BHS 116.1 – Human Physiology and Pathology
Notetaker: Emily Sorenson
Date: 09/30/11, 2 nd hour
Page1
AIMS:

Ventilation (cont.)

Diffusion of O
2
and CO
2
Between alveoli and blood
Topics

Pulmonary (minute) Ventilation o The total amount of new air moved into the respiratory passage each minute

Includes mouth, nasal passage, bronchi, trachea, alveoli o Tidal volume (air brought in) X respiratory rate (12 breaths per min) = 6 L/min
 Rate can be altered: can get up to 40-50 breathes/min

Tidal volume can change: up to 4500 mL o Pulmonary ventilation: 150-200 L/min - can get very HIGH

Max respiratory rate and tidal volume
 Can only sustain this for a short time – until physical exhaustion

Anatomic Dead Space o Alveoli is the only place where air is exchanged with blood o Tidal volume includes air in mouth, nasal passage, trachea, bronchi, etc.
 This is the anatomic dead space because there is no exchange occurring here

About 150 mL o Only 350 mL of new air will actually reach the alveoli with each breath

150mL of total 500mL expired is old air

Comes from anatomic dead space of last breath o Expiration pushes out 500 mL at same time L: 350 (new air) + 150 (old air)

Alveolar Ventilation o Total amount of NEW air that reaches the alveoli / min o Equals : respiration rate X ( tidal volume – dead space volume ) o In normal situation: = 4.2L /min o 1.8 L less than the total amount of air brought in during pulmonary ventilation o Key: this is the new air that gets to alveoli vs. total amount we actually bring in

Respiration o Respiratory rate can change o Tidal volume can change o Dead space volume never changes = always 150 mL

BHS 116.1 – Human Physiology and Pathology
Notetaker: Emily Sorenson
Date: 09/30/11, 2 nd hour
Page2 o Normal Pulmonary ventilation: 6 L / min o Normal alveolar ventilation: 4.2 L / min o During deep, slow breathing
 take in 1200 mL/breathe, but takes longer - so less breaths/min
 increases tidal volume

decreased respiratory rate
 Dead space and pulmonary ventilation don’t change
 Since tidal volume has increased, will have a higher alveolar ventilation

More air brought into alveoli during deep slow breathing

More O
2
into system

Easily exchangeable with blood o Rapid, shallow breathing (hyperventilation)

Respiratory rates = 40 breathes / min but only 150 mL / breathe
 Tidal volume = dead space volume 0 mL/min ventilation

No new air is getting into lungs (alveoli)

No O
2
/CO
2
exchange in blood

NOTE: Residual volume: still air in the lungs and capability of exchange with blood, but will be used quickly if no new air is being delivered

Diffusion of O
2
and CO
2
between Alveoli and Blood o Respiratory passage, functional part of lung = alveoli

Exchange occurs with blood vessels

O
2
goes from blood to the alveoli

CO
2
goes from the alveoli to the blood

Diffusion (simple) o Occurs down concentration gradient

Gas Pressure/ Partial Pressures o Partial pressure is proportional to (gas molecules) o Air is made up of many different gasses
 Total atmospheric pressure: 760 mmHg

79% N

BHS 116.1 – Human Physiology and Pathology
Notetaker: Emily Sorenson
Date: 09/30/11, 2 nd hour
Page3

21 % O – Partial Pressure (pp): 160 mmHg o Partial pressure: fractional amount of the given gas in the total amount of air/atmosphere

(in terms of pressure) o Gas has to diffuse into liquid (blood) : so pp will play a different role when we discuss diffusing a gas into the liquid
 Henry’s Law o Partial pressure = concentration of dissolved gas solubility (diffusion) coefficient

Gas has to be soluble in the liquid o Higher solubility coefficient = less pp required to dissolve specific gas into liquid o Low solubility Coefficient = more pp required to dissolve specific gas into liquid o CO
2
can dissolve in the blood at much lower partial pressure than O
2

Need higher pp of O
2
to dissolve the same amount of particles in the liquid

Net Rate of Diffusion of Gasses in Fluids o Fick’s Law

Looks at diffusion rate
 gasses diffuse in and out of blood at different rates
 there are many factors that play a role in determining a diffusion rate into gas
 change in pressure: ions or gasses travel down gradient
 cross sectional area: greater cross sectional area = greater diffusion rate o depends on size of alveoli or blood vessel
 solubility: More soluble gas will diffuse faster : CO2 faster than O2

Distance of diffusion: how far does it have to diffuse o Distance: normally doesn’t play a role, but with pathological systems, the distance might increase, making it harder to diffuse

