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

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 Vmean) and by near infrared spectroscopy assessed frontal lobe oxygenation (ScO2), 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 Vmean (51.0 ± 6.7 to 34.3 ± 5.8 cm/sec (mean ± SD); r = 0.518, p = .002) and ScO2 (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 Vmean and ScO2, but not to SkBF. We consider TMT holds potential for non-invasive assessment of changes in cerebral perfusion.

Effect of postural changes on cardiovascular parameters across gender.

INTRODUCTION: We investigated the effect of postural changes on various cardiovascular parameters across gender. Twenty-eight healthy subjects (16 male, 12 female) were observed at rest (supine) and subjected to 3 interventions; head-down tilt (HDT), HDT with lower body negative pressure (HDT+ LBNP at -30 mm Hg), and head-up tilt (HUT), each for 10 minutes separated by a 10 minutes recovery period. METHODS: Measurements were recorded for heart rate (HR), standard deviation of the normal-to-normal intervals, root mean square of successive differences between the normal-to-normal intervals, heart rate variability-low frequency (LFRRI), heart rate variability-high frequency (HFRRI), low frequency/high frequency ratio (LFRRI/HFRRI), systolic blood pressure (SBP), mean arterial pressure (MAP), diastolic blood pressure (DBP), total peripheral resistance index (TPRI), stroke index (SI), cardiac index (CI), index of contractility (IC), left ventricular work index, and left ventricular ejection time. RESULTS: Across all cardiovascular parameters, there was a significant main effect of the intervention applied but there was no significant main effect of gender across all parameters. CONCLUSIONS: The results suggest that there are no specific gender differences in regards to the measured variables under the conditions of this study. Furthermore, these results suggest that in healthy subjects, there appears to be evidence that LBNP partially elicits similar cardiovascular responses to HUT, which supports the use of LBNP as an intervention to counteract the effects of central hypovolemia.