Most conceptual models of the organization of the cardiovascular system begin with the premise that the nervous system regulates the metabolic and nonmetabolic reflex adjustments of the circulation. These models assume that all the neurally mediated responses of the circulation are reactive, i.e., reflexes elicited by adequate stimuli. This target article suggests that the responses of the circulation are conditional in three senses. First, as Sherrington argued, reflexes are conditional in that they never operate in a vacuum but in a context together with other reflexes. Guided by functional utility, they interact rather than add. Second, as Pavlov argued, stimuli acquire meanings as a result of experience. This notion of stimulus effect plus the Sherringtonian notion of conditionality suggest that association is one of the ways stimuli eliciting cardiovascular reflexes acquire their meanings and thus their relative strengths. Finally, as Skinner and others have argued, operants are responses that act upon the environment to obtain consequences – that is, stimuli. As operants, cardiovascular responses fulfill a major biological need, functioning proactively. The cardiovascular response is an integral component of the animal's behavior regardless of whether it is an elicited reflex or the eliciting stimulus acquired its properties as a result of the genetic inheritance of the animal or through experience, or the cardiovascular response is emitted in anticipation of an environmental consequence. The main theses of this essay are: (1) behavior is an integrated set of responses and the circulation is one of the response systems comprising behavior; (2) behavior is, in part, determined by its functional significance within a context; (3) the contextual factors operative at the time of the behavior have a major role in determining which of the set of possible responses will determine the final act, that is, which behavior will be the effective response and which other behaviors will be concomitants.

Changes in heart rate, systolic, diastolic and mean blood pressure were measured after extubation in 60 ASA Grade I and II patients to assess the effects of diltiazem (0.2 mg kg−1), verapamil (0.05 mg kg−1) and metoprolol (0.02 mg kg−1) given as a bolus 2 min before tracheal extubation. All the haemodynamic variables measured increased significantly after extubation in the control and diltiazem groups when compared with the base-line recordings (P<0.05). Metoprolol effectively blocked the increases in heart rate after extubation and the increase in blood pressure in this group was less when compared with the control group (P<0.05). Verapamil alleviated the increase in both heart rate and blood pressure. However, profound hypotension and bradycardia requiring therapy, occurred in the verapamil group. For this reason, careful observation is necessary when using variverapamil and the routine use of this drug in patients with coronary artery disease requires further studies.

There is indirect evidence from previous studies that the physiological responses to a liquid test meal may differ from those seen after consumption of a solid meal. The aim of the present study was to determine the metabolic and cardiovascular responses to isoenergetic high-carbohydrate mixed nutrient liquid or solid test meals, providing 2.1 MJ (approximately 70% of which was from carbohydrate), in eight healthy men following an overnight fast. Metabolic rate increased significantly after both meals (P < 0.0001, time effect), but the increase was significantly greater after the solid than after the liquid test meal (0.40 (SE 0.14), 0.26 (SE 0.10) kJ/min respectively, P = 0.001). The respiratory exchange ratio increased significantly after both the liquid and solid test meals, with no significant differences between them. Forearm blood flow increased significantly after the liquid test meal (0.70 (SE 0.33) ml/100 ml per min, P < 0.0001), whilst it decreased after the solid meal (−0.28 (SE 0.16)ml/100ml per min, P< 0.0001). Heart rate increased on both occasions, but the response was significantly greater after the solid meal (P=0.02). There were no significant plasma noradrenaline responses, but there were significantly higher increases in serum insulin and blood glucose following the solid meal. Thus, the physical form of a test meal affects the physiological responses to nutrient ingestion.