Acute cardiovascular and the pulmonary responses to exercise stress

Exercise/stress response pathway type

• Fight or flight (sympathetic nervous response)

What is the hypothalamus’ response to stressor of exercise?

• Hypothalamus stimulates pituitary gland

What does APG stimulation do? (2)

Activates two systems:

• Stimulates APG to activate sympathetic nerve pathway to cause adrenaline secretion via adrenal medulla (Sympathetic Adrenal Medullary (SAM) System)

• ACTHrf → stimulates APG to secrete ACTH → to stimulate adrenal cortex to secrete cortisol + other corticosteroids (Hypothalamic Pituitary Adrenal Cortical System)

Sympathetic Adrenal Medullary (SAM) System function (3)

• Rapid mobilisation of metabolic resources.

• Increased cardiac output.

• Heightened energy alertness

Hypothalamic Pituitary Adrenal Cortical System function (3)

• Provides a backup response for long-term stress coping

• Regulates metabolism and immune response

• Assists in returning the body to general homeostasis

Pulmonary system response to exercise (1)

• Increased pulmonary ventilation

How pulmonary ventilation rate is increased (2) + description (2)

1. Respiration Rate: The frequency of breaths per minute.

2. Tidal Volume: The depth of each individual breath.

Resting vs vigorous exercise ventilation rate

State	Ventilation Rate (Approximate)
Resting	6 Litres per minute
Vigorous Exercise	150 Litres per minute

How is blood composition/pH affected by exercise? (2)

• Decreased O2 + increased CO2 → increased acidity/reduced pH

Which chemoreceptors are sensitive to blood conc./pH changes + what effect do they have?

Chemoreceptors in aorta, brain + muscles detect changes → stimulate increased ventilation to replenish O2 + remove CO2

What is the cardiovascular system’s primary role during exercise? What unit is this measured in?

To increase the rate of circulation (increased cardiac output)

What is cardiac output?

Stroke volume x heart rate

Relationship between heart rate and exercise intensity + systems it’s regulated by

• HR increases fairly linearly w/ exercise intensity

• Regulated by the sympathetic nervous system and the suppression of parasympathetic control

What is anticipatory response + what causes it?

• When HR increases before exercise begins

• Neurons in the medulla

Steady state description

Heart rate plateauing when exercise intensity stays the same

Does stroke volume increase during exercise?

Yes

What causes stroke volume to increase during exercise?

Catecholamines

• Adrenaline and noradrenaline stimulate ventricles to contract with more force, reducing end-systolic volume (blood left in the heart after contraction)

Venous return

• The "muscular pump" (contraction of skeletal muscles) and deeper respiration assist in pushing blood back to the heart, leading to more efficient cardiac filling (increased end-diastolic volume)

Max cardiac output table (maybe don’t need to know)

Individual Type	Resting CO	Max Exercise HR	Max Exercise SV	Max Exercise CO
Untrained	~5 L/min	195 bpm	113 ml	22 L/min
Trained	~5 L/min	195 bpm	179 ml	35 L/min
Elite (XC-Skier)	~5 L/min	191 bpm	210 ml	40 L/min

How does blood pressure change during aerobic exercise? (2)

• Systolic blood pressure increases significantly due to forceful heart contractions

• Diastolic blood pressure remains stable/drops slightly as blood vessels in muscles dilate to allow blood flow

How does blood pressure change during strength training? (1)

Blood pressure responses can be exaggerated, with readings as high as 300/180 mmHg observed

Distribution of blood supply at rest: viscera vs skeletal muscle vs heart vs skin

• High (greatest supply)

• 15-20%

• Constant

• Low

Distribution of blood supply during moderate exercise: viscera vs skeletal muscle vs heart vs skin

• Decreasing

• Increased

• Increased

• Increasing (for heat regulation)

Distribution of blood supply during max exercise: viscera vs skeletal muscle vs heart vs skin

• Decreased

• Increased

• Increased

• Decreased (due skeletal muscle ‘competing’ for blood supply)