Echocardiographic functions and blood pressure levels in children and young adults from a biracial population: The bogalusa heart study

Echocardiographic Functions and Blood Pressure Levels in Children and Young Adults from a Biracial Population: The Bogalusa Heart Study BY LUIS F. SOTO, MD, DAVID A. KIKUCHI, PHD, RENE A. ARCILLA, MD, DANIEL D. SAVAGE, MD, PHD, GERALD S. BERENSON, MD, FAce

ABSTRACT: M-mode echo cardiograms were obtained on 651 healthy subjects, 7-22 years of age, whose diastolic blood pressure levels remained in the same height-, race-, and sex-specific decile during two biannual examinations. Echocardiographic measures of heart size and dynamics were compared across the total blood pressure distribution. Left ventricular stroke volume, cardiac output and ejection fraction, minor axis shortening, velocity of circumferential fiber shortening, and peripheral vascular resistance were correlated with blood pressure levels. There were positive correlations (p < .001) of cardiac output and stroke volume with both systolic and diastolic blood pressure levels. Left ventricular output and stroke volume were associated with measures of body size, especially height, weight, ponderal index, and body surface area (p < .001). The left ventricular output and stroke volume increased with age and with systolic blood pressure quintiles in the four race-sex groups. With adjustment for systolic blood pressure and measures of body size, white males had greater cardiac output (1.25 l/minute for ages 18-22 years, p = .01) and stroke volume than black males. Black males had higher peripheral resistance From the LSU Medical Center, New Orleans, Louisiana, the University of Chicago, Chicago, Illinois, and Morehouse School of Medicine, Atlanta, Georgia. This research is supported by funds from the National Heart, Lung, and Blood Institute of the U.S. Public Health Service, National Research and Demonstration Center-Arteriosclerosis (HL15103 and HL38844). The Bogalusa Heart Study represents the collaborative efforts of many people whose cooperation is gratefully acknowledged. The authors thank Bettye Seal for her outstanding work as community coordinator and Drs. David Akman and Gerardo Aristimuno, who were invaluable in the collection of data for this study. The authors also thank the children of Bogalusa and their parents, without whom this study would not have been possible. Reprint requests: Gerald S. Berenson, MD, Department of Medicine, Louisiana State University Medical Center, 1542 Tulane Avenue, New Orleans, LA 70112-2822. THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES

(4.5 mm Hg/(l/minute), p = .01) than whites. These results suggest that different hemouynamic mechanisms operate in the early phase of hypertension in blacks vs. whites in this population. KEY INDEXING TERMS: Blood Pressure; Hemodynamics; Echocardiography; Hypertension. [Am J Med Sci 1989; 297(5): 271-279.]

T

he predominant hemodynamic disturbance in most forms of hypertension is an increase in total peripheral resistance. l Cardiac output is normal in the absence of heart failure. Several studies have suggested an important role for increased cardiac output in the initial phase of hypertension, whereas total peripheral resistance increases later as an autoregulatory phenomenon. 2 - 4 In young patients with early essential hypertension, peripheral resistance presumably is normal. These observations have generated great interest in the hemodynamics of essential hypertension, and documentation exists that hemodynamic patterns vary with age of the subject and stage of the hypertensive disorder. 5 - s Hypertension is a major risk factor for morbidity from cardiovascular disease. It commonly underlies the onset of heart failure, cerebrovascular accidents, and end-stage renal disease. Cardiac hypertrophy is one ofthe earliest clinical manifestations of sustained hypertension. Although primary hypertension has been recognized as the major cause of elevated blood pressure levels in the general population, its onset in childhood generally has not been appreciated. Criteria for the definition of essential hypertension in children are not clear and blood pressure levels associated with target organ changes early in life are not known. In recent years, functional disturbances of the heart and resistance vessels and morphological changes in the left ventricle have been diagnosed by echocardiography early in the development of hyper271

Echocardlography and Blood Pressure

Table 1. Age Distribution of Participants in the Echocardiographic Study by Race and Sex: The Bogalusa Heart Study, 1973-82 Black

