Reflexes and Surgical influences
Daniel Robbins
Definitions
• Stimulation
Internal (e.g. conscious decision),
External (e.g. mechanical / electrical)
• Orthodromic impulse
An orthodromic impulse runs along an axon in its normal
direction, away from the soma.
• Antidromic impulse
An antidromic impulse in an axon refers to conduction
opposite to the normal
• Reflex
Automated response, different to that of a decisive
reaction,
E.g. does not follow hicks law,
T = blog2(n + 1)
T = time
b = constant determined empirically by fitting a line to measured data
n = number of equally probable choices
Smaller/faster neural pathways etc.
This diagram is not 100% accurate as the
signal would actually be sent from the
muscle not the tendon. However its still
quite nice so I left it in.
Types of Reflex
Autonomic reflex
The intrinsic visceral reflexes mediated by control centers in the brain, particularly in
the hypothalamus and brain stem, and in the spinal cord, particularly in the
lateral horns of thoracic and lumbar spinal cord segments; these reflexes are
involved in the automatic adjustment or negative feedback control of internal
environment = internal homeostasis.
Somatic reflex
Any reflex in which the effectors are skeletal muscles, e.g., the patellar reflex, the
flexor or withdrawal reflex, the crossed extensor reflex, etc.
Categorising reflexes and responses
Stretch-reflex
A stretch reflex is a muscle contraction in response to stretching within the muscle. It is a monosynaptic
reflex which provides automatic regulation of skeletal muscle length.
e.g. Ankle Clonus
H-reflex
The H-reflex is the electrical equivalent of the monosynaptic stretch reflex and is normally obtained in only a
few muscles.
It is elicited by selectively stimulating the sensory (Ia) fibres of the posterior tibial or median nerve. The
stimulus travels along the Ia fibers, through the dorsal root ganglion, and is transmitted across the central
synapse to the anterior horn cell which fires it down along the alpha motor axon to the muscle.
Reflexes and responses cont.
F-wave/F-response
The second of two voltage changes observed after electrical stimulation is applied to the skin surface
above the distal region of a nerve.
F wave properties include:
Amplitude (µV) - F wave height
Duration (ms) - length of F wave
Latency (ms) – period between F wave and initial stimulation
Persistence - the number of measurable F waves divided by the number of stimuli.
M-wave
–
–
–
–
Evoked motor unit action potential
Compound muscle action potential (CMAP)
Massed action potential
Direct muscle response
–
A maximum M-wave (Mmax) is elicited by a supramaximal stimulation of all motor units within
the motor unit pool. The Mmax is the methodological control to ensure that the effective
stimulus intensity to peripheral nerves is consistent across recording sessions.
Anaesthetic effects on reflexes
Isoflurane/Sevoflurane
– No difference in incidence of ankle clonus or mean clonus score
– Greater time to onset in clonus when Sevoflurane is used (1).
– Both isoflurane alone and isoflurane plus nitrous oxide decrease
H-reflex and F-wave amplitude and F-wave persistence (the
number of measurable F waves divided by the number of
stimuli). These effects suggest that isoflurane and nitrous oxide
decrease motoneuronal excitability in the human spinal cord.
This may play an important role in producing surgical immobility
(2).
–
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–
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– High concentrations of Sevoflurane have been shown
to depress tetanic stimulus-induced withdrawal
reflexes to a greater extent than that of Propofol.
Isoflurane/sevoflurane and ankle clonus
(1)
Isoflurane & H-reflex
(2)
Isoflurane and F-wave
(2)
Nitrous oxide/Isoflurane & F-wave
(2)
• Propofol
- Suppresses the H-reflex at concentrations far lower than those needed for surgical
immobility(3).
• Ketamine
- Does not affect peripheral sensory or motor conduction (4).
- Has been shown to effect polysynaptic reflexes but not monosynaptic reflexes
when used in the absence of enhanced GABA-mediated inhibitions (5).
• Pentobarbital
- Does not affect peripheral sensory or motor conduction, but does increase latency
of the initial positive component of the somatosensory cortical response and the
attenuation of the following negative component.
