Ventilation Mechanics Flashcards
ventilation
movement of air in and out of the lungs
respiration
exchange of gases (oxygen and carbon dioxide) at the tissue, b/w tissue and blood, and b/w blood and lung
aerobic tissue respiration
refers to O2 utilization and CO2 production by metabolizing tissues with an ATP endproduct
respiratory quotient (RQ)
volume of CO2 released/volume of CO2 consumed
anaerobic tissue respiration
refers to the production of ATP w/o utilization of oxygen; only few ATP and lots of endproduct
how is CO2 produced in anaerobic respiration?
due to lactic acid production which breaks down into CO2 and water:
carbohydrates → lactic acid (La:H) → La- + H+ H+ + HCO3- ←→ H2CO3 ←→ H2O + CO2
partial pressure
the pressure of each gas in a mixture
Boyle’s Law
PV = k, where pressure and volume are inversely proportional; differences in air pressure drives movement of air into and out of lungs
quiet inspiration
downward movement of diaphragm (1-2cm) + contraction of external ICs = increased thoracic capacity and decreased pressure
forced inspiration
downward movement of diaphragm (8-10cm) + contraction of external ICs + accessory muscles = increased thoracic capacity and decreased pressure
quiet expiration
elastic recoil of lungs and relaxation of musculature
forced exhalation
internal intercostals and abdominal muscles contract and increase lung pressure to expel air
what force allows the lungs to move with the thoracic wall and diaphragm?
hydrostatic force (created by the pleural fluid)
spirometry
a measurement of breathing (or lung volumes) with a spirometer
spirometer
instrument used to measure breathing that consists of a dome that has been turned upside down and is floating in a water tank; the dome will rise when person breathes into tube and drops when person inhales
tidal volume (TV)
amount of air inhaled or exhaled with each breath under resting conditions (~0.5L)
inspiratory reserve volume (IRV)
excess air breathed in w/ accessory muscle recruitment
expiratory reserve volume (ERV)
the volume of additional air that can be forcibly exhaled after a normal exhalation w/ use of accessory muscles
vital capacity (VC)
the max. amount of air that can be moved in and out of lungs, measured during forceful breathing (TV + IRV + ERV)
residual volume (RV)
amount of air remaining in the lungs to prevent alveoli collapse
total lung capacity (TLC)
maximum amount of air contained in lungs after a maximum inspiratory effort (VC + RV)
functional residual capacity (FRC)
volume of air lungs naturally obtain when no muscles of respiration are engaged (end of quiet expiration; inward elastic recoil of lung = outward recoil of thoracic cage)
minute ventilation
tidal volume x respiratory rate
alveolar ventilation
rate of fresh air moving in and out of alveoli; equal to respiratory rate x (VT - dead space)
dead space
the volume of air occupying the non-respiratory segments of the airways (e.g. nose, pharynx, larynx, trachea, bronchi, bronchioles, terminal bronchioles) and does not participate in gas exchange
what are the impedances to ventilation?
elastance and resistance
elastance
a measure of the stiffness of the lungs
low elastance indicates:
compliance, such as in emphysema (compliance = 1/elastance)
high elastance indicates:
stiffness, such as in fibrosis and low surfactant
elastic tissues of the lung are:
highly compliant
surface tension of water and compliance
has low compliance compared to lung elastic tissue; water lining alveoli decreases lung compliance (increases elastance)
what is the effect of surfactant on compliance?
it reduces the surface tension of water and therefore the effort needed to breathe (prod. continually after 27-28 weeks of gestation)
resistance
related to the pressure needed to maintain air flow and can be likened to “drag” (pressure difference on both ends of a tube); rate of flow = change in pressure; equation is ∝ 1 / r^4
what happens ti lungs with high resistance?
obstruction, such as in asthma and COPD
which factor has the biggest influence on resistance?
airway diameter (caliber)
ventilation and pleural pressure
changes in lung vol. occur when the muscles of ventilation move the chest wall and prod. changes in pleural pressure (the lungs are recruited)
intrapulmonary pressure
pressure within the alveoli
pleural pressure
pressure in the pleural cavity
positive ventilation
the lungs are inflated by increasing pressure inside the alveoli (similar to mechanical ventilation)
normal ventilation
lungs are expanded by reducing pressure surrounding lungs to sub-atmospheric pressure (-ve pressure)
what affects pleural pressure?
pneumothorax or excess fluid accum.
pleural pressure
always negative during quiet breathing due to competition between elastic recoil of lung and rib cage (expand), more negative during inspiration (i.e. fluctuates during breathing cycle)
what is the intrapulmonary pressure during inspiration?
negative (less pressure)
what is the intrapulmonary pressure during expiration?
positive (more pressure)
what happens when the intrapulmonary pressure is the same as the atmosphere?
there is no airflow
before inspiration
- no breathing; resp. muscles are relaxed
- lung volume is functional residual capacity
- equally matched forces between lung elastic recoil and thoracic cage elastance to result in a negative pleural pressure
during inspiration
- muscles of respiration expand thoracic cage
- outward forces are greater than inner forces resulting in a more negative plural pressure
- (muscle forces + thoracic cage elastance > recoil)
end of inspiration
- inspiratory muscles active, holding lung at fixed volume
- increased lung elastic recoil due to stretching, thoracic cage elastance + muscle forces tends to make chest wall expand
- forces equally matched to result in even more -ve pleural pressure (forces pull on pleural space)
- intrapulm. pressure is zero = no airflow
during expiration
- inspiratory muscles inactive (allows passive recoil of lung for expiration)
- lung elastic recoil is increased and is larger than thoracic wall elastance (causing lungs’ volume to decrease)
- outward forces are less than inward forces and intrapulm pressure becomes less -ve
pleural pressure at rest
it fluctuates during the breathing cycle but is almost always atmospheric (negative; during inspiration)
