Final answer:
The SVR formula represents the calculation of stroke volume variation. The formula for SVR is (Mean arterial pressure - CVP) / Cardiac output. Assumptions when measuring CVP/PAP/PCWP include representing the filling pressures of their respective compartments. Causes of low preload include dehydration, hemorrhage, or certain medications.
Step-by-step explanation:
The SVR formula represents the calculation of stroke volume variation. Stroke volume is the amount of blood pumped out of the heart with each heartbeat. It can be calculated by subtracting end-systolic volume (ESV) from end-diastolic volume (EDV). The formula for SVR (Systemic Vascular Resistance) is: SVR = (Mean arterial pressure - CVP) / Cardiac output, where CVP is central venous pressure. SVR reflects the resistance encountered by the heart in pumping blood through the systemic circulation.
One of the assumptions when measuring CVP (central venous pressure), CVP/PAP (pulmonary arterial pressure), and PCWP (pulmonary capillary wedge pressure) is that they represent the filling pressures of their respective compartments. These measurements assume that there are no obstructions or other abnormalities in the blood vessels or heart chambers being measured.
The causes of low preload, or low blood volume entering the heart before contraction, can be due to factors such as dehydration, hemorrhage, or the use of certain medications that cause fluid loss or reduced fluid intake.