In these experiments, I used a home blood pressure monitor (upper arm cuff), to measure my blood pressure in the morning, on an empty stomach.
To prepare for each set of readings, I got into position, and waited quietly for 5 minutes before taking the first reading.
I then took a minimum of 3 readings for each position, with 3 minutes between each reading. The results I show you below are the average of the readings for each position. I have also included heart rate for the three positions.
Blood pressure when lying down:
Blood Pressure Average: 115/70
Heart Rate: 66
Blood pressure when sitting down:
Blood Pressure Average: 120/79
Heart Rate: 72
Blood pressure when standing :
Blood Pressure Average: 121/78
Heart Rate: 75
As you can see, my blood pressure (and heart rate) was lowest when lying down. This is as expected, since the body is not having to work too hard to pump blood around the body, which is all pretty much in the same horizontal plane.
When the body then sits up, there is an increase in blood pressure and heart rate. Again, this is as I would have expected, since the body is now having to work a little harder to get the blood around the body.
Finally, when standing, there was no noticeable difference in my blood pressure from the sitting position. I had expected to possibly see a slight drop in blood pressure, though no change is not a big surprise. When you stand up, gravity causes blood to naturally wants to pool in your leg veins causing a drop in blood pressure. However, the autonomic nervous system tries to correct this by narrowing your blood vessels (which increases blood pressure) and increasing your heart rate. We did see the increased heart rate. The reason for no apparent drop in blood pressure is probably because the first reading was taken 5 minutes after standing. This would have given the body time to adjust.