14 Cardiovascular - Respiratory Interactions Flashcards
What are the mechanical respiratory influences on the heart?
in inspiration:
increased venous return to RV
increased left EDV and SV
What happens to HR when you breathe in and out?
in - increases
out - decreases
What are the 2 main mehcanisms accounting respiratory sinus arrhythma
CNS mechanisms
Reflex response
What are the principles of the CNS mechanisms?
inspiratory motor neurones:
increase inspiratory muscle activity
send inhibitory signal to NA, increasing HR
What are the principles of the reflex response?
pulmonary stretch receptors go to NTS, inhibiting NA
this reduces Vagal tone, increasing HR
What chemoreceptor groups are associated with the reflex effects in systemic hypoxia?
carotid bodies
aortic bodies
What is hypoxia?
a fall in PaO2 below 60mmHg (8.1 kPa)
What is the effect of hypoxia if respiration cannot increase?
primary cardiovascular reflex
decreased HR and vasoconstriction
02 CONSERVING
What is the effect of hypoxia if respiration can increase?
increased respiratory effects on HR dominate, so HR increases
Name 5 causes of systemic hypoxia when respiration cannot be increased?
paralysis high spinal transection long dive underwater fetus in utero severe respiratory disease
What are the local effects of hypoxia on the heart?
decreased HR and contractility
What are the local effects of hypoxia on the brain?
vasodilation
What are the local effects of hypoxia on muscle?
vasodilation
What are the local effects of hypoxia on the lungs?
vasoconstriction
What is the net effect of local effects of hypoxia
available oxygen is directed to the brain
What are the bad effects of hypoxia?
pulmonary vasoconstriction may cause oedema
eventually RV failure
What might a patient with respiratory disease look like?
blue bloater
Name 3 causes of systemic hypoxia where respiration can increase
hypoxic atmosphere
high altitude
less severe respiratory disease
What is the difference when respiration can be increased in hypoxia?
reflex effects of peripheral chemoreceptor stimulation on heart rate are overcome by effects of increased respiration on HR
What happens when respiration can increase in hypoxia?
increased respiration
increased HR
general vasoconstrictinoon
What does someone who is hypoxic by can increase respiration look like?
pink puffer
What stimulates the diving reflex?
cold water stimulation on the face / nose (trigeminal)
What does stimulation of the diving reflex cause?
NTS inhibition of central inspiratory neurones
What does the diving reflex cause?
expiratory apnoea decreased HR (increased vagal activity) vasoconstriction
an O2 conserving reflex
What are the clinically significant scenarios for the diving reflex?
sinus washing irritant vapours intubation / bronchoscopy. laryngoscopy lumps of food caught in pharynx quadriplegics when mucous aspirated
how can the diving reflex be fatal?
a strong response can cause expiratory apnoea (cardiac arrest)
How can you relieve someone of the effects of the diving reflex?
mouth - mouth ventilation to terminate apnoea and reverse reflex
When might the diving reflex be useful clinically?
use an ice bag over the face to stop a supraventricular tachycardia
