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Pumps
Positive and negative pressure operation
Hearts and accessory pumps
Valves: Devices for Unidirectional
Flow
Opened
hi gh p ressu re
Closed
mu scl e fo rce
hi gh
pre ssure
mu scl e fo rce
Functional Aspects of Hearts
Force generation (“myocardium”)
Directionality (valves)
Coordination
Myocardial and Nodal Cell
Potentials
Membrane Potential, mV
+40
typical myocardial cell
typical SA nodal
cell
0
-40
resting
membrane
potenital
threshold
threshold
-80
maximum
diastolic
potential
knp
Time
spontaneous
depolarization, also
called the pacemaker
potential
Preferential Bioelectrical Pathways
SA Node
Bachmann's Bundle
AV Node
LA
RA
RV
knp
Purkinje FIbers
LV
Left and Right
Bundle Branches
(Bundles of His)
EC Coupling in the Myocardium
Membrane Potential, mV
+40
0
-40
-80
knp
period of systole
Time
Atrial Conduction
The AV Node
Atrial Side
A V Node
Ventricular Side
knp
atrial myocardium
(fast conduction)
Nodal Cells
Bundles of His
(fast conduction)
Ventricular Conduction
Autonomic Effects on Chronotropicity:
1. Parasympathetic Effects
Parasympathetic (mediated via X cranial (vagus) nerve)
Receptor: muscarinic (inhibitory)
Agonists -- ACH, muscarine, carbachol -- all have
negative chronotropic effects and slow rate from what it
would have been
Antagonists: atropine -- block negative chronotr. effect.
Autonomic Effects on Chronotropicity:
2. Sympathetic Effects
Sympathetic (mediated via “accelerator” nerve and epinephrine).
Receptors: 1 (NE from accelerator) and 1epinephrine.
1
• Agonists: NE and phenylepherine -- both have weak positive
chronotropic effects.
• Antagonist: phenoxybenzomine has a very slight negative or
no chronotropic effect.
1
• Agonists: E, isoproterenol (isupryl) and ephedrine all have
strong positive chronotropic effects.
• Antagonists: propranolol (inderal) -- blocks positive
chronotr. effect.
Nodal Cells and Chronotropicity
Fick’s Principle for Determination
of Cardiac Output
Is there a non-invasive way to determine cardiac output?


V O2  Q(CaO2  CvO2 )


VO 2
Q
(CaO2  CvO2 )
The Frank-Starling Law of the
Heart
Systolic
Pressure,
Force, or
Tension
knp
Diastolic Pressure, Tension, Force, or Length
The Autonomic NS and Ionotropic Effects
Parasympathetic -- no direct effect, indirect effect
only (covered later).
Sympathetic -- strong ionotropic effect (think about
what happens when you are scared).
• Therefore, alpha- & beta-agonists (e.g. epinephrine
and isoproterenol) will have a strong positive
ionotropic effect (and increase electrical
excitability).
• β -blockers (propranolol (inderal)) will generally
cause a decrease in contractile force and stroke
volume (and electrical excitability) as they block the E
that is normally present.
The Effect of Epinephrine on
Contractility
Systolic Pressure
knp
increasing
sympathetic
stimulation
Diastolic Pressure
Cardiac Work Loop
E
150
rapid ejection
125
Pressure,
mHg
100
F
D
75
50
isovolumic
contraction
isovolumic
relaxation
C
A
25
knp
50
75
Ventricular Volume
B
100
125
isovolum.
atrial contract.
rapid
systole
ejection
120
isovolum.
rapid
relax.
reduced
ventric.
ejection
filling
aortic semilunar closes
aortic
semilunar
opens
Pressure
(mm Hg)
reduced
ventric. filling
aortic pressure
80
left ventricular pressure
40
mitral valve closes
mitral valve opens
left atrial pressure
0
4
Aortic
Blood
Flow
(L/min.)
2
0
Ventr.
Vol.
(ml)
38
32
26
20
1
4
Heart
Sounds
2
3
R
EKG
T
P
P
Q
0
knp,
after Berne and Levy, Fig. 29-12,
Physiology. Mosby, 1983
S
0.4
Time (seconds)
0.8
Summary:
the Timing
of
Mechanical
and
Electrical
Events