Evaluation of the Metabolic Compensation After Treadmill Test in Patients with Peripheral Occlusive Arterial Disease Daniel Duprez, M.D., D.Sc., Ph.D., F.I.C.A. Marc De Buyzere, M.D. Annie Van Wassenhove, M.D. and Denis Clement, M.D., F.I.C.A.
GENT, BELGIUM
Abstract Patterns of release of lactate, hypoxanthine, and arginine into the bloodstream after a standardized treadmill test (twelve minutes, 1.6-2.8 mph, inclination 0,5,10,15%) were recorded in 21 consecutive patients with stage II peripheral arterial occlusive disease. Heart rate, systolic blood pressure, ankle blood pressure, and ankle/brachial systolic blood pressure ratio (A/B ratio), as well as plasma lactate, plasma hypoxanthine and serum arginine were recorded before and at fifteen to thirty-minute intervals for up to two hours after the treadmill test. Immediately after the treadmill test, lactate levels (36.6 ± 3.7 mg/L) and hypoxanthine levels (2.73 ± 0.19 mmol/L) were significantly (p < 0.001) increased but returned to preexercise levels after thirty and sixty minutes, respectively. Arginine levels did not change significantly. Ankle blood pressure (57 ± 5 mm Hg) and A/B ratio (0.40 ± 0.04) were significantly (p < 0.001) decreased after exercise, while heart rate and systolic blood pressure were increased. These parameters returned to normal as well within a half hour after exercise. Absolute walking distance correlated significantly (p < 0.01) with the postexercise systolic blood pressure (r 0.63) and A/B ratio (r 0.62), ankle pressure (r 0.72). Induced hypoxanthine and lactate production intercorrelated significantly positively (r 0.57, p = 0.007) but were independent of the absolute walking distance. In contrast with lactate, hypoxanthine production correlated significantly with postexercise ankle pressure (r 0.49, p 0.02) and exerciseinduced fall in A/B ratio (r 0.66, p 0.001). Initial preexercise venous hypoxanthine, but not lactate levels were correlated with postexercise A/B ratio (r 0.49, p = 0.02) but not with the patients’ walking distance. These results indicate that hypoxanthine determination may reflect more closely than lactate the degree of metabolic compensation after exercise in peripheral arterial occlusive disease. =
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From the
Department of Cardiology-Angiology of the University Hospital of Gent, Gent, Belgium
126
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127 Introduction
Energy production and substrate utilization during and after exercise testing have been intensively investigated in apparently healthy volunteers,’ in well-trained athletes,’ and in patients with coronary heart disease,’ but to a lesser degree in patients with walking capacity limited because of peripheral arterial occlusive disease (PAOD).4 Pathophysiologic examinations in PAOD revealed an imbalance between blood supply and substrate requirements, so that even at low work loads an aerobic glycolysis becomes activated. Rexroth et al5 demonstrated that, independent of the work load, calf-exercise-induced femoral venous lactate levels in stage II PAOD patients were significantly higher than in healthy subjects. Another well-characterized phenomenon in metabolic deterioration during tissue hypoxia is the degradation of energy-rich purines with subsequent release into the bloodstream of hypoxanthine, the end product of adenine nucleotide catabolism (ATP-AMP-adenosineinosine-hypoxanthine).6 The majority of these studies have been performed in animal models, and there are only a few reports on the purine nucleotide cycle in naturally and experimentally induced muscle ischemia in human beings&dquo;’ Significant release of hypoxanthine after exercise testing has been described by S~6rlie et al,8 but these authors did not study its role in the prediction of the degree of metabolic compensation in occlusive arterial disease. The aim of the present study is to compare the patterns of release of lactate, hypoxanthine, and arginine in stage II PAOD patients after a standardized treadmill test and to examine the relationship of quantitative release of these metabolic parameters, first to the maximal walking distance and, second, to the fall of ankle systolic blood pressure or ankle/brachial systolic blood pressure ratio (A/B ratio) after exercise. The power of initial preexercise biochemical parameters for prediction of walking distance and of the exercise-induced fall in ankle systolic blood pressure is analyzed as well. Patients and Methods
Twenty-one consecutive patients (19 men, 2 women) with a mean age of 59.8 years (SEM 1.8 years) gave informed consent to be enrolled in this study. All of them had suffered from PAOD for at least several months with an arterial insufficiency at the second stage of Fontaine’s classification. Prognosis and evaluation of PAOD had been established earlier on the basis of a typical clinical history, decrease of exercise-induced ankle systolic blood pressure (by Doppler ultrasound examination), and measurements by venous occlusion plethysmography. None of the studied patients’ exercise capacity was limited by heart failure, unstable angina pectoris, or severe hypertension. In all of them renal function was apparently normal as judged by the mean serum creatinine concentration of 0.9 mg/dL (range 0.7-1.3 mg/dL). Venous blood samples were taken by an indwelling catheter into the brachial vein maintained open by heparinized 0.9~o (w/v) sodium chloride. Ethylenediaminetetraacetate was used as an anticoagulant for plasma samples and the test was started after thirty minutes of supine rest.
