Exploratory Study of StressBuffering Response Patterns from Interaction with a Therapy Dog

Abstract

This exploratory study builds on existing research on the physiological stress response to human-animal interactions in a non-clinical sample of adult dog-owners interacting with their own or an unfamiliar therapy dog under similar conditions. Participants were therapy-dog owners (TDO group; n = 5) interacting with their own dogs and dog owners interacting with an unfamiliar therapy dog (AAA group; n = 5). Following a 30minute baseline period, participants completed a stress task followed by a 30-minute dog interaction and then watched a neutral video for 60 minutes. The outcome variable of interest was the bio-behavioral stress response, measured by systolic and diastolic blood pressure (SBP, DBP), heart rate (HR), salivary cortisol, salivary alpha-amylase, and self-report. Trait anxiety and attitudes toward pets were assessed as moderating variables. Results revealed consistent physiological patterns, showing modest increases with the stressor and decreases from baseline following the intervention, for salivary cortisol, SBP, DBP, HR, and self reported anxiety and stress for both groups. In general, although the TDO group tended to perceive less stress and anxiety during the intervention than the AAA group, greater reductions in physiological measures were observed in the AAA group. Positive attitudes toward pets in the total sample of dog owners were associated with decreased levels of self-reported stress (p < 0.05), salivary cortisol, and SBP, while higher levels of trait anxiety were associated with higher levels of salivary cortisol (p < 0.05). In addition, higher levels of trait anxiety were associated with lower levels of autonomic nervous system indicators of stress (HR; SBP, p < 0.05; DBP, p < 0.05). Results support a buffering effect on the stress response associated with owners interacting with their dogs that may extend to interactions with unfamiliar therapy dogs in AAA, and supports the need for replication studies with larger sample sizes.

Full text

79 Anthrozoös DOI: 10.2752/175303710X12627079939341
Exploratory Study of Stress-
Buffering Response Patterns
from Interaction with a
Therapy Dog
Sandra B. Barker, Janet S. Knisely, Nancy L. McCain,
Christine M. Schubert and Anand K. Pandurangi
School of Medicine Center for Human–Animal Interaction, Virginia
Commonwealth University, USA
ABSTRACT This exploratory study builds on existing research on the
physiological stress response to human–animal interactions in a non-clinical
sample of adult dog-owners interacting with their own or an unfamiliar ther-
apy dog under similar conditions. Participants were therapy-dog owners
(TDO group; n= 5) interacting with their own dogs and dog owners inter-
acting with an unfamiliar therapy dog (AAA group; n= 5). Following a 30-
minute baseline period, participants completed a stress task followed by a
30-minute dog interaction and then watched a neutral video for 60 minutes.
The outcome variable of interest was the bio-behavioral stress response,
measured by systolic and diastolic blood pressure (SBP, DBP), heart rate
(HR), salivary cortisol, salivary alpha-amylase, and self-report. Trait anxiety
and attitudes toward pets were assessed as moderating variables. Results
revealed consistent physiological patterns, showing modest increases with
the stressor and decreases from baseline following the intervention, for sali-
vary cortisol, SBP, DBP, HR, and self reported anxiety and stress for both
groups. In general, although the TDO group tended to perceive less stress
and anxiety during the intervention than the AAA group, greater reductions
in physiological measures were observed in the AAA group. Positive attitudes
toward pets in the total sample of dog owners were associated with de-
creased levels of self-reported stress (p< 0.05), salivary cortisol, and SBP,
while higher levels of trait anxiety were associated with higher levels of sali-
vary cortisol (p< 0.05). In addition, higher levels of trait anxiety were associ-
ated with lower levels of autonomic nervous system indicators of stress (HR;
SBP, p< 0.05; DBP, p< 0.05). Results support a buffering effect on the stress
response associated with owners interacting with their dogs that may extend
to interactions with unfamiliar therapy dogs in AAA, and supports the need
for replication studies with larger sample sizes.
