Gender-Related Difference in Arterial Elastance During Exercise in Patients With Hypertension
Exercise intolerance and heart failure with preserved ejection fraction are common in females. Recently, arterial stiffness has been suggested to be a significant contributor in the development of heart failure. How gender difference affects arterial stiffening and its response to exercise is not well known. We hypothesized that arterial elastance index during exercise would be more abnormal in females with hypertension than males. Arterial elastance index was estimated as arterial end systolic pressure/stroke volume controlled for body surface area and was measured at rest and during graded supine bicycle exercise (25 watts, 3-minute increments) in 298 patients with hypertension (149 males; 149 females; mean age, 59). The subjects were divided into 2 groups by gender. Exercise duration was significantly shorter in females compared to males (692±222 versus 483±128 seconds, P<0.001). Although arterial elastance index at baseline was significantly higher in males, the magnitude of increase was steeper in females with the magnitude of change at 75 W of exercise being significantly higher in females compared to males (0.69±0.83 versus 0.43±0.69, P=0.018). Arterial elastance index at each stage of exercise up to 75 W was independently associated with decreased exercise duration. In conclusion, despite lower arterial elastance index at rest, the increase during exercise was steeper in women with hypertension, suggesting a gender-related difference in dynamic arterial stiffness. The arterial elastance index during exercise was significantly associated with exercise duration in patients with hypertension.
In epidemiology studies, nearly 50% of patients with heart failure have preserved ejection fraction and hypertension is considered to be the most important cause of heart failure with preserved ejection fraction. Interestingly, advanced age and the female gender are known to be associated with development of heart failure with preserved ejection fraction because the prevalence of heart failure with ejection fraction increases sharply with age than systolic heart failure, especially in females.1,2 Recently, arterial stiffness has been suggested to be a significant contributor in the development of heart failure.3,4 Increased aortic stiffness in subjects contributed to increased afterload to the heart while reducing coronary perfusion pressure during diastole.3,4 Greater aortic stiffness may increase myocardial stiffness and left ventricular (LV) diastolic filling pressure, which may be exaggerated during exercise.5 How gender difference affects arterial stiffening and its response to exercise is not well known; therefore, we hypothesized that arterial elastance index (EaI) during exercise would be more abnormal in female patients with hypertension compared to males.
Symptom-limited supine bicycle exercise (25 Watts, 3-minute increments) with simultaneous 2-dimensional and Doppler echocardiography was performed by 298 hypertension patients of 427 hypertensive subjects who performed diastolic stress echocardiography at Yonsei University College of Medicine (149 males, age, 58±9 years; 149 females, age, 59±8 years). Male subjects of similar age profiles as female subjects were selected by 1:1 matching. No patients had symptoms or signs of heart disease, were in sinus rhythm, or had a normal resting 12-lead ECG. Exclusion criteria were significant atrial or ventricular arrhythmia, significant valvular diseases (≥moderate severity), significant coronary artery disease, prior history of myocardial infarction, depressed LV systolic function (ejection fraction <50%, or any regional wall motion abnormality), pericardial disease, and inability to exercise. Subjects were divided into 2 groups according to gender. Study approval was obtained from the Institutional Review Board of Yonsei University College of Medicine.
Two-Dimensional and Exercise Doppler Echocardiography (Diastolic Stress Echocardiography)
Standard 2-dimensional measurements (LV diastolic and systolic dimensions, ventricular septum and posterior wall thickness [PWT], left atrial volume, and LV outflow tract diameter) were obtained with the patient in the left lateral position. LV ejection fraction (EF) was calculated by the modified Quinones method.6 After obtaining rest images from standard parasternal and apical views, a multistage supine bicycle exercise test was performed with a variable load bicycle ergometer (Medical Positioning Inc) as described previously.7 Patients pedaled at a constant speed beginning at a workload of 25 W in increments of 25 W every 3 minute.Echocardiography was performed using a GE Vingmed System 7 ultrasound system with a 2.5-MHz transducer during rest, each stage of exercise, and recovery. The blood pressure was measured at the end of each stage of exercise on the left arm using an oscillometric blood pressure monitoring device (Solar 8000 mol/L patient monitoring device, GE Medical systems).
