Cardiac beat frequency and oxygen supply: A comparative study

Abstract

1. 1. The length of diastole in mammals varies between approx 1 s (elephant) and 38ms (shrew) which makes oxygen supply in high speed cardiac pumps in very small mammals precarious. 2. 2. High capillary density and high blood P 50, are reported in mammals with high frequency cardiac cycle. 3. 3. Both are probably insufficient when cardiac frequency is exceedingly high (shrew: 1000 min −1). 4. 4. High respiratory efficiency due to large relative mitochondrial volume per cell ( > 50%) seems to be preferential solution to maintain sufficient O 2-gradient. 5. 5. Similar strategy, i.e. high relative cardiac mitochondrial volume was reported in analogous situation in ice-fish ( Chaenocephalus aceratus) where O 2 cardiac cell supply is difficult due to the absence of hemoglobin and cardiac myoglobin.