Control of respiratory functions.

Sleep apnea syndrome

Dariusz Nowak

Appropriate rate of alveolar ventilation and lung

perfusion

maintain the relative stable oxygen pressure (PO

2

),

carbon dioxide pressure (PCO

2

) in the arterial blood

PO

2

85-100 mm Hg

PCO

2

35-45 mm Hg

receptors (chemoreceptors)
nerves
respiratory center
effectors

Respiratory center

Localization bilateral , in medulla oblongata and

pons.

Dorsal respiratory group

Ventral respiratory group

Pneumotaxic center

Apneustic center

Chemosensitive area

Respiratory center – dorsal

respiratory group

• Sensory terminal of vagus and glossopharyngeal nerves
Signals from peripheral chemoreceptors
baroreceptors
various type receptors in the lung
• Generates basal rhythm of respiration
2 second inspiratory signal
3 second breake (no inspiratory signal) – passive expiration
Control of inspiratory signal:
A/ rate of signal increase (velocity and strenght of one

breathe)

B/ point at which signal is ceased – frequency of respiration

Respiratory center – pneumotaxic center

• Limits the duration of inspiration
• Increases the respiratory rate

Controls the „switch-off” time-point of

inspiratory signal

Respiratory rate 40 breaths/min or 3

breath/min

Strong or weak pneumotaxic signal.

Respiratory center- ventral respiratory

group

• Inactive during normal quiet respiration
• Active when high levels of pulmoary

ventilation are required (e.g. during exercise)

• Contributes to both heavy inspiration and

expiration (impulses to abdominal muscles)

Respiratory center – apneustic center

• Sends signals to dorsal respiratory group

• Prevents or retards the „switch-off” the

inspiratory signal

• Controls the intensity of inspiration , allows

full inspiration

Additional way controlling

respiration

Hering-Breuer inflation reflex
• Strech receptors (located in muscle wall of bronchi and

bronchioles)

• Vagus nerve
• Dorsal respiratory group

Lungs become overstreached – hyperinflation
Signals act on dorsal respiratory group to „switch-of” inspiratory

signal

Reflex stops further inspiration and increases respiratory rate

(like the pneumotaxic center)

• In humans prevents excessive lung inflation ( reflex is

activated when TV > 1.5 l)

Control of ventilation

We know how the respiratory rate

and the intensity (quiet , deep) of
inspiration and expiration is
controlled

What is the mechanism controlling

current respiratory pattern to
match the ventilatory (metabolic
needs) of our body ?

Chemoreceptors

• Central chemoreceptors – chemosensitive area (in medulla)
• Peripheral chemoreceptors located in carotid and aortic bodies

• [H

+

] – directly stimulates respiratory center via central receptors

• PCO

2

also directly stimulates respiratory center

• PO

2

acts only via peripheral chemoeceptors

Changes in blood PCO

2

or [H

+

]

↓

Chemosensitive area
↓
other parts of respiratory center
↓
increased lung ventilation

chemoreceptors

• [H

+

] does not cross blood-brain barrier

• [H

+

] is the main stimulator ot the chemosensitive

area

• CO

2

rapidly diffuses through b-b barrier

What is the role of CO

2

?

Low buffering capacity and low protein concentration

in the fluid surrounding chemosensitive area

Under normal conditions (healthy subject) [H

+

] and

CO

2

contribute to 80% of impulses responsible for

respiratory drive

20 % - oxygen (PO

2

)

Respiratory center adaptation to

increased PCO

2

Prolonged increase in blood PCO

2

• Stimulation is highest during first few hours after

increase in PCO

2

• Then it decreases to about 20% of the initial (maximal)

value ( after 1 or 2 days)

Why ?
Due to buffering function of the kidneys
• Increase in blood bicarbonate levels
• Diffusion of bicarbonate through blood cerebrospinal fluid

barrier

• Binding of H

+

by bicarbonates in the close neighborhood

of the chemosensitive area

What is a consequence of

adaptation to increased pCO

2

?

Patient with severe chronic respiratory

insufficiency (e.g. With pulmonary emphysema
or COPD)

Has hypercapnia and hypoxemia
Decreased pO

2

is the major factor stimulating

respiratory center

How can we treat patient with oxygen ?
Low flows
Low O

2

concentrations

Why O

2

is not important as CO

2

in

stimulation of respiratory centre under

normal conditions ?

• Hemoglobin saturation is almost total in PO

2

range 60 – 100 mmHg

• Changes of PO

2

from 60 to 100 mmHg have no

significant influence on O

2

content in the

blood and O

2

delivery to tissues.

Thus CO

2

is the most important variable

responsible for respiratory drive regulation
under normal conditions.

Peripheral chemoreceptor

system

localization:
Aortic bodies – along the aorta arch
Carotid bodies – bifurcation of the common carotid artery

• Very high blood flow through these bodies
• They are exposed continously to arterial blood O

2

(PAO

2

)

• Respond to changes in PAO

2

( decrease) and to a

lesser extent to PCO

2

and [H

+

]

• Hihgly senstive to PAO

2

in the range 60 to 30 mmHg

• Why ??

Peripheral chemoreceptors

• PCO

2

– mediated stimulation via peripheral

receptors is 7-8 times lower than that via
chemosensitive area

• But the onset of stimulation occurs 5 times

rapidly

• Increases rapidity of ventilatory response to

CO

2

when we start exercise

Regulation of respiration during

exercise

• Mean arterial PO

2

, PCO

2

and pH remain almost

normal during exercise

What stimulates intense ventilation during exercise ?

• Brain ; motor impulses to muscles are collaterally

transmitted to neurons in respiratory center

• movement of arms and legs ; excited

proprioreceptors (in joints and muscles) transmit
impulses to respiratory centre

• Hypoxia in the muscles during exercise – afferent

nerve signals to respiratory centre ?

• Changes of PCO

2

and PO

2

between expiration and

inspiration ?

Voluntary control of

respiration

• Talking
• Singing
• Eating
• Defecation

Voluntary hypoventilation or hyperventilation
• Not mediated through respiratory center in the

medulla

• Pathway: cortex , spinal tract ,spinal neurons ,

muscles

Depressant of the respiratory center

• Morphine
• Pentobarbital

• Sleep
Alveolar hypoventilation – chemosensitive areas

reveal decreased response to CO

2

Upper airways muscles relaxation – increase in

the airflow resistance