F ‘08
P. Andrews, Instructor

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Respiration



Exchange of gases between an organism and it’s environment
Pulmonary (external) respiration

Occurs in lungs
Cellular (internal) respiration



Occurs in peripheral capillaries
Is the exchange of respiratory gases between RBCs and tissue
Produces CO2

Ventilation

The mechanical process that moves air into and out of lungs


The thorax

Moves air in and out


Oxygen and CO 2 are exchanged
Also contains heart, major vessels, trachea, bronchi, lungs, mediastinum

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Ventilations are controlled by a series of centers in the brain and blood vessels

Main control center – medulla oblongata

Connected to respiratory muscles via VAGUS NERVE

Additional control center
– pons

Apneustic center

Pneumotoxic center


Stretch receptors

Decrease inspiratory stimulus


In the medulla and carotid bodies and arch of the aorta

Stimulated by changes in O 2 and CO 2 as well as pH


Hyoxemia is a profound stimulus of respiration in a normal person

People with COPD retain CO
2
– have chronically elevated PaCO
2

Peripheral chemoreceptors become used to this; CNS stops using PaCO
2 to regulate.

A default mechanism – HYPOXIC DRIVE – is activated

Increased respiratory stimulation when PaO 2 falls; inhibited respiratory stimulation when PaO 2 climbs


Major muscles of respiration

Intercostal muscles


Sternocleidomastoid muscles

Accessory muscles are also used




Scalene muscles
Anterior abdominal muscles
Rhomboid muscles
Cough reflex relies on latissimus dorsi muscles

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

Sternocleidomastoid muscles
 raise upper rib and sternum
Intercostal muscles contract
 elevate ribs and increase anterior-posterior dimension
Diaphragm is the primary muscle of respiration
– it contracts and flattens
 increases volume of cavity.
Pressure in cavity becomes less than atmospheric
 air rushes in to alveoli to equalize pressure


Muscles relax…

Diaphragm moves upward

Ribs and sternum move inferiorly

Ribs move closer together in inferior and posterior position

Thoracic volume decreases

Intrathoracic pressure increases


Changing volume and pressure of thoracic cage also helps with

Pumping blood to and return from systemic circulation

Affects BP and pulse strength

Normally, systolic BP and pulse strength fall during inspiration, rise during exhalation


Adults – 12 – 24 breaths per min.

Children – 18 – 24 breaths per min.

Infants – 40 – 60 breaths per min.


Total lung capacity – TLC

~ 6 L

Tidal Volume – V
T



~ 500 ml (5 – 7 ml/kg)
Dead space volume – V
D

~ 150 ml
Alveolar Volume – V
A

~ 350 ml

Minute volume - V min