ANTHROZOÖS VOLUME 23, ISSUE 1 REPRINTS AVAILABLE PHOTOCOPYING © ISAZ 2010
PP. 79–91 DIRECTLY FROM PERMITTED PRINTED IN THE UK
THE PUBLISHERS BY LICENSE ONLY
Address for correspondence:
Sandra B. Barker,
School of Medicine Center
for Human–Animal
Interaction,
Virginia Commonwealth
University, P. O. Box 980710,
Richmond, VA 23298-0710,
USA. E-mail:
sbarker@mcvh-vcu.edu
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Keywords: animal-assisted therapy, human–animal interaction, stress, therapy dogs
A number of studies have been published concluding that pet ownership is associ-
ated with reduced stress. In one randomized controlled trial, 48 hypertensive stock-
brokers beginning medication therapy with an ACE-inhibitor, lisinopril, were randomly
assigned to acquiring a pet or a wait-list control condition (Allen, Shykoff and Izzo 2001). Fol-
lowing a stressful mental task, heart rate (HR), systolic (SBP) and diastolic blood pressure
(DBP), and renin activity were significantly lower for pet owners than those not owning a pet.
In another randomized, controlled study, normotensive couples completed mental and phys-
ical stressors under four conditions: alone, with a friend or pet, with a spouse, and with a
spouse and pet or friend (Allen, Blascovich and Mendes 2002). Researchers found lower BP
and HR and the least cardiovascular reactivity and fastest recovery in the pet owners follow-
ing the stressors in the pet-present condition. Further support is provided by a study of
normotensive, adult females undergoing a mental stress task alone, with their pet dog, or with
a female friend (Allen et al. 1991). Blood pressure (BP), skin conductance response frequency,
and HR were monitored, and the lowest autonomic reactivity was found with the pets present,
while the highest was with friends present.
Additional evidence suggesting pets buffer the reaction to stress was reported in a
prospective study of physician utilization in 938 Medicare enrollees in California (Siegel 1990).
Pet owners reported fewer physician visits, independent of demographics and health status.
The number of stressful life events was associated with increased physician visits for non-pet
owners; however, dogs buffered the impact of stressful life events for dog owners.
While the aforementioned literature focused on pet ownership, other studies have investi-
gated the effect of animal-assisted activities (AAA) on stress. In a study of older adults with pre-
to mild hypertension, participants had to sit quietly, then talk, then sit quietly again (2 minutes
for each session), with or without an unfamiliar, friendly dog present (Friedmann et al. 2007). Re-
duced BP was found when the dog was present during the speaking condition, providing fur-
ther evidence of a possible buffering effect during stressful activities. Other studies have also
reported positive findings associated with AAA, including reduced BP (Wilson 1987; Vormbrock
and Grossberg 1988; Friedmann et al. 2007), improved HR variability (Motooka et al. 2006), and
reduced stress hormone levels (Barker et al. 2005), although a few studies have reported no
cardiovascular benefit (Craig, Lynch and Quartner 2000; Kingwell, Lomedahl and Anderson
2001). The interventions, participants, and designs of these studies vary considerably.
Most published studies investigating human–animal interaction and stress have focused
on either pet ownership, owners interacting with their own pets, or participants interacting
with an unfamiliar therapy animal and its handler. The participants, settings, stressors (if any),
interventions, and outcomes in these studies differ considerably. What remains unknown is 1)
if physiological stress response patterns are similar when owners are with their own pets com-
pared with owners being with an unfamiliar therapy animal; 2) how much the therapy animal
(versus the animal handler) contributes to the stress response in AAA, and 3) how underlying
trait anxiety may influence the stress response associated with AAA.
The purpose of this exploratory study was to 1) build on existing research into the physi-
ological stress response to human–animal interactions, and 2) investigate response patterns
in a non-clinical sample of adult dog-owners interacting with their own or an unfamiliar ther-
apy dog under similar conditions. Half of the participants were therapy dog owners (TDO
group) interacting with their own dogs and half were dog owners interacting with an unfamiliar
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therapy dog, as typically occurs in animal-assisted activities (AAA group). However, in this
study the impact of the human in the AAA was controlled by not having the therapy dog’s
owner present in the AAA condition. The outcome variable of interest was the bio-behavioral
stress response, measured by BP, HR, salivary cortisol, salivary alpha-amylase, self-report,
and brain wave activity (the latter not addressed in this manuscript). Anxiety was also meas-
ured by self-report, as a related component to stress. Trait anxiety and attitudes toward pets
were considered moderating variables and were also assessed. Of particular interest was
whether response patterns in the AAA group were similar to those of the TDO group.
