Correlation among cardiac autonomic function tests in normal subjects.

Abstract

Cardiac autonomic function tests such as
the Orthostatic Challenge Test (OCT) and
Valsalva Manoeuvre (VM) test are popular
clinical neurophysiological investigations
used to diagnose autonomic disorders.
Analysis of heart rate responses in OCT
(3015 ratio) and VM (Valsalva ratio) evaluates
the parasympathetic responses of the
cardiac autonomic nervous system.The
indices of short-term Heart Variability
Analysis (HRV) that reflects the cardiac
parasympathetic activity are pNN50,
RMSSD and HF power. The current study
investigated whether there was any correlation
between (a) OCT 3015 ratio and
Valsalva ratio (b) OCT 3015 ratio and
pNN50, RMSSD and HF power (c) Valsalva
ratio and pNN50, RMSSD and HF
power. Towards this, the data acquired
from 22 healthy male volunteers were analysed
Five min ECG and respiration were
recorded for short-term HRV analysis. Following
this, the OCT was performed where
the subjects were instructed to stand
abruptly from the supine posture. For VM
the subjects were instructed to blow
through a mouthpiece attached to a mercury
manometer to sustain a pressure
of 40mm of Hg for 10 seconds. The correlation
of short-term HRV parameters and
OCT 3015 ratio and Valsalva ratio was
done using Spearmans correlation test.
The results of our study showed that there
was a weak positive correlation between
the OCT and VM test results (r0.431.
p0.045). The Valsalva ratio showed a
weak but highly significant correlation with
the HF power (r0.559, p 0.007) while the
OCT results showed no correlation with
any of the HRV indices considered.Thus,
in conclusion, though all the tests studied
were evaluating the cardiac parasympathetic
activity, strikingly, the OCT results
showed no correlation with any of the
short- term HRV indices while the VM test
results showed highly significant correlation
with HF power. Thus, even though
VM is more difficult to perform, the Valsalva
ratio appears to be better correlated
with short-term HRV index of HF power.