Downloaded from ang.sagepub.com at UCSF LIBRARY & CKM on March 24, 2015
128 All patients underwent a standardized, multistage, twelve-minute exercise test on a treadmill with adjustable speed and inclination. The walking speed was kept constant (1.6-2.8 mph) depending on the patient’s capacity. For the first three minutes the patients had to walk at an inclination of 0~10, and then the inclination increased every three minutes
FIG. 1. Correlation between the absolute walking distance and the ankle/brachial blood pressure ratio after a treadmill test in 21 patients with peripheral occlusive arterial disease.
5070 up to 1 5 Vo . The test was carried out in the morning in a quiet room at constant temperature after an overnight fast. Systolic and diastolic blood pressure and heart rate were recorded immediately before and after exercise and then every fifteen minutes for two hours during the postexercise recovery period with the patient in supine position. Ankle systolic blood pressure was determined by Doppler ultra sound before and every thirty minutes after the treadmill test for up to two hours after cessation. For all patients anklebrachial systolic blood pressure ratios (A/B ratio) and the absolute walking distance (AWD) on the treadmill were calculated. Venipunctures for assessment of plasma lactate and hypoxanthine and serum arginine took place on the same time schedule as for brachial blood pressure measurements. Plasma lactate concentrations were determined by a commercial enzymatic procedure. Plasma hypoxanthine was assayed by an automated enzymatic procedure on deproteinized blood samples according to Bolhuis et a1.9 Serum arginine was measured by the enzymatic procedure of Konings. 10
by
Statistical Analysis All data are expressed
as mean values ± standard error of the mean (SEM). Differand ences between preexercise postexercise values of the study parameters were analyzed with Student’s t test for paired data or with the Wilcoxon matched-pairs, signed-ranks test with two-tailed probability. The relationship between treadmill-exercise-induced changes
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129
FIG. 2. Correlation between exercise-induced lactate and hypoxanthine production in 21 patients with peripheral occlusive arterial disease. Results are given as the difference in concentrations between values obtained before the treadmill test and values obtained immediately after the end of the test.
in biochemical parameters and ankle systolic blood pressure after exercise was examined by the correlation coefficient of their linear regression equations and considered signifilevel. cant at the p < 0.05 Results The twelve-minute treadmill test was completed by 11 of the 21 patients (52~o); all other patients had to discontinue because of exhaustion. The walking distance was shown to be independent of the patients’ age, preexercise values of heart rate, systolic blood pressure, and ankle pressure and of initial values of lactate and hypoxanthine. A significant correlation was observed between the walking distance and, respectively, the systolic blood pressure (r = -0.62, p = 0.003) and the minimal ankle pressure (r = 0.63, p = 0.002) immediately after treadmill exercise. An even stronger correlation was found between AWD and the corresponding A/B ratio (r .= 0.72, p = 0.0002) (Fig. 1). The evolution of heart rate, systolic blood pressure, ankle pressure, A/B ratio, and lactate and hypoxanthine levels from preexercise to, respectively, zero, fifteen, and thirty minutes after the treadmill test is summarized in Table I. Seven patients (33330) showed slightly increased lactate levels at rest, and resting hypoxanthine was increased in all patients. All study parameters (Table I) changed significantly (p < 0.001 ) immediately after exercise. Already after a recovery period of fifteen minutes heart rate and systolic blood pressure had returned to baseline; after thirty minutes, ankle pressure and A/B ratio had returned to normal as well. Lactate and hypoxanthine levels remained still significantly
Downloaded from ang.sagepub.com at UCSF LIBRARY & CKM on March 24, 2015
130 TABLE I Evolution of AnklelBrachial Systolic Blood Pressure Ratio, Lactate and Hypoxanthine Levels in Patients with Peripheral Arterial Occlusive Disease Before and After a Treadmill Test (Mean ± SEM) (N 21) =
*p < 0.001, mill test
* *p < 0.01 versus values before the treadmill test. One hour after the treadhypoxanthine levels renormalized to 2.13 ±0.12 ~mol/L. nd: not determined.
