Physiology During Exercise the cardiac output rises upto 5 times, but pulmonary vascular resistance only few mm hg. Why? A Sympathetic stimulation causing vasodilatation B Opening of parallel channels C Pulmonary vasoconstriction D J receptors 💡 Explanation During Exercise the cardiac output rises upto 5 times, but pulmonary vascular resistance only few mm hg. Why? ✓ Correct Answer: B. Opening of parallel channels