Effect of healthy aging on renal vascular responses to local cooling and apnea

Abstract

Sympathetically mediated renal vasoconstriction may contribute to the pathogenesis of hypertension in older adults, but empirical data in support of this concept are lacking. In 10 young (26 ± 1 yr) and 11 older (67 ± 2 yr) subjects, we quantified acute hemodynamic responses to three sympathoexcitatory stimuli: local cooling of the forehead, cold pressor test (CPT), and voluntary apnea. We hypothesized that all stimuli would increase mean arterial blood pressure (MAP) and renal vascular resistance index (RVRI) and that aging would augment these effects. Beat-by-beat MAP, heart rate (HR), and renal blood flow velocity (from Doppler) were measured in the supine posture, and changes from baseline were compared between groups. In response to 1°C forehead cooling, aging was associated with an augmented MAP (20 ± 3 vs. 6 ± 2 mmHg) and RVRI (35 ± 6 vs. 16 ± 9%) but not HR. In older adults, there was a positive correlation between the cold-induced pressor response and forehead pain (R = 0.726), but this effect was not observed in young subjects. The CPT raised RVRI in both young (56 ± 13%) and older (45 ± 8%) subjects, but this was not different between groups. Relative to baseline, end-expiratory apnea increased RVRI to a similar extent in both young (46 ± 14%) and older (41 ± 9%) subjects. During sympathetic activation, renal vasoconstriction occurred in both groups. Forehead cooling caused an augmented pressor response in older adults that was related to pain perception.

Keywords: cold face test; noxious cooling; peripheral chemoreflex; renal blood flow; vasoconstriction.

Fig. 1.

Mean arterial blood pressure (MAP) and heart rate (HR) were measured in young (black diamonds, n = 10) and older (white squares, n = 11) subjects during 60 s of forehead cooling (1°C and 15°C water in a plastic bag), as well as a neutral (35°C water) time control. Means ± SE; *group difference at a given time point, P < 0.05.

Fig. 2.

Peak changes in renal vascular resistance index (ΔRVRI) in young (black bars, n = 10) and older (white bars, n = 11) subjects. *Group difference, P < 0.05.

Fig. 3.

Local cold sensation (top) and local pain perception (bottom) in young (black bars, n = 10) and older (white bars, n = 11) subjects. For cold sensation, 0 = neutral, 5 = cold, 10 = very, very cold. For pain, 0 = no pain, 6 = painful, and 10 = unbearably painful. There were no group differences.

Fig. 4.

Relationship between forehead pain and ΔMAP in response to forehead cooling at 1°C. Data from experiments 1 and 2 are presented together.