Two forces come into play:

• Elasticity
• Gravity

• During respiration, they are stretched beyond their resting position
• Upon increasing thorax size, lungs expand as if you had grabbed them and stretched them out
• When muscles that are expanding rib cage relax, lungs tend to return to their original shape and size

• When you inhale and your abdomen protrudes, you are stretching abdominal muscles
• Relaxing inspiratory process will let abdominal muscles return to their original length
• Abdominal muscles will tend to push your abdominal viscera back in and force diaphragm up

• Wet spirometer
• U-tube manometer

Measures respiratory flow, volumes, and capacities

• Involves tube connected to container opened at bottom. This container is placed inside another container that is full of water 
• To measure lung volume, patient breathes into tube causing volume of water to be displaced.
•  Amount of water displaced will give you an accurate estimate of air required to displace it 

Subject is asked to blow on tube, force of subject’s expiration is exerted on column of water that rises as a result.

The more force, the higher column of water rises

Reported as centimeters (cm) of water

If patient has excessive secretions (mucus) in their respiratory passageway, it causes air turbulence, which increases resistance to air flow (‘extra drag’)

Results in increased effort to draw air into lungs which causes rapid fatigue

During quiet respiration, adults complete 12-18 cycles of respiration/minute

Cycle of respiration is defined as one inspiration and one expiration  

Quiet tidal respiration 

More functional units

Refer to combinations of volumes that express physiological limits

Represent functional combinations of volumes

measured in milliliters (ml) which is thousandths of liter

Cubic centimeter (cc) is same as a milliliter

1 liter = 1000 ml or 1000 cc

Pm = Ps = Pal

Intaroral Pressure=Subglottal Presure=Alveolar Pressure

Pressure in space between parietal and visceral pleurae

Pleural pressure will be negative throughout respiration

When one attempts to separate visceral from parietal pleurae, a negative pressure results

Recoil of chest during exhalation obeys laws applying to any elastic material

• Greater you distend or distort material, greater force required to hold it in that position and greater is force with which it returns to rest

Pressure= force exerted over area

Relaxation pressure curve shows result of pressure generated by force of rib cage

Farther rib cage is expanded, greater the force that is trying to return rib cage to rest

Body posture is significant contributor to efficiency of respiration

While sitting or standing erect, gravity is pulling abdominal viscera down, which supports inspiration, and is pulling rib cage down, which supports expiration

While in supine, abdominal viscera shift rostrally, which pushes diaphragm into thoracic cavity; gravity supports neither expiration nor inspiration. Muscles of inspiration must elevate rib cage against gravity  

Although vital capacity (VC) is not affected, ability to completely inflate lungs is

Resting lung volume (Figure 3-12) ~38% of VC in sitting position ~20% of VC in supine

Requires micro-control

As we maintain constant pressure needed for phonation, we can rapidly and briefly change pressure for linguistic purposes, such as syllable stress

Produce sustained voicing of given intensity, we need relatively constant subglottal pressure

With quick bursts of pressure (and laryngeal adjustments), we are able to increase vocal intensity and increase vocal pitch

Bursts are small and fast

We increase subglottal pressure by ~2 cm water to add stress; then return to previous subglottal pressure within 0.1 sec

Inhalation takes up ~40% of cycle

Exhalation takes up ~60% of cycle

Inspiration takes up ~10% of cycle

Expiration takes up ~90% of cycle

 Respiratory control for speech production; we hols inspiratory position to impede outflow of air and let air out slowly in order to maintain constant flow of air through vocal tract, which allows us to accurately control pressure beneath vocal folds

Enlist muscles of expiration to push beyond resting lung volume

Using muscles of expiration, we continue talking beyond point where we would normally take another breath