IOM Exam Results

Check you out! Looks like you’ve been hitting the books and taking this test seriously. Job well done.

Let’s go over the questions to see if there’s anything you missed…

The chemical transmitter that mediates between sympathetic preganglionic fibers and the end organ is:

a. norepinephrine

b. acetylcholine

c. adrenaline

d. epinephrine

In the autonomic nervous system, acetylcholine (ACh) is the neurotransmitter in both the preganglionic sympathetic and parasympathetic neurons. The parasympathetic postganglionic fibers also release Ach, but most of the sympathetic postganglionic fibers release noradrenaline (and are called adrenergic).  

ACh is also the neurotransmitter at the adrenal medulla and serves as the neurotransmitter at all the parasympathetic innervated organs. ACh is also the neurotransmitter at the sweat glands, and at the piloerector muscle of the sympathetic ANS.

 Norepinephrine and epinephrine–also known as noradrenalin and adrenaline–are chemical hormones located in the adrenal glands. Norepinephrine and epinephrine are chemicals that dictate metabolic responses within the body, such as oxygen release in muscles, blood vessel dilation and constriction and raising blood pressure. These processes are activated when the body needs to respond to emergency situations and then recover from them. The two chemical processes complement each other and have only slight differences.

There is a greater amount of somatotopical representation in the motor cortex for the:

a. arm

b. legs

c. erector spinae

d. fingers

You have to look at the Homunculus, based on Penfield’s classic diagram. The hands, lips, and feet have the largest representation, along with the genitals that have a large sensory distribution. If you’re trying to pick a penny off the floor, you need to use a larger area of brain (fine motor skills). If touch is important part of that area, then it will have a larger sensory distribution (palpation and sex).

Which of the following is most closely associated with language comprehension?

a. agnosia

b. Broca’s area

c. Wernicke’s area

d. arcuate fasciculus

Agnosia is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss. It is usually associated with brain injury or neurological illness, particularly after damage to the occipitotemporal border, which is part of the ventral stream. Agnosia only affects a single modality for example vision or hearing may be affected.

Wernicke’s is traditionally considered to consist of the posterior section of the superior temporal gyrus in the dominant cerebral hemisphere (which is the left hemisphere in about 97% of people). It’s also called receptive aphasia and deals with language comprehension. Broca’s area is over the motor area, and deals with a loss of language expression. Expressive aphasia (non-fluent aphasia), is characterized by the loss of the ability to produce language (spoken or written) The arcuate fasciculus are the fibers that connect Wernicke’s and Broca’s areas. Damage to this pathway can cause a form of aphasia known as conduction aphasia, where auditory comprehension and speech articulation are preserved, but people find it difficult to repeat heard speech.

D-wave amplitudess are representative of what?

a. The relative amount of functioning fast-conducting fibers of the CST

b. Functional integrity of the spinal cord’s gray matter

c. Functional integrity of the cord’s lateral distribution of tracts, namely the spinocerebellar tract

d. Same information as motor evoked potentials

D-waves do not monitor the functional integrity of the gray matter of the cord, but rather the white matter (the tracts) of the spinal cord. Motor evoked potentials are far more sensitive to changes in gray matter (anterior horn cells).

Why would you want to include the bulbocavernouse reflex in your multi-modality monitoring of lumbar cases with cuada equina syndrome?

a. This oligosynaptic reflex allows us to assess the functional integrity of both the afferent and efferent fibers of the pudendal nerve along with the reflex center located in the gray matter at S2-4.

b. Large space occupying lesions, causing cauda equina syndrome, can ablate the pudendal nerves.

c. You wouldn’t, seeing as the cauda equina only serves to attach the spinal cord to the first segment of coccyx.

d. You wouldn’t, seeing as the bulbocavernouse reflex only assesses the sensory portion, making it redundant with SSEPs.

In these cases, neurological damage can occur at the cord itself (upper motor neuron lesion) or the nerve roots as they exit at the cauda equina (lower motor neuron lesions). The lower nerve roots are more medial, while the higher roots are more lateral. The pudendal nerve is innervated by the S2-4 roots, which is very midline. Having information about both sensory and motor roots and the gray matter of the cord allows us to pick up changes that are either CNS or PNS. This would be a great complement to other modalities we might run (SSEP, EMG, MEP, bladder monitoring, etc.)

And it’s the filum terminale that connects the cord to the coccyx. Don’t mix it up with the cauda equina, because they might try to trick you like I just did.

Most lesions ablating the pudendal nerve are not going to be able to the spinal cord at the cauda equina. Possible, I guess, but not likely.

