Coordination between ventilatory pressure oscillations and venous return in the cephalopod Sepia officinalis under control conditions, spontaneous exercise and recovery

Venous blood flow was measured for the first time in a cephalopod. Blood velocity was determined in the anterior vena cava (AVC) of cuttlefish S. officinalis with a Doppler, while simultaneously, ventilatory pressure oscillations were recorded in the mantle cavity. In addition, magnetic resonance imaging (MRI) was employed to investigate pulsatile flow in other major vessels. Blood pulses in the AVC are obligatorily coupled to ventilatory pressure pulses, both in frequency and phase. AVC peak blood velocity (v(AVC)) in animals of 232 (+/- 30 SD) g wet mass at 15 degrees C was found to be 14.2 (+/- 7.1) cm s(-1), AVC stroke volume (SVAVC) was 0.2 (+/- 0.1) ml stroke(-1), AVC minute volume (MVAVC) amounted to 5.5 (+/- 2.8) ml min(-1). Intense exercise bouts of 1-2 min resulted in 2.2-fold increases in MVAVC, enabled by 1.6-fold increments in both, AVC pulse frequency (f(AVC)) and v(AVC). As increases in blood flow occurred delayed in time by 1.7 min with regard to exercise periods, we concluded that it is not direct mantle cavity pressure conveyance that drives venous return in this cephalopod blood vessel. However, during jetting at high pressure amplitude (> 1 kPa), AVC blood flow and mantle cavity pressure pulse shapes completely overlap, suggesting that under these conditions, blood transport must be driven passively by mantle cavity pressure. MRI measurements at 15 degrees C also revealed that under resting conditions, f(AVC) and ventilation frequency (f(V)) match at 31.6 (+/- 2.1) strokes min(-1). In addition, rates of pulsations in the cephalic artery and in afferent branchial vessels did not significantly differ from f(AVC) and f(V). It is suggested that these adaptations are beneficial for high rates of oxygen extraction observed in S. officinalis and the energy conserving mode of life of the cuttlefish ecotype in general.