Chapter 16

Dr. D. Washington

Respiratory Physiology

The term respiration includes three separate but related function:

A. Ventilation (breathing): mechanical movement of air between nose and alveoli of the lungs

B. Gas exchange: between the air and the blood; and between the blood and tissues

C. Oxygen utilization: cellular metabolism

E.R. Weibel’s Model of the Human Airways (Morphometry of the Human Lung)

Trachea

Bronchus

Terminal bronchioles

Terminal bronchioles

Alveolar ducts

Alveolar sacs

Co

nd

uctive Z

on

eT

ran

sin

on

al o

rR

es

pira

tory

Zo

ne

Bronchioles

T

Br

BL

TBL

RBL

AD

AS

Zone

1234

1718

21

23

0

Functional Unit of the Lungs

Surfactant decreases the surface tension of fluids linings the alveoli.

Law of LaPlace: the distending pressure (P) in a distensible, hollow object is equal at equilibrium to the tension (T) in wall divided by the 2 principal radii of curvature of the objects (R1 and R2). P

T

v

Alvelus

Secretory cells (type II)(Surfactant)

Squamous cells (type I)Interstitium basement membranes ofcapillary & alveolus

Surface tension causedby the cohesive forcesof water molecules

Air pressure inside the alveolus

Surfactant Effects

Without Surfactant

The clamps represent the forces of surface tension. The greater pressure on the small alveolus would cause it to collapse. With Surfactant

The pressure on the small alveolus is reduced.

.50 _

.25_

Lu

ng

Vol

. Ch

ange

(li

ters

)

expiration

inspiration

Intrapleural pressure (cm H20) (pressure around the lungs)Intrapulmonary pressure Negative pressure = subatmospheric pressure

Pressure - Volume Curve(Compliance)

-4 -5 -6 -7+3 0 -3 -4

Changes in Compliance

A. Decrease (increased resistance)

1. Aleolar edema: decrease caused by increase in pulmonary venous pressure

2. Atelectasis: partial or complete collapse of lungs

3. Pulmonary fibrosis: infiltration or connective tissue

B. Increase (decrease resistance)

1. Age: loss of elastic tissue

2. Emphysema: destruction of alveolar tissue

When the pressure inside the jar isreduced below atm. Pressure, the lung expands.

Elastic Properties of the Lungs

Excised dog lung

(vol. measuredon spirometer)

pump

Lung Volumes

500 ml

3,000 ml

1,000 ml

1,000 ml

150 ml Dead spaceResidual volumeExpiration Reserve volumeTidal volumeInspiration Reserve volume

Lung Capacities(combination of volumes)

TLC - total lung capacity VC - vital capacity IC - inspiration capacityFRC - function residual capacity

TLC VC

RV

IC

FRC

IRV

TVERVRV

Note: If the anatomical dead space is 150ml, and the tidal volume is 500 ml;the percentage of fresh air reaching the alveoli is 350/500 X 100% = 70%

Inspiration Reserve volume

Tidal volume

Expiration Reserve volume

Residual volume

Lung Compartments

Composition of Gases at Sea Level

PP = Partial Pressure

OxygenPP %

CO2

PP %Water

PP %

Nitrogen &rare gasesPP %

Inspirated air 158 21. 0.3 0.04 8 1. 594 78 (20oC; 50%Sat.)

Moist tracheal 149 19.6 0.3 0.04 47 6.2 564 74 air (saturated)

Alveolar air 104 13.7 40 5.3 47 6.6 569 75

Arterial blood 100 13. 40 5.3 47 6.2 573 75

Venous blood 40 5.6 46 6.5 47 6.7 573 81

Expired air 116 15.2 29 4 47 6.2 568 75

Partial Pressure in the BodyInspired Air O2 = 158CO2 = 0.3H20 = 8N2 = 594

Expired Air O2 = 116CO2 = 29H20 = 47N2 = 568

Right Heart O2 = 40CO2 = 46H20 = 47N2 = 573

Left Heart O2 = 100CO2 = 40H20 = 47N2 = 573

Capillaries O2 = 40, CO2 = 46, H20 = 47, N2 = 573

Alveoli O2 = 104CO2 = 40H20 = 47N2 = 569

Veins Arteries

Dead space

Coordination of Ventilation & Perfusion The efficiency of gas exchange in the

lungs is dependent on the adequacy and uniformness of ventilation and perfusion.

Inspired gas and pulmonary blood flow are unevenly distributed.

Ventilation-perfusion ratio inequality is the most common clinical cause of arterial hypoxemia.

Ventilation-Perfusion Ratio VA/Q = 0.8 in a normal person at rest Volume of blood perfusing the lungs

is 1.2 times greater than the Volume of air ventilating the lungs

Coordination of Ventilation & Perfusion

Pathological causes for Non- Uniform Distribution of Ventilation1. Regional Elasticity of Changes

(pulmonary fibrosis)

2. Regional Obstruction of Airways

3. Intrathoracic fluid Accumulation

Coordination of Ventilation & Perfusion

Coordination of Ventilation & Perfusion

Pathological causes for Non- Uniform Distribution of Perfusion1. Compression of Blood Vessels Caused

by Intrathoracic P.

