Pulmonary Mechanics I

Question 1

negative pressure pump

Answer 1

• lung inflates due to a drop in intrapleural pressure outside the lung but inside the chest wall
• diaphragm drops, volume increases, pressure decreases, lung inflates
• respirator inflates using positive pressure and lung deflates due to recoil
• when diaphragm stops contracting, passive elastic recoil deflates lungs
• when relaxed, pressure is less than atmosphere by 5 cm water
• pulmonary pressures given relative to atm pressure, less than atm is negative
• intrapleural is -5
• in absolute terms intralpleural is actually positive because Patm=760/1034 cm h20, then pleural is 1029 cm h20
• when wounded, intrapleural pressure rises to atm and lung collapses

Question 2

inspiration muscles

Answer 2

• accessory- SCM, stermun scalene, facial, neck, head
• external intercostals-lifts ribs up and forward and increases post/ant dimension of chest cavity, adds tone
• diaphragm is primary muscle of inspiration

Question 3

muscles of expiration

Answer 3

• internal intercostals- lower ribs
• abdominal-depresses lower ribs, compresses abd cavity, pushes diaphragm up
• rectus abdominus, external/internal oblique, transversus abdominus

Question 4

eupnea

Answer 4

• quiet breathing
• diaphragm may be only muscle working
• enlarges thoracic cavity by moving downward
• expiration due to passive recoil of lung and the chest wall

Question 5

hypernea

Answer 5

• active breathing during exercise
• inspiration is aided by the contraction of external intercostals
• deeper and faster than normal
• tidal volume and freq increase
• inspiration uses external intercostals
• expiration uses internal intercostals

Question 6

strenuous exercise

Answer 6

• muscles of the chest and neck are used to reduce the resistance to air flow
• expiration aided by internal intercostals over 40L/min
• inspiration and expiration are active

Question 7

tachypnea

Answer 7

-more rapid than normal but not deeper

Question 8

hypoventilation

Answer 8

• muscular dystrophy, respiratory muscle paralysis
• leads to alveolar hypoxia and hypercapnea respiratory acidemia (high CO2, high H+, low pH)
• can’t breathe

Question 9

hyperventilation

Answer 9

• anxiety, panic attack
• breathing faster than required for oxygenation
• alveolar hypocapnea (low CO2, low H+, high pH)
• respiratory alkalosis

Question 10

pulmonary pressures

Answer 10

• alveolar compartment
• intrapleural space
• external space

Question 11

alveolar pressure

Answer 11

• varies during breathing cycle
• air movement requires pressure gradient
• during inspiration, Palv Patm
• if breath held with out and glottis open, pressure are equal

Question 12

intrapleural pressure

Answer 12

• Ppl
• space outside the lung but within the chest wall
• fluid filled and only 10 microns thick
• lung in close apposition to inner chest wall, movements of both elastic vessels lubricated by the fluid in the intrapleural space
• estimated by swallowing esophageal balloon so tip is in intrathoracic esophagus
• esophagus thin walled with little tone and transmits intrathoracic pressure changes
• upper end of balloon exposed to atm if mouth open, lower end changes in Ppl

Question 13

external pressure

Answer 13

• atm
• constant during cycle
• if weight placed on chest, external pressure is greater than Patm and is called body surface pressure

Question 14

transmural pressures

Answer 14

• pressure across and elastic vessel
• internal P minus external P
• outwardly directed positive, inwardly directed negative

Question 15

lung pressure

Answer 15

• Pl
• transmural pressure across lung
• Palv-Ppl (alveolar-intrapleural)
• sets degree of lung infiltration and must be positive to maintain inflation

Question 16

chest wall pressure

Answer 16

• Pc
• across chest wall
• Ppl-Patm (intrapleural minus atm)
• negative at rest

Question 17

total pressure

Answer 17

• Pt
• relaxation pressure
• across lung and chest wall
• Palv-Patm=Plung+Pc

Question 18

muscles relaxed

Answer 18

• mechanical equilibrium
• Pt=0
• Plung=-Pc
• positive outward pressure balanced by inward passive elastic recoil of the lung
• negative inward chest wall pressure balanced by passive outward elastic recoil of the chest wall
• exposed to air- lung collapses and chest wall springs out

