Aging exaggerates blood pressure response to ischemic rhythmic handgrip exercise in humans.

Ischemic skeletal muscle conditions are known to augment exercise-induced increases in blood pressure (BP). Aging is also a factor that enhances the pressor response to exercise. However, the effects of aging on the BP response to ischemic exercise remain unclear. We, therefore, tested the hypothesis that aging enhances the BP response to rhythmic handgrip (RHG) exercise during postexercise muscle ischemia (PEMI). We divided the normotensive participants without cardiovascular diseases into three age groups: young (n = 26; age, 18-28 years), middle-aged (n = 23; age, 35-59 years), and older adults (n = 23; age, 60-80 years). The participants performed RHG exercise with minimal effort for 1 min after rest with and without PEMI, which was induced by inflating a cuff on the upper arm just before the isometric handgrip exercise ended; the intensity was 30% of maximal voluntary contraction force. Under PEMI, the increase in diastolic BP (DBP) from rest to RHG exercise in the older adult group (Δ13 ± 2 mmHg) was significantly higher than that in the young (Δ5 ± 2 mmHg) and middle-aged groups (Δ6 ± 1 mmHg), despite there being no significant difference between the groups in the DBP response from rest to RHG exercise without PEMI. Importantly, based on multiple regression analysis, age remained a significant independent determinant of both the SBP and DBP responses to RHG exercise during PEMI (p < 0.01). These findings indicate that aging enhances the pressor response to ischemic rhythmic exercise.

Contributions of residual hypoxemia to exercise hyperventilation in Fontan patients.

It is unsettled whether increased exercise ventilation in Fontan subjects is due to increased pulmonary dead space or augmented ventilatory drive. Twenty-six Fontan patients underwent symptom-limited treadmill cardiopulmonary exercise testing. Two groups of age- and sex- matched subjects served as controls: the biventricularly repaired (Bi, n = 18), and the "true" control (C, n = 29) groups. Peak oxygen uptake (V̇O2peak) was not different among groups (41.0 +/- 8.4 ml/min/kg, 43.5 +/- 6.6 ml/min/kg, and 45.9 +/- 11.6 ml/min/kg for Fontan, Bi, and C groups, respectively, p = 0.16). Fontan subjects, however, showed steeper alveolar ventilation/carbon-dioxide (V̇A/V̇CO2) regression slope (35.5 +/- 5.3, 28.7 +/- 3.8, and 29.5 +/- 3.0 l/ml, for Fontan, Bi, and C groups, respectively, p<0.0001), and lower end-expiratory carbon-dioxide fraction (FetCO2VAT) at ventilatory threshold (VAT) (4.4 +/- 0.5%, 5.5 +/- 0.5%, and 5.5 +/- 0.4%, for Fontan, Bi, and C groups, respectively, p<0.001). The dead-space ventilation fraction at VAT was similar among groups (0.33 +/- 0.06, 0.33 +/- 0.04, 0.35 +/- 0.05 for Fontan, Bi, and C groups, respectively, p = 0.54). In Fontan subjects, arterial oxygen saturation at rest (SaO2rest) was correlated with V̇A/V̇CO2 regression slope (r = -0.41, p = 0.04) and with FetCO2VAT (p = -0.53, p<0.01). We conclude that Fontan patients show exercise hyperventilation due to augmented central and/or peripheral ventilatory drive, which is further augmented by residual hypoxemia.

Insulin resistance is associated with an exaggerated blood pressure response to ischemic rhythmic handgrip exercise in nondiabetic older adults.

Patients with type 2 diabetes display an exaggerated pressor response to exercise. However, evidence supporting the association between the magnitude of the pressor response to exercise and insulin resistance-related factors including hemoglobin A1c (HbA1c) or homeostatic model assessment of insulin resistance (HOMA-IR) in nondiabetic subjects has remained sparse and inconclusive. Thus we investigated the relationship between cardiovascular responses to exercise and insulin resistance-related factors in nondiabetic healthy men (n = 23) and women (n = 22) above 60 yr old. We measured heart rate (HR) and blood pressure (BP) responses during: isometric handgrip (IHG) exercise of 30% maximal voluntary contraction, a period of skeletal muscle ischemia (SMI) induced by tourniqueting the arm after IHG, and rhythmic dynamic handgrip (DHG) exercise during SMI. Greater diastolic BP (DBP) responses to DHG with SMI was associated with male sex (r = 0.44, P = 0.02) and higher HbA1c (r = 0.33, P = 0.03), heart-ankle pulse wave velocity (haPWV) (r = 0.45, P < 0.01), and resting systolic BP (SBP) (r = 0.36, P = 0.02). HbA1c persisted as a significant determinant explaining the variance in the DBP response to DHG with SMI in multivariate models despite adjustment for sex, haPWV, and resting SBP. It was also determined that the DBP response to DHG with SMI in a group in which HOMA-IR was abnormal (Δ33 ± 3 mmHg) was significantly higher than that of groups in which HOMA-IR was at intermediate (Δ20 ± 4 mmHg) and normal (Δ23 ± 2 mmHg) levels. These data suggest that even in nondiabetic older adults, insulin resistance is related to an exaggerated pressor response to exercise especially when performed under ischemic conditions.NEW & NOTEWORTHY The diastolic blood pressure response to rhythmic dynamic handgrip exercise under ischemic conditions was demonstrated to be correlated with insulin resistance-related factors in nondiabetic older adults. This finding provides important insight to the prescription of exercise in this particular patient population as the blood pressure response to exercise, especially under ischemic conditions, could be exaggerated to nonsafe levels.