Cardiovascular and hormonal responses to hypotension during hypoxia in the conscious goat

Thesis (Ph. D.)--University of Hawaii at Manoa, 1993.Includes bibliographical references (leaves 147-159)Microfiche.xii, 159 leaves, bound ill. 29 cmThe cardiovascular and hormonal responses to hemorrhage and chemically-induced hypotension in conscious goats were assessed in the present study. A progressive hemorrhage (0.5 ml/kg/min for 30 min) under hypoxic (FiO2=0.10) conditions (HH, n =4) reduced mean arterial blood pressure (MABP) after only 20 min of blood loss. An identical hemorrhage under normoxic conditions (NH, n =4) did not reduce MABP until after the blood loss was complete. Heart rate (HR) was significantly increased with hemorrhage only during normoxia. Arginine vasopressin (AVP) responses followed MABP chances, with HH levels being greater at an earlier time point. Final AVP values were not different between NH and HH. Plasma renin activity (PRA) responded in near identical fashion between the two settings, despite the earlier reduction in MABP with HH. Atrial natriuretic factor (ANF) was reduced during hemorrhage with both exposures. Sodium nitroprusside (SNP) infusions sufficient in reducing MABP 20% increased HR only during normoxia (NH, n =4). HR was not changed with hypotension during hypoxia (HH, n =4). AVP levels were increased with SNP infusions during both exposures, with HH values greater than NH. PRA and epinephrine (EPI) increased in similar fashion during NH and HH. Norepinephrine (NE) and ANF were unchanged with SNP induced hypotension. Finally, an acute 60 minute hypoxic exposure increased HR within the first 10 minutes. No transient increases in MASP, plasma NE or EPI were detected over the 60 min period of hypoxia. Thus, hemorrhage during hypoxia poses a greater challenge to the cardiovascular system than does an equal blood loss during normoxia. Further, it appears that hypoxia attenuates the PRA response to hemorrhage. However, when MASP is reduced over an identical time frame during normoxia and hypoxia, no differences in the PRA responses can be observed, while a hypoxic augmentation of the AVP response to hypotension becomes apparent. Finally, the data suggest a hypoxic attenuation of the arterial baroreflex tachycardia with hypotension in conscious goats