2O, airflow begins to decrease as well
Transpulmonary Pressure
=Palv-Pip
-when positive, it means that the lungs are “open”
PAO2 vs. PaO2 vs. PvO2
- Alveolar gas
- Arterial gas
- Venous blood