Methods
A pre-post within-subject design was used in this exploratory study. Following a 30-minute
baseline period during which participants relaxed in a comfortable chair, participants were ad-
ministered a stress task. The five therapy dog owners then interacted for 30 minutes with their
own dog, followed by a 60-minute period during which they watched a neutral video. The
other five adults followed the same protocol, except that their interaction was with an unfamiliar
therapy dog.
Sample
A convenience sample of 10 healthy adult dog-owners participated in this study. Five partici-
pants were selected from volunteers participating in an established animal-assisted activity
(AAA) program at an academic medical center. All participants in the program were sent an e-
mail inviting them to participate in a study of dog owners; the first five people meeting screen-
ing criteria were selected. Five participants were also selected from students, visitors or
employees at the medical center who responded to publicly posted recruitment posters. Par-
ticipants were screened by telephone using inclusion/exclusion criteria. Inclusion criteria were:
age 18 years or older, dog owner, member of medical center’s AAA program (for the TDO
group), and ability to understand and speak English. Those meeting the inclusion criteria were
then referred to a medical monitor who completed a health screening using a review of sys-
tems clinical checklist. Exclusion criteria were: fear of dogs, allergies to dogs or any other aver-
sion to animals, medical disorders or treatment that might affect outcome measures such as
a diagnosis of Addison’s or Cushing’s disease, treatment with steroids, a clinical diagnosis of
any acute or chronic major physical or mental illness, and taking any psychoactive substances
or medications (whether prescribed or illicit). Adults meeting the study criteria were then con-
sented following procedures approved by a university committee for the protection of human
subjects. Additional health exclusion criteria were established for participants enrolled in the
study and applied prior to analysis: two or more of 1) baseline SBP greater than 140, 2) base-
line DBP greater than 90, 3) baseline average HR greater than 90 beats per minute, 4) use of
a beta blocker or steroids, and 5) emergence of other health status information indicating an
active medical problem not previously reported.
Setting
The study was conducted on weekends, in a quiet, private reception area of the medical
center that is closed to patients on weekends. Selected to provide a relaxed, yet controlled
setting, the reception area is large with carpeting, large windows, and comfortable seating.
Participants were seated in comfortable recliner chairs for the study period, but not required
to remain sitting (although most of them did so). Only one participant at a time was involved
in the study protocol.
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Stress Task
The Stroop Color Word Test (Stroop 1935) was administered to increase participants’ stress
levels. The Stroop is one of the most widely used methods to experimentally induce stress in
clinical research. Participants are faced with a cognitively conflicting test in which they must
discriminate color and words presented in conflicting colors. Stroop test software (Xavier Ed-
ucational Software Ltd) was used to electronically present the Stroop test to participants on a
laptop. The computerized version usually takes about 5 minutes to complete.
Intervention
The intervention consisted of 30 minutes with a therapy dog. The intervention was unstruc-
tured and permitted participants to interact with the dogs in any way they wished. All six ther-
apy dogs involved in the study met requirements for the medical center’s AAA program. The
same therapy dog interacted with each of the five non-therapy dog owners in the 30-minute
AAA group. This previously unknown dog to the group was a 14 pound, 4-year-old, mix-
breed, spayed female. Prior to the study, this dog was separated from her owner in a mock
intervention and demonstrated no anxious or distressed behaviors.
Measures
Noninvasive physiological measures of stress were used: HR, SBP, DBP, salivary cortisol, and
salivary alpha amylase. Subjective measures of anxiety and stress were self-reported using
visual analog scales. The covariate of “pet attitude” was measured using the Pet Attitude Scale
(Templer et al. 1981), and the covariate of “trait anxiety” was measured by the Trait Form of
the State-Trait Anxiety Inventory (Spielberger 1983).