(p< 0.001) increased at fifteen minutes, and it took thirty minutes for lactate to return to preexercise values. For hypoxanthine the process of elimination from the plasma compartment took longer (one hour). Relative venous lactate production was more pronounced than for venous hypoxanthine production as evidenced by a ratio of mean postexercise to baseline concentration of 2.01 for lactate vs 1.26 for hypoxanthine. Both biochemical 0.007 for induced lac0.57, p parameters intercorrelated significantly positively (r tate vs induced hypoxanthine release; Fig. 2). Nevertheless, the rise in systemic plasma lactate and hypoxanthine concentrations did not correlate significantly with the individual exercise endurance (AWD). On the other hand a significant correlation was observed between hypoxanthine production and the absolute figures of, respectively, ankle systolic blood pressure (r 0.49, p 0. 51, p 0.023) and A/B ratios (r 0.016) obtained immediately after exercise testing. In sharp contrast the relationship between lactate production and ankle pressure or A/B ratio turned out to be nonsignificant. A still higher sig=
=
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=
=
-
=
nificance could be documented for the correlation between the exercise-induced fall in A/B ratio (difference between baseline and postexercise A/B ratios) and the hypoxanthine production (r = 0.66, p = 0.001; Fig. 3). Figure 4 clearly demonstrates that such a significant correlation is totally lacking for lactate production (r 0.24, p 0.299). Furthermore, initial pretreadmill exercise venous lactate concentrations were of no additional value either for the prediction of the walking distance (r 0.03) or for prediction of the fall in ankle pressure (r 0.20) or in A/B ratio (r 0.23). On the contrary, initial pretreadmill exercise hypoxanthine concentrations correlated much better with postexercise ankle pressure (r 0.45, p 0.037) or Their correlation with the with postexercise A/B ratio (r walking 0.49, p 0.023). distance (r = - 0.26, p = 0.24) was only very weak and not significant. =
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131
FIG. 3.
Correlation between
hypoxanthine production after
a
treadmill test and the induced reduction of ankle/brachial systolic blood pressure ratio in 21 patients with peripheral occlusive arterial disease.
FIG. 4. Correlation between lacproduction after a treadmill test and the induced reduction of ankle/brachial systolic blood pressure ratio in 21 patients with peripheral occlusive arterial disease.
tate
Serum arginine levels did not change significantly during two hours of recovery after the treadmill test: 0.27 ± 0.05 g/L (before); 0.31 ± 0.08 g/L (zero minute); 0.24 ± 0.07 g/L (fifteen minute); 0.28 ± 0.09 g/L (thirty minutes); 0.26 ± 0.08 g/L (sixty minutes), and 0.33 ± 0.08 g/L (one hundred and twenty minutes). This pattern failed to correlate with any further study parameter of the PAOD patient group and could, therefore, be used as an invariant control parameter during the study period.
