The purpose of this study was to determine the effectiveness of local blood flow regulation in the total systemic circulation in maintaining oxygen delivery. In dogs, in which nervous control of the circulation was eliminated by decapitation and alcohol coagulation of the spinal cord, three series of experiments were performed. In the first series, autoregulation of the total circulation was demonstrated by imposing step decreases in arterial pressure and following cardiac output as it returned toward control. A significant direct correlation was found between the initial arteriovenous oxygen difference [(a-v)ΔO2] and the feedback gain of the autoregulatory blood flow control system. No correlation was found between the initial (a-v)ΔO2 and the oxygen consumption following the pressure manipulation. In the second series, the animals were respired with hypoxic gas mixtures and the circulatory responses were recorded while arterial pressure was held constant. Cardiac output increased in each case, thereby maintaining oxygen consumption within 8, 13, and 20% of control when the preparations were respired with 15, 10, and 8% oxygen, respectively. A significant direct correlation was found between the initial (a-v)ΔO2 and the cardiac output response. Oxygen consumption during hypoxia was not affected by initial (a-v)ΔO2. In a third series of experiments, the ability of the preparations to control blood flow in response to a standard step decrease in arterial pressure was studied before and after dinitrophenol (DNP) administration. DNP increased oxygen consumption and cardiac output. Despite the fact that cardiac output was above control, the preparations responded to the same pressure decrease by exerting greater control over blood flow than they had prior to the DNP infusion. The results of all three series of experiments indicate blood flow control is closely linked with the oxygen availability to demand ratio. The results also support the view that peripheral tissues regulate their blood flows locally to maintain oxygen uptake and, in so doing, contribute to the regulation of cardiac output.
ASJC Scopus subject areas
- Physiology (medical)