RSPT 1060

1
RSPT 1060

• MODULE C Applied Physics
• Lesson 1 - Mechanics

2
OBJECTIVES

• At the end of this module, the student should be
  able to
• define the terms and abbreviations used in the
  module.
• draw explain the equation of motion.
• list the forces that oppose lung inflation
  cause the work of breathing.
• list the different types of compliance, their
  normal values equations.

3
OBJECTIVES

• At the end of this module, the student should be
  able to
• differentiate between compliance elastance.
• list some pulmonary disorders that could change
  compliance.
• explain the relationship between pressure,
  surface tension radius.
• explain how LaPlaces Law relates to surface
  tension.

4
OBJECTIVES

• At the end of this module, the student should be
  able to
• explain the purpose of surfactant.
• list the different types of resistance, their
  normal values and equations.
• explain how Poiseuilles Law relates to
  resistance.
• list some pulmonary diseases that will alters
  resistance.
• explain what the equal pressure point is.

5
Ventilation vs. Respiration

• Ventilation The bulk movement of gas in and out
  of the lung.
• Respiration The exchange of gas (specifically
  oxygen and carbon dioxide) at the cellular level.
• Internal Respiration The exchange of gas between
  a peripheral capillary and a cell of the body.
• External Respiration the exchange of gas across
  the alveolar-capillary membrane.

6
EQUATION OF MOTION
7
Equation of Motion
Mechanical positive pressure to inflate
Resistance (gas flow)
Muscle negative pressure to inflate
Compliance (volume)
8
Mechanical Ventilator vs. Spontaneous Breathing
9
Inflation pressure

• Spontaneous Breathing
• Contraction of muscles generates a negative
  pressure in lungs gas is pulled into lungs.
• Work done by patient.
• Mechanical Ventilator
• Positive pressure builds in the ventilator
  circuit gas is pushed into the lungs.
• Work done by machine.

10
WORK OF BREATHING

• FORCES OPPOSING INFLATION
• Elastic (stretch)
• Physical tendency of an object to resist
  stretching
• Non-elastic (friction)
• Occurs only when gas and the system is moving

11
Work of Breathing
Resistance
Compliance
Elastic Work (Stretch)
Non-elastic Work (Friction)
35
65
Tissue Airway
Lungs Chest Wall
(20)
(80)
Lungs Ribs Diaphragm Abd. organs
Surfactant
Tissue Lungs Pleura
Skeletal Muscular Skin
Airways Gas flow
12
COMPLIANCE

• ELASTIC OPPOSITION TO INFLATION
• Elastic and collagen fibers found in lung
  parenchyma give the lungs elasticity.
• Inflation - occurs as a result of forcibly
  stretching lung fibers during inspiration.
  (work)
• Deflation or exhalation is normally passive.
• The resting position of the lung is deflation.

13
Compliance

• Pressure-Volume loop

High Compliance
Normal Compliance
Vol
Low compliance
Pressure
14
Compliance

• Pressure-Volume loop

High volume (over-inflated)
Vol
Normal volume (filling)
Low volume (opening)
Pressure
15
EXPERIMENT

• Balloon
• Initial inflation easy or difficult?
• Normal inflation easy or difficult?
• Over inflation easy or difficult?

16
Compliance

• Compliance Distensibility of the lung
• Elastance Property of resisting deformation or
  desire to return to original shape

17
Comparison

• Example Tennis ball vs. Balloon
• Tennis ball
• High elastance low compliance
• High resistance to change in shape
• Low ability to stretch
• Balloon
• Low elastance high compliance
• Low resistance to change in shape
• High ability to stretch

18
Comparison

• Normal lung vs. Emphysema vs. Pneumonia
• Normal lung
• Normal elastance Normal compliance
• Returns to original shape easily
• Easily filled
• Emphysema
• Low elastance high compliance
• Does not return to original shape easily (floppy)
• Easily stretched until air-trapping occurs
• Pneumonia
• High elastance and low compliance
• Readily returns to collapsed state
• Very difficult to inflate

