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Changes in R wave amplitude during aerobic exercise stress testing in hypertensive adolescents
Changes in R Wave Amplitude During Aerobic Exercise Stress Testing in Hypertensive Adolescents BONITA DAVID
FALKNER,
MD
T. LOWENTHAL,
MD,
FACC
MELTON B. AFFRIME, PharmD BARBARA
Philadelphia,
HAMSTRA,
RN
Pennsylvania
From the Department of Pediatrics and Medicine and Likoff Cardiovascular Institute, Hahnemann Medical College and Hospital, Philadelphia, Pennsylvania. Manuscriot received Auaust 31. 198 1; devised manuscripi received December 14, 1981, accepted January 22, 1982. Address for reprints: Bonita Falkner, MD, Departmentof Pediatrics, Hahnemann Medical Colleae and Hosoital. 230 North Broad Street. Philadelphia, Pen&lvania 19102.
152
July 1982
The change in R wave amplitude during progressive aerobic exercise was studied in hypertensive adolescent boys. A comparable control group consisted of normotensive adolescent boys matched for age, body size and race. Twenty-four normotensive and 22 hypertensive subjects exercised to exhaustion on a treadmill utilizing the Bruce protocol. Blood pressure and heart rate were monitored during exercise and recovery. The change in R wave amplitude in a lead V5 electrocardiogram was determined at each level of exercise. The normotensive group demonstrated a progressive increase in systolic pressure, heart rate and ratepressure product (heart rate X systolic pressure) during exercise and a progressive decrease in R wave amplitude with a significant correlation of R wave change versus the cardiac response variable (p
Hypertension is a major health problem with the morbid consequences of the uncontrolled disease well known. Although full understanding of the pathogenic mechanism remains elusive, evidence does exist that the prevalence of target organ damage is diminished with reduction of blood pressure.1,2 Recognition of a significant prevalence of essential hypertension in adolescence3v4 is emerging together with the concept that the initiating mechanisms for this disorder may be operative in the childhood years.5T6 An intriguing issue is whether the vascular component of the disorder is increased by the pressure level itself and, if so, what level of blood pressure elevation imposes the risk for vasuclar or target organ damage. Exercise stress testing in adults has become a clinically useful means of evaluating symptoms of ischemia and heart disease, and for deriving exercise prescriptions in cardiac rehabilitation. Studies utilizing strenuous aerobic exercise stress testing in young people7,s demonstrated similar patterns of blood pressure and heart rate response during exercise in hypertensive and normotensive adolescents but with higher levels of systolic blood pressure in the former. These studies in the young indicate absence of the typical electrocardiographic abnormalities such as arrhythmias and S-T depression that in adults denote a risk status for significant cardiac disease. -It has been reported9 that changes in the amplitude of the R wave during exercise may be more sensitive than S-T changes as an indicator of myocardial dysfunction in adults. The failure of the ischemic ventricle to decrease its volume during strenuous aerobic exercise may be responsible for absence of the u&al reduction in R wave amplitude.10,11
The American Journal of CARDIOLOGY
Volume 50
R WAVE CHANGE IN HYPERTENSIVE
Baseline Values (mean f standard deviation) Hypertensive Group (n = 22)
Methods Study subjects: Participants in the study included 22 adolescent boys with mild hypertension. All 22 had a casual determination, obtained during sitting, of systolic or diastolic blood pressure, or both, above the 95th percentile6 on at least three occasions over a 3 month period of time. In all, medical evaluations had revealed no secondary cause of the hypertension. Aside from the elevated blood pressure, the 22 hypertensive subjects had no symptoms. All were considered well at the time of testing and were receiving no pharmacologic agents for blood pressure control. The normotensive control group consisted of healthy adolescent boys with similarly obtained systolic and diastolic blood pressure values below the 90th percentile for age.6 Written informed consent on an institutionally approved protocol was obtained from all participants before exercise stress testing. Exercise testing: The methodology for exercise stress testing was similar to that previously described.12 After a period of rest and instruction, each participant underwent a progressive maximal treadmill test according to Bruce protocol. A target heart rate of 200 beats/min was used as the predicted end point of exercise. Blood pressure was obtained by standard auscultation with use of a mercury column sphygmomanometer and appropriate size cuff. It was determined at baseline in the standing position before exercise, at the 2nd minute of each stage of exercise and through the recovery period (10 minutes). Heart rate was obtained at baseline and at 1 minute intervals t.hroughout the test with use of a Quinton oscilloscope electrocardiographic monitor. The electrocardiogram was monitored continuously and a lead V5 tracing was obtained at 1 minute intervals throughout exercise. In the recovery period the determinations of blood pressure and heart rate were obtained with the subject seated. The R wave amplitude was measured from the isoelectric line to the peak of the R wave in millimeters for an average of 10 consecutive beats. The average value at the 2nd minute of each exercise stage was then used as the R wave amplitude for that stage of the Bruce protocol. The difference in R wave amplitude from the resting value in the standing position was computed as the change in R wave amplitude with each level of progressive exercise. Tests for statistical analysis included a two tailed t test for paired and unpaired data where appropriate. Correlation coefficients were computed by linear regression analysis. A two way analysis of variance was performed on the R wave response to determine group differences.
