Zhong Mechanics Of Breathing 1

Front 1

Muscles of Ventilation

Back 1

1. Inspiration (active): diaphragm muscle, external intercostals.
2. Expiration (passive at rest) : a. abdominals, internal intercostals during severe respiratory load

Front 2

Breathing rate

Back 2

1. 10-20 times / minute at rest
2. 40-45 at maximum exercise in adults.

Front 3

Boyle’s Law

Back 3

Pressure (P) x Volume (V) = Constant

Front 4

P changes - at rest

Back 4

Pb = P outside body
Pi = P of inspired air in lung
1. At Rest with mouth open Pb = Pi = 0

Front 5

P changes - inhalation

Back 5

1.Increase Volume of Rib cage
2. Decrease the pleural cavity pressure, Pressure inside (Pi) lungs
3. Pb outside > Pi
4. Air flows down pressure gradient Until Pi = Pb

Front 6

P changes - exhalation (look at slide 14)

Back 6

1. Decrease Rib Cage Volume
2. Increase in pleural cavity pressure, Pi
3. Pi > Pb
4. Air flows down pressure gradient until Pi = Pb again

Front 7

Pressure-Volume Loop

Back 7

1. Pleural P < alveolar P ALWAYS
2.if not, the lung will be
Collapsed (pneumothorax)

Front 8

Pneumothorax formation

Back 8

pleural P = -6
alv P = 0
if pleural P becomes 0 collapses lung

Front 9

Hysteresis

Back 9

P/V loop graph
1. inspiration curve (bottom)
2. expiration curve (top)
3. the difference is called hysteresis
4. lung V for given P, expiration is greater than inspiration

Front 10

Lung compliance

Back 10

1. measure of the distensibility of the lungs
2. Cpulm = DVpulm / DPpulm
3. Different compliances: elastic forces of lungs
a. Compliance reduced by higher or lower lung volumes, higher expansion pressures, venous congestion, alveolar edema, atelectasis & FIBROSIS
b. Compliance increased with age & EMPHYSEMA, secondary to alterations of elastic fibers

Front 11

Elastic Forces of Lung

Back 11

1. elastic tissue of the lung and the thoracic wall
2. surface tension of the fluid that lines the inside wall of the alveoli

Front 12

Air vs. Fluid-filled

Back 12

1.P/V loops shifts to the left with almost no hysteresis
2. V rise with very little P

Front 13

Surface tension

Back 13

1. Law of LaPlace - P = (2 x T) / r
P alv, T (surface tension), r (radius of alveoli)
2. could collapse one and expand the other

Front 14

Surfactant

Back 14

1. Phospholipid produced by alveolar type II cells
2. Lowers surface tension.
a. Reduces attractive forces of hydrogen bonding
- interspersed between H20 molecules.
-Surface tension drops

Front 15

Functions of surfactant

Back 15

1. P is greater in smaller alveoli so surfactant reduces T and equalize P in small and big alveoli (compliance brought back to normal)
2. Increases compliance of lung
3. Reduces work of breathing
4. Promotes stability of alveoli
a. tiny alveoli tend to collapse, reduces forces causing atelectasis
5. Prevents surface tension forces from drawing fluid into alveoli from capillary

Front 16

Relaxation Pressure-Volume Curve

Back 16

1. Elastic properties of both the lung and chest wall determine their combined volume
2. At end of expiration, the inward pull of the lung is balanced by the outward spring of the chest wall

Front 17

Airway Resistance

Back 17

1. internal friction between gas molecules
2. friction between gas molecules and the walls of the airways

Front 18

Laminar Flow

Back 18

1. parallel streams of flow
2. velocity in center may be 2x as fast as in the edge
3. Poiseuille Law
R = (8 * L * n) / (p * r^4)
4. L=length, n = viscosity, r = radius

