Autonomic function tests

1. Autonomic
Function Tests
Prof Vajira Weerasinghe
Professor of Physiology
Available at www.slideshare.net/vajira54

2. Autonomic Nervous system

3. Objectives
Describe the physiological basis of the following autonomic
function tests in relation to cardiovascular system
1.Heart rate variation during respiration
2.Heart rate variation during postural change
3.Valsalva manoeuvre (maneuver)
4.Cold pressor test

4. 1. Heart rate variation during
respiration
•The variation of heart rate with respiration is known as
sinus arrhythmia
•Inspiration increases the heart rate
•Expiration decreases the heart rate
•This is also called Respiratory Sinus Arrhythmia
(RSA)
•This is an index of vagal control of heart rate

5. Sinus Arrhythmia

6. Explanation for sinus
arrhythmia
•Due to changes in vagal control of heart
rate during respiration
•Probably due to following mechanisms
–Influence of respiratory centre on the vagal
control of heart rate
–Influence of pulmonary stretch receptors on
the vagal control of heart rate

7. Heart rate variation during
respiration
•Heart rate increases during inspiration due to
decreased cardiac vagal activity and decreases
during expiration due to increased vagal activity
•This is detected by recording the heart rate by
using the electrocardiograph while the subject is
breathing deeply

8. Deep breathing

9. Procedure
•Connect the ECG electrodes for recording lead II

•Ask the subject to breath deeply at a rate of six
breaths per minute for 3 cycles
(allowing 5 seconds each for inspiration and
expiration)

10. Procedure
•Record maximum and minimum heart rate with each
respiratory cycle
•Average the 3 differences
–Normal > 15 beats/min
–Borderline= 11-14 beats/min
–Abnormal < 10 beats/min

11. Procedure
•Determine the expiration to inspiration
ratio (E:I ratio)

12. E:I ratio
•Mean of the maximum R-R intervals
during deep expiration to the mean of
minimum R-R intervals during deep
inspiration

13. E:I ratio
longest RR interval (expiration)
Ratio =-------------------------------------
shortest RR interval (inspiration)
E:I = 1.2

14. 2. Heart rate variation during
postural change
•Changing posture from supine to standing leads
to an increase in heart rate immediately, usually
by 10-20 beats per minute

16. Heart rate variation during
postural change
•On standing the heart rate increases until it
reaches a maximum at about
–15
th
beat (shortest R-R interval after standing)
–after which it slows down to a stable state at about
–30
th
beat (longest R-R interval after standing)

17. Heart rate response to
standing from supine posture

18. 30:15 ratio
•The ratio of R-R intervals corresponding to the 30
th

and 15
th
heart beat  30:15 ratio
RR interval at 30
th
beat
•30:15 ratio= ------------------------------
RR interval at 15
th
beat
•This ratio is a measure of parasympathetic
response

19. 30:15 ratio
RR interval at 30
th
beat
•30:15 ratio=------------------------------
RR interval at 15
th
beat
•Normal > 1.04
•Borderline = 1.01-1.04
•Abnormal =<1.00

20. 3. Valsalva Manoeuvre
•Assesses integrity of the baroreceptor
reflex
•Measure of parasympathetic and
sympathetic function
•It is “forced expiration against a closed
glottis”

21. Valsalva Manoeuvre
•The Valsalva
maneuver is
performed by
attempting to forcibly
exhale while keeping
the mouth and nose
closed
•It increases
intrathoracic pressure
to as much as 80
mmHg

22. Procedure
•Perform the Valsalva manoeuvre (forced
expiration against a closed glottis) by asking the
subject to breathe forcefully into a mercury
manometer and maintain a pressure of 40
mmHg for 15 seconds
•Record the ECG throughout and for 30 seconds
after the procedure

23. Valsalva Manoeuvre
•4 phases
–Phase I
–Phase II
–Phase III
–Phase IV

24. Four Phases

25. –Transient increase in BP which lasts for a few seconds
–HR does not change much
–Mechanism: increased intrathoracic pressure and mechanical
compression of great vessels due to the act of blowing
Phase I – Onset of straining

26. Phase II - Phase of straining
•Early part – drop in BP lasting for about 4 seconds
•Latter part – BP returns to normal
•Heart rate rises steadily

27. Mechanism
•Early part
–venous return decreases with compression of veins by
increased intrathoracic pressure central venous pressure
decreases  BP decreases
•Latter part
–drop in BP in early part will stimulate baroreceptor reflex 
increased sympathetic activity  increased peripheral
resistance  increased BP ( returns to normal )
•Heart rate increase steadily throughout this phase due to vagal
withdrawal in early part & sympathetic activation in latter part

