The Effect of 0.1 Hz Blood Flow Oscillations on Microvascular Blood Flow Responses Following Severe Ischemia
Authors: Davis K. Austin , Bhuiyan Nasrul , McIntyre Benjamin , Rickards Caroline 
Published: May 2024

Background: We have shown that inducing 10 second (0.1 Hz) oscillations in arterial pressure and blood flow protects against reductions in tissue oxygenation during ischemia, independent of changes in macrovascular blood flow. However, it is unknown whether 0.1 Hz hemodynamic oscillations impacts microvascular function and vasodilatory capacity following severe ischemia. To examine this question, we assessed the reactive hyperemic response following a prolonged peripheral limb ischemia protocol with and without induced 0.1 Hz hemodynamic oscillations. Hypothesis: 0.1 Hz oscillations in blood pressure and blood flow will increase microvascular blood flow, assessed via reactive hyperemia following a 10-min period of ischemia. Methods: Thirteen healthy human participants (6M, 7F; 27.3 ± 4.2 y) completed two experimental protocols separated by ≥48 h. In both conditions, ischemia of the forearm was induced with a pneumatic cuff on the upper arm to decrease brachial artery blood velocity by ~70-80% from baseline. In the oscillation condition (OSC), 0.1 Hz oscillations in mean arterial pressure (MAP) and brachial artery blood flow were induced by inflating and deflating bilateral thigh cuffs every 5-s (10-s cycles; 0.1 Hz) throughout the forearm ischemia period. In the control condition (CON), the thigh cuffs were in place, but were inactive throughout the forearm ischemia period. Beat to beat arterial pressure was measured via finger photo plethysmography, and brachial artery diameter and blood velocity were measured via duplex Doppler ultrasound during baseline, ischemia, and the reperfusion period. The maximum mean brachial artery blood velocity, and 3-min area under the curve (AUC) of mean brachial artery blood velocity were used to determine the reactive hyperemia response. Results: The magnitude of forearm ischemia, indexed by the reduction in brachial artery conductance, was matched between conditions (CON: -74.8 ± 10.4% vs. OSC: -75.6 ± 6.7%, p=0.39). Reactive hyperemia was not different between conditions as indexed by maximum mean brachial artery blood velocity (CON: 36.4 ± 12.4 cm/s vs. OSC: 39.3 ± 11.2 cm/s, p=0.53) or 3-min brachial artery blood velocity AUC (CON: 1495 ± 744 (cm/s)2 vs. OSC: 1596 ± 804 (cm/s)2, p=0.74). Conclusion: Inducing 0.1 Hz hemodynamic oscillations during severe ischemia does not affect microvascular function, indexed by reactive hyperemia following release of the ischemic stimulus. A more direct measure of microvascular blood flow is needed to examine whether 0.1 Hz hemodynamic oscillations improves microvascular perfusion during ischemia. NIH Neurobiology of Aging & Alzheimer’s Disease Training Grant (T32 AG02049; KAD); American Heart Association Transformational Project Award (19TPA34910743; CAR); American Heart Association Predoctoral Fellowship (23PRE1018469; KAD); UNTHSC Physiology and Anatomy Seed Grant 2021 (CAR). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.