Augmentation index (AIx)
For AIx, the SphygmoCor tonometer is placed over the right radial artery and data
are collected as previously described
(27, 28)
. The pressure waves are calibrated
using systolic and diastolic BP obtained in the same arm. The device then
analyses the pulse wave using a validated generalized transfer function
(29)
. Wave
forms collected over an 8-second period are averaged to produce peripheral and
corresponding central (ascending aortic) pressure waveforms. Ascending aortic
pressure and AIx are derived from the central pressure waveform. Aix is the
difference between the main outgoing wave and the reflected wave (RW) of the
central arterial waveform, expressed as a percentage of the central pulse pressure.
It provides a measure of systemic arterial stiffness. Since AIx is affected by heart
rate (HR), values are adjusted to a standard HR of 75 beats/minute (AIx75). An
average of 3 measures is used. The inter-observer difference for AI was found to
be 0.23 ± 0.66% and the intra-observer difference was 0.49 ± 0.93% as compared
to an average AI in healthy children of greater than 3%.
5.1.9.
Markers of Neuropathy
While there is substantial evidence of the epidemiology of neuropathy in adult diabetes
patients, there is limited information available on the prevalence and determinants of
neuropathy among youth with diabetes. Given the large sample size, racial and ethnic
Section 5B - Data Collection (Phase 3 - 1/2011, rev. 8/2011)
Section 5B - Page 7
Cohort
Study
diversity and sizeable numbers of youth with Type 2 diabetes, the SEARCH for Diabetes
in Youth Study presents a unique opportunity to understand the natural history of diabetic
neuropathy (both peripheral and autonomic). Data to be collected during this visit
include: 1) the Michigan Neuropathy Screening Instrument (MNSI), which includes a
brief questionnaire, physical exam inspection, vibration sense, reflex test and
monofilament test for peripheral neuropathy; and 2) cardiac autonomic neuropathy
assessment using electrocardiogram analyses.
5.1.9.1.
Peripheral neuropathy methods
The Michigan Neuropathy Screening Instrument (MNSI) is designed to screen for the
presence of peripheral diabetic neuropathy. The MNSI is designed to be used in an
outpatient setting and will be administered by trained technicians. The first part of
the screening instrument consists of 15 self-administered "yes or no" questions on
foot sensation including pain, numbness and temperature sensitivity. A higher score
(out of a maximum of 13 points) indicates more neuropathic symptoms. The
questions were chosen from among those in the Neuropathy Screening Profile that
showed the highest degree of specificity and sensitivity for diabetic neuropathy
among normal subjects and those with a variety of neuromuscular disorders
(30)
and
have been recently validated
(31)
. The second part of the MNSI is a brief physical
examination involving 1) inspection of the feet for deformities, dry skin, hair or nail
abnormalities, callous or infection, 2) semi-quantitative assessment of vibration
sensation at the dorsum of the great toe using a 128 Hz tuning fork, 3) grading of
ankle reflexes and 4) monofilament testing with a 10 g Semmes-Weinstein
monofilament using a standard protocol. Subjects with an MNSI score > 2, together
with reduced/absent vibration sense, ankle reflexes, and monofilament testing will be
considered to have diabetic neuropathy on screening. Other combinations of results
will also be evaluated.
5.1.9.2.
CAN methods
Measurement of HRV will be performed by trained and certified technicians. The
protocol is based on the software housed in the Sphygmacor instrument (ATCOR
Medical:
http://www.atcormedical.com/
). A resting ECG will be completed for 5-10
minutes. Resting HRV time parameters that are captured include: HRV range,
maximum, minimum; standard deviation, percent of consecutive beat-to-beat
intervals that are greater than 50 milliseconds long (pNN50), Triangular index, and
the root mean squared successive mean standard deviation (RMSSD), a measure of
vagal index. Resting frequency parameters captured include: low frequency max
(Hz); High freq max (Hz); LF:HF ratio, LF power normalized; HF power normalized,
Total power (ms
2
).
Section 5B - Data Collection (Phase 3 - 1/2011, rev. 8/2011)
Section 5B - Page 8
Cohort
Study
5.1.10.
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