Pulmonary Ventilation

• Pulmonary ventilation, or breathing, is the exchange of air between the atmosphere and the lungs.

• As air moves into(Inspiration) and out of the lungs(Expiration), it travels from regions of high air pressure to regions of low air pressure

Boyle's Law: Relationship Between Pressure and Volume • In order to understand ventilation, we must first look at the relationship between pressure and volume. • Pressure is caused by gas molecules striking the walls of a container. • The pressure exerted by the gas molecules is related to the volume of the container.

•The large sphere contains the same number of gas molecules as the original sphere. Notice that in this larger volume, the gas molecules strike the wall less frequently, thus exerting less pressure.

• In the small sphere, the gas molecules strike the wall more frequently, thus exerting more pressure. Notice that the number of gas molecules has not changed.

These demonstrations illustrate Boyle's Law, which states that the pressure of a gas is inversely proportional to the volume of its container. Thus, if you increase the volume of a container, the pressure will decrease, and if you decrease the volume of a container, the pressure will increase

Muscles of RespirationInspiration-Diaphragm.

Muscles of Respiration(Cont,)Inspiration-

-scalene muscles- sternomastoids

External intercostal muscles -Action

- rectus abdominis, - internal and external oblique muscles, and - transversus abdominis

Spirometry

http://www.goldcopd.it/flash/spirometry_eng.swf

Pulmonary Volumes and Capacities—Spirometry

A simple method for studying pulmonary ventilation is to record the volume movement of air into and outof the lungs, a process called spirometry.

spirogram is a fig.. derived from spirometry indicating changes in lung volume under different conditions of breathing.For ease in describing the events of pulmonary ventilation, the air in the lungs has been subdivided in thisdiagram into four volumes and four capacities, whichare the average for a young adult man.

1. The tidal volume is the volume of air inspired orexpired with each normal breath; it amounts toabout 500 milliliters in the adult male.2. The inspiratory reserve volume is the extra volumeof air that can be inspired over and above thenormal tidal volume when the person inspireswith full force; it is usually equal to about3000 milliliters.3. The expiratory reserve volume is the maximumextra volume of air that can be expired byforceful expiration after the end of a normaltidal expiration; this normally amounts to about1100 milliliters.4. The residual volume is the volume of airremaining in the lungs after the most forcefulexpiration; this volume averages about1200 milliliters.

Pulmonary Volumes

Pulmonary CapacitiesIn describing events in the pulmonary cycle, it issometimes desirable to consider two or more of thevolumes together. Such combinations are called pulmonarycapacities.1. The inspiratory capacity(IC = TV + IRV) equals the tidal volumeplus the inspiratory reserve volume. This is theamount of air (about 3500 milliliters) a person canbreathe in, beginning at the normal expiratorylevel and distending the lungs to the maximumamount.2. The functional residual capacity (FRC = ERV + RV) equals theexpiratory reserve volume plus the residualvolume. This is the amount of air that remains inthe lungs at the end of normal expiration (about2300 milliliters).3. The vital capacity(VC = IRV + TV + ERV) equals Inspiratory reserve volume plus the tidal volume plus the Expiratory reserve volume.

VC or forced vital capacity (VC or FVC), represents the maximum volume that is available to us for inspiration

4. The total lung capacity(sum of all lung volumes) is the maximum volume towhich the lungs can be expanded with the greatestpossible effort (about 5800 milliliters), it is equalto the vital capacity plus the residual volume.All pulmonary volumes and capacities are about 20to 25 per cent less in women than in men, and they aregreater in large and athletic people than in small andasthenic people.

