Blockade of beta-1 receptors will have what effect on cardiac output?

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The question asks: Blockade of beta-1 receptors will have what effect on cardiac output?

Option 1: 'No change' — This is unlikely. Beta-1 receptors, when stimulated, increase heart rate (chronotropy) and contractility (inotropy). Blocking them removes this stimulatory effect, so heart performance is typically reduced, leading to at least some change in cardiac output rather than none.

Option 2: 'Varies depending on individual' — Individual differences can influence baseline autonomic tone or compensatory mechanisms, but the primary pharmacologic action of beta-1 blockade is to reduce heart rate and contractility. While magnitude may vary among individuals, the direction of effect on cardiac output is generally toward reduction, not unpredictable variation to the point of consistent increase. This makes the statement incomplete as a general rule.

Option 3: 'Decrease' — This aligns with the fundamental physiology. Beta-1 receptor blockade decreases heart rate (negative chronotropy) and decreases myocardial contractility (negative inotropy). With lower stroke volume and often a reduced heart rate, cardiac output (CO = heart rate × stroke volume) tends to fall. In most clinical scenarios, especially at rest, CO decreases.

Option 4: 'Increase' — This contradicts the primary effects of beta-1 blockade. Blocking beta-1 receptors lowers heart rate and myocardial contractility; there is no direct mechanism by which this would reliably increase cardiac output. An increase would be expected only in negligible or very specific, counter-regulated circumstances, which are not the general outcome.

Summary reasoning: Among the options, the most physiologically consistent outcome of beta-1 blockade is a decrease in cardiac output due to reduced heart rate and reduced contractility. The other choices either imply no change, variable direction, or an opposite effect that contradicts beta-1 pharmacology.

BIOL 251 Clinical Connections 7: Under Pressure

Blockade of beta-1 receptors will have what effect on cardiac output?

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