Blood Pressure: A DINAMAP®PRO 100 Vital Signs Monitor (GE Healthcare) was used to meas-
ure SBP and DBP. Reliability and accuracy of the Dinamap monitors have been demonstrated
in several studies (Bruner et al. 1981; Mundt et al. 1992; Bald, Kubel and Rascher 1994;
Gardner and Montgomery 1998). The cuff pressure range is 0 to 290 mmHG and the inflation
adjustment range is 100 to 250 mmHG in 5 mmHG increments. BP accuracy meets or exceeds
SP 10-1992 AAMI standards. The Dinamap Monitor is auto-calibrated and annually tested with
a calibrated standard. BP was taken in the sitting position at 1-minute intervals for 5 minutes
at each data collection time point. A soft cuff was used for participant comfort and the wires
disconnected during the intervention to minimize interference during the study conditions.
Heart Rate: A Nellcor Oximax NPB-40 Handheld Pulse Oximeter was used to measure HR. The
Oximax NPB-40 provides a pulse rate display range of 20–250 bpm. Pulse rate accuracy with-
out motion is ± 3 digits, with motion ± 5 digits, and with low perfusion ± 3 digits. Measurements
were taken at 1-minute intervals for 5 minutes at each data collection time point.
Salivary Alpha Amylase and Salivary Cortisol: Standardized ELISA kits (Salimetrics, Inc.) were
used to assay salivary alpha amylase and salivary cortisol levels collected in Salivette (Sarst-
edt) containers. Participants were asked to chew on a cotton roll (salivette) for 2 minutes at the
six time points during the study. Salivettes were then placed inside plastic roll retainers and
stored at –20ºC, to enable batch processing. Each saliva sample was assayed for cortisol
using HS-Cortisol enzyme immunoassay kits by Salimetrics LLC. Alpha amylase levels were
expressed in relation to salivary volume for each minute of collection.
Visual Analog Scales (VAS): VAS were used to collect participants’ present levels of self-
reported stress (SVAS) and anxiety (AVAS). Stress on the SVAS is defined as one’s response
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to demanding or unpleasant stimuli or conditions. Anxiety on the AVAS is defined as fear, ap-
prehension, worry. Each scale was 15 cm long and anchored at each end with descriptors of
“none” to “the most severe imaginable.” The authors have used similar scales successfully in
assessing the effect of AAA on anxiety, depression, and fear in adult patients, with acceptable
levels of reliability and validity (Barker, Pandurangi and Best 2003). Barker et al. (2005) re-
ported significant test-retest correlations (r= 0.78, p= 0.0001) on the anxiety VAS, in support
of reliability, as well as significant post-intervention correlations (r= 0.68, p= 0.005) between
patient and nurse ratings, in support of validity.
Pet Attitude Scale (PAS): The PAS (Templer et al. 1981) was used to assess general attitudes
towards animals. The 18 items rated by respondents indicate current agreement with state-
ments related to pets, such as “I would like to have a pet in my home,” using a 7-point Likert
scale ranging from “strongly agree” to “strongly disagree.” Items correlate at least 0.50 with
the total Scale (Templer et al. 1981). The Cronbach’s alpha coefficient is reported to be 0.93.
State-Trait Anxiety Inventory–Trait Form (STAI-T): The STAI-T (Spielberger 1983) measures the
relatively stable personality trait of anxiety. The brief self-report inventory consists of 20 items,
to which respondents indicate how they generally feel on a 4-point scale ranging from
“almost never” to “almost always.” The weighted item responses are summed for a total score,
with higher scores reflecting greater levels of trait anxiety. The internal consistency of the STAI-
T is high, with a median alpha coefficient of 0.92 (Spielberger 1983). The construct validity is
supported by studies showing high correlations between the STAI-T and other standard
measures of trait anxiety (Lazarus and Opton 1966; Spielberger; Gorsuch and Lushene 1970).