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132 Discussion In this
study lactate and hypoxanthine levels have been recorded to measure the degree of metabolic compensation after an exercise test in PAOD. Earlier, significant increases in peripheral venous plasma lactate and hypoxanthine levels had been associated with severe hypoxia in newborns.&dquo; Even in conditions with severe cardiac hypoxia and ischemia-eg, diagnostic cycloergometry, unstable coronary artery disease-no or only limited increase of these parameters in peripheral venous blood could be demonstrated. Only in more severe induced cardiac ischemia-eg, cardioplegia, pacing stress test, percutaneous transluminal angioplasty-could significant arteriovenous concentration gradients be found, and peripheral levels were usually only borderline increased.’2 Exclusion of patients with limitation of exercise capacity because of major cardiac symptoms permitted elimination of possible bias of the test results. Several investigators5’’3’’4 have emphasized that the patterns of purine degradation and hypoxanthine production observed during and after exercise tests are not totally concomitant with that of lactate. During exercise testing, lactate production significantly exceeds hypoxanthine production. One hypothesis is that in the immediate postexercise recovery period there is an antagonism between a continuous elimination process of hypoxanthine and a still ongoing process of ATP degradation and washout of hypoxanthine from the muscles while lactate production stops at the end of the test. In our study we can confirm this hypothesis, since (Table I) the ratio of preexercise to immediate postexercise concentration is much higher for lactate. Furthermore, thirty minutes after the test, lactate levels renormalized, whereas it took one hour for hypoxanthine to do so. Sorlie et al8 have described increased femoral venous resting hypoxanthine values in POAD patients. In addition, in our study, we could demonstrate a weak but significant correlation between resting peripheral venous hypoxanthine (not lactate) and the fall of ankle systolic pressure immediately after cessation of exercise. Among the hypoxanthine precursors in the stepwise ATP degradation process, adenosine and inosine are the most prominent. These molecules are synthesized locally in the muscles and in the vascular endothelium in equimolecular quantities as hypoxanthine. Animal studies&dquo;’ 16 have indicated that, in particular, adenosine plays an important role as a potent vasodilator in the regulation of skeletal muscle blood flow. Therefore, the relationship in PAOD patients of ankle systolic pressure or A/B ratio and exercise-induced hypoxanthine production was evaluated and compared with lactate production. Unlike a rather good correlation between lactate and hypoxanthine release, a significant correlation with the A/B ratio could be calculated only for hypoxanthine. These conflicting data might be partly explained by the above-mentioned difference in pattern of release of both parameters during and after the exercise test. Sorlie et al8 found a good time relationship during the first ten minutes after exhaustive exercise in PAOD patients between muscle blood flow and hypoxanthine release and concluded that purine metabolites play an important role in the autoregulation in skeletal muscle blood flow. These authors did not, however, correlate individual changes in blood flow or pressure with individual changes in hypoxanthine levels. They also introduced the hypothesis that increased venous plasma hypoxanthine con-
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133
centrations at rest may indicate peripheral arterial insufficiency. We could partly confirm their findings, since preexercise hypoxanthine values correlated inversely with the ankle pressure after treadmill exercise but not with the walking distance. Conclusions The present study in stage II PAOD patients demonstrates a high peripheral venous release of lactate and hypoxanthine, but not of arginine, after a standardized twelve-minute treadmill test. A significant correlation is found between postexercise A/B ratio and both walking distance and hypoxanthine production. Preexercise hypoxanthine (not lactate) correlates weakly but significantly with postexercise A/B ratio. These results indicate that hypoxanthine determination may reflect more closely than lactate the degree of metabolic compensation after exercise in PAOD patients.
Acknowledgments The authors wish to thank Mrs. L. Packet for her secretarial assistance in the preparation of the manuscript.
Duprez, M.D., D.Sc., Ph.D., F.I.C.A. Department Cardiology-Angiology University Hospital
D.
De Pintelaan 185
B-9000 Gent, Belgium
References 1. Harkness
2.
3.
4.
5.
6.
7.
8.
RA, Simmonds RJ, Coade SB: Purine transport and metabolism in man: The effect of exercise on concentrations of purine bases, nucleosides and nucleotides in plasma, urine, leukocytes and erythrocytes. Clin Sci 64:333-340, 1983. Poortmans JR: Exercise and renal function. Exercise Sports Sci Rev 5:255-294, 1977. Kugler G: Myocardial release of lactate, inosine and hypoxanthine during atrial pacing and exercise induced angina. Circulation 95:43-49, 1979. Sørlie D, Myhre K, Mjøs OD: Exercise- and postexercise metabolism of the lower leg in patients with peripheral arterial insufficiency. Scand J Clin Lab Invest 38:635-642, 1978. Rexroth W, Hageloch W, Isgro F, et al: Influence of peripheral arterial occlusive disease on muscular metabolism. Part 1: Changes in lactate, ammonia, and hypoxanthine concentration in femoral blood. Klin Wochenschr 67:576-582, 1989. Fox IM: Metabolic basis for disorders of purine nucleotide degradation. Metabolism 30:616-634, 1981. Sutton JR, Toews CJ, Ward GR: Purine metabolism during strenuous muscular exercise in man. Metabolism 29:254-260, 1980. Sørlie D, Myhre K, Saugstad OD, et al: Release of hypoxanthine and phosphate from exercising human legs with and without arterial insufficiency. Acta Med Scand 211:281-286, 1982.
