Wigger’s Diagram Worksheet

 

The objective of this lab exercise is to help students better understand the events of the cardiac cycle including heart sounds, electrical events, flow, changes in pressure, and changes in ventricular volume.  Special attention will also be made to the timing of these events during low (resting) and moderate (exercise) heart rates. These events are sometimes collectively referred to as the “Wiggers’ Diagram”.  In this lab we will not be able to directly record and measure all of these elements.  However, in some cases we can make deductions from related measurements as well as a few educated estimates based on available knowledge to help us fill in the gaps. 

We will be using an EKG, limb lead II to monitor electrical events of the cardiac cycle.  We will be using a phonocardiogram to monitor heart sounds.  We will be using impedance cardiography to record an aortic flow tracing (dz/dt, change in impedance/change in time) and to determine stroke volume. We will determine arterial blood pressure using a blood pressure cuff, sphygmomanometer, and stethoscope.

            After the instructor has hooked up the subject, and the subject has been resting in a seated position for at least a minute, start the recording and record for 20-30 seconds.  After recording, the signal will be processed so that stroke volume can be calculated from the changes in impedance on the recording.

            Where drawings are required during this lab exercise, timing is critical. All drawing will be made on the diagram. Use vertical lines #1-4 on the diagram to help you align these events and use horizontal lines A-E to help you understand pressure and volume changes in the cardiac cycle.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Eugene Braunwald. Circulation Research: Reflections on the Founding Editor, Carl J. Wiggers. Circ. Res. 92: 253-254, 2003

 

Reeves, J. T. Carl J. Wiggers and the pulmonary circulation: a young man in search of excellence . Am J Physiol Lung Cell Mol Physiol . 274: L467-L474, 1998


Procedures

 

Experiment #1 – getting to know the Wiggers’ Diagram

1.      Draw the EKG and label the P, QRS, and T waves

 

2.      Draw the heart sounds and label the first (S1), second (S2) heart sounds.  If the third and/or fourth (S3 and S4) are observed, record them as well.

 

3.      Draw the aortic flow curve. Note that aortic flow begins to go increase shortly after S1 and is back to its low point at S2.

 

4.      Take your subject’s blood pressure

a.       SBP = ______________

b.      DBP = _____________

 

5.      Draw an estimate of the aortic pressure curve using the following guidelines.

a.       Arterial pressures are only slightly lower than aortic pressures, so our blood pressures will provide us with an estimate of aortic pressures, with SBP reflecting the peak aortic pressure and DBP reflecting the lowest Aortic pressure.

b.      The peak aortic pressure (estimated by SBP) should be between S1 and S2, and will occur near the beginning of the T wave or the peak of the aortic flow curve.  Record the SBP on the Y axis.

c.       The lowest aortic pressure (as estimated by the DBP) should occur just before the aortic valve opens, which is approximately when the aortic flow begins to increase (shortly after S1).

 

6.      Draw an estimate of the atrial pressure curve using the following guidelines. 

a.       For our purposes, the pressures in the atria will vary only slightly, remaining close to 10 mmHg, and increasing slightly and momentarily  beginning mid-way through the P-wave.

 

7.      Draw an estimate of the ventricular pressure curve using the following guidelines. 

a.       Ventricular pressure starts slightly below atrial pressure

b.      Ventricular pressure begins to increase during the QRS and exceeds atrial pressure at S1.

c.       Ventricular pressure exceeds aortic pressure when aortic flow begins to increase (near end of S1).

d.      The peak ventricular pressure in a normal heart exceeds aortic pressure by only a few (~1-3 mmHg) during the ventricular ejection period. This peak is approximately near the peak aortic flow and the beginning of the T-wave.

e.       Ventricular pressure falls below aortic pressure at S2 (when aortic flow falls back to its low point)

f.       Ventricular pressure falls below atrial pressure shortly after the end of S2, and slightly before S3, if the third heart sound is observed.

 

 

 

 

 

 

8.      Determine stroke volume using the impedance recording.

a.       SV = _____________

 

9.      Estimate EDV and ESV

a.       Ejection fraction (EF%) is stroke volume divided by end diastolic volume and is considered normal if it is over 55%, but most young, healthy ventricles will eject about 60% of their end diastolic volume each beat. Using the stroke volume you determined (above), what would be the end diastolic volume if the ejection fraction was 60%?

                                                                          i.      EDV = _____________

b.      Estimate ESV, end systolic volume using your SV and estimated EDV from above. Remember SV = EDV-ESV. ESV = ________

 

10.  Draw an estimate of the ventricular volume curve using the following guidelines.

a.       The ventricles are full (EDV) when the ventricles start to contract; by the time S1 occurs (mitral valve shuts) and ventricular pressure exceeds atrial pressure. The volume in the ventricle will remain constant until they begin to eject blood; when ventricular pressure exceeds aortic pressure and aortic flow begins to increase.

b.      The ventricles are done ejecting blood once the pressure in the ventricles falls below aortic pressure and the semilunar valves close (S2).  The volume of blood in the ventricles at this time is the ESV.  The volume will not begin to increase until the ventricles begin to fill (between S2 and S3, if the third heart sound is heard).

c.       Write your EDV and ESV values on the Y-axis.

