Coronary Blood Flow Velocity Responses to Oxygen and Carbon Dioxide in Humans
Notice bibliographique
Résumé
In humans, coronary blood flow (CBF) is tightly regulated by microvessels within the myocardium. While there is clear evidence that CBF rises to match myocardial workload, there is conflicting evidence regarding the inherent sensitivity of the coronary vasculature to changes in the partial pressure of arterial carbon dioxide (PaCO 2 ) and oxygen (PaO 2 ) within the physiological range. The purpose of this study was to investigate the changes in CBF associated with isooxic hypo‐ and hyper‐capnia and isocapnic hypoxia. We hypothesized that a modest systemic increase in end‐tidal partial pressure of CO 2 (PetCO 2 ) or decrease in end‐tidal partial pressure of O 2 (PetO 2 ) would result in a significant increase in coronary blood flow velocity (CBF V ) due to downstream vessel dilatation. Likewise, we hypothesized that hypocapnia would cause a reduction in CBF V . Finally, we hypothesized that normalizing for cardiac workload (W C ) or mechanical energy (E M ) would diminish the observed reactivity. Young men free of cardiovascular disease (age = 23.4 ± 1.3 years, n=14) were exposed to two ventilatory challenges: (1) an isooxic CO 2 test that consisted of six, 8‐min steps of PetCO 2 (−8, −4, 0, +4, and +8 mmHg from baseline values) and (2) an isocapnic hypoxic test that involved three, 8‐min steps of hypoxia (PetO 2 = 64, 52 and 45 mmHg). CBF V was measured using Doppler echocardiography in the mid segment of the left anterior descending coronary artery (LAD). W C and E M were estimated using the rate pressure product (RPP; systolic blood pressure × heart rate) and the area of a derived pressure‐volume loop (PV A ) respectively. The PV A was calculated using volumes derived from echocardiographic measurements, a validated estimation of left ventricular end‐systolic elastance and beat‐by‐beat blood pressure from photoplethsmography. A PetCO 2 of +8 mmHg evoked a 34.6 ± 8.5% increase in mean peak diastolic CBF V (P<0.01). CBF V increased by 38.3 ± 12.6% and 51.4 ± 8.8% in response to a PetO 2 of 52 and 45 mmHg, respectively (P<0.05). RPP and PV A were significantly elevated during hypercapnia (+4, +8 mmHg PetCO 2 ; P<0.05), hypoxia (52 and 45 mmHg PetO 2 ; P<0.01) and were not different during hypocapnia (P>0.05). When CBF V was indexed against either measure of RPP and PV A , the CBF V responses to hypercapnia and hypoxia were abolished. Estimated coronary vascular resistance (CBF V /mean arterial pressure) did not change significantly across any protocols (P>0.05). With respect to absolute changes in CBF V , hypercapnia and hypoxia elicit increases in peak diastolic velocity; though when corrected for changes in RPP and PV A associated with each condition the changes in CBF V were absent (P>0.05). In summary, the lack of sensitivity of the coronary vasculature supplied by the LAD is underscored by the lack of both a CBF V and cardiac workload response in hypocapnia. It can be surmised that the regulation of coronary vessels is mediated primarily through metabolic changes within the heart rather than an inherent sensitivity to changes in arterial blood gases within a physiological range. Support or Funding Information Funding: NSERC, CFI
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
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 | 0,001 |
| 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 | 0,001 | 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 ».