The Effect of Breaths per Minute on Heart Rate
Background and Research Question:
The average adult, while resting, breathes about twelve times a minute. This is called
the ventilation, or respiratory rate.1 The average heart rate, for a healthy adult, is around sixty to
one-hundred beats per minute, but it can be lower, depending on the athleticism of a specific
person.2 This means that each breath, on average, would last about five seconds, (about two
and a half seconds to inhale, and two and a half seconds to exhale). When air is inhaled, it goes
into the lungs, diffuses into the alveoli, and then into the lung capillary. The air then enters the
bloodstream and moves into the pulmonary vein, and goes through the heart by way of the left
atrium and then left ventricle, and is finally moved through the aorta to various parts of the body.
From the aorta, blood is moved to body cells where oxygen diffuses out of the blood and carbon
dioxide and waste diffuse into the blood. Then, the blood is moved from capillary beds in body
cells, to veins, to the superior or inferior vena cava, and then finally back to the right atrium and
right ventricle. Finally, the blood moves to the pulmonary artery and returns to the lungs where
carbon dioxide is expelled by exhalation.3 All this takes place, on average, in about five
seconds. Generally, when we exercise, we have to breathe more often (quicker). Our heart rate
also accelerates.
Is this just a correlation? The research question of this experiment is:
What is the effect of breathing rate on the heart rate?
Hypothesis:
If the subject is breathing slower, then his/her heart rate will be slower; if he/she is
breathing quicker, then his/her heart rate will be quicker.
1
Damon, Alan, Randy McGonegal, Patricia Tosto, and William Ward. "Physiology of exercise." In Biology:
Standard level: developed specifically for the IB diploma. Harlow, Essex: Heinemann International , 2007.
249.
2
Laskowski, Edward R.. "Heart rate: What's normal?." Mayo Clinic.
http://www.mayoclinic.com/health/heart-rate/AN01906 (accessed February 14, 2011).
3
"Human health and physiology" In Biology: Standard level: developed specifically for the IB diploma. 172.
Predictive Graph:
Independent Variable:
The independent variable for this experiment is breathing rate, measured in breaths per
minute (also, seconds per breath). The levels of the independent variable will be thirty (two
seconds per breath), fifteen (four seconds per breath), seven and a half (eight seconds per
breath), six (ten seconds per breath), and three and three-quarters (sixteen seconds per
breath).
Dependent Variable:
The dependent variable for this experiment is heart rate, measured in beats per minute.
Control Variables:
Variable
Effect
Control
Body position
(standing, sitting,
movement, etc.)
Being in different body positions can
make the heart work more or less to
pump the blood to all areas, therefore
skewing our results.
Stay in the same body
position for all trials; do not
move in between.
Outside noise
influence
Surprising loud noises may scare us
and raise our heart rate.
Be in a separate room, away
from other people.
Temperature
Being in a room that is too hot or cold
could lower or increase the difference
in heart rate between trials
Perform the experiment in a
neutral-temperature room
Measurement type
Measuring in different areas of the
body/ having different people measure
other peoples‟ heart rate can make it
difficult to distinguish between when
the heart beats begins and ends.
Each student will measure
their own heart rate, using
two fingers to find their pulse
on the right side of their neck.
Method:
1. Measure resting heart rate at a normal breathing rate. Do this while seated. Count how
many heartbeats there are in thirty seconds and multiply this by two. Record the result in
the data table.
2. Next, for one minute, take small breaths, so that each inhale lasts one second, and each
exhale lasts one second. All in all, the subject should take thirty breaths. Immediately
afterwards, the subject‟s heart rate should be taken. The subject should remain in a
seated position throughout the entire experiment.
3. Next, breathe normally for one to two minutes.
4. For one minute, take slightly larger breaths, so that each inhale lasts two seconds and
each exhale lasts two seconds (15 breaths). Take the heart rate immediately following
one minute of breathing as such.
5. Follow the trial for the second level of the independent variable with another one to two
minutes of normal breathing.
6. Repeat the breathing, heart rate measuring, and resting, for eight second breaths, ten
second breaths, and sixteen second breaths (each inhale/exhale lasts half the given
number).
7. Make sure to record observations.
8. Do this experiment five times (or with five different people, one trial each).
9. Process data and make a graph of the results.
We will control the independent variable by watching the clock closely, and making sure
that each inhale lasts precisely the amount of seconds that it should, and that each exhale also
lasts the proper amount.
We will control the dependent variable by again using a clock and watching it closely.
