Cardiovascular Response to Exercise

Mean Arterial Pressure and Isometric Exercise

During isometric exercise, diastolic blood pressure rises quickly due to the pressure reflex.
This is different from dynamic exercise.

During dynamic exercise (e.g., running), systemic vascular resistance (SVR) drops.
This is a critical point often underappreciated in exercise physiology.
The decrease in SVR is due to vasodilation in active muscle tissue.

Active Tissue (Skeletal Muscle):
- Vasodilates due to accumulating metabolites: hydrogen ions (H^+), increased partial pressure of carbon dioxide (P{CO2}), and extracellular potassium (K^+).
- Metabolites cause local vasodilation, reducing resistance.
Inactive Tissue (Spleen, Gut, Kidney):
- Vasoconstriction occurs, increasing vascular resistance.
- Mediated by the sympathetic nervous system.
- Blood flow is reduced in these areas, allowing redistribution to working muscles.

During isometric contractions, metabolites accumulate rapidly due to a lack of oxygen delivery.
Blood flow is physically occluded by muscle fiber pinching.
Even though metabolites signal for vasodilation, it doesn't occur because blood vessels are compressed and can't dilate.

Accumulating metabolites send signals to the spinal cord which then communicates with medulla.
These signals indicate insufficient oxygen delivery and waste removal.
The medulla responds by increasing sympathetic outflow, leading to:
- Increased heart rate.
- Increased vasoconstriction.
- Increased blood pressure.

Experiments involving dorsal root causeotomy (cutting spinal sensory nerves) in animals reveals that it attenuates the rise in blood pressure during similar activities.
This suggests that chemoreceptors and metabolites accumulating in the muscle contribute significantly to the medullary response.
Cutting the dorsal horns reduces sensory feedback, diminishing the rise in blood pressure.