Biology subjects

Labrecque, L.

Publications and source records attributed to Labrecque, L..

6 recordsLinked to original sources

bioRxiv2021

Directional sensitivity of the cerebral pressure-flow relationship in middle and posterior cerebral arteries using the repeated squat-stand model: within-day reproducibility and impact of diurnal variation in young healthy men and women

We recently employed repeated squat-stands (RSS) to quantify directional sensitivity of the cerebral-pressure flow relationship (i.e. hysteresis) using a novel metric. Within-day reproducibility and diurnal variation impacts of this metric are unknown. We evaluated this metric for: 1) within-day reproducibility and the extent diurnal variation has in middle (MCA; {Delta}MCAvT/{Delta}MAPT) and posterior cerebral arteries (PCA; {Delta}PCAvT/{Delta}MAPT); 2) sex differences. Absolute ({Delta}MCAvT/{Delta}MAPT ; {Delta}PCAvT/{Delta}MAPT) and relative (%MCAvT/%MAPT, %PCAvT/%MAPT) metrics were calculated at seven time-points (08:00-17:00) in 18 participants (8 women; 24 {+/-} 3 yrs) using the minimum-to-maximum MCAv/PCAv and MAP for each RSS at 0.05 Hz and 0.10 Hz. Reproducibility was evaluated with intraclass correlation coefficient (ICC). For all metrics, reproducibility was good (0.75-0.90) to excellent (>0.90). The metric in both arteries was impacted by MAP direction at 0.10 Hz (all p < 0.024). Time-of-day influenced {Delta}MCAvT/{Delta}MAPT (0.05 Hz: p = 0.0028; 0.10 Hz: p = 0.0009), %MCAvT/%MAPT (0.05 Hz: p = 0.035; 0.10 Hz: p = 0.0087), and {Delta}PCAvT/{Delta}MAPT (0.05 Hz: p = 0.0236). Sex differences in the MCA (p = 0.0028) vanished in relative terms and was absent in the PCA. These findings demonstrate within-day reproducibility of this metric in both arteries. Moreover, hysteresis is not impacted by sex.

physiology↗

bioRxiv2020

Utilization of the repeated squat-stand model for studying the directional behavior of the cerebral pressure-flow relationship

Hysteresis in the cerebral pressure-flow relationship describes the superior ability of the cerebrovasculature to buffer cerebral blood flow changes when mean arterial pressure (MAP) acutely increases compared to when MAP acutely decreases. This phenomenon can be evaluated by comparing the change in middle cerebral artery mean blood velocity (MCAv) per change in MAP during either acute increases or decreases in MAP induced by repeated squat-stands (RSS). However, no real baseline can be employed for this particular protocol as there is no true stable reference point. Herein, we characterized a novel metric using the greatest MAP oscillations induced by RSS without using an independent baseline value and adjusted for time intervals ({Delta}MCAvT/{Delta}MAPT). We also examined whether this metric during each RSS transition were comparable between each other over a 5-min period. {Delta}MCAvT/{Delta}MAPT was calculated using the minimum to maximum MCAv and MAP for each RSS performed at 0.05 Hz and 0.10 Hz. We compared averaged {Delta}MCAvT/{Delta}MAPT during MAP increases and decreases in 74 healthy subjects [9 women; 32 {+/-} 13 years]. {Delta}MCAvT/{Delta}MAPT was lower for MAP increases than MAP decreases at 0.10 Hz RSS only (0.91 {+/-} 0.34 vs. 1.01 {+/-} 0.44 cm{middle dot}s-1/mmHg; p = 0.0013). For both frequency and MAP direction, time during RSS had no effect on {Delta}MCAvT/{Delta}MAPT. This novel analytical method supports the use of the RSS model to evaluate the directional sensitivity of the pressure-flow relationship. These results contribute to the importance of considering the direction of MAP changes when evaluating dynamic cerebral autoregulation. News & NoteworthyRepeated squat-stand maneuvers are able to examine the directional sensitivity of the cerebral pressure-flow relationship. These maneuvers induce stable physiological cyclic changes where brain blood flow changes with blood pressure increases are buffered more than decreases. These results highlight the importance of considering directional blood pressure changes within cerebral autoregulation.

physiology↗

bioRxiv2020

Multi-metrics assessment of dynamic cerebral autoregulation in middle and posterior cerebral arteries in young fit women

