Why the study?
Does altered intrathoracic pressure via negative inspiratory pressure or intermittent positive pressure ventilation affect heart rate and right ventricular output in healthy subjects?
Does altered intrathoracic pressure via negative inspiratory pressure or intermittent positive pressure ventilation affect heart rate and right ventricular output in healthy subjects?
Changes in intrathoracic pressure significantly alter right ventricular stroke volume and heart rate, suggesting the presence of heart-rate-regulating reflexes originating from the heart.
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Should not yet alter ventilation strategies in patients; leaves open mechanisms of intrathoracic pressure effects on RV output and sinus arrhythmia.
The respiratory effects on heart rate (HR), right ventricular stroke volume (SVRV), and the pulmonary arterial flow (PAF) have been studied beat-by-beat in 7 conscious, healthy subjects. Tidal volumes (VT) of 1.0 and 2.0 liters at a breathing rate of 6 cXmin-1 were used as controls. With identical VT and respiratory rate intrathoracic pressure was affected by (A) negative inspiratory pressure (NIP) of 5 cm of water and (B) with intermittent positive pressure ventilation (IPPV). In the control experiments all subjects exhibited an inspiratory increase in HR (respiratory sinus arrhythmia) as well as in SVRV. With VT of 1.0 liter, NIP augmented the inspiratory increase in SVRV and the respiratory oscillations of PAF. IPPV decreased SVRV and HR during inspiration. It is concluded that NIP and IPPV affect the SVRV and the right heart blood flow. The similar effects on HR and SVRV suggest a relationship which might be explained by heart-rate-regulating reflexes from the heart.
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Freyschuss et al. (1976) studied this question.
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