Activity 1.1 — the first four clues every medical detective learns to read.
9 days · Four stations · You will measure a real human being (your partner).
Tap any glowing word for the meaning in English and Spanish.
An emergency room is a busy place. Doctors have to make life-and-death choices fast. Like a detective looking for clues, a medical professional uses every piece of evidence to help a patient quickly.
Think about it: a nurse has only two minutes with a new patient. What could they measure in two minutes that would tell them the most about what is wrong?
Vital means necessary for life. Your vital organs are the ones you cannot live without.
A sign is something a person can measure or see from the outside — not just what the patient says they feel.
Vital signs are measurements that show how well a body is working. They are the first evidence in any medical mystery.
Careful: a sign is measured by someone else (a temperature of 101°F). A symptom is what the patient feels and tells you ("my head hurts"). Detectives collect both.
PLTW · While you watch, listen for the FOUR vital signs. Write them on Worksheet 1.
60–100
beats per minute
How fast the heart is beating.
97.8–99.1
degrees Fahrenheit
How warm the body is inside.
12–18
breaths per minute
How often the person breathes.
90/60–120/80
mm Hg
How hard blood pushes on the arteries.
These are average ranges for a healthy person at rest. They are a guide for our reflections — never a diagnosis.
When the heart contracts, it pushes blood into the arteries. The arteries expand and then contract again. That beat is your pulse, and you can feel it wherever a large artery runs close to the skin — like the wrist.
PLTW · This video has no sound — that is not a problem with the speakers. Watch the fingers.
You count for 15 seconds, not a whole minute. To turn that into beats per minute you multiply by 4.
Find the pulse first. Press start only when you can feel it.
Work it out in your head or on Worksheet 2, then check yourself.
Write your answers on Worksheet 2 — Station A.
Every time you breathe in, your lungs pull in oxygen. Counting breaths for one minute gives the respiratory rate.
One rise of the chest = one breath. Count the rises, not the rises and falls.
Unlike the pulse, you do not multiply here. Count for a whole minute, and that number is the respiratory rate.
Your partner should be sitting still and breathing normally.
Inside the normal range (12–18).
Remember: count the rises only, and do not tell your partner you are counting — people change how they breathe when they know. Record it on Worksheet 3.
People change how they breathe when they know you are counting. Many nurses count breaths right after taking the pulse, without saying so.
Write your answers on Worksheet 3 — Station C.
Tomorrow you will measure a temperature. Today you find out what that number actually is — because a detective who does not know what a clue means will read it wrong.
Put a hand on your own arm. You are warm right now. You were warm all night, and you will be warm tomorrow. Your body is doing that on purpose, and it costs energy to keep it up.
Every cell in your body burns food for energy, and heat is what is left over. You are making heat right now, sitting perfectly still.
A part of your brain called the hypothalamus watches your inside temperature and gives orders: shiver to make more heat, sweat to lose it.
The job is to hold the inside of the body steady no matter how hot or cold the room is. Steady on the inside is what keeps the chemistry of life working.
Two words we will use all week. Your core is the inside of your body — brain, heart, lungs, gut. Your skin is the outside, and skin is allowed to get cold. Remember that difference; tomorrow it decides everything.
In 1868 a German doctor, Carl Wunderlich, took more than a million temperatures and reported the average: 98.6 °F. One number, taken from a whole crowd of people. It was never a promise about any one person.
97.8–99.1
degrees Fahrenheit
A healthy person at rest sits somewhere in this range. Newer studies put the true average a little below 98.6.
Think about it: the average height of a 6th grader is about 4 ft 11 in. Does that mean something is wrong with everyone who is 5 ft 2 in? An average describes a crowd. A range describes a person.
Nobody holds one exact number. It drifts down overnight and climbs through the afternoon — a swing of about one whole degree.
So when you measure is part of the evidence. We measure during our own period — write the time down next to the number.
Lowest before dawn, highest in the late afternoon — about a degree either way.
Working muscles make heat. Run to class and you arrive warmer than you left.
A cold drink cools the mouth for several minutes. The body did not change — the mouth did.
Sun, wind, air conditioning and a heavy jacket all change your skin fast. Your core barely moves.
Age and body size shift where a person's own "normal" sits. Normal is personal.
The one on this list a doctor cares about. The other five are noise you can plan around.
