Upright-to-supine exercise transition in younger and older subjects: effects on pulmonary gas-exchange efficiency
Bibliographic record
Abstract
Introduction Aging reduces pulmonary gas-exchange (PGE) efficiency which contributes to exertional dyspnea (breathlessness) and exercise limitation. Previous work has identified an increased physiologic dead space (VDphys; areas of the lung not adequately participating in PGE), secondary to reduced pulmonary perfusion, as a mechanism for reduced PGE efficiency during exercise in older individuals. Importantly, sex also impacts the ventilatory response to exercise as females have smaller lung volumes and airway diameter relative to lung size, and greater airway resistance, leading to lower PGE efficiency compared with males. However, no studies to date have examined the interaction of age and sex on PGE efficiency during exercise. The transition from upright-to-supine position, and associated redistribution of pulmonary perfusion throughout the lung, provides a model for examining this interaction. Therefore, the objective of this study was to utilize posture (upright/supine) to examine the effect of age and sex on PGE efficiency during exercise. Methods Forty-four participants (26 young (18-35 yrs) and 18 older (60-80 years), 50% Female) performed four constant work-rate exercise tests (two upright, two supine) at 50% of peak oxygen uptake to achieve ventilatory steady state. PGE was assessed by breath-by-breath volumetric capnography to measure VDphys and alveolar (VDalv) dead space. Results During rest and exercise, older compared with younger participants had higher VDphys, VDalv, and ventilation relative to CO2 production (V̇E/V̇CO2). Older participants had greater improvement in VDphys in supine vs. upright position, but dead space remained higher in both positions compared with younger individuals. No sex differences between positions were identified. Conclusion In older adults without cardiopulmonary disease, higher VDphys suggests PGE-inefficiency; however, the improvement during exercise reflects preserved capacity for pulmonary capillary recruitment. This study adds to our understanding of the normal age-related decline in PGE efficiency, providing a baseline for assessing PGE in cardiopulmonary disease.
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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".