Browsing by Author "Chouramanis, Nicholas"

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    Effect of acute handgrip and aerobic exercise on wasted pressure effort and arterial wave reflections in healthy aging
    (American Journal of Physiology - Heart and Circulatory Physiology, 2023-10-01) Stock, Joseph M.; Shenouda, Ninette; Chouramanis, Nicholas; Patik, Jordan C.; Martens, Christopher R.; Farquhar, William B.; Chirinos, Julio A.; Edwards, David G.
    Aging increases arterial stiffness and wave reflections that augment left ventricular wasted pressure effort (WPE). A single bout of exercise may be effective at acutely reducing WPE via reductions in arterial wave reflections. In young adults (YA) acute aerobic exercise decreases, whereas handgrip increases, wave reflections. Whether acute exercise mitigates or exacerbates WPE and arterial wave reflection in healthy aging warrants further examination. The purpose of this study was to determine if there are age-related differences in WPE and wave reflection during acute handgrip and aerobic exercise. When compared with baseline, WPE increased substantially in older adults (OA) during handgrip (5,219 ± 2,396 vs. 7,019 ± 2,888 mmHg·ms, P < 0.001). When compared with baseline, there was a robust reduction in WPE in OA during moderate-intensity aerobic exercise (5,428 ± 2,084 vs. 3,290 ± 1,537 mmHg·ms, P < 0.001), despite absolute WPE remaining higher in OA compared with YA during moderate-intensity aerobic exercise (OA 3,290 ± 1,537 vs. YA 1,188 ± 962 mmHg·ms, P < 0.001). There was no change in wave reflection timing indexed to ejection duration in OA during handgrip (40 ± 6 vs. 38 ± 4%, P = 0.41) or moderate-intensity aerobic exercise (40 ± 5 vs. 42 ± 8%, P = 0.99). Conversely, there was an earlier return of wave reflection in YA during handgrip (60 ± 11 vs. 52 ± 6%, P < 0.001) and moderate-intensity aerobic exercise (59 ± 7 vs. 51 ± 9%, P < 0.001). Changes in stroke volume were not different between groups during handgrip (P = 0.08) or aerobic exercise (P = 0.47). The greater increase in WPE during handgrip and decrease in WPE during aerobic exercise suggest that aortic hemodynamic responses to acute exercise are exaggerated with healthy aging without affecting stroke volume. NEW & NOTEWORTHY We demonstrated that acute aerobic exercise attenuated, whereas handgrip augmented, left ventricular hemodynamic load from wave reflections more in healthy older (OA) compared with young adults (YA) without altering stroke volume. These findings suggest an exaggerated aortic hemodynamic response to acute exercise perturbations with aging. They also highlight the importance of considering exercise modality when examining aortic hemodynamic responses to acute exercise in older adults.
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    Effect of age and handgrip exercise on renal oxygenation in healthy adults
    (University of Delaware, 2022) Chouramanis, Nicholas
    Normal aging is associated with significant increases in blood pressure and arterial stiffness, which partially contribute to kidney function decline. Additionally, renal hypoxia has been implicated as a common pathway in the development and progression of renal diseases. However, this is mostly supported by animal studies and computational models. Advancement of modern magnetic resonance imaging (MRI) techniques now permits the assessment of renal oxygenation in humans so that we may better understand the effect of aging on renal oxygenation. Currently, there is limited research that demonstrates mixed results regarding changes in renal oxygenation in healthy aging humans. OBJECTIVES: 1) Determine resting renal oxygenation in older and younger adults as well as evaluate the association between arterial stiffness and renal oxygenation in older adults. 2) Evaluate the effect of age and handgrip (HG) exercise on renal oxygenation in older and younger adults. HYPOTHESES: 1) Cortical and medullary oxygenation will be significantly reduced in older adults compared to younger adults. Arterial stiffness will be negatively associated with cortical oxygenation in older adults. 2) Changes in renal oxygenation during HG exercise will be exaggerated in older adults compared to younger adults. METHODS: Healthy, non-hypertensive and non-obese older and younger adults were recruited. After consent and screening, subjects underwent testing over the course of 2 visits. Carotid-femoral pulse wave velocity (cf-PWV), a measure of arterial stiffness, was assessed via applanation tonometry. Blood-oxygen level dependent (BOLD)-MRI was used to assess the relaxation rate (R2*), a surrogate measure of tissue oxygenation, of the cortex and medulla in the kidney at rest and in response to a 3-minute bout of HG exercise at 30% maximal voluntary contraction. Elevated R2* suggests decreased oxygenation. RESULTS: 13 old healthy (8F/5M; Age: 67±6 years; BMI: 23.8±2.8 kg/m2; MAP: 86±7 mmHg) and 14 young healthy (7F/7M; Age: 27±3 years; BMI: 23.3±2.2 kg/m2; MAP: 77±9 mmHg) adults were recruited. Resting cortical R2* (22.2±3.1 vs. 19.4±1.9 s-1; p=0.009) and medullary R2* (27.3±3.5 vs 22.5±2.7 s-1; p<0.001) were significantly increased in older adults versus younger adults. Cf-PWV was elevated in older adults (8.4±1.9 vs. 5.6±0.7 m/s; p<0.001) but was not associated with cortical oxygenation (r=0.232; p=0.446). In response to HG exercise, changes were observed in cortical R2* (∆4.9±7.6 vs. 9.3±8.2 %) and medullary R2* (∆1.7±5.7 vs 5.1±8.5 %), but there was no difference in the response between older and younger healthy adults. (p=0.162 cortex; p=0.237 medulla). CONCLUSION: Renal oxygenation is significantly reduced in older adults at rest and is not associated with arterial stiffness. Changes in renal oxygenation in response to HG exercise are significant, but not different between older and younger adults.