9. Bolhuis PA, Zwart R, Bär PR, et al: Rapid determination of the hypoxanthine increase in ischemic exercise tests. Clin Chem 34:1607-1610, 1988. 10. Konings CH: A kinetic procedure for the estimation of arginine in serum using arginine kinase. Clin Chim Acta 176:185-194, 1988. 11. Saugstad OD: Hypoxanthine as a measurement of hypoxia. Pediatr Res 9:158-161, 1975. 12. Harmsen E, de Jong JW, Serruys PW: Hypoxanthine production by ischemic heart demonstrated by HPLC of blood purine nucleosides and oxypurines. Clin Chim Acta 115:73-84, 1981. 13. Patterson VH, Kouser KK, Brooke HM: Forearm exercise increases plasma hypoxanthine. J Neur Neurosurg Psych 45:552-553, 1982. 14. Weicker H: Purinnukleotidzyklus und muskulre Ammoniak-produktion. Dt Z Sportmed 39:172-178, 1988. 15. Rubio R, Berne RM, Dobson JG: Sites of adenosine production in cardiac and skeletal muscle. Am J Physiol 225:938-953, 1973. 16. Tominaga S: Local regulation of blood flow in the skeletal muscle. Probable participation of adenosine. Scand J Clin Lab Invest 29:129-133, 1972.
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GENT, BELGIUM
Abstract Patterns of release of lactate, hypoxanthine, and arginine into the bloodstream after a standardized treadmill test (twelve minutes, 1.6-2.8 mph, inclination 0,5,10,15%) were recorded in 21 consecutive patients with stage II peripheral arterial occlusive disease. Heart rate, systolic blood pressure, ankle blood pressure, and ankle/brachial systolic blood pressure ratio (A/B ratio), as well as plasma lactate, plasma hypoxanthine and serum arginine were recorded before and at fifteen to thirty-minute intervals for up to two hours after the treadmill test. Immediately after the treadmill test, lactate levels (36.6 ± 3.7 mg/L) and hypoxanthine levels (2.73 ± 0.19 mmol/L) were significantly (p < 0.001) increased but returned to preexercise levels after thirty and sixty minutes, respectively. Arginine levels did not change significantly. Ankle blood pressure (57 ± 5 mm Hg) and A/B ratio (0.40 ± 0.04) were significantly (p < 0.001) decreased after exercise, while heart rate and systolic blood pressure were increased. These parameters returned to normal as well within a half hour after exercise. Absolute walking distance correlated significantly (p < 0.01) with the postexercise systolic blood pressure (r 0.63) and A/B ratio (r 0.62), ankle pressure (r 0.72). Induced hypoxanthine and lactate production intercorrelated significantly positively (r 0.57, p = 0.007) but were independent of the absolute walking distance. In contrast with lactate, hypoxanthine production correlated significantly with postexercise ankle pressure (r 0.49, p 0.02) and exerciseinduced fall in A/B ratio (r 0.66, p 0.001). Initial preexercise venous hypoxanthine, but not lactate levels were correlated with postexercise A/B ratio (r 0.49, p = 0.02) but not with the patients’ walking distance. These results indicate that hypoxanthine determination may reflect more closely than lactate the degree of metabolic compensation after exercise in peripheral arterial occlusive disease. =
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From the
Department of Cardiology-Angiology of the University Hospital of Gent, Gent, Belgium
126
Downloaded from ang.sagepub.com at UCSF LIBRARY & CKM on March 24, 2015
127 Introduction
Energy production and substrate utilization during and after exercise testing have been intensively investigated in apparently healthy volunteers,’ in well-trained athletes,’ and in patients with coronary heart disease,’ but to a lesser degree in patients with walking capacity limited because of peripheral arterial occlusive disease (PAOD).4 Pathophysiologic examinations in PAOD revealed an imbalance between blood supply and substrate requirements, so that even at low work loads an aerobic glycolysis becomes activated. Rexroth et al5 demonstrated that, independent of the work load, calf-exercise-induced femoral venous lactate levels in stage II PAOD patients were significantly higher than in healthy subjects. Another well-characterized phenomenon in metabolic deterioration during tissue hypoxia is the degradation of energy-rich purines with subsequent release into the bloodstream of hypoxanthine, the end product of adenine nucleotide catabolism (ATP-AMP-adenosineinosine-hypoxanthine).6 The majority of these studies have been performed in animal models, and there are only a few reports on the purine nucleotide cycle in naturally