Pulmonary Physiology: Anatomy and Mechanics of Ventilation

what is the role of the respiratory system?

acquire O2, remove CO2, control blood pH through efficient gas exchange between the blood and the atmosphere

what is the general process of the respiratory system?

loop:
→ sensors of O2, pH, and CO2 (controllers)
→ chest wall (pump)
→ lung (gas exchanger)

what is in the upper respiratory system?

pharynx, vocal cords, esophagus, larynx, tongue, nasal cavity

what is in the lower respiratory system?

trachea, lungs, diaphragm, bronchi

how many lobes is the right lung divided into and what are they?

3 lobes: superior, middle, inferior

how many lobes is the left lung divided into and what are they?

2 lobes: superior, inferior

what are the components of the respiratory tract?

• conduits (airways): bronchi, bronchioles, alveolar ducts

• blood-gas interface (alveoli)

what is the anatomy of the conduits?

upper airways, nasal cavity, pharynx, and larynx

what is the anatomy of the trachea?

branches into 2 primary bronchi

what is the anatomy of the primary bronchus?

divides 22 more times, terminating in a cluster of alveoli

what surrounds each cluster of alveoli?

elastic fibers and a network of capillaries

what happens to the trachea when you cough?

radius decreases, volume flow and linear velocity increases

what is the structure of the extrapulmonary airways in the cross-sectional view of bronchi?

• cartilaginous ring anterior

• muscular wall posterior

what is the structure of the extrapulmonary airways in the longitudinal view of bronchi?

cartilage on first 2nd-3rd divisions

what characteristic of the extrapulmonary airways prevents collapse during coughing?

the first few branches are semi-rigid

what happens to the diameter as you move down the conducting zone?

steadily decreases

what is the conducting zone?

trachea → bronchi → bronchioles → terminal bronchioles

what happens to the length as you move down the conducting zone?

decreases overall

what happens to the # as you move down the conducting zone?

steadily increases

what happens to the total cross-sectional area as you move down the conducting zone?

first decreases, then increases once at terminal bronchioles

what is the transitional and respiratory zones?

respiratory bronchioles → alveolar ducts → alveolar sacs

what happens to the # as you move down the transitional and respiratory zones?

steadily increases

what happens to the diameter as you move down the transitional and respiratory zones?

slowly decreases

what happens to the length as you move down the transitional and respiratory zones?

steadily decreases

what happens to the total cross-sectional area as you move down the transitional and respiratory zones?

steadily increases

what is only found in the conducting zone?

goblet cells, glands, hyaline cartilage

what is found in both the conducting and respiratory zones, but significantly decrease?

epithelium, ciliated cells, smooth muscle, elastic fibers

what are large conducting airways composed of?

ciliated epithelium, 'goblet cells', mucous glands' cartilage

what are small conducting airways composed of?

ciliated epithelium

what is alveolus composed of?

non-ciliated epithelium

what is the direction of mucus transport?

upwards from alveoli to trachea

what is the process of airway epithelial cells?

→ NKCC (Na+-K+-2 Cl- symporter) beings Cl- into epithelial cell from ECF
→ apical anion channels, including CFTR (cystic fibrosis transmembrane regulator channel), allow Cl- to enter the lumen
→ Na+ goes from ECF to lumen by the paracellular pathway, drawn by the electrochemical gradient
→ NaCl movement from ECF to lumen creates a [ ] gradient so water follows into the lumen

what are the cellular components of the alveolar wall?

endothelium, mesenchyme, epithelium alveolar type I (barrier), alveolar type II

what are the cells in alveolar lumen?

pulmonary alveolar macrophage

what are the cellular components of the alveolus?

alveolar wall and alveolar lumen

what is the purpose of type I alveolar cells?

gas exchange

what is the purpose of type II alveolar (surfactant) cells?

synthesizes surfactant

what is the purpose of alveolar macrophage?

ingests foreign material

where does gas exchange between alveolar air space and the plasma occur?

over the endothelium and surfactant

what is the anatomy of the pump?

right/left lung, pleural membrane, chest wall

what is the diaphragm?

the main muscles of respiration

what are the intercostal muscles?

muscles between the ribs used for expiration and inspiration

what are the 2 types of intercostal muscles?

internal and external

what are abdominal muscles used for?

forced expiration

what are characteristics of respiration?

• autonomic (paced rate of breathing)

• continually adjusted to maintain levels of O2 and CO2 tensions within a narrow range

• controlled by a feedback system

what are the components of respiration?

controller, effector, sensor

what is the output of respiration?

ventilation (muscle force and frequency)

what is the input of respiration?

levels of acid (pH and H+) and O2

what are the statics of the respiratory system?

mechanical forces that support the lung at rest

what are the dynamics of the respiratory system?

mechanical forces that move the lung during breathing

what is the diffusion capacity of the lung?

the measure of movement of gas molecules across alveolar/capillary membrane/epithelium

what is the total lung capacity (TLC)?

the volume in the lung at maximal inspiration

what is the forced vital capacity (FVC)?

the volume expired from maximal inspiration to maximal expiration

what is the functional residual capacity (FRC)?

the volume in the lung at resting position (no force applied)

what is the expiratory reserve volume (ERV)?

the volume after maximal expiration

what does a spirometer measure?

