Airway resistance and ventilation

Question 1

Laminar flow vs turbulent flow

What does the airway have?

Answer 1

Laminar: R = 8nl / pi* r^4
Turbulent flow is less efficient than laminar flow.

Airways have transitional flow, a combination of the two

Question 2

factors that can alter airway resistance.

Answer 2

1. Airway radius: R ∝ 1/r4
   So, if radius increases by 2, resistance decreases by 16. And because Flow = ΔP/R, Flow will increase by 16.
2. Chemical factors affect smooth muscle tone of bronchioles
3. Mechanical factors

(note: the last 2 regulate airway radius)

Question 3

Chemical factors affect smooth muscle tone of bronchioles

Answer 3

1. bronchoconstrictors (PNS)
   - constriction of smooth muscle
   - acetylcholine
   - histamine
2. Bronchodilators (SNS)
   - relaxation of smooth muscle
   - norepi at β-receptors
   - other agonists for β- adrenergic receptors (isoproteronol, albuterol)
   - PCO2 in bronchioles

*note (If you have high levels of CO2 (ie. When exercising, you want bronchodilation). Help with ventilation-perfusion mismatch problem.)

Question 4

Mechanical factors that alter airway resistance

Answer 4

1. Mucous (bronchitis): reduces effective radius of bronchioles
2. Lung vol: expansion of lung pulls open alveoli and bronchioles to reduce resistance. But, if you remember, higher lung volume means shorter diaphragm which means reduced force of contraction
3. Dynamic airway collapse

Question 5

dynamic airway collapse and its effect on expiration.

Answer 5

During expiration, PIP can cause collapse of the airways.

- If PTP is negative (bc PIP is POS), airways collapse
    - forced expiration, tends to collapse the airways.

Question 6

Describe the difference between minute ventilation and alveolar ventilation
- which one is more imp?

Answer 6

Ventilation: airflow in the lung

Minute ventilation: volume of airflow through the lung in 1 min
MV = TV * breathing rate (av = 6L)

Alveolar ventilation (VA): volume of airflow in alveolar space in 1 min
(av = 4.5L)
- fxnionally more imp bc this is where gas xchange is occurring

Question 7

Describe factors that influence lung ventilation

Answer 7

1. Obstructive diseases
2. Severe Restrictive diseases (compliance problem)
3. Exercise
4. High altitude
5. Gravity

Question 8

Why do only severe restrictive diseases result in compliance problems?

Answer 8

○ Generally, ventilation is affected only by severe disease because body can compensate for lower ventilation in mild/moderate disease

Question 9

Describe the work of breathing and its influence on breathing rate and tidal volume.
- How do obstructive diseases shift the work curve?

Answer 9

Divide work into resistance and elastic components

• More elastic work = lower frequency and higher tidal volume and vice versa
• Obstructive diseases (you have to do more elastic work) decrease resistance, shifts the curve left, which is low freq, high TV

Question 10

How does deadspace reduce the efficiency of breathing?

Answer 10

there is more wasted ventilation

Question 11

With pulmonary fibrosis, Describe what happens to:

RV FRC TLC VC FEV1/FVC

Answer 11

RV     ↓
FRC    ↓  
TLC     ↓↓
VC      ↓↓
FEV1/FVC   No change/Slight ↑

Pulmonary fibrosis is a compliance problem: lung becomes more rigid

VC ↓ since the difficulty in expanding the lung will prevent the patient from inflating his lung maximally upon a forced inspiration

Question 12

With bronchitis, Describe what happens to:

RV FRC TLC VC FEV1/FVC

Answer 12

The hallmark of chronic bronchitis and emphysema is a limitation in airflow rates, particularly expiratory airflow. In chronic bronchitis the integrity of the alveolar-capillary surface is maintained. Airway resistance occurs because of excessive mucous secretion and bronchial wall inflammation and thickening.

RV       ↑  
FRC      ↑  
TLC     - 
VC      ↓
FEV1/FVC     ↓↓

RV and FRC ↑:
- One reason is air trapping. Because of the limitation of airflow during expiration, there may be extra air trapped inside the lungs at the end of expiration.

Cant take a deep breath in = ↓ VC

In obstructive lung disease, the FEV1 is reduced due to an obstruction of air escaping from the lungs

Question 13

What has more compliance, a used balloon or a new balloon?

Answer 13

a well used balloon as more compliance

(takes less P in add V)

The lungs have high compliance at their volume at rest, so that
it is easier for them to inflate during normal breathing. At high volumes, the compliance decreases, making expansion more difficult.

Question 14

Reduced chest wall compliance

- what happens to TV? why is that significant?

Answer 14

The main impact that this has on breathing is a reduction in the change in volume that the lung undergoes during normal breathing (the tidal volume).

• Reduced tidal volume ultimately results in reduced air-flow in the lung
• Pts w/ Smaller tidal volume: pts learn to breath at higher frequency

Question 15

effects of surface tension

- how do we combat this?

Answer 15

1. decreased lung compliance
   - surface tension favors smaller alveoli
2. water accumulation in the lung
3. collapse of small alveoli
   - P due to surface tension are going to go up due to r getting smaller and smaller and air is then going to continuously flow to larger alveolus.

combat with surfactant! (its efficacy increases at smaller alveoli radii)

Question 16

What week does surfactant begin to be produced?

Answer 16

fetal week 24

- earliest age a pre term infant can survive

Question 17

How does PTP affect airways staying open or close?

Answer 17

• If PTP is positive (bc PIP is NEG), airway stays open
• If PTP is negative (bc PIP is POS), airways collapse
• note: (-) PIP pulls open airways

PTP: difference between air pressure in the lung and the intrapleural pressure in the water in the intrapleural space
(Plung - PIP)

During inspiration, both PTP and PIP are rapidly changing, both becoming more negative, but the increase in negativity for PIP happens more quickly than for PTP.
- PTP lags behind that of PIP