Arterial Baroreflex Control of Multi‐ and Single‐Unit Muscle Sympathetic Nerve Activity in Young Unmedicated Hypertensives
Bibliographic record
Abstract
Pharmacologic investigations of sympathetic baroreflex function in patients with hypertension have reported a shift in operating points to higher pressures. Still controversial is whether baroreflex sensitivity (BRS) is preserved or reduced in the hypertensive state, with most prior work limited to patients >45 yr, commonly medicated, and hypertension status based on past guidelines (systolic and diastolic BP ≥140/90 mmHg). Whether sympathetic BRS is altered in young hypertensives has yet to be investigated. We tested 8 young to middle‐aged (age: 35 ± 8 yr; BMI: 29 ± 4 kg/m 2 ), unmedicated male hypertensives (10 min supine BP 137 ± 4/77 ± 3 mmHg; characterized by new guidelines of BP ≥130/80 mmHg) and 8 age‐ (29 ± 7 yr, p=0.13) and BMI‐(29 ± 4 kg/m 2 , p=0.94) matched male normotensives (112 ± 5/64 ± 4 mmHg, both p<0.001). Beat‐to‐beat heart rate (electrocardiography) and BP (Finometer) and multi‐ and single‐unit muscle sympathetic nerve activity (MSNA; microneurography) were obtained during 3–10 min of supine rest preceding a modified‐Oxford protocol, which involved a bolus injection of 100–150 μg sodium nitroprusside followed by 100–150 μg phenylephrine hydrochloride 1 min afterwards. Resting heart rate (60 ± 9 vs 64 ± 12 bpm, p=0.43), multi‐unit MSNA burst frequency (32 ± 14 vs 35 ± 12 bursts/min, p=0.60), total MSNA (854 ± 542 vs 1262 ± 515 AU/min, p=0.14), and single‐unit MSNA spike frequency (22 ± 24 [n=26] vs 25 ± 28 [n=29] spikes/min, p=0.69) were similar between normotensives and hypertensives, although hypertensives had higher resting multi‐unit burst amplitude (32 ± 5 vs 39 ± 4 % largest burst, p=0.007). We assessed the likelihood of a MSNA burst (burst incidence) and spike (spike incidence), as well as burst amplitude (% largest burst), for each given 3 mmHg diastolic BP bin observed throughout the modified‐Oxford protocol. Using linear segments of the MSNA‐BP response curves, we quantified sympathetic BRS as the slope of a weighted linear regression. Strong (r>0.6) negative relationships were attained for multi‐unit MSNA in all 16 participants and in all MSNA single‐units (n=55). Multi‐ (−5.7 ± 2.0 vs −5.0 ± 1.6 bursts/100 heartbeats/mmHg, p=0.48; −3.9 ± 1.6 vs −4.0 ± 2.4 % largest burst/mmHg, p=0.96) and single‐unit (−2.8 ± 1.3 vs −2.5 spikes/100 heartbeats/mmHg, p=0.45) MSNA BRS were similar between normotensives and hypertensives, however, the multi‐unit MSNA‐BP response curve was shifted to a higher operating point in hypertensives (64 ± 6 vs 79 ± 6 mmHg eliciting 50 bursts/100 heartbeats, p<0.001). Our observations of increases in resting MSNA burst amplitude and preserved BRS suggest increased central sympathetic outflow independent of the arterial baroreflex in early‐stage hypertension. Support or Funding Information Natural Sciences and Engineering Research Council of Canada (NSERC) Canada Graduate Scholarship, Michael Smith Foreign Study Supplement, and Discovery Grant (06019); Coordination for the Improvement of Higher Education Personnel (CAPES); Foundation for Research Support of the Federal District (FAPDF) This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| 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) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".