28. Phase III - Release of straining
•Transient decrease in BP lasting for a
few seconds
•Little change in heart rate

29. Mechanism
•Mechanical displacement of blood
into pulmonary vascular bed, which
was under increased intrathoracic
pressure  BP decreases

30. Phase IV – further release of strain
•BP slowly increases and heart rate proportionally decreases
•BP overshoots
•Occurs 15-20 s after release of strain and lasts for about a
minute or more

31. Mechanism
•Due to increase in venous return, stroke
volume and cardiac output

32. •With this high pressure there is no venous
return since no venous blood can enter
the thorax
•The blood in the lungs and heart will be
expelled at a higher pressure than normal

33. Phases
¨ Phase I Decrease in BP
¨ Phase IIDecrease in BP, Tachycardia
¨ Phase IIIDecrease in BP
¨ Phase IVOvershoot of BP, Bradycardia

34. Valsalva Ratio
•Measure of the change of heart rate that takes
place during a brief period of forced expiration
against a closed glottis
•Ratio of longest R-R interval during phase IV
(within 20 beats of ending maneuver) to the
shortest R-R interval during phase II
•Average the ratio from 3 attempts

35. Valsalva Ratio
Longest RR
Valsalva Ratio =-----------------------------
Shortest RR
³ 1.4
Values
•more than 1.21 normal
•less than 1.20  abnormal

36. Valsalva manoeuvre
•Valsalva maneuver evaluates
–1. sympathetic adrenergic functions using the
blood pressure responses
–2. cardiovagal (parasympathetic) functions
using the heart rate responses

37. 4. Cold pressor test
•Submerge the hand in ice cold water
•This increases
–systolic pressure by about 20 mmHg
–diastolic pressure by 10 mmHg

38. Medullary
cardiovascular
control
center
Carotid and aortic
baroreceptors
Change in
blood
pressure
Parasympathetic
neurons
Sympathetic
neurons
Veins
Arterioles
Ventricles
SA node
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

39. Figure 15-21 (1 of 10)
Blood Pressure
Change in
blood
pressure
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

40. Figure 15-21 (2 of 10)
Blood Pressure
Carotid and aortic
baroreceptors
Change in
blood
pressure
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

41. Figure 15-21 (3 of 10)
Blood Pressure
Medullary
cardiovascular
control
center
Carotid and aortic
baroreceptors
Change in
blood
pressure
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

42. Figure 15-21 (4 of 10)
Blood Pressure
Medullary
cardiovascular
control
center
Carotid and aortic
baroreceptors
Change in
blood
pressure
Parasympathetic
neurons
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

43. Figure 15-21 (5 of 10)
Blood Pressure
Medullary
cardiovascular
control
center
Carotid and aortic
baroreceptors
Change in
blood
pressure
Parasympathetic
neurons
Sympathetic
neurons
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

44. Figure 15-21 (6 of 10)
Blood Pressure
Medullary
cardiovascular
control
center
Carotid and aortic
baroreceptors
Change in
blood
pressure
Parasympathetic
neurons
Sympathetic
neurons
SA node
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

45. Figure 15-21 (7 of 10)
Blood Pressure
Medullary
cardiovascular
control
center
Carotid and aortic
baroreceptors
Change in
blood
pressure
Parasympathetic
neurons
Sympathetic
neurons
SA node
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

46. Figure 15-21 (8 of 10)
Blood Pressure
Medullary
cardiovascular
control
center
Carotid and aortic
baroreceptors
Change in
blood
pressure
Parasympathetic
neurons
Sympathetic
neurons
Ventricles
SA node
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

47. Figure 15-21 (9 of 10)
Blood Pressure
Medullary
cardiovascular
control
center
Carotid and aortic
baroreceptors
Change in
blood
pressure
Parasympathetic
neurons
Sympathetic
neurons
Arterioles
Ventricles
SA node
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

48. Figure 15-21 (10 of 10)
Blood Pressure
Medullary
cardiovascular
control
center
Carotid and aortic
baroreceptors
Change in
blood
pressure
Parasympathetic
neurons
Sympathetic
neurons
Veins
Arterioles
Ventricles
SA node
Integrating center
Stimulus
Efferent pathway
Effector
Sensor/receptor
KEY

49. Baroreceptor Reflex

50. Valsalva manoeuvre in diabetic autonomic
neuropathy

51. Other ANS tests in CVS
•Head up tilt test (HUT)
–Heart rate and BP response
•BP Response to standing
•BP Response to sustained handgrip
•Plasma norepinephrine measured with the subject
supine and after a period of standing provides another
method of studying adrenergic function