Mechanics Breathing Flashcards
Functions of respiration
- Pulmonary ventilation
- Diffusion of O2 and CO2
- Transport of O2 and CO2
- Regulation of ventilation and respiration
External respiration
Mechanics of breathing
Moving gas in and out of the body
Gas transfer from lungs to tissues
Maintains body and cellular homeostasis
Internal respiration
Intracellular oxygen metabolism
Cellular transformation
Krebs cycle
Mitochondria and O2 utilization
Main purpose of ventilation
Maintain and optimal composition of alveolar gas
Alveolar gas
Acts as a stabilizing buffer between environment and pulmonary capillary blood
O2 and CO2 are constantly being diffused
Physiological lung structure
Lung weighs 1.5% of body weight
Large surface area- 70m^2, 40x the body surface area
Short diffusion pathway for gases permits rapid and efficient gas exchange, 500ml blood in lungs
Factors required to alter lung volumes
Respiratory muscles inflate and deflate
Tissue elasticity and resistance impede
Distribution of air in the lung, resistance in airway
Overcoming surface tension in alveoli
How are changes in alveolar pressure generated?
By changes in pleural pressure
Diaphragm & nerve innervation
75% of inspiratory effort
Pulls down 1cm - 10cm when forced
Pulls abdominal contents downward and forward
Prenic nerve C 3,4,5
Paradoxical movement when paralyzed- when diaphragm is enervated- causes upward movement with inspiratory drop of intrathoracic pressures
External intercostal & nerve innervation
25% of inspiratory effort
Pulls ribs upward and forward on inspiration
Intercostal nerves ventral rami T1-T11
Alterations to FRC
Increase: upright position, reverse trendelenburg, prone
Decrease: pregnancy, obesity, bowel obstruction, laparoscopic surgery, ascites, abdominal mass, trendelenburg, valsalva maneuver
Inspiratory accessory muscles
Scalene- attach cervical spine to apical rib, raise first to ribs during forced expiration
Sternocleidomastoid- attach base of skull to top of sternum, raise sternum during forced expiration
Expiratory accessory muscles
Rectus abdominus/ abdominal obliques- move diaphragm upward, intra thoracic pressure rises and forces air out
Internal intercostals- pull ribs downward and inward, decrease thoracic volume
These muscles are also used in coughing, vomiting, and defecation
TPP
Difference between alveolar pressure and pleural pressure
Alveoli collapse together when pleural pressure pulls outward
Elastic forces that collapse the lung during respiration is recoil pressure
Two parts of pleural membrane
Visceral pleura- thin serous lining of lungs
Parietal pleura- lines inner surface of chest
Pleura cavity is made of serous fluid
Pleura fluid maintains -5cmH2o pressure via lymphatic drainage, acts as a lubricant, and adherence
What happens if pleural pressure become positive
Pneumothorax
Hemothorax
Chylothorax
FRC
ERV + RV
2.5L
TLC
RV+ERV+TV+IRV
5.5L
VC
IRV+TV+ERV
4.5L
IC
TV+IRV
3L
How can FRC and TLC be determined?
CANNOT be measured by spirometry
Helium dilution, nitrogen washout, or body plethysmography
Compliance
What does it measure?
Change in volume / change in pressure
Measures distensibility of lungs
Normal static compliance
70-100cm H2O
Alterations in compliance
Increased with ages, emphysema
Decreased with with lower lung volumes, higher lung volumes, higher expansion pressure, venous congestion, alveolar edema, atelectasis, fibrosis
Surfactant
A synthesized fatty acid
Lowers surface tension of alveoli
DPPC Dipalmitoyl phosphatidyl choline- hydrophobic and hydrophilic ends , alignment of intermolecular forces, opposed water self attractant elastic force, reduce surface tension greater when film compressed
Elastic lung tissue
-Elastin and collagen fibers of lung parenchyma
Natural state if these fibers is contracted coils
-surface air fluid interface- 2/3 of total elastic force in lung, surface tension of h2o,
Functions of surfactant
Lowers surface tension
Promotes stability of alveoli
Prevents transudation of fluid in alveoli
Alveolar ventilation
70% of total ventilation
Always less than total ventilation
Alveolar O2 concentration steady state achieved when supply matches demand
Dead space
Vt = Va + Vd
30%
2ml/kg
Wasted ventilation
Deviation from the ideal ventilation relative to blood flow
Includes anatomical dead space PLUS any part of alveolar ventilation that is not working properly
Clot or emboli
Vt= Vt + Vd + Vad
Airway closure
The base of lung during exhalation does not have all of gas compressed out
Dependent regions only intermittently ventilating leading to defective gas exchange
Closing volume= volume when small airways collapse
Poiseulle law
R= pir4/8Ln
Describes resistance to flow thru a tube (laminar flow)
Pressure increases proportional to flow rate and gas viscosity
Smaller airway radius and longer distance increase resistance
Reduce radius by 16% will double R
llength
n viscosity
Ohm’s law
P=FR
P pressure
F flow
R resistance
Chief site of airway resistance
Major resistance is at medium sized bronchi
7th division most pressure drop
Very little resistance at small bronchioles
Factors determining airway resistance
Lung volume
Bronchial smooth muscle - low co2, acetylcholine, direct stimulation, histamine, cold
Density & viscount of inspired gas - density is a bigger factor
Work of breathing
W=PV
Illustrated by pressure volume curve
Oxygen consumption can be used to measure WOB
Quiet breathing - 5%
hyperventilation - 30%
High O2 cost in OLD
