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respiratory physiolgy, Essays (university) of Physiology

respiratory system human physiology ventilation

Typology: Essays (university)

2016/2017

Uploaded on 05/02/2017

dratosh-katiyar
dratosh-katiyar 🇬🇧

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During inspiration the pressure inside the lungs (the
intrapulmonary pressure) decreases to -1 to -3 mmHg compared
to the atmosphere. The variation is related to the forcefulness and
depth of inspiration. During expiration the intrapulmonary pressure
increases to +1 to +3 mmHg compared to the atmosphere.
The pressure oscillates around zero or atmospheric pressure.
The intrapleural pressure is always negative compared to the
atmosphere. This is necessary in order to exert a pulling action on
the lungs. The pressure varies from about -4 mmHg at the end of
expiration, to -8 mmHg and the end of inspiration.
Respiratory output is determined by the minute volume, calculated
by multiplying the respiratory rate time the tidal volume.
Minute Volume = Rate (breaths per minute) X Tidal
Volume (ml/breath)
Rate of respiration at rest varies from about 12 to 15 bpm. Tidal
volume averages 500 ml
•Assuming a rate of 12 breaths per minute and a tidal volume of
500, the restful minute volume is 6000 ml. Rates can, with strenuous
exercise, increase to 30 to 40 bpm and volumes can increase to
around half the vital capacity.
Not all of this ventilates the alveoli, even under maximal conditions.
The volume air in conducting zone is about 150 ml (dead space) and
does not extend into the respiratory zone.
•The Alveolar Ventilation Rate, AVR, is the volume per
minute ventilating the alveoli and is calculated by multiplying
the rate times the (tidal volume-less the conducting zone
volume).
AVR = Rate X (Tidal Volume - 150 ml)
For a calculation using the same restful rate and volume as
above this yields 4200 ml.
The tendency of the lungs to expand, called compliance
or distensibility, is due to the pulling action exerted by
the pleural membranes. Expansion is also facilitated by
the action of surfactant in preventing the collapse of the
alveoli.
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During inspiration the pressure inside the lungs (the intrapulmonary pressure ) decreases to -1 to -3 mmHg compared to the atmosphere. The variation is related to the forcefulness and depth of inspiration. During expiration the intrapulmonary pressure increases to +1 to +3 mmHg compared to the atmosphere.

The pressure oscillates around zero or atmospheric pressure.

The intrapleural pressure is always negative compared to the atmosphere. This is necessary in order to exert a pulling action on the lungs. The pressure varies from about -4 mmHg at the end of expiration, to -8 mmHg and the end of inspiration.

Respiratory output is determined by the minute volume , calculated by multiplying the respiratory rate time the tidal volume.

Minute Volume = Rate (breaths per minute) X Tidal

Volume (ml/breath)

Rate of respiration at rest varies from about 12 to 15 bpm. Tidal volume averages 500 ml •Assuming a rate of 12 breaths per minute and a tidal volume of 500, the restful minute volume is 6000 ml. Rates can, with strenuous exercise, increase to 30 to 40 bpm and volumes can increase to around half the vital capacity.

Not all of this ventilates the alveoli, even under maximal conditions. The volume air in conducting zone is about 150 ml (dead space) and does not extend into the respiratory zone.

•The Alveolar Ventilation Rate, AVR, is the volume per

minute ventilating the alveoli and is calculated by multiplying

the rate times the (tidal volume-less the conducting zone

volume).

AVR = Rate X (Tidal Volume - 150 ml)

For a calculation using the same restful rate and volume as

above this yields 4200 ml.

• The tendency of the lungs to expand, called compliance

or distensibility , is due to the pulling action exerted by

the pleural membranes. Expansion is also facilitated by

the action of surfactant in preventing the collapse of the

alveoli.

1.Compliance of lungs & the thoracic wall :normal value is about 0.13litre/

cm H2O 2.Compliance of lungs only:0.22 litre/cm H2O

Compliance increases in: Emphysema,old age Compliance decreases in: pulmonary congestion (lungs filled with blood), pulmonary fibrosis, pulmonary edema

The opposite tendency is called elasticity or recoil , and is the process by which the lungs return to their original or resting volume.

  • Recoil is due to the elastic stroma of the lungs and the series elastic elements of the respiratory muscles, particularly the diaphragm.

In emphysema compliance increases and elasticity decreases, In this buildup of toxins from cigarette smoke and resulting mucus production leads to destruction of the alveolar and capillary walls and fibrosis of the tissue.

This produces large thick-walled chambers replacing the normal small thin-walled alveoli. It results in a larger volume in the lungs but impaired gas transport and reduced ability to expire the trapped air.

Many emphysema sufferers have the characteristic "barrel chest" as a result. Carbon dioxide tends to increase in alveolar air and in the blood, in some individuals interfering with normal respiratory stimuli and responses.