White Males

Males

Females

Females

Age (years)

n

%

n

%

n

%

n

%

7-9 10-11 12-13 14-15 16-17 18-19 20-22 Total

5 35 59 38 21 9 9 176

2.9 20.0 33.1 21.7 12.0 5.1 5.1 100

6 41 42 30 19 9 6 153

3.9 26.8 27.5 19.6 12.4 5.9 3.9 100

4 21 19 12 13 8 4 81

4.9 25.6 23.2 15.8 15.8 9.8 4.9 100

3 16 21 14 16 11 11 92

3.2 17.4 22.8 15.2 17.4 12.0 12.0 100

Includes only those subjects with good quality echocardiograms (502 of 651 participants).

tension. 9 - 13 Specifically, an increase in left ventricular dimensions has been observed. 14- 1S The present echocardiographic study was undertaken in children and young adults in the Bogalusa Heart Study to delineate the hemodynamic characteristics that occur at different blood pressure levels. The hemodynamic characteristics of black and white children with early hypertension in a free living population were compared to improve our understanding of the natural history of hypertensive cardiovascular disease. Method$ Population. The Bogalusa Heart Study is a long-

term epidemiologic study of cardiovascular disease risk factors from birth through early adulthood. The community of Bogalusa, Louisiana, has a population of about 22,000; the population is two-thirds white and one-third black. The sample of651 subjects studied by M-mode echocardiography has been described previously. IS Sample Selection. Children with stable blood pressure levels during a 2- to 3-year period were selected for the echocardiographic study. Specifically, those children whose height-, race-, and sex-specific diastolic blood pressure rank remained within 10% from either the second (1976-1977) to the third (19781979) or the third (1978-1979) to the fourth (19811982) school survey were eligible to participate. Ages of the participants ranged from 7 to 22 years, with 83% between 10 and 17 years (Table 1). The sample had equal numbers of males and females. Approximately two-thirds of the participants were white and one-third black, the same composition as that of the general community. The children were selected by blood pressure rank. They represent the entire spectrum of systolic and diastolic blood pressure levels. General Examinations. All experimental protocols were reviewed and approved by the LSU Medical Center Institutional Review Board. Informed consent (written) was obtained from a parent or guardian of 272

each child. Blood pressure measurements were taken in the right arm from seated, relaxed subjects, according to standardized protocols reported earlier. 19 Systolic and diastolic blood pressures were recorded three times as the first and fourth Korotkoff phases by three trained examiners using mercury sphygmomanometers and an automatic instrument. The mean of six readings taken with mercury sphygmomanometers (W. A. Baum Co., Inc., Copague, NY) was used in the analyses. Anthropometric measurements used in this study included two manual measurements each of height to the nearest 0.1 cm and weight to the nearest 0.1 kg. The mean of two measurements for both height and weight was used in all analyses. Ponderal index (weight/height3) was used as a measure of weight-forheight instead of the body mass index (weight/ height2) because of the weaker correlation with height. 19 Body surface area (BSA) was computed from height and weight according to the formula of DuBois and DuBois. 20 Triceps skinfold thickness was measured to the nearest 1.0 mm with Lange skinfold calipers (Cambridge Scientific Industries, Cambridge, MD),21 and the mean of three measurements was used. More than half of all eligible children (1258 eligible, 651 participants, 51 %) were studied by echocardiography. After obtaining the blood pressures, the participants were randomly assigned to undergo anthropometric measurements, electrocardiogram, or echocardiogram. M mode echocardiographic examinations were performed by standard techniques in the supine position with a system 2 instrument (Irex Medical Systems, Inc., Ramsey, NJ) by one of three cardiologists from LSU Medical Center. The examinations were then sent to the University of Chicago for digitizing of records and measurements according to the recommendation of the American Society of Echocardiography, with the exceptions listed in our previous report. 1S Quality of echocardiograms received was assessed when they arrived for digitization, and 502 May 1989 Volume 297 Number 5

Soto et 01

Table 2. Echocardiographic Measures of Cardiac Function in Male Children and Young Men:· The Bogalusa Heart Study (Means) White Males Age (years)

