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/cm 5 ; P =0.006) and cold pressor test (−386±179 dyne×s/cm 5 ; P =0.011) were significantly reduced compared with no intervention (−488±173 dyne×s/cm 5 ). 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.

The preponderance of initial orthostatic hypotension in postural tachycardia syndrome

Significant initial orthostatic hypotension (IOH) occurs in ~50% of postural tachycardia syndrome (POTS) patients and 13% of controls. Heart rate and blood pressure recovery are prolonged in IOH sustaining lightheadedness; IOH is more prevalent and severe in POTS. Altered cerebral blood flow and cardiorespiratory regulation are more prevalent in POTS. Altered heart rate variability and baroreflex gain may cause nearly instantaneous lightheadedness in POTS. IOH alone fails to confer a strong probability of POTS.

26 Initial Orthostatic Hypotension in Older Persons: Results from the Malaysian Elders Longitudinal Research Study

Objectives Initial orthostatic hypotension (IOH) is defined as a reduction in systolic or diastolic blood pressure (1) of 40 mmHg or 20 mmHg or greater within 15 seconds of standing. However, little is known about the characteristics of individuals with IOH and its relevance in the older population. The present study aimed to determine factors associated with IOH and classical orthostatic hypotension (COH) and their relationship with physical, functional and cognitive performance. Design Cross-sectional observational study. Setting and Participants Individuals aged ≥55 years were recruited through the Malaysian Elders Longitudinal Research (MELoR) study and continuous non-invasive BP was monitored over five minutes of supine rest and three minutes of standing. Measures Physical performance was measured using timed up and go, functional reach (FR), hand grip (HG) and Lawton’s functional ability scale; cognition was measured with Montreal Cognitive Assessment (MoCA). BP response to standing was categorized as non-OH, COH, IOH or COH and IOH Results 1245 participants were recruited, 623 (50%) had COH, 165 (13%) had IOH and 145 (12%) met the criteria for COH and IOH. COH was associated with increasing age, hypertension, transient ischemic attacks, diabetes mellitus, anti-hypertensive medications and reduced functional reach compared to individuals without COH. IOH was associated with younger age, normo-tension, and the absence of cerebrovascular disease or diabetes. Individuals with IOH had significantly better TUG, FR and HG scores compared to individuals without IOH. Conclusions This study suggests that IOH is associated with better physical performance. Further research is now required to fully elucidate the clinical relevance of IOH and its relationship to COH, as well as determine appropriate clinical cut-offs.

Case 35: Initial Orthostatic Hypotension

Initial orthostatic hypotension (IOH)is characterized by a rapid decrease in blood pressure in response to standing up quickly, with restoration of blood pressure in less than a minute. IOH is not associated with autonomic failure.

Case 99: Mixed Tilt Patterns in Rheumatoid Arthritis

Autonomic testing may reveal combined initial orthostatic hypotension and orthostatic hypotension due to a combination of volume depletion and adrenergic failure, presyncope with prominent vasodepressor component, and small fiber neuropathy.