1. Identification of Sural Nociceptive flexion reflex Ratio in adult Males 20-40 years of age
Thien Ngo MD
PGY – 4
UK PM&R
5/23/2013
Advisors: Drs. Lumy Sawaki & Oscar Ortiz
background information, proposed objectives, proposed methods and anticipated results.

2. Outline Introduction Objectives Experimental Design Method Results
References

3. Introduction 1
Pain is a subjective experience, and its measurement has been traditionally based on self reported instruments.
Absence of objective instruments
Quantitative sensory testing and nociceptive flexion reflex (NFR) threshold have been explored as options to measure pain more objectively

4. Introduction 2 NFR in theory
The NFR is a polysynaptic spinal reflex subserving withdrawal from potentially noxious stimuli.
Provide indirect evidence of supraspinal modulation
The higher the threshold the more inhibition of spinal nociceptive transmission
NFR is induced by an electric stimuli applied in the sural nerve at the ankle2,3. When the stimulus intensity is high enough to induce stimulation of the A-delta fibers (stimulus threshold), the sensory nerve action potential (SNAP) can be measured by electromyography2,3,4. It appears that lower threshold is associated with subjects more sensitive or susceptible for various types of pain5. This technique has been demonstrated to be reliable, reproducible and correlated well with clinical findings within subject5. More specifically, pain threshold has been found to be directly related to pain perception and appears to change proportionally with level of pain5.

5. Introduction 3
NFR threshold is defined by the lowest noxious stimulation intensity required to trigger a reflex motor response in the biceps femoris muscle.
NFR is induced by an electric stimuli applied in the sural nerve at the ankle2,3. When the stimulus intensity is high enough to induce stimulation of the A-delta fibers (stimulus threshold), the sensory nerve action potential (SNAP) can be measured by electromyography2,3,4. It appears that lower threshold is associated with subjects more sensitive or susceptible for various types of pain5. This technique has been demonstrated to be reliable, reproducible and correlated well with clinical findings within subject5. More specifically, pain threshold has been found to be directly related to pain perception and appears to change proportionally with level of pain5.

6. Introduction 4
Pooled estimates of nociceptive flexor reflex (NFR) threshold standardized mean difference and its confidence interval in primary headaches [1,7,20,44,50] (solid
squares), fibromyalgia [3,7,16,26] (solid triangles), knee pain [13,14] (solid stars), and whiplash [3,56] (solid diamonds) versus healthy controls. Pooled estimates of subgrouped
clinical conditions are indicated by empty symbols, while pooled estimate of all clinical conditions is indicated by the cross.
Employed stimuli parameters vary between studies, with inter-pulse duration (P=0.044) being identified by multiple regression analysis as independent predictors of the variability in NFR threshold in healthy controls. The results indicate that there is evidence of central hyperexcitability in people with chronic musculoskeletal pain. Our review also suggests that shorter inter-pulse duration tends to yield smaller variability in NFR threshold. However, further research investigating optimal stimulation parameters is still warranted.
Central hyperexcitability as measured with nociceptive flexor reflex threshold in chronic musculoskeletal pain: a systematic review.
Lim EC, Sterling M, Stone A, Vicenzino B.
Pain Aug;152(8): Epub 2011 Apr 27

7. Introduction 5 Promising results in multiples experimental studies.
Reliable, reproducible, and correlated well with clinical findings within subjects
Significant variability between subjects, despite efforts for standardization, makes it unsuitable for clinical use or establishment of normal values.

8. Introduction 6
Propose alternative standardized method to measure NFR that avoid variability (mostly due to changes in skin resistance).
NFRI =
Sural SNAP amplitude using NFRT stimulus
Sural SNAP amplitude (supramaximal)
x 100
SNAP sensory nerve action potential.
AN1 amplitude

9. Objectives
The goal of this pilot study is to begin to establish normative data of NFRI in young male adults. Our proposed study has 2 specific aims:
Specific Aim #1:Identify the “normal” sural nociceptive flexion reflex threshold (NRFT) and the sural nociceptive flexion reflex ratio (NFRR) in male adults of 20 to 40 years of age.
Specific Aim #2:Measure the correlation between the NFRI and level of pain as measured by Visual Analogue Scale (VAS).
so the objective was dual... to try to identify normal values in young people and to identify an index/ratio that could facilitate the comparison between them.   The nfrt values in this "normal" young population shows a huge variability, as expected, that made the definition of "normal NFRT"  impossible... and we could not find and index or ratio that could change that.

