Influence of sex on the reliability of cerebral blood velocity regulation during lower body negative pressure and supine cycling with considerations of the menstrual cycle

To examine the feasibility, utility and safety of superimposed lower body negative pressure (LBNP) and tilt during supine cycling in individuals suffering from persisting post‐concussive symptoms (PPCS). Eleven individuals aged 17–31 (6 females/5 males) participated in two randomized separate visits, 1 week apart. A ramp‐incremental test was performed during both visits until volitional failure. Visits included no pressure (control) or LBNP at −40 Torr (experimental) with head‐up tilt at 15 degrees (females) or 30 degrees (males). Transcranial Doppler ultrasound was utilized to quantify middle cerebral artery velocity (MCAv), while symptom reports were filled out before and 0, 10, and 60 min post‐exertion. Ratings of exertion and overall condition followed similar trends for participants across both tests. The relative increase in MCAv was blunted during the experimental condition (8%) compared to control (24%), while a greater heart rate (17 beats/min) was achieved during the LBNP condition (P = 0.047). Symptom severity at the 0 and 10 min post‐exertion time points displayed negligible‐to‐small effect sizes between conditions (Wilcoxon's r < 0.11). Symptom reporting was lower at the 60 min post‐exertion time point with these displaying a moderate effect size (Wilcoxon's r = 0.31). The combination of LBNP and tilt during supine cycling did not change the participants’ subjective interpretation of the exertional test but attenuated the hyperpnia‐induced vasodilatory MCAv response, while also enabling participants to achieve a higher heart rate during exercise and reduced symptoms 1 h later. As this protocol is safe and feasible, further research is warranted in this area for developing PPCS treatment options.Highlights What is the central question of this study?What are the feasibility, safety and utility of combining head‐up tilt with lower body negative pressure during supine cycling for blunting the increase in cerebral blood velocity seen during moderate‐intensity exercise in individuals experiencing persisting post‐concussion symptoms? What is the main finding and its importance?Although no differences were found in symptoms between conditions within the first 10 min following exertion, symptom severity scores showed a clinically meaningful reduction 60 min following the experimental condition compared to the non‐experimental control condition.

Feasibility of superimposed supine cycling and lower body negative pressure as an effective means of prolonging exercise tolerance in individuals experiencing persisting post‐concussive symptoms: Preliminary results

Javra,

Burma,

Johnson

et al. 2024

Examining the upper frequency limit of dynamic cerebral autoregulation: Considerations across the cardiac cycle during eucapnia

Burma,

Neill,

Fletcher

et al. 2024

There are differences within the literature regarding the upper frequency cut‐off point of the dynamic cerebral autoregulation (CA) high‐pass filter. The projection pursuit regression approach has demonstrated that the upper frequency limit is ∼0.07 Hz, whereas another approach [transfer function analysis (TFA) phase approaching zero] indicated a theoretical upper frequency limit for the high‐pass filter of 0.24 Hz. We investigated how these limits accurately represent the CA upper frequency limit, in addition to extending earlier findings with respect to biological sexes and across the cardiac cycle. Sixteen participants (nine females and seven males) performed repeated squat–stand manoeuvres at frequencies of 0.05, 0.10, 0.15, 0.20 and 0.25 Hz, with insonation of the middle and posterior cerebral arteries. Linear regression modelling with adjustment for sex and order of squat completion was used to compared TFA gain and phase with 0.25 Hz (above the theoretical limit of CA). The upper frequency limit of CA with TFA gain was within the range of 0.05–0.10 Hz, whereas TFA phase was within the range of 0.20–0.25 Hz, and consistent between vessels, between sexes and across the cardiac cycle. Females displayed greater middle cerebral artery gain compared with males (all P < 0.047), and no phase differences were present (all P > 0.072). Although sex‐specific differences were present for specific TFA metrics at a given frequency, the upper frequency limit of autoregulation was similar between cerebral conduit vessels, cardiac cycle phase and biological sex. Future work is warranted to determine whether an upper frequency limit exists with respect to hysteresis analyses.

Challenging dynamic cerebral autoregulation across the physiological CO₂ spectrum: Influence of biological sex and cardiac cycle

Johnson,

Burma,

Neill

et al. 2024

This study applied alterations in partial pressure of end‐tidal carbon dioxide () to challenge dynamic cerebral autoregulation (dCA) responses across the cardiac cycle in both biological sexes. A total of 20 participants (10 females and 10 males; aged 19–34 years) performed 4‐min bouts of repeated squat–stand manoeuvres (SSMs) at 0.05 and 0.10 Hz (randomized orders) with clamped at ∼40 mmHg. The protocol was repeated for hypercapnic (∼55 mmHg) and hypocapnic (∼20 mmHg) conditions. Middle cerebral artery (MCA) and posterior cerebral artery (PCA) were insonated via transcranial Doppler ultrasound. Dynamic end‐tidal forcing clamped , and finger photoplethysmography quantified beat‐to‐beat changes in blood pressure. Linear regressions were performed for transfer function analysis metrics including power spectrum densities, coherence, phase, gain and normalized gain (nGain) with adjustment for sex. During hypercapnic conditions, phase metrics were reduced from eucapnic levels (all P < 0.009), while phase increased during the hypocapnic stage during both 0.05 and 0.10 Hz SSMs (all P < 0.037). Sex differences were present with females displaying greater gain and nGain systole metrics during 0.10 Hz SSMs (all P < 0.041). Across stages, females displayed reduced buffering against systolic aspects of the cardiac cycle and augmented gain. Sex‐related variances in dCA could explain sex differences in the occurrence of clinical conditions such as orthostatic intolerance and stroke, though the effect of fluctuating sex hormones and contraceptive use on dCA metrics is not yet understood.