Autonomic Cardiovascular Control in Children and Adolescents

This thesis investigated the impact of pubertal maturation and sex on cardiovagal baroreflex sensitivity (BRS) and arterial properties of the common carotid artery (CCA), and the relationship between CCA arterial properties and BRS. This thesis also investigated the effect of orthostatic stress on arterial properties of the CCA and carotid sinus (CS), as well as their impact on BRS in response to orthostatic stress. Children and adolescents between the ages of 8-18 years were examined. To assess pubertal maturation participants were organized into five pubertal groups based on the criteria of Tanner. BRS was assessed by transfer function analysis in the low frequency range (0.05 – 0.15Hz). Pulse pressure (PP) was measured at the CCA (PPCCA) and CS (PPCS) using applanation tonometry, and at the finger (PPFinger) using photoplethysmography. Ultrasound sonography and applanation tonometry were used to determine the distensibility coefficient (DC) at the CCA (DCCCA) and CS (DCCS). A moderate posture stimulus was implemented by passively moving participants into a 50° seated-recumbent (SR) position. The results demonstrated a sex-by-maturation interaction on BRS (p= 0.019). BRS decreased from earlyto post-puberty in males (p<0.01), and remained unchanged in females. Females demonstrated greater BRS compared to males post-puberty (p<0.05). CCA distensibility was not affected by sex or maturation and was not related to BRS. PPCS was greater than PPCCA (p<0.001), while PPFinger was greater than both PPCCA (p<0.001) and PPCS (p<0.001). In response to SR, the relative change in PPFinger was significantly different than the relative change in PPCCA (p<0.001) and PPCS (p<0.001), Ph.D. Thesis – D. Chirico; Brock University – Health Biosciences iii while the relative change between PPCCA and PPCS were not different. Finally, in response to SR there was a significant decrease in DCCS (p=0.001), but not DCCCA. The relative change in BRS in response to SR was significantly correlated to the relative change in DCCS (p=0.004), but not DCCCA. The findings demonstrated an important sex-dependent maturation effect on BRS in children and adolescents that was not explained by CCA distensibility. Also, the CS and CCA responded differently to orthostatic stress. The CS was more suitable to evaluate the effect of arterial distensibility on BRS in response to posture change. Ph.D. Thesis – D. Chirico; Brock University – Health Biosciences iv Acknowledgements There is not one great accomplishment, worth achieving, that can be accomplished alone. The work presented in this thesis is a culmination of the hard work, support, encouragement, and guidance of many. I would like to take this opportunity to thank all of those who were instrumental in the successful completion of this thesis. First, I would like to thank my advisor, Dr. Deborah O’Leary, for this tremendous opportunity. The completion of this thesis would not be possible without your guidance and support. You have shown great trust in me, inspired and motivated me to be my best, and have provided me with the knowledge and skills to be successful in the future. After working with you for close to 6 years I have witnessed how passionate you are about your students, how much you care about their success, and what it takes to be a great mentor. Thank you for everything! I would also like to sincerely thank my committee members Drs Nota Klentrou, Jian Liu, and Kevin Shoemaker. You have all provided me with the guidance, support, and insight necessary to continue on and complete this thesis. I have learned a great deal from you, and your contributions to this project are invaluable. I appreciate all of the time and effort you have put in to assisting me, and I have been able to take unique research values from each of you and make them into my own. I am grateful for all of your support. I would like to thank my labmates, both past and present (Nicole P, Stephen, Austin, Kylie, Kathryn, Chelsea, and Samantha). You guys were always there to listen, help, and most important of all, entertain me. I truly enjoyed every minute we spent together in the dungeon. I would like to give a special thanks to Steve and Nicole; you both were instrumental to the completion of this project. You made the long hours working in the lab, and the late Friday night and early Saturday morning testing sessions much more enjoyable. I know you will both go on to be successful in your future endeavors. I also want to thank my family for their continuous support throughout my academic career. I am fortunate to have amazing parents who have taught me the value of hard work and dedication, and have always believed in me and given me every opportunity to be successful. Words cannot describe what you’ve done for me. Hopefully one day you’ll understand what it is I’m actually doing. To my brothers, if I didn’t have you to keep up with, I don’t know that I would’ve been able to overachieve and complete this. Thank you for your encouragement throughout. The journey to completing a PhD is not a flat road, but an uphill battle. It takes the support of those who believe in you to carry you through. I was fortunate enough to have someone believe in me and see my true potential, even when I couldn’t see it myself, and without whom, completing this would not be possible. You have done more for me than you could ever know and for that, I am truly grateful. Ph.D. Thesis – D. Chirico; Brock University – Health Biosciences ii Table of