Cardiac baroreflex sensitivity and heart rate variability are lower in humans with high affinity hemoglobin compared to typical affinity hemoglobin
Bibliographic record
Abstract
Background Humans with high O 2 affinity hemoglobin (HAH) have a markedly lower partial pressure of O 2 at which 50% of hemoglobin is saturated (P 50 ) and a leftward shift of the oxy‐hemoglobin dissociation curve. Humans with HAH have attenuated heart rate responses during both acute and chronic hypoxic exposure relative to humans with typical P 50 . Despite the attenuated heart rate responses to hypoxia, there are typically no blood pressure differences found in humans with HAH relative to humans with typical P 50 . Due to the blunted heart rate and normal blood pressure responses to hypoxia in humans with HAH, this study aimed to investigate the impact of HAH on cardiac autonomic function during normoxia and hypoxia. We hypothesized that humans with HAH would have lower cardiac baroreflex sensitivity (cBRS) and heart rate variability (HRV) during normoxia and hypoxia relative to individuals with typical P 50. Methods Nine humans with a HAH mutation (6 female, Age: 40±12yrs, P 50 : 16±1 mmHg) and 12 controls with typical affinity hemoglobin (6 female, Age: 40±10yrs, P 50 : 26±1 mmHg) laid supine for 10‐minutes prior to 20‐minutes of isocapnic hypoxia, titrated to reduce arterial O 2 pressure to ~50 mmHg (Avg. F i O 2 = 11.9±0.0%). Beat‐to‐beat arterial pressures (arterial catheter) and heart rate (electrocardiogram) were continuously recorded. Data were averaged in five‐minute segments starting with the last five minutes of supine normoxic rest. Spontaneous cBRS was quantified using the sequence method. HRV was measured in time and frequency domains. Standard deviation of the RR interval (SDRR) was calculated as the standard deviation of all RR intervals in a data segment. Low frequency (LF) HRV was calculated using Fast Fourier Transformation and assessed as absolute spectral intensity in the LF band (0.04‐0.15Hz). Results Arterial oxygen (P a O 2 ) and carbon dioxide (P a CO 2 ) pressures were not different between humans with HAH and controls during normoxia or isocapnic hypoxia [P a O 2 : (HAH vs. Control): 48±3 vs. 47±2 mmHg, p=0.612; P a CO 2 : (HAH vs. Control): 40±3 vs. 39±1 mmHg, p=0.328] exposure. cBRS was lower in humans with HAH compared to controls in normoxia and throughout isocapnic hypoxia [normoxia (HAH vs. Control): 7±4 vs. 16±10 ms/mmHg; hypoxia minutes 15‐20 (HAH vs. Control): 4±3 vs. 14±11 ms/mmHg; Hb type, p=0.024]. Several metrics of HRV were lower in humans with HAH relative to control (SDRR: Hb type, p≤0.001; LF: Hb type, p=0.030) and HRV was blunted to a similar extent in both groups with hypoxia (SDRR: time effect, p=0.009). Conclusion The findings of this study are twofold. Compared to controls, humans with HAH have: 1) attenuated cardiac baroreflex sensitivity and 2) lower heart rate variability in both normoxia and isocapnic hypoxia.
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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 | 0.000 |
| 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) | 0.002 | 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".