From the apical window, a 1- to 2-mm pulsed Doppler sample volume was placed at the mitral valve tip and mitral flow velocities from 5 to 10 cardiac cycles were recorded. Mitral inflow velocities were traced and the following variables were obtained: peak velocity of early (E) and late (A) filling, and deceleration time of E-wave velocity. SV was measured from LV outflow tract diameter and pulse−wave Doppler signal as previously described.8 Mitral annular velocity was measured by Doppler tissue imaging using pulse-wave Doppler mode. The filter was set to exclude high frequency signal, and the Nyquist limit was adjusted to a range of 15 to 20 cm/s. Gain and sample volume were minimized to allow for a clear tissue signal with minimal background noise. Early diastolic (E′) and systolic (S′) velocities of the mitral annulus were measured from the apical 4-chamber view with a 2- to 5-mm sample volume placed at the septal corner of the mitral annulus. Effective arterial elastance (Ea) was estimated as ESP/SV. End-systolic pressure (ESP) was estimated as systolic pressure ×0.9 as described previously.9,10 The arterial elastance index (EaI) was estimated by normalizing the arterial elastance to body surface area as described previously.9,11 These measurements were performed at baseline, each stage of exercise, and recovery in the same sequence. All data were stored digitally, and measurements were taken at the completion of each study. Two-dimensional echocardiographic images from apical views at rest and during exercise were acquired, digitized, recorded, and analyzed for the wall motion analysis.
Continuous variables were summarized as a mean±SD. Categorical variables were summarized as a percentage of the group total. Unpaired Student t test and χ2 analysis were used to compare continuous and categorical variables, respectively. Independent predictors for exercise duration were determined using multiple linear regression analysis. Four models entering arterial elastance index at baseline and each stage of exercise into the equation were assessed. Variables that showed significant association with exercise duration (age, gender, E/E′ at baseline, S′ at baseline, presence of diabetes, and left ventricular mass index [LVMI]) were entered into the equation. Statistical analysis was performed using SPSS 13.0 statistical program (SPSS Inc). Statistical significance was defined as <0.05.
The comparison between 2 groups with regard to clinical variables is presented in Table 1. There was no significant difference in the proportion of patients being treated for hypertension at the time of study enrollment. Exercise duration (483±128 versus 692±222 s, P<0.001) was significantly shorter in females compared to males. There were no regional wall motion abnormalities either at rest or during exercise in both groups.
Baseline Echocardiographic Findings
Table 1 shows the comparison of echocardiographic findings between the 2 groups. Women had smaller LV cavity and LVMI compared to men. However, there was no significant gender difference in the proportion of subjects with LV hypertrophy, left atrial volume index, E velocity, A velocity, E/A ratio, and DT.
Hemodynamic Response to Exercise
The effect of supine bicycle exercise on heart rate and blood pressure is shown in Table 2. In both groups, heart rate, systolic blood pressure, and diastolic blood pressure were increased after exercise compared to those at rest. There were no significant differences in systolic blood pressure at rest or during exercise up to 75 W. However, peak systolic BP at peak exercise was significantly higher in males, most likely because of the higher maximal workload that was achieved in men (Table 2). Heart rate during exercise was significantly higher at 25 W, 50 W, and 75 W of exercise in females. Diastolic blood pressure was significantly lower in females at baseline, 25 W, and peak exercise.
The comparison of Doppler echocardiographic variables during exercise demonstrated significantly higher E velocity and A velocity at 25 W and 50 W of exercise in females. E′ was also significantly lower at 25 W in females. E/E′, an index of LV filling pressure, was significantly elevated at rest, 25 W, and 50 W of exercise in females. S′, an index of LV longitudinal contraction, was significantly decreased at rest and during all stages of exercise in females (Table 3).
EaI at Rest and Exercise
In females, SV was significantly lower than males at baseline and up to 75 W of exercise (Table 3). Despite lower EaI at rest, the increase of EaI during exercise was steeper in females (Figure 1) with the magnitude of change in EaI at 75 W of exercise being significantly higher in females compared to males (0.69±0.83 versus 0.43±0.69, P=0.018; Figure 2).
Arterial Elastance and Exercise Capacity
Multiple linear regression analysis was performed to determine the independent association of exercise duration with arterial elastance index while controlling for confounding factors such as age, female gender, diabetes, E/E′ at baseline, S′ at baseline, and LV mass index. The results demonstrated an independent association of arterial elastance index at each stage of exercise with exercise duration in hypertensive subjects (Table 4).