Question 19

static compliance

Answer 19

-determines what particular volume the lung and chest wall will assume for a given transmural pressure when elastic vessels at mechanical equilibrium

Question 20

spirometer

Answer 20

• attached through a breathing tube connected to pressure gauge
• patient inspires then holds breath with glottis open, then relaxes muscles against weighted spirometer
• must be relaxed because passive elastic recoil is measured
• weight maintains lung inflation while the muscles are relaxed
• Ct about 0.1L/cm H20 near resting position of lung

Question 21

total compliance

Answer 21

-Ct=deltaV/deltaPt
-also equals deltaV/deltaPalv because P is Palv-Patm, but Patm is zero so P is Palv
-transmural pressures are additive
-Pt=Pl+Pc
-delta Pt=deltaPl +deltaPc
elastance:
-deltlaP/deltaV=deltaPl/deltaV+deltaPc/deltaV
-1/Ct=1/Cl +1/Cc (Ct=Cl+Cc)
-compliance of 1 lung is 1/2 of both lungs
-to normalize, specific compliance is used=deltaV/VdeltaP

Question 22

lung compliance

Answer 22

• need to separate from total to find source of problem
• deltaV/deltaPl
• remember Pl= Palv-Ppl (alveolar- intrapleural)

Question 23

chest wall compliance

Answer 23

• Cc=deltaV/deltaPc

- Pc= Ppi-Patm (intrapleural minus atm)

Question 24

functional residual capacity

Answer 24

• lung volume when Pt equals 0
• end expiratory
• 36% of vital capacity
• Pc=-Pl
• when lung is expanded to mechanical resting position of chest wall when Pc=0, only elastic force of lung opposes inspiration
• at larger lung volume when Pc>0, elastic recoil of both the lungs and chest wall provide passive DF for expiration

Question 25

forced expiration

Answer 25

• volumes below FRC, expansive force of chest wall provides DF for return of lung to FRC
• compliance depends on degree of inflation and is measured at FRC

Question 26

intrapleural pressure

Answer 26

• positive when muscles relaxed and the weight is on spirometer
• larger degrees of inflation, becomes more positive (contrasts with negative Pl during breathing)

Question 27

lung compliance in disease

Answer 27

• increased in emphysema

- decreased in fibrosis

Question 28

emphysema

Answer 28

• smoke contains inhibitor of alpha1 antitrypsin (normally inhibits proteases) so proteases aren’t inhibited- cuts CT up
• destruction of alveolar septae, merging of adjacent alveoli and formation of large blebs with loss of SA
• loss of elastic recoil and increased compliance
• neutrophils accumulate in lung to remove inhaled smoke, release the proteases, which aren’t checked

Question 29

pneumoconioses

Answer 29

• induced by inhalation of dust asbestos, coal, silica, other toxic particles
• induce granulomas and fibrous tissues
• decrease compliance
• stiffer lung
• changes in compliance also change total lung capacity and functional residual capacity

Question 30

air filled vs saline filled

Answer 30

• surface tension reduces compliance in air filled lung

- fluid removes recoil pressure leaving only elastic fiber recoil

Question 31

surfactant

Answer 31

• contains insoluble lipoprotein with diapalmitoyl lecithin
• lowers surface tension and increases compliance
• deficiency in surfactant increases surface tension and increases elastic recoil and deflates lung

Question 32

respiratory distress syndrome

Answer 32

• hyaline membrane disease
• premies
• no surfactant
• can’t keep lungs inflated due to decreased compliance
• use continuous positive airway pressure
• permeable to plasma proteins-glassy hyaline appearance

Question 33

bubbles

Answer 33

• if two bubbles have same surface tension, smaller bubble has larger internal pressure
• without surfactant, smaller alveolus empties into larger
• with surfactant, pressures are equal, surface tension increases with radius, larger area dilutes surfactant (less surface tension equalizes pressure)
• less surfactant per unit area and increase surface tension and pressure
• p=2T/r