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Running Head: MEASURING EFFECTS OF A THERAPY DOG INTERVENTION
Measuring Stress and Immune Response in Healthcare Professionals Following
Interaction with a Therapy Dog: A Pilot Study
Sandra B. Barker
Janet S. Knisely
Nancy L. McCain
Al M. Best
Virginia Commonwealth University
Address correspondence and reprint requests to: Sandra B. Barker, Ph.D., Department of
Psychiatry, Virginia Commonwealth University, P. O. Box 980710, Richmond, VA 23298-
0710, Phone 804-828-4570, Fax 804-828-4614, email sbarker@vcu.edu.
Grant Support: This research was supported by The Iams Company and General Clinical
Research Center grant M01 RR00065, MCRR, NIH.
Psychological Reports, 2005, 96, 713-729
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Measuring Stress and Immune Response in Healthcare Professionals Following
Interaction with a Therapy Dog: A Pilot Study
Summary. This study investigated the optimal time for measuring stress and immune function
in 20 healthcare professionals (19 females and 1 male) following interaction with a therapy dog. A
non-clinical sample of healthcare professionals was assigned to 20 minutes of quiet rest, and 5 and 20
minutes with a therapy dog. Serum cortisol, epinephrine and norepinephrine were collected at
baseline, 5, 15, 30, 45, and 60 minutes post condition. Salivary cortisol, salivary IgA, and blood for
lymphocytes were collected at baseline, 30, 45, and 60 minutes post condition. Analysis indicated
significant reductions in serum and salivary cortisol. The optimal time for measuring serum or salivary
cortisol following interaction with a therapy dog was found to be 45 minutes, with changes in salivary
cortisol reflecting serum cortisol changes. Findings also suggest stress reduction in healthcare
professionals may occur after as little as 5 minutes of interaction with a therapy dog and warrants
further investigation.
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Measuring Stress and Immune Response in Healthcare Professionals Following
Interaction with a Therapy Dog: A Pilot Study
Introduction
As the popularity of visiting therapy animals in healthcare settings has grown in the last decade,
researchers have focused on investigating the health benefits of such activities for patients. While a
few authors make distinctions between animal-assisted therapy (incorporation of a therapy animal by a
healthcare professional into a patient’s treatment plan) and animal-assisted activities (less structured
pet visitation by an approved pet and its owner), most studies use the term animal-assisted therapy
broadly to encompass both activities. A number of studies have documented positive outcomes of
such therapy for several patient populations. These outcomes include decreased levels of anxiety, fear,
loneliness, and depression and increased socialization (Barker & Dawson, 1998; Marr, French,
Thompson, Drum, Greening, Mormon, Henderson, & Hughes, 2000; Barak, Savorai, Mavasbev, &
Beni, 2001; Kanamori, Suzuki, Yamamoto, Kanda, Matsui, Kojima, Fukawa, Sugita, & Oshiro, 2001;
Barker, Pandurangi, & Best, 2003).
Several studies have focused on benefits of animal-assisted therapy for hospitalized psychiatric
patients. Decreased anxiety has been reported for patients with a variety of psychiatric diagnoses after
such therapy (Barker & Dawson, 1998). For psychiatric patients waiting for electroconvulsive therapy,
a significant reduction in fear was found after patients spent 15 minutes interacting with a therapy dog
(Barker, Pandurangi, & Best, 2003). In a related study designed to find a difference of Δ = .5, with
power = 70%, a nonsignificant trend (p=.08) toward decreased anxiety was found in a similar sample
after spending time in the presence of a fish aquarium (Barker, Rasmussen, & Best, 2003). Other
authors have reported increased socialization, activity, and responsiveness to surroundings among
psychiatric patients participating in animal-assisted therapy (Marr, et al., 2000). In addition to
increased socialization, improved activities of daily living were reported in a study of elderly patients
with schizophrenia (Barak et al., 2001). Adolescent psychiatric patients have also been found to have
increased socialization (Bardill & Hutchinson, 1997).
In addition to positive outcomes documented in psychiatric facilities, benefits from animal-
assisted therapy have been reported for patients in other healthcare settings, particularly those serving
the elderly. Studying residents in a skilled rehabilitation unit, Jessen et al. found decreased depression
for patients assigned a companion bird (Jessen, Cardiello, & Baun, 1996). Similar reductions in
depression were attributed to therapy with a dog in a study of residents in assisted living facilities and
healthcare communities (Hagman, 1999). Decreased loneliness as well as increased social interaction
and behavior have been associated with such interventions in long-term care facilities (Banks, 1998;
Bernstein & Malaspina, 2000).