Procedure
Three trained research assistants collected the data for this study. Following completion of in-
formed consent, participants were asked to provide basic demographic information (date of
birth, gender, race, and pet ownership) and complete the STAI-T and PAS. They were then pro-
vided with written instructions for their study session day, designating the date and time of their
session, eating and drinking restrictions, and medication use and reporting.
Participants reported to a separate room at the study site where 24 leads were placed on
the scalp by an electroencephalograph (EEG) technician, for continuous EEG recording
throughout the study session. The ambulatory EEG equipment has a long (33 foot) cable, al-
lowing participants to move around the room, if desired, and enables the technician and
recording equipment to remain unobtrusively at a distance. Participants were then seated in
a comfortable recliner chair and asked to simply relax during a 30-minute baseline EEG record-
ing. After the baseline period, the stress and anxiety VAS were administered, followed by HR
and BP measurement. Saliva for cortisol and alpha-amylase was then collected. The Stroop
Color Word Test was administered followed by collection of the same physiological and VAS
data. The wires to the blood pressure cuff were then detached to enable the participant to
more freely interact with the dog. The research assistant walked the dog on a leash into the
room and informed the participant that they were leaving the dog with them for 30 minutes.
They were informed that they were free to interact with the dog however they wished, but that
they must remain in the room and keep the dog leashed.
HR, BP, and VAS were collected during the last five minutes of the intervention. HR and
BP were again collected immediately following the intervention, followed by salivary collection
for cortisol and alpha-amylase. The VAS was then administered. Participants were then asked
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to select one of three neutral 50-minute videos (documentary of the racehorse Seabiscuit,
birds, or space flight). HR, BP, and saliva were collected at 30, 45, and 60 minutes post-
intervention. Before and after the intervention, the dogs were kept in a separate room by
members of the study team or family members/friends, if they accompanied the participant.
Data Analysis
Descriptive statistics were computed for demographic variables, trait anxiety, and pet attitude,
overall and by group (TDO and AAA). T-tests were used to examine statistical differences be-
tween groups for mean age, STAI-T and PAS total scores. Trends in mean outcome meas-
urements of alpha amylase, cortisol, SBP, DBP, HR, anxiety, and stress VAS were examined
in plots by group for up to seven measurement time points: baseline, post-stressor, during the
intervention, and 1, 30, 45 and 60 minutes post-intervention. Changes in outcome measure-
ments were further examined at each time point through computations of differences from
baseline (any measurement minus baseline measurement). Originally planned, repeated meas-
ures models were sought to describe the changes in stress response for both the TDO and
AAA groups. However, when such models failed to converge, paired t-tests were used to test
for significant differences in stress between the primary time points associated with the inter-
vention, that is, from post-stressor to 1 minute post-intervention. We hypothesized decreases
in outcome variables between these time points. Additional analysis focused on the associa-
tions between outcome measures and trait anxiety and the pet attitude scores. These were
examined through Pearson product moment correlations at each time point.
Results
All ten participants completed the study; however, data from one subject in the AAA group
were excluded from analyses after meeting medical exclusion criteria (BP results and observed
illness).
T-tests revealed no significant differences between the TDO and AAA groups on demo-
graphic variables, STAI-T scores or PAS scores. Mean age was 51.5 years (SD = 10.5) for the
TDO group and 48.1 years (SD = 15.8) for the AAA group. PAS mean scores were high for
both groups: 117.2 (SD = 8.1) for the TDO group and 115 (SD = 9.0) for the AAA group,
indicating positive attitudes to pets. Mean STAI-T scores were slightly higher in the AAA group
(36.8, SD = 6.4) than the TDO group (31.0, SD = 4.1). Both groups were primarily female,
with one male in each group, and predominantly Caucasian (one minority in the AAA group).
All participants were current and past pet owners, with all but one in each group owning more
than one dog.
Results are presented for each outcome variable, followed by correlations between the
outcome variables and pet attitude and trait anxiety.
Salivary Alpha Amylase
The alpha amylase response from baseline to each time point showed no particular response
pattern. Therefore, no analysis was conducted for alpha amylase.