- No significant differences in M-Wave or H-reflex.
- Effects are greater and longer in duration than that of Ketamine (4).
Reflex Changes in response to SCI/SCT
• Spinal Shock
– Characterised by complete paralysis, loss of sensation, muscle hypotonia and
absent reflexes caudal to the lesion.
– In patients with acute SCI, H-reflex and F-wave responses are absent or
markedly suppressed early after injury
– Similar responses can be observed following perturbation/manipulation of the
spine during surgery (6).
• Interestingly this study reports that H-reflexes are not affected by depth of anaesthesia,
an observation contrary to most literature…
Four-phase model of Spinal Shock
(7)
Phase 1
(0-1 days)
Phase 2
(1-3 days)
Phase 3
(1-4 weeks)
Phase 4
(1-12 months)
Areflexia /
hyporeflexia
Initial reflex
return
Initial hyperreflexia
Final hyperreflexia
Loss of
descending
facilitation
Denervation
supersensitivity
Axon-supported
synapse growth
Somasupported
synapse growth
Recovery of reflexes: four phases of
spinal shock
(7)
Reflex
0-1 Day
1-3 Days 1-4 Days 1-12 Months
Delayed Planter reflex (S1-2)
+++
+++
+/0
+/0
Bulbocavernosus (S3-5)
+/0
++
++
++
Anal wink (S4)
+/0
++
++
++
Cremasteric (L1-2)
+/0
++
++
++
Babinski sign
0
+
++
++
Flexor withdrawal reflex
0
+/0
++
+++
Deep tendon reflex (Ankle L5-S2, Knee L3-4)
0
+/0
++
+++
Tibial H-reflex
0
++
+
+++
Extensor spasm
0
0
0
+++
Interlimb reflexes
0
0
0
+++
Reflex neurogenic bladder (L4-S3)
0
0
0
+++
Autonomic hyper-reflexia
0
0
0
+++
Return of Reflexes
(8)
•
•
Plantar response
Babinski
Return of Reflexes
(8)
Return of Reflexes
(8)
References
1)
2)
3)
4)
5)
6)
7)
8)
Ewen, A. Cox, R.G. Davies, S.A. Luntley, J.B. Rubin, Y. Fick, G.H. Bevin, B.B. (2005) The
ankle clonus test is not a clinically useful measure of spinal cord integrity in children. Can J
anesth 52,5,524-529
Zhou, Henry H. MD, PhD; Mehta, Mahesh MD; Leis, A. Arturo MD (1997) Spinal Cord
Motoneuron Excitability during Isoflurane and Nitrous Oxide Anaesthesia. Anaesthesiology
Volume 86(2) February pp 302-307
Baars,J.H. Dangel, C. Herold, K.F Hadzidiakos, D.A. Rehberg. (2006) Suppression of the
human spinal H-reflex by propofol: a quantitative analysis. Acta anaesthesiol scand 50 193200.
Goss-Sampson, M.A. Kriss, A. (1991) Effects of pentobarbital and Ketamine-xylazine
anaesthesia on somatosensory, brainstem auditory and peripheral sensory-motor responses in
the rat. Laboratory Animals 25, 360-366.
Lodge, D. Anis, N.A. (1984). Effects of Ketamine and three other anaesthetics on the spinal
reflexes in the cat. Br J Anaesth. 56, 1143-1151.
Leiss, A.A. Zhou, H.H. Mehta,M. Harkey, H.L. Paske. (1996) Behaviour of the H-reflex in
humans following mechanical injury to rostral spinal cord.
Ditunno, J.F. Little, Tessler, J.W. Burns, A.S. (2004) Spinal shock revisited: a Four phase
model. Spinal cord. 42. 383-395.
Kyo, H-Y. Ditunno, JF. Graziani, V. Little, J.W. (1999) The pattern of reflex recovery during
spinal shock. Spinal Cord 37, 402-409.
Thanks for listening
Questions ???