Haemorrhage, fainting and exercise

Question 1

What’s the word to describe severe blood loss that reduces blood volume? Explain the process

Answer 1

Hypovolaemia
- Reduction in venous return
- Reduction in CO
- Reduction in MAP
- Reduction in perfusion of regional circulations —> circulatory shock

Question 2

Which pressure value determines types of shock?

Answer 2

• > 45 mmHg = nonprogressive/compensatory shock —> bodily compensatory mechanisms cause full recovery
• <45 mmHg = progressive shock —> without therapy, shock worsens until death (vicious cycles)

Question 3

Baroreceptor/vascular and chemoreceptor reflexes during haemorrhage:
- Initial haemorrhage and reduction in ___ triggers ___ reflexes initiated by ___ and other ___ receptors (systemic arteriolar constriction increases ____, ___ of veins and venous reservoirs helps to maintain adequate ___, HR increases from ~___ bpm to ~___ bpm)
- ___ intensity doesn’t increase past MAP < 60 mmHg (peak) —> inadequate blood flow (reduction in ___) strongly stimulates ___ —> further enhancement of ____
- ___ also increases ___ —> promotes ___ by reducing ___ pressure (___ pump)

Answer 3

• MAP, sympathetic, arterial baroreceptors, vascular stretch, TPR, constriction, venous return, 60, 180
• Baroreceptor reflex, PO2, peripheral chemoreceptors, peripheral vasoconstriction
• Chemoreflex, rate/depth of respiration, venous return, intrathoracic, respiratory

Question 4

Explain what causes the second plateau when MAP falls to ~50 mmHg

Answer 4

• Caused by activation of CNS ischaemic response resulting from reduction in PO2 and increase in PCO2 in the brain —> extreme stimulation of SN system —> vasoconstriction and cardiac contractility
• Last ditch response to try to prevent any further reduction in MAP

Question 5

• Reduced ___, increased ___ and reduced ____ all decrease capillary hydrostatic pressure
• Promotes reabsorption of large quantities of ____
• Colloid osmotic pressure of plasma ____ due to dilution of blood by tissue fluid (lower [protein])

Answer 5

• MAP, TPR, venous pressure
• Interstitial fluid
• Decreases

Question 6

Renal salt and water conservation:
- Reduction in MAP reduces _____
- Reduction in MAP increases ____: increased production of ___ stimulates releases of ___ from ___ cortex, increased ___ in ___
- ____ promotes renal water reabsorption —> release stimulated by ___ and ___ receptors (___ = potent ___ secreted by the pituitary in response to haemorrhage)

Answer 6

• renal glomeruli filtration rate
• renal sympathetic nerve activity, angiotensin II, aldosterone, adrenal, salt and water reabsorption, nephrons
• ADH (vasopressin), baroreceptors, vascular stretch, ADH, vasoconstrictor

Question 7

Sympathetic reflexes stimulate release of ___ and ___ from adrenal medulla –> reinforces effects of SN activation

Answer 7

• adrenaline and noradrenaline

Question 8

Compensatory mechanisms:
- ___ become maximally activated within 30-60 sec after haemorrhage
- ___ and ___ mechanisms require 10-60 min to respond completely
- Readjustment of blood volume by ___ from interstitial spaces and intestinal tract may require 1-48 hours

Answer 8

• Sympathetic reflexes
• Angiotensin and vasopressin
• Absorption of fluid

Question 9

Explain progressive shock of cardiac failure

Answer 9

Question 10

Explain progressive shock of increased tissue hypoxia

Answer 10

Question 11

Explain progressive shock of acidosis

Answer 11

• Reduced O2 delivery —> increased cellular production of acidic metabolites (lactic acid)
• Impaired kidney function —> slows excretion of H+
• Reduction of pH in blood
• Metabolic acidosis —> further depresses cardiac function and reduces vasoconstriction by decreasing sensitivity to noradrenaline

Question 12

Explain progressive shock of CNS depression

Answer 12

• Reduction in cerebral perfusion —> depresses activity of cardiovascular control centres —> further reduction in sympathetic outflow

Question 13

Explain progressive shock of sludged blood

Answer 13

• Small blood vessels: acidosis causes blood agglutination —> small blood clots —> very small plugs in small vessels (sludged blood)
• Further acidosis —> cellular release of thromboxane A —-> further platelet aggregation

Question 14

Explain progressive shock of endotoxin release

Answer 14

• Macrophages in the liver detoxify endotoxins release into circulation by intestinal bacteria
• Shock —> depresses their phagocytic activity —> increased levels off endotoxins = widespread vasodilation (septic shock) —> depresses cardiac function

Question 15

Answer 15

Question 16

Most syncotic episodes are caused by ___ or ___
- ___ caused by low arterial ___ levels
- ___ caused by low ___ —> not sufficient to perfuse cerebral circulation

Answer 16

Hypoxia or hypotension
- Hypoxia, PO2
- Hypotension, MAP

Question 17

Explain the process of vasovagal syncope + possible triggers

Answer 17

Variety of triggers (heat exposure, sight off blood or having blood drawn, intense fear or emotional shock) stimulate the NTS:
- Activation of vagal centre of medulla —> reduced HR
- Inhibition of spinal sympathetic nerves —> reduced vasoconstrictor tone
- Rapid fall in MAP —> reduced blood flow to brain —> loss of consciousness

