Cardiovascular changes in the unanaesthetized lingcod (Ophiodon elongatus) during short-term, progressive hypoxia and spontaneous activity

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Abstract
Cardiac output (.ovrhdot.Q) and arterial blood pressures in the ventral and dorsal aortae (PVA and PDA) were measured directly and simultaneously in the lingcod. The branchial and systemic conductances to blood flow (Gg and Gs) were calculated. During progressive hypoxia .ovrhdot.Q, Gg, Gs, PVA and PDA were all reduced when the water PO2 [partial pressure of O2] decreased below 45 mm Hg (1 mm Hg = 133.322 Pa [pascal]). Spontaneous activity was characterized by an initial bradycardia and concurrent reduction in .ovrhdot.Q, Gs, GS, PVA and PDA. Longer periods of activity were subsequently followed by a period of restitution where .ovrhdot.Q, Gg, Gs, PVA and PDA were all elevated. The beat by beat oscillations in flow were usually synchronized with, and in the same direction as, those in vascular conductance during both activity and hypoxia. This synchrony was most apparent between Gs and .ovrhdot.Q during the rapid cardiovascular adjustments occurring with activity. Apparently, the observed relationship between flow and conductance changes was a result of passive changes in conductance when flow was altered, plus an active component which involved reflex vasoactivity.