An examination of respiratory sinus arrhythmia is presented. Sinusoidal breathing was varied over a wide frequency range and the amplitude and phase of the accompanying fluctuations of heart rate were observed. These data show that heart rate is not necessarily in phase with respiration as previously described, but rather that the phase angle between heart rate fluctuations and respiration varies with frequency of breathing in a characteristic fashion. The usual descriptions of respiratory sinus arrhythmia are judged to be inadequate since they are shown to represent only a single point on the entire frequency response curve correlating breathing rate with sinus arrhythmia. heart rate fluctuation and respiratory frequency in man; frequency amplitude analysis of respiration-heart rate relationship; heart rate versus breathing: amplitude and phase angle; breathing-induced heart rate changes: phase angle; respiration-induced heart rate changes: phase angle respiratory sinus arrhythmia; respiration versus heart rate: amplitude and phase angle; sinus arrythmia and respiration: amplitude and phase angle Submitted on July 22, 1963

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Sinusoidal oscillatory flow of blood and of aqueous glycerol solutions was produced in rigid cylindrical tubes. For aqueous glycerol, the amplitude of the measured pressure gradient wave form conformed closely to that predicted by Womersley's theory of oscillatory flow, up to Reynolds numbers approaching 2000. Blood differed significantly from aqueous glycerol solutions of comparable viscosity, especially at low frequencies and high hematocrits. As frequency increased, the hydraulic impedance of blood decreased to a minimum at a frequency of about 1-2 CPS, increasing monotonically at higher frequencies. The dynamic apparent viscosity of blood, calculated from Womersley's theory, decreased with increasing flow amplitude. The reactive component of the hydraulic impedance increased with frequency as predicted by theory; the resistive component decreased with increasing frequency, differing from the resistance of a Newtonian fluid which increased with frequency.

It has been shown that respiratory sinus arrhythmia correlates fundamentally with lung volume changes. The correlation with thoracic circumference changes is incidental and quantitatively unreliable. Extensive measurements on one subject and limited measurements on four other subjects demonstrate the existence of a systematic relationship between heart rate and lung volume under reasonably static conditions, a high heart rate corresponding to the expiratory position and a low heart rate to the inspiratory position. This relation has been described successfully with an exponential equation. heart rate and lung volume: exponential relation; heart rate: lung volume dependence; lung volume and thoracic circumference: calibration; respiration and heart rate: static lung volume effect; respiratory sinus arrhythmia: held lung volume and heart rate; sinus arrhythmia: static lung volume dependence; thoracic circumference and lung volume: calibration Submitted on July 22, 1964

No abstract