This document describes 4 autonomic function tests used to assess the cardiovascular system: 1) Heart rate variation during respiration measures vagal control of heart rate, 2) Heart rate variation during postural change assesses parasympathetic response, 3) The Valsalva maneuver evaluates sympathetic and parasympathetic function through blood pressure and heart rate responses in 4 phases, 4) The cold pressor test increases blood pressure through sympathetic discharge triggered by cold stress. These tests are used to evaluate autonomic nervous system function.

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

2. 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

3. 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 due to changes in vagal control of heart rate
– by the influence of respiratory centre
– by the influence of pulmonary stretch receptors

4. Sinus Arrhythmia

5. E:I ratio
• Ask the subject to breath deeply at a rate of six
breaths per minute for 3 cycles
• Record maximum and minimum heart rate with
each respiratory cycle

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

7. 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

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

10. 30:15 ratio
• The ratio of R-R intervals corresponding to the 30th
and 15th
heart beat  30:15 ratio
RR interval at 30th
beat
• 30:15 ratio = ------------------------------
RR interval at 15th
beat
• This ratio is a measure of parasympathetic response
Normal > 1.04
Borderline = 1.01-1.04
Abnormal =<1.00

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

12. 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

13. Four Phases

14. – 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

15. 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

16. 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

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

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

19. 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

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

21. • 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

22. Phases
♦ Phase I Increase in BP
♦ Phase II Decrease in BP, Tachycardia
♦ Phase III Decrease in BP
♦ Phase IV Overshoot of BP, Bradycardia

23. 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

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

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

26. 4. Cold pressor test
• Submerge the hand in ice cold water
• This increases
– systolic pressure by about 20 mmHg
– diastolic pressure by 10 mmHg
• Temperature and other environmental stressors are known to affect HR and
BP
• Sudden and increasingly painful cold stress causes massive discharge of
the sympathetic nervous system and release of norepinephrine
• This sympathetic discharge triggers arteriolar constriction, increased HR,
and increased cardiac contractility
• These responses combine to increase BP which is known as the cold
pressor response
• The test is used to evaluate cardiovascular autonomic functions

27. Baroreceptor Reflex

29. Valsalva manoeuvre in diabetic autonomic
neuropathy

30. 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