Effect of hemorrhagic hypotension on oxygen consumption of dogs

¹ Department of Physiology and Biophysics, University of Mississippi Medical Center, Jackson, Mississippi

The effects of hematocrit, Dibenzyline, and epinephrine on oxygen consumption were studied in 220 dogs whose arterial pressure was lowered to and maintained at 30 mm Hg. Oxygen consumption was recorded previous to and during the period of hypotension. The average oxygen consumption was 7.20 ml/kg min prior to hemorrhage. Ten minutes after hemorrhage the oxygen consumption was 3.58 ml/kg min (50% of control). After 30 min of hypotension the oxygen consumption was 4.70 ml/kg min (65% of control), and the oxygen consumption increased to 5.33 ml/kg min (74% of control) after 1 hr. Pretreatment with Dibenzyline increased the oxygen consumption during the early stages of hypotension but had little effect in the latter stages. Epinephrine administration decreased the oxygen consumption during the entire hypotensive period. Previous studies have shown that the oxygen utilization coefficient approaches its maximal value during the hypotensive period; therefore, oxygen uptake becomes limited by the blood flow and the changes in oxygen consumption indicate changes in flow rate to active tissue. Simultaneous studies showed that the hematocrit influenced oxygen transport by effects on both the blood oxygen content and the blood flow. The results illustrate that animals with hematocrits of 35–39 are able to transport more oxygen than animals with other hematocrits. Evidence is presented to show that the initial fall and the subsequent rise in oxygen consumption during hypotension may be a local autoregulation of blood flow.

Key Words: autoregulation • blood flow • Dibenzyline • epinephrine • hematocrit • hemorrhage • oxygen debt • oxygen content • oxygen transport • shock

Submitted on January 23, 1964