Alveolar Ventilation, Lung Volumes, and Gas Laws Lecture 3

Question 1

What are three determinants of volume in the lungs?

Answer 1

1. Lung compliance
2. Chest wall compliance
3. Pathology of lungs or chest wall

Question 2

Define residual volume and normal values?

Answer 2

• Amount of gas left in the lungs after a maximal forced expiration
• Determined by the force generated by the muscle of expiration and the inward elastic recoil of the lungs
• Prevents lungs from collapsing at low volumes
• RV usually about 1.5 L

Question 3

Define expiratory reserve volume and normal values

Answer 3

• Expiratory reserve volume is the amount of gas that is expelled during a maximal forced expiration that begins at the end of normal VT
• Determined by the difference between the FRC and RV
• ERV about 1.5L

Question 4

Define inspiratory reserve volume and normal values

Answer 4

• Inspiratory reserve volume is the amount of gas inhaled during a maximal forced inspiration beginning at the end of a normal VT
• Determined by the strength of contraction of the inspiratory muscles and inward elastic recoil of the lungs
• IRV is usally 2.5 L

Question 5

Identify lung volumes which comprise the vital capacity

Answer 5

• Amount of air that may be maximally exhaled after a maximal inspiratory effort
• IRV + VT + ERV

Question 6

Identify lung volumes which comprise the functional residual capacity

Answer 6

• Amount of air remaining in the lung at the end of a normal exhalation
• ERV + RV

Question 7

Identify lung volumes which comprise the inspiratory capacity

Answer 7

• Amount of air that can be maximally inhaled at the end of a normal exhalation
• IRV + VT

Question 8

Identify lung volumes which comprise the total lung capacity

Answer 8

• Amount of air in the lungs after a maximal inspiratory effort
• IRV + VT + ERV + RV

Question 9

List seven factors in our practice that may affect lung volumes

Answer 9

1. Height
2. Position (supine, trendelenberg)
3. Obstructive lung disease (Asthma, COPD)
4. Restrictive lung disease (Morbid obesity, kyphoscoliosis)
5. Age (Decreased closing volume with age)
6. Surgery (decreased FRC, VC)
7. Anesthesia (decreased FRC, VC)

Question 10

Describe the universal gas law

Answer 10

• PV = nRT
• R = 8.3 J/Kelvin/mol

Question 11

Define Avogadro’s Law and the relationship between gas molecule quality and volume

Answer 11

• One mole of an ideal gas occupies a volume of 22.4 L at 1 atm and 0 cel
• Equal volumes of different gasses at the same temperature and pressure contain the same number of molecules
• If the amount of gas in a container increases, volume increases

Question 12

Define Boyle’s Law and the relationship of pressure to volume

Answer 12

• The volume of a given mass of gas is inversely proportional to the pressure, provided that the temperature remains constant
• If the pressure doubles the volume will decrease by one-half if the pressure is halved the volume will double
• P1 x V1 = P2 x V2

Question 13

Define Charle’s Law and the relationship between tempearture and volume

Answer 13

• The volume of a given mass of an ideal gas is proportional to the absolute temperature, provided that the pressure remains constant
• Must convert to Kelvin
• Therefore, as temperature increases, volume increases as long as pressure remains constant
• V1/T1 = V2/T2

Question 14

Define Gay- Lussac’s Law and the relationship between temperature and pressure

Answer 14

• The pressure of a given mass of an ideal gas is proportional to the absolute temperature, provided taht the volume remains constant
• PV=nRT
• Must convert to Kelvin
• As temperature increases, pressure increases, so that P1/T1 = P2/T2
• Increased temperature of a container makes molecules hit container walls harder, pushing container outward

Question 15

Shapiro’s Law

Answer 15

• PaO2 = FiO2 x 5

Question 16

Identify the effect of surgical positions on FRC and IRC

Answer 16

Question 17

Identify the effect of residual muscle relaxation and thoracic surgery on VC and IC

Answer 17

• VC and IC decrease with residual NDMR and thoracic surgery (Affects ability to cough, deep breath)

Question 18

Identify the effects of restrictive and obstructive lung disease on TLC, FRC, and IC, and RV

Answer 18

• Restrictive lung capacities are equally lower
• TLC increased in obstructive, decreased in restrictive lung disease.

Question 19

List 5 methods for measuring lung volumes

Answer 19

1. Spirometry
2. Nitrogen washout
3. Helium Dilution Technique
4. Body plethysmography
5. Fowlers method for determining anatomic deadspace

Question 20

Compare and contrast FVC, FEV1, and FVC/FEV1 in obstructive and restrictive lung disease

Answer 20

• COPD have higher volumes
• Restrictive disease limited by expansion and also volume

Question 21

List four examples of obstructive lung disease (ACCE)

Answer 21

1. Asthma
2. COPD
3. Emphysema
4. Chronic Bronchitis

Question 22

List four examples of restrictive lung disease

Answer 22

1. Pulmonary fibrosis
2. Morbid obesity
3. Chest wall disease (Kyphoscoliosis)
4. Neuromuscular disease (ALS, Myasthenics, NDMR)

Question 23

List five effects of anesthesia on lung volumes

Answer 23

1. Decrease in tidal volume
2. Increase in respiratory rate
3. Increase in closing capacity
4. Increase in shunt
5. Decrease in FRC

Question 24

Define anatomic deadspace as it relates to lung anatomy and ventilation/ perfusion

Answer 24

• Anatomic dead space is ventilation without perfusion
• VD
• Conducting zone is the anatomic dead space
• Seen in the first 16 generations, no respiratory exchange occurs here.

Question 25

Define alveolar ventilation as it relates to tidal volume and minute ventilation

Answer 25

* Alveolar ventilation is that portion of tidal volume that reaches alveoli * Always less than minute ventilation * Alveolar ventilation (V) typically matches alveolar perfusion (Q) * V/Q mismatch known as shunt * Perfusion without ventilation is seen in the obese population

Question 26

Compare and contrast anatomic and alveolar dead space as they relate to physiologic dead space

Answer 26

* Alveolar dead space is the respiratory zone/ volume that does not have perfusion * Physiologic dead space = (anatomic dead space + alveolar dead space) * Anatomic and alveolar dead space make up the physiologic deadspace * Known as the BOHR equation

Question 27

BOHR equation use to calculate VD

Answer 27

VD/ VT = (PaCO2 - PetCO2) / PaCO2

Question 28

Describe the normal anesthesia circuit deadspace (including anatomic) and identify the delivery system with the most VD

Answer 28

* Normal dead space during anesthesia is 30% * ET tube and connector increase dead space to 51% * Upper airway, facemask, and connector increases dead space to 68 %

Question 29

Identify the effect of volatile agents on tidal volume and minute ventilation

Answer 29

* Depress ventilation in a dose dependent fashion * Ventilatory response to PCO2 and PO2 depressed * Tidal volume depressed but respiratory rate increased so that minute ventilation only moderately decreased * Ratio of dead space to total ventilation increases * Substitution of N20 for equal MAC * Fraction of anesthetic lessens the increase in PCO2

Question 30

Partial pressure of respiratory gases.

Answer 30

Question 31

Describe the effect of the anesthesia machine and circuit on airway resistance.

Answer 31

* Dead space and resistance increases due to circuit and airway caliber * Conversion to positive pressure ventilation from negative pressure ventilaion nos as efficient and higher pressures required * Always an increase in shunt as more less efficient ventilation means less alveolar ventilation