Five of these six are factors we can control by choosing how we measure. Controlling them is the entire job of a good procedure.
| Where you measure | What it really reads | Next to a reading under the tongue |
|---|---|---|
| Rectal | the core | about 1 °F higher |
| Ear (eardrum) | close to the core | about 0.5 °F higher |
| Mouth, under the tongue | close to the core | the usual comparison |
| Forehead, no-touch | the skin over an artery | about 0.5–1 °F lower |
| Armpit | the skin | about 1 °F lower |
Not one of these thermometers is broken. They disagree because they are measuring different places. Tomorrow we use the forehead one — which means we are reading skin, and skin is the part of you the room can get to.
While you fight an infection, the brain raises its own target. Many germs grow poorly when it is hot, and your defences work faster.
100.4
°F and above
The number most doctors call a fever.
Once the target moves up, your ordinary temperature suddenly feels too cold — so you shiver under a blanket while the thermometer says you are hot.
A fever is a sign, not the illness. It tells a detective that a body is fighting something — never what. We will not diagnose anyone in this room, including ourselves.
98.6 °F is an ______, not a ______.
Two healthy people can differ because ______ and ______.
A forehead reading could be wrong if ______.
Write your answers on Worksheet 4 — Body Temperature.
Yesterday you learned what body temperature is. Today you measure one. Your body holds its core steady near 98.6 °F, and a reading outside the normal range is a strong clue that something is going on.
A change of plan. Our dot-matrix strips have not arrived, so we are improvising with a handheld no-touch forehead thermometer. It reads infrared — the heat glowing off the skin — from an inch or two away, and nothing touches anyone. It also means we are measuring skin, not core. You predicted yesterday why that might matter. Today you get to find out.
This thermometer just prints the number on a screen — no dots to count. The detective work is deciding what the number means. Move it and watch.
Record each one on Worksheet 5 — Station B.
You have a resting reading already. Now we try to fool the thermometer on purpose.
Indoors, sitting, hair off the forehead. Take your partner's temperature and write it down.
Step outside into direct sunlight. Face the sun, forehead uncovered, for one full minute.
Immediately take the forehead temperature a second time. Do not wipe or cool the forehead first.
Subtract. How far did the number move in sixty seconds — and did your partner's body move with it?
Baseline first. Nobody starts the clock until both partners have a resting number written down.
Safety: one minute only, nobody looks at the sun. Anyone who feels dizzy, or who is told by a doctor to stay out of the sun, uses the indoor version — a hand cupped over the forehead for a minute, or a sunny window. No sun today? Indoor version for everyone; it changes the skin the same way.
A measurement is valid when it really measures the thing it claims to measure. A thermometer can be perfectly accurate — right about the skin — and still not be valid evidence about the body.
Write your answers on Worksheet 5 — Station B.
Blood does not drift around your body. It is pushed. Every time your heart squeezes, it shoves blood into the arteries, and that blood presses out against the artery walls.
Blood pressure is how hard that push is.
Why "mm Hg"? Old machines measured the push by how many millimeters it could lift a column of mercury (Hg). The machines changed; the unit stuck.
Your heart squeezes about 100,000 times a day. Each squeeze fires roughly a cup of blood into the arteries all at once.
Arteries are not stiff pipes. They stretch as blood arrives, then spring back — which is exactly what you feel as a pulse.
The springing back keeps blood moving between beats. In a stiff pipe, flow would stop dead every time the pump rested.
Hold on to this: there are two different moments in every heartbeat — the squeeze and the rest. That is why blood pressure needs two numbers instead of one.
The hardest push, at the instant the heart contracts. Always the bigger number.
The push that never goes away, while the heart refills between beats.
Why the bottom number matters: the squeeze lasts a fraction of a second, but the arteries live with the diastolic pressure all day and all night. That is the pressure that slowly wears them out.
It is the upper edge of healthy for an adult — a line drawn by doctors after studying huge numbers of people, not a measurement of any one person. Nobody’s heart is aiming at it.
90/60–120/80
mm Hg, adult at rest
Anywhere in here is normal. Kids and teens usually run lower than adults, and blood pressure creeps up as people age.
The same trap as temperature: 98.6 °F was an average and 120/80 is a ceiling — neither is a rule your body promised to obey. One reading is never a diagnosis, and we do not diagnose anyone in this room.
