Respiratory Cycle DSA Flashcards
Diaphragm
- Innervated by phrenic nerve
- Contracting, flattens into abdomen
- Increases volume of thorax
Contraction of inspiratory
muscles
• Increase in thoracic volume
Muscles that elevate rib cage
• External intercostals
Scalene
– raise 1st and 2nd rib
Sternomastoids
– raise sternum
Muscles of Expiration, passive or active?
Mostly passive – recoil when
inspiratory muscle relax
Muscles that compress rib cage
• Abdominals – displace diaphragm
• Internal intercostals – decrease AP diameter, increase
intra-abdominal pressure
Residual Volume (RV)
volume of
air that cannot be forced out, no
matter how hard one tries.
“getting the wind knocked out of you”
Tidal Volume (VT)
is the amount of
air inspired or expired in a single
breath, can vary
500ml
Inspiratory Reserve Volume (IRV)
volume of air breathed above tidal
volume (VT)
3000ml
Expiratory Reserve Volume (ERV)
volume of air that can be forced out
in addition to tidal volume (VT).
1100-1200 ml
Vital capacity (VC)
amount of air that
can be maximally inspired following a
maximal expiration
4600-4700 ml
What is VC influenced by?
influenced by posture, ability of diaphragm to
contract/relax, strength of respiratory muscles, thoracic wall
expansibility, resistance to air flow, lung elasticity, disease
Inspiratory capacity (IC) –
capacity
of air that can be maximally inspired
following a normal exhale
3500ml
Functional residual capacity (FRC)
amount of air that remains in the lungs
following a normal expiration
2300-2400 ml
Total Lung Capacity (TLC)
– maximal
volume to which lungs can be
expanded with greatest effort
TLC = IC + FRC = VC + RV
= ERV + RV + IRV + VT
5800-6000 ml
Nitrogen-Washout Technique:
Determines FRC
Individual breaths 100% O2 through one-way valve, all expired gas is
collected, monitored until N2 reaches zero.
Total volume of all gas expired is determined, and multiplied by % of N2
in mixed expired air (80%).
Helium (He) dilution:
Inhalation of a known concentration
(C1) of helium [insoluble in blood]
from a known volume (V1)
Change in concentration (C2) allows
for determination of V2 = FRC
Body plethysmography:
Enclosed rigid box Breath against shutter • Pressure in lungs change • Pressure in box changes proportionally in opposite direction
Intrapleural pressure
less than atmospheric pressure, near -5 cm H2O
During Inspiration, Ppl
Decreases to near -8 cm H2O
As thoracic cavity increases in size, alveolar pressure and pleural pressure
Ap: decreases
Pp: increases
Respiratory Cycle: Mid Inspiration
Volume is increasing
Pa is decreasing
Ppl is decreasing
Air is flowing into lungs
Respiratory Cycle: end of inspiration
volume has reached peak increase?
Respiratory cycle Mid Expiration
Volume is decreasing?
Respiratory cycle End Expiration
Volume has returned to resting
Pa decreases to zero
Ppl returns to resting
Respiratory Cycle summary
- rest
- mid inspiration
- end inspiration
- mid inspiration
- rest
Dead space
areas of lung that receive air but not blood
Anatomic dead space
space in respiratory system other than alveoli
Physiological dead space
basically alveolar dead space, in healthy individuals almost zero
alveolar dead space
alveoli receive air but not blood
At end of inspiration, anatomical dead space:
has entered the lungs
