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CLINICAL STUDY

Attenuated cardiovascular reserve during prolonged submaximal cycle exercise in healthy older subjects

Luis C. L. Correia, MD^*, Edward G. Lakatta, MD^*, Frances C. O’Connor, MPH^*, Lewis C. Becker, MD, FACC, Jon Clulow, ARRT, CNMT, Susan Townsend, RN, Gary Gerstenblith, MD, FACC and Jerome L. Fleg, MD, FACC^*,*

^* Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
Division of Cardiology, Johns Hopkins Hospital, Baltimore, Maryland, USA

Manuscript received July 18, 2001; revised manuscript received May 7, 2002, accepted June 27, 2002.

^* Reprint requests and correspondence: Dr. Jerome L. Fleg, National Heart, Lung, and Blood Institute, DECA, Rockledge 2, Room 8112, 6701 Rockledge Drive, MSC 7936, Bethesda, Maryland 20892, USA.
flegj{at}nhlbi.nih.gov

OBJECTIVES: The goal of this study was to determine the effect of age on the hemodynamic response to prolonged submaximal aerobic exercise in healthy volunteers.

BACKGROUND: Reductions in peak work rate, heart rate (HR), and left ventricular (LV) emptying but higher blood pressure (BP) and systemic vascular resistance occur in healthy older versus younger humans during short bursts of graded maximal aerobic exercise. However, the effect of aging on the cardiovascular response to prolonged exercise at submaximal work rates typical of daily aerobic activities remains unknown.

METHODS: We evaluated cardiovascular performance throughout prolonged submaximal upright cycle ergometry in 40 carefully screened healthy untrained volunteers, 8 men and 12 women <50 years old, mean = 37 ± 8 years (younger), and 10 men and 10 women 50 years old, mean = 66 ± 9 years (older), during upright cycle exercise at 70% of peak cycle oxygen consumption (VO₂) to exhaustion or a maximum of 120 min. Cardiac volumes were acquired by gated blood pool scans with ^99mTc at rest and every 10 min throughout exercise.

RESULTS: Duration of exercise was similar in younger ([81 ± 28 min] versus older [71± 29 min] subjects, p = NS). At 10 min of exercise in the steady state, older subjects demonstrated lower VO₂ (1.1 ± 0.2 l/min vs. 1.3 ± 0.3 l/min) and lower HR (118 ± 17 vs. 135 ± 11 beats/min, p < 0.001) but larger end-diastolic (80 ± 11 ml/m² vs. 73 ± 8 ml/m², p = 0.03) and end-systolic volume index (ESVI) 20 ± 6 ml/m² vs. 17 ± 4 ml/m², p < 0.05) than younger ones. Between 10 min and exercise termination, with VO₂ held constant in both groups, increases in HR (14.0 ± 12.4 beats/min vs. 5.9 ± 11.5 beats/min, p = 0.04), cardiac index (1.6 ± 1.0 l/min/m² vs. 0.8 ± 1.1 l/min/m², p = 0.03), and LV ejection fraction (7.1 ± 4.0% vs. 2.9 ± 4.4%, p = 0.003) were greater in younger than older subjects, respectively, as was the reduction in ESVI (–5.1 ± 3.0 ml/m² vs. –1.8 ± 3.3 ml/m², p = 0.002), despite similar declines in systolic BP (–12.3 ± 6.3 mm Hg vs. –12.1 ± 15.0 mm Hg, p = NS).

CONCLUSIONS: Thus, age-associated deficits in chronotropic and LV systolic reserve performance occur during prolonged submaximal upright cycle ergometry, analogous to those observed during graded maximal exercise.

Abbreviations and Acronyms   a-vO2   arteriovenous oxygen   BLSA   Baltimore Longitudinal Study of Aging   BP   blood pressure   CI   cardiac index   CNTR   contractility index   DBP   diastolic blood pressure   EAI   arterial elastance index   EDV   end-diastolic volume   EDVI   end-diastolic volume index   EF   ejection fraction   ESV   end-systolic volume   ESVI   end-systolic volume index   HR   heart rate   LV   left ventricular   MBP   mean blood pressure   PSE   prolonged submaximal exercise   SBP   systolic blood pressure   SV   stroke volume   SVI   stroke volume index   TSVR   total systemic vascular resistance   VO2   oxygen consumption   VO2max   maximal oxygen consumption

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