N

LV-OUT

LV-EF

LV-SV

RESIS

LV-ET

LV-PEP

VCF

MAShort

HRATE

7-9 10-11 12-13 14-15 16-17 18-19 20-22

5 35 59 38 21 9 9

3.3 3.9 4.6 5.0 4.5 5.3 4.4

71 69 71 70 68 66 64

43.8 52.4 66.1 76.9 73.8 77.8 66.0

25.2 21.4 18.6 17.3 20.0 17.4 20.9

0.28 0.29 0.29 0.30 0.30 0.31 0.31

0.08 0.10 0.10 0.10 0.11 0.11 0.16

1.19 1.09 1.16 1.13 1.04 1.00 1.00

33.8 32.9 33.7 33.6 32.2 30.2 29.0

74.0 73.9 69.3 66.0 62.5 66.1 68.1

Black Males Age (years)

N

LV-OUT

LV-EF

LV-SV

RESIS

LV-ET

LV-PEP

VCF

MAShort

HRATE

7-9 10-11 12-13 14-15 16-17 18-19 20-22

4 21 19 12 13 8 4

3.5 3.5 4.4 3.9 4.6 3.8 3.0

75 72 70 65 71 66 60

47.3 51.9 64.0 63.1 71.7 70.8 56.5

23.3 24.1 19.6 21.9 20.3 21.3 27.9

0.27 0.29 0.29 0.29 0.29 0.31 0.31

0.10 0.09 0.10 0.10 0.10 0.11 0.14

1.36 1.15 1.17 1.83 1.15 0.98 0.83

37.0 35.2 33.4 30.5 34.1 30.3 25.9

73.3 67.1 68.8 63.7 64.5 56.8 55.8

• Adjusted for systolic, diastolic, height, weight, ponderal index and body surface area. LV-OUT = cardiac output (l/minut e); LV-EF =, left ventricular ejection fraction (%); LV-SV = left ventricular stroke volume (ml); RESIS = peripheral resistance (mm Hg/l/minute), L V-ET = left ventricular ejection time (second); LV-PEP = left ventricular pre-ejection period (second); VCF = velocity of circumferential fiber shortening (eire/second); MAShort = minor axis shortening (%); HRATE = heart rate (beats/minute).

(77%) of the measurements were determined to be of good quality and to form the basis for the present analysis. A 25% random sample of echo cardiograms was sent in a blinded fashion to the University of Chicago for a second digitization to allow estimation of measurement error for the different measures of cardiac anatomy. No significant differences were noted between any of the original and duplicate measures of heart size digitized at different points in time. IS Standard formulas were used to calculate end-systolic and enddiastolic volumes, left ventricular stroke volume, left ventricular ejection fraction, left ventricular cardiac output, minor axis shortening, velocity of circumferential fiber shortening, and total peripheral resistance (see Appendix). Statistical Analysis. Means and standard errors were computed on the Statistical Analysis System (Cary, NC), with adjustment of concomitant variables by ~omp\,lting population marginal means. 22 Adjustment for age was up to cubic power because of its nonlinear relationship with the echocardiographic variables, blood pressures, and anthropometric measures. Statistical significance was computed at level 0.05, unless otherwise stated. All tests were two-sided. Age trends in hemodynamic variables were tested by correlation coefficients with age. These correlation coefficients were adjusted for race and sex unless otherwise stated. THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES

Results

Tables 2 and 3 show the echocardiographic measures of cardiac function of the population sample across age, race, and sex distributions. As noted earlier,Is gender and growth of children have a marked influence on heart size and a potential effect on hemodynamic function. An increasing age trend (growth) of cardiac output occurred (r = .29, P < .001) until approximate adult stature was reached around 16 to 18 years of age, with slight race and sex differences noted. Stroke volume increased across the age span (r = .43, p < .001) (Figure 1). Because heart rate consistently decreased with age in childhood and young adulthood (r = -.36, p < .001), the cardiac output increase was attributable to stroke volume. The greatest increases in stroke volume occurred in black females, from 45.9 ml for ages 7-9 years to 86.5 ml for ages 2022 years, an 89% change. Similar increases were noted for the other groups but were less consistent in black males. The difference could be due to the smaller sam. pIe size. Because · of differences in heart rate and stroke volume, cardiac output was greater in white males than black males. A difference of 1.25 l/minute (p = .01) was observed for the 18 to 22 age group, (Figure 2). The left ventricular ejection fraction was unchanged in females but decreased slightly in males across the age distribution (5% to 7.0%, r = -.19, P = .01, white males; 9% to 15%, r = -.34, p = .002,