The present study is, to our knowledge, the first to demonstrate the gender difference of arterial elastance during exercise in patients with hypertension. In addition, echocardiographically derived EaI was associated with exercise duration. These data may suggest that increase in arterial elastance during exercise in females may contribute to exercise-induced diastolic dysfunction and exercise intolerance in hypertensive subjects.
Gender Difference of EaI
After the onset of established clinical diseases, compensatory response differs between males and females. Previous investigations have shown higher rates of HF in females despite higher EF than males after myocardial infarction.12,13 Females with HF tended to experience more symptoms and a higher number of hospitalizations than among males.14 In addition, exercise intolerance and HF with preserved EF are more common in females; however, little is known about the mechanism underlying the gender difference in risk of HF in patients with hypertension. EaI is an index of pulsatile arterial load that correlates well with aortic impedance data as described previously.9,11 Although EaI is determined by both systemic vascular resistance and pulsatile arterial load, the main determinant during exercise has been demonstrated to be systemic arterial compliance, which is increased during exercise.15,16 Because age-adjusted EaI has been described to be higher in females compared to males, we hypothesized that there would be a greater increase of EaI during exercise in females, which may be a contributing factor for the gender difference in the prevalence of diastolic heart failure.6 Females have been shown to demonstrate a greater age-related increase in proximal aortic stiffness and pulse pressure compared to males.15,17 Arterial elastance at each stage of exercise was significantly higher in females, and the difference was driven by the fact that end systolic pressure at each stage of exercise was similar despite the significantly lower SV. This may be attributable to the lower arterial compliance in females compared to males. When arterial elastance was corrected for BSA to adjust for gender difference in body size, there was no significant gender difference for EaI at each stage of exercise because of the fact that SV corrected for BSA was higher in females compared to males at baseline, 25 W, and 50 W of exercise. However, the magnitude of increase of SV index at each stage of exercise was decreased in females despite similar levels of end systolic pressure. This was associated with the magnitude of increase of arterial elastance being steeper in females with the change in EaI at 75 W of exercise being significantly higher in females compared to males (0.69±0.83 versus 0.43±0.69, P=0.018; Figure 2). Because the main determinant of EaI during exercise is arterial compliance, the steeper rise of EaI during exercise may be attributable to gender difference in inherent arterial elasticity even when corrected for the discrepancy in body size. The steeper rise of arterial elastance may subsequently increase systolic pulsatile load to the heart and have a deleterious effect on myocardial function during exercise.
Association Between EaI and Exercise
We performed a multiple linear regression analysis to determine the relationship of EaI at each stage of exercise with exercise duration controlled for age, gender, presence of diabetes, E/E′ at baseline, S′ at baseline, and LVMI. The result demonstrated an independent association of EaI at each stage of exercise but not at baseline. This suggests that the increase in pusatile load, which is the determinant of EaI during exercise, may have an important role in determining exercise capacity. A recent study by Borlaug et al demonstrated the importance of pulsatile arterial afterload on cardiac function during exercise.18 In this study, there was a significant correlation of the magnitude of change of EaI at 75 W of exercise with E/E′ at 50 W and S prime at peak exercise (Table 5), demonstrating that the increased pulsatile arterial load during exercise may have significant impact on myocardial relaxation and contractile function during exercise and have a significant impact on exercise capacity.
In conclusion, despite lower EaI at rest, the increase in EaI during exercise was steeper in females with hypertension, suggesting a gender-related difference in dynamic arterial stiffness. EaI at rest as well as during exercise was significantly associated with exercise duration in patients with hypertension. Further studies to determine whether the steeper rise of EaI during exercise in females is associated with increased development of diastolic dysfunction and congestive heart failure are needed.
The limitation of this study may be the relatively high proportion of treated hypertensive subjects at the time of enrollment; however, we believe that the effects of treatment were minimized by the similar proportion of treated patients and by the absence of significant differences in baseline systolic blood pressure between females and males. The second limitation is the use of brachial arterial pressure rather than the central aortic pressure measurements in determining the arterial elastance index. Because the heart rate at 75 W of exercise in females was significantly higher than that of males, the difference in heart rate and its effect on pressure amplification may impact the actual measurement of central aortic pressure during exercise. However, noninvasive calculation of end systolic pressure derived from brachial artery pressure has been shown to accurately predict end systolic pressure derived from direct measurement of central aortic pressure.10,11 In addition, because the mean age of study population of the present study is relatively old, we believe that there would be a less effect of pressure amplification from the central to the peripheral arteries. In a study by Wilkinson IB et al, older subjects over the age of 50 showed significant decrease in pressure amplification compared to younger subjects.19 Although it would be ideal to match heart rate and measure central blood pressure during exercise, it may not be practical to do in a large number of study subjects.