While most studies have used psychological measures to assess outcomes, one study assessed
the neurochemical response to human-animal interacton. Although not investigating a patient
population, Odendaal (Odendaal, 2000) completed an initial study of 18 dog owners interacting with
their own and an unfamiliar dog. He found increases in neurochemical indicators of affiliation (beta-
endorphin, oxytocin, prolactin, phenylacetic acid, and dopamine) in both humans and dogs and
decreased stress (measured by serum cortisol) in owners after 5 to 24 minutes of interacting with their
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own or an unfamiliar dog. Only a few published studies have investigated psychoneuroimmunological
enhancement with non-traditional or complementary approaches, and investigators have reported
conflicting results. For example, no significant declines in salivary cortisol were reported after
relaxation activities, music therapy, resting quietly, guided imagery, or watching a humorous movie
(Benson, 1975; Green & Green, 1987; Hubert, Moller, & De Jong-Meyer, 1993; Kirschbaum &
Hellhammer, 1994; Pawlow & Jones, 2002). Practicing Tai Chi, however, was reported to reduce
levels of salivary cortisol (Jin, 1989, 1992). A more recent study showed a significant reduction in
salivary cortisol after 20 to 25 minutes of progressive muscle relaxation (Pawlow & Jones, 2002).
In a review of research related to positive emotional states, Chesney, Darbes, Hoerster, Taylor,
Chambers, and Anderson (in press) provide emerging evidence suggesting that positive emotions can
be associated with health-promoting effects. While research in this area has scarcely begun,
particularly with regard to underlying mechanisms, many of the same mechanisms by which negative
affect might adversely affect health are being investigated from the perspective of opposing
mechanisms through which positive affect may enhance health.
For example, Davidson, Coe, Dolski, and Donzella (1999) reported that greater relative left-
sided prefrontal brain activity, which is associated with positive affect, was associated with larger
increases in NK function in response to films that elicited positive affects. It also has been reported that
an increased positive emotional style was associated, in a dose-response manner, with a lower risk of
developing a cold following a viral challenge. Although positive emotional style was related to lower
levels of epinephrine, norepinephrine, and cortisol, these hormone levels were not significantly
associated with colds (Cohen, Doyle, Turner, Alper, & Skoner, 2003). As a final example, a recently
published study demonstrated that persons with high self-enhancement (a personal characteristic that
emphasizes individuals’ positive qualities) have lower baseline cortisol levels, lower cardiovascular
responses to stress, and more rapid cardiovascular recovery than those with less self-enhancement. The
association between self-enhancement and cortisol was mediated by psychological resources (Taylor,
Lerner, Sherman, Sage, & McDowell, 2003). Each of these groups of investigators suggested that
further work is needed to explain the complexity and dynamics of potential mediation of such
relationships.
Although anecdotal reports and a few surveys have been published indicating positive staff
attitudes to the presence of animals in healthcare facilities ( Chinner & Dalziel, 1991; Cassidy, Webb,
McKeown, & Stiles, 1995), no experimental studies have assessed the effects of brief animal
interactions on healthcare providers, a group known to have high work-related stress levels (Lederberg,
1998; Alexander & Klein, 2001; Killien, 2004). In earlier studies, the current authors readily observed
healthcare providers to break from their hectic workplace and smile, pet, talk to, and briefly play with
therapy animals brought into healthcare facilities. Based on these observations, we were interested in
the possible mediating effect such interactions may have on markers of physiological stress and
immune function in healthcare professionals. With the long-term goal of investigating stress hormone
and immune responses to brief interactions with a therapy dog in the natural environment, the purpose
of this preliminary study was to first investigate this response in a controlled setting. A two-phase
pilot study was therefore conducted. A pre-pilot study was conducted to determine the time required
for cortisol response to return to baseline following venipuncture in healthcare professionals. A pilot
study was then conducted to determine 1) the optimal time for measuring physiological indicators of
stress (salivary and serum cortisol, epinephrine and norepinephrine) and immune function (salivary
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immunoglobulin A and lymphocyte proliferation) following interactions with a therapy dog, and 2) the
correlation between changes in salivary and serum cortisol across time following interactions with a
therapy dog.
Method
Subjects
Healthcare professionals were recruited from inpatient services at an academic medical center
to serve as subjects for a pre-pilot study (n = 5) and pilot study (n = 20). Recruitment posters were
hung in nursing stations. Pre-screens were conducted over the phone to evaluate inclusion/exclusion
criteria. Volunteers who met criteria were invited to participate and appointments were scheduled to
obtain informed consent. The Western Institutional Review Board approved the study procedures and
consent form. Pre-pilot subjects were paid $25 and pilot subjects were paid $50 in cash at the end of
the study. Pre-pilot subjects were ineligible to participate in the subsequent pilot study.
