Reduced Vasoreactivity in Older Compared to Young Adults Following Handgrip Exercise and Cold Pressor Test.

INTRODUCTION: Aging is associated with increased sympathetic nerve activity (SNA) and reduced vasoreactivity. Cold pressor test (CPT) increases SNA and may thus counteract exercise-induced local vasodilation. We tested the hypothesis that older adults would exhibit less vasoreactivity following acute rhythmic handgrip (HG) exercise coupled with CPT compared to young adults.

METHODS: Twenty older adults (60 ± 5 yrs; 10F) and 12 young adults (24 ± 4 yrs; 6F) underwent a bed study of 5-min baseline, 4-min 40% MVC rhythmic HG, 2-min CPT superimposed with HG (HG+CPT), and 5-min recovery. Brachial artery measures included diameter (B-mode Doppler), blood velocity (pulsed-wave Doppler), blood flow, shear rate, and resistance, as well as heart rate (HR, ECG) and mean arterial pressure (MAP, finger plethysmography). Vasoreactivity was assessed with minimum and peak values within 60 s post-HG+CPT. Statistics included mixed methods ANOVA and ANCOVA (p< 0.05).

RESULTS: Brachial blood flow and velocity had condition effects (p < .001) but no interaction or group effects (p > .05). Both groups increased blood flow and velocity from baseline to HG (Δ201 ± 148 mL/min, p < .001; Δ26 ± 11 cm/s, p < .001) and further increased during HG+CPT (Δ47 ± 96 mL/min, p= .021; Δ3 ± 7 cm/s, p= .017). Post-HG+CPT blood flow and velocity decreased (Δ-194 ± 208 mL/min, p< .001; Δ-20 ± 19 cm/s, p< .001) and then increased to peak values greater than HG+CPT (Δ73 ± 177 mL/min, p< .001; Δ13 ± 10 cm/s, p< .001) before decreasing to above baseline levels after 5-min (Δ26 ± 52 mL/min, p= .016; Δ3 ± 5 cm/s, p= .002). A group × condition interaction (p = .042) revealed greater brachial diameter in older (4.27 ± 0.76 mm) compared to young adults (3.24 ± 0.81 mm, p = .002) at each condition (all p < .05). Diameter did not change during HG or HG+CPT (all p > 0.05). Post-HG+CPT diameter first decreased in young adults (2.69 ± 0.91 mm, p = .003) and then increased to a peak value in both young (3.61 ± 0.90 mm; p = .006) and older adults (4.58 ± 0.88 mm, p = .003). Diameter returned to baseline after 5-min in young (3.35 ± 0.78 mm, p = .154) and older adults (4.17 ± 0.76 mm, p = .329). Resistance was not different between groups (p = .147) but dropped during HG (Δ-9 ± 10 mmHg/mL/min, p< .001) and remained low during HG+Cold (Δ1 ± 11 mmHg/mL/min, p= .334) before returning to baseline levels after 5-min (Δ-2 ± 7 mmHg/mL/min, p< .196). Shear rate (Δ279 ± 180 s-1 , p< .001), MAP (Δ8 ± 6 mmHg, p< .001), and HR (Δ8 ± 6 bpm, p< .001) increased from baseline to HG in all participants. HG+CPT further increased shear rate (Δ38 ± 94 s-1 , p= .005), MAP (Δ9 ± 7 mmHg, p< .001) and HR (Δ4 ± 7 bpm, p= .002) before decreasing to above baseline levels of shear rate (Δ30 ± 54 s-1 , p= .003) and MAP after 5-min (Δ2 ± 6 mmHg, p= .034). HR returned to baseline in older adults (Δ0 ± 3 bpm, p= .656) and fell below baseline in young adults (Δ-3 ± 4 bpm, p= .008). MAP (109 ± 11 vs. 100 ± 11 mmHg, pooled p= .039) was greater in older compared to young adults across conditions.

CONCLUSION: Immediately following the simultaneous cessation of HG and CPT, young but not older adults demonstrate a transient reduction in brachial artery diameter, indicative of reduced vasoreactivity.