Salivary Cortisol
Figure 1 shows the response pattern for salivary cortisol from baseline to each measurement time
point. From baseline, the cortisol response pattern for the AAA group showed a small increase
with the stressor and a negligible mean decrease from baseline of 0.01 (SEM = 0.01) with the
intervention. While the pattern was similar for the TDO group, the changes from baseline showed
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Figure 1. Mean salivary cortisol changes from baseline (with standard
error) in therapy dog owners (TDO) interacting with their own therapy
dog and dog owners interacting with an unfamiliar therapy dog (AAA)
following a stress task (Stroop Color Word Test).
Blood Pressure
Figure 2 shows the SBP and DBP response patterns from baseline to each measurement
time point. Both SBP and DBP showed a negligible response to the stress task for both
groups. There was a negligible drop during the intervention for both groups, which remained
below baseline at 60 minutes post-intervention, with the exception of the TDO group at 1
minute post-intervention. A similar, but non-significant, decline in DBP below baseline was
found through 60 minutes for both groups. The mean change from post-Stroop to 1 minute
post-intervention was negligible for the TDO group. For the AAA group, mean SBP dropped
by 3 mmHg (SEM = 2.88) and mean DBP by 4.05 mmHg (SEM = 2.66).
Heart Rate
As with the other physiological stress indicators, HR changed little from baseline to post-stres-
sor (see Figure 3). During the last 5 minutes of the intervention, HR increased modestly from
baseline for both groups, decreasing by an average of 1.33 (SEM = 1.84) beats per minute, 1
minute post-intervention. Reductions in HR were small and remained below baseline for the AAA
group and were close to baseline for the TDO group throughout the post-intervention period.
Changes in mean HR from post-stressor to 1 minute post-intervention were not significant.
Anxiety and Stress Visual Analog Scales
Anxiety and stress were measured at baseline, post-stressor, during the last 5 minutes of the
intervention, and 1 minute post-intervention. As shown in Figure 4, changes in anxiety and
stress mirrored each other. Anxiety and stress scores for both TDO and AAA groups tended
to increase from baseline to post-stressor, drop below baseline with the dog, and remain below
baseline 1 minute post-dog. Only the mean decrease in stress for the TDO group from post-
stressor to 1 minute post-dog was statistically significant (p= 0.04).
considerably smaller responses to the stressor, but a significant decrease from post-stressor to
1 minute post-intervention (mean = –0.03, SEM = 0.009, p= 0.026). A small, non-significant de-
crease in cortisol was seen for the same period for the AAA group (mean = –0.05, SEM = 0.019).
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Pet Attitude and Trait Anxiety Correlations
Table 1 (on page 88) shows the correlations for the total scores on the Pet Attitude Scale (PAS)
and State-Trait Anxiety Inventory-Trait Form (STAI-T) and the mean outcome measurements
at each time point for the combined subject groups. Significant and relatively high (Cohen et
al. 2003) negative correlations were found between PAS scores and the Anxiety VAS 1 minute
after the intervention, and with the Stress VAS post-stressor, as well as during and 1 minute
after the intervention. Although not significant, moderate negative correlations were noted be-
tween PAS scores and cortisol, SBP, and HR at several time points.
Relatively high and significant positive correlations were found between STAI-T scores and
mean cortisol levels post-stressor and 1 minute post-intervention. The correlations with mean
cortisol levels at all time points following the intervention ranged from 0.59 to 0.70. Significant
and relatively high negative correlations were found with SBP and DBP during the intervention
and with SBP 45 minutes after the intervention. Although not significant, moderate negative
correlations were found between STAI-T scores and SBP and DBP at all time points.
Figure 2. Mean systolic (SBP) and diastolic blood pressure (DBP) changes
from baseline (with standard error) in therapy dog owners (TDO) interacting
with their own therapy dog and dog owners interacting with an unfamiliar
therapy dog (AAA) following a stress task (Stroop Color Word Test).