Heart failure with preserved ejection fraction is highly prevalent in hypertensive patients and is more prevalent in females. The main pathogenesis of heart failure with normal ejection fraction is explained by diastolic dysfunction. The increased diastolic dysfunction with aging is explained by steeper increase of arterial elastance (EaI) and LV end-systolic elastance (Ees) with age. Although the vascular-ventricular coupling is maintained despite steeper increase in arterial elastance because of the compensatory increase in LV elastance, the increase in LV elastance may increase the sensitivity of systolic pressure to changes in volume status, which may be exaggerated during exercise. However, the mechanism underlying the gender difference for the risk of heart failure in patients with hypertension has not been well defined. This study demonstrated that in hypertensive females, there was a steeper rise of EaI during exercise and EaI was an independent determinant of exercise duration. Because EaI during exercise is determined by the pulsatile arterial load, the steeper increase has a significant impact on myocardial relaxation and contractile function during exercise, which may result in decreased exercise capacity. The dynamic increase of arterial elastance, resulting in increase of dynamic pulsatile load during exercise, may be one of the mechanisms for the gender difference in the incidence of diastolic dysfunction and heart failure in hypertension.
Sources of Funding
This work was supported by the Korea Science and Engineering Foundation (KOSEF) and a grant from the Korean government (M10642120001-06N4212-00110).
- Received December 1, 2007.
- Revision received December 19, 2007.
- Accepted January 9, 2008.
Senni M, Tribouilloy CM, Rodeheffer RJ, Jacobsen SJ, Evans JM, Bailey KR, Redfield MM. Congestive heart failure in the community: a study of all incident cases in Olmsted county, Minnesota, in 1991. Circulation. 1998; 98: 2282–2289.
Rerkpattanapipat P, Hundly G, Link KM, Brubaker PH, Hamilton CA, Darty SN, Morgan TM, Kitzman DW. Relation of aortic distensibility determined by magnetic resonance imaging in patients ≥60 years of age to systolic heart failure and exercise capacity. Am J Cardiol. 2002; 90: 1221–1225.
Hundley WG, Kitzman DW, Morgan TM, Hamilton CA, Darty SN, Stewart KP, Herrington DM, Link KM, Little WC. Cardiac cycle dependent changes in aortic area and distensibility are reduced in older patients with isolated diastolic heart failure and correlate with exercise intolerance. J Am Coll Cardiol. 2001; 38: 796–802.
Bonapace S, Rossi A, Cicoira M, Franceschini L, Golia G, Zanolla L, Marino P, Zardini P. Aortic distensibility independently affects exercise tolerance in patients with dilated cardiomyopathy. Circulation. 2003; 107: 1603–1608.
Quinones MA, Waggoner AD, Reduto LA, Nelson JG, Young JB, Winter WL, Ribeiro LG, Miller RR. A new, simplified and accurate method for determining ejection fraction with two-dimensional echocardiography. Circulation. 1981; 64: 744–753.
Oh JK, Seward JB, Tajik AJ. The Echo Manual. Second ed. Philadelphia, Pa. Lippincott Williams & Wilkins; 1999.
Redfield MM, Jacobsen SJ, Borlaug BA, Rodeheffer RJ, Kass DA. Age and gender-related ventricular-vascular stiffening: A community based study. Circulation. 2005; 112: 2254–2262.
Kelly RP, Ting CT, Yang TM, Liu CP, Maughan WL, Chang MS, Kass DA. Effective arterial elastance as index of arterial vascular load in humans. Circulation. 1992; 86: 513–521.
McMurray J, McDonagh T, Morrison CE, Dargie HJ. Trends in hospitalization for heart failure in Scotland 1980–1990. Eur Heart J. 1993; 14: 1158–1162.
Wilkinson IB, Franklin SS, Hall IR, Tyrrell S, Cockroft JR. Pressure amplification explains why pulse pressure is unrelated to risk in young subjects. Hypertension. 2001; 38: 1461–1466.