The population of healthcare professionals at this institution was multicultural. The five
subjects participating in the pre-pilot study consisted of four women and one man with a mean age of
47 years (range 33-53). Three subjects were Caucasian, one African American and one Hispanic
American. Two subjects were married, two were separated and one was divorced. The mean years of
education for the group were 15.8 and all were employed full-time as nurses.
The 20 subjects recruited for the pilot study were Caucasian (n = 16), Indian (n = 2), African
American (n = 1), and Hispanic (n = 1) and were primarily female (n = 19). Their mean age was 38.6
years (range 23-58). Ten were married and all subjects had at least a high school education. Most (n =
15) were nurses, followed by resident physicians (n = 2), and occupational therapists (n = 2). Most
subjects were current pet owners (n = 16) and/or had owned pets in the past (n = 18).
Inclusion and Exclusion Criteria
Inclusion criteria for both the pre-pilot study and pilot study were 18 years of age or older and
ability to provide informed consent. Exclusion criteria were active smoking, pregnancy, active use of
anti-inflammatory drugs, and hormonal therapy (e.g., synthyroid), because these conditions have been
found to influence cortisol changes and/or immune function ( Tanaka, Tanaka, Kanemoto, & Tsuboi,
1998; Kirschbaum, Kudielka, Gaab, Schommer, & Helhammer, 1999). A diagnosis of Cushing’s
syndrome and adrenal tumor were also exclusions, as these conditions are associated with abnormally
heightened levels of cortisol (Kirschbaum & Hellhammer, 1989). Likewise, Addison’s disease was an
exclusionary condition as this disease may cause lower than normal levels of cortisol (Berkow, Beers,
& Fletcher, 1997). Subjects were excluded if they were taking any medications that included
prednisone, as it can have a considerable cross-reactivity with the antisera used for cortisol
determination (Kirschbaum & Hellhammer, 1989). For pre-pilot subjects, those taking estrogen were
excluded (Kirschbaum & Hellhammer, 1989). Since the pilot study had a within-subjects design,
subjects were not excluded if they had been taking oral contraceptives or hormone replacement therapy
for at least the past two months and intended to stay on the medication during the study period. For
pilot subjects only, additional exclusion criteria were pet allergies and fear of dogs.
Therapy Dog Intervention
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The medical center in which the study was conducted encouraged approved dogs and their
volunteer owners to visit patients in specified areas of the hospital. The hospital policy on animals in
the medical center required the owner-dog team to meet a series of veterinary, behavioral, volunteer,
and hospital requirements, reflected in national certification programs for therapy dogs. The dog and
handler serving as the intervention were nationally certified (Delta Society Pet Partners) as a therapy
team and approved for hospital visitation in the medical center. The medium-size, 9 year old dog was a
neutered male, husky type dog with over 3 years of hospital visitation experience with children and
adults. The dog’s owner was a 42 year old, Caucasian male. As required by hospital policy, the dog
was bathed within 24 hours of each visit and groomed the morning of each visit. During the
intervention time, the owner was instructed to encourage participants’ interaction with the dog and
focus conversation on the dog and pets in general.
Neuroendocrine Stress Indicators
Well known to increase with stress and reflect hypothalamic-pituitary-adrenal axis reactivity,
cortisol is often selected as a measure of physiological stress. Many studies have reported that salivary
cortisol reliably reflects free serum cortisol levels, and salivary cortisol has been extensively used as an
outcome measure to investigate the body’s physiological response to stressors (Vining, McGinley,
Maksvytis, & Ho, 1983; Kahn, Maxwell, & Barron, 1984; Kirschbaum & Hellhammer, 1989;
Kirschbaum & Hellhammer, 1994). In our pilot study in a controlled setting, no stressor was
introduced; rather, we were interested in determining the timeline for changes in salivary cortisol and
in free serum cortisol levels after presumably positive interaction with a therapy dog. Measuring
salivary cortisol, as opposed to serum, avoids the introduction of stress known to be associated with
venipuncture (Kirschbaum & Hellhammer, 1994) and has been found to be unrelated to salivary flow
(Kirschbaum & Hellhammer, 2000). Use of this simple, relatively unobstrusive measure to document
changes over short time periods will have important implications for future studies with animal and
other potentially immunoenhancing complementary interventions. Many studies have documented the
strong relationship between serum and salivary cortisol values (Holm, 1995); however, this study was
focused on the relationship between the change in serum to change in salivary cortisol across time in
non-stressed subjects. Because of normal circadian changes, cortisol concentration and pulse
amplitude are highest in the early morning and fall considerably before mid-day. This study was
conducted in the afternoon, when cortisol levels are most stable, in an effort to more accurately
measure short-term changes due to the interventions (Kirschbaum & Hellhammer, 1989).
