May 15, 1995Circulation
Morning Sympathetic Nerve Activity Is Not Increased in Humans
Why the study?
Is muscle sympathetic nerve activity higher in the morning compared to the afternoon in healthy subjects?
Population
8 healthy subjects (mean age, 42 +/- 4 years)
Comparison
Morning physiological assessments including… vs Afternoon physiological assessments in the same…
Design
Cross-sectional
Authors
Discussion
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Implication
No morning MSNA elevation in healthy subjects; hypothesis-generating for alternative drivers of circadian cardiovascular risk.
Key Points
- The aim is to assess if sympathetic nerve activity is higher in the morning due to circadian effects or posture changes.
- Measured sympathetic nerve activity using microneurographic recordings from healthy subjects in morning and afternoon
- Conducted intraindividual comparisons during supine rest, postural changes, and exercise
- Assessed plasma cortisol and norepinephrine levels after different activities
- No significant difference in muscle sympathetic nerve activity between morning and afternoon (38 bursts/min, P=NS)
- Plasma norepinephrine levels were similar morning (157 pg/mL) and afternoon (173 pg/mL, P=NS)
- Sympathetic response to postural stress and handgrip exercise showed no significant morning increase (P=NS)
Structured PICO
Is muscle sympathetic nerve activity higher in the morning compared to the afternoon in healthy subjects?
P
Population
8 healthy subjects (mean age, 42 +/- 4 years)
I
Intervention
Morning (6:30 to 8:30 AM) physiological assessments including supine rest, lower body negative pressure (LBNP), and sustained handgrip
C
Comparator
Afternoon (2:00 to 4:00 PM) physiological assessments in the same subjects
O
Outcome
Muscle sympathetic nerve activity (bursts per minute)surrogate
Morning sympathetic nerve activity is not increased compared to the afternoon, challenging the hypothesis that enhanced morning sympathetic outflow drives the circadian pattern of sudden cardiac death.
Cite This Study
Middlekauff et al. (1995) studied this question.