Physiology of the vasovagal reflex

W Wieling
AMC
Amsterdam
Physiology of the
Vasovagal Reflex
Sept 2011- sept 2014
About 500 patients
VASOVAGAL SYNCOPE
• parasympathetic (vagal) outflow
increases slowing the heart
• simultaneously, the activity of
efferent sympathetic
vasoconstrictor nerves decreases,
leading to systemic vasodilatation
5 sec
MSFP about 20 mm Hg
ISSUE 3 STUDY
BrignoleM, Donateo et al. Circulation. Arrhythmia and Electrophysiology2014;7:10-16.
STANDING
Central blood volume (CBV) 
Cardiac filling 
Stroke volume 
Cardiac output 
CBV
CBV
Vasomotor tone

Opposes fall in blood pressure
Skeletal muscle tone 
Opposes venous pooling
CBV
CBV
CENTRAL BLOOD VOLUME
• Amount of blood available for the
heart to pump
• Stabilizer of the Circulation
• A heart cannot pump blood that it
does not receive
Wieling W, de Lange FJ, Jardine DL.
Frontiers in Physiology 2014; epub eahead of print
- intermittent heart block.
- CBV normal
- Pacing: Effective
- Orthostatic vasovagal faint.
- CBV
- Pacing: Ineffective
CBV
CBV
HISTORICAL BACKGROUND
• Clinical observations. Cotton & Lewis
1918.
• Around midcentury: intra-arterial BP,
CO, FBF measurements
• Around 1990 Finapres
1990ties Penaz &
Wesseling: Finger
arterial pressure
Finometer
Nexfin
PULSE WAVE ANALYSIS
Academic Medical Centre around 1995
Rapid
recovery
FAINTING MECHANISMS
• Large decrease in CO (50%) typically
occurs in presyncope
• No pronounced vasodilatation in
presyncope. TPR on average about
40% above supine control
• Huge variety in individual responses
v
18seconds
Weissler et al Vasodepressor syncope. Factors influencing cardiac output.
Circulation 1957; 25:875-82.
Inflation of antigravity suite
Transit time
TRANSIT TIME
• about 5 heart beats
• Probably >> 5 heart beats if central
blood volume is depleted
31-years
69-years
Verheyden et al. Impact of age on the vasovagal response provoked by
sublingual nitroglycerine in routine tilt testing. Clin Sci 2007;113:329-337
old: 51 years
young: 30 years
Verheyden et al. Impact of age on the vasovagal response provoked by
sublingual nitroglycerine in routine tilt testing. Clin Sci 2007;113:329-337
Wieling et al. Reflex control of heart rate in normal subjects relation
to age: A Data Base for Cardiac Vagal Neuropathy. Diabetologia 1982;22:163-166.
“ISSUES” TO BE ADDRESSED
• conventional wisdom is that the
decrease in vagal tone with aging is
due to impaired efferent vagal
pathways
• incompatible with the observations in
the ISSUE studies
VAGAL NERVE FUNCTION IN
SENIORS
• efferent impairment of the vagal
nerve
• subnormal resting levels of vagalcardiac nuclei by baroreceptor input
• abnormal, but reversible central
“setting” of the activity of vagalcardiac motor nuclei
TILTBACK
30 s
PPFH
• decreased cardiac contractility
resulting from increased vagal and
decreased sympathetic outflow
• sustained central suppression of
central excitatory mechanisms.
TAKE HOME MESSAGE
• a heart cannot pump blood that it
does not receive
• increased vagal outflow decreases
cardiac contractility
Wieling W, de Lange FJ, Jardine DL. A heart cannot pump blood that it does not receive.
Frontiers in Physiology 2014; epub eahead of print
Coote JH. Myths and realities of the cardiac vagus. J Physiol 2013;591:4073-4085
Sir Thomas Lewis 1881-1945
• Heart block 1908
• Vasovagal syncope and the carotid
sinus mechanism with comments on
Gowers's and Nothnagel's syndrome.
Br Med J 1932
• personally disliked the term
cardiologist and preferred to be
considered a cardiovascular disease
specialist