Variable-Frequency Nerve Stimulation for Accurate Threshold Detection
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Solution Overview
Problem
Existing intraoperative monitoring systems for nerve-muscle response during surgeries face inaccuracies due to muscular blockade, variability in muscle unit responses, and false positives from transient noise disturbances, leading to unreliable stimulation threshold determination.
Innovation Solution
A method and system for determining nerve stimulation thresholds using graded electrical stimulation, incrementally adjusting current levels and frequencies to ensure accurate and repeatable muscular responses, utilizing EMG and MMG sensors to detect threshold levels and display them on a user interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency stimulation (10-20 Hz) is used to condition the neuro-muscular junction, then response accuracy in the presence of partial muscular blockade is improved, but muscular tetany occurs which confounds results
Solution Approach 1:
The patent applies dynamics by varying the stimulation frequency over time rather than using a fixed frequency. The system starts with higher frequencies (10-20 Hz) to condition the neuro-muscular junction and improve response accuracy, then transitions to lower frequencies (1-5 Hz) to avoid muscular tetany. This dynamic adjustment allows the system to benefit from both high-frequency conditioning and low-frequency safety.
Solution Approach 2:
The patent implements periodic action by using a train of stimulation pulses with specific inter-pulse intervals. Multiple pulses are delivered in sequence at controlled frequencies, allowing the neuro-muscular junction to be conditioned through repeated stimulation while maintaining sufficient recovery time between pulses to prevent sustained muscle contraction and tetany.
2Productivity
If stimulation intensity is increased dramatically to quickly find threshold (bisecting algorithm), then speed of threshold finding is improved, but adequate conditioning for accurate response is not provided
Solution Approach 1:
The patent applies segmentation by dividing the threshold-finding process into multiple phases: an initial screening phase using higher intensity increments to quickly identify the approximate threshold region, followed by a refinement phase using smaller intensity steps and lower frequencies to accurately determine the precise threshold. This segmented approach balances speed and accuracy.
Solution Approach 2:
The patent implements preliminary action by delivering a train of conditioning pulses at higher frequencies before attempting to elicit a threshold response. This preliminary conditioning ensures the neuro-muscular junction is properly prepared to respond accurately to subsequent threshold-testing stimuli, even when those stimuli are delivered at lower frequencies for safety.
3Object-affected harmful factors
If low frequency stimulation (1-5 Hz) is used to avoid tetany, then safety is improved, but adequate conditioning of the neuro-muscular junction is not provided
Solution Approach 1:
The patent maintains continuity of useful action by delivering multiple pulses in a train rather than single isolated pulses. Even though the overall frequency is kept low (1-5 Hz) to avoid tetany, the continuous delivery of pulses within each train provides sufficient conditioning of the neuro-muscular junction to ensure accurate threshold responses, bridging the gap between safety and effectiveness.
4Productivity
If stimulation threshold is approached from higher intensities, then speed is improved, but variability in PCMAP response increases leading to inaccurate thresholds
Solution Approach 1:
The patent applies feedback by continuously monitoring the muscular response (PCMAP) to each stimulation pulse and using this information to adjust subsequent stimulation parameters. When approaching the threshold from higher intensities, the system detects the point at which muscle activation begins and adjusts the stimulation protocol accordingly, reducing variability and improving accuracy through real-time response-based adjustments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Provides rapid and accurate detection of nerve proximity and health by minimizing false positives and accounting for muscular blockade, ensuring precise nerve localization during surgeries.
Implementation Method 1
stimulation pulses delivered at a frequency sufficient to depolarize a nerve
Implementation Method 2
resulting in activation of one or more muscles
Data Source
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AI summary
A method for determining a stimulation threshold current level to avoid tetany associated with one or more muscles. The method comprises stimulating tissue of a patient as a sequence of pulses delivered at a current level and a frequency, the stimulating including increasing the current level of each pulse in the sequence of pulses from an immediately preceding pulse by a first current increment. The method comprises determining that a first evocation pulse from the sequence of pulses evokes a first muscular response, the first evocation pulse reaching predetermined criteria. The method comprises stimulating the tissue with a second evocation pulse from the sequence of pulses to evoke a second muscular response, the stimulating comprising: decreasing the frequency of the delivery of each pulse in the sequence of pulses; and, increasing the current level of one or more pulses in the sequence of pulses from the immediately preceding pulse by a second current increment. The method comprises determining that the second evocation pulse from the sequence of pulses evokes the second muscular response.