Week 1: Physiology Part 1

Question 1

Pulmonary Function Tests

Answer 1

1. Static lung compartments: lung volumes
2. Airflow
3. alveolar membrane permeability: DLCO (diffuse limited CO)
   PURPOSE
4. categorize restrictive vs. obstructive
   -obstructive: FEV1/FVC is less than 70%
   -DLCO distinguishes between emphysema and chronic bronchitis, e.g.
5. Assessment of disease severity
6. post treatment evaluation of lung function

Question 2

TV, FRC, IC

Answer 2

• Tidal Volume (TV): amount of air the enters or leaves the lung in a single respiratory cycle (~500mL)
• Functional Residual Capacity (FRC): volume of gas in lungs at end of passive expiration
• Inspiratory Capacity (IC): max volume of gas that can be inspired from FRC

Question 3

IRV, ERV, RV

Answer 3

• inspiratory reserve volume (IRV): additional amount of air that can be inhaled after a normal inspiration
• Expiratory reserve volume (ERV): addition volume that can be expired after a normal expiration
• residual volume (RV): amount of air in lungs after maximal expiration

Question 4

VC, TLC

Answer 4

• Vital capacity: max volume that can be expired after a maximal inspiration (after TLC)
• Total lung capacity: amount of air in lung after a maximal inspiration

Question 5

Function of FRC?

Answer 5

• there are two periods of apneas, at end of inspiration and expiration
• FRC is a buffer to allow continued air exchange during those periods

Question 6

Two types of dead space

Answer 6

1. Anatomic
   -airway regions not capable of air exchange: conducting zone
   -size approximated in mL by person’s weight in lbs
2. Alveolar dead space
   -alveoli containing air but without blood flow in surround capillaries
   -can’t be measured
   Physiological dead space=anatomic+alveolar

Question 7

Alveolar ventilation

Answer 7

-the room air delivered to the respiratory zone per minute
-VA=(VT-VD) x f
f=respiratory rate
VD=dead space
VA=alveolar ventilation

Question 8

Muscles of respiration

Answer 8

1. Inspiration (active)
   - diaphragm
   - muscles of the chest wall: external intercostal muscles (pulls ribs up and out)
2. Expiration (passive)
   - due to relaxation of muscles above
   - accessory: EOA, rectus abdominus, IAO, transverse abdominal muscles

Question 9

Forces acting on the lung system

Answer 9

1. lung recoil

2. intrapleural pressure/transpulmonary pressure

Question 10

Intrapleural pressure

Answer 10

• pressure in the thin film of fluid between lung and chest wall (has slightly negative pressure because chest is pulling out and lung is pulling in)
• subatmospheric pressure: (negative) act to expand the lung
• intrapleural pressure is less negative at the base of the lung compared to apex because of weight of the lung (is more supported at base by ribs and diaphragm to balance downward forces)
• alveoli at apex are more distended then at the base

Question 11

Transpulmonary pressure

Answer 11

• pressure difference between the inside and outside of the lung (alveolar minus pleural pressure)
• if it is positive: lungs tend to inflate
• opposite of elastic recoil of the lung
• under physiologic conditions, transpulmonary pressure is always positive

Question 12

Describe the transpulmonary pressure vs volume curve

Answer 12

• inhalation is different from expiration: hysteresis
• lung volume at any given pressure during inhalation is less than the lung volume at any given pressure during exhalation
• as compliance decreases, the loop widens because it takes more pressure to open the lungs

Question 13

Pressures during the breathing cycle.

Answer 13

Before inspiration begins
-intrapleural pressure is -5cm due to elastic recoil of lung balanced against chest wall outward tendency
-alveolar pressure is 0, no airflow
During inspiration
-chest wall expands, intrapleural pressure falls. As volume increases in alveolar, pressure falls, causing airflow into lungs
End of Inspiration
-lung expands until the recoil force is equal to intrapleural pressure
-air inflow returns alveolar pressure to zero
Expiration
-chest wall recoils, intrapleural pressure increases (less negative)
-lung deflation until lung recoil force decreases to equal intrapleural pressure

Question 14

Describe changes in lung volume, intrapleural pressure, flow, and alveolar pressure under resting conditions during inspiration and expiration

Answer 14

INSPIRATION
-lung volume increases
-intrapleural pressure drops
-flow is into alveoli
-alveolar pressure decreases then increases
EXPIRATION
-lung volume decreases
-intrapleural pressure increases
-flow is out of alveoli
-alveolar pressure increases then decreases