Keep on movin’ don’t stop Starling’s Equation Keep on movin’ don’t stop Group Members: Sahra Adan, Claire Anderson, Aminah Coleman, Wai Chum, Joseph Early, Mindy Gunn, Kyle McIntyre, Monicah Ngugi, Kathryn Sjolund, Lise Thorsvig, Lindsey Tripp, & Vincent Witwer

Filtration through membranes Affected by 3 factors: Hydrostatic pressure (HP) gradient (pushing) Oncotic pressure gradient (OP) (pulling) Permeability of membrane (through what?) Where does water go? …. In the direction where the force is GREATER!!!!! Net: HP (Side A) – HP (Side b) Net: OP (side A) – OP (side B) Hydrostatic pressure: force generated by water, due to the force of gravity Oncotic pressure: force generated by solutes (major solute: albumin) Determine the net force by calculating hydrostatic and osmotic pressure at two different sides of a membrane, Hydrostatic pressure (side A) - Hydrostatic pressure (side B) Oncotic pressure (side A) - oncotic pressure (side B) B A

Membrane Characteristics: Lp, s (little) and s (big) Lp and S (big) affect HYDROSTATIC pressure: Lp- porosity of the membrane S (big) - membrane surface area S (little) affects OSMOTIC pressure: S (little)- permeability of a membrane to a solute Ranges from 0 (completely permeable) to 1 (completely impermeable) Solute diffusion      as permeability The membrane factors affecting hydrostatic pressure are rarely clinically relevant. Permeability of a membrane to a solute is clinically relevant in disorders which disrupt membrane integrity (such as sepsis).

The Math of Starling’s Equation Means Movement of water between interstitial space and capillaries Increased hydrostatic pressure = positive net filtration inside the capillary Increased oncotic pressure = negative net filtration Interstitial space Taking into account all factors, the Starling’s Law can be rewritten mathematically as: net filtration pressure = [Lp x S (BIG)] )(capillary hp – interstitial hp) – [s(little) x (capillary op – interstitial op)]

Importance of Starling’s Law This affects the flow of fluid and filtrates into and out of your capillaries... At the ARTERIAL end of the capillary: Net filtration pressure is POSITIVE, causing water, oxygen and nutrients to be pushed OUT of the capillary and into the interstitial fluid. At the VENOUS end of the capillary: Net filtration pressure is NEGATIVE, allowing the veins to pick up excess water, carbon dioxide, and other wastes from the interstitial fluid.  

Clinical Correlations: Pleural Fluid Analysis High [ protein ] Low [protein ] due to damaged capillaries due to hydrostatic pressure -or- oncotic pressure “Exudate” “transudate” Inflammation, Infection, Trauma, chf, cirrhosis, severe malnutrition, Malignancy, ARDS nephrotic syndrome transudate and exudate are classifications of pleural fluid (pleural effusion) Determining the amount of protein and other factors contained in the fluid can help determine if the fluid collection is due to a change in hydrostatic pressure, osmotic pressure or capillary permeability (changes in capillary permeability are typically a result of damage). Although the fluid from peripheral edema cannot be analyzed, thinking about the differential diagnosis in terms of which aspect of Starling’s law has been altered is useful. A “transudative peripheral edema” is associated with CHF and cirrhosis while an “exudative peripheral edema” is associated with infection (local or systemic), trauma and malignancy. Diagnostic criteria: One the following is required for the pleural fluid to be considered an exudate. LDH = lactate dehydrogenase. pleural fluid protein more than 50% of serum protein • pleural fluid LDH more than 60% of serum LDH 66% of the upper limit of normal for serum LDH

Clinical Correlations Fluid collections always result from a change in one component of Starling’s law ascites, peripheral edema, pulmonary edema, pleural effusion Changes in net osmotic pressure do not become clinically significant until the plasma albumin concentration is less than 2 g/dL (normal 3.5 to 5.5 g/dL). Decreased plasma protein concentration can be due to decreased production (e.g., chronic liver disease, severe malnutrition) or increased loss (e.g., nephrotic syndrome, protein losing enteropathies)

Clinical Correlations: Albumin Gradient albumin gradient = plasma albumin – ascitic albumin High Gradient >1.1 g/dL Low Gradient < 1.1 g/dl Cirrhosis malignancy Hepatitis tb CHF pancreatic disease Portal vein thrombosis nephrotic syndrome myxedema Ascites

Summary

In words Starling’s Law explains the maintenance of fluid balance between the vasculature and the interstitial space. Fluid balance is determined by hydrostatic and oncotic pressure balance In a healthy person: high hydrostatic pressure forces water to filter out of capillaries at the arterial end At the venous end, hydrostatic pressure is decreased, thus oncotic pressure - mainly the pull of the plasma proteins – returns water into the vasculature In a disease state: hydrostatic or oncotic pressure are altered and water flows from the vasculature to the interstitial space Membrane permeability also impacts the flow of water.