What is the typical threshold for the recurrent laryngeal nerve on stimulation, and what is the typical max response stimulated at?

a. 1.0mA, 3.0mA

b. 0.05mA, 0.1mA

c. 6mA, 10mA

d. 0.4mA, 0.8mA

This come out of the ASNM meetings. It might not be set in stone, but it should be in that ballpark. Good to know for the test, and if you’re doing these cases.

What is the frequency of EMG activity that is a cause of concern?

a. <20 Hz

b. >20 Hz

c. >60 Hz

d. >120 Hz

EMG activity that has a lower frequency than 60Hz have been pretty benign. That number suits me just fine,  since it’s the same as the frequency of the noise common in the USA. Nothing to do with each other, but easier to remember.

What does cerebral oximetry measure?

a. oxygenation of venous blood in the brain.

b  oxygenation of arterial blood in the brain.

c. blood flow velocity

d. blood flow volume

TDC measures blood flow velocity, Xe/CT CBF is a measure of blood flow and cerebral oximetry doesn’t do anything with the arteries, just the veins. It’s looking at pooled blood in the veins. There’s probably at least 1 question in there that deals with what measures what.

In BAERs, conductive losses affect all the following except:

a. amplitudes

b. interpeak latencies

c. amplitudes and interpeak latencies

d. none of the above

Conductive hearing loss occurs when there is a problem conducting sound waves anywhere along the route through the outer ear,tympanic membrane (eardrum), or middle ear (ossicles). This type of hearing loss may occur in conjunction with sensorineural hearing loss or alone. When you think of a conduction loss, think of some sort of blockage, usually fluid.

Have you ever done a crani case and seen how much betadine can get in that ear hole? That’s why you should tape over the ear, to keep all that out. So this blockage can cause a hearing loss past the point of its blockage, but it won’t cause any neurological damage. Increases in interpeak intervals is a definite warning sign, since it correlates with neurological problems, not a blockage problem.

What is the class, the speed and the name of the receptors when we stimulate the light touch receptors?

a. A-alpha cutaneous and Alpha motor neurons, 20-50m/s, Pacinian corpuscle or touch receptors

b. A-alpha cutaneous and Alpha motor neurons, 70-120m/s, Pacinian corpuscle or touch receptors

c. A-delta cutaneous, 70-120m/s, Pacinian corpuscle or touch receptors

b. A-alpha cutaneous and Alpha motor neurons, 70-120m/s, Meissner corpuscle

It’s just memorizing the different receptors, the motor neurons, the speed of conductions, etc.  http://books.google.com/books?id=rum-MTlA1cAC&pg=PA69&dq=A-alpha+cutaneous&hl=en&sa=X&ei=XbcaUYKqK4nq9ATNu4G4AQ&ved=0CC0Q6AEwAA#v=onepage&q=A-alpha%20cutaneous&f=false

What are significant changes in VEP?

a. all-or-none amplitude loss

b. 50% change in amplitude

c. latency shift of 40-50 msec

d. both b and c

The early phase of the P1 component with a peak around 95-110 msec, is likely generated in dorsal extra striate cortex of the middle occipital gyrus.  The later negative component N2 (N150) is generated from several areas including a deep source in the parietal lobe (DiRusso et al., 2002). This “P100″ or P1 in the jargon of evoked potentials, is very reliable between individuals and stable from about age 5 years to 60 years (except while under anesthesia). The mean peak latency of the “PI00″ only slows about one millisecond per decade from 5 years old until 60 years old. However, the variability of the flash on the retina can have changes seen in the P100 recordings.   Even with the alarm criteria as stated above (which is probably the correct answer if asked in a multiple choice test), the only reliable criteria for abnormality is complete absence of the recordings from monocular vision.

What is a sampling rate?

a. the number of samples contained in a 1 second of data and indicates how often the samples are collected.

b. process of converting the amplitude of an analog signal into a series of numbers, known as samples.

c. repeated presentation of a stimulus, recording an addition of each response to the preceding ones, divide the sum by the total number of responses.

d. a factor equal to the square root of the number of trials used to average.

That’s just memorizing what the definition of sampling rate, which you should. But also know why we need to know that definition. It has to do with avoiding aliasing.  

The Nyquist–Shannon sampling theorem states that perfect reconstruction of a signal is possible when the sampling frequency is greater than twice the maximum frequency of the signal being sampled, or equivalently, when the Nyquist frequency (half the sample rate) exceeds the highest frequency of the signal being sampled. If lower sampling rates are used, the original signal’s information may not be completely recoverable from the sampled signal. For example, if a signal has an upper band limit of 100 Hz, a sampling frequency greater than 200 Hz will avoid aliasing and would theoretically allow perfect reconstruction.

