A comparative study of central blood pressures in five amphibians.

A number of articles written in recent years about the pattern of blood flow through the amphibian heart have described results which differ quite widely (Simons, 1957, 1959; de Graaf, 1957; Johansen, 1963; Shelton & Jones, 1965a, b). One of the main difficulties in interpretation has been that all the work cited above has been done on different species of anuran and urodele. It is clearly possible to ascribe many of the major differences to variation between species in anatomical or physiological adaptation to different environments (Foxon, 1964). However, the doubt must remain that some of the differences may be due to experimental methods, involving as they do variation in anaesthesia, operative technique and recording method. The problem of the amphibian circulation has been developed along two distinct lines. In one, recognizable materials (coloured dyes or particles, radio-opaque materials, oxygen) have been introduced into the blood stream and their route through the heart into the arterial arches followed (Foxon, 1947; Simons, 1959; ^ Graaf 1957; Johansen, 1963). In the other, pressures have been measured in various parts of the system and attempts made to assess blood flow from the gradients which are found (Simons, 1957; de Graaf, 1957; Johansen, 1963; Shelton & Jones, 19656). Although the two methods are complementary and full analysis is impossible with either taken alone, it is to the second type of determination that the present paper relates. In Amphiuma tridactylum Johansen (1963) claimed that the peak systolic pressure produced by ventricular contraction was very much greater when measured in the ventricle than a short distance downstream in the conus. Contraction of the conus produced a second pressure peak which was roughly the same size as the first, ventricular peak. Johansen thus assigned to the conus a major function of smoothing blood flow from the ventricle and extending the period of flow from the heart so that it was no longer intermittent. In Rana pipiens, on the other hand, Shelton & Jones (19656) were unable to confirm the very considerable smoothing suggested by Johansen and found that pressures in ventricle and conus followed one another closely until the time of ventricular relaxation. Divergence of the two pressures then occurred because of continued conus contraction but outflow of blood from the conus was negligible and came to an end when the conus relaxed. Outflow from the heart was intermittent, with the conus playing a very small part in the total pumping activity when compared with the ventricle. The contributions on Amphiuma and Rana are the only ones in which serial pressure