Size: larger molecules = slower diffusion

Alveolar Air o Air comprised of : N, O, AND small amounts of CO
2
and H
2
O o Air moves from atmosphere through respiratory passage into alveoli o In transit, from atmos. to alveoli, air will get humidified through trachea and bronchi
 now water has larger component
 pp O
2
will drop (to about 100 mmHg)

BHS 116.1 – Human Physiology and Pathology
Notetaker: Emily Sorenson
Date: 09/30/11, 2 nd hour
Page4

Due to fact that it is getting humidified and that the alveoli is constantly exchanging with the blood, (O
2
molecules are leaving, pp decreases)

CO
2
is also much higher in the alveoli (140mmHg) because the blood is constantly bringing it to the alveoli

Difference between the pp of atmospheric air that we bring in to the pp that are observed in the air in the alveoli

Alveolar Air Replacement Rate o 2700 mL of air in lungs after tidal volume is taken in o Of that, only 350mL is new (1/7 – 1/8 th of total amt of air is replaced during each breath)

Prevents sudden changes in blood gas concentrations (partial pressures)

Partial Pressure Changes Across Respiratory & Systematic Membranes o O
2
diffuses from the lungs (alveolar system) into pulmonary capillaries and then out of systemic tissue capillaries into tissues: downward diffusion
 O
2
diffuses out of lungs into tissues o CO
2
diffuses out of tissues at systesmic capillaries, carried through venous system, leaves pulmonary capillaries into alveoli

CO
2
out of tissues into alveoli (lungs) o Partial Pressures driving exchange
 pp O
2
in alveoli is 100mmHg
 pp O
2
in tissues is 40mmHg (because being used in tissues for metabolism)
 pp CO
2
of in alveoli is 40mmHg
 pp CO
2
in tissues is 46mmHg (because this is being produced via metabolism) o Blood equilibrates to whichever region it is located

Arteriole blood: pp O
2
=100mmHg; pp CO
2
=40mmHg
 Venous blood: pp O
2
=40mmHg; pp CO
2
= 46mmHg

Respiratory Unit o Alveoli and the pulmonary capillaries = where exchange is occurring in the lung

BHS 116.1 – Human Physiology and Pathology
Notetaker: Emily Sorenson
Date: 09/30/11, 2 nd hour
Page5

Respiratory Membrane o Consists of all the cell membranes and other components lining the respiratory units
 alveolar cell membranes, capillary epithelial cell membranes, Surfactant, water, interstitial tissue/fluid o Total distance = 0.5 µ m o Alveoli and capillary are very close but there is some interstitial space between them o Main components making up membrane

Pulmonary capillary alveolar fluid
 Type 1 alveolar cell

Cells of the Alveoli o Type 1: primary alveolar cell, lines the alveoli

Equivalent of endothelial cell lining the capillary
 1 cell thick o Type 2 : produce and secrete surfactant

Release into alveoli o Type 3: macrophages

Aka: Dust cell
 Phagocytes that take up dust particles, virus, bacteria, etc

Gas Diffusion Through Respiratory Membrane o 6 layers O
2
diffuses through:

Fluid and surfactants
 Alveolar epithelium: Type I

Alveolar epithelial basement membrane
 Interstitial space: this is very small (this is where problems occur in pathology)

Capillary endothelial cell basement membrane
 Capillary endothelial cells

Factors affecting the rate of gas diffusion through the respiratory membrane o Can see changes with:

Surface area, thickness of membrane, and pp changes o Thickness of respiratory membrane (6 layers)
 rarely changes - only during pathological changes o Surface area – can have expanded alveoli or blood vessels could diffusion rate o Diffusion coefficients of gasses (doesn’t change)

BHS 116.1 – Human Physiology and Pathology
Notetaker: Emily Sorenson
Date: 09/30/11, 2 nd hour
Page6 o Primary factor: Partial pressure difference between the blood and alveoli

Chart explains how certain changes affect the diffusion at respiratory membrane
 Under constant resting conditions: we don’t usually see this changes, but

Diffusion Capacity of the Membrane o Volume of gas that will diffuse through it per minute (based on 1 mmHg change)
 we do see them during exercise:

Under exercise: o Bring more air in o Expanding alveoli o Delivering more blood to lungs o Blood vessels increase in diameter o Increase surface area of respiratory membrane o Diffusion is easier for O
2
and CO
2

Above conditions decrease with pathological circumstances
During Exercise the Diffusion Capacity Changes due to: o Looking at the affects of normal diffusion capacity of O
2
and CO
2

