Respiratory Flashcards
What are the conducting airways?
From trachea, main bronchi (R and L), then lobar bronchi then segmental bronchi.
This process continues down until terminal bronchioles - smallest airways without alveoli
Function of conducting airways
o To lead inspired air to the gas exchanging regions of the lung
o As the airways become smaller, the amount of cartilage decreases and smooth muscle increases - the very small distal airways are composer mostly of smooth muscle.
o Because there is no gas exchange, they constitute the anatomic dead space - areas with ventilation but no blood flow.
Anatomical dead space
Space of conducting airways where there is no gas exchange
About 150mL
What is the respiratory zone?
o The terminal bronchioles divide into respiratory bronchioles, which have occasional alveoli budding from their walls
o Then alveolar ducts, completely lined with alveoli
What is an acinus
Portion of the lung distal to a terminal bronchiole, forms an anatomical unit called acinus
Airways zones
Blood-gas interface
o Extremely thin (0.2-0.3um) over much of its area
o Big surface area of 50-100m2
What are the main 4 lung volumes?
Tidal volume
Inspiratory reserve volume
Expiratory reserve volume
Residual volume
Tidal volume
Volume inspired or expired with each breath
Inspiratory reserve volume (IRV)
o Is the volume that can be inspired over and above the tidal volume.
o Is used during exercise.
Expiratory reserve volume (ERV)
The volume that can be expired after the expiration of a tidal volume.
Residual volume (RV)
The volume that remains in the lungs after a maximal expiration. cannot be measured by spirometry.
What are the main lung capacities?
Inspiratory capacity
Functional residual capacity
Vital capacity
Total lung capacity
Inspiratory capacity (IC)
Sum of tidal volume and inspiratory residual volume
Functional residual capacity (FRC)
o Sum of expiratory reserve volume and residual volume
o Is the volume remaining in the lungs after a tidal volume is expired.
o Includes the RV, so it cannot be measured by spirometry.
Vital capacity (VC) (aka forced vital capacity - FVC)
o Is the sun of tidal volume, IRV, and ERV.
o Is the volume of air that can be forcibly expired after a maximal inspiration.
Total lung capacity (TLC)
o Is the sum of all four lung volumes.
o Is the volume in the lungs after a maximal inspiration.
o Includes RV, so it cannot be measured by spirometry.
Graph of lung capacities / volumes - draw
Physiologic dead space
o Is a functional measurement.
o Is defined as the volume of the lungs that does not participate in gas exchange.
o Is approximately equal to the anatomic dead space in normal lungs.
o May be greater than the anatomic dead space in lung diseases in which there are ventilation/perfusion (V/Q) defects.
Equation to calculate physiological dead space
Minute ventilation
Volume of gas inhaled or exhaled per minute
Minute ventilation = Vt x RR (bpm)
Alveolar ventilation - VA
VA = (VT - VD) x RR (bpm)
VT = tidal volume
VD = physiological dead space
A person with a tidal volume (VT) of 0.5 L is breathing at a rate of 15breaths/min. The PCO2 of his arterial blood is 40mmHg, and the PCO2 of his expired air is 36 mm Hg. What is his rate of alveolar ventilation?
Muscles of inspiration
- Diaphragm
o Is the most important muscle for inspiration.
o When the diaphragm contracts, the abdominal contents are pushed downward, and the ribs are lifted upward and outward, increasing the volume of the thoracic cavity.
- External intercostal and accessory muscles
o Not used for inspiration during normal quiet breathing.
o Used during exercise and in respiratory distress.