Download Physics of Respiration

Physics of Respiration
Boyle’s Law - the universal law of gases
PV = nRT
P1V1 = P2 V2
Physics of Respiration
• Dalton’s Law
In a mixture of gases the total pressure is the
sum of the pressure each gas would exert it
were alone. In dry atmospheric air the
barometric pressure is 760 mm Hg the PO2 is
159.2 20.95% of 760, of nitrogen PN2 is 600.6
79.02% of 760 and of CO2 is 0.2 mm Hg 0.03%
of 760.
Physics of Respiration
Atmospheric air is never completely dry, and its
water vapor exerts a partial pressure PH2O
corresponding to the water vapor content in
the air . The water content in the air of course
is dependent on air temperature The partial
pressure of the other gases is than reduced
in exact proportion
Physics of Respiration
If the 760 mm Hg contains 6.2% of water vapor
(the quantity it contains at body temperature)
PH2O OF 46.9 The total pressure of the
remaining gases is 713 mm Hg and their
individual partial pressures are in proportion
of their relative concentrations to make up
713 mm Hg
Physics of Respiration
In the alveoli some oxygen diffuses into the
pulmonary capillaries which reduces the PO2
in alveolar gas.. In alveolar gas the F of O2 is
normally 14.3% or .143 (760-47)= 103 mm Hg.
The deficit is made up by CO2 that enters
from the blood FACO2 = 5.6% 0.056 x (760 47) = 40 mm Hg. OVERHEAD
Physics of Respiration
• Henry’s Law
When a mixture of gases is in contact with a
liquid each gas will dissolve in the liquid in
proportion to its partial pressure
Ventilation
Movement of air bulk flow is proportional to
difference in pressure
Flow = (P atmospheric - P alveolar)
Inspiration = decrease alveolar pressure below
atmospheric
Expiration = increase alveolar pressure above
atmospheric
Ventilation
Inspiration -Active process
expands the thoracic cavity by expanding rib
cage (contracting external intercostal
muscles) and lowering the diaphragm ( dome
shape at rest, contraction causes it to flatten
and hence position). This causes the visceral
pleura and causes the lungs to expand-
Ventilation (insp cont.)
causing the alveolar pressure to drop to -2 mm
Hg air flows in until pressure equalizes- quiet
respiration called costal breathing labored
inspiration called diaphragmatic breathing
involves accessory muscles which help
increase the size of the thoracic cavity further
(sternocleidomastoid-elevates sternum,
scalenes- elevate superior two ribs, pectoralis
minor- elevates third through fifth rib
Ventilation
Expiration- passive process
inspiratory muscles relax, As the internal
intercostal relax ribs move downward and as
the diaphragm relaxes it resumes its dome
shape and pushes upwards . The elastic
properties of the lungs help them recoil. As a
result lung volume decreases the alveolar
pressure increases to + 2 mm Hg and air
flows out until pressure equilibrate.
Ventilation (expir. cont.)
In labored expiration the process becomes
active , abdominal muscles contract moving
ribs downward which compress abdominal
viscera which push the diaphragm upwards.
Contraction of intercostals depress rib cage.