The Cardiac and Cerebrovascular Response to Lower Body Negative Pressure in Patients with Postural Orthostatic Tachycardia Syndrome
Bibliographic record
Abstract
Introduction: Postural orthostatic tachycardia syndrome (POTS) is characterized by excessive heart rate response upon standing and symptoms that drastically reduce quality of life. Symptoms are often cerebral in nature (e.g., dizziness, headache), however the relationship between the underlying physiology and the symptoms is unknown. We tested the hypothesis that, compared to healthy controls (HC) individuals with POTS would have greater decreases in cardiac, and cerebral hemodynamic function during a simulated orthostatic challenge (lower-body negative pressure; LBNP) measured using magnetic resonance (MR) imaging. Methods: Eleven patients with POTS (17±1yrs; 1 male) and 10 HC (18±2yrs; 1 male) were studied at rest (supine in MRI) and during 20-minutes of -25mmHg LBNP. Symptoms were measured by Vanderbilt Orthostatic Symptom Score (VOSS). Heart rate and blood pressure (BP) were measured using an automated cuff and finger pulse oximeter, respectively. Left and right ventricular volumes, ejection fraction, stroke volume (SV), and cardiac output (Qc) were determined by cardiac MR. Cerebral oxygen utilization (VO 2 ) was calculated as cerebral blood flow (CBF) multiplied by venous oxygen saturation (SVO 2 ), measured by MR phase contrast and susceptomtery-based oximetry in the superior sagittal sinus. Results: At rest, there were no differences between groups for any cardiac hemodynamic measure (p>0.05 for all), however cerebral SvO 2 and VO 2 were lower in the POTS group (p=0.02 for both). In response to LBNP, patients with POTS had greater VOSS (25±21 vs 5±12; p=0.02). Heart rate increased in response to LBNP (p<0.001), but the increase was not different between groups (HC: +9±8bpm; POTS: +13±11bpm; p=0.35). SV and Qc decreased during LBNP (both, p<0.01), despite no change in mean arterial BP (p=0.13) which did not differ between groups (HC: +9±8mmHg; POTS: 3±6mmHg; p=0.377). Additionally, both left and right ventricular volumes as well as ejection fraction decreased during LBNP (p<0.01 for all). The decreased Qc during LBNP coincided with lower CBF in the superior sagittal sinus (p=0.01) although the response was not different between groups (HC: -17±13ml/min; POTS: -25±32ml/min; p=0.51). Cerebral SvO 2 also decreased during LBNP (p=0.03) indicating increased oxygen extraction, resulting in no change in cerebral VO 2 during LBNP (p=0.28) and no difference between groups in the VO 2 response (HC: -0.2±3.7ml/min; POTS: +1.1±2.0ml/min; p=0.33). Conclusion: In response to a simulated orthostatic challenge (-25mmHg LBNP), patients with POTS do not have impaired cardiac function or cerebral oxygenation despite having a higher symptom score; however, a stronger stimulus may have been necessary to expose differences. Further investigations are needed to elucidate mechanisms of autonomic dysfunction in this population. Women and Children's Health Research Institute. 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.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".