19
Compliance
?Volume (liters)

• Compliance

?Pressurepl (cmH2O)

• Total Compliance is composed of
• Lung Compliance
• Chest Wall Compliance

20
Lung Compliance

• Disease states that cause a change in lung
  compliance?
• Decrease
• Fibrosis
• Adult Respiratory Distress Syndrome
• Pulmonary Edema
• Increase
• Emphysema

21
Lung Compliance

• How will a patient with decreased lung compliance
  breathe?
• Rapid
• Shallow

22
Experiment

• Wrap belt tightly around chest.
• Breathe slow deep
• Breath rapid shallow
• Which feels better?

23
Chest Wall Compliance

• Stiffness of chest wall
• When thorax is intact, its resting level is FRC
• With disruption to chest wall lung collapse and
  chest wall expands (open pneumothorax)
• Force of movement of chest wall is opposite that
  of lung
• Chest Wall has tendency to expand (pull out)
• Lung has tendency to collapse (pull in)
• At rest they balance (FRC)

24
Chest Wall Compliance

• Disease states that cause a change in chest wall
  compliance?
• Decrease
• Chest trauma
• Chest burns
• Kyphosis
• Scoliosis
• Chest wall deformity

25
Total Compliance

• Normal Lung compliance 0.2 L/cmH2O
• Normal Chest wall compliance 0.2 L/cmH2O
• Normal Total compliance 0.1 L/cmH2O
• Why is total less than the individual
  compliances?
• Lungs at rest collapse
• Chest wall at rest expansion
• They are working in opposite directions

26
Calculation of Total Compliance

• Clinically we measure Dynamic and Static Lung
  Compliance

With air movement
Tidal Volume Vt (liters)
CDYN

Peak Pressure PEEP (cmH2O)
No air movement
Tidal Volume Vt (liters)
CSTAT

Plateau Pressure PEEP (cmH2O)
NOTE PEEP stands for Positive End Expiratory
Pressure. It is the BASELINE or starting pressure.
27
Calculations

• Normal compliance 0.1 Liter/cmH2O
• Volume 0.5 liters 0.1 L/cmH2O
• Pressure 5 cmH2O

28
Calculations

• Low compliance 0.05 Liter/cmH2O
• Volume 0.5 liters 0.05 L/cmH2O
• Pressure 10 cmH2O
• Stiffer lung needs more inflation pressure.

29
Calculations

• High compliance 0.17 Liter/cmH2O
• Volume 0.5 liters 0. 17 L/cmH2O
• Pressure 3 cmH2O
• Floppier lung needs less inflation pressure.

30
SURFACE TENSION

• The alveoli are like bubbles lined with fluid and
  filled with air.
• Surface tension is the attractive force exerted
  by like molecules at the liquids surface.
• Surface tension forces cause the bubble to
  collapse.

31
The Force of Surface Tension in a drop of liquid.
Cohesive force (arrows) attracts molecules inside
the drop to one another. Cohesion can pull the
outermost molecules inward only, creating a
centrally directed force that tends to contract
the liquid into a sphere.
32
LaPlaces Law
Two bubbles of different sizes with the same
surface tension. Bubble A, with the smaller
radius, has the greater inward or deflating
pressure and is more prone to collapse than the
larger bubble B. Because the two bubbles are
connected, bubble A would tend to deflate and
empty into bubble B. Conversely, because of
bubble A's greater surface tension, it would be
harder to inflate than bubble B.
33
Calculation of Surface Tension

• LaPlaces formula

4ST
Pressure in a bubble

r
P
P
ST surface tension If surface tension
increases, the pressure to inflate the bubble
increases. R radius If the radius decreases,
the pressure to open the alveoli increases.
34
(No Transcript)
35
Surfactant

• Alveoli are lined with a surface-tension lowering
  agent (surfactant) produced by alveolar type II
  cells.
• Surfactant has a low attractive force exerted by
  its molecules.
• Surfactant helps stabilize the alveoli so they do
  not collapse completely on each exhalation.
• Destruction of surfactant will significantly
  decrease compliance and increase the work of
  breathing.

