Cardiorespiratory interactions during fixed pace resistive
breathing.
Blaber, A. P., and R. L. Hughson.
Department of Kinesiology, University of Waterloo, Waterloo,
Ontario N2L 3G1, Canada
APStracts 3:0002A, 1996.
We tested the hypothesis that the arterial baroreflex was important in
the origin of respiratory sinus arrhythmia (RSA) under conditions of
normal and resistive breathing. That is, mechanical effects of
breathing (indicated by instantaneous lung volume, ILV) would
directly influence left ventricular stroke volume (LVSV), which would
in turn influence systolic arterial blood pressure (SAP), causing
variation in RR-interval through the baroreflex. Eight healthy young
subjects (4 men, 4 women) were monitored in the supine position while
breathing with a fixed frequency (0.2 Hz) and tidal volume for 15 min
through each of three resistances (R0, R1, and R2) producing
inspiratory (-) and expiratory (+) pressures of +/-1.6 cm H2O, +/-5.4
cm H2O, and +/-16.6 cm H2O respectively. LVSV was estimated by stroke
distance (SDist by Doppler ultrasound). There were no differences
across R0, R1, and R2 for the mean values of RR-interval, SDist, or
SAP. Cross-spectral analysis showed that at R0, each of RR-interval,
SDist, and SAP lagged ILV by about 80 degrees . At R1 and R2 phase
was reduced from ILV to SDist and RR-interval, and transfer magnitude
for SDist (R2 only), SAP, and RR-interval increased. The transfer
magnitude from SDist to SAP significantly increased as a function of
resistance breathing, while that from SAP to RR-interval
significantly decreased. There were no changes in phase
relationships, from SDist to SAP to RR-interval. Thus, the magnitude
of RSA (ILV to RR-interval) was increased, but the transfer through
the arterial baroreflex (SAP to RR-interval) was reduced. Although
factors other than the arterial baroreflex are probably involved in
the genesis of RSA, the constant phase relationship across the levels
of breathing resistance between SDist, SAP, and RR-interval suggests
an important functional link caused by mechanical effects of
breathing.
Received 2 June 1995; accepted in final form 14 December 1995.
APS Manuscript Number A580-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96