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UCB Physio Lab Finals - Set 1
7.2 ECG 7.3 Effects of exercise on ECG 7.5 Heart sounds
Terms in this set (38)
Picture, display, or print out of the small voltage change across the body that are caused by the cardiac action potentials
The contraction phase of the cardiac cycle is called
The relaxation phase of the cardiac cycle is called
The sinoatrial node (SA node)
is the normal pacemaker of the heart, initiating each electrical and mechanical cycle. When the SA node depolarizes, the electrical stimulus spreads through atrial muscle causing the muscle to contract. Thus, the SA node depolarization is followed by atrial contraction.
The SA node impulse also spreads to
The atrioventricular node (AV node) via the internodal fibers. The electrical signal is delayed in the AV node for 0.2 sec when the atria contract.
The signal is then relayed to the ventricles via the bundle of His, right and left bundle branches, and Purkinje fibers.
The P wave represents
The T wave represents
The Q wave represents
Ventricular Septal Depolarization
The R wave represents
Fast general ventricular depolarization
The S wave represents
Basal ventricular depolarization
electrical activity in the papillary muscle
total ventricular depolarization
PQ or PR interval
time from beginning of atrial depolarization and AV node conduction
gives an estimate of the time the ventricles are contracting. less than 0.38 secs
gives an estimate of the time the ventricles are relaxing.
is the time between heartbeats. Dividing 60 by this time gives the heart rate.
The heart rate and strength of contraction of the heart are modified by the
sympathetic and parasympathetic divisions of the autonomic nervous system.
The sympathetic division
increases the heart rate. Sympathetic influence increases during inhalation.
The parasympathetic division
decreases the heart rate. Parasympathetic influence increases during exhalation.
Abnormal or irregular heartbeat.
Abnormal conduction originating above AV node.
DP spreads to Vs normally.
LF: narrow QRS complexes
Slow conduction through ventricles (more dangerous), slow p/w through PFibres.
Why are ventricular arrhythmias so serious?
It is because the heart can't pump effectively if the ventricles contract first. Also, the heart is relying on its fail-safe mechanism.
normal ECG except slower than 60 beats/min
is the most common heart arrhythmia. It is an electrical problem in the heart that causes an irregular and/or more rapid heart beat (pulse). Often as fast as 300 to 600 times per min (normal adult rate is 60-100 beats per min).
very rapid atrial waves (about 300 per min).
≥ 3 consecutive ventricular beats at a rate ≥ 120 beats/min.
partial or complete interruption of impulse transmission from the atria to the ventricles.
The most serious of all arrhythmias.
-Ventricles are unable to contract normally, death will occur if not immediately addressed
-The heart's electrical activity becomes disordered and the ventricles contract in a rapid unsynchronized way
-The ventricles begin to "flutter"
-The heart pumps little or no blood
-The most common cause is a heart attack
What might a ventricular fibrillation reading indicate?
Person loses consciousness, precursor to cardiac arrest. Defibrillation required.
Describe the regulatory mechanisms that produce an increase in cardiac rate during exercise. Explain how these changes affect the ECG.
- At the beginning of the exercise, there is a decrease in the activity of the parasympathetic (vagus) innervation of the heart.
- This causes an increase in cardiac rate that is further raised during greater levels of exercise by increased sympathetic nerve (cardiac) activity.
- As a result of the faster rate, the period of diastole is shortened so that the time between the T wave of one ECG tracing and the P wave of the next tracing is significantly reduced.
- At higher heart rates the increased conduction velocity shortens the period of systole as shown by a decrease in the QRS-T interval.
What is the cause of the 1st Heart Sound? lub
Closure of AV Valves at BEGINNING of Systole. Contraction of Ventricles -> Sudden Backflow of Blood against AV Valves -> AV Valves Close & Bulge toward Atria until Chordae Tendinae abruptly stop the Bulging -> Elastic Tautness of Chordae Tendinae cause the back surging blood to BOUNCE FORWARD again into the Ventricles -> Blood, Taut Valves & Ventricular Walls VIBRATE -> Chest Wall
What is the cause of the 2nd Heart Sound? dub
Closure of Semilunar Valves at END of Systole. Semilunar Valves Close -> Bulge Backward toward Ventricles -> Elastic Stretch Recoils the blood back into Arteries -> Reverberation of Blood back & forth b/t Walls of Arteries & Semilunar Valves & b/t Ventricular Walls & Semilunar Valves -> Chest Wall
Lub (1st heart sound)
the lub sound is the closure of the atrioventricular valves at the beginning of ventricular systole.
Dub (2nd heart sound)
the dub sound is closure of the semilunar valves at the end of ventricular systole and the beginning of ventricular diastole.
Correlation of the heart sounds with the ECG waves:
The QRS wave represents ventricular depolarization. When the ventricles depolarize they are stimulated to contract, causing pressure to rise in the ventricles and the AV valves to close, with vibrations that produce the first heart sound.
The T wave represents ventricular repolarization. When the ventricles repolarize electrically they begin to relax mechanically, causing the aortic and pulmonary semilunar valves to close, with vibrations that produce the second heart sound.
How are heart sounds normally produced?
Heart sounds are normally produced by pressure changes causing two valves of the heart to close simultaneously, producing vibrations that can be heard with a stethoscope.
The first heart sound, "lub," is caused by the closure of the right and left atrioventricular valves. The second heart sound, "dub," is caused by the closure of the aortic and pulmonary semilunar valves (pulmonic valves).
Describe some conditions that can cause heart murmurs
Heart murmurs are caused by structural defects in the valves that affect the pattern of blood flow through the heart. Abnormal patterns of blood flow produced by defective valves can cause abnormal vibrations and thus abnormal heart sounds that can be heard by auscultation.
Heart murmurs may be caused by an irregularity in a valve, a septal defect, or the persistent fetal opening (foramen ovale) between the right and left atria after birth.
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