10. Experimental Design Recruitment: Flyers and volunteer subjects
Screening process and informed consent
Inclusion Criteria:
Healthy male 20-40
Exclusion Criteria:
Avoiding confounding factors of NFR and NFRT recording
Head injury, alcohol/drug abuse, psychiatric illness, on psychiatric/pain medications, neurological disorder, chronic pain, h/o cancer, and peripheral neuropathy
IRB protocol for privacy and security

11. Method (Step 1) (Sural sensory nerve action potential)
Nociceptive flexion reflex will be obtained using surface EMG.  The pick-up electrode will be placed 4 fingers’ breadth proximal to the fibula head, over the biceps femoris muscle.  The reference electrode will be 3 cm proximal over the same muscle.  The ground electrode will be placed over the anterior patella.   Intermittent and random electrical stimulation (pausing at an interval selected from a random list of values ranging from 3 to 10 seconds)  will be administered by a surface electrode bar in the sural nerve, at the same level as described for the sural SNAP study . The intensity of the stimulation will be gradually increased up to 10 mA until biceps femoris reflex is identified. Then stimulation is decreased by 3 mA until the nociceptive reflex cannot be elicited.  The nociceptive flexion reflex threshold would be the lowest intensity to produce the reflex in 2 out of 3 attempts. 

12. EMG Machine

13. Method (Step 2) (Nociceptive Flexion Reflex)
Nociceptive flexion reflex will be obtained using surface EMG.  The pick-up electrode will be placed 4 fingers’ breadth proximal to the fibula head, over the biceps femoris muscle.  The reference electrode will be 3 cm proximal over the same muscle.  The ground electrode will be placed over the anterior patella.   Intermittent and random electrical stimulation (pausing at an interval selected from a random list of values ranging from 3 to 10 seconds)  will be administered by a surface electrode bar in the sural nerve, at the same level as described for the sural SNAP study . The intensity of the stimulation will be gradually increased up to 10 mA until biceps femoris reflex is identified. Then stimulation is decreased by 3 mA until the nociceptive reflex cannot be elicited.  The nociceptive flexion reflex threshold would be the lowest intensity to produce the reflex in 2 out of 3 attempts. 

14. EMG machine - Biceps Femoris Reflex

15. Graph 1: Subject by Subject Responses: biceps reflex, pain index, and NFRR
Graph 1. Pain index and NFRR showed a closed correlation with subject 1, 2, 4, 6, & 7. There was no significant correlation between pain and biceps reflex intensity.

16. Graph 2: Correlation between pain index vs biceps reflex
Graph 2. Biceps Reflex (mA) vs Pain Index showed 59% correlation

17. Graph 3: Pain index vs NFRR
in retrospect, we also realized that we might have made a mistake in choosing our gold standard.  we compared the nfrt and our index to the pain (VAS) caused by the stimulus that defined the nfrt and not by a fixed standard stimulus, which can explain the variability seen.
Graph 3. Lack of a correlation between pain index and NFRR

18. Conclusion/Discussion:
No significant findings
Variability
Take away points
Revise gold standard
Minimal threshold for SNAP
Standard stimulus for pain index
in retrospect, we also realized that we might have made a mistake in choosing our gold standard.  we compared the nfrt and our index to the pain (VAS) caused by the stimulus that defined the nfrt and not by a fixed standard stimulus, which can explain the variability seen.

19. References
1.) Giorgio, S. et al. “The lower limb flexion reflex in humans”. (2005) Progress in Neurobiology 77:
2.) Rhudy, J. & France, C. “Defining the nociceptive flexion reflex (NFR) threshold in human participants: A comparison of different scoring criteria”. (2007) Pain 128:
3.) France, C. et al. “Using normalized EMG to define the nociceptive flexion reflex (NFR) threshold: Further evaluation of standardized NFR scoring criteria”. (2009) Pain 145:
4.) Terry, E. et al. “Standardizing procedures to study sensitization of human spinal nociceptiveprocesses: Comparing parameters for temporal summation of the nociceptive flexionreflex (TS-NFR)”. (2011) International Journal of Psychophysiology 81:
5.) Micalos, P. et al. “Reliability of the nociceptive flexor reflex (RIII) threshold and association with Pain threshold”. (2009) Eur J Appl Physio 105:

20. Thank you!