36
Surface Tension

• Disorders altering or destroying surfactant
• Prematurity
• Adult respiratory Distress Syndrome
• Oxygen toxicity

37
(No Transcript)
38
(No Transcript)
39
RESISTANCE

• INELASTIC OPPOSITION TO INFLATION
• Occurs only when the system is in motion and air
  is moving. (friction)
• Tissue Viscous Resistance
• Airway Resistance

40
Tissue Resistance

• Tissue Viscous Resistance (20)
• Things that increase tissue resistance
• Obesity
• Fibrosis
• Abdominal distention

41
Airway Resistance

• Airway Resistance (80)
• Mainly in upper airway
• Only 20 in small airways (less than 2 mm)
• Things that increase airway resistance
• High gas flow
• Turbulent gas flow
• Narrow airway
• Long airway
• Viscous gases

42
Poiseuilles law

• Pressure ? 8 l V
• -r4
• ? gas viscosity l tube length
• V gas flow r tube radius

Pressure increases with increased tube length
and gas viscosity. Pressure increases with
decreased radius
43
Poiseuilles law

• Reducing the radius of a tube by ½ requires an
  increase in pressure 16 fold to maintain the same
  speed of gas flow through the tube.

Pressure 1 cmH2O
Pressure 16 cmH2O
44
Poiseuilles law

• Egan
• Rule of Thumb page 215
• Mini Clini page 215

45
Airway Size

• If a smaller radius causes increased resistance
  then why is resistance less in the smaller
  airways?
• More cross section
• Slower flow
• Laminar flow
• Large airways have less cross section higher
  more turbulent flows thus more resistance.

46
(No Transcript)
47
Calculation of Airway Resistance
Pressure (cmH2O)

• RAW

X 60
Flow (Liters/min.)
48
Calculations

• Normal Resistance 0.5 2.5 cmH2O/L/sec
• Pressure 10cmH2O 2 cmH2O/L/sec
• Flow 5 L/sec

49
Calculations

• Increased Resistance 4 cmH2O/L/sec
• Pressure 20 cmH2O 4 cmH2O/L/sec
• Flow 5 L/sec
• Narrower airways require more pressure.

50
Resistance

• Diseases that cause an increase in airway
  resistance
• Asthma
• Emphysema
• Excessive sputum production
• Tumors
• Things that decrease airway resistance
• Bronchodilators
• Anti-inflammatory agents

51
Resistance

• How will a patient with increased airway
  resistance breathe?
• Slow
• Deep

52
Experiment

• Breathe through a straw or coffee stirrer
• Breathe slow deep
• Breath rapid shallow
• Which feels better?

53
EQUAL PRESSURE POINT

• See Egan page 217 Figure 9-9
• Point where the pressure within the airway is
  equal to the pressure outside the airway.
• The airway will collapse downstream from the EPP.

54
(No Transcript)
55
EPP

• Airway caliber is determined by
• Anatomical support from cartilage and traction by
  tissues
• Pressure differences across their walls
• Inside pressure gt outside open
• Inside pressure lt outside collapse
• During forced exhalation, outside pleural
  pressure can become higher than inside airway
  pressure and airways collapses.

56
EPP Emphysema

• Low compliance found in emphysema results in less
  recoil pressure and less pressure inside the
  airway.
• Airways collapse sooner and more gas is trapped
  as EPP moves upstream toward smaller airways.
  (increased resistance)
• Encourage slow deep inspiration and slow
  exhalation through pursed lips.

57
Air Trapping
FIG 28-3, page 609
58
Assignments

• READ Egan
• Chapter 6 Surface tension - pgs. 99-100
• Chapter 10 Mechanics of Ventilation - pgs.
  216-224
• Do Sibberson Math Book Chapter 13
• First Third sample sets
• Practice exercises pgs. 160 171
• Look to objectives