Respiratory Sinus Arrhythmia in Man: Relation to Cardiovascular Pressures

Abstract

The relationship of respiratory sinus arrhythmia (RSA) to the accompanying oscillations of cardiovascular pressures has been studied in five healthy subjects. Tidal volumes (V_T) of 1.0, 1.5, and 2.0 1 at a breathing rate of 6 c-min-¹ were used as reference. With identical V_T, oesophageal pressure was varied by negative inspiratory pressure (NIP) and intermittent positive-pressure ventilation (IPPV). Compared with control, NIP with 1.01 significantly increased RSA, the oscillations of brachial artery pressures (p < _ba), and the net filling pressures of the ventricles. IPPV did not significantly change the variations of P_ba but reduced RSA and the respiratory variations of the right ventricular end-diastolic net pressure. During control breathing and with NIP the acceleration of heart rate during inspiration was associated with rising P_ba and rising net filling pressures of both ventricles. The results indicate that RSA may be elicited by cardiovascular reflexes due to changes in venous filling of the heart rather than by the variations in systemic arterial pressure.

Key Words:

• Baroreceptor reflexes
• heart rate regulation
• intermittent positive-pressure ventilation
• venous return