HB101 Lecture Notes - Lecture 2: Cardiovascular Disease, Cardiac Cycle, Blood Vessel
HPE110-Lecture 2
Part 2
• Describe the control of HR
• Describe the relationship between HR, SV and Q
• Describe the factors influencing SV
• Understand the circulatory adjustments that occur during exercise
Humoral Control of HR
• Circulating hormones in the blood can influence HR
• Epinephrine and norepinephrine are powerful hormones that increase HR
• Thyoid hooe ↑H‘
• ↑Body Tep also auses the “A ode to dishage oe uikly ieasig H‘
Peripheral Input
• Modification of HR as a result of input received from:
• Muscle chemoreceptors (eg. d/t K+, La-)
• Arterial chemorecptors (d/t Δ O2, CO2, pH)
• Specific mechanoreceptors
– provide feedback to the CNS to regulate blood flow and pressure.
• E.g. Baroreceptors in the aortic arch and carotid sinus and
cardiopulmonary mechanoreceptors
Heart Rate
• Is high at birth i.e. 140 bpm at rest.
• Is lower at adolescence e.g. 70 – 80 at rest.
• Resting HR rises again as you get older
• Maximal HR decreases with age
– (the rule of thumb 220 – age is the usual estimate).
Stroke volume and Cardiac Output
• Stroke Volume (SV) = Volume ejected per beat
• Cardiac output abbrev.
– Or sometimes CO
– Cardiac Output ( ) = HR x SV (ml/min or L/min)
Cardiac Output
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Fick Equation
• Understand Fick principle:
– VO2 = Q(CaO2 – CvO2)
– VO2 = HR x SV (CaO2 – CvO2)
• The volume of oxygen consumed by the cells is equal to the cardiac output
multiplied by the amount of oxygen extracted from the blood
Whats VO2?
• The volume of oxygen consumed by the cells
• Consumed or used, not inhaled
• Units are usually l/min or ml/kg/min
• Resting VO2 is 1 met = 3.5ml/kg/min
Cardiac Output
• Can be determined using the Fick Equation if we know the a-vO2 and VO2
Q = VO2 (ml.min-1) x 100
a-vO2 (ml.dL-1)
e.g ml.min-1
Cardiac Output
• Carbon dioxide re-breathing method
• Q = VCO2
v – aCO2
Cardiac Output and Exercise
• Musles ad ogas euied ↑BF
• ↑BF a esult fo edistibution from
non-working muscles and organs and/ or
↑Q
• SV = EDV – ESV
– EDV = End Diastolic Volume
– ESV= End Systolic Volume
• ↑ diastoli olue ↑ “V =“taligs la
Starlings Law of the heart.
• Intrinsic control of SV
• The “V ↑ i espose to a ↑ i the olue of lood pio to otatio
– Cardiac muscle increases its strength when stretched
– Cardiac m. is similar to skeletal m. in that in its resting state its length is less
than that which yields maximal tension
• And marked over stretch results in decreased tension
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Stretch tension relationship
Factors that increase EDV
• Ay fato that ↑ eous etu o slows HR
– Produces greater ventricular filling
– ↑EDV = ↑steth = ↑foe of otatio = ↑“V
– Note effet of ↓H‘ ith training
Regulation of cardiac output
Extrinsic Control of SV
• ↑ “N“ atiity ad oepiephie elease
– ↑ otatility
– ↑H‘
• ↑ Cotatility
– Important because diastolic filling time is significantly reduced at very high
heart rates
Changes in the Cardiac cycle during exercise
% Time spent in Diastole
At rest 0.5/0.8 =
62.5%
During Exercise
0.13/0.33 = 39%
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Document Summary
Part 2: describe the control of hr, describe the relationship between hr, sv and q, describe the factors influencing sv, understand the circulatory adjustments that occur during exercise. Humoral control of hr: circulating hormones in the blood can influence hr, epinephrine and norepinephrine are powerful hormones that increase hr, thy(cid:396)oid ho(cid:396)(cid:373)o(cid:374)e h , body te(cid:373)p also (cid:272)auses the a (cid:374)ode to dis(cid:272)ha(cid:396)ge (cid:373)o(cid:396)e (cid:395)ui(cid:272)kly i(cid:374)(cid:272)(cid:396)easi(cid:374)g h . Peripheral input: modification of hr as a result of input received from, muscle chemoreceptors (eg. d/t k+, la-, specific mechanoreceptors. Provide feedback to the cns to regulate blood flow and pressure: e. g. Baroreceptors in the aortic arch and carotid sinus and cardiopulmonary mechanoreceptors. Is high at birth i. e. 140 bpm at rest. Is lower at adolescence e. g. 70 80 at rest: resting hr rises again as you get older, maximal hr decreases with age (the rule of thumb 220 age is the usual estimate).
