Respiration Student Notes

Properties of Gases

• Pressure=force/area

• Absolute pressure: in relation to complete vacuum

• Gage pressure: in relation to atmospheric pressure

Gas Laws

Dalton's LawIn a gas mixture the pressure exerted by each individual

gas in a space is independent of the pressure exerted by other gases.

Patm=PH2O+PO2+PN2

Pgas=% total gases * Ptotal

Boyle's Law P1V1=P2V2

Compliance

LungVolume

Inflation (transpulmonary) Pressure

Factors Affecting Compliance

1) Elasticity (opposes inflation, aids deflation)a) Tissue forces

i) Elastin (low to medium volume)ii) Collagen (sets upper limit of inflation – along with Hering-

Breuer reflex which can abruptly stop inspiration)iii) Smooth muscle

b) Surface tension (very powerful alone, but minimized by….c) ….Surfactant (phospholipids, protein, etc.) – prevents

Respiratory Distress of the Newborn (RDS) and Atelectasis (tobe discussed later).

2) Resistive forces (to prevent inflation)a) Airway resistance

i) Flow rateii) Diameter (pathology example: Chronic Obstructive

Pulmonary Diseases, COPD, such as Asthma or Bronchitis)iii) Length of Airways

b) Tissue resistance forces (of minimal significance)c) Elastic recoil (from elastic forces, above)

At equilibrium, deflated 760 mm Hg, atmospheric pressure

Inflation forces = deflation forces

Inflation p. = intrapleural p. + elastic recoil

760 mm = 756 mm + 4 mm

760

4

756

What is Elastic Recoil?



760 mm = 756 mm + 4 mm

764

4 mm Elastic Recoil

It is the force generated on the lung that causes it to contract, compressing the air inside.

If the lung was removed, partly filled with air, and its bronchus was sealed, there would be about 764 mm Hg pressure (~ 4 mm above ambient pressure) inside the lung due to this squeezing.

760 mm Hg, atmospheric pressure

764 mm = 760 mm + 4 mm

Starting to inhale …. 760 mm Hg, atmospheric pressure



e.g., it drops ~6 mm, to 750 mm ….

760 mm >> 750 mm + 4 mm

758

4

750

Pleural cavity’s volume increases*, and therefore its pressure decreases!

Actually, as air flows into the lung, pressure in the lung (Alveolar p.) drops to 758 because of airway resistance, but it’s still greater than 754, still enough pressure gradient.

* The action of muscles

(diaphragm, ext. intercostals, etc.) do this.

Inhaling …. 760 mm Hg, atmospheric pressure



758

4

750

No longer in equilibrium, the lung’s now greater inflation pressure allows air to fill it and it expands

As it expands, it now encroaches on and reduces the intrapleural volume that had initially increased ….


760

4

756

At equilibrium, inflated



The intrapleural volume is now reduced (by the inflated lung) to the same as it was, and therefore pressure returns to 756 again.Air no longer flows into the lung, and alveolar pressure is again 760 – equilibrium returns!


762

4

758

Beginning to exhale ….

* Either passive (elastic recoil), or with muscles (int. intercostals, abdominals, etc.



Pleural cavity’s volume decreases*, and therefore its pressure increases!

e.g., it rises ~2 mm, to 758 mm ….

760 mm << 758 mm + 4 mm

Actually, as air flows out of the lung, pressure in the airway follows a gradient from 762 to 760. But this could be higher if muscles are used!

Ending exhalation …. 760 mm Hg, atmospheric pressure



762

4

758

The lung deflates as air flows out, and now taking up less of the pleural cavity’s volume, the volume increases and the pressure drops.

