The RR interval variations present during resting conditions represent beat-by-beat variations in cardiac autonomic inputs. However, efferent vagal (parasympathetic) activity is a major contributor to the HF component, as seen in clinical and experimental observations of autonomic maneuvers such as electrical vagal stimulation, muscarinic receptor blockade, and vagotomy. More problematic is the interpretation of the LF component, which was considered by some as a marker of sympathetic modulation (especially when expressed in normalized units) but is now known to include both sympathetic and vagal influences. For example, during sympathetic activation the resulting tachycardia is usually accompanied by a marked reduction in total power, whereas the reverse occurs during vagal activation. Thus the spectral components change in the same direction and do not indicate that LF faithfully reflects sympathetic effects.

Weighing
In
Grades 3 - 5
What you'll need

A grocery scale or your scale at home
What to do

- Help your child examine the scale in the grocery store or the one
you have at home. Explain that pounds are divided into smaller parts
called ounces and 16 ounces equal a pound.

- Gather the produce you are purchasing, and estimate the weight of
each item before weighing it. If you need 1 pound of grapes, ask your
child to place the first bunch of grapes on the weighing scale, and
then estimate how many more or fewer grapes are needed to make exactly
1 pound.

- Let your child hold an item in each hand and guess which item weighs more. Then use the scale to check.
- Ask questions to encourage thinking about measurement and estimation.
You might want to ask your child: How much do you think 6 apples will
weigh? More than a pound, less than a pound, or equal to a pound? How
much do the apples really weigh? Do they weigh more or less than you
estimated? Will 6 potatoes weigh more or less than the apples? How much
do potatoes cost per pound? If they cost 10 cents per pound, what is
the total cost?

- Try weighing items using the metric system. How many grams does an
apple weigh? How many kilograms does a sack of potatoes weigh? How does
a kilogram compare to a pound?

Parent Pointer There are many opportunities to increase estimation and measurement skills by weighing objects in the produce section of the grocery store.

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