Ventilatory and cardiovascular responses of a python (Python molurus) to exercise and digestion

To investigate the potential limiting steps of peak metabolic rates, we exa mined gas exchange rates ((V) over dot(O2),(V) over dot(CO2)), respiratory exchange ratio (RER), breathing frequency, tidal volume, minute ventilation volume (V) over dot(E)) as well as the heart rate, systemic blood flow and stroke volume of Burmese pythons (Python molurus) while fasting at rest, e xercising, digesting and exercising while digesting. All measured variables increased significantly during exercise (crawling at 0.4 km h(-1) and at ( V) over dotO(2max)), highlighted by a 17-fold increase in (V) over dot(CO2) and a 24-fold increase in (V) over dot(E). During the digestion of a meal equivalent to 25% of the snake's body mass, pythons responded with increase s in (V) over dot(O2) and heart rate similar to those experienced during ex ercise, along with a 4.5-fold increase in systemic blood flow. Interestingl y, pythons hyperventilated while exercising, whereas they hypoventilated du ring digestion. The combined demands of exercise and digestion resulted in significantly higher (V) over dot(O2), (V) over dot(CO2), breathing frequen cy and heart rate than during either exercise or digestion alone, Evidently , the capacities of the ventilatory and cardiovascular systems to transport oxygen to locomotor muscles are not a limiting factor in the attainment of peak metabolic rates during exercise in pythons.