September 1, 1999Journal of Cardiovascular Electrophysiology
Differential Effects of Parasympathetic Blockade and Parasympathetic Withdrawal on Heart Rate Variability
Why the study?
Does partial parasympathetic blockade with low-dose atropine result in different heart rate variability changes compared to parasympathetic withdrawal with nitroprusside in normal volunteers?
Population
27 normal volunteers
Comparison
Low-dose atropine to achieve partial… vs Graded doses of nitroprusside to achieve…
Design
Other
Follow-up
5-minute ECG recordings
Authors
Discussion
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Implication
Low-dose atropine reduces HRV more than nitroprusside; leaves open whether HRV indexes vagal tone versus modulation in patients.
Key Points
- To evaluate whether parasympathetic withdrawal via baroreflex unloading and partial parasympathetic blockade result in similar reductions in heart rate variability.
- Twenty-seven normal volunteers received complete beta-adrenergic blockade, followed by graded nitroprusside infusions to induce baroreflex-mediated parasympathetic withdrawal and low-dose atropine (0.01 mg/kg) to induce partial parasympathetic blockade.
- Five-minute ECG recordings were analyzed and compared in 19 participants who had paired recordings with mean RR intervals differing by < 50 msec (low-dose atropine: 869 +/- 96 msec vs nitroprusside: 875 +/- 99 msec).
- Root mean square of successive RR interval differences was significantly lower following low-dose atropine than during nitroprusside-induced withdrawal (16 +/- 11 msec vs 22 +/- 15 msec; P < 0.02).
- Low-frequency power (0.443 +/- 0.474 bpm² vs 0.917 +/- 0.602 bpm²; P < 0.005) and high-frequency power (0.198 +/- 0.207 bpm² vs 0.501 +/- 0.521 bpm²; P < 0.02) were markedly lower during partial parasympathetic blockade than parasympathetic withdrawal.
Structured PICO
Does partial parasympathetic blockade with low-dose atropine result in different heart rate variability changes compared to parasympathetic withdrawal with nitroprusside in normal volunteers?
P
Population
27 normal volunteers
I
Intervention
Low-dose atropine (0.01 mg/kg) to achieve partial parasympathetic blockade, following complete beta-adrenergic blockade
C
Comparator
Graded doses of nitroprusside to achieve baroreflex-mediated parasympathetic withdrawal, following complete beta-adrenergic blockade
O
Outcome
Heart rate variability (HRV) parameters including root mean square of successive RR interval differences, low-frequency (LF) power, and high-frequency (HF) powersurrogate
Low heart rate variability reflects the character of parasympathetic modulation rather than parasympathetic tone per se, and can be explained by either diminished vagal discharge or resistance of cardiac muscarinic receptors to vagal discharge.
Cite This Study
Challapalli et al. (1999) studied this question.