Abstract
Blood pressure (BP) measurement accuracy depends on consistent changes in Korotkoff sounds (KorS) for manual measurement and oscillometric pulses for automated measurement, yet little is known about the direct effect of respiration on these physiological signals. The aim of this research was to quantitatively assess the modulation effect of respiration on Korotkoff sounds and oscillometric pulses. Systolic and diastolic blood pressures were measured manually from 30 healthy subjects (age 41 ± 12 years). Three static cuff pressure conditions were studied for two respiratory rates. Cuff pressure [with oscillometric pulses (OscP)], ECG, chest motion respiration [respiration signal (Resp), from magnetometer] and Korotkoff sounds (KorS, from digital stethoscope) were recorded twice for 20 s. The physiological data were evenly resampled. Respiratory frequency was calculated from Resp (fR), OscP (fO) and KorS (fK) from peak spectral frequency. There was no statistically significant difference between fR and fO or fK. Respiratory modulation was observed in all subjects. OscP amplitude modulation changed significantly between the two respiratory rates (p < 0.05) and between the three cuff pressures (p < 0.0001), and decreased significantly with decreasing cuff pressure (p < 0.05). The phase shift between Resp and modulation of OscP was statistically significant with respiratory rates (p < 0.05), but not with cuff pressures. It is accepted that BP in individuals is variable and that this relates to respiration; we now show that this respiration modulates oscillometric pulse and Korotkoff sound amplitudes from which BP is measured.
Highlights
It is well accepted that respiration influences beat-bybeat blood pressure (BP) changes [6]
Respiratory modulation of oscillometric pulses (OscP) and Korotkoff sounds (KorS) amplitudes was observed in all 30 subjects
This study has shown significant respiratory modulation of the oscillometric pulse and Korotkoff sound amplitudes from which BP is measured
Summary
It is well accepted that respiration influences beat-bybeat blood pressure (BP) changes [6]. Many different techniques have been used to study the phase relationship between the interbeat interval (or instantaneous heart rate) and the systolic blood pressure (SBP) recorded noninvasively with paced breathing. They include frequency domain cross-spectral analysis [2, 14, 17, 19], wind-kessel model [5], time domain cross-correlation [3, 9], mutual information analysis [20] and a numeric model of the closed loop regulation system [13]
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