When exhaling ends, the pleural pressure drops from 758 to 756 mm

760 mm = 756 mm + 4 mm

And we have a new equililbrium

At equilibrium, deflated 760 mm Hg, atmospheric pressure



760 mm = 756 mm + 4 mm

760

4

756

Lever Action – the Ribs and Respiration

Vertebral column Sternocleido-Ribs mastoid

(via sternum)

ExternalIntercostalMuscle fibers

Lever Action – the Ribs and Respiration

InternalIntercostalMusclefibers

Governor Corzine’s Injuries (2007):

Include:

1) Broken R. Femur (2 breaks)

2) Fractured Lumbar Vert.

3) Fractures of both Clavicles

4) Fractured Sternum

5) 12 Fractured ribs (6 on each side), or, in other words, a Flail Chest, for which an endotracheal tube has been inserted.

How does this tube help him?

An Endotracheal Tube looks like this:

Inflatable cuff

Valve

And is inserted like this:

The inflated cuff seals the airway around the ET tube, so that air can’t leak past.

Mammalian Respiration, because of their unique characteristic of having a diaphragm, uses Negative Pressure Breathing.

This means that the driving force to inhale air is by creating a negative pressure around the lungs, generated by a decreased (relative to ambient) intrapleural pressure around the lungs from the action of the diaphragm, intercostal muscles, etc.

All other vertebrates (amphibians, reptiles, and birds) are Positive Pressure breathers.This means that they force air into their lungs by generating a positive pressure – i.e., one that is greater than the ambient pressure – that forces air into the lungs and pushes outward against the chest wall to inflate the lungs (overcoming the ambient pressure which otherwise compresses the chest and keeps the lungs deflated).

Ever watch a frog breathe?1) It draws air into its mouth through its nares

(nostrils). As the mouth fills with air, the floor of the jaw drops (you can see it swell as the nares open).

2) Then it closes its nares (there’s a valve flap).3) Then the muscles in the floor of the mouth tighten

and compresses the air in the mouth – you can see the floor rise.

4) As that happens, that air is forced into the lungs – you can watch the body swell, indicating that the lungs are inflating.The mouth’s muscles “pumped” the air, under positive pressure, into the lungs.

The Endotracheal Tube, when attached to a respirator – a machine that cyclicly pumps air through the tube into the lungs to inflate them – essentially turns a patient into a Positive Pressure breather (the machine = the frog’s mouth’s muscles). Thus, a patient such as the Governor doesn’t have to rely on an intact chest wall that is required of Negative Pressure breathers.No doubt, after the ribs and sternum are repaired, he’ll no longer need the tube.

Collapsed Lung:

Closed Pneumothorax (air in pleural cavity, via lungs)

1) Punctured lung (e.g., broken rib)

2) Spontaneous (disease weakened visceral pleura)

Puctured Pneumothorax (air in cavity, via chest wall perforation)

1) Sucking chest wound – tissue around perforation, especiallyexternal to internal, creates a “valve” allowing more air toenter than to leave. This usually progresses to a ….

2) ….Tension Pneumothorax – air in the pleural cavity becomeshigher than outside pressures (“Full Tension”), not only collapsing the lung completely (making it useless) but, morecritically, inflating that pleural cavity severely, causing themediastinum to shift, squeezing the SVC (and the heart) andblocking blood flow. This is extremely critical!

Flail Chest – trauma (auto crash, fall) breaks many ribs, allowing the anterior wall to move and volume to vary with pressure changes,thus preventing lungs from inflating or deflating. Suffocation isimminent.

Factors Influencing Respiration

Sensory Regions: Factors :

Medulla Only CO2 because of the bloodbrain barrier – only CO2 getsthrough, but it is the subsequentpH shift that the cells respond to.This amounts to 85% of the total“relaxed” chemostimulatory drive!

Aortic Arch O2 , CO2 and pH are all factors, butCO2 is the overwhelmingly most

Carotid Sinus powerful factor – not oxygen level.

Shallow Water Blackout

BloodGasLevels

Oxygen CarbonDioxide

Elapsed Time during a Dive

Normal

Unconsciousness

level to compel breathing

normal level

level after hyperventilating

Explanation of low Pulmonary Circuit Pressure

Why only 20 mmHg pressure from the right ventricle?

