• Anatomical review
• Requirements for effective pumping
• Cardiac cycle
• Cardiac output
• The Fick principle

Please review the image below. Note correct path of blood flow, names of chambers and valves, etc.

Cardiac conduction anatomy

The heart as a “functional syncytium” (i.e. acting as one synchronous unit) with a specialized conducting system.

Key features:

SA Node: right atrium near superior Vena cava. Intrinsic pacemaker

AV Node: right atrial septum. Slow conduction causes a delay

Bundle of HIS: enters IV septum. Splits to...

Right and left bundle branches

Purkinje fibers: allow for rapid depolarization of the ventricles

5 Requirements for effective cardiac pumping

• Contractions of individual cardiac cells must occur at regular intervals and be synchronized.
• Valves must open fully (not stenotic)
• Valves must not leak (not be insufficient or regurgitant)
• Muscle contraction must be forceful (not failing)
• Ventricles must fill adequately during diastole

Cardiac Cycle Fig 11.4. Review the left heart pressures and volumes. Know these terms:

Systole Diastole Isovolumetric contraction Isovolumetric relaxation

Cardiac Output (Q)

What’s the equation?

Q = HR x SV

Q = HR x (EDV-ESV)

Ejection Fraction

EF = (SV/EDV) x 100

Fick Principle Applied to VO2 max

Equation: VO2 (ml/min) = Q (L/min) x a-vO2dif (ml/L)

Example:

• SV = 120 ml/beat
• HR = 200 bpm
• [Hb] is 15 g/dl and 100% saturated on arterial side
• Venous O2 concentration is 6 ml/dl

What’s the Q?

• 200 bpm x 120 ml/beat = 24,000 ml/min = 24 L/min

What’s the a-vO2 dif?

• arterial O2 = 15 gHb/dl x 1.34 mlO2/g = 20.1 ml/dl
• a-vO2 dif = 20.1 ml/dl – 6 ml/dl = 14.1 ml/dl
• Convert to ml/L…14.1 ml/dl x 10 dl/L = 141 ml/L

VO2 (ml/min) = 24 L/min x 141 ml/L = 3384 ml/min

For next time:

Read the first journal club article (Atrial Fib and Exercise). Janice will do a sample journal club presentation then assign you to your learning teams. Don't miss it!