Direct measurement of myocardial oxygen tension and high energy phosphate content under varying ventilatory conditions in rabbits / Messung von myokardialem Sauerstoffpartialdruck und energiereichen Phosphaten unter verschiedenen Beatmungsbedingungen beim Kaninchen
Bibliographic record
Abstract
Effective myocardial oxygen supply should not be compromised during cardiac surgery as it is essential to avoid circulatory and cardiac dysfunction. Local measurement of myocardial oxygen partial pressure (pO 2 ) was therefore introduced into the operative monitoring of myocardial ischemia. The aim of the present study was to assess whether myocardial oxygen partial pressure correlates with the content of high energy phosphates (HEPs). Seven male rabbits were examined in parallel with measurement of myocardial pO 2 by an implanted Clark electrode and 31 phosphorus-NMR spectroscopy. The ventilatory management established hyperoxygenation followed by systemic hypoxia with hypercapnia for 20 min. Additionally, analysis of end-expiratory gas composition in combination with blood gas analysis was performed simultaneously, and hemodynamic parameter was recorded. Under hypoxic conditions the cardiovascular system was severely compromised, whereas the myocardial pO 2 was only moderately impaired (pO 2 M 45.0±16.0 mm Hg). Immediately before cardiac arrest, low values of arterial and venous pO 2 were found (17.6±6.0 and 12.9±6.1 mm Hg). In contrast to near normal myocardial pO 2 , HEP content in the myocardium was considerably reduced and inorganic phosphorus was increased. Artificial ventilation leading to systemic hypoxia and eventually circulatory arrest resulted in almost normal myocardial pO 2 but severely compromised HEP content. This somewhat unexpected finding requires further clarification, but is in accordance with findings reported previously where regulatory mechanisms have been shown to play a role in the pathophysiology of severe hypoxic conditions such as those for cellular oxygen delivery and demand, P/O coupling and finally control of HEP production facilitating the interaction between respiratory chain and myoglobin oxygen transport. Zusammenfassung Für die Abwendung eines Herz-Kreislauf-Versagens ist eine ausreichende Sauerstoffversorgung des Herzens unerlässlich. Im Verlauf eines kardiochirurgischen Eingriffes ist daher gegen eine Beeinträchtigung der myokardialen Sauerstoffversorgung vorzusorgen. Für den Nachweis einer perioperativen Ischämie findet mittlerweile die direkte Messung des regionalen myokardialen Sauerstoffpartialdruckes Anwendung. In der vorliegenden Studie wurde untersucht, inwieweit diese Messung mit dem aktuellen myokardialen Gehalt an energiereichen Phosphaten korreliert. An sieben männlichen Kaninchen wurden parallel der myokardiale Sauerstoffpartialdruck über eine implantierte Clark-Elektrode und der Gehalt an energiereichen Phosphaten mittels 31 P-NMR-Spektroskopie bestimmt. Entsprechend dem gewählten Beatmungsmuster erfolgten eine Hyperoxygenation und systemische Hypoxie mit begleitender Hypercapnie über ein Intervall von 20 Minuten. Begleitend wurden simultane Atemgasanalysen, Blutgasanalysen und die Aufzeichnung hämodynamischer Daten durchgeführt. Unter diesen extrem hypoxischen Bedingungen fanden sich bei deutlich eingeschränkten Kreislaufparametern nur geringfügig verminderte Sauerstoffpartialdrücke (pO 2 M=45,0±16,0 mm Hg) am Messpunkt. Niedrigere Sauerstoffpartialdrücke fanden sich im arteriellen und venösen Blut (17,6±6,0 and 12,9±6,1 mm Hg) unmittelbar vor dem Herzstillstand. Im Gegensatz dazu war der myokardiale Gehalt an energiereichen Phosphaten (HEP) deutlich reduziert und das anorganische Phosphat exzessiv erhöht. Diese gegensätzlichen Befunde unterstreichen die Notwendigkeit weiterer Untersuchungen. Unter deutlich eingeschränkter Beatmung kam es zum Kreislaufversagen, obwohl sich fast normale Sauerstoffpartialdrücke im Myokard zeigten. Neben der notwendigen Überprüfung der Grenzen des Messsystems müssen jedoch auch Regulationsmechanismen, die zwischen Sauerstoffangebot und -verbrauch, der Kopplung von Phosphorylierung und Oxidation sowie bei der HEP-Synthese überprüft werden, da sie die Wechselwirkung zwischen Atmungskette und Sauerstofftransport durch Myoglobin bestimmen.
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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 | 0.000 |
| 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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".