273

Echocardlography and Blood Pressure

Table 3. Echocardiographic Measures of Cardiac Function in Female Children and Young Women:* The Bogalusa Heart Study (Means) White Females Age (years)

N

LV-OUT

LV-EF

LV-SV

RESIS

LV-ET

LV-PEP

VCF

MAShort

HRATE

7-9 10-11 12-13 14-15 16-17 18-19 20-22

6 41 42 30 19 9 6

4.1 3.8 4.3 4.5 4.7 5.4 5.2

72 70 72 69 68 79 72

49.2 49.6 56.8 63.5 68.5 77.7 70.7

17.5 21.6 19.7 19.3 19.2 15.7 17.4

0.27 0.28 0.28 0.29 0.30 0.29 0.27

0.09 0.10 0.10 0.10 0.10 0.11 0.13

1.23 1.22 1.24 1.12 1.07 1.23 1.29

34.7 33.7 35.1 32.6 31.7 36.1 34.5

85.1 77.7 77.2 72.2 68.5 70.5 75.4

Black Females Age (years)

N

LV-OUT

LV-EF

LV-SV

RESIS

LV-ET

LV-PEP

VCF

MAShort

HRATE

7-9 10-11 12-13 14-15 16-17 18-19 20-22

3 16 21 14 16 11 11

2.5 4.0 4.1 4.0 4.6 5.1 5.7

68 72 73

45.9 50.0 56.2 58.4 69.5 76.1 86.5

30.6 20.6 20.2 22.1 20.2 17.3 16.0

0.29 0.28 0.29 0.29 0.29 0.30 0.28

0.11 0.09 0.09 0.10 0.11 0.11 0.07

1.10 1.26 1.24 1.16 1.20 1.16 1.18

32.4 34.7 35.4 34.1 34.6 34.1 34.8

74.1 79.3 74.7 71.1 66.4 68.3 65.2

71

72 71 72

* Adjusted for systolic, diastolic, height, weight, ponderal index and body surface area. LV-OUT = cardiac output (l/minute); L V-EF = left ventricular ejection fraction (%); L V-SV = left ventricular stroke volume (ml); RESIS = peripheral resistance (mm Hg/l/minute); L V-ET = left ventricular ejection time (second); LV-PEP := left ventricular pre-ejection period (second); VCF = velocity of circumferential fiber shortening (eire/second); MAShort = minor axis shortening (%); HRATE = heart rate (beats/minute).

black males). Peripheral resistance decreased across the age span for white males (r = -.26, p < .001) and females (r = - .10, p > .2), with less consistent changes noted for black males. In black males, increasing values were noted in the older age groups, with a significant difference of 4.5 mm Hg/{l/minute) (p = .01) in the 18 to 22 age group compared to white males (Figure 2). Left ventricular ejection time increased by about .04 seconds across ages 7 to 22 (r = .26, p < .001). Similarly, the pre-ejection period increased by about .08 seconds (r = .31, p < .001). The decreases in velocity of circumferential fiber shortening were small but significant (r = -.21, p < .001). Minor axis shortening also decreased (r = -0.17, P < .001). Table 4 shows the various cardiac variables studied by race and sex, with echocardiographic functions adjusted for height, weight, ponderal index, body surface area, and age. Black females as a group were somewhat older. Stroke volume and cardiac output were greater in white males than in the other race and sex groups; white children had greater cardiac outputs than blacks. White males tended to have lower peripheral resistances than the other race-sex groups, and black males had significantly greater peripheral resistances than white males, 2.6 mm Hg/{l/minute), p < .001. Females had higher values for velocity of circumferential fiber shortening than males. Cardiac output was positively correlated with

