Hemodynamic Changes in the Prefrontal Cortex during Functional Activation in Essential Hypertension Measured by Near Infrared Spectroscopy

• Author / Creator

  Grant, Hercules

• Chronic hypertension induces microvascular changes in the prefrontal cortex (PFC) which could influence oxygenation status. However, hypertension-related changes in oxygenation in the PFC and cognition, especially during functional stresses, remain poorly investigated. This project consisted of three separate studies, evaluating and comparing normotensive and stage 1 hypertensive males (19 – 56 yrs.) for: (1) the reliability of the hemodynamic responses, namely, oxyhemoglobin (O2Hb), deoxyhemoglobin (HHb), total hemoglobin (tHb) and hemoglobin difference (HbDiff) at the PFC during postural change and carbon dioxide (CO2) rebreathing, (2) cognitive performance (digit span and auditory consonant trigrams - CCC) at rest, and (3) cognitive performance (modified Stroop task) at rest and during cycling at 50 Watts and up to 75%HRmax. Functional near infrared spectroscopy (fNIRS) was used to measure the bilateral PFC hemodynamic responses in real-time during these interventions. Delta values (peak minus baseline or peak minus control) were calculated for each hemodynamic variable and subjected to appropriate analysis to test the study hypotheses.
  Moderate to high reliability coefficients were observed for all hemodynamic and CO2 reactivity responses with intraclass correlation coefficients (ICCs) for O2Hb and tHb ranging between 0.67 and 0.901 (normotensive, N=25), and 0.61 and 0.823 (hypertensive, N=15). No significant difference was noted in CO2 reactivity with postural change between the groups after matching for age level. Significant impairment in digit span and CCC performance was observed in the hypertensives (P=0.027) after age matching 15 participants for each group. Both groups demonstrated similar trends in the acute hemodynamic responses during the digit span and CCC tests. However the delta values were not significantly different between the two groups. Significant correlations were observed between digit span performance and delta values of O2Hb as well as tHb, only in the hypertensive group in both the right and left PFC. During the cycling tests, no significant differences were observed in modified Stroop test performance on any of the hemodynamic responses, except tHb, which was higher in the normotensive group. Significant positive correlations were observed for the hypertensives in Stroop performance scores and O2Hb and HbDiff changes at rest only. The conflicting findings in the hypertensive group could be due to the wide age range of participants and the period of hypertension which could influence microvascularity at the PFC. The evidence suggests a less than straightforward relationship between cognition and performance in hypertension and provides new perspectives that can be used in structuring rehabilitation programs for this clinical population.

• Subjects / Keywords

  • Near Infrared Spectroscopy
  • Hypertension
  • Oxygenation
  • Prefrontal Cortex

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3T370

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.