title: Relationship between blood pressure and cerebral blood flow during supine cycling: influence of aging.
abstract: The cerebral pressure-flow relationship can be quantified as a high-pass filter, where slow oscillations are buffered (<0.20 Hz) and faster oscillations are passed through relatively unimpeded. During moderate intensity exercise, previous studies have reported paradoxical transfer function analysis (TFA) findings (altered phase or intact gain). This study aimed to determine whether these previous findings accurately represent this relationship. Both younger (20-30 yr; n = 10) and older (62-72 yr; n = 9) adults were examined. To enhance the signal-to-noise ratio, large oscillations in blood pressure (via oscillatory lower body negative pressure; OLBNP) were induced during steady-state moderate intensity supine exercise (∼45-50% of heart rate reserve). Beat-to-beat blood pressure, cerebral blood velocity, and end-tidal Pco2 were monitored. Very low frequency (0.02-0.07 Hz) and low frequency (0.07-0.20 Hz) range spontaneous data were quantified. Driven OLBNP point estimates were sampled at 0.05 and 0.10 Hz. The OLBNP maneuvers augmented coherence to >0.97 at 0.05 Hz and >0.98 at 0.10 Hz in both age groups. The OLBNP protocol conclusively revealed the cerebrovascular system functions as a high-pass filter during exercise throughout aging. It was also discovered that the older adults had elevations (+71%) in normalized gain (+0.46 ± 0.36%/%: 0.05 Hz) and reductions (-34%) in phase (-0.24 ± 0.22 radian: 0.10 Hz). There were also age-related phase differences between resting and exercise conditions. It is speculated that these age-related changes in the TFA metrics are mediated by alterations in vasoactive factors, sympathetic tone, or the mechanical buffering of the compliance vessels.
authors.affiliation: Centre for Heart, Lung and Vascular Health; School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Canada; jonathan.smirl@ubc.ca.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Smirl
authors.affiliation: Centre for Heart, Lung and Vascular Health; School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Canada;
authors.forename: Keegan
authors.initials: K
authors.lastname: Hoffman
authors.affiliation: Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, Wellington, New Zealand.
authors.forename: Yu-Chieh
authors.initials: YC
authors.lastname: Tzeng
authors.affiliation: Centre for Heart, Lung and Vascular Health; School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Canada;
authors.forename: Alex
authors.initials: A
authors.lastname: Hansen
authors.affiliation: Centre for Heart, Lung and Vascular Health; School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Canada;
authors.forename: Philip N
authors.initials: PN
authors.lastname: Ainslie
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001642:Bicycling / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D001795:Blood Pressure Determination / Q000379:methods; D001921:Brain / Q000098:blood supply; D002560:Cerebrovascular Circulation / Q000502:physiology*; D015444:Exercise / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure / Q000379:methods; D008297:Male; D020768:Middle Cerebral Artery / Q000502:physiology; D059629:Signal-To-Noise Ratio; D055815:Young Adult
keywords: aging; blood pressure; exercise; oscillatory lower body negative pressure; transfer function analysis