Mechanics of Breathing

Question 1

What is ventilation, and what is needed to allow it to occur?

Answer 1

ventilation is the process of moving air into & out of the lungs. In order for air to pass in and out of our lungs a change in pressure needs to occur.

Question 2

Explain what happens before inspiration to intrapulmonary pressure and the effect this has.

Answer 2

Before inspiration, the thorax expands and intrapulmonary pressure falls below atmospheric pressure. Because intrapulmonary pressure is now less than atmospheric pressure, air will naturally enter our lungs until the pressure difference no longer exists- this is because air flows from areas of high pressure to low pressure.

Question 3

How does the thorax expand? How does this effect the lungs?

Answer 3

Simultaneous contraction of the external intercostal muscles and the diaphragm this expands the thorax. As the parietal pleura is firmly adherent to the diaphragm expands the thorax. As the parietal pleura is firmly adherent to the diaphragm and the inside of the ribcage, it is pulled out along with them. This pulls the visceral pleura out too, since the 2 pleura are held together by the thin film of pleural fluid. Therefore, the lung tissue is also pulled outward with the ribs and downwards with the diaphragm. This expands the lungs which is what causes the pressure within alveoli and air passages to fall, drawing air into the lungs to equalise pressure.

Question 4

Why is inspiration an active process?

Answer 4

It requires energy for muscle contraction.

Question 5

Describe expiration.

Answer 5

Relaxation of the intercostal muscles and the diaphragm results in a downward and inward movement of the ribcage and elastic recoil of the lungs. As this occurs pressure inside the lungs rises and expels air from the respiratory tract. The lungs still contain some air and are prevented from collapse by the intact pleura. This process is passive.

Question 6

What is total lung capacity?

Answer 6

the amount of gas in the lungs after maximal inspiration. this is usually 6L in men and 4.5L in women

Question 7

what is vital capacity?

Answer 7

the amount of gas that can be exhaled after a maximal inspiration

Question 8

What is residual volume?

Answer 8

the amount of gas remaining in the lungs after a maximal expiration, usually 20% of total lung capacity

Question 9

vital capacity + residual volume = ???

Answer 9

total lung capacity

Question 10

what is tidal volume?

Answer 10

the amount of gas you inspire and expire during normal quiet breathing, 7-8% of total kung capacity

Question 11

what is inspiratory reserve volume?

Answer 11

the amount of gas an individual can inhale above a tidal inspiration, normally 60% of the total lung capacity

Question 12

what is expiratory reserve volume?

Answer 12

the amount of gas an individual can exhale beyond a tidal expiration, 20% of total lung capacity

Question 13

tidal volume + inspiratory reserve volume + expiratory reserve volume = ???

Answer 13

vital capacity

Question 14

what is functional residual capacity?

Answer 14

the amount of gas remaining in the lungs after tidal expiration, 40% of total lung capacity

Question 15

what is inspiratory capacity?

Answer 15

the amount of gas an individual can inhale starting at tidal expiration

Question 16

what is functional residual capacity?

Answer 16

volume in lungs after normal expiration

Question 17

what is pleural pressure?

Answer 17

it is pressure in the pleural cavity. when pleural pressure is less than alveolar pressure, the alveoli then to expand

Question 18

Describe lung compliance

Answer 18

lung compliance is a measure of the ease with which the lungs and thorax expand. Lung compliance is a measure of the stretchability of the lungs i.e. the effort required to inflate the alveoli. A healthy lung is very compliant and inflates with very little effort. When lung compliance is low the effort needed to inflate the lungs is greater than normal- this can happen in diseases where elasticity is reduced or when insufficient surfactant is produced.