4-Respir Mechanics

Question 1

pulmonary ventilation

definition

Answer 1

mechanical process to initiate movement of air into/out of lungs
-to meet oxygen requirements

Question 2

boyle’s law

Answer 2

pressure of a gas inversely related to volume of container
-inspiration = small vol > larger so dec pressure
-expiration = large vol > small so inc pressure

Question 3

muscles of inspiration

Answer 3

act to expand vol of thorax
1. diaphragm
2. intercostal muscles-external

Question 4

accessory muscles inspiration

Answer 4

1. scalenes
2. SCM

help elevate ribcage

Question 5

expiration process

Answer 5

usually passive and driven by pressure gradient + elastic recoil of lungs/chest wall

if not passive then use internal intercostals + abdominals to force diaphragm upward

Question 6

active expiration conditions

Answer 6

1. normal if exercising
2. pathologic if asthma, bronchitis, COPD

Question 7

transpulmonary pressure =

Answer 7

alveolar pressure - intrapleural P

intrapleural should be lower than inside lung (alv)

Question 8

P at end of expiration

Answer 8

P in lung = P in atmosphere

transpulmonary P is pos (0-neg # = pos)

Question 9

elastic forces

Answer 9

lungs have opposite forces as chest wall
-chest wants to expand, lungs want to collapse
-forces are equally balanced at end of expir/functional residual capacity

Question 10

pressures during inspiration

Answer 10

-elastic recoil of lungs inc (bc wants to shrink back)
-pressure in lungs less than atmospheric bc inc vol
-intrapleural pressure becomes more negative than end of expiration

Question 11

alveolar pressure changes

Answer 11

1. alveoli expand = pressure dec
2. dec P so air from atmo moves down pressure gradient into lungs
3. inc in gas moles counteracts the fall in P
4. gas flow until alveolar and atmo are equal and no gradient

Question 12

pleural pressure changes

Answer 12

1. thorax expands = P dec
2. inspiration ends and vol dec during expir so pleural P less neg
3. restings size of thorax returns pleural P to baseline

Question 13

why transpulmonary matters

Answer 13

important for work of breathing
-inc trans P with accessory muscles to expand lungs if mechanics off

Question 14

compliance

Answer 14

measure of how much force it takes to distend an elastic structure
-inc in length or vol when a distending force applied

aka lung distensibility based on pressure-volume curve

Question 15

elastance

Answer 15

measure of tendency to return to og length/vol when distending force removed ‘snap back ability’

Question 16

shallow slope

Answer 16

low compliance
difficult to distend
-usually at low lung vol and maximal volume

Question 17

determinants of compliance

Answer 17

1. elastic forces of lung tissue
2. elastic forces of surface tension/surfactant (more ST lower comp)
3. resistance forces to airflow

Question 18

hysteresis

Answer 18

diff b/t inspiration and expiration P-V curves
-higher levels of surface tension at low lung vol so low compliance (inspiration)
-surface tension already been overcome during expiration so curve looks diff/steeper

Question 19

surface tension

Answer 19

generated at air-water interface
-exerts inward pressure vs walls of alveoli to resist expansion

water moles will be attracted inward and to each other

Question 20

surfactant

Answer 20

type II alveolar cells disrupts intermolecular forces of water to dec surface tension and dec collapsing force

dipalmitoylphosphatidycoline aka lecithin mostly

Question 21

neonatal rspiratory distress syndrome

Answer 21

infants premature have insuff lecithin so insuff surfactant = high surface tension and fluid accumulation

surfactant administered, ventilate

Question 22

emphysema

Answer 22

normal chest wall + dec lung elastic recoil = higher functional residual capacity

steeper compliance curve bc easier to distend lungs (loss of elastic fibers) = inc compliance, barrel shape bc breathing in high volumes

Question 23

pulmonary fibrosis

Answer 23

inc lung elastic recoil + dec chest wall = dec functional residual capacity and compliance (more diff to distend, shallow curve)

from collapsed alveoli, pulmonary edema, or lung fibrosis

Question 24

chest wall abnormalities

Answer 24

-pectus excavatum
-kyphosis

Question 25

airway resistance determined primarily by

Answer 25

radius of an individual airway
-small radius changes = large resist changes

Question 26

airway resistance is highest

Answer 26

in early airway (larger diameter) bc cross sectional area smaller