(b) Yes, the relation shown in the graph is specially named as a function. A function is an equation that shows the relationship between a dependent variable, which in this case is y(x) and an independent variable, x. Also, to determine if the relation is a function, a vertical line can be drawn through the graph. If the relation is not a function, the graph will have at least 2 points with the same x-coordinate but with different y-coordinates. Since this relation does not have at least 2 of the same x-coordinates and a different y-coordinates when a vertical line is drawn, this relation shown in the graph is a function.

 Cardiac output = stroke volume × heart rate

Heart rate refers to the number of times the heart beats per minute and the resting heart rate of an individual could be affected by a variety of factors such as stress levels, level of physical activeness as well as genetics. Increase in heart rate increases cardiac output as the volume of blood released into the body increases with respect to it. Stroke volume is the amount of blood your heart pumps each time it beats, and your heart rate is the number of times your heart beats per minute. A healthy heart with a normal cardiac output pumps about 5 to 6 litres of blood every minute when a person is resting.

The increasing of left ventricle dimensions, reduced systemic peripheral resistance and a
greater blood volume account for increases in resting, submaximal and maximal stroke volume, typically, after an endurance training programme.

One method of determining cardiac output is the thermodilution method. It adapts the
indicatordilution principle to injectates that cause changes in blood temperature detected
downstream The thermodilution (TD) method blood temperature detected downstream. ¾ an injectate of known volume and temperature is injected into the right atrium and the cooled blood traverses a thermistor in a major vessel branch downstream over a duration of time.

 Another method is the dye dilution method. It is based on injecting a known quantity of a dye at one site into the circulatory system, and withdrawing blood at a distal site for determination of a concentration curve of the dye. The dye dilution method is one of the most accurate methods of determining cardiac output during exercise. The error of a single calculation of cardiac output values at rest and during exercise is less than 5%. This method does not allow measurement of 'beat to beat' changes, and requires a cardiac output that is stable for approximately 10 s during exercise and 30 s at rest.