Ventilation

Question 1

Ventilation (general) definition

Answer 1

• amount of air-flow in the lungs

Question 2

Minute ventilation vs. Alveolar ventilation

Answer 2

• minute = volume of air that flows into or out of the lung in one minute
  
  • @ rest ≈ 6L
• alveolar = volume of air that flows into or out of the alveolar spance in one minute
  
  • @ rest ≈ 4.2L
• minute is always > alveolar b.c it includes alveoli + conducting paths

Question 3

Factors that impact alveolar ventilation

Answer 3

1. bronchodilators/constrictors
2. exercise
3. altitude
4. obstructive/restrictive diseases
5. gravity

Question 4

Excercise impact on alveolar ventilation

Answer 4

• moderate excerise ==> ~10x increase in ventilation

Question 5

Bronchodilators/contrictors impact on alveolar ventilation

Answer 5

• bronchodilators ==> increased ventilation
• bronchoconstrictors ==> decreased ventilation

Question 6

Obstructive/restrictive disease impact on alveolar ventilation

Answer 6

• reduces ventilation by incresing airway resistance and/or altering lung compliance
  
  • e.g. emphysema
• in mild-moderate, overal ventilation may stay the same but w/regional reductions and increases elsewher

Question 7

Gravity impact on alveolar ventilation

Answer 7

• contributes to regional differences in ventilation
• | P_IP @ apex | > | P_IP @ base | ==> larger volumes ==> more poorly ventilated (b/c alveoli are less compliant at high volumes)
• reduced compliance @ apex ==> smaller change in volume vs. @ base ==> base ventilates 2.5x more than apex

Question 8

Factors that impact work of breathing

Answer 8

• work of breathing ≈ “work” done by respiratory muscles on lungs
• increased work of breathing occurs b/c:
  
  1. increase in elastic recoil (decreased compliance)
  2. increase in airway resistance
  3. combination of #1 & #2

Question 9

Changes in work of breathing at high/low tidal volumes

Answer 9

• @ low tidal volumes: elastic work is small, but resistance work is large (high frequency of breaths = smaller lung volumes)
• @ high tidal volumes: elastic work is large, but resistance work is small

Question 10

Dead-space characteristics

Answer 10

• ~150ml out of 500ml or air/breath remains in conducting path ==> “anatomic dead-space”
• “alveolar dead-space” = well-ventilated but don’t exchange gas
  
  • occur @ unperfused regions of lung
• “physiologic dead-space” = anatomic + alveolar
  
  • @ healthy ppl ==> anatomic ≈ physiologic
  • large difference btwn physiologic and anatomic ==> disease

Question 11

Residual volume/functional residual capacity definition

Answer 11

• RV=volume or air remaining in lungs after maximal expiration
  
  • RV = ~1.5L
• FRC=volume of gas present in lung/upper airways @ end of normal expiration
  
  • FRC = ~2.5L

Question 12

Total lung capacity definition

Answer 12

• TLC = volume of air inside lungs @ maximal inspiration
• TLC = ~7.5L

Question 13

Tidal volume/Vital capacity definition

Answer 13

• V_T = difference in lung volume between normal inspiration and normal expiration
  
  • volume of air that enters and exits during one breathing cycle
  • V_T ≈ 500ml
• VC = volume of air exhaled after maximal inpiration followed by maximal expiration
  
  • VC = TLC - RV

Question 14

Minute ventilation/volume definition

Answer 14

• total volume of air breathed per minute
• MV = tidal volume x frequency of breathing

Question 15

Measurements of lung volumes

Answer 15

• V_T and V_c ==> spirometer
• FRC ==> body plethysmograph: breath through moutpience in airtight chambger
• forced expirogram = dynamic measurement ==> separates normal from obstructive/restrictive disease
  
  • spirometer measuring volume when subject inspires maximally and expires maximally
  • FEV_1.0 = volume expired in first second
  • FVC = VC = total volume expired
  • FEV_1.0/FVC = 80% when normal

Question 16

Restrictive disease results on pulmonary function tests

Answer 16

• e.g. pulmonary fibrosis ==> decreased compliance/difficult inspiration
• ==> decrease in vital capacity
• may not show significantly reduced FEV_1.0/FVC

Question 17

Obstructive disease results on pulmonary function tests

Answer 17

• e.g. chronic brochitis or asthma ==> increased airway resistance
• FEV_1.0/FVC decreases significantly
• increase in FRC (functional residual capacity) and RV (residual volume)
• VC may be normal, slightly decreased or increased