We will use the same clock each time to make sure that, even if the clock is incorrect, we will
have the same margin of error each time.
*Both variables involve counting: we cannot count partial seconds in a breath, and we
cannot count half a heartbeat.
Materials:
● Clock
● Chairs
Sufficiency of Data:
The experiment performed was a 5x5 (five trials for five levels of the independent
variable), giving us a small data sample (twenty-five data points).
Raw Data/ Processed Data:
The Effect of Breathing Rate on the Heart Rate
Condition:
Breaths per
minute
Heart Rate of Subjects 1 through 5
(beats per minute) +/- 1 bpm
% Change
1
2
3
4
5
AVG
S.D.
30
68
80
92
96
76
82
11.5
17.1
15
70
78
72
80
76
75
4.2
7.1
7.5
72
76
70
74
74
73
2.3
4.3
6
64
68
68
72
70
68
3.0
-2.9
3.75
60
64
64
74
66
66
5.2
-5.7
Normal
56
76
82
70
68
70
9.8
„--
Calculations:
Average: (Value 1+Value 2+Value 3+Value 4+Value 5)/5
(68+80+92+96+76)/5 = 82 (Average HR for 30 breaths per minute)
Percent change: [(New - Resting) / Resting] * 100
[(82-70)-70]*100 = 17 (Percent change for 30 breaths per minute)
Conclusion:
My hypothesis, “if the subject is breathing slower, then his/her heart rate will be slower; if
he/she is breathing quicker, then his/her heart rate will be quicker” was supported by the data.
As seen in the graph, the general trend of the data is a linear increase; heart rate increased at
the same time as breaths taken per minute increased. For example, when the subjects breathed
thirty times per minute, the average heart rate was 82 beats per minute. This is sixteen beats
per minute greater than that of when we breathed only approximately four times per minute (66
bpm at 3.75 breaths). Also, as seen in the red line in the graph representing the average normal
heart rate when breaths per minute were not monitored, the slower breathing rate‟s
corresponding heart rate was lower than that of the normal heart rate, and the heart rate which
corresponds to the quicker breathing rate was greater than the normal heart rate. As seen in the
graph examining percent change (of the heart rate of monitored breathing versus resting heart
rate breathing normally), taking 3.75 and 6 breaths per minute resulted in a negative percent
change. All other breathing rates greater than 6 breaths per minute experienced a positive
change, in relation to resting heart rate. Additionally, in general, breathing quicker than the
normal heart rate created a greater change in heart rate than breathing slower than the normal
breathing rate. For example, at 3.75 breaths per minute, subjects on average experienced about
a 17 percent change. On the other hand, when subjects breathed 15 times in a minute, they
only experienced a net change of 2.86 percent (negative). Further experimentation could be
done to see whether breathing slower for longer amounts of time could have a greater affect on
the heart rate. Small anomalies were due to the difficulty we faced and effort exerted in trying to
control our breathing. Based on the averages I found, our group had the resting heart rate most
close to that between taking six and seven and a half breaths per minute. This is interesting,
seeing as the average adult takes five second breaths. A further experiment could be made in
different parts of the country and with different demographics, such as age, race, gender, and
weight to see if my group had some common characteristic that allows us to have a normal
resting heart rate while taking more breaths than the average adult.
Evaluation and Improvement
Factor Affecting
Effect on Data
Improvements
Speed/ style of breath taking quick breaths
and then holding
breath vs. taking a
breath that lasts the
whole X seconds.
A quicker breath and then
holding the breath could raise
the heart rate because
initially, oxygen is being
inhaled much quicker.
Additionally, this would not
really change the breathing
rate much.
Instruct each student on how to
breathe slowly (through the nose);
specify in the method whether the
students should be doing deep
abdominal breathing or regular
chest breathing.
Food/ mood of the
subjects
If the subject has consumed
food with caffeine, their heart
rate will be greater; if the
student is very excited, the
heart rate will also be greater.
Make sure that the subjects have
either not consumed any caffeine in
the past three hours, or have all
consumed caffeine; try to have the
subjects clear their minds before
doing the experiment.
Measurement errors
It was hard to keep each
breath lasting the specified
amount; breathing more times
per minute raised the heart
rate and breathing fewer times
per minute lowered the heart
rate. Additionally, it was
sometimes hard to measure
the heart rate; beats could
have been skipped or added
due to the flow of other blood
being counted instead.
Use a more specific form of time
measurement (i.e. a timer that
beeps after a minute), perhaps use
a stethoscope to make sure that
the counting of the heart beats is as
accurate as possible.