Cardiorespiratory interactions previously identified as mammalian are present in the primitive lungfish

Abstract

Heart rate variation during air breathing indicates similarities between mammals and primitive lungfish.

Evolutionary and cardio‐respiratory physiology of air‐breathing and amphibious fishes

“…The immediate increase in heart rate on surfacing implies an instantaneous change in autonomic tone. This was reflected in the measured conduction velocity of cardiac vagal fibres, which matched mammalian B‐fibres and, like them, were shown to be myelinated . Its presence in the L. paradoxa as well as in tetrapods suggests an ancient origin of myelination of the vagal efferents, which may be functionally important for allowing instantaneous beat‐to‐beat control of heart rate.…”

“…Following the injection of atropine, L. paradoxa, increased air‐breathing frequency . This increase was accompanied by an increase in total oxygen consumption, suggesting that the effectiveness of gas exchange over the lung was maintained .…”

“…In L. paradoxa each air‐breathing episode was accompanied by an immediate and marked increase in heart rate, due solely to withdrawal of a cholinergic parasympathetic tonus . The immediate increase in heart rate on surfacing implies an instantaneous change in autonomic tone.…”

“…Following the injection of atropine, L. paradoxa, increased air‐breathing frequency . This increase was accompanied by an increase in total oxygen consumption, suggesting that the effectiveness of gas exchange over the lung was maintained . Subsequent injection of propranolol (an inhibitor of beta‐adrenergic receptors) increased tidal volume and oxygen uptake per breath by 25% .…”

“…Together with the increased heart rate, increased pulmonary perfusion would imply that oxygen uptake over the lung could be enhanced. Clearly, this was not the case as oxygen uptake per breath was markedly reduced, inviting the conclusion that control of patterns of blood and airflow over the lung surface are generally under tight tonic neural control, rather than responding to bulk changes in flow …”