In addition to hypothalamic-pituitary-adrenal axis reactivity, Frankenhaeuser (1991)
recommends including measures of the sympathetic-adrenal-medullary system (SAM) in stress-related
studies. For this pilot study, epinephrine and norepinephrine were selected as measures of SAM
reactivity. While changes in epinephrine and norepinephrine are reported to occur more quickly than
cortisol, salivary samples of these neuropeptides do not accurately reflect plasma levels (Jasnoski &
Kugler, 1987). Therefore, only plasma levels of these stress-related neuroendocrine mediators were
measured.
Immune Stress Indicators
While high levels of cortisol have been shown to have detrimental anti-inflammatory and
immunosuppressive effects (Schurmeyer & Wickings, 1999), there have been few studies evaluating
immunoenhancement through complementary therapies. Because AAT has been shown to have
positive psychological effects, the investigators were interested in any immunoenhancement effect of
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therapy animals. Salivary immunoglobulin-A (sIgA) and lymphocyte proliferation were selected as
outcome measures for this study. IgA is important in mucosal immunity and is found in respiratory
and gastrointestinal secretions as well as in salivary and mammary glands and tear ducts (Westermann
& Exton, 1999). sIgA has been found to increase following relaxation techniques and to decrease with
psychological stress (Jasnoski & Kugler, 1987; Kugler, Reintjes, Tewes, & Schedlowski, 1996;
Sherman, Carlson, McCubbin, & Wilson, 1997). Although measurement of lymphocytes requires
venipuncture, lymphocytes are known to be the primary cells responsible for specific (acquired)
immune responses (Westermann & Exton, 1999). Lymphocyte proliferation has also been found to
decrease in response to psychological stress and may also serve as a measure of immunoenhancement
(Weisse, Pato, McAllister, Littman, Breier, Paul, & Baum, 1990; Gloger, Puente, Arias, Fischman,
Caldumbide, Gonzalez, Quiroz, Echavarri, & Ramirez, 1997).
Pre-pilot Study
A pre-pilot study was conducted to measure salivary and serum cortisol levels following
venipuncture to determine the appropriate recovery period to use in the pilot study. After informed
consent, five subjects were scheduled for an assessment visit in the General Clinical Research Center
of the medical center. Study dates were scheduled such that no subject had to make a shift change
(from days to nights or vice versa) 24 hours prior to the visit, because partial and/or acute sleep
deprivation may alter the normal functioning of the hypothalamic-pituitary-adrenal axis, thus altering
cortisol levels following sleep deprivation and during the subsequent recovery period (Leproult,
Buxton, & Van Cauter, 1997; Vgontzas, Mastorakos, Bixler, Kales, Gold, & Chrousos, 1999). To
minimize the discomfort (and associated stress) of repeated venipunctures, blood samples were drawn
using an indwelling venous catheter. Prior to the insertion of a catheter, subjects were provided with a
topical anesthetic, and instructed by a nurse on its proper application. Subjects were also instructed not
to eat (including gum or candy) or drink anything, except water, for 30 minutes prior to the study.
At the scheduled visit, subjects were escorted to the treatment room and an intravenous catheter
was inserted in the hand or arm (pretreated with topical anesthetic) by the nurse. To assess cortisol, a
saliva sample was collected prior to catheterization and both saliva and blood samples were collected
at 0 (baseline), 5, 10, 15, 20, and 30 minutes post-catheterization. Between 0.5-1 ml saliva was
collected within one minute by passive drool through a straw (since this method would be used in the
pilot study to collect saliva for both cortisol and IgA) into a cyrovial for salivary cortisol. For serum
cortisol, 4 ml of blood were collected in vacutainer tubes without preservative. Levels of salivary
cortisol were determined using high sensitivity cortisol enzyme immunoassay (ELISA) kits
(Salimetrics, Inc.), and serum cortisol levels were determined using radioimmunoassay tests (American
Laboratory Products Company), following the manufacturers’ instructions.
