cardiac physiology basics for nursing students

1. Applied Cardiac
Physiology
Dr. ASRAF HUSSAIN MBBS MD
DM CARDIOLOGY RESIDENT

2. Learning Objectives
•Understand basic cardiac physiology
•Devise a nursing plan based on disease-
specific hemodynamic goals.

3. The Heart
•It is a hollow muscular organ located in
the center of the chest cavity
(mediastinum) and rests on the
diaphragm

5. Functions
• Transportation of oxygen and other
nutrients to the cells
• Removal of carbon dioxide and
wastes
• Distributes hormones
• Control heat transfer

6. Cardiac Output
Cardiac Output
=
Heart Rate x Stroke Volume
Stroke volume
Volume of blood pumped by each ventricle
in one contraction

7. •CO = HR x SV
•5250 ml/min = 75 beats/min x 70
mls/beat
•Norm = 5000 ml/min
•Entire blood supply passes through body
once per minute.
•CO varies with demands of the body.

8. • CO = SV x HR. SV = EDV – ESV and thus is affected by preload,
afterload and contractility.
ddah.org.uk

9. •Preload reflects the stretch of ventricular
myofilaments produced by the LVEDV.
•Afterload is the pressure against which the LV
must propel blood.
•Contractility is the intrinsic force of
myocardial contraction independent of
preload, afterload, or HR.

10. Regulation of Heart Rate
• Increased heart rate
–Sympathetic nervous system
• Crisis
• Low blood pressure
–Hormones
• Epinephrine
• Thyroxine
–Exercise
–Decreased blood volume

11. The Heart: Regulation of Heart
Rate
s
 Decreased heart rate
Parasympathetic nervous system
High blood pressure or blood volume
Dereased venous return
In Congestive Heart Failure the heart is
worn out and pumps weakly. Digitalis
works to provide a slow, steady, but
stronger beat.

12. Stroke volume usually remains
relatively constant
Starling’s law of the heart – the more that
the cardiac muscle is stretched, the
stronger the contraction
Changing heart rate is the most
common way to change cardiac output

13. The Heart: Cardiac Cycle
 Atria contract simultaneously
 Atria relax, then ventricles contract
 Systole = contraction
 Diastole = relaxation

15. Pulse
 Pulse –
pressure wave
of blood
 Monitored at
“pressure
points” where
pulse is easily
palpated
Figure 11.16

19. Blood Pressure
 Measurements by health professionals
are made on the pressure in large
arteries
Systolic – pressure at the peak of
ventricular contraction
Diastolic – pressure when ventricles relax
 Pressure in blood vessels decreases as
the distance away from the heart
increases

22. Fallacies
•BP is different in each arm: a difference >10 mmHg
(alert)
• Record the highest pressure
•Wrong cuff size: the bladder should be
approximately 80% of the length and 40% of the
width of the upper arm circumference.
•A standard adult cuff - bladder approximately 13 ×
30 cm and suits an arm circumference 22–26 cm.
•In obese patients a standard adult cuff will
overestimate BP, so use a large adult (bladder 16 ×
38 cm) or thigh cuff (20 × 42 cm)

23. •Auscultatory gap: up to 20% of elderly
hypertensive patients have Korotkoff sounds
which appear at systolic pressure and
disappear for an interval between systolic
and diastolic pressure.
• If the first appearance of the sound is
missed, the systolic pressure will be recorded
at a falsely low level.
•Avoid this by palpating the systolic pressure
first

24. •Patient’s arm at the wrong level: the patient’s
elbow should be level with the heart.
Hydrostatic pressure causes ~5 mmHg change in
recorded systolic and diastolic BP for a 7 cm
change in arm elevation. Dependency of the arm
below heart level leads to an overestimation of
systolic and diastolic pressures and raising the
arm above heart level leads to underestimation.
•Terminal digit preference: record the true
reading rather than rounding values to the
nearest 0 or 5

25. •Postural change: the pulse increases by about
11 bpm, systolic BP falls by 3–4 mmHg and
diastolic BP rises by 5–6 mmHg when a
healthy person stands.
•The BP stabilises after 1–2 minutes.
• Check the BP after a patient has been
standing for 2 minutes; a drop of ≥20 mmHg
on standing is postural hypotension

26. •Atrial fibrillation: makes BP assessment
more difficult because of beat-to-beat
variability.
• Deflate the cuff at 2 mmHg per beat
and repeat measurement if necessary.

28. Blood Pressure: Effects of Factors
 Neural factors
Autonomic nervous system adjustments
(sympathetic division)
 Renal factors
Regulation by altering blood volume
Renin – hormonal control

29. Blood Pressure: Effects of Factors
 Temperature
Heat has a vasodilation effect
Cold has a vasoconstricting effect
 Chemicals
Various substances can cause increases or
decreases
 Diet

31. • SVR is the quantitative value for left ventricular afterload
• In patients who are in shock or hypotensive, SVR calculation
helps to differentiate among etiologies and can guide therapy.
• A hypotensive patient with a low SVR may have sepsis, a
patient in cardiogenic shock often has hypotension with an
elevated SVR
• Normal SVR is between 900 and 1440 dyn/s/cm− 5.
SVR in Wood units or mmHg/L/min =(MAP−Right atrial
pressure) /CO
SVR in Woodunits×80=SVR in dyn/s/cm−5
MAP=(SBP+2DBP)/3

32. •Increased SVR can be useful when CO is insufficient
for adequate systemic perfusion pressure with
normal SVR.
•On the other hand, SVR increased beyond that
needed for adequate SAP increases systemic
ventricular afterload and may therefore negatively
affect CO.
•MAP=COxSVR.

33. Alarming signs/symptoms
• Abnormal heart sounds (S3, S4)
• Angina
• Anxiety, restlessness
• Change in level of consciousness
• Crackles, dyspnea, orthopnea, tachypnea
• Decreased activity tolerance
• Decreased peripheral pulses; cold, clammy skin/poor capillary refill
• Decreased venous and arterial oxygen saturation
• Dysrhythmia
• Hypotension
• Increased central venous pressure (CVP)
• Tachycardia
• Weight gain, edema, decreased urine output

34. •Queries ???

35. •Thank You