Effect of acidosis on patients with myocardial ischemia Reduction in pH is known to decrease O 2 affinity (Bohr effect) and increase the rate of O 2 release from blood. It provides a potential mechanism for increasing O 2 transport to the myocardium. Fifteen patients with refractory, chronic angina were studied by treadmill exercise tolerance tests and whole blood-oxygen release rate measurements before and 4 days after beginning treatment with oral acetazolamide (10 to 20 mg Ikg body weight). Positive treadmill exercise test or myocardial necrosis was present in each case. There was a correlation between an increased O 2 release rate from blood and relief of symptoms. The major side effect in 2 patients was pathologic fatigue believed to result from acidosis. Of the 7 patients who obtained relief from angina, in each there was a 27% increase in the rate of release of O 2 from their whole blood. Seven patients did not obtain relief; they showed no change in the rate of release. In the 4 patients who became worse the rate of deoxygenation decreased by 22%. All changes in deoxygenation rate coincided with the clinical findings. The treatment of ischemic heart disease with acetazolamide or other acidifying agents should not, however, be attempted until further investigation establishes their clinical value.
J. W. Holsinger, Jr., M.D., Ph.D., and V. F. Miscia, M.D. Newington, Conn., and Omaha, Nebr. Veterans Administration Hospital, and Department of Internal Medicine, University of Nebraska Medical Center
It is well known 9 that certain patients with
ischemic heart disease may have changes in hemoglobin-oxygen binding. It is less well known that such patients may have changes in the rate of release of oxygen from whole blood. We became interested in determining whether the effects of metabolic acidosis that produce the Bohr effect would also produce a change in the rate of release of oxygen from whole blood. Lenfant, Torrance, and Reynafarje 5 reported that individuals pretreated with acetReceived for publication May 31,1975. Accepted for publication Aug. 12, 1975. Reprint requests to: Dr. J. W. Holsinger, Jr., Chief·of-Staff, Veterans Administration Hospital, Newington, Conn. 06111.
594
azolamide (Diamox) prior to exposure to high altitude have a lower incidence of altitude sickness; the acidosis resulting from acetazolamide decreased the affinity of oxygen for whole blood. We postulated that the objective signs of myocardial ischemia and its symptoms could be relieved by the improvement in the rate of release of oxygen by the blood if the potential increase in available oxygen from whole blood was also associated with an increase in the rate at which oxygen was released from whole blood. A rightward shift of the dissociation curve has been thought to be of benefit in certain conditions that require a greater amount of oxygen release to the tissue level. Woodson 9
Acidosis in angina
Volume IS Number 5, Part I
595
Table I. Results of acetazolamide therapy pH Treadmill result Group 1 Improved
B
Group 2 Stayed the same
n = 7 Group 3 Became worse
n=4
I
A
7,38
7.48
n = 7
2,3-DPG
I
B
15,26 ±2,05
* 7.46 ±0.03
B
A
11.81 ±2,68
7,36 ±0,04
13.49 ±0,82
7,37 ±0,01
p < 0,01
kc
A
3,84
B
1.64 ±0,25
3.67 ±0,09
NS
4.15 ±0,51
1.82 ±0.31
5,05
3,79
p < 0,05
A
I
2,07 ±0.29
%
+27%
1.86 ±0,36
+2%
NS
NS 9,77 ±0,67
I
P < 0.05
* 11.47 ±0,51
13,55 ±0.45
I
3,96
NS
P < 0,01 7.43 ±0,03
ATP
2,05 ±0.23
1.60 ±0,04
-22%
P < 0,02
*
Pooled data
7.45 ±0,03 n = 18
7,32 ±0,06
P < 0,001
13,80 ±1.15
11.04 ±1.95
p < 0,01
4,21 ±0,60
3,79 ±0,17 NS
1.80 ±0.29
1.88 ±0.31
+4%
NS
B: before acetazolamide therapy, A: after acetazolamide therapy. NS: not significant. *Not enough data to do statistics.