Study groups: The age, body size and baseline data of the two groups are provided in Table I. The hypertensive and normotensive control subjects were matched for age and race and did not differ significantly in height or weight. However, blood pressure during standing and heart rate were significantly greater in the hypertensive group. Effects of exercise on heart rate and blood pressure: During the graded multistage treadmill exercise all participants exercised to exhaustion. The duration of exercise and level of the Bruce protocol completed were similar in the two groups. In each
ET AL.
TABLE I
The objective of this study was to determine if R wave amplitude during exercise stress testing differed in adolescent boys with mild hypertension and those with normal blood pressure.
Results
ADOLESCENTS-FALKNER
Age W Weight (kg) SBP (mm Hg)’ Height (cm) DBP (mm Hg)’ HR Ibeats/min)’
Normotensive Group (n = 24)
p Value
15.9 f 2.0 79.0 f 19
16.4 f 72.0 f
1.4 12.8
NS NS
142 f 9.8 14 175.9 91 f 10 91 f 17
133 f 173.0 79f 79f
17 10.0 13 19
<%5
‘Before exercise (erect). DBP = diastolic blood pressure; HR = heart rate; NS = not significant: p = probability; SBP = systolic blood pressure.
subject there was a progressive increase in systolic pressure and heart rate whereas the diastolic pressure generally decreased. At each stage of exercise the systolic pressure and heart rate were higher in the hypertensive than in the normotensive subjects (Fig. 1). The systolic pressure of the two groups increased during exercise and decreased during recovery in a parallel manner, the hypertensive group manifesting higher systolic pressure at each level (p CO.01). The two groups manifested parallel increases in heart rate and the rate-pressure product (heart rate X systolic pressure) during exercise, with significantly higher values in the hypertensive group. Effect on R wave amplitude: In the normotensive group there was a progressive decrease in the R wave amplitude during graded exercise. In the hypertensive group the mean R wave amplitude increased slightly during exercise, and decreased slightly from the baseline value only at completion of exercise at maximal heart rate. An analysis of variance on the R wave response in the two groups indicates a significant difference (p
July 1992
The Amertcan Journal 01 CARDIOLOGY
Volume 50
153
13 WAVE CHANGE IN HYPERTENSIVE ADOLESCENTS-FALKNER
I
T
BRSE
I/Z
I
BRUCE
2
3
PROTOCOL
‘+
5
ET AL
X-
HYPERTEN5IVE5
q-
NORMALS
6
Ro
R,
RS
RIO
5TREE5
body size or exercise duration. The graded treadmill exercise stress test provoked a circulatory response pattern that was similar in the two groups, but with higher values for systolic pressure, heart rate and ratepressure product at every exercise level in the hypertensive group. The diastolic pressure decreased during exercise in both groups. These results are similar to previous findings.7,8q12 No typical electrocardiographic abnormalities such as S-T depression or conduction abnormalities were identified in either group. However, the changes in R wave amplitude were quite different in the two groups. The normotensive boys had a progressive decrease in R wave amplitude during exercise that correlated significantly with the increase in systolic pressure, heart rate and rate-pressure product. In contrast, the hypertensive boys had a smaller decrease in R wave amplitude and higher values for systolic pressure, heart rate and rate-pressure product.