Typical Range for Volumes and Capacities

To measure these parameters two common types of spirometers are used. A volume-time spirometer and a flow-volume spirometer. Some of these parameters cannot be measured with a spirometer, e.g. total lung capacity, FRC and residual volume – Helium Dilution and Plethysmography

Spirometry Vol/Time

Vo

lum

e (

L)

0

1

2

3

4

5

6

Time (s)0 1 2 3 4

FEV1

In normal circumstances FEV1 should be ~80% of

total volume expired FEV1/FVC ratio

4.5/5.5*100=~80% Slope of the initial line

gives the flow rate FEF25-75

Vita

l Cap

acity

From fully inspired state patient expels all air in their lungs as forcefully as possible

FEV2

FEV3

25%

75%

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Spirometry in Disease States

Vo

lum

e (

L)

0

1

2

3

4

5

6

Time (s)0 1 2 3 4

Restrictive Lung Disease e.g. lung fibrosisTotal Volume reduced

FEV1 reduced But FEV1/FVC ratio =normal

FEV1/FVC = 4.5/5.5*100 = ~80%

FEV1/FVC = 2.5/3*100 = ~80%

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Spirometry in Disease States

Vo

lum

e (

L)

0

1

2

3

4

5

6

Time (s)0 1 2 3 4

Obstructive Lung Disease (COPD, chronic bronchitis, emphysema,

asthma)Total Volume may be normal

but FEV1 is reduced And FEV1/FVC ratio <0.8

FEV1/FVC = 4.5/5.5*100 = ~80%

FEV1/FVC = 2.5/5.5*100 = ~45%

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Flow/Volume Spirometry

restrictive lungDisease.

Obstructive lungDisease.

Normal pattern.

A 43 year old man undergoes spirometry in a pulmonary function laboratory. The spirogram Dipicted above shows changes in lung volume during normal breathing and when the patientInhales maximally as much air as possible from the lungs.What is the residual volume of this patient?A. 0.5LB. 1.0LC. 3LD. Cannot be determined.

Anatomic DEAD SPACE -Space in the respiratory passages filled with air where gas exchange does not take place. i.e. mouth, pharynx, larynx, trachea, bronchi,bronchioles – all conducting airways. Typically 150 ml. These areas are ventilated, i.e. air moves into them, but since they do not contribute to gas exchange it is known as wasted ventilation -- Vd.

Alveolar DEAD SPACE – Some gas exchange surfaces are not as efficient as they should be. Some alveoli are poorly ventilated or ventilated but with no or poor perfusion. The volume of air ventilated into regions that should be gas exchanging but is NOT is the alveolar dead space

Physiologic Dead Space = Anatomic + alveolarIn a normal healthy individual the physiological dead space should be only slightly larger than the anatomic dead space. Alteration in ventilation/perfusion changes this pattern (see later)

Anatomic DEAD SPACE

volume of the Physiologic Dead Space

In words, the equation states that the volume of the physiologic dead space is the tidal volume (volume inspired with a single breath) multiplied by a fraction. The fraction represents the dilution of alveolar PCO2 by dead space air (which contributes no CO2).

Minute Ventilation

• Definition – volume of air moved in & out of the lungs per unit time

fVV TE

• VT tidal volume – typically ~500 ml

• f breathing frequency

Therefore minute ventilation – • (0.5 liters)x(12 min-1) = 6 liters min-1

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Alveolar Ventilation

• Minute ventilation(VE) gives volume flow per minute through lung

• But – not all that ventilation contributes to gas exchange (ventilation to the dead space is called wasted ventilation-Vd)

• Ventilation contributing to gas exchange is the alveolar ventilation – which is the minute ventilation minus the dead space ventilation

VA = VE – Vd

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VA = VE - Vd = (VT – Vd)f = VTf - Vdfi.e. alveolar ventilation = (tidal vol x freq) –(wasted ventilation x freq)• Rapid shallow breathing is not good for gasexchange since it only ventilates dead space (VT150, 40 min-1). • To increase gas exchange the tidal volume must be increased above dead space volume. So that fewer but deeper breaths result in a significant increase in alveolar ventilation.• In diseases where dead space is high, e.g. COPD, a large increase in tidal volume is required for maintenance of normal alveolar ventilation, increasing the workload of breathing.

ALVEOLAR VENTILATION EQUATION