has reported a progressive decline in hemoglobin-oxygen affinity with a decrease in cardiac function. This alteration in hemoglobinoxygen binding represents a significant mechanism for adaptation to the limited oxygen supply imposed by the cardiac lesion. Salhany, Eliot, and Mizukarni 6 have shown that a significant acidosis results in an increase in the rate of release (kinetics) of oxygen from hemoglobin, With these concepts in mind we became interested in determining whether we could relieve myocardial ischemia by accelerating blood oxygen transport. 1 Methods
Fifteen patients with objective evidence of myocardial ischemia form the basis of the report. Objective evidence was demonstrated by electrocardiographic evidence of myocardial infarction (transmural, 4 patients; subendocardial, I patient) or abnormal graded treadmill exercise tests. An abnormal graded treadmill exercise test was demonstrated by
electrocardiographic evidence of I mm of horizontal or down sloping st segment depression lasting for 0.08 sec or longer. None of the patients were receiving digitalis and no patient demonstrated electrolyte abnormalities, hyperventilation, or changes on assuming a standing position. The classic changes produced by exercise testing in heart rate and blood pressure were noted. Of the 15 patients, 10 had undergone selective coronary arteriography, 3 of whom had at least one vessel with 70% or more intraluminal obstruction, Seven patients had normal coronary arteries angiographically associated with abnormal treadmill exercise tests and symptoms of angina. Five patients were not catheterized but had symptoms of angina associated with abnormal treadmill exercise tests. Each patient was treated with acetazolamide, 10 to 20 mg/kg body weight, in order to produce a metabolic acidosis. Before and 4 days after treatment, a series of studies consisting of measurement of the rate of release of oxygen
596
Clinical Pharmacology and Therapeutics
Holsinger and Miscia
from whole blood (ke) utilizing a modified Durrum-Gibson stopped flow apparatus 2 • 7 and graded exercise studies were carried out. The level of 2,3-disphosphoglycerate (2,3-DPG) in the red cells was measured by the method of Keitt,4 and adenosine triphosphate (ATP) levels were measured using a spectrophotometer. 8 Following treatment with acetazolamide, each patient was examined for evidence of a decrease in symptomatology and an improvement in treadmill performance. Improvement was judged by a reduction of episodes of angina or a reduction in shortness of breath. An increase in work tolerance was demonstrated by the patient being able to perform on the treadmill for longer periods of time at a progressively increased speed. Those patients whose symptoms became worse were found to have an increase in episodes of angina or shortness of breath. In addition, they demonstrated a decrease in work performance on the treadmill. Myocardial oxygen consumption was not measured in these patients. Results
Table I summarizes the data including pH, 2,3-DPG, ATP, and the deoxygenation rate constant (ke). A total of 15 patients were studied on 18 separate occasions; 7 patients improved symptomatically (Group 1), in 7 there was no change (Group 2), and in 4 there was an increase in symptoms (Group 3). Thus only 39% of patients treated with acetazolamide improved. When a comparison is made between the pooled data before and after treatment with acetazolamide, acidosis (p < 0.001) was produced in all cases as well as a fall in the level of 2,3-DPG (p < 0.01), but no significant change could be demonstrated in the pooled before and after results for ATP and k e. An apparent classic Bohr effect occurred in that pH decreased, 2,3-DPG decreased, and ATP increased slightly. The ke increased slightly, indicating that P 50 had shifted to the right, producing a decrease in the affinity of oxygen for hemoglobin. It appears that more phosphate may be available from the phosphatolysis of 2,3-DPG, thereby increasing the phosphate
pool and providing substrate for the synthesis of ATP. When the data is divided into groups according to the change in symptoms and exercise tolerance, it may be possible to draw certain conclusions. Whereas there was significant acidosis in all groups (Table I), in Group 1 there was a decrease in 2,3-DPG that was not statistically significant, a slight decrease in ATP, and an increase in kc (p < 0.05), in Group 2 there was a slight decrease in 2,3-DPG, slight increase in ATP, and no change in ke, and in Group 3 there was a fall in 2,3-DPG (p < 0.05), a rise in ATP, and a fall in kc (p < 0.02). Thus in each group the clinical result correlated with the change in k e. Perhaps the most notable aspect of this finding is that in Group 1 patients the kinetic rate constant prior to treatment was abnormally low while after acetazolamide it rose above normal (Norm = 1.90 sec-l). The Group 2 patients showed no change in symptoms and were found to have slightly lower than normal ke values both before and after treatment with acetazolamide. In those patients in Group 3, not only did their symptoms increase but ke decreased to abnormally low values. There was a correlation between the oxygen release rate from blood and the relief of symptoms: In Group 1 the rate of release of oxygen increased 27% (p < 0.05); in Group 2 there was a 2 % increase (NS), and in Group 3 there was a 22 % decrease in rate of release (p < 0.02). Discussion
These data suggest that in patients treated with acetazolamide the rate of oxygen release from whole blood can be increased and that in some this effect may result in improvement in treadmill exercise testing. Clinical and treadmill improvement parallels changes in bloodoxygen release. There is a rightward shift in the oxyhemoglobin dissociation curve with a fall in pH in these patients. Our data suggest that oxygen transport functions change in a beneficial manner in some patients (Group 1). Acetazolamide causes acidosis but exactly how it produces an increase in the rate of re-
Acidosis in angina
Volume 18 Number 5, Part 1
lease of oxygen from whole blood remains unknown, Pathologic fatigue is the most common side effect noted in this study and limits the value of acetazolamide in the treatment of ischemic heart disease. It may be caused by the acidosis or by a direct central nervous system effect. 3 From data presented it is suggested that any usefulness of this form of therapy is confined to the Group 1 patients-those patients with a lower than normal k c . Such patients responded with a clinical improvement and by an increase in kc (to normal or above), representing a 27% increase in the rate of release of oxygen from whole blood (p < 0.05). Our results warrant further investigation along these lines. The clinical application of these findings should not be applied to ischemic heart disease until further investigation demonstrates their clinical value.