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Figure 3. Mean heart rate (HR) changes from baseline (with standard
error) in therapy dog owners (TDO) interacting with their own therapy
dog and dog owners interacting with an unfamiliar therapy dog (AAA)
following a stress task (Stroop Color Word Test).
Figure 4. Mean anxiety (AVAS) and stress visual analog scale (SVAS) changes
from baseline (with standard error) in therapy dog owners (TDO) interacting
with their own therapy dog and dog owners interacting with an unfamiliar
therapy dog (AAA) following a stress task (Stroop Color Word Test).
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Discussion
This study explored response patterns in dog owners who interacted with their own or an un-
familiar therapy dog following a stressful task. The small convenience sample of dog owners
were of middle age, predominantly white females owning more than one dog, with positive at-
titudes toward pets. STAI-T scores were close to the mean (31.79, SD = 7.78) for working,
adult females aged 50 –69 years (Spielberger 1983). Although SBP was higher at baseline for
the TDO group, the study focus was on within-group changes.
Only a mild response to the Stroop Color Word Test was observed in the participants, pri-
marily reflected in VAS scores. Thus, the task may have been perceived as a mild stressor by
this sample, particularly with no performance consequences. The small physiological reaction
to stress is consistent with larger studies of dog owners showing reduced cardiovascular
stress reactivity (Allen, Shykoff and Izzo 2001; Allen, Blascovich and Mendes 2002), as well as
studies showing that pets appear to buffer the impact of stressful events (Siegel 1990).
Patterns seen in response to the intervention phase suggest a trend of relaxation associ-
ated with interacting with the therapy dog, whether one’s own or an unfamiliar dog. Significant
differences in salivary cortisol and self-reported stress were found for the TDO group from post-
stressor to immediately post-intervention. Because participants were permitted to interact freely
with their dogs during the intervention, the small increase in HR for both groups during this
period may simply reflect increased movement or activity (petting, talking). Coupled with a pat-
tern suggesting relaxation in the other physiological measures and the decline in HR noted 1
minute after the intervention, the increase in HR does not appear to be indicative of stress.
Table 1. Correlations between Pet Attitude Scale and State-Trait Anxiety Inventory—
Trait Form total scores and mean physiological and self report levels of stress in dog
owners interacting with a therapy dog following a stress test (Stroop Color Word Test).
Baseline Post With 1 min 30 min 45 min 60 min
Stroop Dog Post Dog Post Dog Post Dog Post Dog
Pet Attitude Scale
Amylase U/ml –0.19 –0.21 – 0.09 –0.01 –0.11 -0.29
Cortisol Ug/dl –0.24 –0.50 – –0.35 –0.30 –0.37 -0.13
SBP (mmHg) –0.34 –0.36 –0.12 –0.12 –0.20 –0.30 -0.35
DBP (mmHg) –0.11 –0.22 –0.20 –0.04 –0.16 –0.30 -0.31
HR (bpm) 0.13 0.02 0.15 0.27 0.31 0.33 0.34
AVAS –0.65 –0.60 –0.73 –0.75* – – –
SVAS –0.64 –0.77* –0.78* –0.73* – – –
State-Trait Anxiety Inventory—Trait Form (Y)
Amylase U/ml 0.35 0.06 – 0.33 0.30 0.06 0.40
Cortisol Ug/dl 0.38 0.69* – 0.70* 0.66 0.59 0.64
SBP (mmHg) –0.59 –0.48 –0.79* –0.66 –0.54 –0.68* –0.61
DBP (mmHg) –0.57 –0.45 –0.79* –0.65 –0.53 –0.61 –0.61
HR (bpm) –0.27 –0.15 –0.04 –0.31 –0.37 –0.39 –0.21
AVAS –0.05 –0.24 –0.22 –0.23 – – –
SVAS 0.15 –0.13 –0.23 –0.24 – – –
* p< 0.05; Amylase = Salivary alpha-amylase; Cortisol = Salivary cortisol; SBP = Systolic blood
pressure; DBP = Diastolic blood pressure; HR = Heart rate; AVAS = Anxiety visual analog scale;
SVAS = Stress visual analog scale; – = not collected at that time point.