Previous studies on cardiovascular response to exercise in the young: Previous studies of cardiovascular responses to dynamic exercise stress testing in the young have reported similar blood pressure and heart
FIGURE 1. Systolic blood pressure is depicted at baseline (BASE), and at each stage of exercise and the recovery (R) phase in minutes. The mean value of systolic blood pressure f standard error of the mean is presented for the hypertensive boys (crosses) and the normotensive boys (rectangles). * = p
rate responses.7~8J2~13 Fixler et a1.8 observed higher blood pressure in hypertensive children but no difference between the peak systemic oxygen consumption values of hypertensive and normotensive children.8 However, studies in normal adults14 demonstrated that systemic oxygen consumption does not correlate significantly with changes in blood pressure, whereas myocardial oxygen consumption may be a better correlate. Hemodynamic studies15 during exercise in healthy young men demonstrated that heart rate correlates with myocardial oxygen consumption and that an even better predictor of myocardial oxygen is the product of systolic blood pressure and heart rate (rate-pressure product). 14,15 A higher than normal rate-pressure product was reported in male and female adolescents with mild hypertension12 and also in a group of young women who were previously hypertensive during a pregnancy in teenage years.16 The observation of a greater rate-pressure product in young hypertensive subjects during exercise is consistent with earlier reports on hemodynamics in borderline hypertension in young adults.17
Significance of R wave amplitude changes during exercise: The previous studies of dynamic exercise TABLE II Cardiac Response Variables Versus R Wave Change Hypertensive Group (n = 22) Correlation SBP vs. R DBP vs. R HR vs. R (HR X SBP) vs. R
r* 0.54 0.51 0.70 0.69
<&l <0.05
Normotensive Group (n = 24) r2 0.93 0.93 0.92 0.95
(HR X SBP) = product of systolic pressure X heart rate. Other abbreviations as in Table 1.
154
July 1982
The American Journal of CARDIOLOGY
Volume 50
stress testing uniformly report the absence of any significant electrocardiographic abnormalities that could be predictive of ischemia, coronary artery disease or myocardial dysfunction in young hypertensive subjects although systolic pressure and heart rate are higher.8 During exercise in normal persons catecholamine stimulation and increasing heart rate result in decreases of left ventricular volume.10 With the smaller intraventricular blood volume during exercise the R wave amplitude decreases.g In a study of exercise electrocardiograms and coronary angiograms of adult patients, the normal response to exercise was a decrease in R wave amplitude, while
R WAVE CHANGE IN HYPERTENSIVE
ADOLESCENTS-FALKNER
ET AL.
T Li
1
HEART
RATE
5Y5TOLIC
BP
X
X
\
(MM
HE)
X
X
Y.
IS’121 HR -
El
-24 !
-3+
I
i
-23.1
,2 -
1
0.90
(AR)
+
17lzl
X 211
I9lzl
107.9 I
- -lZ.Z(AR)
+ 151.4
(p< 0.001) = 0.96
Vf
( p ( 0.001)
B
1
X-
HYPERTEN5IVE5
Cl-
NORMRL5
FIGURE 2. Change in R wave amplitude versus heart rate (lefl panel) and change in R wave amplitude versus systolic blood pressure (right panel). Crosses indicate the hypertensive boys and rectangles the normotensive boys.