3. 4.
5,
6.
7.
8.
References I. Eliot, R, S., Holsinger, 1, W., Hawkins, H. M.,
and Salhany, 1. M,: Relief of myocardial ischemia associated with increased blood oxygen release, Clin, Res. 20:67, 1972. 2. Gibson, Q. H.: Stopped-flow apparatus for the
9.
597
study of rapid reactions, Discuss. Faraday Soc. 17:137-139, 1954. Goodman, L. S., and Gilman, A .. editors: The pharmacologic basis of therapeutics, ed. 4, New York, 1970, The MacMillan Co., p. 853. Keitt, A. S.: Reduced nicotinamide adenine dinucleotide-linked analysis of 2,3-diphosphoglyceric acid. Spectrophotometric and fluorometric procedures, 1. Lab. Clin. Med. 77:470475, 1971. Lenfant, c., Torrance, J. D" and Reynafarje, C.: Shift of the 02-H6 dissociation curve at altitude: Mechanism and effect, J. App!. Physiol. 30:625-631, 1971. Salhany, J. M., Eliot, R, S., and Mizukami, H.: The effects of 2,3-diphosphoglycerate on the kinetics of deoxygenation of human hemoglobin, Biochem. Biophys. Res. Commun. 39: 10521057, 1970. Salhany, J. M., Keitt, A, S., and Eliot, R. S.: The rate of deoxygenation of red blood cells. Effect of the intracellular 2,3-diphosphoglycerate and pH, FEBS Lett. 16:257-261, 1971. Torrance, J., Jacobs, P., Restrepo, A., Eschbach, J., Lenfant, c., and Finch, C. A.: Intraerythrocyte adaptation to anemia, N. Eng!. J. Med. 283:165-169, 1970. Woodson, R. D., Torrance, 1. D., Shappell, S. D., and Lenfant, c.: The effect of cardiac disease on hemoglobin-oxygen binding, J. Clin. Invest. 49:1349-1356, 1970.
J. W. Holsinger, Jr., M.D., Ph.D., and V. F. Miscia, M.D. Newington, Conn., and Omaha, Nebr. Veterans Administration Hospital, and Department of Internal Medicine, University of Nebraska Medical Center
It is well known 9 that certain patients with
ischemic heart disease may have changes in hemoglobin-oxygen binding. It is less well known that such patients may have changes in the rate of release of oxygen from whole blood. We became interested in determining whether the effects of metabolic acidosis that produce the Bohr effect would also produce a change in the rate of release of oxygen from whole blood. Lenfant, Torrance, and Reynafarje 5 reported that individuals pretreated with acetReceived for publication May 31,1975. Accepted for publication Aug. 12, 1975. Reprint requests to: Dr. J. W. Holsinger, Jr., Chief·of-Staff, Veterans Administration Hospital, Newington, Conn. 06111.
