Human experimentation: no accurate, quantitative data?

This Viewpoint addresses two issues in comparing data from humans and animals in studies of cardiovascular physiology: 1) accuracy of methods and 2) limits in extrapolating data from one species to another. You are invited to submit a brief commentary on this Viewpoint, which will be reviewed by Journal of Applied Physiology editors for possible publication in the Journal. Please limit your comment to 250 words and 5 peer-reviewed published references. IN A RECENT POINT:COUNTERPOINT debate in the Journal of Applied Physiology, Hainsworth and Drinkhill (5) state: “Unfortunately, as it is not possible to obtain accurate quantitative data from humans, we have to rely on results extrapolated from animal studies, mainly on dogs and cats.” The purpose of this viewpoint, which takes Hainsworth’s unqualified comment at face value, is to rebut this notion. Understanding of human physiology indeed rests in part on what we have learned from other species, but a great body of knowledge comes from studies performed on human subjects that entailed measurements as accurate and quantitative as those possible in work with animals. Extrapolation as a means of learning about one species from another has its limits (and dangers)—we would have little luck in understanding the problems for cardiovascular regulation in the giraffe from studies on dogs. No amount of extrapolation would have revealed particular features of human physiology that set this species apart. Examples in cardiovascular physiology include the special hemodynamic problems that accompany changes in posture and exercise in humans. The uniqueness of human skin, an organ of temperature regulation, cannot be appreciated from studies of thermal balance in dogs or cats. Nor can the overall problem of coping with the stress of prolonged exercise in humans be appreciated from studies with these laboratory animals. The initial focus here is on some quantitative methods that have been employed in accomplishing our present understanding of human cardiovascular, metabolic, and thermal responses. These methods were key to resolving the dispute over species differences vs. methods.