an increase during exercise indicated increased left ventricular volume and myocardial ischemia.g,18 In our present study there was strong correlation in normotensive adolescent boys between the increase in heart rate and rate-pressure product, both predictors of myocardial oxygen consumption, and the decreasing R wave amplitude with progressive exercise. This correlation was quite different in the hypertensive boys in whom the decrease in R wave amplitude was less while the heart rate and rate-pressure product were greater. The hypertensive boys were able to exercise to levels of effort similar to those of the normal boys and they did not exhibit any angina1 symptoms or consistent S-T depression. Although coronary angiography was not performed, it is unlikely that these hypertensive adolescents had any significant coronary artery disease to account for a greater left ventricular volume as reflected by the R wave response to exercise. Clinical implications: Essential hypertension in adolescents usually corresponds with the features of the hyperkinetic cardiovascular state of early hypertension. This stage is characterized by an increased cardiac output, increased blood pressure and normal peripheral
vascular resistance.lg Although this stage is unlike later hypertension in which cardiac output is normal, blood pressure is increased and vascular resistance is increased, some workers’O have suggested that peripheral vascular resistance is inappropriately normal in early hypertension when vascular resistance should be lower to offset the increased cardiac output. Thus, in our study the greater left ventricular volume in the hypertensive subjects as reflected by the attenuated R wave change may be due to peripheral vascular resistance that is higher or “inappropriately normal” relat,ive to that of normotensive control subjects. ‘I’he variation in R wave amplitude change in response to exercise demonstrated in the young hypertensive boys in this study reflects some degree of myocardial dysfunction. Whether this variation reflects intrinsic myocardial dysfunction or is a secondary response to sympathetic stimulation or level of peripheral vascular resistance has yet to be determined. Also to be determined is the potential reversibility of these R wave amplitude changes after therapy to normalize blood pressure in young patients requiring treatment for hypertension.
July 1982
The American Journal of CARDIOLOGY
Volume 50
155
R WAVE CHANGE IN HYPERTENSIVE
ADOLESCENTS-FALKNER
ET AL
References 1 Hypertension Detection and Follow-Up Program, Cooperative Group. Five year findings of hypertension detection and follow-up program. I. Reduction in mortality of persons with high blood pressure including mild hypertension. JAMA 1979;242:256271. 2. Hypertension Detection and Follow-Up Program, Cooperative Group. Five year findings of the hypertension detection and follow-up program. II. Mortality by race, sex and age. JAMA 1979; 24212572-7. 3. Kilcoyne MM. Adolescent hypertension, Am J Med 1975;58: 735-9. 4. Johnson AL, Cornoni JC, Cossel JC, Tyrolin HA, Heyden S, Hames CG. Influence of race, sex and weight on blood pressure behavior in young adults. Am J Cardiol 1975;35:523-30. 5. Londe S, Bourgoignie JJ, Robson AM, Goldring D. Hypertension in apparently normal children. J Pediatr 1971;76:569-77. 6. Blumenthal S, Epps RP, Heavenrich R, et al. Report of the Task Force on Blood Pressure Control in Children. Pediatrics 1977; 59:suppl:797-820. Goldring D, Hwnandez A, Choi S, Lee JY, Londe S. Blood pressure in high school population. J Pediatr 1979;95:296-304, Fixler DE, Laird WP, Brown R, Fitzgerald V, Wilson S, Vance R. Response of hypertensive adolescents to dynamic and isometric exercise stress. Pediatrics 1979;64:579-83. Bonoris PE, Greenburg PS, Christeson GW, Cosiellanet MJ, Ellestad MH. Evaluation of R wave amplitude changes versus ST segment depression in stress testing. Circulation 1976;57:90410.
