Homeostatic imbalances

1
Homeostatic imbalances

• Pericarditis? inflammation of the pericardium
• Endocarditis? bacterial infection of the
  endocardium can lead to valvular stenosis
• Myocardial infarction? heart attack/coronary
• Heart block? any damage to the AV node results in
  irregular beating of ventricles
• Murmurs? abnormal or unusual hearts sounds

2
ECG normal and abnormal
3
Alterations in Electrocardiogram
Clinical Cardiology Concepts for Vets
4
Cardiac Output

• Cardiac Output - the amount of blood pumped by a
  ventricle per minute. Units may be in milliliters
  or Liters per minute.
• Heart Rate - number of cardiac cycles per minute.
  Average for males 64-72/min. Average for
  females 72-80/min.
• Stroke Volume - amount of blood pumped out of a
  ventricle each beat. Average resting stroke
  volume 70 ml.

5
Cardiac Output

• CO (mL/min) SV (70 mL/beat) X HR (75 beat/min)
• Cardiac output stroke volume X heart rate
  5250ml/min
• SV EDV - ESV
• Stroke volume end diastolic volume end
  systolic volume
• Cardiac reserve is the difference between a
  persons maximum cardiac output and cardiac
  output at rest.

6
Frank Starling Law of the Heart

• The more cardiac muscle is stretched within
  physiological limits, the more forcibly it will
  contract.
• Rubber band analogy
• Increasing volumes of blood in ventricles
  increase the stretch thus the force generated
  by ventricular wall contraction.
• Greater stretch means more blood volume is pumped
  out, up to physical limits.

7
Regulation of stroke volume

• Preload is the degree of stretch on the heart.
• Contractility is the force of ventricular
  contractions.
• Afterload is the pressure that must be exceeded
  to eject blood from the ventricles.
• The Frank-Starling law of the heartpreload is
  the critical factor controlling SV (stroke
  volume).

8
Regulation of heart rate

• When blood volume drops or the heart is weakened,
  SV drops and the HR increases.
• Positive chronotropic factors increase HR.
• Negative chronotropic factors decrease HR.
• Extrinsic regulation by the ANS
• Sympathetic nervous system increases firing of
  the pacemaker and enhances Ca2 entry into heart
  cells.
• Parasympathetic nervous system reduces heart rate
  through ACh which opens K channels.
• Under resting conditions the PNS is dominant

9
Chemical Regulation

• Hormones
• Epinephrine enhances HR and contractility
• Thyroxine enhances effects of Epi and NE and
  leads to slower more sustained increase in HR
• Ions
• Hypocalcemia (Ca2)depresses the heart
• Hypercalcemia prolongs the plateau phase and lead
  to heart irritability
• Hyperkalemia (K) may lead to heart block and
  cardiac arrest hypokalemia leads to arrhythmia
  and weakened contractions.
• Excess Na blocks Ca2 inflow, decreasing
  contractile strength

10
Other Factors

• Exercise leads to a reduced HR when at rest.
• Working large body muscles for at least 20
  minutes elevates cardiac output and accelerates
  metabolism.
• Athletes have a larger heart and a resting HR of
  40-60 beats per minute
• Increased temperature increases heart rate
  decreased temperatures reduce heart rate and
  oxygen needs.

11
Homeostatic imbalances

• Congestive heart failure
• Caused by? Coronary artherosclerosis
• Caused by ? Persistent high blood pressure
• Caused by? Multiple myocardial infarcts
• Left side failure ?Pulmonary congestion
• Rights side failure? Peripheral congestion

12
Angina Pectoris

• Medical term for chest pain due to coronary heart
  disease.
• It occurs when the myocardium doesnt get as much
  blood (Oxygen) as it needs.
• Insufficient blood supply is called ischemia.
• May initially occur during physical exercise,
  stress, or extreme temperatures.
• It is a sign of increased risk of heart attack.

13
Cardiac Arrhythmias

• Arrhythmias? irregular heart rhythms that may
  lead to fibrillation
• Tachycardia Heart rate in excess of 100bpm
• Bradycardia Heart rate less than 60 bpm
• Sinus arrhythmia Heart rate varies 5 during
  respiratory cycle and up to 30 during deep
  respiration
• Premature atrial contractions Occasional
  shortened intervals between one contraction and
  succeeding, frequently occurs in healthy people

14
Aneurysm

• Weakness of the wall of an artery causing an
  abnormal enlargment or bulge.
• The aorta or the arteries that supply the heart,
  brain, legs or kindeys are most commonly affected.

15
Atherosclerosis (Arteriosclerosis)

• Narrowing and hardening of arteries and
  impairment of blood flow due to the deposition of
  fatty materials and calcium in their walls.
• Risk factors include
• smoking
• inactivity
• diabetes
• high blood cholesterol
• personal or family history of heart disease
• Atherosclerosis Animation

16
Resources

• Heart Sounds Cardiac Arrhythmias
• Live Cardiac Exam Video
• Anatomy Links
• Cardiac Cycle
• Cardiac Cycle Graphics
• Interactive Physiology Review
• AP II Notes Homepage

17
Conducting System of Heart