Mechanic work of the heart.

•The pumping of the heart sends out blood under pressure to the arteries.

•Blood pressure is greatest in the aorta; the wall of the left ventricle is thicker than that of the right ventricle and pumps blood to the entire body.

•Blood pressure then decreases as the cross-sectional area of arteries and then arterioles increases.

Path of blood through the heart

Cardiac cycle• The cardiac cycle refers to the repeating pattern

of contraction and relaxation of the heart. The phase of contraction is called systole, and the phase of relaxation is called diastole.

• When these terms are used without reference to specific chambers, they refer to contraction and relaxation of the ventricles. It should be noted, however, that the atria also contract and relax. There is an atrial systole and diastole. Atrial contraction occurs toward the end of diastole, when the ventricles are relaxed; when the ventricles contract during systole, the atria are relaxed.

Cardiac cycle

Cardiac Output

•Volume of blood pumped per unit time from the ventricle

•In mammals this is the volume ejected from either the left or right ventricle, not the combined total

•Volume of blood ejected per beat is the stroke volume

•Stroke volume determined by dividing cardiac output by heart rate

•Stroke Volume = end diastolic volume - end systolic volume

•Cardiac Output = SV X heart rate (HR)•Determinants of EDV

▫1. venous filling pressure▫2. atrial contraction pressure▫3. dispensability of the ventricular wall▫4. time for filling

•Determinants of ESV▫1.ventricular pressure during

contraction▫2. pressure in the outflow channels

(arterial)

Frank Starling Mechanism

• increased work due to increased EDV based on increased venous filling pres- sure and the con- current length-tension changes in cardiac muscle

The Heartbeat•Each heartbeat is called a cardiac cycle.

•When the heart beats, the two atria contract together, then the two ventricles contract; then the whole heart relaxes.

•The heart sounds, lub-dup, are due to the closing of the atrioventricular valves, followed by the closing of the semilunar valves.

Heart rate

•- Normal range is 60-100 beats per minute

•- Tachycardia is greater than 100 bpm•- Bradycardia is less than 60 bpm•- Sympathetic system INCREASES HR•- Parasympathetic system (Vagus)

DECREASES HR (CBQ)

Intrinsic Control of Heartbeat

•The SA (sinoatrial) node, or pacemaker, initiates the heartbeat and causes the atria to contract on average every 0.85 seconds.

•The AV (atrioventricular) node conveys the stimulus and initiates contraction of the ventricles.

•The signal for the ventricles to contract travels from the AV node through the atrioventricular bundle to the smaller Purkinje fibers.

Conduction system of the heart

Extrinsic Control of Heartbeat

•A cardiac control center in the medulla oblongata speeds up or slows down the heart rate by way of the autonomic nervous system branches: parasympathetic system (slows heart rate) and the sympathetic system (increases heart rate).

•Hormones epinephrine and norepinephrine from the adrenal medulla also stimulate faster heart rate.

ECG•The way of excitation which spreads through

the heard wall consists of changes in the electrical activity of the membrane of cardiac muscle cells. Like nerve and skeletal muscle, the outer surface of active cardiac muscle is electrically negative to the resting cardiac muscle ahead of the zone of excitation. The electrical currents generate lines of force similar to those produced by a magnet and are conducted through the salty water-like body fluids to the surface of the body and can be received, amplified and recorded by electrodes of an instrument – an electrocardiograph. The record obtained is an electrocardiogram (ECG).

The Electrocardiogram

•An electrocardiogram (ECG) is a recording of the electrical changes that occur in the myocardium during a cardiac cycle.

•Atrial depolarization creates the P wave, ventricle depolarization creates the QRS wave, and repolarization of the ventricles produces the T wave.

Electrocardiogram

ELECTRODE PLACEMENTELECTRODE PLACEMENTApplication of ElectrodesApplication of Electrodes

Choose site over soft Choose site over soft tissues or close to the bone; tissues or close to the bone; not over bony prominences, not over bony prominences, thick muscles or skin foldsthick muscles or skin folds

Skin PreparationSkin Preparation Use rough patch on back Use rough patch on back of electrode , dry of electrode , dry washcloth, or gauze pad to washcloth, or gauze pad to rub each site until skin rub each site until skin reddensreddens Clip areas of dense hairClip areas of dense hair For oily skin, clean each For oily skin, clean each site with alcohol pad, site with alcohol pad, letting it air dryletting it air dry

• An ECG depicts electrical activity as waves, segments, and intervals. By convention, upward deflection of the waves is defined as positive (+), and downward deflection as negative (!). The electrical activity associated with atrial depolarization is defined as the Pwave ("0.3mV, "0.1 s). Repolarization of the atria normally cannot be visualized on the ECG since it tends to be masked by the QRS complex. The QRS complex ("0.1 s) consists of one, two or three components: Q wave (mV " 1/4 of R, "0.04 s), Rwave and/or S wave (R+S #0.6 mV).

• The potential of the mean QRS vector is the sum of the amplitudes of the Q, R and Swaves (taking their positive and negative polarities into account). The voltage of the mean QRS vector is higher (in most leads) than that of the P wave because the muscle mass of the ventricles is much larger than that of the atria. The Rwave is defined as the first positive deflection of the QRS complex, which means that R waves from different leads may not be synchronous. The QRS complex represents the depolarization of the ventricles, and the T wave represents their repolarization.

• Although opposing processes, the T wave usually points in the same direction as the R wave (+ in most leads). This means that depolarization and repolarization do not travel in the same direction (QRS and T: vector arrows point in the same direction despite reversed polarity during repolarization). The PQ (or PR) segment (complete atrial excitation) and the ST segment (complete ventricular excitation) lie approx. on the isoelectric line (0 mV).

• The PQ (or PR) interval (!0.2 s) is measured from the beginning of the Pwave to the beginning of the Q wave (or to the R wave if Q wave is absent) and corresponds to the time required for atrioventricular conduction. The QT interval is measured from the start of the Q wave to the end of the T wave. It represents the overall time required for depolarization and repolarization of the ventricles and is dependent on the heart rate (0.35 to 0.40 s at a heart rate of 75 min–

1).

ECG

During each cardiac cycle 2 heart sounds can be heart through a stethoscope applied to the chest wall.

Auscultation The sounds may be represented phonetically:

These sounds repeated with every cardiac cycle i.e. about 70 times per minute in the average healthy adult at rest.If the valves have been damaged by disease additional sounds (murmurs) can be heart as the blood flows forwards through narrowed valves or leaks backwards through incompetent valves. Systolic murmurs occure between LUBB and DUP. Diastolic murmurs occur between DUB and the next LUBB.