and experimentally induced muscle ischemia in human beings&dquo;’ Significant release of hypoxanthine after exercise testing has been described by S~6rlie et al,8 but these authors did not study its role in the prediction of the degree of metabolic compensation in occlusive arterial disease. The aim of the present study is to compare the patterns of release of lactate, hypoxanthine, and arginine in stage II PAOD patients after a standardized treadmill test and to examine the relationship of quantitative release of these metabolic parameters, first to the maximal walking distance and, second, to the fall of ankle systolic blood pressure or ankle/brachial systolic blood pressure ratio (A/B ratio) after exercise. The power of initial preexercise biochemical parameters for prediction of walking distance and of the exercise-induced fall in ankle systolic blood pressure is analyzed as well. Patients and Methods
Twenty-one consecutive patients (19 men, 2 women) with a mean age of 59.8 years (SEM 1.8 years) gave informed consent to be enrolled in this study. All of them had suffered from PAOD for at least several months with an arterial insufficiency at the second stage of Fontaine’s classification. Prognosis and evaluation of PAOD had been established earlier on the basis of a typical clinical history, decrease of exercise-induced ankle systolic blood pressure (by Doppler ultrasound examination), and measurements by venous occlusion plethysmography. None of the studied patients’ exercise capacity was limited by heart failure, unstable angina pectoris, or severe hypertension. In all of them renal function was apparently normal as judged by the mean serum creatinine concentration of 0.9 mg/dL (range 0.7-1.3 mg/dL). Venous blood samples were taken by an indwelling catheter into the brachial vein maintained open by heparinized 0.9~o (w/v) sodium chloride. Ethylenediaminetetraacetate was used as an anticoagulant for plasma samples and the test was started after thirty minutes of supine rest.
Downloaded from ang.sagepub.com at UCSF LIBRARY & CKM on March 24, 2015
128 All patients underwent a standardized, multistage, twelve-minute exercise test on a treadmill with adjustable speed and inclination. The walking speed was kept constant (1.6-2.8 mph) depending on the patient’s capacity. For the first three minutes the patients had to walk at an inclination of 0~10, and then the inclination increased every three minutes
FIG. 1. Correlation between the absolute walking distance and the ankle/brachial blood pressure ratio after a treadmill test in 21 patients with peripheral occlusive arterial disease.
5070 up to 1 5 Vo . The test was carried out in the morning in a quiet room at constant temperature after an overnight fast. Systolic and diastolic blood pressure and heart rate were recorded immediately before and after exercise and then every fifteen minutes for two hours during the postexercise recovery period with the patient in supine position. Ankle systolic blood pressure was determined by Doppler ultra sound before and every thirty minutes after the treadmill test for up to two hours after cessation. For all patients anklebrachial systolic blood pressure ratios (A/B ratio) and the absolute walking distance (AWD) on the treadmill were calculated. Venipunctures for assessment of plasma lactate and hypoxanthine and serum arginine took place on the same time schedule as for brachial blood pressure measurements. Plasma lactate concentrations were determined by a commercial enzymatic procedure. Plasma hypoxanthine was assayed by an automated enzymatic procedure on deproteinized blood samples according to Bolhuis et a1.9 Serum arginine was measured by the enzymatic procedure of Konings. 10
by
Statistical Analysis All data are expressed
as mean values ± standard error of the mean (SEM). Differand ences between preexercise postexercise values of the study parameters were analyzed with Student’s t test for paired data or with the Wilcoxon matched-pairs, signed-ranks test with two-tailed probability. The relationship between treadmill-exercise-induced changes
Downloaded from ang.sagepub.com at UCSF LIBRARY & CKM on March 24, 2015
129
FIG. 2. Correlation between exercise-induced lactate and hypoxanthine production in 21 patients with peripheral occlusive arterial disease. Results are given as the difference in concentrations between values obtained before the treadmill test and values obtained immediately after the end of the test.
