European Stars and Stripes (Newspaper) - August 3, 1993, Darmstadt, Hesse                                Built for Earth s fastest mammal the pronghorn Antelope my have evolved by evading North american cheetahs now extinct. Comparisons with the Goat show How systems that maximize oxygen metabolism underlie the pronghorns performance. A potato Are the same Quot said Peter d. Wagner a physiologist at the University of California at san Diego. Quot the cardiac output of the athlete is higher but the lungs Aren t matched to the higher flow rate. Quot in this sense and in several others Champion athletes Are like race horses. As it flies around the track its snout thrust Forward its eyes practically popping from its Skull the race horse too is limited by the unchangeable size of its  yet As relentlessly As elite human athletes May push the envelope of their pulmonary Power they do not show signs like those seen in thoroughbred horses that they have gone Over the Edge. It turns out that nearly All thoroughbreds bleed into their lungs after a race a Clear sign physiologists said of the dangers of Breeding animals for one purpose alone. The bleeding results from the great volumes of blood coursing through the lungs putting unbearable pressure on the lung capillaries and causing them to burst. Some horses Are so fragile they even begin to bleed through the nose during an easy Trot. Quot race horses have been selected so strongly for a single characteristic Speed that the rest of the animal has t had the Opportunity to evolve ways to handle it Quot said Stan l. Lindstedt a physiologist at Northern Arizona University in Flagstaff who has studied pronghorn performance. Quot pronghorns Are much More stable. They la Flat out beat horses but there s no indication of bleeding into the a lungs. They have had millennia to work out their . But horses like Many other mammals with great. Aerobic capacity do have a skill that humans Lack. When horses begin running their spleens contract and spew out Large volumes of red blood cells the cells that carry oxygen. Quot it s a luge effect Quot said Wagner. Quot within 75 seconds the number of circulating red blood cells  the Only Way humans can increase their red blood cell concentration is to inject More cells a trick Nancy  new Yah time.  la Muley Echt Ellov we called blood doping in which a person injects himself with his own or another s blood right before a race. The practice can indeed improve performance but it is illegal in most sporting events. In conducting their comparative experiments the researchers have in veiled a wide spectrum of animals into galloping themselves windless on treadmills and sticking their snouts in masks where expired air can be captured for analysis to see How much oxygen is metabolized each second. They have Analysed blood gases and taken muscle biopsies to count the number of capillaries that feed into , bearing the red blood cells Rich with haemoglobin which engages the needed oxygen. The different species have been More or less amenable file porcupines Are among the most lethargic animals. To study depending on their natural inclination for exercise. Lindstedt said the pronghorns have happily participated in the workouts. Quot they liked it so much that you d open the door to the lab in the morning and they d run right in and jump on the Treadmill Quot he said. V not so the goats or the steers. Quot they la Only run for you if you give them a ton of Grain Quot said Job rfcs. Quot they figure of of if this is what i have to do to get my treats Quot a from comparative experiments physiologists have Learned that the single biggest Factor determining How much oxygen a mammal uses is its size the smaller the animal the More oxygen it takes in for every ounce of its flesh. Quot a Gram of shrew muscle metabolizes 50 times As much oxygen As a Gram of whale muscle Quot said David e. Leith a physiologist at the veterinary medical College at Kansas state University in Manhattan. Why smaller animals must Rev up at such a High metabolic rate is one of the great mysteries of physiology. Quot people used to think it was because smaller animals have More surface area relative to their weight than do bigger animals and so they needed a higher metabolism to keep their body temperature up Quot said Kim e. Longworth a research fellow at the University of California at Davis. Quot but the relationship Between the two measurements has t held up so this is still a big question in the  whatever the reason for the difference in metabolic rates scientists have worked out in general How Small mammals manage to take in and use so much oxygen. A tiny animal like the shrew breathes about 50 times As often As an elephant. Its Windpipe accordingly Are quite Large relative to its body size to accommodate a High influx of air. The shrew s lungs have greater internal surface area relative to its size and thus they can trap More oxygen. To remove the oxygen from the lungs As swiftly As possible the shrew s heart beats 1,200 times a minute compared with the human heart rate of about 75 beats per minute. The pumped blood is exceptionally Rich in haemoglobin the molecular Carrier that shuttles the oxygen through the body. The animal s Muscles Are dense with capillaries to take in oxygen and expel Carbon dioxide waste. Of great importance the muscle cells themselves Are designed to pm the delivered oxygen to immediate use up to 50 percent of their volume is taken up with mitochondria the Little powerhouse structures where oxygen along with sugar is converted into Energy. By contrast the muscle cells of a cow an animal whose most vigorous activity is Likely to be swatting flies with its Tail Are built of Only about 3 percent mitochondria. The concentration of mitochondria in human muscle cells Falls somewhere Between the two figures and it turns out that this density is yet another Factor that can be improved with physical activity. Apart from the general correlation Between Small size and High oxygen metabolism animals of the same dimensions often possess very different aerobic abilities. A Gopher and a Blue Fox for example both weigh about 10 pounds but the Fox is far More efficient at burning oxygen. Examining Why Longworth has found that the key is the Fox s extremely elevated heart rate. She has been Able to show that in the Fox the blood is driven so quickly through the lungs that the pressure of oxygen in the lung spaces is always greater than it is in the bloodstream a difference that ends up easing the diffusion of oxygen from the lung Chambers into the blood vessels. Comparing goats with the aerobic miracles the pronghorns Lindstedt found that the antelopes have no structures the goats Lack but merely have More of everything on the oxygen transport pathway. The pronghorns lungs have five times the surface area and thus five times the Opportunity to pick up oxygen. Their hearts Are three times As big and thus can pump three times the volume of blood through the body. Their Trachea Are much wider their muscle mass is greater their concentrations of haemoglobin in the blood and mitochondria in the muscle cells Are much denser. Lindstedt proposes that the pronghorns evolved the Talent for Speed As a Way to evade now extinct ancestral cheetahs that once lived on the continent and evolved their endurance to escape wolves predators that Hunt Over Long distances. But the pronghorns pay a Price for their extraordinary design. Quot they have virtually no body fat Quot said Lindstedt. Quot in a bad Wyoming Winter Many of them die of  August 3, 1993 the stars and stripes 19