Respiratory Rate - physiology of deterioration

What centre controls respiration?

Medullary respiratory centres

What is the medullary respiratory centers made up of ?

Ventral and dorsal

What is the ventral group is responsible for?

Rhythmicity of breathing

What is the dorsal group is responsible for?

Inspiration - diaphragm

What is the another respiratory centre located in the pons?

Pounine respiratory centre

How do the two respiratory centers interact?

Pontine interacts with the medulla to smooth respiration

What is the most important muscles in respiration?

Diaphragm

Intercostal muscle - in between the ribs

What can influence the respiratory system ?

Higher centers of brain - voluntary control, perception of pain, emotion and temperature. These can all influence RR. Either stimulate or suppressing the pontine respiratory centre which then will stimulate or suppress the medullary respiratory center and respiration itself.

What are the main regulatory or influencer of RR?

Peripheral chemoreceptors - located in carotid and aortic bodies

What are Peripheral chemoreceptors?

They detect chemical changes in the blood. E.g. if they detect decrease in O2 and pH and increase in C02. This will then trigger the receptors and stimulate the respiratory centre which will therefore increase RR trying to neutralise everything.

What are central chemo receptors?

Detect changes in pH. e.g. decrease pH and increase in CO2 will stimulate the chemo receptor to stimulate the respiratory system so you can breathe faster, therfore breathing out more Co2 and inhaling more 02

Additional receptors

There are also receptors in muscles and joints - for exercise

There are also irritant receptors in your lungs that help blow off the irritant. When they are stimulated they will suppress the respiratory centre and slow down respiration

There are also stretch receptors in the lungs which cause the hering breuer reflex. A reflex that is protective. Protective intiiated by over inflation of the lungs. When initiated they will suppress RR.

What is tachypnoea?

Tachypnoea is defined as a fast respiratory rate that is greater than 20 breaths per minute.

The normal respiration rate is 12-10 breaths per minute in adults.

What is the significance of tachypnoea?

Although it can be a normal physiological response (eg with strenous exercise), in the acute setting a fast respiratory rate is one of the first and most significant signs of patient deterioration. Yet audits of observation charts show that assessing respiratory rate is often neglected.

Conditions associated with tachypnoea may be produced by many different system pathologies including: 

• cardiac

• respiratory

• CNS

• infectious

• psychiatric

Any state changing levels of oxygen, carbon dioxide or acid-base will affect respiratory drive.

Tachypnoea compensatory response to what three conditions?

In the context of patient deterioration, tachypnoea occurs in most situations as a compensatory response to either:

• a drop in pO2 (hypoxaemia)

• a rise in pCO2 (hypercapnia)

• a drop in blood pH from respiratory and/or metabolic causes (acidosis.

Where do Central and/or peripheral chemoreceptors send messages too?

The brain stem

Central chemoreceptors in the medulla and peripheral chemoreceptors in the aortic arch and carotid body measure a combination of pO2, pCO2 and pH and send messages to the brainstem.

The respiratory centres in the medulla and pons receive messages from the chemoreceptors and respond by increasing respiratory rate and tidal volume to compensate for the fluctuations.

What is bradypnoea?

Is defined as a slow respiratory rate less than 12 breaths per minute, although this varies between 8 and 12 depending on the literature.

SiThe normal respiration rate is 12-10 breaths per minute in adults.

Significance of bradypnoea

Although not specific, bradypnoea in an unwell patient is often a sign of serious dysfunction and requires immediate investigation.

In asthma and respiratory failure, bradypnoea often precedes respiratory arrest.

Conditions associated with bradypnoea:

Bradypnoea may occure in any condition or state that affects the respiratory/ventilatory centres of the brain or brainstem

More common factors

• Drugs, such as opiates, benzodiazepines, barbiturates, anaesthetic agents

• Respiratory failure

• Brain injury and raised intracranial pressure

• Hypothyroidism

• Excess alcohol consumption

Less common factors

• Hypothermia

• Uraemia

• Metabolic alkalosis

What can bradypnoea be induced by?

• Decreased central nervous system output

  → A defect or reduction in central respiratory drive that diminishes messages ‘telling’ the body to breathe (e.g. brain injury, raised ICP, opiate overdose).

• Neuromuscular junction

  → Disorders in the nerves connecting to the respiratory muscles, where neurotransmission at the neuromuscular junction is disrupted (e.g. motor neuron disease).

• Decreased respiratory muscles function

  → Disorders affecting the muscles associated with breathing (e.g. diaphragmatic fatigue in respiratory failure and sepsis).

• Respiratory compensation

  → Central respiratory compensation in response to a metabolic process (e.g. in response to metabolic alkalosis, central respiratory centres will reduce respiration in an attempt to retain carbon dioxide and acids).