Estimation of left ventricular stroke volume by impedance cardiography: its relation to the aortic reservoir
Notice bibliographique
Résumé
New Findings What is the central question of this study? Thoracic impedance has been used to calculate left ventricular stroke volume for decades, while its theoretical basis remains controversial and the parameters generated have not been related satisfactorily to the haemodynamic events. What is the main finding and what is its importance? We provide mechanistic explanations for the following: (i) why the upstroke of the change in thoracic impedance (Δ Z ) waveform is constantly delayed with respect to that of the central aortic pressure; (ii) why the contour of the Δ Z waveform is ‘blunted’ compared with that of the central aortic pressure; (iii) what mechanism is related to the ‘second bump’ of the Δ Z waveform in early diastole (the ‘O‐wave’); and (iv) the mechanism that is likely to be associated with the decreasing Δ Z waveform in later diastole. Impedance cardiography is a non‐invasive technique used to estimate left ventricular (LV) stroke volume (SV) using the change in thoracic impedance (Δ Z ). It remains controversial, partly because impedance cardiographic parameters have not been successfully related to haemodynamic events. We hypothesized that the change in Δ Z may be proportional to the variation in thoracic (primarily aortic) blood volumes. Nine anaesthetized and ventilated dogs were divided into the following two groups: the ‘aortic volume group’ ( n = 5), in which aortic and IVC (inferior vena caval) dimensions were measured ultrasonically; and the ‘reservoir volume group’, in which aortic and IVC reservoir volumes were calculated using the reservoir–wave model. Measurements were made in control conditions, in the presence of nitroprusside and methoxamine and after volume loading. In both the aortic volume group and the reservoir volume group, the maximal rate of increase in Δ Z [(d Z /d t ) max ] strongly correlated with the maximal rate of change in aortic/reservoir blood volume ( R 2 = 0.85 and 0.95, respectively), which in turn was proportional to the LV SV. The LV and IVC contributions to Δ Z were small in control conditions (∼5 and 1%, respectively), but the LV contribution increased slightly (to 7%) with administration of methoxamine and after volume loading (to 10%). It is concluded that the change in thoracic impedance (Δ Z ) during the cardiac cycle is proportional to the change in aortic reservoir (i.e. Windkessel) volume, which provides a mechanistic explanation for previously demonstrated good correlations with standard measures of cardiac output.
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 distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| 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) | 0,000 | 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 tête enseignante, 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 ».