Effects of Human Pregnancy on Chemoreflex and Non-Chemoreflex Drives to Breathe
Bibliographic record
Abstract
Human pregnancy is characterized by significant increases in minute ventilation (VE) and reductions in arterial carbon dioxide tensions (PaCO2). The mechanism(s) of these changes are poorly understood but may be due to the stimulatory effects of gestational hormones on chemoreflex and (or) non-chemoreflex drives to breathe. PURPOSE: To examine the effects of human pregnancy on chemoreflex and non-chemoreflex drives to breathe. The contribution of gestational hormones to ventilatory adaptations was also studied. METHODS: Nineteen women (31.3±0.9 yrs; FEV1 = 103±2 %predicted; mean ± SE) performed a carbon dioxide (CO2) rebreathing procedure that includes prior hyperventilation and maintenance of iso-oxia in late gestation (TM3, 36.3±0.2 wk) and 18.3±0.7 wk post-partum (PP). Resting arterialized venous blood samples for the determination of PaCO2, pH, plasma progesterone ([P4]) and 17β-estradiol ([E2]) concentrations were also measured. During rebreathing trials, end-tidal carbon dioxide tension (PETCO2) increased, whereas end-tidal oxygen tension was maintained at a constant hyperoxic (150 mmHg) level. The point at which VE increased as PETCO2 increased was identified as the central chemoreflex ventilatory recruitment threshold for CO2 (VRTCO2). VE below (VEB) and above (VES) this threshold, representing non-chemoreflex and chemoreflex drives to breathe, respectively, was determined. RESULTS: Pregnancy was associated with increased: [P4] (p<0.001); [E2] (p<0.001); pH (TM3, 7.44±0.00 vs. PP, 7.41±0.00, p<0.001); VEB (TM3, 14.6±0.9 vs. PP, 12.1±1.2 L/min, p<0.05); VES (TM3, 4.5±0.4 vs. PP, 2.4±0.2 l/min/mmHg, p<0.001); and decreased: PaCO2 (TM3, 31.9±0.4 vs. PP, 40.2±0.6 mmHg, p<0.001); VRTCO2 (TM3, 40.5±0.5 vs. PP, 47.6±0.7 mmHg, p<0.001). Pregnancy-induced changes (Δ) in [P4] and [E2] were not significantly correlated with ΔPaCO2, ΔVEB, ΔVRTCO2 or ΔVES. However, a positive correlation was observed between Δ PaCO2 with Δ VRTCO2 (r = 0.49, p<0.05). CONCLUSIONS: Pregnancy significantly increased ventilatory drive at rest. This effect may be due, at least in part, to significant increases in both chemoreflex and non-chemoreflex drives to breathe. Our inability to demonstrate a relationship between the change in gestational hormone levels and indices of ventilatory control, support the hypothesis that progesterone may have no additional stimulatory effect on VE following progesterone receptor saturation. [Supported by: Ontario Thoracic Society, William M. Spear Respiratory Research Endowment Fund at Queen's University]
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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".