156
July 1982
The American Journal of CARDIOLOGY
Volume 50
10. Body DA. A theoretical analysis of intracavity blood loss influence on the heart-lead relationship. Circ Res 1956;4:731-6. 11. Voukydls PC. Effect of intracardiac blood on the electrocardiogram. N Engl J Med 1974;291:612-6. 12. Falkner B, Lowenthal DT. Dynamic exercise response in hypertensive adolescents. Int J Pediatr Neph 1980;1:161-5. 13. Strong WB, Miller MD, Striplln Y, Salehbai M. Blood pressure response to isometric and dynamic exercise in healthy black children. Am J Dis Child 1976: 132:567-91. 14. Nelson RR, Gobel FL, Jorgensen CR, Wang K, Wang Y, Taylor HL. Hemodynamic predictors of myocardial oxygen consumption during static and dynamic exercise. Circulation 1974;50: 117969. 15. Kitamura K, Jorgensen CR, Gobel FL, Taylor HL, Wang Y. Hemodynamic correlates of myocardial oxygen consumption during upright exercise. J Appl Physiol 1972;32:516-22. 16. Cottrill CM, Kotchen JM, Guthrie G, Kotchen T. Cardiovascular response to exercise following adolescent hypertensive pregnancy. J Adolesc Health Care 1960;1:91-5. 17. Lund-Johansen P. Hemcdynamics in early hypertension. Acta Med Stand 1967;181:1-10. ia. Boudoulas H. Dervenagas S, Lewis RP, Kollbash AJ. Adrenergic stimulation and R wave magnitude. J Cardiac Rehab 1961;l: 108-14. 19. Julius S, Conway J. Hemodynamic studies in patients with borderline hypertension. Circulation 1966;38:282-6. 20. Julius S, Pascual A, Sannerstedt R, Mitchell C. Relationship between cardiac output and peripheral resistance in borderline hypertension Circulation 1971; 43:362-6.
FALKNER,
MD
T. LOWENTHAL,
MD,
FACC
MELTON B. AFFRIME, PharmD BARBARA
Philadelphia,
HAMSTRA,
RN
Pennsylvania
From the Department of Pediatrics and Medicine and Likoff Cardiovascular Institute, Hahnemann Medical College and Hospital, Philadelphia, Pennsylvania. Manuscriot received Auaust 31. 198 1; devised manuscripi received December 14, 1981, accepted January 22, 1982. Address for reprints: Bonita Falkner, MD, Departmentof Pediatrics, Hahnemann Medical Colleae and Hosoital. 230 North Broad Street. Philadelphia, Pen&lvania 19102.
152
July 1982
The change in R wave amplitude during progressive aerobic exercise was studied in hypertensive adolescent boys. A comparable control group consisted of normotensive adolescent boys matched for age, body size and race. Twenty-four normotensive and 22 hypertensive subjects exercised to exhaustion on a treadmill utilizing the Bruce protocol. Blood pressure and heart rate were monitored during exercise and recovery. The change in R wave amplitude in a lead V5 electrocardiogram was determined at each level of exercise. The normotensive group demonstrated a progressive increase in systolic pressure, heart rate and ratepressure product (heart rate X systolic pressure) during exercise and a progressive decrease in R wave amplitude with a significant correlation of R wave change versus the cardiac response variable (p
Hypertension is a major health problem with the morbid consequences of the uncontrolled disease well known. Although full understanding of the pathogenic mechanism remains elusive, evidence does exist that the prevalence of target organ damage is diminished with reduction of blood pressure.1,2 Recognition of a significant prevalence of essential hypertension in adolescence3v4 is emerging together with the concept that the initiating mechanisms for this disorder may be operative in the childhood years.5T6 An intriguing issue is whether the vascular component of the disorder is increased by the pressure level itself and, if so, what level of blood pressure elevation imposes the risk for vasuclar or target organ damage. Exercise stress testing in adults has become a clinically useful means of evaluating symptoms of ischemia and heart disease, and for deriving exercise prescriptions in cardiac rehabilitation. Studies utilizing strenuous aerobic exercise stress testing in young people7,s demonstrated similar patterns of blood pressure and heart rate response during exercise in hypertensive and normotensive adolescents but with higher levels of systolic blood pressure in the former. These studies in the young indicate absence of the typical electrocardiographic abnormalities such as arrhythmias and S-T depression that in adults denote a risk status for significant cardiac disease. -It has been reported9 that changes in the amplitude of the R wave during exercise may be more sensitive than S-T changes as an indicator of myocardial dysfunction in adults. The failure of the ischemic ventricle to decrease its volume during strenuous aerobic exercise may be responsible for absence of the u&al reduction in R wave amplitude.10,11
