Session 11 - Pulmonary ventilation

Question 1

Three basic steps of respiration

Answer 1

•Pulmonary ventilation (breathing) •External (pulmonary) respiration •Internal (tissue) respiration

Question 2

Pulmonary ventilation/ breathing

Answer 2

exchange of air between the atmosphere and the alveoli •is made possible by changes in the intrathoracic (in the chest) pressure/volume

Question 3

Explain the two phases of pulmonary ventilation/breathing What is the atmospheric pressure?

Answer 3

•Inhalation/inspiration: Air moves into lungs when pressure inside the lungs is less than atmospheric pressure

•Exhalation/expiration: Air moves out of the lungs when pressure inside the lungs is greater than atmospheric pressure o Atmospheric pressure = 760 mm Hg

Question 4

Explain Boyle’s law in relation to lungs

Answer 4

our lungs inflate and deflate according to Boyle’s law

As you increase the volume of a chamber the pressure inside that chamber decreases

• as you decrease the volume of the chamber the pressure inside that chamber increases

Question 5

Inhalation and exhalation pressure changes

Answer 5

o Pressure changes: Created by contraction and relaxation of respiratory muscles.

o During inhalation: The diaphragm contracts, the chest expands increasing thoracic cavity, the lungs are pulled outward, and alveolar pressure decreases. This allows air to rush in and fill lungs with air.

o During exhalation: The diaphragm relaxes, the lungs recoil inward, and alveolar pressure increases, forcing air out of the lungs.

Question 6

Which muscles contract when we inhale?

Answer 6

The diaphragm and external intercostals

Question 7

Which muscles contract during force inhalation? ( when you try breathing in as much air as possible)

Answer 7

normal contraction of diaphragm and external intercostal muscles but also Involves accessory muscles of inspiration:

– sternocleidomastoids, scalenes, and pectoralis minor lift chest upwards

Question 8

Expiration is a passive process - what does this mean?

Answer 8

o Normal/quiet expiration:

A passive process because no muscular contractions

are involved.

starts when the inspiratory muscles relax

It is assisted by the elastic recoil of the chest wall and lungs:

The recoil of elastic fibers that were stretched during

inhalation occurs

The inward pull of surface tension due to the film of alveolar fluid.

Question 9

Forced/ laboured expiration ( e.g during exercise )

What type of process? and what muscles are contracted?

Answer 9

o An active process

o Also invlolves contraction of the internal intercostals and abdominal muscles:

• Abdominal muscles force diaphragm up • Internal intercostals depress ribs

o Increases pressure in the abdominal region and thorax.

Question 10

What are the factors affecting pulmonary ventilation?

Answer 10

The rate of airflow and the amount of effort needed for breathing depends on:

• Pressure Changes
• Alveolar surface tension
• Compliance of the lungs
• Airway resistance.

Question 11

What is the function of surfactant in the respiratory system

Answer 11

Pulmonary surfactant greatly reduces alveolar surface tension, increasing compliance allowing the lung to inflate much more easily, thereby reducing the work of breathing. It reduces the pressure difference needed to allow the lung to inflate.

Surfactant reduces the surface tension of fluid in the lungs and helps make the small air sacs in the lungs (alveoli) more stable. This keeps them from collapsing when an individual exhales.

Question 12

Factors affecting pulmonary ventilation:

What is compliance of the lungs and what does it depend on?

Answer 12

oCompliance: The effort required to stretch the lungs and chest wall.

depends on:

• Elasticity of lungs ( connective tissue in our lungs)
• Surface tension ( from surfactant)

oHigh compliance: Lungs and chest wall expand easily

oLow compliance: Lungs resist expansion

oEmphysema : Destruction of elastic fibers in alveolar walls

Question 13

Factors affecting pulmonary ventilation:

Airway Resistance

Answer 13

oResistance to airflow depends upon airway size

oLarger-diameter airways:Have decreased resistance, and greater airflow

oDuring exhalation: Diameter of bronchioles decreases and Airway resistance increases ( becomes harder )

Question 14

Pulmonary air volumes exchanged in ventilation are:

•Tidal volume (500 ml), (How much air goes in and out of our lungs - breathe in 500mL, breathe out 500mL)

Additional amounts on top of your tidal volume that can be attained if you really tried

• Inspiratory reserve volume (3100 ml),
• Expiratory reserve volume (1200 ml),
• Residual volume (1200 ml)

Question 15

The Minute Ventilation(MV):

Answer 15

The total volume of air inhaled and exhaled each minute

•MV = Respiratory rate X Tidal volume

e.g 12- 15 breathes per minute x 500mL

Question 16

How much of the tidal volume actually reaches the alveoli ( the respiratory zone where gas exchange occurs)

What’s the alveolar ventilation rate?