274

stroke volume and inversely correlated with peripheral resistance (r = .86 and -.90, respectively) (Table 5). A high negative correlation between stroke volume and peripheral resistance was noted (r = -.79), and high positive correlations were found between ejection fraction and the velocity of circumferential fiber shortening and minor axis shortening (r = .67 and .99, respectively). A high positive correlation also was noted between the velocity of circumferential fiber shortening and minor axis shortening (r = .68). These correlations were comparable among the four groups studied. Table 6 shows the correlations of cardiac function with blood pressure and anthropometric measurements. Significant positive relationships, p < .001, were noted between cardiac output and systolic and diastolic blood pressure (r = .30 and r = .18, respectively), height (r = .41), weight (r = .52), ponderal index (r = .30), triceps (r = .19), and body surface area (BSA) (r = .51). Left ventricular stroke volume was similarly correlated with systolic and diastolic blood pressure, height (r = .57), weight (r = .62), ponderal index (r = .26), and BSA (r = .64). Significant inverse correlations existed between peripheral resistance and height (r = -.28), weight (r = -.35), ponderal index (r = -.20), and BSA (r = -.34). Important echocardiographic changes were found related to blood pressure levels when stratified across Mav 1989 Volume 297 Number 5

Soto et al

80

70 60

::§:so Q)

~ 40

~

-een Q)

30 20 10

o

7-11

12-14

15-17

18-22

Age • AdjJsted for systolic, diastolic, height, weight, ponderoslty, BSA

Figure 1. Left ventricular stroke volume of children and young adults across four age groups by sex and race calculated from echocardiographic measures. Note the trend toward increasing stroke volume with age, even after adjustment for anthropometric characteristics and blood pressure levels.

the quintile distribution (Figures 3 and 4). The left ventricular stroke volume increased about 15 ml, and the cardiac output increased about 1 lfminute across the five quintiles of systolic blood pressure in the four groups studied. White males had higher values than black males. Heart rate was about seven beats per minute faster for white males than black males at the fourth quintile (p = .03) (Figure 3). Stroke volume was about 10 ml higher (p = .02) in white males than black males at the second quintile (Figure 3), while cardiac output was greater by 0.6 Ifminute and 0.8 If minute (p = .05 and p = .02) for white males than black males at the second and fourth quintiles, respectively (Figure 4). There were no significant differences between black and white females (data not shown). Figure 4 shows higher values of peripheral resistance for black males than for white males. Peripheral resistance was about 4 mm Hgf(lfminute) higher in black males than white males at the second (p = .01) and fourth (p = .009) systolic blood pressure quintiles. There were no significant differences between black and white females. The data reflect significant hemodynamic changes related to racial differences across the blood pressure levels in males. These differences are noted when values are adjusted for height, weight, ponderal index, and body surface area. Discussion

During the last 15 years, a large number of blood pressure studies have been conducted on populations of children. These studies now provide normative distributions of blood pressure levels in the general population and have contributed to understanding the early natural history of essential hypertension. Further, they have established that hypertension and hyTHE AMERICAN JOURNAL OF THE MEDICAL SCIENCES

pertensive disease begin early in life. This concept is documented by blood pressure tracking studies,23,24 familial history studies,25 autopsy evidence 26,27 and echocardiographic studies that document increased left ventricular thickness in childhood. 16 ,17,2s,29 Racial (black-white) contrasts related to blood pressure observed in the Bogalusa Heart Study also reflect on the multiple mechanisms that underlie hypertension. 30 The higher blood pressure levels already evident in black children are consistent with the occurrence of more severe hypertensive disease in blacks at an earlier age. Considerable controversy has arisen regarding the definition of abnormal blood pressure levels in childhood. Differences in measurement techniques, biologic variations of blood pressure, imperfect tracking, and the lack of observations of target organ changes that arise from hypertension add to the difficulty of defining hypertension in childhood. Echocardiographic studies are beginning to aid in understanding the significance of blood pressure levels and in defining the percentiles at which the anatomic changes of hypertensive disease occur. Several studies have reported increased left ventricular wall thickness, wall stress, and increased wall mass in children with blood pressure levels at the 95th percentile. 16,17,2S,29 Our studies of children stratified over the range of blood pressure levels indicate that, after adjusting for race, sex, and body anthropometric measures, a residual increase of left ventricular thickness and wall stress occurs at the top quintile. Further echocardiographic studies are warranted to identify anatomic as well as hemodynamic changes that occur with early hypertension. Echocardiographic profiling in our study has documented race and sex differences in hemodynamic characteristics of children and adolescents. Greater wall dimensions with higher blood pressure, in which cardiac output increases with higher blood pressures, have been reported. IS But our most striking finding is that at high blood pressure levels, young black males 6

5 4

'i3 :;::;2

1 0

Cardiac Output

•

~

.... '

• p
7-11 12-14 15-17 18-22

30

E25 $20 ~15 :r: E 10

!.

