Cerebral oxygenation and regional cerebral perfusion responses with resistance breathing during central hypovolemia

Abstract

Resistance breathing improves tolerance to central hypovolemia induced by lower body negative pressure (LBNP), but this is not related to protection of anterior cerebral blood flow [indexed by mean middle cerebral artery velocity (MCAv)]. We hypothesized that inspiratory resistance breathing improves tolerance to central hypovolemia by maintaining cerebral oxygenation (ScO), and protecting cerebral blood flow in the posterior cerebral circulation [indexed by posterior cerebral artery velocity (PCAv)]. Eight subjects (4 male/4 female) completed two experimental sessions of a presyncopal-limited LBNP protocol (3 mmHg/min onset rate) with and without (Control) resistance breathing via an impedance threshold device (ITD). ScO (via near-infrared spectroscopy), MCAv and PCAv (both via transcranial Doppler ultrasound), and arterial pressure (via finger photoplethysmography) were measured continuously. Hemodynamic responses were analyzed between the Control and ITD condition at baseline (T1) and the time representing 10 s before presyncope in the Control condition (T2). While breathing on the ITD increased LBNP tolerance from 1,506 ± 75 s to 1,704 ± 88 s ( = 0.003), both mean MCAv and mean PCAv were similar between conditions at T2 ( ≥ 0.46), and decreased by the same magnitude with and without ITD breathing ( ≥ 0.53). ScO also decreased by ~9% with or without ITD breathing at T2 ( = 0.97), and there were also no differences in deoxygenated (dHb) or oxygenated hemoglobin (HbO) between conditions at T2 ( ≥ 0.43). There was no evidence that protection of regional cerebral blood velocity (i.e., anterior or posterior cerebral circulation) nor cerebral oxygen extraction played a key role in the determination of tolerance to central hypovolemia with resistance breathing.

Tolerance to a haemorrhagic challenge during heat stress is improved with inspiratory resistance breathing

“…preserved central blood volume, enhanced venous return, improved cardiac filling and/or maintained cerebral perfusion) are responsible for the ITD‐induced improvements in tolerance need to be investigated further. Furthermore, on the account of the expanding body of evidence suggesting that cerebral hypoperfusion does not play as pivotal of a role in the tolerance to central hypovolaemia (Ainslie, Hoiland, & Bailey, ; Jeong, Shibata, Levine, & Zhang, ; Kay et al., ; Lucas et al., ; Lucas, Pearson, Schlader, & Crandall, ) as previously thought, future research directed at elucidating the specific physiological processes that improve tolerance to haemorrhage during heat stress is highly warranted.…”

“…In a normothermic state, the ITD improves tolerance to a simulated haemorrhagic challenge (Kay, Sprick, & Rickards, ; Rickards, Ryan, Cooke, Lurie, & Convertino, ). In swine, the ITD is effective in the rescue of hypotension resulting from heat stroke (Voelckel, Yannopoulos, Zielinski, McKnite, & Lurie, ).…”

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

“…Syncope is associated with a decrease in cerebral blood velocity (CBV), often monitored in middle cerebral arteries (MCA) (Kay, Sprick, & Rickards, 2017;Schondorf, Benoit, & Stein, 2001;van Lieshout, Wieling, Karemaker, & Secher, 2003). However, both MCAs supply the anterior part of the brain and questions arise as to whether the posterior irrigation could rather be linked to the appearance of pre-syncopal symptoms.…”

“…Emergence of orthostatic symptoms (such as dizziness, nausea and blurred vision) could therefore refer to posterior cerebral hypoperfusion, notably in posterior cerebral arteries (PCA). Kay & Rickards (2016) demonstrated that individuals with low tolerance to orthostatic stimulation show greater decrease in PCA mean blood velocity (PCAvmean) during a progressive lower body negative pressure protocol where tolerance was evaluated as the onset of presyncope/appearance of symptoms (Kay et al, 2017). Conversely, these investigators did not report any differences in MCA mean blood velocity (MCAvmean) changes during the protocol compared to baseline.…”

“…Of note, young women display greater prevalence of orthostatic intolerance (Fu et al, 2004) and symptoms of cerebral hypoperfusion than young men (Ali et al, 2000). Therefore, their posterior cerebral circulation could be prone to greater decreases in blood flow when blood pressure lowers (Kay et al, 2017).…”