When you say your blood pressure is 120/80 that means

说血压为 120/80 的意思是
120 mmHg above Atmospheric;

比大气压高一百二十毫米汞柱
80 mmHg above Atmospheric.

比大气压高八十毫米汞柱
Otherwise our blood vessels would collapse

否则我们的血管会塌陷的
because we're surrounded by air that's 760 mmHg,

因为周围的空气压力是七百六十毫米汞柱
that to inflate those vessels you have to be at pressures above that.

为了使血管膨胀内压应高于大气压
Since all we care about are pressure differences

既然我们要重点关注压差
then the pressure that you measure

我们就要测量压强
when you measure blood pressure is pressure above Atmospheric.

测量血压就是测量它比大气压高多少
Does that make sense?

听懂了没
ΔP is in mmHg,

ΔP的单位是毫米汞柱
Q is in L/min,

Q的单位是升每分钟