August 1, 1998
View Full PaperAugmented Cardiopulmonary and Integrative Sympathetic Baroreflexes but Attenuated Peripheral Vasoconstriction With Age
Key Result
Older men exhibited approximately 150% greater sympathetic nerve activity responses to hypovolemia (P<0.01) but 50% smaller forearm vascular resistance responses (P<0.05) compared to young men.
Study Design
Type
Cross-Sectional (n=23)
Structured PICO
Does aging affect cardiopulmonary and integrative sympathetic baroreflex control during hypovolemia in healthy men?
P
Population
23 healthy adult men (11 young, 12 older) evaluated for sympathetic nerve activity and vascular resistance during progressive hypovolemia.
E
Exposure
Progressive hypovolemia produced by graded (-5 to -40 mm Hg) lower body negative pressure (LBNP).
C
Comparator
Young versus older subjects.
O
Outcome
Skeletal muscle sympathetic nerve activity (MSNA) and forearm vascular resistance (FVR) responses to hypovolemia.surrogate
Aging augments central sympathetic outflow during hypovolemia, but reflex-mediated increases in limb vascular resistance are smaller due to attenuated vasoconstrictor responsiveness.
Main Result
Effect estimate: ~150% greater
p-value: p=<0.01
Abstract
Based on observations of smaller increases in limb vascular resistance during acute incremental hypovolemia in older adults, cardiopulmonary and integrative (combined cardiopulmonary and arterial) baroreflex control of sympatho-circulatory function is thought to be impaired with aging in humans. We tested this hypothesis directly by making intraneural measurements of skeletal muscle sympathetic nerve activity (MSNA; peroneal microneurography) in groups of young (23+/-1 years; n=11) and older (64+/-1 years; n=12) healthy adult men during progressive hypovolemia produced by graded (-5 to -40 mm Hg) lower body negative pressure (LBNP). Baseline levels of MSNA and arterial blood pressure were higher and heart rate was lower in the older subjects (P<0.05). Lower levels of LBNP (-5 to -20 mm Hg) did not affect arterial blood pressure or heart rate in either group; systolic and pulse pressures declined during higher levels of LBNP (-30 and -40 mm Hg) but only in the young subjects (P<0.05). Graded LBNP evoked progressive, linear reductions in peripheral venous pressure (PVP) and increases in MSNA, plasma norepinephrine concentration (PNE), and forearm vascular resistance (FVR) in both groups (all P<0.05). DeltaMSNA/ deltaPVP was approximately 150% greater in the older versus young men during both lower and higher levels of hypovolemia (P<0.01); however, deltaFVR/deltaPVP was approximately 50% smaller in the older men (P<0.05). There was no difference in the MSNA-PNE relation with age, but deltaFVR/deltaMSNA was approximately 65% to 70% smaller in the older subjects (P<0.05). Our findings indicate that cardiopulmonary and integrative baroreflex control of central sympathetic outflow during hypovolemia is augmented, not impaired, with age in healthy humans. However, the reflex-mediated increases in limb vascular resistance during hypovolemia are smaller in older adults because of attenuated vasoconstrictor responsiveness to sympathetic stimulation.