TLC, FVC, ERV
FRC - ERV = residual volume (RV)

what does N washout measure?

FRC

what is tidal volume?

the volume of a normal breath

what is dead space?

not used in gas exchange

how do you calculate minute ventilation?

tidal volume x frequency

how do you calculate alveolar ventilation?

(tidal volume - dead space) x frequency

what are timed volumes?

spirometer tracing while the paper is moving

what is FEV1?

forced expiratory volume in one second

how do you calculate the major index of obstruction?

FEV1/FVC

what is the major index of restriction?

reduced lung volumes with normal FEV1/FVC ratio

how do you calculate transmural pressure?

alveolar pressure - intrapleural pressure

what occurs where there is no air flow (at the end of expiration)?

• atm pressure = alveolar pressure = 0cm H2O

• intrapleural pressure: -5cm H2O

• transmural pressure = +5cm H2O

• outward recoil of chest wall = inward recoil of alveoli

what occurs when air flows in (during inspiration)?

• atm pressure = 0cm H2O > alveolar pressure = -1cm H2O

• intrapleural pressure: -8cm H2O

• transmural pressure = +7cm H2O

• outward recoil of chest wall < inward recoil of alveoli

• force outward generated by inspiratory muscles

what does transmural pressure drive?

negative pressure breathing

what measures lung function?

spirometry (volume), pneumotachograph (flow), esophageal balloon (intrapleural pressure)

what is the intrapleural and alveolar pressure at rest?

• intrapleural = -5cm H2O

• alveolar = atm = 0 cm H2O

what pulls the lungs open?

contraction of the inspiratory muscles

what occurs when the lungs open?

→ intrapleural pressure falls
→ causes fall in alveolar pressure
→ air flows in, tidal volume increases

what happens as the air flows into the alveoli?

→ alveolar pressure returns to 0cm H2O
→ airflow into the lung ceases
→ tidal volume is reached

what happens at 2 seconds during tidal breathing?

→ elastic recoil of the tissue (alveolar wall distension)
→ intrapleural pressure increases
→ alveolar pressure exceeds atmospheric and becomes (+)
→ air flows out
→ tidal volume falls

what happens when intrapleural pressure reaches -5cm H2O?

→ reduced lung volume reduces elastic recoil force
→ alveolar pressure falls to atm pressure
→ airflow ceases

what is the relationship between transmural pressure and volume?

increasing pressure leads to increased volume

why is the pressure volume loop non-linear?

tissue more easily expands at lower volume

why does expiration not match inspiration?

hysteris and surfactant effects

what is pulmonary compliance?

describes the ease with which the tissue is stretched

how are compliance in parallel are summed?

directly: 2 lungs greater compliance than one

how are compliance in series summed?

as reciprocals: 1/Ct = 1/C_lung + 1/C_chest wall

how is transmural pressure change measured?

esophageal balloon: deep breath, exhale, and stop (static compliance)

how can lung disease be assessed?

by changes in compliance curves

what are the characteristics of loss of compliance?

• rightward shift

• processes that result in a "stiffer" lung

• results in increased work of breathing

what increase compliance?

diseases that results in tissue destruction

how do chest wall dysfunction alter whole lung compliance?

obesity, kyphoscoliosis, burn injury

what is elastic recoil?

an inherent property of the lung tissue that involves elastin and collagen

what is the laplace law?

pressure = 2(tension)/radius

what is the pulmonary surfactant?

specialized fluid made by type II cells of alveolar epithelium that consist of 85-90% phospholipid and mostly dipalmitoyl phosphatidylcholine

how is surface tension regulated by surface area?

• active incorporation of DPPC to the surface monolayer with expansion

• tension increases with area, allowing for differential alveolar areas

what does hysteresis show?

differential processes for incorporation and loss

what is the purpose of prematurity and ARDS?

use of exogenous surfactant to lower work of breathing

what happens in negative pressure breathing?

expansion is great at the periphery

what happens in positive pressure breathing?

there is a concertina (accordion) effect

what is the principle of diffusion capacity?

CO is a gas that is bound irreversibly to Hb

how do you measure diffusion capacity?

dilute [CO] is inhaled, breath is held for 10 sec, and CO uptake is computed

how do you interpret diffusion capacity?

CO uptake (D_LCO) is low when barrier is thickened or when alveolar surface area is decreased

how does the lung maintain acid-base balance?

regulates CO2 (weak acid) quickly

how does the kidney maintain acid-base balance?

regulates HCO3 (base) slowly