week 2 mechanics of respiration cont Flashcards
Flow-Volume Loop
slide 31
Compliance is a measure of
the distensibility of the lungs
Compliance =
change in lung volume/ change in lung pressure
Cpulm = change of Vpulm / change of Ppulm
The extent of lung expansion is dependant on
increase of transpulmonary pressure
Normal static compliance is?
70-100 ml of air/cm of H2O transpulmonary pressure
is Compliance reduced by?
by higher or lower lung volumes, higher expansion pressures, venous congestion, alveolar edema, atelectasis & fibrosis
Compliance increased
with age & emphysema secondary to alterations of elastic fibers
Lung Volumes Changes Related To
Transpulmonary Pressure
pressure-volume curve
slide 36
Elastic Lung Tissue
- Elastin & Collagen fibers of lung parenchyma
- Natural state of these fibers is contracted coils
- Elastic force generated by the return to this coiled state after being stretched and elongated
- The recoil force assists to deflate lungs
Surface Air-fluid Interface
- 2/3 of total elastic force in lung
- Surface tension of H2O
Complex synergy between air & fluid holds alveoli open - Without air in the alveoli a fluid filled lung has only lung tissue elastic forces to resist volume changes
- Surfactant in the alveoli fluid reduces surface tension, keeps alveoli from collapsing
normal pt I:E ratio
1:2
copd or emphysema I:E ratio
1:3
Surface Tension Elastic Forces
The net effect on the lung to simultaneously
attempt to collapse alveoli by water tension
surfactant does what to the alveoli?
keeps them open. Surfactant lowers the surface tension of the alveoli fluid. reduces work of breathing.
surfactant is produced by what cell type?
Type II pneumocyte
DPPC-Dipalmitoyl phosphatidyl choline
- DPPC opposes water self-attractant elastic force to reduce alveolar surface tension
- Reduction of surface tension greater when film compressed closer as DPPC repel each other more
Total Ventilation or Minute Ventilation
Total volume of air conducted into lungs per minute
Single breath = Tidal Volume (VT)
VT varies with age, sex, body position & activity
Normal VT is 0.5 L
Minute ventilation = VT * freq
6 L/min. = 0.5 L * 12 breaths/min.
Alveolar Ventilation
Volume of fresh air entering alveoli each minute (70% of total ventilation or minute ventilation)
Alveolar ventilation is always less than total ventilation
Anatomical dead space and its portion of tidal volume (30%) affect amount of gas exchanged in alveoli
Alveolar O2 concentration steady state achieved when supply matches demand
Anatomic Dead Space = how much also what is it
150/500
Dead Space = ventilated but not perfused
dead space is roughly how many ml/kg
2 ml/kg
Wasted Ventilation is
The concept of physiologic dead space (VPD) describes a deviation from ideal ventilation relative to blood flow
what does wasted ventilation include?
anatomical dead space plus any portion of alveolar ventilation that does not exchange O2 or CO2 with pulmonary blood flow (alveolar dead space)
Ventilation/blood flow (V/Q) mismatch
where blood flow blocked ( clot or emboli)
Airway Closure is
The base of lung during exhalation does not have all of gas compressed out
Small airways in region of respiratory bronchioles collapse
Gas trapped in distal alveoli
who have airway closing issues?
Airway closure occurs at very low lung volumes in normal young subjects in the lowermost lung regions
Occurs in normal elderly lungs at higher volumes & can be present at FRC
Frequently develops in patients with chronic lung disease
Laminar flow is
parallel streams of flow
Velocity in center of airway twice as fast than at edges of tube T/F
true
Poiseuille Law describes
resistance to flow through a tube
Pressure increases proportionally to flow rate & gas viscosity
Smaller airway radius & longer distances increase flow resistance
decreasing the radius of the tube will do what to the resistance?
it will double the resistance
Turbulent Flow occurs at ___ flow rates or air velocity
higher
an increase in what will make turbulence more probable
density, velocity & airway resistance
Chief Site of Airway Resistance is at ?
Major resistance is at the medium-sized bronchi
Most of pressure drop occurs at what division?
also slide 57
seventh
Factors Determining Airway Resistance
- Lung Volume
- Bronchial Smooth Muscle
- Density & Viscosity Of Inspired Gas
As lung volume is reduced -
airway resistance increases
Contraction of airways increases
resistance
Bronchoconstriction caused by
PSN, acetylcholine, low Pco2, direct stimulation, histamine, environmental, cold
what is most likely to cause bronchospasm?
antibiotics and rocc
Density & Viscosity Of Inspired Gas
Changes in density rather than viscosity have more influence on resistance
Work of Breathing
Work is required to move the lung & chest
Work represented as pressure * volume (W=P*V)
O2 cost of quiet breathing is
5% of total resting oxygen consumption
Hyperventilation increases O2 cost to
30%
High O2 cost in obstructive lung disease limits exercise ability
