Sixty Days of Head‐Down Tilt Bed Rest Augments Muscle Sympathetic Nerve Activity Responses to Maximal End‐Inspiratory Apnea: Evaluation of Sympathetic Neural Recruitment Strategies
Notice bibliographique
Résumé
The objective of this study was to evaluate the impact of 60‐days head‐down tilt (−6°) bed rest (HDBR) on muscle sympathetic nerve activity (MSNA) responses to a maximal end‐inspiratory apnea (apnea) and the sympathetic neural recruitment strategies underlying the MSNA response. Thirteen male individuals ( n = 13, 30 ± 2 yr, 180.7 ± 1.5 cm, 77.7 ± 1.8 kg, 23.8 ± 0.4 kg/m 2 ) provided baseline MSNA data pre‐ and post‐HDBR, whereas eight participants provided complete apnea data as well. Heart rate (HR; ECG), blood pressure (Finometer) and MSNA (microneurography) were measured pre‐ and post‐HDBR, during ~3‐min of baseline and the last ~30‐s of a maximal end‐inspiratory apnea (apnea). Sympathetic action potentials (AP) were detected from the filtered raw MSNA signal using AP detection software. APs were binned based on peak‐to‐peak amplitude into clusters defined by Scott's rule. Values are mean ± SE. Apnea duration was 74 ± 5 s in the pre‐ and 85 ± 7 s in the post‐HDBR conditions ( P = 0.09). Baseline mean arterial pressure (MAP; 104 ± 5 to 94 ± 4 mmHg, P = 0.04) and pulse pressure (PP; 59 ± 3 to 50 ± 4 mmHg, P < 0.01) were reduced with HDBR. MAP during apnea (112 ± 5 to 103 ± 4 mmHg, P = 0.14) was similar pre‐ and post‐HDBR, while PP during apnea (55 ± 3 to 49 ± 4 mmHg, P = 0.06) trended towards being reduced in the post‐HDBR session. HR was similar across testing sessions at baseline (66 ± 2 to 68 ± 5 bpm, P = 0.24) and during apnea (66 ± 2 to 70 ± 2 bpm, P = 0.17). Baseline integrated MSNA (burst frequency: 13 ± 2 to 18 ± 2 bursts/min; burst incidence: 20 ± 2 to 27 ± 4 bursts/100beats, all P > 0.05) and baseline AP indices (AP frequency: 62 ± 22 to 106 ± 27 spikes/min; AP incidence: 92 ± 31 to 159 ± 40 spikes/100 beats; AP/burst: 4 ± 0.8 to 6 ± 0.9 spikes/burst; active clusters/burst: 3 ± 0.3 to 3 ± 0.4 clusters/burst; total clusters: 7 ± 0.9 to 9 ± 0.6 clusters, all P > 0.05) were similar pre‐ and post‐ HDBR. However, the change in integrated MSNA burst frequency, from baseline to apnea, was greater post‐HDBR (Δ 28 ± 3 bursts/min) than pre‐HDBR (Δ 15 ± 2, P < 0.01). This exaggerated response to apnea post‐HDBR was a function of increased AP firing frequency (pre‐HDBR, post‐HDBR: Δ 94 ± 25, Δ 317 ± 55 AP/min, P < 0.01). Although the change in integrated burst amplitude, from baseline to apnea, was similar pre‐ (Δ 0.040 ± 0.01) and post‐HDBR (Δ0.080 ± 0.02, P = 0.15), AP analysis suggests that the change in the number of active sympathetic clusters per burst, from baseline to apnea, was greater post‐HDBR (Δ 1 ± 0.2 clusters/burst) than pre‐HDBR (Δ 0 ± 0.2 clusters/burst, P = 0.02), while the change in total sympathetic clusters, from baseline to apnea, trended towards greater recruitment post‐HDBR (Δ 2 ± 0.7 clusters) than pre‐HDBR (Δ 0 ± 0.5 clusters, P = 0.07). Also, the change in the number of APs per burst, from baseline to apnea, was greater post‐HDBR (Δ 3 ± 0.8) than pre‐HDBR (Δ 1 ± 0.4, P = 0.02). These findings suggest that reflex MSNA‐arousal imposed by apnea is exaggerated by 60‐days HDBR, primarily by mechanisms involving augmented AP firing rate with minimal contributions from recruitment of latent sub‐populations of sympathetic axons. Support or Funding Information This work was supported by Natural Sciences and Engineering Research Council of Canada (NSERC) Grant 217916‐2013 (awarded to J. K. Shoemaker).
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».