Individuals with low orthostatic tolerance show greater decrease in posterior cerebral artery mean blood velocity (PCAvmean). Since young fit women often experience presyncopal symptoms, their posterior cerebral circulation may be prone to greater decreases in PCAvmean, probably explained by an attenuated dynamic cerebral autoregulation (dCA). Regional differences in dCA have never been evaluated in young fit women. We compared dCA in the middle cerebral artery (MCA) and posterior cerebral artery (PCA) in 11 young fit women (25 {+/-} 4y; [Formula]) in response to a sit-to-stand (5 min sitting followed by 5 min standing) and repeated squat-stand maneuvers performed at 0.05 Hz and 0.10 Hz. The cerebral pressure-flow relationship was characterized using four metrics: 1) percent reduction in blood velocity (BV) per percent reduction in MAP (% BV/% MAP) during initial orthostatic stress (0-15 s after sit-to-stand); 2) onset of the regulatory response (i.e. time delay before an increase in conductance (BV/MAP); 3) rate of regulation (RoR), following sit-to-stand and; 4) transfer function analysis (TFA) of forced MAP oscillations induced by repeated squat-stands. Upon standing, the relative decline in MCAvmean and PCAvmean was similar (-25 {+/-} 9 vs. -30 {+/-} 13%; p=0.29). The onset of the regulatory response (p=0.665), %{Delta}BV/%{Delta}MAP (p=0.129) and RoR (p=0.067) were not different between MCA and PCA. In regard to TFA, there was an ANOVA artery effect for gain (p<0.001) and a frequency effect for phase (p<0.001). These findings indicate the absence of regional differences in dCA in young fit women. New findingsO_ST_ABSWhat is the central question of this study?C_ST_ABSAre there regional differences in the dynamic cerebral autoregulation in young fit women? What is the main finding and its importance?The key finding of this study is that there are no differences in dynamic cerebral autoregulation between both arteries. These results indicate that dynamic cerebral autoregulation does not seem to be responsible for making the posterior cerebral circulation more vulnerable to transient reduction in blood pressure in young fit women.

physiology↗

bioRxiv2019

Dynamic cerebral autoregulation of endurance-trained men following 6 weeks of high-intensity interval training to exhaustion

Elevated cardiorespiratory fitness (CRF) is associated with reduced dynamic cerebral autoregulation (dCA), but the impact of exercise training per se on dCA remains equivocal. In addition, resting cerebral blood flow (CBF) and dCA after high-intensity interval training (HIIT) in individuals with already high CRF is unknown. We examined to what extent 6 weeks of HIIT affect resting CBF and dCA in cardiorespiratory fit men and explored if potential changes are intensity-dependent. Endurance-trained men were assigned to group HIIT85 (85% of maximal aerobic power, 1 to 7 min effort bouts, n = 8) and HIIT115 (115% of maximal aerobic power, 30 s to 1 min effort bouts, n = 9). Training sessions were completed until exhaustion 3 times/week over 6 weeks. Mean arterial pressure (MAP) and middle cerebral artery mean blood velocity (MCAvmean) were measured continuously at rest and during repeated squat-stands (0.05 and 0.10 Hz). Transfer function analysis (TFA) was used to characterize dCA on driven blood pressure oscillations during repeated squat-stands. Neither training nor intensity had an effect on resting MAP and MCAvmean (both P > 0.05). TFA phase during 0.10 Hz squat-stands decreased after HIIT irrespective of intensity (HIIT85: 0.77 {+/-} 0.22 vs. 0.67 {+/-} 0.18 radians; HIIT115: pre: 0.62 {+/-} 0.19 vs. post: 0.59 {+/-} 0.13 radians, time effect P = 0.048). These results suggest that HIIT over 6 weeks have no apparent benefits on resting CBF, but a subtle attenuation in dCA is seen posttraining irrespective of intensity training in endurance-trained men.\n\nNEW & NOTEWORTHYThe novel findings of this study are that 6 weeks of submaximal and supramaximal high-intensity interval exercise to exhaustion reduce dynamic cerebral autoregulation irrespective of training intensity in endurance-trained men. However, these HIIT protocols do not influence resting cerebral blood flow in these individuals. The results indicate the cerebrovasculature of endurance-trained men has an attenuated ability to react to large and rapid changes in blood pressure following HIIT.

physiology↗

bioRxiv2019

Cardiac remodeling after six weeks of high-intensity interval training to exhaustion in endurance-trained males