To determine the recovery time following venipuncture, analysis of a bivariate fit of serum and
salivary cortisol by duration showed a return to baseline 15 minutes after venipuncture. Since both
salivary and serum cortisol levels were stable by 15 minutes post-venipuncture, 15 minutes was used
as the time period between venipuncture and baseline measurements for the pilot study.
Pilot Study Procedures.
Following informed consent, participants were scheduled for three study visits at either 1:00
PM or 3:00 PM in the clinic: Monday visits entailed the 20-minute rest (comparison) condition, and
Tuesday/Thursday visits involved 5 and 20 minutes with a therapy dog (treatment condition). Session
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order was counter-balanced so that half of the subjects received the 5- and 20-minute AAT sessions on
Tuesday and Thursday, respectively, and the other half received the 20- and 5-minute sessions on
Tuesday and Thursday, respectively. Subjects were scheduled at the same study time for all three
days. The same procedures as described for the pre-pilot study were followed for avoiding shift
changes, applying the topical anesthetic, avoiding eating and drinking, and inserting the intravenous
catheter. Subjects were allowed to adjust to the treatment room after catheter insertion for 15 minutes
(recovery time determined by the pre-pilot study) prior to baseline sample collection. During this time,
demographics and information regarding pet ownership were collected.
Specimen collection involved collection of between 0.5-1 ml saliva within one minute by
passive drool through a straw into a cyrovial. Each saliva sample was used for both salivary cortisol
and sIgA assays. Seven ml of blood were collected for serum cortisol (in vacutainers without
preservative) and plasma epinephrine and norepinephrine (in vacutainer tubes with EDTA) assays.
Ten ml of blood were collected in heparinized tubes for lymphocyte proliferation assays. Saliva and
blood samples for salivary cortisol, sIgA, and lymphocyte proliferation were collected at baseline and
30, 45, and 60 minutes post-intervention. Blood samples for serum cortisol, epinephrine, and
norepinephrine were collected at baseline and 5, 15, 30, 45, and 60 minutes post-intervention.
Assay Procedures
Salivary cortisol and sIgA. After collection, saliva samples were stored in a -20 degree Celsius
freezer until all samples had been collected. Prior to assay, saliva was thawed completely, vortexed,
and centrifuged at 1500 x g (@3000 rpm) for 15 minutes. Clear samples were then pipetted into
appropriate wells and tubes. Levels of salivary cortisol were determined using high sensitivity cortisol
ELISA kits and levels of IgA were determined using salivary secretory IgA indirect ELISA kits (both
kits by Salimetrics, Inc.), following manufacturer’s instructions.
Serum cortisol, plasma epinephrine and norepinephrine. After collection, blood samples were
centrifuged and then frozen in a -20 degree Celsius freezer where they were kept until all samples had
been collected. Serum cortisol levels, plasma epinephrine and norepinephrine levels were determined
using radioimmunoassay tests (American Laboratory Products Company), following the
manufacturer’s instructions.
Lymphocyte Proliferation. After collection, blood samples were stored briefly (less than 4
hours) at room temperature, followed by lymphocyte separation using Becton-Dickinson CPT®
separator tubes. Lymphocytes were then cryopreserved using a controlled-rate freezer and stored in
liquid nitrogen until they were thawed and batch processed for each participant to reduce interassay
variability. Lymphocyte proliferation levels were determined using the
3
sam-thymidine incorporation
assay. Purified lymphocytes (1 x 10
6
cells) were incubated with or without concavalin A (ConA) in
triplicate in a 96-well plate for 72 hours in a CO
2
incubator. Lymphocyte proliferation was determined
by calculating cellular uptake of radioactively labelled thymidine by stimulated cells in comparison to
resting cells.
Data Analysis
A repeated-measures ANOVA was used to model the response variables across time and
between the three conditions. Similar analyses were conducted for each of the secondary measures
(sIgA, lymphocyte proliferation, salivary and serum cortisol, epinephrine, norepinephrine). Pearson
9
correlations were used to estimate the strength of the relationship between changes in salivary cortisol
and serum cortisol.
The distribution of most of the response variables was positively skewed; therefore a log-
transformed value was used for all analyses except lymphocyte proliferation. Since the change across
time was of interest, a change score was then calculated (measurement – baseline, where ‘baseline’
was the log-transformed time 0 value and ‘measurement’ was the log-transformed subsequent value).
The log of a zero measured value was analyzed as a small positive number; this adjustment was
necessary for only a few measurements. Each subject’s values were measured under the three different
conditions and up to 5 non-baseline time points. Therefore, a mixed-model repeated-measures
ANOVA was used. An interaction test was used to verify that differences across time or between
groups were consistent.
