© 1998 by European Society of Cardiology
Copyright © 1998, European Society of Cardiology
Autonomic control of cardiovascular performance and whole body O2 delivery and utilization in swine during treadmill exercise
Experimental Cardiology, Thoraxcenter, Cardiovascular Research Institute COEUR, Erasmus University Rotterdam, 3000 DR Rotterdam, Netherlands
* Corresponding author. Tel.: +31 10 408 8029; Fax: +31 10 436 5607; E-mail: duncker@tch.fgg.eur.nl
Objective: The present study determined the role of the autonomic nervous system (ANS) in the regulation of systemic and pulmonary circulation and of O2 delivery and utilization in swine at rest and during graded treadmill exercise. Methods: Instrumented swine (n=12) were subjected to treadmill exercise (1–5 km/h) under control conditions and in the presence of single and combined β-adrenergic, 
-adrenergic and muscarinic (M) receptor blockade. Results: Exercise produced a four-fold increase in body O2 consumption, due to a doubling of both cardiac output and the arterio–mixed-venous O2 content difference. The latter resulted from an increase in O2 extraction, from 45±1% at rest to 74±1% at 5 km/h, as the O2 carrying capacity [haemoglobin concentration (Hb)] increased by only 
10%. The increase in cardiac output resulted from a doubling of the heart rate and a small (<10%) increase in stroke volume. The mean aortic pressure (MAP) was unchanged, implying a 50% decrease in systemic vascular resistance (P
0.05). In contrast, exercise had no significant effect on pulmonary vascular resistance. The sympathetic division of the ANS-controlled O2 delivery via β-adrenoceptors (heart rate and contractility) and Hb concentration via -adrenoceptor-mediated splenic contraction. In addition, the sympathetic division modulated systemic vascular tone via - and β-adrenoceptors, but also exerted a vasodilator influence on the pulmonary circulation via β-adrenoceptors. The parasympathetic division controlled O2 delivery in part directly (heart rate) and in part indirectly via inhibition of β-adrenoceptor activity (heart rate and contractility), even during heavy exercise. In addition, the parasympathetic division exerted a direct vasodilator influence on the pulmonary, but not on the systemic, circulation. Conclusions: Thus, in swine, in a manner similar to that in humans, both the sympathetic and parasympathetic division of the ANS contribute to cardiovascular homeostasis during exercise up to levels of high intensity.
KEYWORDS Autonomic nervous system; Exercise; O2 consumption; O2 extraction; Pulmonary circulation; Systemic circulation; Swine