Δευτέρα 12 Σεπτεμβρίου 2016

Quantifying cerebrovascular reactivity in anterior and posterior cerebral circulations during voluntary breath holding

The central respiratory chemoreflex contributes to blood gas homeostasis, particularly in response to accumulation of brainstem CO2. Cerebrovascular reactivity (CVR) affects chemoreceptor stimulation inversely through CO2 washout from brainstem tissue. Voluntary breath-holding imposes alterations in blood gases, eliciting respiratory chemoreflexes, potentially contributing to breath-hold duration (i.e., break-point). However, the effects of cerebrovascular reactivity on break-point have yet to be determined. We tested the hypothesis that the magnitude of CVR contributes directly to BHD in 23 healthy human participants. We developed and validated a cerebrovascular stimulus index methodology (SI; PETCO2/PETO2) to quantify CVR by correlating measured and interpolated values of PETCO2 (r = 0.95, P < 0.0001), PETO2 (r = 0.98, P < 0.0001), and SI (r = 0.94, P < 0.0001) during rebreathing. Using transcranial Doppler ultrasound, we then quantified the CVR of the middle (MCAv) and posterior (PCAv) cerebral arteries by plotting cerebral blood velocity against interpolated SI during a maximal end-inspiratory breath-hold. The MCAv CVR magnitude was larger than PCAv (P = 0.001; +70%) during breath-holding. We then correlated MCAv and PCAv CVR with the physiological (involuntary diaphragmatic contractions) and psychological (end-point) break-point, within-individuals. There were significant inverse but modest relationships between both MCAv and PCAv CVR and both physiological and psychological break-points (r[LEFTWARDS ARROW]0.53, P < 0.03). However, these relationships were absent when MCAv and PCAv cerebrovascular conductance reactivity was correlated with both physiological and psychological break-points (r > –0.42; P > 0.06). Although central chemoreceptor activation is likely contributing to break-point, our data suggests that CVR-mediated CO2 washout from central chemoreceptors plays no role in determining break-point, likely due to a reduced arterial-tissue CO2 gradient during breath-holding. (250 words)

This article is protected by copyright. All rights reserved



from Physiology via xlomafota13 on Inoreader http://ift.tt/2c3EeWf
via IFTTT

Δεν υπάρχουν σχόλια:

Δημοσίευση σχολίου

Σημείωση: Μόνο ένα μέλος αυτού του ιστολογίου μπορεί να αναρτήσει σχόλιο.