Secondary analyses were performed for any measures found to significantly change following
the interventions. Least squares means were calculated for each condition-duration combination to
determine change from baseline. These data were back-transformed to estimate the ratio of the value
at each time point relative to the value at baseline. For each of the three conditions, baseline geometric
means and the relative change from baseline are reported with 95% confidence intervals on these
estimates. For those measures for which significant differences were found, figures are presented
which show the 95% confidence intervals for each point. If the 95% confidence interval does not cross
the baseline ratio = 1 line, then the value is different from baseline. These figures are helpful in
determining optimum assessment times for measures that significantly changed following the
interventions.
Results
Thirty-two subjects began the study. Twelve subjects were unable to complete the study after
completing informed consent. Three subjects cancelled because of their own or family illness, six had
work schedule changes that conflicted with the study times, one subject became ineligible when she
resumed smoking, and two subjects did not complete for unknown reasons. A total of 20 subjects
completed the study.
At baseline, there were no significant differences on any of the outcome measures by gender,
marital status, race, pet ownership, or order of intervention presentation (5 minute dog condition versus
20 minute dog condition). The baseline values for each of the outcome measures are shown in the top
row of each section of Table 1. The serum cortisol findings from the mixed-model repeated-measures
ANOVA are first presented in some detail with reference to the top section of Table 1. Findings from
the other variables (salivary cortisol, epinephrine, norepinephrine, salivary IgA, and lymphocyte
proliferation) are summarized and the details of the comparisons may be seen in the other sections of
Table 1.
Serum Cortisol
At baseline, serum cortisol was in the normal range (Elin & Wyngaarden, 1988) for all three
conditions (95% CI = 10.3–13.8 μg). These results confirmed that the 15-minute rest period following
venipuncture was sufficient for recovery from possible stress related to venipuncture. Results of the
mixed-model repeated-measures ANOVA for serum cortisol showed that there was a significant
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change across time [see Table 1, section 1, p < .0001], with a decrease in cortisol for all three
conditions, but there was no significant difference between the three conditions [Table 1, change %, p
= 0.11]. Within each condition, a significant difference was found across the 5 time points. Within the
20-minute resting condition the ratio of serum cortisol to baseline cortisol at 45 minutes was 69.8%, a
significant decrease across all five time points [Table 1, p = 0.0007]. Within the 5-minute dog
condition serum cortisol decreased to 85.8% [Table 1, p = 0.02], and within the 20-minute dog
condition serum cortisol decreased to 77.4% [Table 1, p = 0.001]. Although overall the conditions
were not different, at each time point after 5 minutes post-treatment the difference between the three
treatment values approached significance suggesting a possible dose effect (ps < .2). This effect-size
may be seen in comparing the 95% confidence intervals of the change % estimates for each condition.
The least squares means showed significant declines in serum cortisol detected 15 minutes after
the 20-minute rest condition and the 20-minute dog condition. These were maintained at 30, 45, and 60
minutes. There was also a significant decline following the 5-minute dog condition that reached
significance at 45 minutes and was still detected at 60 minutes. As can be seen in Figure 1, there was
no significant change from baseline in serum cortisol at 5 minutes post-condition, but by 45 minutes,
levels for all three conditions were significantly lower than baseline.
Salivary Cortisol
The results for salivary cortisol are summarized in the second section of Table 1. Baseline
salivary cortisol were not different for the three conditions (95% CI = 0.139–0.195). There was a
significant decrease in cortisol across time [p = 0.004] and the decrease was consistent for the three
conditions. However, follow-up results indicated that only in the comparison condition (20-minute
rest) could it be demonstrated that they had different means at the 3 time points (p = 0.003). Two
samples were below detectable levels and were analyzed as log (0.005).
Least squares means showed a significant change in salivary cortisol at 30 minutes for both 20-
minute conditions that was maintained at 45 and 60 minutes (see Figure 2).. By 45 minutes, all three
conditions were significantly lower than baseline.
Epinephrine
The results for epinephrine are summarized in the third section of Table 1. Baseline
epinephrine were not different for the three conditions (95% CI = 7.79–15.53 pg/ml). Four sample
measurements per occasion were at the non-detectable level and these were analyzed as log(0.5). The
mixed-model repeated-measures ANOVA for epinephrine showed no evidence for a change across
time [p = 0.79] or differences between groups [p = 0.49].
Norepinephrine
The results for norepinephrine are summarized in the fourth section of Table 1. Baseline
norepinephrine were not different for the three conditions (95% CI = 2.96–9.10 pg/ml). As many as 1-
sample measurements per occasion were at the non-detectable level and these were analyzed as
log(0.5). Results for norepinephrine showed no evidence for a change across time [p = 0.36] or
differences between groups [p = 0.68].