5 0

Peripheral Resistance

~ ....... ~-------...... BM

~-I\M

7-11 12-14 15-17 18-22

Age (years) Adjusled for sysioBc, diastoBc, height, weight, ponderosily, BSA Figure 2. Echocardiographically measured left ventricular cardiac output and peripheral resistance on boys and young men across age groups and by race. Cardiac output tended to be greater in white males, with a difference of 1.25 l/minute in the 18 to 22 year age group, and higher values of peripheral resistance were noted for black males with a difference of 4.5 mm Hg/{l/minute) in the 18 to 22 year age group.

275

Echocardiography and Blood Pressure

Table 4. Cardiac Function in Children and Young Adults by Race and Sex: The Bogalusa Heart Study Black

White

Age Systolic Diastolic LV-SV LV-EF LV-OUT RES IS VCF MAShort HRATE

Race Differences

Sex Differences

Males

Females

Males

Females

(p<)

(p<)

14.2 (0.2) 10B.1 (0.6) 66.4 (0.5) 67.6 (1.2) 70 (00) 4.55 (0.1) 18.9 (0.4) 1.11 (0.02) 33.0 (0.4) 68.6 (0.7)

13.8 (0.2) 107.0 (0.7) 67.5 (0.5) 59.3 (1.2) 70 (00) 4.32 (0.1) 20.1 (0.5) 1.19 (0.02) 33.6 (0.4) 75.5 (0.7)

14.1 (0.3) 109.4 (0.9) 67.0 (O.B) 62.7 (1.7) 69 (01) 4.09 (0.1) 21.5 (0.6) 1.13 (0.02) 33.2 (0.5) 66.4 (1.0)

15.2 (0.3) 107.0 (0.9) 6B.3 (0.7) 60.1 (1.6) 72 (01) 4.24 (0.1) 20.6 (0.6) 1.21 (0.03) 34.6 (0.5) 73.4 (0.9)

.001*

.00Bt

NS

.07t

NS

NS

.02*

.001§

NS

.03t

.002*

.06§

.001*

.06§

NS

.004§

NS

.03t

.06t

.08

.001

* Females only; tblacks only; *males only; §whites only. NS (not significant) designates p > .1. Means are adjusted for height, weight, ponderal index, BSA, age, and age to the second and cubic power. For abbreviations, see Table 2.

show increased peripheral resistance and young white males show increased cardiac output. There were no black-white differences in females. Other epidemiologic studies relating blood pressure to left ventricular performance have concentrated on contrasting children with high-range to those with midrange blood pressure levels.!5,!? Only children with blood pressures in the upper deciles have higher peripheral resistance. 3 ! Our study found trends in peripheral resistance, especially in young black males, across the blood pressure distribution. Heart size increases as a child grows and is greater in males. Persistently elevated blood pressure eventually leads to abnormal cardiac enlargement in adults

that may well begin in childhood. In the current study, the changes in cardiac function associated with blood pressure were adjusted for age and measures of body build, and the changes in cardiac function associated with age were adjusted for blood pressure. A residual effect of blood pressure on cardiac function occurred independently of a normal cardiovascular growth and development pattern, which we feel reflects adaptation to the increased blood pressure level. The greater peripheral resistance observed in black males compared to white males suggests that different mechanisms operate in the control of blood pressure in the two races. Variations with age and with blood pressure levels suggest determinants that vary during

Table 5. Partial Correlations Between Echocardiographic Measures of Cardiac Function: The Bogalusa Heart Study

Heart rate ' LV-OUT LV-EF LV-ET LV-PEP VCF MAShort LV-SV

LV-OUT

LV-EF

LV-ET

LV-PEP

VCF

MAShort

LV-SV

RESIS

.35*

-.05 .28*

-;50* -.08 .09

-.04 -.04 -.18* -.23*

.16t .27* .67* -.32* -.10*

-.05 .2B* .99* .08 -.18* .68*

-.13t .86* .31* .17* -.03 .20* .31*

-.32* -.90* - .29* .07 .06 -.25* -.28* -.79*

* p < .05; tp < .01; *p < .001. Partial correlation coefficients are adjusted for age, systolic and diastolic blood pressures, height, weight, ponderal index and body surface area. For abbreviations see Table 2.

