Dynamic baroreflex sensitivity in anesthetized horses, maintained at 1.25 to 1.3 minimal alveolar concentration of halothane

Peter W. Hellyer From the Department of Anatomy, Physiological Sciences, and Radiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606.

Search for other papers by Peter W. Hellyer in
Current site
Google Scholar
PubMed
Close
 DVM, MS
,
John R. Dodam From the Department of Anatomy, Physiological Sciences, and Radiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606.

Search for other papers by John R. Dodam in
Current site
Google Scholar
PubMed
Close
 DVM, MS
, and
Gwen S. Light From the Department of Anatomy, Physiological Sciences, and Radiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606.

Search for other papers by Gwen S. Light in
Current site
Google Scholar
PubMed
Close
 DVM, MS

Click on author name to view affiliation information

SUMMARY

Dynamic baroreflex sensitivity for increasing arterial pressure (dbsi) was used to quantitatively assess the effects of anesthesia on the heart rate/arterial pressure relationship during rapid (≤ 2 minutes) pressure changes in the horse. Anesthesia was induced with iv administration of xylazine and ketamine and maintained with halothane at a constant end-tidal concentration of 1.1 to 1.2% (1.25 to 1.3 minimal alveolar concentration). Systolic arterial pressure (sap) was increased a minimum of 30 mm of Hg in response to an iv bolus injection of phenylephrine HCl. Linear regression was used to determine the slope of the r-r interval/sap relationship. During dynamic increases in sap, a significant correlation between r-r interval and sap was observed in 8 of 8 halothane-anesthetized horses. Correlation coefficients between r-r interval and sap were > 0.80 in 5 of 8 horses. Mean (± sd) dbsi was 4.8 ± 3.4 ms/mm of Hg in anesthetized horses. A significant correlation between r-r interval and sap was observed in only 3 of 6 awake horses during dynamic increases in sap. Lack of correlation between r-r interval and sap in 3 of 6 awake horses indicated that rapidly increasing sap with an iv phenylephrine bolus is a poor method to evaluate baroreceptor-mediated heart rate changes in awake horses. Reflex slowing of heart rate in response to a rising arterial pressure appeared to have been overridden by the effects of excitement. Mean (± sd) dbsi (3 horses) was 7.3 ± 3.3 ms/mm of Hg in awake horses.

SUMMARY

Dynamic baroreflex sensitivity for increasing arterial pressure (dbsi) was used to quantitatively assess the effects of anesthesia on the heart rate/arterial pressure relationship during rapid (≤ 2 minutes) pressure changes in the horse. Anesthesia was induced with iv administration of xylazine and ketamine and maintained with halothane at a constant end-tidal concentration of 1.1 to 1.2% (1.25 to 1.3 minimal alveolar concentration). Systolic arterial pressure (sap) was increased a minimum of 30 mm of Hg in response to an iv bolus injection of phenylephrine HCl. Linear regression was used to determine the slope of the r-r interval/sap relationship. During dynamic increases in sap, a significant correlation between r-r interval and sap was observed in 8 of 8 halothane-anesthetized horses. Correlation coefficients between r-r interval and sap were > 0.80 in 5 of 8 horses. Mean (± sd) dbsi was 4.8 ± 3.4 ms/mm of Hg in anesthetized horses. A significant correlation between r-r interval and sap was observed in only 3 of 6 awake horses during dynamic increases in sap. Lack of correlation between r-r interval and sap in 3 of 6 awake horses indicated that rapidly increasing sap with an iv phenylephrine bolus is a poor method to evaluate baroreceptor-mediated heart rate changes in awake horses. Reflex slowing of heart rate in response to a rising arterial pressure appeared to have been overridden by the effects of excitement. Mean (± sd) dbsi (3 horses) was 7.3 ± 3.3 ms/mm of Hg in awake horses.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 52 52 8
PDF Downloads 19 19 2
Advertisement