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Which of the following is TRUE concerning pediatric physiology?
A. An increase in heart rate will increase contractility in an infant
B. Neonatal cardiac circulation is a parallel circuit
C. Extremes of heart rate are well tolerated in neonates
D. Neonates mainly increase cardiac output by increasing afterload
Answer
The answer is A.
I know, crazy. It is not intuitive as to why changes in heart rate alter contractility. The mechanism is known as the force-frequency relationship. Anderson and others conducted experiments using controlled loading conditions with changes in heart rate. They noted an increase in stroke volume with an increases in heart rate (at constant load conditions).Therefore, an increase in heart rate increased contractility. Thus, an increased heart rate improves contractility. This increase in contractility with an increase in heart rate is due to the increase in intracelluar calcium. In the human population, this force-frequency relationships is most likely minimal at birth, but increases in infancy.[1][2][3]]
Notes
- ↑ Anderson, P. A., et al. "The effect of heart rate on in utero left ventricular output in the fetal sheep." The Journal of Physiology 372.1 (1986): 557-573.[1]
- ↑ Parilak, Leonard D., et al. "Contribution of frequency-augmented inward Ca2+ current to myocardial contractility." Canadian journal of physiology and pharmacology 87.1 (2009): 69-75.[2]
- ↑ Wiegerinck, Rob F., et al. "Force frequency relationship of the human ventricle increases during early postnatal development." Pediatric Research 65.4 (2009): 414-419.[3]
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