594
azolamide (Diamox) prior to exposure to high altitude have a lower incidence of altitude sickness; the acidosis resulting from acetazolamide decreased the affinity of oxygen for whole blood. We postulated that the objective signs of myocardial ischemia and its symptoms could be relieved by the improvement in the rate of release of oxygen by the blood if the potential increase in available oxygen from whole blood was also associated with an increase in the rate at which oxygen was released from whole blood. A rightward shift of the dissociation curve has been thought to be of benefit in certain conditions that require a greater amount of oxygen release to the tissue level. Woodson 9
Acidosis in angina
Volume IS Number 5, Part I
595
Table I. Results of acetazolamide therapy pH Treadmill result Group 1 Improved
B
Group 2 Stayed the same
n = 7 Group 3 Became worse
n=4
I
A
7,38
7.48
n = 7
2,3-DPG
I
B
15,26 ±2,05
* 7.46 ±0.03
B
A
11.81 ±2,68
7,36 ±0,04
13.49 ±0,82
7,37 ±0,01
p < 0,01
kc
A
3,84
B
1.64 ±0,25
3.67 ±0,09
NS
4.15 ±0,51
1.82 ±0.31
5,05
3,79
p < 0,05
A
I
2,07 ±0.29
%
+27%
1.86 ±0,36
+2%
NS
NS 9,77 ±0,67
I
P < 0.05
* 11.47 ±0,51
13,55 ±0.45
I
3,96
NS
P < 0,01 7.43 ±0,03
ATP
2,05 ±0.23
1.60 ±0,04
-22%
P < 0,02
*
Pooled data
7.45 ±0,03 n = 18
7,32 ±0,06
P < 0,001
13,80 ±1.15
11.04 ±1.95
p < 0,01
4,21 ±0,60
3,79 ±0,17 NS
1.80 ±0.29
1.88 ±0.31
+4%
NS
B: before acetazolamide therapy, A: after acetazolamide therapy. NS: not significant. *Not enough data to do statistics.
has reported a progressive decline in hemoglobin-oxygen affinity with a decrease in cardiac function. This alteration in hemoglobinoxygen binding represents a significant mechanism for adaptation to the limited oxygen supply imposed by the cardiac lesion. Salhany, Eliot, and Mizukarni 6 have shown that a significant acidosis results in an increase in the rate of release (kinetics) of oxygen from hemoglobin, With these concepts in mind we became interested in determining whether we could relieve myocardial ischemia by accelerating blood oxygen transport. 1 Methods
Fifteen patients with objective evidence of myocardial ischemia form the basis of the report. Objective evidence was demonstrated by electrocardiographic evidence of myocardial infarction (transmural, 4 patients; subendocardial, I patient) or abnormal graded treadmill exercise tests. An abnormal graded treadmill exercise test was demonstrated by
electrocardiographic evidence of I mm of horizontal or down sloping st segment depression lasting for 0.08 sec or longer. None of the patients were receiving digitalis and no patient demonstrated electrolyte abnormalities, hyperventilation, or changes on assuming a standing position. The classic changes produced by exercise testing in heart rate and blood pressure were noted. Of the 15 patients, 10 had undergone selective coronary arteriography, 3 of whom had at least one vessel with 70% or more intraluminal obstruction, Seven patients had normal coronary arteries angiographically associated with abnormal treadmill exercise tests and symptoms of angina. Five patients were not catheterized but had symptoms of angina associated with abnormal treadmill exercise tests. Each patient was treated with acetazolamide, 10 to 20 mg/kg body weight, in order to produce a metabolic acidosis. Before and 4 days after treatment, a series of studies consisting of measurement of the rate of release of oxygen
596
Clinical Pharmacology and Therapeutics
Holsinger and Miscia
from whole blood (ke) utilizing a modified Durrum-Gibson stopped flow apparatus 2 • 7 and graded exercise studies were carried out. The level of 2,3-disphosphoglycerate (2,3-DPG) in the red cells was measured by the method of Keitt,4 and adenosine triphosphate (ATP) levels were measured using a spectrophotometer. 8 Following treatment with acetazolamide, each patient was examined for evidence of a decrease in symptomatology and an improvement in treadmill performance. Improvement was judged by a reduction of episodes of angina or a reduction in shortness of breath. An increase in work tolerance was demonstrated by the patient being able to perform on the treadmill for longer periods of time at a progressively increased speed. Those patients whose symptoms became worse were found to have an increase in episodes of angina or shortness of breath. In addition, they demonstrated a decrease in work performance on the treadmill. Myocardial oxygen consumption was not measured in these patients. Results
