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Temperature-dependent hysteresis in somatosensory and auditory evoked potentials
O N Markand1, C Warren, G S Mallik
1Department of Neurology, Indiana University School of Medicine, Indianapolis.
Electroencephalography and Clinical Neurophysiology
|November 1, 1990
Summary
Hypothermia during open heart surgery affects evoked potentials. Latency changes during cooling differ from warming, indicating a hysteresis effect in temperature-induced neurological responses.
Area of Science:
- Neuroscience
- Cardiovascular Surgery
- Anesthesiology
Background:
- Induced hypothermia is used during open heart surgery to reduce metabolic demand and protect organs.
- Monitoring neurological function during hypothermia is crucial for patient safety.
- Evoked potentials (EPs) like SSEPs and BAEPs are sensitive indicators of neural pathway integrity.
Purpose of the Study:
- To investigate the relationship between core body temperature and evoked potential (EP) latencies during induced hypothermia and rewarming in cardiac surgery patients.
- To determine if the temperature-latency relationship differs between cooling and rewarming phases.
- To explore the phenomenon of hysteresis in EP responses to temperature changes.
Main Methods:
- Median nerve short-latency somatosensory evoked potentials (SSEPs) and brain-stem auditory evoked potentials (BAEPs) were recorded in adult patients undergoing open heart surgery.
- Data were collected during induced hypothermia (cooling from 36°C to 19°C) and subsequent rewarming.
- Temperature-latency relationships for SSEP and BAEP components were analyzed during both cooling and warming phases.
Main Results:
- Hypothermia increased latencies of major SSEP and BAEP components; latencies normalized upon rewarming.
- The temperature-latency relationship differed significantly between cooling and warming phases, especially below 30°C.
- Hysteresis was observed, with EP latencies at a given temperature below 30°C depending on whether the temperature was reached during cooling or warming.
Conclusions:
- A distinct hysteresis effect exists in the relationship between temperature and evoked potential latencies during induced hypothermia and rewarming.
- The observed hysteresis suggests that the physiological response of neural pathways to temperature changes is not symmetrical during cooling and warming.
- These findings have implications for interpreting neurological monitoring during hypothermic procedures and highlight the importance of considering the thermal history.