Cardiovascular Physiology

Just finished Cardiovascular Physiology by David Mohrman and Lois Heller. All I have to say is - holly crap why didn't anyone tell me that biology is really interesting!?!?

Ok, really I have a bit more to say than that. I started reading the book because I figured if I'm working on a defibrillator it would be nice to understand something about the heart. The first part that really drew me in was the electrical coordination of the heart. I was quite surprised to see that the heart uses a lot of the same electrical techniques and tricks as circuits I have worked on (or maybe the other way around). For an example: the heart increases the rate at which an electrical signal travels across it by putting a sharp spike at the front of a rectangular pulse. In electronics this is called pre-emphasis and an output driver that uses pre-emphasis is one of the last things I worked on at Teradyne. It is a common trick in high speed digital systems. In addition, the way the heart generates the pre-emphasis is by adding a sharp pulse to the normal signal and generates the pulse by using what is basically an AND gate with one input inverted and delayed from the other. This is a classic pulse generator which I've studied in 6.374 (Analysis and design of digital integrated circuits) for dual edge registers and is also a very cheap way to double the rate of a clock (although the duty cycle of the result isn't so hot).

There was some stuff about how the muscles actually contract which was interesting for a bit but then they lost me (the book is intended as a review for the USMLE so there were a number of things that went over my head). Then they got into the overall function. This was really interesting because I knew that at times more blood flows to one place than another but the book got into how that actually occurs. The part I found amazing is the complexity of the feedback loops involved in the cardiovascular system. Normally if an engineer sees more than a few feedback loops interacting he/she gets quite concerned, but the body has tons of them.

Then it got into what happens in various cases, such as exercise and when bad stuff happens. I knew that cardio workouts are good for the heart (hence the name...) but I didn't realize that weight lifting is also good for the heart but in a different way. In cardio the main issue the heart faces is pumping huge volumes of blood through the body. So during exercise the heart gets bigger and better at that activity. But when weight lifting, it takes a huge amount of pressure to get blood into the contracted muscle, so the heart has to get stronger and better at creating large pressures. I also didn't realize that stuff other than your heart helps to pump blood. Such as when muscles contract and relax they pump blood (mostly in the veins) and when you breathe the changes in pressure pump blood. This is part of the reason why standing still is uncomfortable - the blood in your veins in your leg builds up and you need to use your leg muscles to help pump the blood back up (the veins have one way valves which keep the blood going in the right direction - if you don't know why I think one way valves are super cool - ask me about 6.270 sometime).

Anyway I should stop rambling. If you wanted to know more than that you could just read the book (or those who didn't avoid biology probably already know). Also I should note that I know almost nothing about biology so anything I said in this post could be completely wrong.