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acid reflux (% total time pH < 4) off therapy and total
number of impedance events on therapy by patient sub-
group. As expected, patients with a normal upper
endoscopy and normal pH testing exhibited a significantly
(P < 0.001) lower % total time pH < 4 (3.08% [1.99%–
4.89%]), compared to the patients with a normal upper en-
doscopy and abnormal pH testing (10.45% [7.35%–
15.10%]) and those with esophagitis (9.98% [6.70%–
12.66%]) (Fig. 1). However, there was no significant differ-
ence among the three groups with respect to median
(IQR) total number of impedance events on therapy (P ¼
0.61) (27.50 [21.25–47.25];39 [24–51]; 42 [23.25–52.75],
respectively) (Fig. 2). Median (IQR) lower esophageal
sphincter pressure for the three groups were similar (P ¼
0.78) between the three groups (3.0 [1.0–7.0], 5.5 [0.4–
15.5], and 8.0 [1.3–29], respectively).
Predictors of Impedance Findings
No significant overall relationship was observed
between the total number of impedance events and the
traditionally recognized physiologic parameters for
reflux. Specifically, there was no correlation (r ¼ 0.15, P
¼ 0.2) between the total number of impedance events on
therapy and the total % time pH < 4 off therapy (Fig.
3A). Presence or absence of hiatal hernia did not change
this relationship (Fig. 3B). However, among patients
with endoscopic evidence of esophagitis, there was a
weak significant correlation (r ¼ 0.54, P ¼ 0.045)
between the on therapy impedance and off therapy pH
parameters (Fig. 3C). However, the impedance parame-
ters on therapy could not be predicted based on severity
of reflux parameters at baseline. Number of impedance
events on therapy were similar (P ¼ 0.99) between
patients who had no or mild reflux (% time pH < 4 of
less than 10%) compared to those with moderate to
severe reflux (% time pH < 4 of more than 10%) (Fig. 4).
DISCUSSION
In a unique cohort of patients who had both off and
on therapy testing, we sought to determine if on therapy
impedance data can be predicted from the more tradi-
tionally recognized and commonly employed off therapy
upper endoscopy, manometry, or pH parameters. In this
stepwise diagnostic approach, we found that among
patients with extraesophageal reflux refractory to PPI
Fig. 2. Individual and group median (IQR) total number of imped-
ance events for the three patient subgroups. Impedance events
were similar between the groups.
Fig. 3. Correlation between % total time pH < 4 off therapy and total
number of impedance events on therapy for Overall (A), stratified by hi-
atal hernia (B), and stratified by endoscopic presence of esophagitis
(C). HHþ ¼ hiatal hernia present; HH ¼ no hiatal hernia; Esop ¼
no esophagitis; Esopþ ¼ esophagitis. [Color figure can be viewed in
the online issue, which is available at ]
Laryngoscope 123: October 2013 Kavitt et al.: The Role of Impedance Monitoring in Extraesophageal Symptoms
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