Respiratory System

Nose and mouth
Pharynx, larynx, to the trachea
Right and left main stem bronchi
Lobar bronchi (Upper, mid, and lower)
Branches to terminal bronchioles (branches 16 times from trachea to t. bronchioles)
Respiratory bronchioles (branches 4 to 7 more times)
Alveolar duct to alveolar
Also alveoli are also clustered in alveolar sacs

Bronchi contain cartilage in their walls (bronchioles do not)
The entire structure contains smooth muscle, collagen, and elastic fibers that encircle the airways
Collage and elastic fibers network throughout the lungs
Alveoli appear in bronchioles, however, they are most abundant around alveolar sacs
Alveoli mostly appear to have a "honeycomb" structure and are very elastic

Alveolar type I cells allow O₂ and CO₂ exchange
Alveolar type II cells are made up of surfactant and macrophages. Surfactant is defined as a lipoprotein mixture that coats the surface of the alveolar and prevents it from collapse by reducing the surface tension of pulmonary fluid.
Surrounded by capillaries (see diagram below)

The pulmonary artery divides into the right and left pulmonary arteries
Pulmonary arterials follow bronchioles
Terminal pulmonary arteries (diameter - 35 microns) = terminal bronchiole
Terminal pulmonary arteriole divides into approximately 1000 capillaries (diameter is 7-8 microns) surrounding the alveolar
There are approximately 250 to 300 million alveoli in the human system
Distance between a capillary and an alveolus is 0.05 to 0.1 μm
Wall thickness between capillaries and alveoli is between 70 to 80 μ²
Exchange of O₂ and CO₂occurs
Blood then returns via the pulmonary venous system (vein) to the left atrium

Located in and around the lungs
Lymphatic vessels travel to the hilum of the lung
The lymphatic fluid drains from the lymph nodes and the mediasternum
Generally is this is not a concern with a V/Q procedure unless there is a lot of fluid build up in the thoracic cavity (CHF)

Tidal volume is the volume of air breathed out in a normal breath
Total lung capacity is the maximum capacity of air inhaled in the lungs
Functional residual capacity is the amount of air left in the lungs after a normal exhalation
Residual volume is the amount of air left in the lungs after a forced exhalation
About 1/3 of the air does not exchange during inhalation (nose to alveoli) which is defined as anatomical dead space
Resistance to breathing (80 to 90%) occurs in the larger bronchi and is due to turbulence caused in these large tubular areas
The change in pressure caused by muscles results in breathing. This measurement of this exchange is defined as compliance

Closing capacity is the collapsing of the smaller bronchioles during exhalation and is resistance to airflow
Closing capacity is greatly affected by small airway disease and COPD

Consider the role of gravity pulling down on the lungs where the mass of the lungs is greater at its base (should a person be in an upright position)
Ventilation in the upright position (air exchange) is 1.5 to 2.0 greater in the upper third portion when compared to the lower third portion
Circulation in the upright position (blood flow) increases from the apex to the base and is 3 to 5 times greater at the lung base when compared to the apex
The role of gravity pulls down on the lungs no matter which position the lungs are in, however, it occurs to a lesser degree when the patient is in the supine position (less tissue at that angle)
As air is exhaled, the gradient of blood flow becomes equal between the apex and base as it reaches functional residual capacity
Ventilation to Blood flow (ratios)

Where do most of the particles go if the patient is in the upright position and then injected ^99mTcMAA? Why?

Maximum ventilation causes all four sites on the molecule to contain O₂
When ventilation is reduced, not all the hemoglobin sites will contain O₂, but will have CO₂

PO₂ levels determine the amount of O₂ being delivered to the patient's bloodstream

The procedure is called arterial blood gas (ABG) test, which requires an arterial draw - link
The normal PO₂ level is between 90 - 110
Reduced levels of PO₂relate to the lack of O₂ being delivered to the alveoli (which may be due to)

Single large PE - blocks blood flow but not ventilation - Perfusion will show a large cold wedge segment, and the ventilation should look normal

Many PE - blocks blood flow but not ventilation - Perfusion shows several to many smaller cold wedged segments and may sometimes show a "rat bite" defect on the edges of the lung where the ventilation will look normal

COPD - chronic condition affects both ventilation and perfusion - Perfusion will look normal to patchy, and the ventilation will appear patchy. The "patchy" defect is due to the absence of activity in that area of the lung. This is caused by damage to the surrounding tissue or could even be mucous plugs. In either case, the ventilation dose has difficulty in entering.

Perfusion Image

Ventilation Image
Tumor: suppresses the bronchioles and smaller pulmonary arteries/arterioles - Perfusion and ventilation will usually show a similar large cold defect