Reflex responses practical

Question 1

What is the importance of an equilibration period before starting blood pressure and heart rate measurements?

Answer 1

Movement and talking can raise blood pressure and heart rate, so need to wait for it to return to resting levels so it is accurate. Waiting for sympathetic activity to reduce and parasympathetic activity to increase.
Without equilibration, the patient might be diagnosed hypertensive, trying to avoid false positives.

Question 3

What happens when you raise the hand above the heart?

Answer 3

This increases venous return because of gravity.
Hydrostatic pressure is reduced because of gravity.
So blood pressure is lower.

Question 4

What happens when you lower the hand to hip level?

Answer 4

Hydrostatic pressure increases because of gravity.
Venous return is reduced.
Blood pressure is increased.

Question 5

What is the effect of the height of the vertical column on blood pressure?

Answer 5

For every 10cm increase above the heart, blood pressure decreases by 8mmHg.
For every 10cm below the heart, blood pressure increases by 8mmHg.

Question 6

How does heart rate change in inspiration and expiration?

Answer 6

Inspiration, increased heart rate due to decreased vagal tone.
Expiration, reduced heart rate, due to increased vagal tone.

Question 7

What happens to heart rate if atropine is given?

Answer 7

Atropine is an antagonist which blocks the parasympathetic vagal action of ACh, so heart rate is increased.
The heart rate does not slow during expiration, so respiratory sinus arrythmia is reduced.
Atropine is used in surgery to reduce fluctuations in heart rate.

Question 8

Why might the changes in heart rate change in respiration until your breathe deeply and slowly?

Answer 8

In normal quiet breathing the pressure changes are small so might not see the changes in heart rate.
In deep inspiration there is a larger decrease in intrathoracic pressure, so greater venous return (respiratory pump) which causes reflex vagal withdrawal and heart rate increases.
In slow expiration, there is increased intrathoracic pressure, so reduced venous return and vagal reactivation, so heart rate decreases.
This shows that parasympathetic modulation is subtle under normal conditions.

Question 9

What happens to heart rate and blood pressure when standing?

Answer 9

Immediate decrease in blood pressure and increase in heart rate.
Heart rate increases to try and counter the decrease in blood pressure so you don’t faint.
After a few minutes these are normalised.

Question 10

Why does blood pressure decrease when standing?

Answer 10

Upon standing there is more effect of gravity, so venous pooling in the legs - more blood in the venous system and less returned to the heart.
This reduces stroke volume and cardiac output, so systolic pressure decreases.

Question 11

Why does heart rate increase when standing?

Answer 11

The baroreceptors detect the fall in ABP, so stimulates the sympathetic system to increases heart rate.
Baroreceptors also causes blood vessels to vasoconstrict which increases total peripheral resistance and therefore blood pressure.

Question 12

What happens to blood pressure and heart rate in someone who has less sympathetic control, on vascular tone, when standing?

Answer 12

Blood pressure decreases very low, which would normally be maintained by baroreflex to ensure perfusion. This person lacks the baroreflex, so heart rate continues to increase to compensate.

Question 13

What happens to blood pressure and heart rate in someone with less sympathetic control, upon crouching?

Answer 13

Crouching, reduces the effect of gravity on blood pressure, so blood pressure increases, and heart rate begins to decrease.
Crouching also constricts the blood vessels which decreases blood flow, and increases total peripheral resistance, and therefore ABP.

Question 14

What is the baroreflex sensitivity assessment?

Answer 14

Plots systolic blood pressure when falling against the heart rate.
The slope of the line shows the sensitivity.
BRS is decreased in emotional and environmental stress, and there is a rest in the operating level in exercise, which are acute changes.
BRS is decreased in heart failure, which is a chronic change.

Question 15

What does the diving reflex achieve?

Answer 15

Conserves oxygen by reducing heart and blood flow to non-essential tissues, maintains brain circulation and oxygenation. Decreases heat loss from the body. Decreases O2 requirements of the heart. Releases blood rich in red blood cells from the spleen so increases O2 carrying capacity of circulation. Supports prolonged immersion.

Question 16

What is the heart rate in the first exposure to ice?

Answer 16

The diving reflex and the alerting/defence response are activated.
The diving reflex activates the vagus nerve which reduces heart rate.
The alerting/defence response increases sympathetic activity which increases heart rate.
In this data, the heart rate looks fairly normal because the reflexes cancel each other out, but there can be different integration of the responses.

Question 17

What is the heart rate in the second exposure to the ice?

Answer 17

The heart rate is further decreased, because there is less activation of the alerting/defence response because it is not a new stimulus, and it has habituated.
If it happens soon after, it might be because peripheral vasoconstriction and splenic contraction have already been activated, so there is a less dramatic decline in heart rate to conserve oxygen.

Question 18

What happens to heart rate if they were exposed to the ice in an expiratory apnoea?

Answer 18

Holding the breath after expiration reduces the lung volume and oxygen stores, so hypoxia develops more quickly.
Pulmonary stretch receptors are not activated, and the inspiratory drive is lost, so the vagus nerve is inhibited.
Accelerates the drive for oxygen conservation, strengthens vagal activity.
So there will be stronger bradycardia (slow heart rate) which is maintained.