in biochemical parameters and ankle systolic blood pressure after exercise was examined by the correlation coefficient of their linear regression equations and considered signifilevel. cant at the p < 0.05 Results The twelve-minute treadmill test was completed by 11 of the 21 patients (52~o); all other patients had to discontinue because of exhaustion. The walking distance was shown to be independent of the patients’ age, preexercise values of heart rate, systolic blood pressure, and ankle pressure and of initial values of lactate and hypoxanthine. A significant correlation was observed between the walking distance and, respectively, the systolic blood pressure (r = -0.62, p = 0.003) and the minimal ankle pressure (r = 0.63, p = 0.002) immediately after treadmill exercise. An even stronger correlation was found between AWD and the corresponding A/B ratio (r .= 0.72, p = 0.0002) (Fig. 1). The evolution of heart rate, systolic blood pressure, ankle pressure, A/B ratio, and lactate and hypoxanthine levels from preexercise to, respectively, zero, fifteen, and thirty minutes after the treadmill test is summarized in Table I. Seven patients (33330) showed slightly increased lactate levels at rest, and resting hypoxanthine was increased in all patients. All study parameters (Table I) changed significantly (p < 0.001 ) immediately after exercise. Already after a recovery period of fifteen minutes heart rate and systolic blood pressure had returned to baseline; after thirty minutes, ankle pressure and A/B ratio had returned to normal as well. Lactate and hypoxanthine levels remained still significantly
Downloaded from ang.sagepub.com at UCSF LIBRARY & CKM on March 24, 2015
130 TABLE I Evolution of AnklelBrachial Systolic Blood Pressure Ratio, Lactate and Hypoxanthine Levels in Patients with Peripheral Arterial Occlusive Disease Before and After a Treadmill Test (Mean ± SEM) (N 21) =
*p < 0.001, mill test
* *p < 0.01 versus values before the treadmill test. One hour after the treadhypoxanthine levels renormalized to 2.13 ±0.12 ~mol/L. nd: not determined.
(p< 0.001) increased at fifteen minutes, and it took thirty minutes for lactate to return to preexercise values. For hypoxanthine the process of elimination from the plasma compartment took longer (one hour). Relative venous lactate production was more pronounced than for venous hypoxanthine production as evidenced by a ratio of mean postexercise to baseline concentration of 2.01 for lactate vs 1.26 for hypoxanthine. Both biochemical 0.007 for induced lac0.57, p parameters intercorrelated significantly positively (r tate vs induced hypoxanthine release; Fig. 2). Nevertheless, the rise in systemic plasma lactate and hypoxanthine concentrations did not correlate significantly with the individual exercise endurance (AWD). On the other hand a significant correlation was observed between hypoxanthine production and the absolute figures of, respectively, ankle systolic blood pressure (r 0.49, p 0. 51, p 0.023) and A/B ratios (r 0.016) obtained immediately after exercise testing. In sharp contrast the relationship between lactate production and ankle pressure or A/B ratio turned out to be nonsignificant. A still higher sig=
=
-
=
=
=
-
=
nificance could be documented for the correlation between the exercise-induced fall in A/B ratio (difference between baseline and postexercise A/B ratios) and the hypoxanthine production (r = 0.66, p = 0.001; Fig. 3). Figure 4 clearly demonstrates that such a significant correlation is totally lacking for lactate production (r 0.24, p 0.299). Furthermore, initial pretreadmill exercise venous lactate concentrations were of no additional value either for the prediction of the walking distance (r 0.03) or for prediction of the fall in ankle pressure (r 0.20) or in A/B ratio (r 0.23). On the contrary, initial pretreadmill exercise hypoxanthine concentrations correlated much better with postexercise ankle pressure (r 0.45, p 0.037) or Their correlation with the with postexercise A/B ratio (r walking 0.49, p 0.023). distance (r = - 0.26, p = 0.24) was only very weak and not significant. =
=
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Downloaded from ang.sagepub.com at UCSF LIBRARY & CKM on March 24, 2015
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131
FIG. 3.
Correlation between
hypoxanthine production after
a
treadmill test and the induced reduction of ankle/brachial systolic blood pressure ratio in 21 patients with peripheral occlusive arterial disease.
