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Michael Eleruja
University of North Texas Health Science Center
Michael Eleruja, a graduate student at University of North Texas Health Science Center, investigated the effects of Pulsatile Perfusion Therapy (PPT) on baroreflex sensitivity (BRS) and cerebral autoregulation (CA) during central hypovolemia. Using two PPT modalities, oscillatory lower body negative pressure (OLBNP) and repeated thigh cuff inflations, in healthy participants, the study assessed cardiovascular and cerebral responses under stress. Results showed that BRS decreased with hypovolemia, while CA remained unchanged, and importantly, PPT did not improve BRS or CA in either modality. No differences were observed between OLBNP and thigh cuffs. Overall, these findings suggest that PPT does not significantly influence key regulatory mechanisms of blood pressure or cerebral blood flow during hypovolemia, despite its known benefits for tissue oxygenation. Michael will present this research at the at the American Physiology Summit in Minneapolis, Minnesota in April.
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ABSTRACT
Background
Baroreflex sensitivity (BRS) and cerebral autoregulation (CA) are key physiological mechanisms that maintain arterial pressure and cerebral blood flow under both resting conditions and during hypovolemic challenges such as hemorrhage. Pulsatile Perfusion Therapy (PPT) has been developed by our laboratory as a potential treatment for tissue hypoperfusion. PPT induces arterial pressure and blood flow oscillations at 0.1 Hz (10-s cycles) via oscillatory lower body negative pressure (OLBNP) or bilateral inflatable thigh cuffs; both PPT modalities protect cerebral tissue oxygenation under hypovolemic conditions. However, the effects of PPT on BRS and CA, which are critical during hypoperfusion, remain unclear. The purpose of this study was to evaluate the effects of PPT on BRS and CA responses to central hypovolemia, and to compare responses between the two PPT modalities (OLBNP and repeated thigh cuff inflations). Due to the protective effect of PPT under hypovolemic conditions, we hypothesized that PPT via either modality would increase BRS and CA, with no differences in responses between modalities.
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Methods
In this retrospective cross-sectional analysis, 14 healthy young participants (11 males, 3 females) underwent a 10-min OLBNP protocol (between −30 and −90 mmHg every 5 seconds), and 13 healthy young participants (7 males, 6 females) underwent a 10-min bilateral thigh cuff protocol (between 0-250 mmHg every 5 seconds) during -60 mmHg LBNP. LBNP of -60 mmHg for 10-min was used for the control condition for both PPT modalities. Cardiac BRS was assessed in the time domain as Δ heart rate (HR)/Δ systolic arterial pressure (SAP), and in the frequency domain using low-frequency (LF; 0.04-0.15 Hz) transfer function gain between SAP and R-R intervals (SAP–RRI LF gain). CA was assessed in the time domain as Δ middle cerebral artery velocity (MCAv)/∆ mean arterial pressure (MAP), and in the frequency domain using MCAv–MAP LF gain. Two-way repeated-measures ANOVAs were used to evaluate the effects of PPT modality and time on frequency and time-domain measures, while independent t-tests were used to compare relative changes in time- and frequency-domain measures between PPT modalities (OLBNP vs. repeated thigh cuff inflations).
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Results
SAP-RRI LF gain (i.e., cardiac BRS) decreased with LBNP (time effect, p< 0.001), with no effect of the PPT modality (p=0.434). The time domain measure of cardiac BRS decreased with application of LBNP, but there was no effect of condition (p=0.132, control vs. PPT) or PPT modality (p=0.989, OLBNP vs. thigh cuffs). There were also no differences in relative BRS responses between the two PPT modalities in either time domain (p=0.80) or frequency domain (p=0.93). MCAv-MAP LF gain (i.e., dynamic CA) did not change with LBNP (time effect, p=0.146), and there was no effect of PPT modality (p=0.273). The time domain measure of CA remained unchanged with application of LBNP, and there was no effect of condition (p=0.617) or PPT modality (p=0.470). There were also no differences in relative CA responses between the two PPT modalities in either the time domain (p=0.53) or frequency domain (p=0.16).
Conclusion
Contrary to our hypothesis, PPT via OLBNP or repeated thigh cuff inflations did not affect cardiac baroreflex sensitivity or cerebral autoregulation responses to central hypovolemia. Furthermore, no differences in these responses were observed between the two modalities of PPT.
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