Answer 16

oOnly about 350 ml of the tidal volume actually reaches the alveoli, the other 150 ml remains in the airways in the anatomical dead space.

oThe alveolar ventilation rate: The volume of air per minute that actually reaches the respiratory zone.

Question 17

What is a Spirometer/Respirometer:

Answer 17

The apparatus used to measure the volume of air exchanged during breathing and the respiratory rate. The record is called a spirogram.

Question 18

Explain exchange of oxygen and carbon dioxide

And what two gas laws govern this exchange

Answer 18

oThe exchange of oxygen and carbon dioxide between alveolar air and pulmonary blood occurs via passive diffusion.

Simply put = The exchange = The air inside our alveolar and the gas that’s dissolved in the blood

oGoverned by two gas laws:

• Dalton’s law:explains how gases move down their pressure differences by diffusion ( Moving from an area of high concentration to low concentration)
• Henry’s law:explains how the solubility of a gas relates to its diffusion

Question 19

Explain Dalton’s law in regards to gases in the blood and lungs

Answer 19

oDiffusion of Gases:From areas of higher partial pressureto areas of lower partial pressure.

oThe greater the difference in partial pressure, the fasterthe rate of diffusion.

**Refer to picture**

Oxygen moves into the blood because of the partial pressure differences e.g 159 > 105 > 100 > 40 ( high to low)

We breathe out CO2 because of the partial pressure differences e.g 45 in the blood and 40 in the alveoli - it’s moving from high to low=- Daltons law

Question 20

Explain Henry’s law

Answer 20

The quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility.

Solubility of CO2 is 24 times greater than that of O2, more CO2 is dissolved in blood plasma.

• O2 has poor solubility and that is why the need for an oxygen carrying molecule (haemoglobin) is important

o Breathing O2 under pressure dissolves more O2 in the blood

Question 21

How is Henry’s law used in clinical application?

Answer 21

Hyperbaric oxygenation: A major clinical application of Henry’s law

• use of pressure to dissolve more O2 in the blood
• treatment for patients with anaerobic bacterial infections (tetanus and gangrene)
• anaerobic bacteria die in the presence of O2

o Hyperbaric chamber pressure raised to 3 to 4 atmospheres so that tissues absorb more O2

o Used to treat heart disorders, carbon monoxide poisoning, cerebral oedema, bone infections, gas embolisms and crush injuries

Question 22

Factors affecting rate of diffusion:

Answer 22

o Partial pressure difference of gases in air - high pressure difference, high rate of diffusion

o Surface area available for gas exchange - We have an enormous surface area as we have millions of alveoli

o Diffusion distance - diffusion distance is very small - the gas only has to travel a short distance going from the alveoli to the blood and vice versa

o Solubility and molecular weight of gases

Question 23

External respiration

Answer 23

oPulmonary gas exchange:between alveoli of the lungs and pulmonary blood capillaries

oConverts deoxygenated blood coming from the right side of the heart into oxygenated blood that returns to the left side of the heart

Question 24

Internal respiration

Answer 24

o Systemic gas exchange: The exchange of O2 and CO2 between systemic capillaries and tissue cells

o Converts oxygenated blood of systemic circulation into deoxygenated blood

Question 25

Breathing Patterns:

Define Eupnoea

Answer 25

normal pattern of quiet breathing consists of shallow, deep, or combined shallow and deep breathing.

Question 26

Breathing patterns:

Define Apnoea

Answer 26

Breath holding

Question 27

Breathing patterns:

Define Dyspnoea

Answer 27

painful or difficult breathing.

Question 28

Breathing patterns:

Trachypnoea

Answer 28

rapid breathing rate.

Question 29

Breathing patterns:

Costal breathing

Answer 29

A pattern of shallow chest breathing that requires contraction of external intercostal, usually during need for increased ventilation, as with exercise.

Question 30

Breathing patterns:

Diaphragmatic breathing

Answer 30

A pattern of deep abdominal breathing that involves contraction and descent of the diaphragm.