The American Journal of CARDIOLOGY
Volume 50
R WAVE CHANGE IN HYPERTENSIVE
Baseline Values (mean f standard deviation) Hypertensive Group (n = 22)
Methods Study subjects: Participants in the study included 22 adolescent boys with mild hypertension. All 22 had a casual determination, obtained during sitting, of systolic or diastolic blood pressure, or both, above the 95th percentile6 on at least three occasions over a 3 month period of time. In all, medical evaluations had revealed no secondary cause of the hypertension. Aside from the elevated blood pressure, the 22 hypertensive subjects had no symptoms. All were considered well at the time of testing and were receiving no pharmacologic agents for blood pressure control. The normotensive control group consisted of healthy adolescent boys with similarly obtained systolic and diastolic blood pressure values below the 90th percentile for age.6 Written informed consent on an institutionally approved protocol was obtained from all participants before exercise stress testing. Exercise testing: The methodology for exercise stress testing was similar to that previously described.12 After a period of rest and instruction, each participant underwent a progressive maximal treadmill test according to Bruce protocol. A target heart rate of 200 beats/min was used as the predicted end point of exercise. Blood pressure was obtained by standard auscultation with use of a mercury column sphygmomanometer and appropriate size cuff. It was determined at baseline in the standing position before exercise, at the 2nd minute of each stage of exercise and through the recovery period (10 minutes). Heart rate was obtained at baseline and at 1 minute intervals t.hroughout the test with use of a Quinton oscilloscope electrocardiographic monitor. The electrocardiogram was monitored continuously and a lead V5 tracing was obtained at 1 minute intervals throughout exercise. In the recovery period the determinations of blood pressure and heart rate were obtained with the subject seated. The R wave amplitude was measured from the isoelectric line to the peak of the R wave in millimeters for an average of 10 consecutive beats. The average value at the 2nd minute of each exercise stage was then used as the R wave amplitude for that stage of the Bruce protocol. The difference in R wave amplitude from the resting value in the standing position was computed as the change in R wave amplitude with each level of progressive exercise. Tests for statistical analysis included a two tailed t test for paired and unpaired data where appropriate. Correlation coefficients were computed by linear regression analysis. A two way analysis of variance was performed on the R wave response to determine group differences.
Study groups: The age, body size and baseline data of the two groups are provided in Table I. The hypertensive and normotensive control subjects were matched for age and race and did not differ significantly in height or weight. However, blood pressure during standing and heart rate were significantly greater in the hypertensive group. Effects of exercise on heart rate and blood pressure: During the graded multistage treadmill exercise all participants exercised to exhaustion. The duration of exercise and level of the Bruce protocol completed were similar in the two groups. In each
ET AL.
TABLE I
The objective of this study was to determine if R wave amplitude during exercise stress testing differed in adolescent boys with mild hypertension and those with normal blood pressure.
Results
ADOLESCENTS-FALKNER
Age W Weight (kg) SBP (mm Hg)’ Height (cm) DBP (mm Hg)’ HR Ibeats/min)’
Normotensive Group (n = 24)
p Value
15.9 f 2.0 79.0 f 19
16.4 f 72.0 f
1.4 12.8
NS NS
142 f 9.8 14 175.9 91 f 10 91 f 17
133 f 173.0 79f 79f
17 10.0 13 19
<%5
‘Before exercise (erect). DBP = diastolic blood pressure; HR = heart rate; NS = not significant: p = probability; SBP = systolic blood pressure.
