REBUTTAL FROM DR. ROTHE

Abstract

POINT-COUNTERPOINTREBUTTAL FROM DR. ROTHEPublished Online:01 Oct 2006https://doi.org/10.1152/japplphysiol.00561b.2006MoreSectionsPDF (43 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Hainsworth and Drinkhill (2) concluded that active venoconstriction is not important in raising end-diastolic volume (EDV) or stroke volume during exercise and orthostasis. They do admit that active venoconstriction exists, but in their last paragraph, they conclude that it only provides a small venous return enhancement. I fully agree with the following. 1) The skeletal muscle pump during exercise can provide the major part of the maintenance or increase in EDV (7). 2) Active venoconstriction occurs primarily in the abdominal splanchnic bed. 3) Skin and skeletal muscle venous responses are minimal. 4) The spleens of dogs are much larger than that of humans. 4) In response to changes in flow and venous distending pressure, passive changes in venous volume are indeed important.However, Hainsworth and Drinkhill did not support the assumption that constant pressure perfusion eliminates concurrent active venoconstriction in assessing the magnitude of the passive venous responses. Changing the carotid sinus pressure between 60 and 195 mmHg, Hainsworth and Drinkhill (2) claim a 3 ml/kg change in effective circulatory volume (the total stressed volume) of the liver and intestinal bed. In conjunction with a total body compliance of 2.5 ml·kg−1·mmHg−1, this would change the Pmcf by 1.2 mmHg. Assuming that the Pra at equilibrium would be increased by the same amount, they then claim, using “Guyton's curves,” that this would increase the cardiac output by only 20%. Herndon and Sagawa (Ref. 3, Fig. 7) suggest that the sensitivity of cardiac output to changes in Pra is 52 ml·min−1·kg−1 change in flow per millimeter mercury change in Pra. Thus a change in cardiac output from a 1.2 mmHg change in Pra would be a much larger increase of 60 ml·min−1·kg−1. Other studies have reported much larger active venous changes than the 3 ml/kg. For example, for dogs, carotid baroreceptor changes, a 7.0 ml/kg change (1); maximum sympathetic simulation, with spleen intact 7.2 ml/kg, without spleen 4.3 ml/kg (4); carotid sinus pressure changes, with spleen 8.4 ml/kg, without spleen 7.2 ml/kg (8).They also claim (Ref. 2; Fig. 2) that the intestinal bed provides a negligible active venoconstriction response based on the data from the study by Noble et al. (4). We (6) evaluated active and passive venoconstriction in segments of dog jejunum. Norepinephrine caused an active change in intestinal blood volume of 24% and a passive change of 62%. Active venoconstriction is important.REFERENCES1 Brunner MJ, Shoukas AA, and MacAnespie CL. The effect of the carotid sinus baroreceptor reflex on blood flow and volume redistribution in the total systemic vascular bed of the dog. Circ Res 48: 274–285, 1981.Crossref | PubMed | ISI | Google Scholar2 Hainsworth R and Drinkhill MJ. Counterpoint: Active venoconstriction is not an important adjunct to maintaining or raising end-diastolic volume and stroke volume during exercise and orthostasis. J Appl Physiol. In Press.Google Scholar3 Herndon CW and Sagawa K. Combined effects of aortic and right atrial pressure on aortic flow. Am J Physiol 217: 65–72, 1969.Link | ISI | Google Scholar4 Karim F and Hainsworth R. Responses of abdominal vascular capacitance to stimulation of splanchnic nerves. Am J Physiol 231: 434–440, 1976.Link | ISI | Google Scholar5 Noble BJ, Drinkhill MJ, Myers DS, and Hainsworth R. Reflex control of splanchnic blood volume in anesthetized dogs. J Physiol 513: 363–272, 1998.Google Scholar6 Rothe CF, Johns BL, and Bennett TD. Vascular capacitance of dog intestine using mean transit time of indicator. Am J Physiol Heart Circ Physiol 234: H7–H13, 1978.Link | ISI | Google Scholar7 Sheriff D. Point: The muscle pump raises muscle blood flow during locomotion. J Appl Physiol 99: 371–372, 2005.Link | ISI | Google Scholar8 Shoukas AA, MacAnespie CL, Brunner L, and Watermeier MJ. The importance of the spleen in blood volume shifts of the systemic vascular bed caused by the carotid sinus baroreceptor reflex in the dog. Circ Res 49: 759–766, 1981.Crossref | PubMed | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 101Issue 4October 2006Pages 1265-1266 Copyright & PermissionsCopyright © 2006 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00561b.2006History Published online 1 October 2006 Published in print 1 October 2006 Metrics