calculate_gomez: Gomez formulas for renal afferent/efferent resistance

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Gomez formulas for renal afferent/efferent resistance

Description

Calculates renal resistance measures using the formulas originally reported by Gomez, referred to as the "Gomez Formulas". For review of this method see Bjornstad. For discussion of the additionally reported A value see Kimura.

Usage

calculate_gomez(GFR, RPF, Hct, total_protein, MAP = NULL, sbp, dbp, hr, DM = F)

Arguments

GFR	Glomerular filtration rate measured by iohexol clearance or other precise method (mL/min), not adjusted by BSA.
RPF	Renal plasma flow, determined by PAH infusion (mL/min), not adjusted by BSA.
Hct	Hematocrit (fraction)
total_protein	Total protein in plasma (g/dL). Recommended default value of 7.0
MAP	Mean Arterial Pressure (mmHg). If not provided, MAP is calculated from sbp, dbp, and hr. The MAP calculation uses the formula reported by Gomez adjusting for HR, rather than the standard formula.
sbp	Systolic Blood pressure (mmHg)
dbp	Diastolic Blood pressure (mmHg)
hr	Heart rate (bpm)
DM	Diabetes (T/F). defaults to FALSE. This changes the value used for the Gross Filtration Coefficient (Kfg) to 0.1012 mL/s/mmHg.

Details

Assumptions imposed by Gomez equations are as follows:

1. Intrarenal vascular resistances are divided into afferent, postglomerular, and efferent

2. Hydrostatic pressures within the renal tubules, venules, Bowman’s space, and interstitium (PBow) are in equilibrium of 10 mmHg

3. Glomerulus is in filtration disequilibrium

4. Gross filtration coefficient KF is 0.0867 mL/s/mmHg given a normal kidney. Alternative assumed values include 0.1012 mL/s/mmHg for patients with Diabetes or heart failure.

Other caveats :

1. assumes PAH elimination is nearly complete, e.g. determination of RPF by PAH infusion is accurate.

2. assumes the Filtation coefficient is not affected by disease. alternate values may needed for other disease such as diabetes.

3. accurate only when Plasma total protein is between 5-8 g/dL, and the albumin/total protein ratio is between 0.55-0.65.

4. assumes RBP is at least 1/3 of normal value (RPF > 400 mL/min))

5. Some equations may be inaccurate for GFR <50 mL/min

6. for Filtration Fraction > 0.33 the equations may be inaccurate

7. for estimated Glomerular pressure >75 or <40, the equations may be inaccurate

8. Association does not imply causation.

Value

a Data.frame of calculated values:

• gomez_map Mean arterial pressure (MAP),mmHg

• gomez_ff Filtration Fraction, unitless

• gomez_rbf Renal Blood Flow (RBF), mL/min

• gomez_rvr Renal Vascular Resistance (RVR), mmHg min/L

• gomez_kfg Gross Filtration Coefficient, mL/s/mmHg

• gomez_cm Capillary Mean Plasma protein concentration, g/dL

• gomez_pf Filtration Pressure across Glomerular cappilaries, mmHg

• gomez_Pbow Bowman's Space Pressure, mmHg

• gomez_piGlom Glomerular cappilary Oncotic Pressure, mmHg

• gomez_pglom Glomerular Pressure, mmHg

• gomez_ra Resistance afferent arteriole (Ra), dyne s/cm^5

• gomez_re Resistance efferent arteriole (Re), dyne s/cm^5

• gomez_ra_re_ratio Ra to Re Ratio

• gomez_A A - theoretical mean arterial pressure at which sodium excretion is zero

Examples

calculate_gomez(GFR=85, RPF=377, Hct=0.432,
                sbp=125, dbp=73, hr=70, #MAP=93,
                total_protein=7, DM=F)
                
# Ribstein avg values
calculate_gomez(GFR = 102, RPF = 445, Hct = 0.44, total_protein = 7, sbp=169, dbp=97, hr=65, DM=F)
calculate_gomez(GFR = 93, RPF = 422, Hct = 0.44, total_protein=7, MAP=121, DM=F)


# Lytvyn data
# healthy control
calculate_gomez(GFR = 109, RPF = 621, Hct = 0.44, total_protein = 7, sbp=109, dbp=65, hr=61, DM=F)
# type I DM
calculate_gomez(GFR = 117, RPF = 685, Hct = 0.44, total_protein = 7, sbp=114, dbp=66, hr=70, DM=F)

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