subject there was a progressive increase in systolic pressure and heart rate whereas the diastolic pressure generally decreased. At each stage of exercise the systolic pressure and heart rate were higher in the hypertensive than in the normotensive subjects (Fig. 1). The systolic pressure of the two groups increased during exercise and decreased during recovery in a parallel manner, the hypertensive group manifesting higher systolic pressure at each level (p CO.01). The two groups manifested parallel increases in heart rate and the rate-pressure product (heart rate X systolic pressure) during exercise, with significantly higher values in the hypertensive group. Effect on R wave amplitude: In the normotensive group there was a progressive decrease in the R wave amplitude during graded exercise. In the hypertensive group the mean R wave amplitude increased slightly during exercise, and decreased slightly from the baseline value only at completion of exercise at maximal heart rate. An analysis of variance on the R wave response in the two groups indicates a significant difference (p
July 1992
The Amertcan Journal 01 CARDIOLOGY
Volume 50
153
13 WAVE CHANGE IN HYPERTENSIVE ADOLESCENTS-FALKNER
I
T
BRSE
I/Z
I
BRUCE
2
3
PROTOCOL
‘+
5
ET AL
X-
HYPERTEN5IVE5
q-
NORMALS
6
Ro
R,
RS
RIO
5TREE5
body size or exercise duration. The graded treadmill exercise stress test provoked a circulatory response pattern that was similar in the two groups, but with higher values for systolic pressure, heart rate and ratepressure product at every exercise level in the hypertensive group. The diastolic pressure decreased during exercise in both groups. These results are similar to previous findings.7,8q12 No typical electrocardiographic abnormalities such as S-T depression or conduction abnormalities were identified in either group. However, the changes in R wave amplitude were quite different in the two groups. The normotensive boys had a progressive decrease in R wave amplitude during exercise that correlated significantly with the increase in systolic pressure, heart rate and rate-pressure product. In contrast, the hypertensive boys had a smaller decrease in R wave amplitude and higher values for systolic pressure, heart rate and rate-pressure product.
Previous studies on cardiovascular response to exercise in the young: Previous studies of cardiovascular responses to dynamic exercise stress testing in the young have reported similar blood pressure and heart
FIGURE 1. Systolic blood pressure is depicted at baseline (BASE), and at each stage of exercise and the recovery (R) phase in minutes. The mean value of systolic blood pressure f standard error of the mean is presented for the hypertensive boys (crosses) and the normotensive boys (rectangles). * = p
rate responses.7~8J2~13 Fixler et a1.8 observed higher blood pressure in hypertensive children but no difference between the peak systemic oxygen consumption values of hypertensive and normotensive children.8 However, studies in normal adults14 demonstrated that systemic oxygen consumption does not correlate significantly with changes in blood pressure, whereas myocardial oxygen consumption may be a better correlate. Hemodynamic studies15 during exercise in healthy young men demonstrated that heart rate correlates with myocardial oxygen consumption and that an even better predictor of myocardial oxygen is the product of systolic blood pressure and heart rate (rate-pressure product). 14,15 A higher than normal rate-pressure product was reported in male and female adolescents with mild hypertension12 and also in a group of young women who were previously hypertensive during a pregnancy in teenage years.16 The observation of a greater rate-pressure product in young hypertensive subjects during exercise is consistent with earlier reports on hemodynamics in borderline hypertension in young adults.17
Significance of R wave amplitude changes during exercise: The previous studies of dynamic exercise TABLE II Cardiac Response Variables Versus R Wave Change Hypertensive Group (n = 22) Correlation SBP vs. R DBP vs. R HR vs. R (HR X SBP) vs. R
r* 0.54 0.51 0.70 0.69
<&l <0.05
Normotensive Group (n = 24) r2 0.93 0.93 0.92 0.95
(HR X SBP) = product of systolic pressure X heart rate. Other abbreviations as in Table 1.
154
July 1982
The American Journal of CARDIOLOGY
Volume 50
stress testing uniformly report the absence of any significant electrocardiographic abnormalities that could be predictive of ischemia, coronary artery disease or myocardial dysfunction in young hypertensive subjects although systolic pressure and heart rate are higher.8 During exercise in normal persons catecholamine stimulation and increasing heart rate result in decreases of left ventricular volume.10 With the smaller intraventricular blood volume during exercise the R wave amplitude decreases.g In a study of exercise electrocardiograms and coronary angiograms of adult patients, the normal response to exercise was a decrease in R wave amplitude, while
R WAVE CHANGE IN HYPERTENSIVE
ADOLESCENTS-FALKNER
ET AL.
T Li
1
HEART
RATE
5Y5TOLIC
BP
X
X
\
(MM
HE)
X
X
Y.
IS’121 HR -
El
-24 !
