Airflow

What are 2 way stop treat elevated airway resistance?

1) medication --> bronchodilator, B2 agonist 2) decrease density of inspired gas -->replace N2 with He gas

What is the formula Airway resistance (laminar flow)?

R = (8nl)/(pi*r^4) R proportional to 1 / r^4

At what lung volume is the MOST Non-Elastic/Resistive Work done?

SMALL lung volume (Why? resistive = alveoli distension. more breaths = more times it has to open/close)

At what lung volume is the LEAST Elastic Work done?

SMALL lung volume (why? less movement of chest wall)

What is the formula for Ohm's Law?

V = ∆P / R

When is turbulent flow more likely?

large airway diameter fast airflow small total cross-sectional area

What is tidal breathing?

normal ventilation that you achieve on each breath at rest ~0.5L

What will happen to flow if there is an airway obstruction/constriction?

patient will probably make more effort / increase velocity --> more resistance --> turbulent flow

What mostly dictates Reynolds number?

radius & velocity (density and viscosity of air are usually constant)

When is the minimum TOTAL work done?

respiration rate in the mid-teens (at rest)

When is laminar flow more likely?

small airway diameter slow airflow large total cross-sectional area

What part of a Maximal Expiratory Flow-Volume Curve is effort-dependent?

the first part of the curve! (how hard you push)

What part of a Maximal Expiratory Flow-Volume Curve is effort-independent?

the latter part of the curve --> pushing harder doesn't make a difference because the airway collapses at mid-low lung volume

Why is PIP during inspiration more negative than expected?

there is frictional resistance to airflow --> have to overcome it with a more negative PIP

What is mainly responsible for decreasing resistance in the periphery?

# of parallel airways!!

How do you calculate Transpulmonary Pressure?

PTP = Palv - PIP

What is a healthy FEV1 %?

if you can exhale 80% of your FVC in 1 sec

What happens to the pressure in the intramural space during inspiration?

- P in intramural space becomes more negative - increase in distension P --> airway dilates

What determines alveolar driving pressure?

- muscle strength (Pmus = PIP) - lung recoil (P inward) **pressure gradient drives air out of lungs**

What determines airway resistance?

- size of airways - # of parallel airways - collapsibility of airway walls

How much of the total energy expenditure in a normal person at rest is utilized to perform the work of breathing?

5%

What is the average minute ventilation?

5-6 L/min

What airways have the smallest total cross-sectional area?

Conducting zone --> bulk of resistance is in proximal airways (Respiratory zone has greatest total cross-sec area)

What happens to FEV in an obstructive lung disease? (i.e. asthma)

FEV lowers and FEV % / FVC reduced!!

What happens to FEV in a restrictive lung disease? (i.e. pulmonary fibrosis)

FEV lowers but so does FVC --> FEV % is still high!

What are the determinants of flow?

Flow = Alveolar Driving Pressure / Resistance

What is FEV1?

Forceful Vital Capacity at 1 sec into exhalation (amount you can exhale)

Where in the tracheobronchial tree is the airway resistance highest?

Genreation 4-16 segmental bronchi --> terminal bronchioles

At what lung volume is the LEAST Non-Elastic/Resistive Work done?

LARGE lung volume (Why? less breaths = less times alveoli open/close)

At what lung volume is the MOST Elastic Work done?

LARGE lung volume (why? a lot of work to distend lungs!)

Is airways resistance a constant?

NO! it varies with lung volume (highest when lung volume is lowest // lowest at TLC)

What happens to Pressure during exhalation?

P falls as it dissipates --> net pressure is collapses --> airway lumen narrows

As gas moves into peripheral airways, what happens to airflow?

airflow SLOW

Why is PIP during expiration more positive than expected?

energy is stored in the lungs when inflated --> PIP is greater than needed to overcome resistance

During what stage of breathing would an airway disease manifest?

expiration

What does a spirometry graph demonstrate?

flow as a rate above line: expiration below line: inspiration