Understanding respiratory signals and positive airway

pressure

Requirement for this lecture: • one balloon that is easy to inflate and • one that is difficult to inflate

Respiratory WaveformsNasal Flow via nasal cannula

Oral/nasal flow via thermistor

Effort via esophageal pressure (not often used)

Rib cage and abdominal movement via RIP (respiratory inductive plethysmograph)

Rib cage and abdominal belts (RIP)During quiet, unobstructed breathing the

belts move in and out together. This reflects the RC(rib cage) and Ab(abdomen) expanding and relaxing together.

With partial obstruction the belts can begin to move out of phase with each other.

Rib cage and abdominal belts (RIP)With significant or full obstruction the belts

will move in paradox; that is one moves out when the other moves in. This is because the airway is now a closed system-the volume doesn’t change. So, if you expand your chest (increasing chest volume) you have to decrease your abdominal volume and vice versa.

Now fill your balloon with air (or water if you like) and tie it off. What happens to the top of the balloon if you squeeze the bottom? What happens to the bottom if you squeeze the top? That is PARADOX!

ThermistorThis measures temperature change as air

moves in an out.It can tell you the presence of air flow but

cannot give you information about the quality of that flow such as flow limitation.

Nasal cannulaActually measures the pressure changes as

air moves past the cannula.In a closed system like a nasal mask (with no

leak) pressure equals flow. In a small area (like the inside of the nose)

pressure is very similar to flow. This would not work for oral flow because it

is not a closed area.The signal you see is showing the rate of

change of the inspiratory and expiratory pressure

Unobstructed Airflow measured by mask or nasal canula

Inspiratory flow

Expiratory flowZero flow

Notice that the unobstructed inspiratory flow (pressure) signal is rounded. As the signal moves up it is showing the flow rate increasing and as the signal moves back to zero the rate of flow is decreasing.

The expiratory signal is pointed and gradually returns to zero. Inspiratory flow should always be up.

Partially obstructed inspiratory flow (UAR)

Notice the concave shape of the inspiratory flow signal

This occurs because during inspiration the airway narrows and the rate of inspiratory flow decreases despite increasing effort.

Compare the obstructed and unobstructed breaths

Esophageal Pressure (Pes)

A balloon on a catheter is placed through the nose into the esophagus.

This pressure reflects the pressure being generated in the larynx.

When you breathe in the negative pressure changes the pressure in the balloon and it returns to normal during relaxed exhalation.

The harder it is to breathe (increased resistance, snoring, upper airway obstruction) the more negative pressure you have to develop to draw in air.

Esophageal pressure (Pes)Notice that Pes is negative during inspiratory flow. This indicates the negative (suction) pressure generated by the expansion of the lungs that causes inspiratory flow. Pressure returns to zero during relaxed expiration.The next slide shows you how pressure and flow change from wake to sleep to increased resistance/snoring.

Notice the rounded inspiratory flow, little effort (Pes-esophageal pressure indicates how hard you work to pull in air), and RC and AB are in phase

Wake

Sleep-openairway

Sleep-Flowlimitation

The airway is still open although breathing frequency is higher than awake – rounded flow, little effort, and RC and AB are still in phase

Notice now the inspiratory flow signal is not rounded but is collapsed a little, Pes is bigger indicating much more pressure has to be developed to breath and RC and AB are paradoxing

RC and AB in phase

Rounded inspiratory flow

Little effort

Insp. Flow is collapsed Indicating flow limitation

Greater pressure Development means more work

RC and AB out of phase

Respiratory belts, airflow and respiratory effort (Pes) when partial obstruction resolves

This picture shows an individual moving from partial obstruction to a fully open airway.

Notice that when airflow (measured by nasal pressure in the first few breaths

of channel “e”) shows flow limitation –the RC (a) and AB (b) are in paradox. The pressure developed (f) is large.

In the last breath, with no flow limitation, the belts are in phase and little pressure is developed

Why does this happen?

Remember:The upper airway is composed partially of

muscle.Upper airway muscles relax in sleepThis allows the airway to narrow in everyone

and in some to partially or fully collapse.

The next slide shows the airway changing from wake to sleep to snoring to hypopnea to apnea. Below that are the effects on flow and pressure.

Sleep on the upper airway and its consequences

CPAP on the Upper airwayCPAP’s positive airway pressure essentially

takes the place of the relaxed muscles to hold open the airway. Get your easy to inflate balloon and blow just enough air in to stretch it a little. Now try it again with the stiffer balloon. Can you tell that it takes more pressure for you to inflate the second balloon?

Peoples airways are like balloons with different degrees of stiffness. This is why they need different levels of PAP.

Bilevel Pressure on the Upper Airway

Bilevel pressure is a combination of CPAP (which is the expiratory pressure) and mechanical ventilation which helps to inflate the lungs.

Now blow enough air in one balloon just to hold it open (point A.) That is the CPAP.

Now, holding that pressure inflate your balloon a little (point B) then let the pressure back to point A.

This simulates what bilevel pressure does. It hold the airway pressure at a certain level to keep it open then adds more air pressure during inspiration to increase the size of the breath.