CNIM Practice Question Set - Expert-Verified Solutions

CNIM Practice Question Set - Expert-Verified Solutions What time constant would be the most effective for cutting out low frequency noise from your SSEP cortical responses? - answer - Answer: 10 mS SSEP cortical responses are in the typical frequency range of 100-200 Hz. That being said, let's see what time constant would give us a good Low Frequency Filter. Remember LFF filters out everything below the cut off frequency and passes higher frequencies. Formula to know: Cut off Frequency = 1 / Time Constant (tc) 1/.01 s = 100 Hz 10 ms = .01 s This answer would filter out everything below 100 Hz so it would eliminate all the frequencies lower than 100 Hz and pass desired response and all higher frequencies. In order to achieve asynchronous stimulation you need to: - answer - delay the second stimulator, so the stim goes "left, right, left, right" What is the active electrode for recording popliteal fossa sciatic nerve response after PTN stimulation at the ankle? - answer - PF distal: appropriate montage for recording pop fossa response is Pf (distal) - Pf (proximal). The distal electrode is placed directly behind the knee in the leg crease, and the proximal electrode is placed 2-4 cm proximal. The response recorded is the N9 propagated afferent volley A negative electrical field is recorded by the negative input of the amplifier channel, while a reference electrode in the positive input records no activity of interest. What is true about the output? - answer - An upward deflection represents a negative polarity waveform. By convention, activity of interest is applied to the negative input of the amplifier. At a distinct moment in time, the differential amplifier subtracts the negative input from the positive input, yielding the "difference" between the two inputs. If the output is a positive number, the waveform will point upward, and this upward deflection represents the fact that the information input was MORE NEGATIVE than the information in the positive input. Requirements for classifying SSEP data as "replicating" and therefore monitorable prior to surgical manipulation - answer - Replicating amplitude within 15% Minimum of 2 trials (300-500 averages each) per limb Replicating morphology of the waveform Replicating latency within 1% Appropriate SSEP replication criteria - answer - 1% latency, 15% amplitude Which contact lies on the precentral gyrus? - answer - 4 precentral gyrus = motor cortex How can the polarity of waveform B be described? - answer - Negative in the referential channel, cancelled in the bipolar channel First look at the montage to determine the obligate waveform of interest. B is the N34 waveform. We know this because it is recorded by a scalp electrode that is referenced to a non-cephalic electrode. Since the generator of the N34 is the brainstem, we know that a scalp-scalp (bipolar) channel will cancel the waveform. Most common complication of TcMEPs - answer - tongue lacerations If you run a TcMEP with the anode at C4 and the cathode at C3 - answer - the left AH response should be larger remember: unlike other modalities, the action potentials fire under the anode (+) for TcMEPs. The TcMEP pathway decussates in the medulla (around 85-90% of fibers cross over before descending down the corticospinal tract). Ipsilateral muscles (same side as anode) will likely record small CMAPs (or absent but not necessarily). Contralateral responses should be larger. During resection of an intracranial tumor that is located in midline and near the central sulcus, which of the following will be the most beneficial modality? - answer - PTN SSEPs Phase reversal is of course beneficial when working near the central sulcus. However, most sources indicate that phase reversal SSEPs are only most effectively performed following upper limb stimulation, not PTN stimulation. Therefore, PTN SSEPs will be the more critical modality. Following TcMEP stimulation at C1-C2, you successfully elicit responses fro