Heart rate responses to exercise in a unique populations cardiovascular physiology. Flashcards
Compare the heart rate response to exercise in the individuals with quadriplegia and heart transplantation. How does the absence of cardiac parasympathetic innervation affect the heart rate response to exercise?
The individual with heart transplantation does not have a rapid rise in heart rate at the onset of exercise because the heart has no significant autonomic innervation. The rise in heart rate is due to the effect of circulating catecholamines. The individual with quadriplegia has an initial rapid rise in heart rate due to the withdrawal of cardiac parasympathetic efferent activity; however, heart rate does not rise further because of the absence of cardiac sympathetic efferent activity.
Compare the maximum heart rate response to exercise in the individuals with quadriplegia and
heart transplantation. What accounts for the similarity in maximum heart rate?
The maximum heart rate responses in the individual with quadriplegia and heart transplantation are similar because the maximum increase in heart rate in both individuals is due to the effect of circulating catecholamines.
What factors contribute to the increase in heart rate in the individuals with quadriplegia and heart transplantation?
Factors that contribute to the increase in heart rate in the individual with quadriplegia are withdrawal of the parasympathetic tone and the effect of circulating catecholamines, whereas only the circulating catecholamines contribute to the increase in heart rate in the individual with heart transplantation. At this point it is important to note that circulating catecholamines (norepinephrine and epinephrine) increase heart rate by activating β1-adrenergic receptors on the sinoatrial node.
Compare the heart rate response to exercise in the individual with heart transplantation with the sedentary individual. How would the absence of cardiac innervation affect the heart rate response to exercise?
The sedentary individual has an initial rapid increase in heart rate due to withdrawal of cardiac parasympathetic efferent activity and a further increase to an age-dependent maximum due to an increase in cardiac sympathetic efferent activity. There is no rapid rise in heart rate at the onset of exercise in the individual with heart transplantation because of absence of cardiac parasympathetic innervation; the rise in heart rate occurs because of the effect of circulating catecholamines.
Compare the resting heart rate, slope of the increase in heart rate, and maximum heart rate in the sedentary and athletic individuals. How are they different? What accounts for this difference?
Autonomic adaptations associated with chronic endurance training result in an enhanced cardiac parasympathetic efferent activity, and therefore the athlete has a resting bradycardia. Note that the heart rate response at similar workloads is lower in the athlete compared with the sedentary individual; however, both individuals achieve a similar age-dependent maximum heart rate.
