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
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
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
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
15.
16. 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)
18. 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
19. 30:15 ratio
RR interval at 30th
beat
•30:15 ratio = ------------------------------
RR interval at 15th
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
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
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 II Decrease in BP, Tachycardia
♦ Phase III Decrease in BP
♦ Phase IV Overshoot 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
≥ 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
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
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