CARDIAC OUTPUT OF HUMAN HEART, Slides of Human Physiology

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CARDIAC

OUTPUT

When the heart

Abhigyan Singh

Chauhan

Cardiac Output

Cardiac output is the amount of blood pumped from Usually, each ventricle.

Usually, it refers to left ventricular output 1. Stroke through aorta. Cardiac

output is the most important factor in cardiovascular system because rate of

blood flow through different parts of the body depends upon cardiac output, it is

expressed by the following equation:

CO = SV x HR  (^) Where:  (^) CO is cardiac output expressed in L/min (normal ~5 L/min)  (^) SV is stroke volume per beat  (^) HR is the number of beats per minute

The output of the two ventricles is exactly the same. Thus, each ventricle pumps 5-6L of

blood into the circulation per minute

Heart Rate (HR) Heart rate is directly proportional to cardiac output  (^) Adult HR is normally 80-100 beats per minute (bpm.)  (^) Heart rate is modified by autonomic, immune, and local factors.  (^) For example:

1. An increase in parasympathetic activity via M 2 cholinergic receptors in the heart will decrease the heart rate.
2. An increase in sympathetic activity via B 1 and B 2 adrenergic receptors throughout the heart will increase the heart rate.  (^) SV = EDV - ESV  (^) Is determined by three factors: preload , afterload , and contractility.  (^) Preload gives the volume of blood that the ventricle has available to pump  (^) Contractility is the force that the muscle can create at the given length  (^) Afterload is the arterial pressure against which the muscle will contract.  (^) These factors establish the volume of blood pumped with each heart beat. Stroke Volume (SV)

 (^) Preload : Preload is the muscle length prior to contractility, and it is dependent of ventricular filling (or end diastolic volume …EDV)  (^) This value is related to right atrial pressure.  (^) The most important determining factor for preload is venous return.  (^) Contractility : Contractility is the intrinsic ability of cardiac muscle to develop force for a given muscle length.  (^) Afterload : Afterload is the tension (or the arterial pressure ) against which the ventricle must contract.  (^) If arterial pressure increases, afterload also increases.  (^) Afterload for the left ventricle is determined by aortic pressure  (^) Afterload for the right ventricle is determined by pulmonary artery pressure.

Chemical Regulation of the Heart  (^) The hormones epinephrine and thyroxine (T 4 ) increase heart rate.  (^) Hormonal Regulation of Blood Pressure

1. Renin
2. ADH
3. Aldosterone  (^) Intra- & extracellular ion concentrations must be maintained for normal heart function Homeostatic Imbalances  (^) Hypocalcemia – reduced ionic calcium depresses the heart  (^) Hypercalcemia – dramatically increases heart irritability and leads to spastic contractions  (^) Hypernatremia – blocks heart contraction by inhibiting ionic calcium transport  (^) Hyperkalemia – leads to heart block and cardiac arrest

 DIRECT METHOD

 (^) 1.Cardiometer  (^) 2.Flowmeter

 INDIRECT METHODS

 (^) 1. Fick principle.  (^) 2. Indicator (dye) dilution technique.  (^) 3. Thermodilution technique.  (^) 4. Oesophageal ultrasonic doppler transducer technique.  (^) 5. Doppler echocardiography.  (^) 6. Ballistocardiography. Catheter is a thin radiopaque tube, made up of elastic web, rubber, plastic, glass or metal. Cardiac catheterization is an invasive procedure in which a catheter is inserted intravascularly into any chamber of the heart or a blood vessel. MEASUREMENT OF CARDIAC OUTPUT CARDIAC CATHETERIZATION