Lower body muscle preactivation and tensing mitigate symptoms of initial orthostatic hypotension in young females.

BACKGROUND: Initial orthostatic hypotension (IOH) is a form of orthostatic intolerance defined by a transient decrease in blood pressure upon standing. Current clinical recommendations for managing IOH includes standing up slowly or lower body muscle tensing (TENSE) after standing. Considering that IOH is likely due to a large muscle activation response resulting in excessive vasodilation with a refractory period (<2 minutes), we hypothesized that preactivating lower body muscles (PREACT) before standing would reduce the drop in mean arterial pressure (MAP) upon standing and improve presyncope symptoms. OBJECTIVE: The purpose of this study was to provide IOH patients with effective symptom management techniques. METHODS: Study participants completed 3 sit-to-stand maneuvers, including a stand with no intervention (Control), PREACT, and TENSE. Continuous heart rate and beat-to-beat blood pressure were measured. Stroke volume and cardiac output were then estimated from these waveforms. RESULTS: A total of 24 female IOH participants (mean ± SD: 32 ± 8 years) completed the study. The drops in MAP following PREACT (-21 ± 8 mm Hg; P <.001) and TENSE (-18 ± 10 mm Hg; P <.001) were significantly reduced compared to Control (-28 ± 10 mm Hg). The increase in cardiac output was significantly larger following PREACT (2.6 ± 1 L/min; P <.001) but not TENSE (1.9 ± 1 L/min; P = .2) compared to Control (1.4 ± 1 L/min). The Vanderbilt Orthostatic Symptom Score following PREACT (9 ± 8 au; P = .033) and TENSE (8 ± 8 au; P = .046) both were significantly reduced compared to Control (14 ± 9 au). CONCLUSION: Both the drop in MAP and symptoms upon standing improved with either PREACT or TENSE. These maneuvers provide novel symptom management techniques for patients with IOH.

Mitigating Initial Orthostatic Hypotension: Mechanistic Roles of Muscle Contraction Versus Sympathetic Activation.

BACKGROUND: Initial orthostatic hypotension (IOH) is defined by a large drop in blood pressure (BP) within 15 s of standing. IOH often presents during an active stand, but not with a passive tilt, suggesting that a muscle activation reflex involving lower body muscles plays an important role. To our knowledge, there is no literature exploring how sympathetic activation affects IOH. We hypothesized involuntary muscle contractions before standing would significantly reduce the drop in BP seen in IOH while increasing sympathetic activity would not. METHODS: Study participants performed 4 sit-to-stand maneuvers including a mental stress test (serial 7 mental arithmetic stress test), cold pressor test, electrical stimulation, and no intervention. Continuous heart rate and beat-to-beat BP were measured. Cardiac output and systemic vascular resistance were estimated from these waveforms. Data are presented as mean±SD. RESULTS: A total of 23 female IOH participants (31±8 years) completed the study. The drops in systolic BP following the serial 7 mental arithmetic stress test (-26±12 mm Hg; P=0.004), cold pressor test (-20±15 mm Hg; P<0.001), and electrical stimulation (-28±12 mm Hg; P=0.01) were significantly reduced compared with no intervention (-34±11 mm Hg). The drops in systemic vascular resistance following the serial 7 mental arithmetic stress test (-391±206 dyne×s/cm5; P=0.006) and cold pressor test (-386±179 dyne×s/cm5; P=0.011) were significantly reduced compared with no intervention (-488±173 dyne×s/cm5). Cardiac output was significantly increased upon standing (7±2 L/min) compared with during the sit (6±1 L/min; P<0.001) for electrical stimulation. CONCLUSION: Sympathetic activation mitigates the BP response in IOH, while involuntary muscle contraction mitigates the BP response and reduces symptoms. Active muscle contractions may induce both of these mechanisms of action in their pretreatment of IOH. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03970551.