Brrrrrr…it’s ff-ree-zzing out there. This cold weather has chilled me to the core and I can’t stt-opp sh-shiver-ring. Luckily for me, my caretaker is bringing me inside and covering me with plenty of blankets. Maybe there will be a fireplace inside, too! It’ll warm me up AND provide a lovely romantic setting for my Valentine’s Day dinner with HugMe Christi. It seems she can tolerate the cold much better than myself and I have no idea why.
This question bugged me, so I asked my colleague, Dr. Ken McKeever for help. As it turns out, he just finished his research on thermoregulation and cardiac capacity in young and old horses. He measured something called the cardiac output (CO), which is a fancy phrase meaning the volume of blood being pumped by the heart every minute. This is essential as blood carries oxygen and nutrients to help cells (especially muscle cells) work during exercise. Cardiac output (CO) is determined by multiplying the heart rate (HR) by the stroke volume (SV) or the amount of blood being pumped through a mathematical equation (CO=HR x SV).
In the study, he discovered that older horses had a higher heart rate (HR), greater sweat loss, and less plasma volume than young horses. Plasma volume is the additional fluid in the blood caused by exercise training, which then increases the stroke volume (SV). Plasma volume also enhances the thermoregulatory response. This is important since old horses like me have a hard time keeping warm. Currently, it is unclear what mechanism causes the older horse to have less plasma volume, but it has been observed in other species as well (not just horses). Maybe one of you young scientists will find out what it is!
In older horses, their heart has to pump faster to get the same amount of blood to the body to have the same cardiac output (CO). This puts a lot of strain on the heart. Young horses don’t need a high heart rate to pump the same volume of blood. For example, think of inflating a bike tire. If you push the handle down from a high distance, then a large volume of air fills the tire quickly. However, if you push down from an inch away, then you only fill the tire with a little spurt of air. You probably have to push 30 little times (very quickly) in order to get the same amount of air as the long distance pump. And your arms will hurt after! The heart works the same way. To learn more about the heart and exercise, play “Exercising HorsePower”. You can even put ME on a treadmill—but make sure to hang a doughnut in front of me first!
The only exercise I will be doing this Valentine’s Day is being with my gal pal, Christi. My heart always races a mile a minute (as if I’m running the Kentucky Derby) and I get a warm feeling in my belly just at the sight of her!
Stay warm and hug your Valentine!