276

May 1989 Volume 297 Number 5

Solo el 01

Table 6. Partial Correlations of Echocardiographic Measures of Cardiac Function with Blood Pressure and Anthropometric Measurements: The Bogalusa Heart Study Systolic

Diastolic

Height

Weight

Ponderal

Triceps

BSA

.11t .30* .09* -.05 -.02 .08 .09 .27* -.02

.05 .18* -.09* -.08 .09 -.05 -.09* .16* .13t

-.35t .41* -.14t .31* .19* -.22* -.14t .57* -.28*

-.22* .52* -.09 .23* .15t -.18* -.08 .62* -.35*

.07 .30* .06 -.03 .01 .02 .07 .26* -.20*

.07 .19* .05 -.01 -.01 -.01 .04 .14t -.14t

-.28* .51* -.11* .27* .18* -.20* -.11* .64* -.34*

Heart rate LV-OUT EF LV-ET LV-PEP VCF MA-SHORT LV-SV RESIST

* p < .05; tp < .01; *p < .001. Partial correlation coefficients are adjusted for race and sex. For abbreviations see Table 2.

the early phase of hypertension. The cardiovascular profile of early or borderline hypertension is believed to be associated with increased cardiac output and normal peripheral resistance. 32-35 This conclusion is based on the results of earlier studies performed in white populations. Presumably, as noted in adults, with moderate essential hypertension of several years duration, the dominant hemodynamic disturbance is increased total peripheral resistance with lower cardiac output than normotensive controlsy,34,35 Consequently, concentric left ventricular hypertrophy arises directly from the increased peripheral resistance. An inverse relation eventually develops between relative wall thickness and cardiac output in patients with mild to moderate hypertension. Eventually, in patients with severe hypertension and a pronounced increase in total peripheral resistance, cardiac output and stroke volume decrease markedly.5,35-38 Savage et al39 have suggested that the hemodynamic profile of young black males who have early or Hoort Rate

80 70 60

•

~

,..0--_---

~ ~~

_SO

SO

.:5. 40

40 30 20 0

2

...... __ BM VIM

30 20

• p
Xl

0

Stroke Volume

80 70 60

Xl 0

3

4

5

0

2

3

4

5

SBP Ouintile adjusted for diaslofic, height, weight, ponderosity, age, BSA Figure 3. Heart rate and echocardiographically measured left ventricular stroke volume across systolic blood pressure (SBP) quintiles in males by race. Note that the heart rate tends to be faster for white males, consistent with observations of cross-sectional surveys in the Bogalusa Heart Study. Also note the trend toward increasing stroke volume throughout the SBP distribution with white males having higher values than black males. THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES

borderline hypertension may be more similar to hypertensive individuals of older ages than individuals of the other race-sex groups ofthe same ages. The current study supports this view. Further, our study extends this unique relationship between peripheral resistance and cardiac output to normotensive black male adolescents. Recent studies have consistently shown greater pressor and vasoconstrictor responses to standardized stresses in young normotensive black men than young normotensive whites. 40-42 An important question is whether adolescents with greater peripheral vascular resistance have greater vascular responsiveness to standardized stressors. Studies by Falkner43 ,44 with Na+ loading and ours with orthostatic, hand grip, and cold-pressure responses 45 suggest this mechanism. Such stress responses may identify individuals at greatly increased risk of permanent elevation of blood pressure. Persistent hypertension may arise from vascular changes in the kidney triggered by vasoconstriction and followed by structural changes. These changes have been proposed by Falkner46 and Tobian 47 and are observed in our limited autopsy data,26,48 which show vascular changes in renal arteries related to high blood pressure in children and young adults following accidental death. Messerli et al 10 reported increased renal blood flow in early essential hypertension and a correlation between cardiac output and renal blood flow. In established hypertension, renal blood flow decreases and renal vascular resistance increases, and histologic changes appear that have been reported in adults. The "vasoconstrictor" hemodynamic profile described in young black males in this study contrasts with the "volume load" and increased cardiac output profile of obese children. The latter is more characteristic of the other race-sex groups in this study, especially white males. Echocardiographic evaluation of the structural changes of the heart also may reflect these various hemodynamic profiles. 13 ,49 The differ277

