Microvascular Physiology, Nephrology & Critical Care Medicine
Starling Capillary Filtration & Oncotic Edema Formula
Calculate Microvascular Outward Hydrostatic Gradient (Pc - Pi), Staverman-Weighted Inward Oncotic Pull sigma*(pi_c - pi_i), Net Starling Filtration Pressure (mmHg), and Transcapillary Fluid Flux Jv (mL/min).
Balance capillary hydrostatic push against albumin oncotic pull across endothelial glycocalyx!
Clinical edema in congestive heart failure (elevated venous Pc), nephrotic syndrome or cirrhosis (hypoalbuminemia lowering pi_c), and sepsis (leaky endothelium lowering reflection coefficient sigma) is governed by the Starling-Landis microvascular filtration equation: J_v = K_f * [(P_c - P_i) - sigma * (pi_c - pi_i)]! Outward Hydrostatic Driving Pressure (P_c - P_i) pushes plasma ultrafiltrate out of the capillary lumen—note that sub-atmospheric interstitial pressure P_i (e.g., -2 mmHg) INCREASES outward suction because 25 - (-2) = +27 mmHg! Opposing inward Colloid Osmotic (Oncotic) Pull equals Staverman’s protein reflection coefficient sigma (0 = freely permeable, 1 = impermeable to albumin) times (pi_c - pi_i); multiplying Net Filtration Pressure by hydraulic conductance K_f gives fluid flux J_v (+ outward filtration, - inward reabsorption)!
Verify at the Arteriolar End of a Systemic Capillary Bed—Capillary_Hydrostatic P_c = 25 mmHg (B2), Interstitial_Hydrostatic P_i = -2 mmHg (B3 -> Outward Hydrostatic Gradient = 27.00 mmHg in E2), Plasma_Oncotic pi_c = 28 mmHg (B4), Interstitial_Oncotic pi_i = 8 mmHg (B5), Endothelial_Reflection sigma = 0.90 (B6 -> Effective Oncotic Pull = 0.90 * 20 = 18.00 mmHg in E3), and Filtration_Coeff K_f = 0.50 mL/(min*mmHg) (B7): Net Starling Pressure is 27 - 18 = +9.00 mmHg (E4), driving +4.50 mL/min of net outward filtration (E5)!
| Starling Microvascular Metric (Pc=25, Pi=-2, pi_c=28, pi_i=8, sigma=0.9, Kf=0.5) | Formula | Verified Output |
|---|---|---|
| Outward Hydrostatic Push (mmHg) | P_capillary - P_interstitial | 27.00 mmHg (12.00 @ Pc=10) |
| Effective Oncotic Pull (mmHg) | sigma * (pi_capillary - pi_interstitial) | 18.00 mmHg |
| Net Driving Pressure (mmHg) | (Pc - Pi) - sigma * (pi_c - pi_i) | +9.00 mmHg (-6.00 @ Pc=10) |
| Transcapillary Flux Jv (mL/min) | K_f * Net_Driving_Pressure | +4.50 mL/min (-3.00 Reabsorption) |
Starling-Landis Transcapillary Fluid Flux Formula
Validate P_c > 0, non-negative oncotic pressures pi_c and pi_i, valid reflection coefficient 0 <= sigma <= 1, and K_f > 0!
=LET(p_cp, B2, p_in, B3, o_cp, B4, o_in, B5, sg_m, B6, k_fl, B7, IF(OR(p_cp <= 0, o_cp < 0, o_in < 0, sg_m < 0, sg_m > 1, k_fl <= 0), "Invalid Starling Microvascular Input", ROUND(k_fl * ((p_cp - p_in) - sg_m * (o_cp - o_in)), 2)))Venular-End Reabsorption Check (Set Capillary Pressure Pc = 10 mmHg)
Drop Capillary_Hydrostatic B2 to 10 mmHg at the venular end: Outward Push falls to 12 mmHg (< 18 mmHg oncotic pull), flipping Net Driving Pressure E4 to -6.00 mmHg and Flux E5 to -3.00 mL/min net reabsorption!
=IF(ISTEXT(E2), E2, ROUND((B2 - B3) - B6 * (B4 - B5), 2))Try the example
Use the original values or change them to test your understanding.