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LETTER TO THE EDITOR

Commentary on Viewpoint "Human experimentation: No accurate, quantitative data?"

Baroreceptor reflexes can be studied in humans by intravenous injections of vasoactive substances or by applying pressures to the carotid regions. While this gives useful information, it fails adequately to describe the reflex, because, in the "open loop" situation, any response would quickly be altered ("buffered") by other reflexes affected by the stimulus, the response, or both. In animals, both the reflexogenic area and the effector organs can be isolated, thereby avoiding this problem (2).

We described, in anesthetized dogs, a powerful baroreceptor reflex from the coronary arteries (6). The complex experimental preparation necessitated isolating the stimulus site and other reflexogenic areas. All this is clearly impossible in people, but we have shown in humans undergoing cardiac surgery that the reflex does exist, at least qualitatively, but certainly not accurately or quantitatively (3).

Rowell referred to our Counterpoint article on vascular capacitance. Capacitance is the volume of blood (in a region) at constant distending pressure (1). Both arterial inflow and venous pressure must be controlled or passive volume changes would occur (4). Responses in humans, at present therefore, must be inferred from animal data, taking into account known species differences such as the absence of a large contractile spleen in people.

FOOTNOTES

Address for reprint requests and other correspondence: R. Hainsworth, Institute for Cardiovascular Research, Univ. of Leeds, Leeds LS2 9JT, UK (e-mail: medrh{at}leeds.ac.uk)

REFERENCES

1. Hainsworth R. Vascular capacitance: its control and importance. Rev Physiol Biochem Pharmacol 105: 101–173, 1986.[ISI][Medline]
2. Hainsworth R, Karim F. Responses of abdominal vascular capacitance in the anaesthetized dog to changes in carotid sinus pressure. J Physiol 262: 659–677, 1976.[Abstract/Free Full Text]
3. Kincaid K, Ward M, Nair U, Hainsworth R, Drinkhill M. The coronary baroreflex in humans. J Extra Corpor Technol 37: 306–310, 2005.[Medline]
4. Noble BJ, Drinkhill MJ, Myers DS, Hainsworth R. Reflex control of splanchnic blood volume in anaesthetized dogs. J Physiol 513: 263–272, 1998.[Abstract/Free Full Text]
5. Rowell L. Human experimentation: No accurate, quantitative data? J Appl Physiol. In press.
6. Wright C, Drinkhill MJ, Hainsworth R. Reflex effects of independent stimulation of coronary and left ventricular mechanoreceptors in anaesthetized dogs. J Physiol 528: 349–358, 2000.[Abstract/Free Full Text]

This Article Full Text (PDF) Free Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hainsworth, R. Articles by Drinkhill, M. J. Search for Related Content PubMed PubMed Citation Articles by Hainsworth, R. Articles by Drinkhill, M. J.