2. Embolism

3. Regional Vasoconstriction (ANS)

Regulation of Respiration

I. IntrinsicMedulla of Respiratory Center found

in the brain stem

Regulation of Respiration

II. Extrinsic

A. Chemoreceptors1. Peripheral

carotid and aortic bodies

2. Central Nervous System (Medulla) 70 - 80% main cause for change

Regulation of Respiration

II. Extrinsic

B. The Hering-Breuer reflexesMaintains normal tidal volume.

(more important in infants)

1. H-B inflation reflex

2. H-B compression reflex

Respiratory CenterCortical & midbrain stimuli

glassopharyngeal glassopharyngeal & vagus& vagus

Cord facillatoryCord facillatoryimpulsesimpulses

PneumotaxicPneumotaxicinhibits respirationinhibits respiration

ApneusticApneusticstimulates respirationstimulates respiration

MedullaryMedullaryrythmicity centerrythmicity center

Impulses Impulses toto respiratory respiratory

musclesmuscles

Rhytmic Oscillation in the Respiratory Center

inspiratory expiratory

I Eneurons neurons

muscles of muscles ofinspiratory expiratory

Respiration neurons in Brain StemDorsal View; Cerebelium removed

D

A

B

C

Vagi intact

Vagi cut

All transected in A & B

IX

X

XI

XII

Parabrachials N.(pneumotaric center)

Middle cerebellar peduncle

Apneustic centerin 4th ventrical

Dorsal grouprespiratory neurons

Ventral grouprespiratory neurons

Respiration neurons in Brain StemDorsal View; Cerebelium removed

Effects of Transection

A. Above pons - regular breathing continues

B. Below pneumotaxic area - inspiratory neutrons fire continuously (sustained inspriation -apneusis. However, if the However, if the vagus is intact respiration continues (effects from lungs).vagus is intact respiration continues (effects from lungs).

C. Below apneustic area - gasping type irregular respiration continues with or with our vagus

D. Below medulla - respiration stops (phrenic nerve cut)(phrenic nerve cut)

Increased ventilation

Increased arterial Pco2

Plasma CO2Blood pH

BloodCSF

Chemoreceptorsin medulla oblongata

Respiratory centerin medualla oblongata

Chemoreceptorsin aortic &

carotid bodies

Sensory neurons

Spinal cordmotor neurons Negative

feedback

Respiratorymuscles

Decreased ventilation

Effects of Po2, Pco2 + ph on Alveolar Ventilation

Fluctuation of one variable at a time

Co2

phO2

Pco2 35 40 45 50 55Po2 120 100 80 60 40ph 7.5 7.4 7.3 7.2 7.1

Alv

eola

r V

enti

lati

on

(b

asal

rat

es) 7

6543210

Effects of Po2, Pco2 + ph on Alveolar Ventilation

Free Fluctuation Co2

ph

O2

Pco2 40Po2 100ph 7.4

Oxygen SolubilityHenry’s Law

The concentration of a gas dissolved in a fluid is directly proportional to the partial pressure of that gas.

Solubility Coefficients of O2 in blood =

24cc/L/atmos.

Arterial Po2 = 100mmHg

therefore,

dissolved O2 = = 3/15cc/l100mmHg x 24cc/L

760 mmHg

CH2

CH2

COOH

C

C

HemeCH3

CH3

CH3

CH3

CH2

CH2

CH2

CH2

CH

CH

CH

COOH

HC

C

HC

C

CC

C

C

C

C

C

CC

C CN

N

N

NFeC

C

Effect of Changes inPo2 on Blood

Oxyhemoglobin Saturation and Oxygen Content (figure 15.34)

Po2

Amount of O2

unloaded to Tissues

Pe

rce

nt

oxy

hem

og

lob

in s

atu

rati

on

Ozy

ge

n c

on

ten

t

(ml O

2/10

0 m

l blo

od

)(mm Hg)

Veins(at rest)

Arteries

100

80

60

40

20

00 20 40 60 80 100

20

15

10

5

0

Oxygen Dissociation

half saturations myglobin = 6mm Hg

hemoglobin = 24 mm Hg

O2 pressure mmHG

% S

atu

rati

on

0 20 40 60 80 100

hemoglobin

myglobin100

80

60

40

20

0

507%

38%

dis

soci

ated

Th O2 dissociation curve for myoglobin follows the law of mass action

with a dissociation constant of 3.3, the Po2 has to fall almost to 0 before the O2 is releases to the cells

Oxygen Dissociation

Mb +Po2K =Mbo2

Bohr Effect(effect of pH on O2 Dissociation)

0 20 40 60 80 100

100

80

60

40

20

0

Po2

% O

2 sa

tura

tio

n

pCO2 = 40pCO2 = 80pCO2 = 20

pCO2 = 20 high pH, shift left

pCO2 = 80 low pH, shift right

A drop in pH at any pO2, causes an In O2 Dissociation.

Bohr Effect(effect of pH on O2 Dissociation)

Factors affecting O2 Dissociation

1. pH (or Co2 ) - deoxyhemogloblim binds H+ more actively then oxyhemogloblim

2. Temperature - effects metabolic rate

[CO2]

CO2+ H20 H2O H2CO3 H+ + HCO3

3. 2,3 - DPG (diphosphoglycerate) of RBC.

Carbon Dioxide Transport the Chloride Shift in Tissue Capillaries

Plasma

Tissue CellsTissue Cells

Carbonic anhydrase

CO2+ H2O H2CO3

H2CO3 H++HCO3 -

H+ combines with hemoglobin

CO2 combined with

hemogloblin to form carbaminohemoglobin

(20%)

CO2CO2 dissolved in plasma (10%)

Red blood cellsHCO 3 - (70%)Cl- Chloride shift