-3+
I
i
-23.1
,2 -
1
0.90
(AR)
+
17lzl
X 211
I9lzl
107.9 I
- -lZ.Z(AR)
+ 151.4
(p< 0.001) = 0.96
Vf
( p ( 0.001)
B
1
X-
HYPERTEN5IVE5
Cl-
NORMRL5
FIGURE 2. Change in R wave amplitude versus heart rate (lefl panel) and change in R wave amplitude versus systolic blood pressure (right panel). Crosses indicate the hypertensive boys and rectangles the normotensive boys.
an increase during exercise indicated increased left ventricular volume and myocardial ischemia.g,18 In our present study there was strong correlation in normotensive adolescent boys between the increase in heart rate and rate-pressure product, both predictors of myocardial oxygen consumption, and the decreasing R wave amplitude with progressive exercise. This correlation was quite different in the hypertensive boys in whom the decrease in R wave amplitude was less while the heart rate and rate-pressure product were greater. The hypertensive boys were able to exercise to levels of effort similar to those of the normal boys and they did not exhibit any angina1 symptoms or consistent S-T depression. Although coronary angiography was not performed, it is unlikely that these hypertensive adolescents had any significant coronary artery disease to account for a greater left ventricular volume as reflected by the R wave response to exercise. Clinical implications: Essential hypertension in adolescents usually corresponds with the features of the hyperkinetic cardiovascular state of early hypertension. This stage is characterized by an increased cardiac output, increased blood pressure and normal peripheral
vascular resistance.lg Although this stage is unlike later hypertension in which cardiac output is normal, blood pressure is increased and vascular resistance is increased, some workers’O have suggested that peripheral vascular resistance is inappropriately normal in early hypertension when vascular resistance should be lower to offset the increased cardiac output. Thus, in our study the greater left ventricular volume in the hypertensive subjects as reflected by the attenuated R wave change may be due to peripheral vascular resistance that is higher or “inappropriately normal” relat,ive to that of normotensive control subjects. ‘I’he variation in R wave amplitude change in response to exercise demonstrated in the young hypertensive boys in this study reflects some degree of myocardial dysfunction. Whether this variation reflects intrinsic myocardial dysfunction or is a secondary response to sympathetic stimulation or level of peripheral vascular resistance has yet to be determined. Also to be determined is the potential reversibility of these R wave amplitude changes after therapy to normalize blood pressure in young patients requiring treatment for hypertension.
July 1982
The American Journal of CARDIOLOGY
Volume 50
155
R WAVE CHANGE IN HYPERTENSIVE
ADOLESCENTS-FALKNER
ET AL
References 1 Hypertension Detection and Follow-Up Program, Cooperative Group. Five year findings of hypertension detection and follow-up program. I. Reduction in mortality of persons with high blood pressure including mild hypertension. JAMA 1979;242:256271. 2. Hypertension Detection and Follow-Up Program, Cooperative Group. Five year findings of the hypertension detection and follow-up program. II. Mortality by race, sex and age. JAMA 1979; 24212572-7. 3. Kilcoyne MM. Adolescent hypertension, Am J Med 1975;58: 735-9. 4. Johnson AL, Cornoni JC, Cossel JC, Tyrolin HA, Heyden S, Hames CG. Influence of race, sex and weight on blood pressure behavior in young adults. Am J Cardiol 1975;35:523-30. 5. Londe S, Bourgoignie JJ, Robson AM, Goldring D. Hypertension in apparently normal children. J Pediatr 1971;76:569-77. 6. Blumenthal S, Epps RP, Heavenrich R, et al. Report of the Task Force on Blood Pressure Control in Children. Pediatrics 1977; 59:suppl:797-820. Goldring D, Hwnandez A, Choi S, Lee JY, Londe S. Blood pressure in high school population. J Pediatr 1979;95:296-304, Fixler DE, Laird WP, Brown R, Fitzgerald V, Wilson S, Vance R. Response of hypertensive adolescents to dynamic and isometric exercise stress. Pediatrics 1979;64:579-83. Bonoris PE, Greenburg PS, Christeson GW, Cosiellanet MJ, Ellestad MH. Evaluation of R wave amplitude changes versus ST segment depression in stress testing. Circulation 1976;57:90410.
156
July 1982
The American Journal of CARDIOLOGY
Volume 50
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