Artificial Ventilation and Heart-Lung Interaction

Question 1

What is Surfactant?

Answer 1

main function: to lower surface tension between air and alveolar fluid –> to prevent alveolar collapse at the end of expiration

• pulmonary host defense

Question 2

How to inflate the Alveoli?

Answer 2

• requires an excess pressure inside the alveoli relative to their surroundings –> pressure in thoracic cavity negative with respect to atmospheric pressure
• amount of pressure required for inflation depends on:
  • surface tension
  • radii of alveoli

Question 3

LaPlace’s Law

relation of vessel radius and tension

Answer 3

• the larger the vessel radius, the larger the wall tension required to withstand a given internal fluid pressure
• for a given vessel radius and internal pressure, a spherical vessel will have half the wall tension of a cylindrical vessel

Question 4

Why does the wall tension increase with radius?

Answer 4

• larger radius –> less curvature –> total tension must be greater in order to get the same downward component of tension

Question 5

Pendelluft

Answer 5

-transient movement of gas out of some alveoli and into others

–> larger alveoles increase their volume while smaller alveoles collapse

Question 6

What happens in case of ARDS?

Answer 6

The efficiency of ventilation is reduced so much that blood gases are affected

Question 7

Reasons for ARDS

Answer 7

1) pulmonary: diseases of the lung
- external incidents affecting the lung:
- drowning
- exposure to smoke

2) extrapulmonary: ventilation control problems, Motor Neuron Diseases (ALS), lung edema, Sepsis

Question 8

Defintion of Respiratory Failure

Answer 8

1) Hypoventilation: paCO2 > 45 mmHg

2) acute respiratory failure: paO2 < 50 mmHg

Question 9

ventilatory vs. parenchymal failure

Answer 9

pulmonary ventilatory failure: insufficient elimination of CO2

pulmonary parenchymal failure: inadequate oxygenation

Question 10

Negative Pressure Ventilation

Answer 10

e. g. Tank Respirators
- negative ambient pressure surrounding body

• -> reduced danger of pneumonia
  but: high mechanical efforts

Question 11

Advantages & Disadvantages - Positive Pressure Ventilation

Answer 11

Advantages:

• easy access to patient
• -> surgical procedures possible

Disadvantages:

• unphysiological pressures
• bacteria may enter lung –> pneumonia

Question 12

Categories of Respiratory Support - Classification Types

Answer 12

1) Classification by work of breathing (WOB)

2) Classification by the dependent variable
- volume control
- pressure control

3) Classification by Access to the Lung
- invasive vs. non-invasive

Question 13

WOB

Continuous Mechanical Ventilation

Answer 13

• Volume / Pressure controlled Ventilation systems
• PEEP = 0 –> intermittent positive pressure ventilation
• PEEP > 0 –> continuous positive pressure ventilation

Question 14

WOB
Assisted Ventilation (Synchronized!)

Answer 14

Ventilator provides mandatory breath, but patient has to trigger it

Question 15

WOB

Spontaneous Ventilation with Support

Answer 15

ventilator ensures a minimum minute Ventilation

Question 16

WOB

Pure Spontaneous Ventilation

Answer 16

patient is capable to breath spontaneously
–> weaning mode

• PEEP is used to prevent lung collapse

Question 17

intrinsic PEEP

Answer 17

= P(alv) at the end of expiration

but not necessarily = PEEP when deflation is not long enough

Question 18

Components of Ventilator

Answer 18

• dosing units
• mixing chamber
• pressure sensors
• inspiration & expiration tube

Question 19

COPD

& effects of COPD

Answer 19

Chronic Obstrusive Pulmonary Disease
- increased airway resistance
- intrinsic PEEP
- increased paCO2 & WOB
- often hyperinflated lungs with increased FRC (functional residual capacity)
- decreased FEV1/FVC
Emphysema

FEV: forced expiratory volume per second
FVC: orced vital capacity

Question 20

Asthma

Answer 20

muscle contraction makes airways narrower

–> increased expiratory resistance to air flow

Question 21

Emphysema

Answer 21

increased FRC

FRC: Functional Residual Capacity

• permanent expansion of airspaces
• -> barrel chest

Question 22

Positive vs. Negative Pressure Ventilation

Answer 22

• positive pressure ventilation may primarily ventilate ventral parts of the lung
• in a lying patient, perfusion is largest in the dorsal regions –> positive pressure ventilation producues V’/Q’ mismatch

Question 23

How is acute respiratory distress syndrome (ARDS) defined?

Answer 23

paO2/FiO2 < 200mmHg

• clinical signs: lung edema & Atelectasis
• FEV and FVC reduced

Question 24

Where in the paO2-pressure graph would the ventilation of ARDS lungs be least harmful?

Answer 24

at the beginning of the descending limb of hysteresis

Question 25

What kind of signal is set in Pressure Controlled Ventilation?

Answer 25

square signal

Question 26

What induces a hysteresis in the pV - diagram?

Answer 26

Atelectasis

Question 27

What is the difference between Intermittent and Continuous Positive Pressure Ventilation?

Answer 27

the value of PEEP

Question 28

The mechanical breathing power is a function of … and …

Answer 28

mechanical breathing power is a function of respiratory rate and tidal volume

• tidal volume is a function of frequency