Salivary IgA (sIgA)
The results for sIgA are summarized in the fifth section of Table 1. Baseline median values for
sIgA were not different for the three conditions (95% CI = 347–526 μg/ml). Results for sIgA showed
11
no evidence for a change across time [ p = 0.14] or differences between groups [p = 0.34]. However,
with quiet rest, there was a significant reduction in sIgA across time [p = 0.03]. The least squared
means showed sIgA was significantly lower than baseline at 60 minutes after quiet rest.
Lymphocyte Proliferation
The results for sIgA are summarized in the last section of Table 1. There was no difference in
baseline values for lymphocyte proliferation in response to ConA (ConA value– unstimulated value)
(95% CI =43631–58375 μg/ml). The results showed no significant difference across time [p = 0.69] or
between conditions [p = 0.83].
Target Times for Detecting Change
For future studies of interventions using therapy dogs, this study addresses the optimal time to
measure these physical stress markers. Although multiple variables were measured, significant
changes over time were only found for the response measures of salivary and serum cortisol. All three
conditions were different from baseline on salivary and serum cortisol by 45 minutes. Therefore, 45
minutes post-intervention appears to be an optimal time to obtain samples.
Relationship Between Salivary and Serum Cortisol
While many studies document the strong relationship between serum and salivary cortisol
values, this analysis focused on the relationship between the change in serum to change in salivary
cortisol at the target sampling time of 45 minutes. Results support the positive and significant
relationship between the two change values (r = 0.34, p = 0.009). The results are consistent at 30
minutes (r =0.26, p = 0.04).
Discussion
The results of this preliminary study provide direction for future investigations of the
benefits of animal-assisted therapy in healthcare facilities. The purposes of this study were to
determine 1) the optimal time for measuring physiological indicators of stress (salivary and serum
cortisol, epinephrine and norepinephrine) and immune function (sIgA and lymphocyte proliferation)
following animal-assisted therapy, and 2) the correlation between changes in salivary and serum
cortisol across time following interactions with a therapy dog.
In identifying the optimal time for measuring these indicators of stress and immune function,
we looked first at the assessment times at which outcome measures were significantly different from
baseline for both intervention conditions. Serum and salivary cortisol were the only measures meeting
this criterion and both were significant at 45 and 60 minutes. Therefore, 45 minutes after AAT appears
to be the optimal time for assessing these measures of stress.
The second purpose was to determine if any changes in salivary cortisol reflected changes in
serum cortisol. The relationship between the change in serum to change in salivary cortisol at the
target sampling time of 45 minutes showed the two changes are correlated. Based on these pilot test
results, changes of salivary cortisol in response to interaction with a therapy dog reflect underlying
changes in serum cortisol and, thus, saliva only may be used as an outcome measure in future studies.
As a pilot, this study has a number of limitations. A convenience sample of volunteers was
obtained and the sample size was small. Therefore, generalizations to other healthcare professionals
12
should be made with caution. While a counterbalanced, within-subjects design in a controlled setting
was implemented to minimize threats to internal validity, a true counterbalance was not obtained (13
subjects received the 5-minute treatment first, and 7 received the 20-minute treatment first). Statistical
analysis was conducted on the effect of order and no such effect was found.
Several results appeared in the physiological data regarding the effectiveness of animal-assisted
therapy that are worth noting. The small sample size and the large variability in these
psychoneuroimmunology-based variables prevent any firm inferences from being made. A larger study
based on these pilot study results will permit such inferences regarding the effectiveness of animal-
assisted therapy on stress and immune function indicators in healthcare professionals.
Serum and salivary cortisol were found to consistently decline in healthcare professionals
following 5- and 20-minute interactions with a therapy dog, and after 20 minutes of quiet rest. The
pattern found is clearly not related to expected ultradian cortisol bursts or patterns. With no between-
group differences, these results suggest that the 5-minute interaction with the dog is associated with
cortisol reduction equivalent to a 20-minute intervention or 20 minutes of quiet rest. Such results have
important implications, since 20-minute interventions for stress reduction are not practical for busy
healthcare professionals in their natural settings, while 5-minute interventions may be feasible.
However, the data did suggests a possible dose-dependent effect of greater stress reduction with longer
exposure to the dogs, indicating that further investigation with larger sample sizes is needed to assess
this effect. In addition, based on the epinephrine and norepinephrine results, neither the brief nor
longer interactions with the dog were associated with even mild stress for the healthcare providers.
