Preload is increased by -
Ans. is 'a' i.e.. Increase blood volume Preload (Degree of ventricular filling during diastole)o Cardiac preload is represented by volume of venous blood that distends the ventricle, i.e., venous return determines the preload. An increase in preload, i.e., increase in venous return results in a higher end-diastolic volumeQ (PreloadQ).o This results in stretching of myocardial fiber and this increase in length of myofibril increases the strength of cardiac contraction in accordance with the Frank-Starling law or Starling's law of the hearto According to Starling's lawr, greater the initial length of muscle fiber, greater is the force of contraction,o The initial length of muscle fiber (length of fiber at the initiation of contraction/systole) refers to length of the fiber at the end of the diastole, i.e., end-diastolic fiber length.o Thus, the factors which improve venous return increase the cardiac output by increasing end-diastolic ventricular volume and length, i.e.. preload,o Opposite is true for factors which decrease venous return.| Stroke volume| Stroke volumeFactors Increasing end-diastolic ventricular muscle fiber length (Factors increasing venous return or preload)Factors decreasing end-diastolic ventricular muscle fiber length (Factors decreasing venous return or preload)o Increased total blood volumeQo Decreased total blood volumeo Increased venous toneQo Decreased venous toneo Increased pumping action of skeletal muscleo Decreased pumping action of skeletal muscleso Increased negative intrathoracic pressureQ (e.g. inspiration)o Less negative or positive intrathoracic pressure (expiration)o Sitting or standingQ (venous pooling of blood)o Lying down from sitting or standing position o Sympathatic discharge causing decrease in venous capacitance by decreasing venous compliance
Increased blood volume
Increased total peripheral resistance
Standing
Sitting
Circulation: Cardiac Output, Venous Return