Confused about the bottom number for blood pressures


Hi, I'm in the CNA class and we are learning how to take manual blood pressues. I understand the top number but I'm totally confused about the bottom number. I was told that it is when you stop hearing any noise, but I continue to hear noise even when it's very low. So i'm thinking the bottom number is when the noise stops being as loud, is that correct? Thanks for any help.


28 Posts

Specializes in Home Health, Long Term, Psychiatric.

The systolic is the first sound that you hear and the diastolic is the exact point when you stop hearing the sound. At the systolic pressure you will hear something tapping and as it goes on it will start sounding lighter and lighter and will almost have a blowing sound to it. Once you don't hear anything at all that is the diastolic pressure. So if you are still hearing something then you haven't reached diastolic yet.

I hope this helps! :)

locolorenzo22, BSN, RN

1 Article; 2,396 Posts

Specializes in Ortho, Neuro, Detox, Tele. will get softer and softer until you hear nothing. invest in a good stethoscope. I have heard numbers below 40...but usually I get someone to recheck it if that doesn't seem in line with the top 120/80 or 120/60....120/30 is a big jump for example. when do you stop hearing a sound usually?


125 Posts

Specializes in Pediatric Critical Care.

Maybe you need a better stethascope.. Littman works great


18 Posts

I have a Littman Cardiology III.. I was thinking the stethoscope was too good and that is why i continue to hear the beat so low, lol.

Specializes in Emergency/Cath Lab. Has 6 years experience.

are you sure you arent hearing artifact noise? is the head of the steho on the bp cuff, are your tubes grinding together?

morte, LPN, LVN

7,015 Posts

i was taught that in some elderly the bottom number can get very low d/t the reduced elasticity of the arteries...


18 Posts

It does not sound like artifact noise. I hear the loud beats and then it just sounds like the beats get quieter and quieter but never completely disappear. I have tried it on my boyfriend who is 30 so it's definitely not from old age, lol. Maybe I will get some help from my instructor.


198 Posts

Has 11 years experience.

Actually, the point at which the diastolic is measured is a little controversial. Most accept that the point in which the sounds disappear represent the diastolic, however, the texbooks that medical students learn physical exams from state that one should make a note of the systolic, then the point where the sounds muffle and disappear. The point where the sounds muffle and disappear are usually only a few mmHg apart (e.g., 120/80/75). The American Heart Association and most medical textbooks just recommend using the disappearing point as the diastolic, therefore disregarding the muffling point.

In some cases, such as hyperthyroidism and aortic regurgitation, these Korotkoff sounds don't disappear until zero pressure. In these cases you should use the muffling point since a diastolic of zero is not possible. There may be other conditions where these sounds are heard to zero, but if you're hearing them in normal healthy individuals, then I'd be wondering about my technique. If someone is sitting and resting for a period of greater than 5 minutes (more is better), then you shouldn't have this problem.