Veterinarians - Dogs and Respiratory Alkalosis

A question for all you veterinarians out there.

I was watching a dog panting this afternoon after playing with her in my friend’s yard and I was wondering about the process of panting.

In humans, breathing at that rate for a prolonged period of time would lead to hyperventilation, respiratory alkalosis and lightheadedness/passing out.

So I ask you, what is the mechanism by which dogs avoid this? My fellow MDs and I surmised that it may be a function of decreased tidal volume, but the chocolate lab we were observing was flaring nostrils and having intracostal retractions to some extent, all signs of respiratory distress in a human.

If he’s panting that hard, he probably is in mild respiratory distress. Of course, in this kind of weather, a dog who gets hot enough to pant like that is probably on the verge of heat stroke, so respiratory alkalosis is really the least of his problems.

And in short, you’re essentially right. When dogs are just lying around panting because it’s a bit warm, you’ll notice that the breaths are very short and shallow, not like the big gulps of air humans take in when we pant. The shallow breathing is a compensatory mechanism. Since dogs don’t sweat (not an appreciable amount, anyway), they have to rely on other methods of evaporative cooling. A wet nose helps carry off some heat, but the bulk of a dog’s cooling comes from panting.

Man, I love this place because I’m always learning something new.

You’re right about the importance of tidal volume. Panting involves moving air in the upper respiratory pathway, where oxygen exchange is minimal. This reduces the rate at which a dog will go into respiratory alkalosis (the increase of bicarbonates in the bloodstream). But the dog will have to take regular breaths to get air into the aveolar sacs so that oxygen exchange can occur. So, he “pantspantspantspantspants” stops and breathes regularly for a bit, then “pantspantspantspantspants.” And so on. Those big, slobbery dog tongues (which are highly vascular) provide a nice large surface for heat transfer via evaporation.

This I already knew from physiology classes. What I didn’t know was that the act of panting does not require a lot of muscular work. Muscular work generates heat, and could be counter-productive if the idea is to blow off heat. But panting is done at a rate that is the natural oscillation frequency of the chest cavity, and this means very little muscular work to move air during the pant breaths. This is pretty cool, so thanks for asking the question!

(And like **CCL ** suggests, sometimes behavioral/physiological actions fail to counteract high body heat. Denatured proteins trump respiratory alkalosis. :eek: )