How do you find the common mode rejection ratio?

a. = (differential gain) / (common mode gain)

b. = (common mode gain) X (differential gain)

c. = (common mode gain) / (differential gain)

d. = (differential gain) + (common mode gain)

It’s important in reducing noise. The common-mode rejection ratio (CMRR) of a differential amplifier (or other device) is the tendency of the device to reject the input signals common to both input leads. A high CMRR is important in applications where the signal of interest is represented by a small voltage fluctuation superimposed on a (possibly large) voltage offset, or when relevant information is contained in the voltage difference between two signals.

What is Coulomb’s Law?

a. opposites attract and same repels.

b. it has to do with the polarity of the nucleus of a cell and the orbiting electrons that revolve around it in the atom.  The further away the electron ring from the nucleus, the weaker the bond.

c. both are true

d. both are false

Coulomb’s inverse-square law is a law of physics describing the electrostatic interaction between electrically charged particles. The force of attraction or repulsion between two point charges is directly proportional to the product of magnitude of each charge and inversely proportional to the square of distance between them.

What impedance rate demonstrates good electrode placement?

a. <1 Ohms

b. <1 Kilohm

c. <5 Ohms

d. <5 Kilohms

I mainly use a Cadwell or Axon, and both of them use 10 Kilohms as their cutoff. Those could easily be the answer on a test. But none of the other one’s make sense, so 5 Kilohms wins out here. Make sure you know how many kilohms in 1 ohm (0.001), how many ohms in 1 megaohm (1,000,000), and so on. 

What is the most common cause of 60 cycle noise?

a. bair huggers

b. unequal electrode impedance

c. power outlet in the UK

d. surgical table

There are many things in the OR than can cause electrical noise, but it asked for the most common cause. Also, remember the US uses 60 Hz, 120V, and most of the world uses 50Hz, 210-240V.

How many unique voltage values does 8 bit allow?

a. 256

b. 64

c. 80

d. 960

This is a math one, sort of. You have to know the difference b/t a bit and a byte.  A bit is the smallest possible piece of information.  If you have heard someone say that “everything in the computer is all one’s and zero’s,” they are actually referring to bits.  A bit can have only two possible states: 1 or 0. Although a single bit can have only one of two possible values, by gathering groups of bits together, we can make much more complicated information. 

There turns out to be a simple way of calculating this:
1 bit  –>   2^1 = 2  different possible values
2 bits –>  2^2  (2×2) = 4  different possible values
3 bits –>  2^3   (2x2x2) = 8  different possible values 

A byte is simply a group of 8 bits.  How many different possible values  can a byte have? If it’s 8 bit, you do 2^8, or 2 to the 8^th power, or 2X2X2X2X2X2X2X2 = 256 possible values.

Confused? Let me say it another way.  All bytes are composed of 8 bits, and each bit is either a 0 or a 1. If you only have 2 bits, you do not have a byte (which is 8 bits), but you do have 4 different possible values (2^2=4).

Chances are they’ll ask about the 8 bits = 256 possible values, but it’s better if you understand the whole thing.

Ketamine is a ____________ and can affect cortical SSEP amplitudes (increase them), but have little effects on __________and ___________ amplitudes.

a. analgesic, subcortical, MEPs

b. analgesic, EEGs, MEPs

c opiate, BAER, MEPs

d. opiate, subcortical, MEPs

Ketamine and etomidate will increase your SSEP cortical waveforms. That’s always something they ask. For all meds, make sure you know a little bit more about the mechanism of action, why they are clinically used, how they affect our modalities, etc.

The artery of Adamkiewicz arises at _______ in the majority of the population after branching off of _______?

a. T4-7, off the anterior spinal artery

b. T9-12, off the posterior spinal artery

c. T4-7, off the posterior spinal artery

d. T9-12, off the anterior spinal artery

A pure memorization question, but one that a lot of national boards like to ask. It’s pertinent information to know with scoli patient’s that have a rigid curve. They will some time do an anterior approach, and MEPs can be of great help.

What do EEGs record?

a. It is a graphic display of a difference in voltages from two sites of brain function recorded over time

b. Electrical activity of cortical and deep brain structures

c. Using Ohm’s law, it’s the difference in currents between electrodes over cortical structures

d. Depth of anesthesia

Remember that EEGs are not very sensitive at recording deep brain structures. That’s why SSEPs are a nice complement to EEGs when monitoring carotid endarterectomies.  EEG uses voltages, not current. Just think about your screen when running EEGs. It’s measure using volts, not amperes. Don’t let something like that trip you up. As for depth of anesthesia, one could argue that EEGs can help determine the depth of anesthesia (although I challenge you to find research that shows evidence to its clinical accuracy). However, that’s something that it can record, not what it does record. Read the questions carefully and pick the best answer.

If you like what you’ve seen on this quiz, there’s plenty more where that came from. Check out my Pass The CNIM and Pass The DABNM for more information.