16
chapter i
Water, Acids, Bases, and Buffers
[H+] directly as nanomoles per liter in order to better eval-
uate acid-base changes and interpret laboratory tests. A
blood pH of 7.40 corresponds to 40 nM [H+], which is
the mean of the normal range (Figure 1-14). The normal
range is 7.36-7.44 on the pH scale, or 44-36 nM [H+], If
the pH of blood falls below pH 7.36 ([H+] > 44 nM), the
condition is called
acidemia.
Conversely, if the pH rises
above pH 7.44 ([H+] < 36 nM), the condition is called
alkalemia.
The suffix
-emia
refers to blood and usually to
an abnormal concentration in blood. Over the pH range
of 7.20-7.50, for every change of 0.01 pH unit, there is
a change of approximately 1 nM [H+] in the opposite
direction.
Since the Henderson-Hasselbalch expression uses pH
terms, its utility in clinical situations is less than optimal.
Kassirer and Bleich have derived a modified Henderson-
Hasselbalch expression that relates [H+], instead of pH,
to
PCo2
and HC07, as follows:
H
2
C 0
3
^ H+ + HCO
3
for which
K , _
[HCQ
3
-][H+]
[H
2
c o 3]
Substituting a x Pco^ for [H
2
C 03], as in Equation (1.16),
yields
VJ
[HCQ
3
-][H+]
a
x PCo
2
and
Clinical applications of Equation (1.23) are discussed in
Chapter 39.
Supplemental Readings and References
Properties of Water
M. F. Colombo, D. C. Rau, and V. A. Parsegian: Protein solvation in allosteric
regulation: A water effect on hemoglobin.
Science
256,
655 (1992).
M. A. Knepper: Molecular physiology of urinary concentrating mechanism:
Regulation of aquaporin water channels by vasopressin.
American Journal
of Physiology
272
(Renal Physiology
41),
F3 (1997).
M. A. Knepper, J. G. Verbalis, and S. Nielsen: Role of aquaporins in water
balance disorders.
Current Opinion in Nephrology and Hypertension
6
,
367 (1997).
M. D. Lee, L. S. King, and P. Agre: The aquaporin family of water channel
proteins in clinical medicine.
Medicine
76, 141 (1997).
R. P. Rand: Raising water to new heights.
Science
256,
618 (1992).
P. M. Wiggins: Role of water in some biological processes.
Microbiological
Reviews
54,
432 (1990).
Acid-Base Chemistry and Respiratory Function
of Hemoglobin
H. J. Androgue and N. E. Madias: Management of life-threatening acid-base
disorders.
New England Journal of Medicine',
First of two parts
338,
26
(1998); Second of two parts
338,
107 (1998).
C. C. W. Hsia: Respiratory function of hemoglobin.
New England Journal
of Medicine
338,
239 (1998).
Nuclear Magnetic Resonance and Magnetic
Resonance Imaging
_
K'a
x PCo
2
“
[HC
0
3
-]
(
1
.
22
)
In Equation (1.22),
K'
and
a
are constants, and the numer-
ical value of
K'a
is 24 when Pco
2
is expressed in mm Hg,
[HCO
3
] in mM, and [H+] in nM. Therefore,
24 x Pco,
[h c ° 3
-]
(1.23)
The above formulation expresses the interdependence of
three factors; if two of them are known, the third can
be readily calculated. For example, at a blood [HCCfj"]
of 24 nM and a Pco
2
of 40 mmHg, [H+] is 40 mM.
R. R. Edeman and S. Warach: Medical progress: Magnetic resonance imag-
ing.
New England Journal of Medicine',
First of two parts
328,
708 (1993);
Second of two parts
328,
785 (1993).
S. Gilman: Medical progress: Imaging of the brain.
New England Journal
of Medicine',
First of two parts 338, 812(1998); Second of two parts 338,
889(1998).
S. J. Knoury and H. L. Weiner: Multiple sclerosis.
Archives of Internal
Medicine
158,565 (1998).
L. A. Moulopoulos and M. A. Dimopoulos: Magnetic resonance imaging of
the bone marrow in the hematologic malignancies.
Blood
90,2127 (1997).
A. Schulze, T. Hess, R. Wevers, et al.: Creatine deficiency syndrome caused
by guanidinoacetate methyltransferase deficiency: Diagnostic tools fora
new inborn error of metabolism.
Journal of Pediatrics
131,
626 (1997).
S. Stockler-Ipsiroglu: Creatine deficiency syndromes: A new perspective on
metabolic disorders and a diagnostic challenge.
Journal of Pediatrics
131,
510(1997).
