What is the clinical evidence from this study?

Study design: Cross-Sectional. Population: Healthy aging (n=50). Intervention: Healthy aging (Older age) vs. Young adults. Primary outcome: Peak change in renal vascular resistance index (ΔRVRI) during 1°C forehead cooling (p=0.039).

May 3, 2013Open Access

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

Key Result

Healthy aging was associated with an augmented increase in renal vascular resistance index (35% vs. 16%) and mean arterial blood pressure (20 vs. 6 mmHg) in response to 1°C forehead cooling compared to young adults.

Study Design

Type

Cross-Sectional (n=50)

Blinding

Open-label

Randomization

Randomized order of stimuli

Multicenter

Structured PICO

Does healthy aging augment the acute hemodynamic and renal vascular resistance responses to local cooling and apnea?

Population

50 healthy, normotensive young and older adults underwent acute physiological testing to evaluate cardiovascular and renal responses to sympathoexcitatory stimuli.

Exposure

Three acute sympathoexcitatory stimuli: 1) local cooling of the forehead (1°C and 15°C for 60 seconds), 2) cold pressor test (CPT, hand in 1°C water for 2 minutes), and 3) maximal voluntary end-expiratory apnea.

Comparator

Baseline resting measurements, neutral forehead time control (35°C), and comparison of responses between the young and older age groups.

Outcome

Acute changes from baseline in mean arterial blood pressure (MAP), heart rate (HR), and renal vascular resistance index (RVRI)surrogate

Main Result

Absolute Event Rate: 35% vs 16%

p-value: p=0.039

Limitations

Inability to measure renal artery diameter reliably with Doppler ultrasound.
Investigator performing renal blood flow velocity measurements was not blinded during data analysis.
Kidney is under autoregulatory control, so acute blood pressure changes may differentially influence RVRI independent of the autonomic nervous system.
Cause and effect mechanism for the observed age-related differences is yet to be determined.

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.

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