High-intensity interval training (HIIT) improves physical performance of endurance athletes, although studies examining its cardiovascular effects are sparse. We evaluated the impact of HIIT on blood pressure, heart rate and cardiac cavities size and function in endurance-trained adults. Seventeen endurance-trained males underwent 24-hour ambulatory blood pressure monitoring (ABPM) and Doppler echocardiography at baseline and after 6 weeks of HIIT. Participants were divided in 2 groups (85% maximal aerobic power (MP); HIIT85, n=8 and 115% MP; HIIT115, n = 9) in order to compare the impact of different HIIT intensities. ABPM and cardiac chambers size and function were similar between groups at baseline. HIIT reduced heart rate (55 {+/-} 8 vs. 51 {+/-} 7 bpm; p= 0.003), systolic blood pressure (SBP; 121 {+/-} 11 vs 118 {+/-} 9 mmHg; p = 0.01), mean arterial pressure (MAP; 90 {+/-} 8 vs 89 {+/-} 6 mmHg; p = 0.03) and pulse pressure (52 {+/-} 6 vs 49 {+/-} 5 mmHg; p = 0.01), irrespective of training intensity. Left atrium (LA) volumes increased after HIIT (maximal: 50 {+/-} 14 vs 54 {+/-}14 ml; p= 0.02; minimal: 15 {+/-} 5 vs 20 {+/-} 8 ml; p = 0.01) in both groups. Right ventricle (RV) global longitudinal strain lowered after training in the HIIT85 group only (20 {+/-} 4 vs. 17 {+/-} 3%, p = 0.04). In endurance-trained males, six weeks of HIIT reduce SBP and MAP and increase LA volumes irrespective of training intensity, whereas submaximal HIIT deteriorates RV systolic function.\n\nKey pointsO_LIHigh-intensity interval training improves physical performance of endurance athletes, although studies examining its cardiovascular effects are sparse.\nC_LIO_LIWe evaluated the impact of submaximal (85% maximal aerobic power) and supramaximal (115% maximal aerobic power) high-intensity interval training on ambulatory blood pressure, heart rate and cardiac cavities size and function in endurance-trained adults.\nC_LIO_LIIrrespective of training intensity, six weeks of high-intensity interval training increase left atrial volumes in endurance-trained adults, whereas the submaximal training decreases right ventricular systolic function.\nC_LIO_LIThese results may help identify the exercise threshold for potential toxicity of intense exercise training for at-risk individuals and ideal exercise training regimens conferring optimal cardiovascular protection and adapted endurance training for athletes.\nC_LI

physiology↗

bioRxiv2017

Diminished dynamic cerebral autoregulatory capacity with forced oscillations in mean arterial pressure with elevated cardiorespiratory fitness

The effect that cardiorespiratory fitness has on the dynamic cerebral autoregulatory capacity during changes in mean arterial pressure (MAP) remains equivocal. Using a multiple-metrics approach, challenging MAP across the spectrum of physiological extremes (i.e. spontaneous through forced MAP oscillations), we characterized dynamic cerebral autoregulatory capacity in 19 male endurance athletes and 8 controls via three methods: [1] onset of regulation (i.e., time delay before an increase in middle cerebral artery (MCA) conductance [MCA flow velocity (MCAv)/mean arterial pressure (MAP)] and rate of regulation, after transient hypotension induced by sit-to-stand, and transfer function analysis (TFA) of MAP and MCAv responses during [2] spontaneous and [3] forced oscillations (5-min of squat-stand maneuvers performed at 0.05 and 0.10 Hz). Reductions in MAP and mean MCAv (MCAVmean) during initial orthostatic stress (0-30 s after sit-to-stand) and the prevalence of orthostatic hypotension were also determined. Onset of regulation was delayed after sit-to-stand in athletes (3.1{+/-}1.7 vs. 1.5{+/-}1.0 s; p=0.03), but rate of regulation was not different between groups (0.24{+/-}0.05 vs. 0.21{+/-}0.09 s-1; p=0.82). While both groups had comparable TFA metrics during spontaneous oscillations, athletes had higher TFA gain during 0.10 Hz squat-stand vs. recreational controls (p=0.01). Reductions in MAP (p=0.15) and MCAVmean (p=0.11) during orthostatic stress and the prevalence of initial orthostatic hypotension (p=0.65) were comparable between groups. These results indicate an intact ability of the cerebral vasculature to react to spontaneous oscillations but an attenuated capability to counter rapid and large changes in MAP in individuals with elevated cardiorespiratory fitness.\n\nNew findingsO_ST_ABSWhat is the central question of this study?C_ST_ABSO_LIWhat is the impact of cardiorespiratory fitness on dynamic cerebral autoregulatory capacity?\nC_LI\n\nWhat is the main finding and its importance?O_LIOur results indicate an intact ability of the cerebral vasculature to react to spontaneous oscillations but an attenuated capability to counter rapid and large changes in mean arterial pressure in individuals with elevated cardiorespiratory fitness.\nC_LI

physiology↗