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Interestingly, while the results suggested dog owners perceived less stress and anxiety
when interacting with their own dogs compared with those interacting with an unfamiliar dog,
other results suggested greater reductions in cortisol, SBP, DBP, and HR for those interacting
with the unfamiliar dog. This pattern is surprising, as some literature suggests a greater benefit
for those with greater pet attachment (Melson, Peet and Sparks 1991; Sable 1995;
Triebenbacher 1998), which would be expected in those interacting with their own dogs.
Larger-scale studies are needed to replicate and test such differences for significance.
Pet attitude was found to be related to several of the outcome measures in this study. Of
particular interest was the strong, significant inverse relationship found between pet attitude
and perceived anxiety and stress, and low to moderate inverse relationships between pet at-
titude and cortisol and SBP. These findings suggest that dog owners with positive attitudes
toward pets may experience stress reduction from interacting with unfamiliar dogs at times
when their own dogs are not present, such as occurs in AAA. These relationships were most
noticeable immediately following the stress task, and during and after interacting with the dog.
Such findings emphasize the need to control for attitudes toward pets in human–animal
interaction research.
Correlations between trait anxiety and outcome measures revealed strong positive and
significant relationships between trait anxiety and cortisol, and moderate to strong inverse re-
lationships between trait anxiety and HR, SBP, and DBP. These relationships were evident pri-
marily after the stress task, during interaction with the dog, and at all time points post-dog
interaction. These response patterns suggest that trait anxiety scores are consistent with un-
derlying physiological stress reflected in cortisol levels, and also provide preliminary evidence
of construct validity of the STAI-T in human–animal interaction research. However, patterns also
reflected decreasing HR and BP levels associated with increasing trait anxiety. With these pre-
liminary findings considered in their totality, we could hypothesize that dog owners might have
developed adaptive responses to their anxiety traits and thus do not show strong hemody-
namic responses to stress. These relationships warrant further investigation, as several stud-
ies conclude that pet ownership may buffer the impact of stressful events (Siegel 1990; Allenet
al. 1991; Allen, Blascovich and Mendes 2002). In this exploratory study, similar patterns were
seen for SBP and HR, but not for cortisol. The differential responses reflected in these
pathways are intriguing and warrant further study.
The self-report measures showed meaningful changes, with both anxiety and stress VAS
scores increasing with the stress task and sharply declining below baseline during and fol-
lowing the intervention. While these results may be partially due to the inability to blind the par-
ticipants to the intervention, most of the physiological results show a similar, albeit less
pronounced, pattern. The relationship between the VAS scales and physiological variables
lend further support to the validity of these brief, self-report scales.
We note several limitations in study design that limit the conclusions that can be drawn from
this exploratory study, notably, the small convenience sample and lack of a comparison group
of non-dog owners or control group, due to resource limitations. Without a control group that
did not have a dog present, conclusions regarding the stress buffering effect of therapy dogs
can not be made. However, the drop below baseline in all measures (except amylase and
SBP for the AAA group) following the dog interaction, and the trend in most measures to re-
main below baseline 60 minutes post interaction suggests a buffering effect in need of further
investigation. We also could not blind the participants to the interventions they received. The
strength of this study lies in the implication of the findings for future human–animal interaction
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90 Anthrozoös
research, specifically 1) the feasibility of a complex design in assessing human–animal
interactions, 2) the consistent physiological patterns suggesting a relaxation effect that was ob-
served in therapy dog owners interacting with their own dog and mirrored in dog owners in
an AAA condition, without the confounding effect of the dog’s handler, 3) the inverse relation-
ship found between pet attitude and both self-report and physiological stress indicators
(cortisol and SBP), 4) the positive relationship found between trait anxiety and salivary cortisol,
5) the inverse relationship found between trait anxiety and autonomic nervous system indica-
tors of stress (HR, SBP, DBP), and 6) further support for the use of simple visual analog scales
in human–animal interaction research.
Acknowledgements
The authors acknowledge the contributions of Dr. Alican Dalkilic for medical screening and
Aaron Wolen for data collection.
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