Normal:

CO
2
: 20 fold greater diffusion capacity because its diffusion coefficient is greater

**always easier for CO
2
to diffuse than O
2

Exercise

Diffusion capacity of both increase sufficiently

Due to increase in surface area of respiratory membrane

Capillaries open up (that weren’t open prior)

Alveoli expand because we are bringing more air in

BOTH of these together increase the diffusion capacity of O
2

Ventilation-Perfusion Ratio (VP ratio) o Ventilation: brings air into alveoli o Perfusion: blood flow to alveoli o Zero ratio if we don’t have any ventilation (no air brought in)

BHS 116.1 – Human Physiology and Pathology
Notetaker: Emily Sorenson
Date: 09/30/11, 2 nd hour
Page7 o Infinity ratio if we don’t have any blood flow o During either of these cases, there is NO gas exchange

Either shut off O
2 delivery or blood flow o Physiological shunts

VP ratio is less than normal
 Due primarily to decreased ventilation

Blood flow is typically normal or increased to the area
 ventilation decreases and doesn’t match the blood flow

Blood flows through but no O
2
exchange

Effects:

Alveolar pp O
2
will be less than 100 mmHg
 not bringing in enough fresh air (ventilation decreased)

Blood pulls it out, but alveoli isn’t delivering
 pp CO
2
will be more than 40mmHg , because blood keeps delivering
CO
2
to the alveoli, but it isn’t getting expired as frequently o Physiological dead space
 Plenty ventilation but decreased blood flow to that area

O
2
cannot be given up into blood and thus not delivered to tissues
 Effects:

Bring in plenty of O
2
so pp O
2
is greater or equal to 100mmHg

No blood flow to pull O
2
away at the normal rate

O
2
will build

CO
2
is less than 40mmHg because no blood brings the CO
2
there o Graphically (lecture 25, pg 7):
 Black line: VP ratio

X axis: sections of the lung: top to bottom (L-R)
 Top of lung = dead space, air gets in no problem but blood flow is much lower than at the bottom

The top of the lung is above the heart; heart must pump harder to get it
UP to the top of the lung

BHS 116.1 – Human Physiology and Pathology
Notetaker: Emily Sorenson
Date: 09/30/11, 2 nd hour
Page8

Greater ventilation than Perfusion at top of lung, creates the dead space

Higher pp O
2
and Lower pp CO
2

Bottom of the lung = (opposite: physiologic shunt)

Less air relative to perfusion

Bottom of lung is right next to heart high perfusion levels of blood

Air flow is a lot lower than perfusion: no match of blood flow to air flow

Alveolar pp O
2
less than 100mmHg, pp CO
2
are much higher than
40mmHg o Lung Picture (Lecture 25, pg 7)

Upper lung :

VP ratio high (dead space in this area)

Lower blood flow compared to ventilation
 Bottom Lung:

Low VP ratio

Greater blood flow than air flow
 When we exercise:

Dilate blood vessels

More blood to lungs

More air intake into lungs

Normalizes both areas to normal VP ratio of 1 : better match of blood flow to air flow during exercise o Helps to normalize top and bottom portions of lung o Better 0
2
delivery and CO
2
expiration during exercise o Entire lung is under normal VP ratio, rather than just the middle

Local Controls of Ventilation-Perfusion Ratio o Local Controls

Physiological shunt:

High profusion, Low ventilation

Smooth muscle of arteriole and bronchioles will help to equalize 2 factors: o Increase CO
2
in alveoli = causes relaxation of bronchiolar smooth muscle

BHS 116.1 – Human Physiology and Pathology
Notetaker: Emily Sorenson
Date: 09/30/11, 2 nd hour
Page9

Dilate airways : Increases air flow o Decreased O
2
in alveoli = causes contraction of pulmonary arteriolar smooth muscle

Blood flow decreases
 Air flow increases

Dead space

Lots of airflow, little blood flow o Decrease in CO
2
= causes contraction of bronchiolar smooth muscles
 Constriction of airways, increased resistance, decreased air flow o Increase in O
2
= Causes dilation of local arterioles
 Increase in blood flow to the area o Body has normal regulatory controls based on O
2
and CO
2 concentration affecting bronchiolar and pulmonary arteriolar smooth muscle
Q: When is pulmonary ventilation equal to alveolar ventilation?
1.
When tidal volume inc
2.
When tidal volume decrease
3.
When respiratory rate is increased
4.
When respiratory rate is decreased
5.
Never **CORRECT: we always have dead space. They can NEVER be equal. There will always be regions where they are equal with the blood.