Blood pressure dips at night and starts climbing before you wake up — your body raises it to get you going.
Running up stairs pushes the top number up a lot. The bottom number barely moves, because the arteries open wider to let more blood through.
Being nervous raises it. So many people read high at the doctor’s office that the effect has a name: white coat blood pressure.
Detective question: if it moves this much, why does a nurse bother measuring it at all? Because the pattern across several readings is evidence — one number alone is not.
| What the patient does | Effect on the top number | Why |
|---|---|---|
| Talking during the measurement | about +10 | Speaking works muscles and changes breathing |
| Full bladder | about +10 | The body is under stress and holding tension |
| Legs crossed | about +2 to +8 | Squeezes the vessels in the leg |
| Back or feet unsupported | about +6 | Muscles are working to hold the body up |
| Arm hanging below the heart | reads high | Gravity adds its own push |
| Cuff too small for the arm | reads high | It must squeeze harder to stop the flow |
These are estimates published by the American Heart Association, not exact laws — but the direction is always the same: almost every mistake makes the number look too high. Tomorrow, every step of our procedure exists to cancel one of these.
Usually there is nothing to feel — no pain, no dizziness, nothing. That is why it is called the silent problem, and why it is measured at almost every visit. Over years, the extra push wears out arteries, the heart, the kidneys and the eyes.
Not enough push means not enough blood reaching the brain. People feel dizzy or faint, especially standing up fast. A sudden drop can be a sign of heavy bleeding or serious illness.
The top number tells us ______ and the bottom number tells us ______.
Talking during the test would make the number go ______ because ______.
The arm must be level with the heart because ______.
Write your answers on Worksheet 6 — Blood Pressure.
Blood pressure is written as one number over another, like 118/76, measured in millimeters of mercury.
The push while the heart squeezes blood out.
The push while the heart rests between beats.
Memory hook: Systolic = Squeeze. The heart is working, so that number is always the bigger one.
Write your answers on Worksheet 7 — Station D.
You and a partner will visit all four stations and measure each other. Every number goes on Worksheet 8 — Evidence Log.
| Name | Pulse (bpm) | Temperature (°F) | Respiratory rate | Blood pressure (mm Hg) |
|---|---|---|---|---|
| Your name | ____ | ____ | ____ | ____ / ____ |
| Partner's name | ____ | ____ | ____ | ____ / ____ |
| Vital sign | Average low | Average high | What it measures |
|---|---|---|---|
| Pulse | 60 bpm | 100 bpm | Heartbeats in one minute |
| Temperature | 97.8 °F | 99.1 °F | How warm the body is inside |
| Respiratory rate | 12 breaths/min | 18 breaths/min | Breaths in one minute |
| Blood pressure | 90/60 mm Hg | 120/80 mm Hg | Push of blood on the arteries |
Important: these ranges change with age, sex, family history, lifestyle, and medication. Use them to guide your reflection — never to diagnose anyone, including yourself.
“My ______ was ______, which is inside / outside the normal range of ______.”
“My partner's ______ was ______ than mine because ______.”
“If I ______, I think my ______ would go up / down because ______.”
Answer on Worksheet 9 — Analyze the Data.
The lesson: the vital sign that solved this case was not the one connected to where it hurt. That is why you check them all.
Emergency room staff are trained to read vital signs fast. They are not the only ones.
Measures vital signs in a moving ambulance.
Checks an athlete's pulse and breathing on the field.
Decides who rests, who goes home, who needs a doctor.
Takes vital signs on animals that cannot describe symptoms.
PLTW · This is the mystery you will spend the whole unit solving. Take notes on anything that sounds like evidence.
There is an outbreak in a local community. You are part of the team investigating it. Across this unit you will collect clues, and in the final problem you will name the cause.
Vital signs are where every one of those investigations starts. Remember what you learned this week — you will need it in December.
Claim — answer the question in one sentence.
Evidence — give a number or a fact from this activity.
Reasoning — explain how your evidence proves your claim.
Answer on Worksheet 10 — Conclusion.
Every question in this activity has a place to write on paper.
Next up: Activity 1.2 — Exploring What's Vital, where you design your own experiment about a vital sign.
Every academic word in Activity 1.1. Tap one for the full card.
Click any slide to jump there.