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

Abstract

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 eight controls via three methods: (1) onset of regulation (i.e., time delay before an increase in middle cerebral artery (MCA) conductance [MCA blood velocity (MCAv)/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 (MCAV mean) during initial orthostatic stress (0‐30 sec 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 sec; P = 0.03), but rate of regulation was not different between groups (0.24 ± 0.05 vs. 0.21 ± 0.09 sec−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 versus recreational controls (P = 0.01). Reductions in MAP (P = 0.15) and MCAV mean (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.

Implications of habitual endurance and resistance exercise for dynamic cerebral autoregulation

“…() found no change in rate of regulation in the upright position – functionally significant given the threat orthostasis presents to the cerebral circulation. While comparing studies that used differential analyses is difficult (Tzeng et al., ), we have shown increased TFA‐derived gain during 0.10 Hz MAP oscillations in endurance athletes, utilizing the same technique employed in the current study (Labrecque et al., ). Notably, Labrecque et al.…”

“…Notably, Labrecque et al. () found no differences in TFA‐derived metrics during spontaneous fluctuations or the rate of regulation in response to a sit‐to‐stand manoeuvre. The reason for these differences between the current findings and those of Labrecque et al.…”

“…Our finding of no difference in dCA between endurance and sedentary is consistent with results from others using repeated sit–stand manoeuvres (Aengevaeren et al., ) and bilateral thigh cuff release in the upright position (Ichikawa et al., ). However, some authors have reported an increased gain and normalized gain during forced oscillations in MAP produced by repeated squat–stand manoeuvres (Labrecque et al., ) and bilateral thigh cuff release, respectively (Lind‐Holst et al., ) – indicative of a reduced damping ability of the cerebral circulation. Whilst the reason for these disparate data is not clear, the method of perturbing blood pressure and subsequent analysis may be partially responsible and is discussed below.…”

“…The participant then stood for 1 min and then commenced the first bout of squat–stands. This method has been used previously to provide rhythmic and forced oscillations in MAP for the assessment of dCA (Claassen, Levine, & Zhang, , Labrecque et al., ). Oscillations of 0.05 Hz (20 s cycle: 10 s squat, 10 s standing) and 0.10 Hz (10 s cycle: 5 s squat, 5 s standing) were timed by metronome.…”

“…Notably, in the same study they reported that the rate of regulation was actually reduced in endurance‐trained individuals in the supine position. During forced oscillations in arterial blood pressure, induced by repeated squat–stand manoeuvres, it was found young male endurance athletes demonstrated an increased gain compared to sedentary individuals (Labrecque et al., ). However, no change was observed in masters athletes compared with age‐matched sedentary individuals (Aengevaeren, Claassen, Levine, & Zhang, ) using the same squat–stand technique.…”