Heart rate-arterial blood pressure relationship in conscious rat before vs. after spinal cord transection.
This experiment quantified the initial disruption and subsequent adaptation of the blood pressure (BP)-heart rate (HR) relationship after spinal cord transection (SCT). BP and HR were recorded for 4 h via an implanted catheter in neurally intact, unanesthetized rats. The animals were then anesthetized, and their spinal cords were severed at T(1)-T(2) (n = 5) or T(4)-T(5) (n = 6) or sham lesioned (n = 4). BP was recorded for 4 h daily over the ensuing 6 days. The neurally intact rat showed a positive cross correlation, with HR leading BP at the peak by 1.8 +/- 0.8 (SD) s. The cross correlation in unanesthetized rats (n = 2) under neuromuscular blockade was also positive, with HR leading. After SCT at T(1)-T(2), the cross correlation became negative, with BP leading HR, and did not change during the next 6 days. The cross correlation also became negative 1-3 days after SCT at T(4)-T(5), but in four rats by day 6 and thereafter the cross correlation progressively reverted to a positive value. We propose that the positive cross correlation with HR leading BP in the intact rat results from an open-loop control that depends on intact supraspinal input to sympathetic preganglionic neurons in the spinal cord. After descending sympathetic pathways were severed at T(1)-T(2), the intact vagal pathway to the sinoatrial node dominated BP regulation via the baroreflex. We suggest that reestablishment of the positive correlation after SCT at T(4)-T(5) was attributable to the surviving sympathetic outflow to the heart and upper vasculature reasserting some effective function, perhaps in association with decreased spinal sympathetic hyperreflexia. The HR-BP cross correlation may index progression of sympathetic dysfunction in pathological processes.
Baldridge
Bobby R
BR
Department of Biology, Asbury College, Wilmore, Kentucky 40390-1198, USA.
Burgess
Don E
DE
Zimmerman
Ethan E
EE
Carroll
Jonathan J
JJ
Sprinkle
Aletia G
AG
Speakman
Richard O
RO
Li
Sheng-Gang
SG
Brown
David R
DR
Taylor
Robert F
RF
Dworkin
Susan
S
Randall
David C
DC
D000818:Animals; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D003243:Consciousness; D006339:Heart Rate / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013119:Spinal Cord Injuries / Q000503:physiopathology*; D013564:Sympathetic Nervous System / Q000502:physiology