BSCI450: Surface Tension Compliance

what factors affect force required behind inhalation and exhalation

surface tension, alveolar elasticity, compliance

volume of tidal breaths

500 mL

main cause of premature infant death

lack of surfactant production -> high surface tension

what is inside the alveoli

air and water layer

what creates surface tension in alveoli

water layer (polar)

types of alveolar cells

type I - form 1-cell-thick alveolar walls

type II - produce surfactant

what percent of alveolar cells are type II

5

what is the role of surfactant

decrease surface tension

do small or large alveoli have a bigger problem from surface tension

small

what would happen in the absence of surfactant

alveoli collapse

compliance formula

deltaV/deltaP

Law of LaPlace

P = 2T/r

P = pressure

T = surface tension of fluid

r = radius

what is the impact of the inward pull from surface tension on compliance

decreases

if alveoli is less compliant… it is ____ to inflate

harder

how does surfactant decrease surface tension

break interactions between H2O molecules

what is the impact of surfactant on compliance

result

increases

easier to inflate

what is surfactant made of

80% phospholipids

10% proteins

10% neutral lipids

what is dipalmitoylphosphatidyl choline (DPPtdCho)

phospholipid

pressure of small alveoli

pressure of large alveoli

high

low

what happens between small and large alveoli without surfactant

small alveoli have higher pressure -> collapse -> empty into large ones (high to low pressure)

compare effects of surfactant on small vs large alveoli

decreases surface tension (T) more in small alveoli

how does surfactant equalize pressure across small and large alveoli

P = 2T/r

small alveoli: small r -> large P BUT lower T

large alveoli: large r -> small P BUT higher T

infant respiratory distress syndrome (RDS)

premature babies lack surfactant

treatments for infant RDS

prenatal therapy: give high dose glucocorticoid to mom to stimulate production of surfactant by type II

synthetic surfactant aerosolized and delivered to infant’s lungs

minimum age for infant viability

24 weeks

two categories of lung disease

restrictive

obstructive

name 2 restrictive lung diseases

pulmonary fibrosis

tuberculosis

name 2 obstructive lung diseases

emphysema

asthma

pulmonary fibrosis/tuberculosis

scarring in lung due to irritants

non-elastic scar tissue restricts inhalation

reduced lung compliance -> hard to expand and hard to inhale

emphysema

smoke activates elastase -> destroys alveolar elastin

reduced recoil of alveoli

increased lung compliance -> hard to exhale

in obstructive diseases, what happens with stale/fresh air

trapped stale air dilutes fresh air

Ficks law reflects

flux of gas across membrane

Fick’s law

Vgas = AD(P1 - P2)/T

Vgas = rate of gas transfer

A = SA contact between alveoli and capillaries
D = diffusion constant

T = thickness of membranes

(P1 - P2) = partial pressure gradient

what is the max rate of O2 flux

rate of O2 metabolism

what happens to air pressure with increasing altitude

decreases

what happens to composition of air with increasing altitude

stays the same

composition of air

nitrogen, oxygen, CO2, other

Dalton’s law

total pressure exerted by mixture of gases = sum of pressures exerted by individual gases

how to find partial pressure of a gas

fraction of gas(total pressure)

Hagen-Poiseuille

R = Ln/r^4

what happens to partial pressure of gas at increasing humidity

decreases

what happens to partial pressure of gas at increasing temps

decreases

how to find partial pressure of gas in HUMID air

Pgas = (Patm - PH2O)(percent gas)

what contributes to partial pressure in humid enviros

water vapor

how does moisture in air affect breathing

increases viscosity -> increases resistance -> harder to breathe

what three factors decrease PO2 in alveoli relative to atmosphere

dead space

residual volume

water vapor pressure

what sets up pressure gradient

exchange of gas between alveoli and capillaries

mixing atmospheric air with anatomic dead space air

saturation of alveoli with water vapor