Evaluation of PO2 within the anoxic-reoxygenated myocardium: Because it was technically difficult to measure PO2 directly within the embryonic myocardium, the instantaneous profile of PO2 during anoxia-reoxygenation transitions was evaluated by using a finite element computation of the oxygen concentration according to the Fick equation of diffusion. Parameters considered for the computer simulation were initial concentration of oxygen in the tissue equilibrated with air (200 |J.M); thickness of the flattened heart (approximately 300 |J.m); diffusion coefficient of oxygen in the embryonic tissue (2.5×10-5 cm2/s at 37°C); myocardial oxygen consumption (6 nmol O2/s/cm3 ); and number of finite elements (ie, 10 layers).
The reported values are mean ± SD, except where otherwise stated. Online shopping will cost you less – find cheap ventolin inhalers and enjoy the experience.
Forty hearts isolated from three-day-old chick embryos were investigated. Heart rate increased from 57±5 beats/min (n=20) at room temperature (approximately 24°C) to 137±12 beats/min (n=25) at 37.5°C after a period of stabilization of about 40 mins. Under the present experimental conditions, the end-diastolic external perimeter of the ventricle was 2.0±0.5 mm (n=4) and S during normoxia was 52±8 (n=3), corresponding to a perimeter shortening fraction of about 11% during each cardiac cycle. Whatever the conditions of oxygenation, maximal Cv (mCv) was systematically higher than maximal Rv (mRv) with a ratio close to 1.3. The preparation was quite stable over time because HR was constant during at least 5 h under normoxic stop-flow conditions (no renewal of culture medium).