1) Capillaries of (inflated) lungs are very delicate and can literally burst from too much pressure.

2) The density of Hg is about 13.6 g/ml., whereas thedensity of blood is a little more than 1 g/ml.Thus, 20 mmHg is equivalent to about 260 mm blood(column height, as in a manometer filled with bloodinstead of mercury). And this is about 10”, or enough forblood to rise 10” above the right ventricle – just theheight of the uppermost part of the lungs, relative to theheart.

Ventilation Perfusion Balance

Unlike Systemic capillaries which display hypoxic vasodilation (to ensure blood delivery to tissues that most need it), Pulmonary capillaries display

Hypoxic Vasoconstriction !

During relaxed breathing:1) The lung is neither uniformly ventilated (referring to air flow)

nor uniformly perfused (referring to blood flow).

a) Most air flows in the apex (superior lobe) – due to lesserlength of air passages and therefore less resistance.

b) Most blood flows through the base (inferior lobe) – bloodpressure is greater here (lower – viz., gravity).

2) Hypoxic Vasoconstriction prevents blood from wastefullyflowing through poorly ventilated regions of the lungs – mostblood flows through the most aerated portions of the lungs.


However, during rigorous exercise, the increased breathingand heart rate, combined with greater oxygen demandlowers blood pO2, quickly lowers alveolar pO2 (due to rapidHb uptake), and causes overall hypoxia throughout the lung, eliminating air heterogeneity.

Recruitment: This resulting “whole lung hypoxia”constricts capillaries throughout the lung, causes a“back pressure” to the right ventricle and raisingpulmonary arterial pressure from 20 mmHg to as high as30 mm or more. Blood flow throughout the lungbecomes homogeneous, and the entire lung is betterutilized.


In contrast to temporary rigorous exercise and breathing,environmental (chronic) hypoxia (also “whole lung”) canhave harmful subsequent effects (some of which includevarieties of “Mountain Sickness” to be discussed later):

1) Pulmonary Hypertension

2) Pulmonary capillary damage

3) Pulmonary edema (which here falsely mimics left-side orcongestive heart failure)

4) actual Right-side Heart enlargement, and eventuallyHeart Failure

Problems in Abnormal Atmospheres

I. Unusual or special cases of high Oxygen concentration

A. High oxygen concentration (near 100%) – Alveolar collapse, orAtalectasis (same effect as premature’s RDS, lacking surfactant,but a different cause).

B. Retinopathy of Prematurity (Retrolental Fibroplasia)

C. Oxygen toxicity (requires higher pressure, too).

II. Unusual cases of high atmospheric pressure

A. Nitrogen narcosis

B. Bends

Solubility of Gases versus Pressure

Solubility

Pressure (or Depth)

Mammalian Diving Reflex – surviving prolonged immersion Most developed in youngest children – adults lose this response.

Stimulated by immersion (in adults, requires icy-cold water on the face).

Responses:1) extensive precapillary vasoconstriction to almost all body

tissues except coronary and cerebral blood vessels – i.e., blood flow largely limited to brain and heart – and the rest of the body goes anaerobic, thus reducing body’s total oxygen use.

2) limited blood circulation allows severe bradycardia – it may, attimes, be imperceptible (especially in the field, by paramedics).

3) blood held in vessels provides large store of oxygen, to beslowly used almost exclusively by the brain and heart.

Benefits:Combined with small body size (large surface area/volume), explains“miraculous” survival of “drowned” children in icy waters (e.g.,plunging through ice on skating pond) – rapid chilling of brain,reduced oxygen consumption, stored oxygen reserves, etc. allcontribute to minimizing damage from oxygen deprivation.

ER Dictum: “No one is dead until they’re warm and dead!”

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Respiration Student Notes