Echocardiography and Blood Pressure

Peripheral Reslsiance

••

••

~ • p
+

O+--r~--.-.--.-­

o

5 O+--r-.--~-r-.-­

o

3

SBP Quintiie Adjusted for dostofic, height, weight, ponderosHy, oge, BSA Figure 4. Echocardiographically measured left ventricular cardiac output and peripheral resistance across systolic blood pressure (SBP) quintiles in white and black males. Note the trend toward increasing cardiac output throughout the SBP quintiles, with higher values for white males and the peripheral resistance being greater in black males. No consistent difference by race was noted in females.

ence in functional profiles raises the possibility that, with time, the young black men might be expected to be the first group to show concentric left ventricular hypertrophy, and the other race-sex groups might show a greater tendency to develop eccentric left ventricular hypertrophy. The higher total peripheral resistance of young black men may be associated with an acceleration of target organ damage, as seen clinically.50 Exercise is known to influence the functional and structural characteristics of the cardiovascular system, but these responses also may vary in race-sex groups. The different race-sex characteristics that we observed in this population of children suggest that echocardiographic evaluation can be used to identify early in life subgroups at high risk for sustained hypertension and cardiovascular disease. The high prevalence of cardiovascular disease underscores the need to develop techniques such as echo cardiography to identify hypertensive cardiovascular pathology early in life. References 1. Freis ED: Hemodynamics of hypertension. Physiol Rev 40:2754,1960. 2. Hejl Z: Changes in cardiac output and peripheral resistance during simple stimuli influencing blood pressure. Cardiologica 31:375-381,1957. 3. Guyton AC, Cowley AW JR, Coleman TG, Dellue JW, Norman RA, Manning DA: A disease of abnormal circulatory control. Chest 65:328, 1974. 4. Fejfar Z, Widimsky J: Juvenile hypertension, in Cort JH, Fencl V, Hejl Z, Jirka J (eds): The Pathogenesis of Essential Hypertension. Prague, State Medical Publishing House, 1961, p 33. 5. Frohlich ED, Tarazi RC, Dustan HP: Re-examination of the hemodynamics of hypertension. Am J Med Sci 257:9-23, 1969. 6. Sannerstedt R: Differences in hemodynamic pattern in various types of hypertension. Triangle 9:293-299, 1970. 7. Lund-Johansen P: Hemodynamics in essential hypertension. Clin Sci 59:343S-354S, 1980. 8. Birkenhager WH, Schalekamp MADH: Control Mechanisms in Essential Hypertension. Amsterdam, Elsevier, 1976.

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Appendix

Standard formulas were used for the calculation of end-systolic and end-diastolic volume (LV-ESV and LV-EDV), left ventricular cardiac output (LV-OUT), left ventricular stroke volume (LV -SV), left ventricular ejection fraction (LV -EF), the minor axis shortening (MAShort), velocity of circumferential fiber shortening (VCF), and peripheral resistance (RESIS) as follows: LV-ESV LV-EDV LV-OUT LV-SV LV-EF MAShort

= = = = = =

LVESD (ml) LVEDD (ml) 0.001 (LV-SV) X HRT (l/minute) LV-EDV - LV-ESV (ml) LV-SV/LV-EDV X 100 (%) 100 X (LV-EDD - LV-ESD)/LV-EDD (%)

VCF = MAShort/LV-ET (%) RESIS = MAP/LV-OUT (mm Hg/[lfminute]) Where LV-ESD = left ventricular end-systolic dimension (ems); LV-EDD = left ventricular end-diastolic dimension (ems); HRT = heart rate (beats/ minute); LV-ET = left ventricular ejection time (second); and MAP = mean arterial blood pressure (mmHg). Formulas are taken from Feigenbaum H: Echocardiography. Philadelphia, Lea & Febiger, 1986, ed 4, pp 129-131,207-208.

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