5. CP Respiratory Cycle Flashcards by Liz Pennington

What is the normal intrapleural pressure?

-5 cm H2O

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What is the average intrapleural pressure upon full, normal inspiration?

-8 cm H2O

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What is the alveolar pressure during inspiration?

-1 cm H2O

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How much does the volume of the lungs increase during a normal breath?

500ml (.5L)

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When are the expiratory muscles used?

During forced expiration only! Gentle expiration is passive.

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What is the alveolar pressure at mid expiration?

+1 cm H2O

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How do we calculate minute ventilation?

Tidal volume x breaths per minute

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How do we calculate minute alveolar ventilation?

(Tidal volume - dead space) x breaths per minute

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How do we calculate transpulmonary pressure?

Alveolar pressure - intrapleural pressure

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How does air enter the lungs (Boyle’s Law)?

pressure and volume are inversely proportional

V1P1=V2P2

when there is an increase in lung volume, the pressure decreases and air enters

when there is a decrease in lung volume, pressure increases and air exits

(the pressure of the air outside the lungs is higher than the pressure inside the lungs when the volume is increased, so O2 rushes into the lungs moving from a high to low gradient)

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How do the inspiratory muscles contract to allow for inspiration?

the diaphragm and external intercostal muscles contract to increase thoracic volume

these muscles are not directly in contact with the lungs but allow the chest wall to expand despite the lungs wanting to collapse

this interplay allows for inspiration (along with pressure/volume relationship)

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Describe intrapleural pressure

(Ppl)

less than atm. (neg) -5 cm H2O at rest

basically the intrathoracic pressure everywhere in the thorax except the blood vessels/lymph and airways

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What happens to the intrapleural pressure during quiet inspiration?

volume increases so Ppl decreases to -8 cm H2O

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What happens to alveolar pressure as thoracic cavity increases in volume during quiet inspiration?

alveolar pressure decreases from 0 cm H2O (at rest) to -1 cm H2O

this is because the volume in alveoli increases

this pressure gradient allows air to flow into the lungs

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What is transpulmonary pressure?

It is the pressure of the Palv-Ppl

Palv-alveolar pressure

Ppl-intrapleural pressure

transpulmonary pressure is -5cm H2O at rest

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What would happen if transpulmonary pressure was 0?

pretty sure no gas exchange or air flow would occur because 0 cm H20 is equivalent to atm. pressure.

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Respiratory Cycle at Rest

Volume

Palv

Ppl

Air flow

Volume=0

Palv=0

Ppl=-5

AF=0L/s

Respiratory Cycle Mid-Inspiration

Volume

Palv

Ppl

Air flow

Volume=increasing (250)

Palv=decreasing (-1)

Ppl=decreasing (-5 to -8)

AF=air flowing into lungs (-1)

Respiratory Cycle-End Inspiration

Volume

Tidal Volume

Palv

Ppl

Air Flow

volume=reached peak

TV=500ml

Palv=returned to zero

Ppl=decreased to -8cm H2O

AF=ceased

Respiratory Cycle-Mid Expiration

Volume

Palv

Ppl

Air Flow

Volume=decreasing (250)

Palv=rises (+1)

Ppl=starts to rise (-8 to -5)

AF-exits (+1)

Respiratory cycle-End Expiration

Volume

Palv

Ppl

Air Flow

volume=returned to resting

Palv=decreases to zero

Ppl=returns to resting

AF=exited lungs

What is the change in transpulmonary pressure throughout the respiratory cycle?

rest

mid-insp.

end insp/start exhal.

mid-exhal.

rest 5cm

mid-insp.5.5cm

end-insp/start exhal. 8cm

mid-exhal. 7.5

What is minute volume and how is it calculated?

Minute Volume (Ve) is the volume of air inhaled every minute

TV=Vt (tidal volume)

Ve=Tv x Frequency

ex: 14 breaths per min x 500ml/breath=7000ml/min (normal)

What is anatomic dead space?

space in respiratory system other than alveoli

150lb person=150ml of Vds

What is physiologic dead space?

aka alveolar dead space alveoli receive air but no blood should be nearly 0 in healthy ppl

Is dead space a feature of inspiration or expiration?

inspiration at end expiration, there is residual volume left over at end inspiration, there is air filling conducting system, air in the lungs doing gas exchange and left over air from expiration the air that is in the conducting system is the "dead space" because there is no gas exchange occuring

how is minute alveolar ventilation calculated?

alveolar volume is found by subtracting dead space volume from tidal volume Valv=Vt-Vds ~350 (for 150lb person) can find minute alveolar ventilation by taking V(dot)alv=Valc x frequency

Describe the pressure-volume curve of the normal lung and explain the inspiration piece

at the start of inspiration, the lung has lower volme and must work harder to get a little increase in volume. At this point, the lungs are harder to stretch (like a balloon animal type balloon) once there is a little air in the lungs, a little pressure change will produce a large volume change (easier to stretch lungs, like a "started" balloon") as lungs expand toward TLC, it becomes difficult to stretch again. A small pressure change produces small change in volume.

Why does exhalation look different on the pressure-volume curve than inhalation?

due to surfactant reducing the surface tension moreso in the smallest alveoli than in the larger ones This occurs according to LaPlace's Law contributes to hysteresis (difference between inspiration and expiration)

what is compliance? How do you calculate it? when is it highest?

how easy the lungs can stretch higher compliance means easier to stretch (reduces workload) C=change in V/change in P highest during normal breathing range, normal TV

If compliance is too high or too low, what happens? What is the opposite of complance?

the lung has to work harder Elasticity (recoil/bounce back ability)

What is the compliance and workload of a newborn's lungs?

compliance is low/lung volume is low effort is high

How does fibrosis effect compliance?

lowers compliance such that more change in pressure is required for change in volume same applies for obesity requires shallower volume and more frequent breaths

How does age effect compliance?

increases with age as elasticity decreases with age due to loss of elastin and increased collagen

How does compliance change with Emphysema?

increases compliances as it destroys alveolar septal tissue that normally opposes lung expansion

How do the lungs and chest wall work against each normally and in a PTX?

lungs have a lot of elastic fibers so they want to shrink (minimal volume) rib cage has joints/cartilages that want to allow it to expand in the intact system, the elastic recoil of the lungs and chest wall counter each other at Functional Residual Capacity In a PTX, they both get what they want (lung collapses, chest wall expands)

Normally, the elastic in the lungs would make them collapse. What helps them to stay structurally intact?

shared walls of alveoli and airways prevents collapse as recoild opposes each other losing some of the walls will alter or lose forces that would normally counter collapse when alveoli walls are destroyed (smoking, age) the remaining alveoli can collapse during expiration

When is the work of breathing increased?

as airway resistance increases, it takes a greater pressure change to generate flow into the lungs therefore, it takes more pressure to generate a change in volume there will be increased work with increased tidal volume

Draw and memorize resp cycle graphs

and pressure volume curve

What are general age related changes in lung capacity? What are general obesity related changes in lung capacity

no change in TLC INcrease in FRC and RV decrease in FRC with minmal change between seated and supine

What changes do you see in a non-obese person with seated and supine measurements of lung capacity?

decrease in IRV and TLC (?) decrease in Vt decrease in ERV no change in RV (FRC is lower in obese indiv.)