Question 18

Explain orthostatic hypotension
- Sudden but transient drop in ___ caused by ________ —> gravity causing rapid movement of ___ from abdomen/thorax into legs —> decreased ___ —> decreased ___ —> decreased ___ —> ___
- ___ rapidly restores normal MAP
- Can cause ___ in people who have ___, ___ or medication (____)

Answer 18

• MAP, rapid movement from standing to sitting position, venous blood, venous return, CO, MAP, head rush/dizzy
• Baroreceptor reflex
• syncope, chronic hypotension, hypovolaemia, alpha1 blockers

Question 19

Anticipation/initiation of exercise inhibits ___ impulses to heart and increases ___ —> immediate increase in ___ and ___ —> increased ___

Answer 19

• Vagal, sympathetic discharge, myocardial contractility and tachycardia, CO

Question 20

Explain what happens when SN is stimulated during exercise:
- ___ of skin; ___ and ___ circulation diverts blood flow from these regions (up to 2 L/min of extra blood flow diverted to active muscles and heart)
- ___ prevents constriction in cerebral and coronary circulation
- Increase in circulation ___ released by adrenal medulla —> enhances effects of ___ stimulation

Answer 20

• vasoconstriction, splanchnic and inactive muscle
• functional sympatholysis
• catecholamines, SN

Question 21

Vascular responses to exercises:
- Myocardium and active muscles: local production of ___ triggers vaasodilation, increasing blood flow to these regions (active ___)
- Vasodilation also opens ___ that were closed at rest due to sympathetic ___
- As body temperature rises: ______

Answer 21

• vasodilatory metabolites, active hyperaemia
• additional capillaries, tone
• vasodilation in skin circulation assisted by stimulated by sweat production —> promotes heat loss

Question 22

Explain what happens to CO, HR and SV during exercise

Answer 22

• CO = HR x SV
• Increased CO is due mainly to tachycardia
• Increased intensity of exercise —> HR increases to max 180 bpm
• SV doesn’t increase much because tachycardia reducing filling time —> decreases EDV

Question 23

Increased venous return moves blood from ___ to heart and into ___ —> increases ___, ___ and ___

Answer 23

capacitance vessels, arterial system, EDV, SV, CO

Question 24

Factors that increase venous return during exercise

Answer 24

1. SNS-induced vasoconstriction of venules in tissues/muscles moves additional blood toward heart
2. Contracting skeletal and respiratory muscles pump venous blood back to heart, valves in vein prevent back flow
3. Increased depth/rate of ventilation decreases intrathoracic pressure —> increasing blood flow into thoracic cavity (increased ΔP)

Question 25

Explain what happens to TPR in different types of exercise

Answer 25

• MAP = CO x TPR (CO always increases, TPR depends on type of exercise)
• Intense exercise using few muscles (weightlifting): vasodilation in those muscles + vasoconstriction in inactive muscles —> large increase in TPR —> MAP can increase to 170 mmHg
• Whole-body exercise (running, swimming): vasodilation in large masses of active muscle —> TPR decreases during exercise + slight rise in MAP as effect of increased CO predominates. Vasoconstriction in inactive muscles prevents major drop in TPR

Question 26

Exercise causes a greater increase in ___ pressure than ___ pressure —> caused by ___

Answer 26

• systolic, diastolic
• caused by increased SV —> pulse pressure increases during exercise

Question 27

Explain what happens on cessation of exercise

Answer 27

• HR and CO are quickly reduced, accumulation of vasodilatory metabolites keeps TPR low
• MAP may fall briefly until corrected by baroreceptor reflex

Question 28

Equation of VO2

Answer 28

VO2 = HR x SV x (PaO2 - PvO2) where a = arterial and v = venous

Question 29

• ___ levels fall rapidly in contracting muscle as additional O2 is consumed
• Unloading of O2 is facilitated by ___ of oxyHgb curve —> increase in ___, ___ and ___ + decrease in ___
• ___ increases

Answer 29

• PO2
• right shift, temperature, [2,3 DPG], pCO2, pH
• (PaO2 - PvO2) —> arteriovenous O2 difference

Question 30

Explain what happens during severe exercise

Answer 30

• Anaerobic respiration increases [lactate] and arterial pH falls (acidosis) —> anaerobic threshold —> stimulates very high rate of ventilation via chemoreceptors
• Beyond anaerobic threshold, reduction in tissue pH determines exercise tolerance (muscle pain, exhaustion)

Question 31

Explain results in regular exercise and fitness

Answer 31

Regular exercise results:
- Improved capacity to deliver O2 to active muscles
- Improved utilisation of O2 by muscles
- Progressive increase in VO2 Max

Fitness:
- Lower HR, increased SV (increased ventricular filling) —> higher vagal tone, lower sympathetic tone
- Decreased TPR: capillary density in muscles increases, improved endothelial function (increased production of NO)
- Improved extraction of O2 from blood (increased arteriovenous difference due to increased of size and number of mitochondria)