Table I summarizes the data including pH, 2,3-DPG, ATP, and the deoxygenation rate constant (ke). A total of 15 patients were studied on 18 separate occasions; 7 patients improved symptomatically (Group 1), in 7 there was no change (Group 2), and in 4 there was an increase in symptoms (Group 3). Thus only 39% of patients treated with acetazolamide improved. When a comparison is made between the pooled data before and after treatment with acetazolamide, acidosis (p < 0.001) was produced in all cases as well as a fall in the level of 2,3-DPG (p < 0.01), but no significant change could be demonstrated in the pooled before and after results for ATP and k e. An apparent classic Bohr effect occurred in that pH decreased, 2,3-DPG decreased, and ATP increased slightly. The ke increased slightly, indicating that P 50 had shifted to the right, producing a decrease in the affinity of oxygen for hemoglobin. It appears that more phosphate may be available from the phosphatolysis of 2,3-DPG, thereby increasing the phosphate
pool and providing substrate for the synthesis of ATP. When the data is divided into groups according to the change in symptoms and exercise tolerance, it may be possible to draw certain conclusions. Whereas there was significant acidosis in all groups (Table I), in Group 1 there was a decrease in 2,3-DPG that was not statistically significant, a slight decrease in ATP, and an increase in kc (p < 0.05), in Group 2 there was a slight decrease in 2,3-DPG, slight increase in ATP, and no change in ke, and in Group 3 there was a fall in 2,3-DPG (p < 0.05), a rise in ATP, and a fall in kc (p < 0.02). Thus in each group the clinical result correlated with the change in k e. Perhaps the most notable aspect of this finding is that in Group 1 patients the kinetic rate constant prior to treatment was abnormally low while after acetazolamide it rose above normal (Norm = 1.90 sec-l). The Group 2 patients showed no change in symptoms and were found to have slightly lower than normal ke values both before and after treatment with acetazolamide. In those patients in Group 3, not only did their symptoms increase but ke decreased to abnormally low values. There was a correlation between the oxygen release rate from blood and the relief of symptoms: In Group 1 the rate of release of oxygen increased 27% (p < 0.05); in Group 2 there was a 2 % increase (NS), and in Group 3 there was a 22 % decrease in rate of release (p < 0.02). Discussion
These data suggest that in patients treated with acetazolamide the rate of oxygen release from whole blood can be increased and that in some this effect may result in improvement in treadmill exercise testing. Clinical and treadmill improvement parallels changes in bloodoxygen release. There is a rightward shift in the oxyhemoglobin dissociation curve with a fall in pH in these patients. Our data suggest that oxygen transport functions change in a beneficial manner in some patients (Group 1). Acetazolamide causes acidosis but exactly how it produces an increase in the rate of re-
Acidosis in angina
Volume 18 Number 5, Part 1
lease of oxygen from whole blood remains unknown, Pathologic fatigue is the most common side effect noted in this study and limits the value of acetazolamide in the treatment of ischemic heart disease. It may be caused by the acidosis or by a direct central nervous system effect. 3 From data presented it is suggested that any usefulness of this form of therapy is confined to the Group 1 patients-those patients with a lower than normal k c . Such patients responded with a clinical improvement and by an increase in kc (to normal or above), representing a 27% increase in the rate of release of oxygen from whole blood (p < 0.05). Our results warrant further investigation along these lines. The clinical application of these findings should not be applied to ischemic heart disease until further investigation demonstrates their clinical value.
3. 4.
5,
6.
7.
8.
References I. Eliot, R, S., Holsinger, 1, W., Hawkins, H. M.,
and Salhany, 1. M,: Relief of myocardial ischemia associated with increased blood oxygen release, Clin, Res. 20:67, 1972. 2. Gibson, Q. H.: Stopped-flow apparatus for the
9.
597
study of rapid reactions, Discuss. Faraday Soc. 17:137-139, 1954. Goodman, L. S., and Gilman, A .. editors: The pharmacologic basis of therapeutics, ed. 4, New York, 1970, The MacMillan Co., p. 853. Keitt, A. S.: Reduced nicotinamide adenine dinucleotide-linked analysis of 2,3-diphosphoglyceric acid. Spectrophotometric and fluorometric procedures, 1. Lab. Clin. Med. 77:470475, 1971. Lenfant, c., Torrance, J. D" and Reynafarje, C.: Shift of the 02-H6 dissociation curve at altitude: Mechanism and effect, J. App!. Physiol. 30:625-631, 1971. Salhany, J. M., Eliot, R, S., and Mizukami, H.: The effects of 2,3-diphosphoglycerate on the kinetics of deoxygenation of human hemoglobin, Biochem. Biophys. Res. Commun. 39: 10521057, 1970. Salhany, J. M., Keitt, A, S., and Eliot, R. S.: The rate of deoxygenation of red blood cells. Effect of the intracellular 2,3-diphosphoglycerate and pH, FEBS Lett. 16:257-261, 1971. Torrance, J., Jacobs, P., Restrepo, A., Eschbach, J., Lenfant, c., and Finch, C. A.: Intraerythrocyte adaptation to anemia, N. Eng!. J. Med. 283:165-169, 1970. Woodson, R. D., Torrance, 1. D., Shappell, S. D., and Lenfant, c.: The effect of cardiac disease on hemoglobin-oxygen binding, J. Clin. Invest. 49:1349-1356, 1970.
