Summary
Background: Evaluating the accurate responses of the cardiovascular system to external stimuli
is important for a deeper understanding of cardiovascular homeostasis. However, the
responses should be distorted by the conventional time domain analysis when a frequency
of the effect of external stimuli matches that of intrinsic fluctuations.
Objectives: The purpose of this study is to propose a mixed signal processing of time domain
and respiratory phase domain to extract the response waveforms of heartbeat and blood
pressure (BP) to external stimuli and to clarify the physiological mechanisms of swallowing
effects on the cardiovascular system.
Methods: Measurements were conducted on 12 healthy humans in the sitting and standing positions,
with each subject requested to swallow every 30 s between expiration and inspiration.
Waveforms of respiratory sinus arrhythmia (RSA) and respiratory-related BP variations
were extracted as functions of the respiratory phase. Then, respiratory effects were
subtracted from response waveforms with reference to the respiratory phase in the
time domain.
Results: As a result, swallowing induced tachycardia, which peaked within 3 s and recovered
within 8 s. Tachycardia was greater in the sitting position than during standing.
Furthermore, systolic BP and pulse pressure immediately decreased and diastolic BP
increased coincident with the occurrence of tachycardia. Subsequently, systolic BP
and pulse pressure recovered faster than the R-R interval.
Conclusions: We conclude that swallowing-induced tachycardia arises largely from the decrease
of vagal activity and the baroreflex would yield fast oscillatory responses in recovery.
Keywords
Heart rate variability - Hilbert transform - respiratory phase - blood pressure variability
- swallowing
