Tympanic membrane temperature decreases during head up tilt: relation to frontal lobe oxygenation and middle cerebral artery mean blood flow velocity

Abstract

Introduction: Changes in blood flow influence temperature of surrounding tissues. Since the internal carotid artery (ICA) and internal jugular vein (IJV) neighbor the tympanic membrane, changes in their blood flow most likely determine changes in tympanic membrane temperature (TMT). We sought to evaluate the relationship between changes during a head-up tilt (HUT) induced reduction in cerebral blood flow (CBF) and TMT.

Methods: Ten male subjects (age 19–28 years) underwent 50° HUT until presyncope. A non-contact infrared sensor in the ear canal targeted the tympanic membrane. Changes in CBF were monitored by transcranial Doppler which determined the mean blood flow velocity in the middle cerebral artery (MCA V_mean) and by near infrared spectroscopy assessed frontal lobe oxygenation (S_cO₂), while skin blood flow (SkBF) was evaluated by laser Doppler flowmetry.

Results: During HUT, TMT decreased by 0.6 °C (median; range 0.2 to 1.6 °C) related to a decrease in MCA V_mean (51.0 ± 6.7 to 34.3 ± 5.8 cm/sec (mean ± SD); r = 0.518, p = .002) and S_cO₂ (78.6 ± 5.4% to 69.0 ± 5.7%; r = 0.352, p = .043), but not to SkBF (120 ± 78 to 69 ± 37 PU; r = 0.245, p = .142).

Conclusion: During an orthostatic challenge TMT decreases and the decrease is related to a reduction in CBF as indicated by MCA V_mean and S_cO₂, but not to SkBF. We consider TMT holds potential for non-invasive assessment of changes in cerebral perfusion.

Keywords:

• Cerebral blood flow
• ear thermometer
• internal carotid artery
• internal jugular vein
• orthostatic intolerance
• presyncope
• skin blood flow
• tympanic membrane

Acknowledgements

The authors would like to thank Professor Eva Svanborg, Professor Dan Loyd, Johan Skoog and Dr. Marcus Lindenberger for their constructive comments on the manuscript, Dr. Lonnie Petersen for her statistical help, Professor Jan Hillman for his discussions on the possible thermal relation between the tympanic membrane and the internal carotid artery and Dr. Henrik Harder for his help in developing the ear mold methodology for targeting the tympanic membrane.

Disclosure statement

The authors have no conflicts of interest to report in relation to this study.

Additional information

Funding

This study was supported by the University of Copenhagen through a private source provided by Dr. Niels V. Olsen of the Department of Neuroscience and Pharamacology.