 

11.  Determine the duration of (electromechanical) systole and diastole

a.       Duration of the cardiac cycle, RR interval =_________

b.      Atrial systole lasts from the beginning of the P-wave to S1, AS = ________

c.       Atrial diastole lasts from S1 until the beginning of the next P-wave.  AD = _______

d.      Ventricular systole lasts from the peak of the QRS complex to S2, VS = _______

e.       Ventricular diastole lasts from S2 until the peak of the next QRS, VD = _______

f.       Percentage of time spent in

                                                                          i.      AS = ________ %, AD = ________ %

                                                                        ii.      VS = ________ %, VD = ________ %

 

12.  Determine the periods of the cardiac cycle

a.       Isovolumetric ventricular contraction (IVC) = ________

                                                                          i.      Measure from S1 to the beginning of the increase in aortic flow

b.      Ventricular ejection period/left ventricular ejection time (LVET) = ________

                                                                          i.      Measure from the beginning of the increase in aortic flow until S2

c.       Ventricular filling time, FT (& isovolumetric ventricular relaxation, IVR) = ________

                                                                          i.      Please note that if S3 is not apparent it would be difficult to estimate IVR, so these two periods are being combined here. Measure from S2 to S1 of the next beat.

                                                                        ii.      If S3 is observed, determine IVR and filling time

1.      IVR, measure from S2 until just before S3. IVR  = ______

2.      FT , measure from just before S3 until S1 of the next beat. FT = ______

d.      What percentage of the cardiac cycle is spent in each

                                                                          i.      IVC = ________ %

                                                                        ii.      LVET = ________ %

                                                                      iii.      FT (& IVR) = ________ % (IVR = ________ %, FT = ________ %)

 

13.  Calculations

a.       Calculate heart rate (HR) using the RR interval, HR = ______

b.      Calculate cardiac output (Q) using HR and SV,    Q  = ______

c.       Calculate MAP using SBP and DBP,    MAP = ______

d.      Calculate TPR using MAP and Q, TPR = ______

 

14.  Cold pressor test (CPT)

a.       Start the recording, get a baseline recording and take a baseline blood pressure

b.      Leave the computer recording on and have subject submerge hand in ice water bath

c.       Take blood pressures at 1 min and 2 min into the CPT

d.      Go back and record HR and SV from the computer recording

e.       Record data below and complete the calculations

 

HR

SV

SBP

DBP

Q

MAP

TPR

resting

________

________

________

________

________

________

________

CPT 1min

________

________

________

________

________

________

________

CPT 2min

________

________

________

________

________

________

________

f.       What happened to MAP? What events (and reflex arc components) are involved in this change?

 

 

 

 

g.      Was the change in pressure between rest and 1min due to changes in Q or TPR? Explain your answer.

 

 

h.      Did MAP begin to decrease towards normal between minute 1 and minute 2? If so, what is causing this to occur (and what reflex arc components may be involved)?

 

 

 

 


15.  Effects of exercise on the cardiac cycle and the cardiovascular system.

a.       Get baseline recording and blood pressures, then have subject exercise at a moderate intensity on a cycle ergometer and record again.

 

Rest

 

Exercise

 

RR interval

________

 

________

 

VS, VS %

________

________

________

________

VD, VD %

________

________

________

________

 

 

 

 

 

HR

________

 

________

 

SV

________

 

________

 

Q

________

 

________

 

SBP

________

 

________

 

DBP

________

 

________

 

MAP

________

 

________

 

TPR

________

 

________

 

RPP

________

 

________

 

b.       What happened to the duration of ventricular diastole when heart rate increased? What does this suggest about ventricular filling time?

 

 

c.       What would you expect to happen to preload (EDV) when filling time is reduced? What effect would you expect this to have on the strength of cardiac contraction? (think Starling’s law of the heart)

 

 

 

d.      How can SV increased if ventricular diastole and ventricular filling time were lower?

 

 

 

 

e.       How might this situation have been different if heart rate increased suddenly while at rest (paroxysmal tachycardia)? What symptoms might a subject experience if this happened?

 

 

 

 

f.       What does the change in rate pressure product (RPP) during exercise suggest about the heart’s oxygen requirements?

 

 

 

g.      Coronary blood flow occurs mostly (70%) during ventricular diastole. If ventricular diastole decreases during exercise, what must happen in order to deliver adequate amounts of blood to the myocardium?

 

 

 

 

h.      The sympathetic nervous system is very active during exercise.  What role did the SNS play during exercise (how does it help increase muscle blood flow)?

 

 

 

 

 

i.        What happened to TPR during exercise and what caused it to change this way?