Front 19

Turbulent flow

Back 19

1. Local eddies form at sides of airway & stream lines
2. Breath sounds heard with a stethoscope
3. Pressure no longer proportional to flow
4. Increases in density, velocity & airway resistance make turbulence more probable

Front 20

Chief site of airway resistance

Back 20

1. *Major resistance is at the medium-sized bronchi
2. Most of pressure drop occurs at seventh division
3. Very small bronchioles have very little resistance - prodigious number of small airways in parallel

Front 21

Factors Increase Airway Resistance

Back 21

1. Any factor that decreases airway diameter, or increases turbulence
a. Rapid breathing
b. Narrowing airways as in asthma, parasympathetic stimulation
c. Emphysema
2. Increase of the density (more influence) and viscosity of the inspired gas
3. Lung volume
a. As lung volume is reduced - airway resistance increases
b. linear relationship between lung volume and conductance

Front 22

Isovolume Pressure-Flow Curves

Back 22

1. at the high lung volume: a rise in intrapleural pressure obtained by increasing expiratory effort results in a greater expiratory flow
2. at mid and low volumes: flow becomes independent of effort after a certain intrapleural pressure has been exceeded

Front 23

Equal pressure point – normal lungs

Back 23

1. divides the airways into downstream (alv to EP) and upstream segments (EPP to mouth)
2. driving pressure (10) for airflow is now alveolar pressure(40) minus the pleural pressure (30)
3. PL = PA - PPL
4. PA = PL + PPL
40 = 10 + 30
5. Airways are subjected to compression during forced expiration from the EPP to the trachea.

Front 24

Dynamic Compression of Airways

Back 24

1. Limits air flow in normal subjects during a forced expiration
2. flow = alveolar pressure minus pleural pressure
3. exaggerated in some lung diseases
a. reduced lung elastic recoil
b. loss of radial traction on airways

Front 25

Obstructive vs. Restrictive Airway Disease

Back 25

1. Obstructive airway diseases
a. Increased airway resistance
b. Asthma, Emphysema, Bronchiectasis, Bronchitis, and Chronic obstructive pulmonary disease (COPD).
2. Restrictive Airway Disease
a. Decreased lung volume, compliance
b. Increased work of breathing
c. Diseases include Pulmonary Fibrosis, Asbestosis, Silcosis.

Front 26

Work of breathing with diseases

Back 26

1. restrictive disorder: the inspiratory work of breathing is increased.
2. obstructive disorder: Airway resistance is increased, which requires more energy to force air out of the lungs during expiration.

Front 27

Flow-Volume Curves in Lung Diseases

Back 27

1. Restrictive disease: peak expiratory flow (PEF) and total lung capacity (TLC) are decreased. The effort-independent part of curve is similar to the normal.
2. Obstructive disease: the residual volume (RV) is greatly increased. The effort-independent portion of curve is depressed inward.

Front 28

Intrapleural Pressure

Back 28

1. pressure of the fluid in the space between the lung pleura (visceria) & chest wall pleura (parietal), ALWAYS NEGATIVE
2. at rest: suction creates a negative pressure at beginning of inspiration (-5cmH20)
3. suction holds the lungs open at rest
4. Pressure - more negative during inspiration; -7.5cmH20 allowing for negative pressure respiration
5. pleural pressure becomes positive the lung will collapse: Pneumothorax, Hemothorax, Chylothorax

Front 29

Trans-pulmonary Pressure

Back 29

1. pressure difference between the alveolar pressure & pleural pressure on outside of lungs
2. THE ALVEOLI tend to collapse together while the PLEURAL PRESSURE attempts to pull outward
3. elastic forces which tend to collapse the lung during respiration is RECOIL PRESSURE

Front 30

Work of Breathing

Back 30

1. pressure * volume (W=P*V)
2. Oxygen consumption measurements
a. quiet breathing ~ 5%
b. hyperventilation ~ 30%
3. Graph: P on X, V on Y: upper left area= elastic work, area between two lines=airway resistance work