Figure

Relation between dietary sodium (Na), extracellular fluid (ECF) volume, and mean arterial pressure (MAP). A, Relation between the dietary intake of Na, ECF volume, and urinary Na excretion at steady state in a normal person. Note that 1 g of Na equals 43 mmol (43 mEq) of Na. At steady state, urinary Na excretion essentially is identical to the dietary intake of Na. As discussed in Figure 2-2, ECF volume increases linearly as the dietary intake of Na increases. At an ECF volume of under about 12 L, urinary Na excretion ceases. The gray bar indicates a normal dietary intake of Na when consuming a typical Western diet. The dark blue bar indicates the range of Na

989694929088 86 84 82 80

Urinary sodium excretion, g/d 2 3 4 5

Sodium intake, g/d intake when consuming a "no added salt" diet. The light blue bar indicates that a "low-salt" diet generally contains about 2 g/d of Na. Note that increasing the dietary intake of Na from very low to normal levels leads to an 18% increase in ECF volume. B, Relation between the dietary intake of Na and MAP in normal persons. MAP is linearly dependent on Na intake; however, increasing dietary Na intake from very low to normal levels increases the MAP by only 1%. Thus, arterial pressure is regulated much more tightly than is ECF volume. (A, Data from Walser [1]; B, Data from Luft and coworkers [3].)

SG 100 1SG 200 MAP, mm Hg

Arterial pressure

Total peripheral resistance vy-

SG 100 1SG 200 MAP, mm Hg

Kidney volume L_Q_ output I

Cardiac output ^

Autoregulation

Net volume intake

Rate of change of extracellular fluid volume

NaCland fluid intake

Venous return

Nonrenal fluid loss

Extracellular fluid volume

Blood volume m:

Mean circulatory filling pressure

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