FIG. 4. Correlation between lacproduction after a treadmill test and the induced reduction of ankle/brachial systolic blood pressure ratio in 21 patients with peripheral occlusive arterial disease.
tate
Serum arginine levels did not change significantly during two hours of recovery after the treadmill test: 0.27 ± 0.05 g/L (before); 0.31 ± 0.08 g/L (zero minute); 0.24 ± 0.07 g/L (fifteen minute); 0.28 ± 0.09 g/L (thirty minutes); 0.26 ± 0.08 g/L (sixty minutes), and 0.33 ± 0.08 g/L (one hundred and twenty minutes). This pattern failed to correlate with any further study parameter of the PAOD patient group and could, therefore, be used as an invariant control parameter during the study period.
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132 Discussion In this
study lactate and hypoxanthine levels have been recorded to measure the degree of metabolic compensation after an exercise test in PAOD. Earlier, significant increases in peripheral venous plasma lactate and hypoxanthine levels had been associated with severe hypoxia in newborns.&dquo; Even in conditions with severe cardiac hypoxia and ischemia-eg, diagnostic cycloergometry, unstable coronary artery disease-no or only limited increase of these parameters in peripheral venous blood could be demonstrated. Only in more severe induced cardiac ischemia-eg, cardioplegia, pacing stress test, percutaneous transluminal angioplasty-could significant arteriovenous concentration gradients be found, and peripheral levels were usually only borderline increased.’2 Exclusion of patients with limitation of exercise capacity because of major cardiac symptoms permitted elimination of possible bias of the test results. Several investigators5’’3’’4 have emphasized that the patterns of purine degradation and hypoxanthine production observed during and after exercise tests are not totally concomitant with that of lactate. During exercise testing, lactate production significantly exceeds hypoxanthine production. One hypothesis is that in the immediate postexercise recovery period there is an antagonism between a continuous elimination process of hypoxanthine and a still ongoing process of ATP degradation and washout of hypoxanthine from the muscles while lactate production stops at the end of the test. In our study we can confirm this hypothesis, since (Table I) the ratio of preexercise to immediate postexercise concentration is much higher for lactate. Furthermore, thirty minutes after the test, lactate levels renormalized, whereas it took one hour for hypoxanthine to do so. Sorlie et al8 have described increased femoral venous resting hypoxanthine values in POAD patients. In addition, in our study, we could demonstrate a weak but significant correlation between resting peripheral venous hypoxanthine (not lactate) and the fall of ankle systolic pressure immediately after cessation of exercise. Among the hypoxanthine precursors in the stepwise ATP degradation process, adenosine and inosine are the most prominent. These molecules are synthesized locally in the muscles and in the vascular endothelium in equimolecular quantities as hypoxanthine. Animal studies&dquo;’ 16 have indicated that, in particular, adenosine plays an important role as a potent vasodilator in the regulation of skeletal muscle blood flow. Therefore, the relationship in PAOD patients of ankle systolic pressure or A/B ratio and exercise-induced hypoxanthine production was evaluated and compared with lactate production. Unlike a rather good correlation between lactate and hypoxanthine release, a significant correlation with the A/B ratio could be calculated only for hypoxanthine. These conflicting data might be partly explained by the above-mentioned difference in pattern of release of both parameters during and after the exercise test. Sorlie et al8 found a good time relationship during the first ten minutes after exhaustive exercise in PAOD patients between muscle blood flow and hypoxanthine release and concluded that purine metabolites play an important role in the autoregulation in skeletal muscle blood flow. These authors did not, however, correlate individual changes in blood flow or pressure with individual changes in hypoxanthine levels. They also introduced the hypothesis that increased venous plasma hypoxanthine con-
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133
centrations at rest may indicate peripheral arterial insufficiency. We could partly confirm their findings, since preexercise hypoxanthine values correlated inversely with the ankle pressure after treadmill exercise but not with the walking distance. Conclusions The present study in stage II PAOD patients demonstrates a high peripheral venous release of lactate and hypoxanthine, but not of arginine, after a standardized twelve-minute treadmill test. A significant correlation is found between postexercise A/B ratio and both walking distance and hypoxanthine production. Preexercise hypoxanthine (not lactate) correlates weakly but significantly with postexercise A/B ratio. These results indicate that hypoxanthine determination may reflect more closely than lactate the degree of metabolic compensation after exercise in PAOD patients.
Acknowledgments The authors wish to thank Mrs. L. Packet for her secretarial assistance in the preparation of the manuscript.
Duprez, M.D., D.Sc., Ph.D., F.I.C.A. Department Cardiology-Angiology University Hospital
D.
De Pintelaan 185
B-9000 Gent, Belgium
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