The significant change in salivary IgA 60 minutes after quiet rest is interesting, particularly
since the reduction is in the opposite direction of what we would expect. This effect of reduced sIgA
at 60 minutes was not seen in either treatment condition. Other studies have found sIgA to decrease
with psychological stress, however these subjects were at rest. Perhaps the participants in this study
were not able to relax in close proximity to their work settings. Further studies are needed to
investigate whether resting quietly in a controlled setting may eventually become stressful for
healthcare professionals. There was no related increase in cortisol to support this explanation,
however. While salivary flow was not measured in this pilot study of healthy subjects, flow rate may
have an effect on sIgA outcomes. Collecting sIgA over a longer timeframe may also present different
results.
Also important for future studies is the recovery period identified following venipuncture.
Fifteen minutes appears to be sufficient for healthcare providers to recover from stress that may be
associated with venipuncture.
No attempt was made in this pilot study to separate the effects of the dog from its handler. If
physiological effects are found in larger studies, component analyses will be an important next step to
determine how much of the effect is due to the animal versus the handler.
In the controlled setting of this study, most of the stress values were in the low range, with a
number of values so low as to be nondetectible. Such low values present a challenge to assessing
further reductions due to an intervention. Replicating this study in the natural setting (with its inherent
stressors) with a larger sample may shed further light on the impact of therapy animals on
psychoneuroimmunological indicators in healthcare providers.
13
Acknowledgements
The authors thank Stephanie Fox, Ph.D., for her valuable assistance with data collection, and
Jay McLaughlin, M.S., and his therapy dog Ivory, for their valuable contributions as the treatment
intervention.
14
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17
Table 1
Comparison of conditions at baseline and across time
20-minute quiet
rest
5-minute
treatment
20-minute
treatment
Serum Cortisol
p-
value
Baseline (μg/dl) 12.31 10.76 12.73
(9.77- 15.5) (8.1- 14.28) (9.64- 16.81)
Change % 69.8 85.8 77.4 0.11
(60.8- 80.0) (75.3- 97.6) (67.6- 88.5)
p-value 0.0007 0.02 0.001 <.0001
Salivary Cortisol
Baseline (μg/dl) 0.177 0.155 0.162
(0.144- 0.217) (0.12- 0.2) (0.105- 0.25)
Change % 67.1 67.1 73.6 0.94
(57.2- 78.8) (50.3- 89.5) (58.9- 92.1)
p-value 0.003 0.14 0.19 0.004
Epinephrine
Baseline
(pg/ml)
9.42 15.14 9.35
(5.16- 17.18) (9.06- 25.28) (4.45- 19.65)
Change % 100.6 102.8 134.9 0.49
(67.7- 149.7) (70.5- 150.0) (86.3- 210.7)
p-value 0.25 0.89 0.95 0.79
Norepinephrine
Baseline
(pg/ml)
3.80 7.50 4.91
(1.43- 10.1) (2.53- 22.27) (1.79- 13.44)
Change % 215.2 198.0 128.4 0.68
(90.1- 514.1) (71.5- 548.2) (50.6- 325.6)
p-value 0.65 0.65 0.69 0.36
Salivary IgA
Baseline (μg/dl) 415.7 410.4 456.7
(280.7- 615.5) (278.9- 603.9) (314.3- 663.8)
Change % 83.1 105.7 100.0 0.34
(62.4- 110.7) (81.9- 136.5) (76.2- 131.3)
p-value 0.03 0.60 0.95 0.14
Lymphocyte proliferation response to ConA
Baseline (μg/dl) 45593 53094 54639
(34184- 5
7003) (39023- 67166) (39429- 69850)
Change % 120.4 99.3 103.0 0.83
(87.6- 165.5) (71.5- 137.9) (79.0- 134.2)
p-value 0.19 0.30 0.22 0.69
18
Notes: The "baseline" values are the geometric mean values within each condition and the
associated 95% confidence intervals in parentheses. The "% change" values are the ratio of the
geometric mean at 45 minues to the baseline geometric mean, expressed as a percentage. The
95% confidence intervals on the 45-minute change from baseline are also shown for each
condition in parenthases. The "p-value" shown in the "Change %" row tests whether the
conditions were different. The "p-value" row shows the result of the test of change across up to
5 time points separately for each condition and then, in the final columns the test of change
across up to 5 time points in any of the three conditions.
19
Figure 1
Change in serum cortisol over time
Serum Cortisol
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 1020304050
Time (minutes)
Baseline Ratio
60
20 min. rest
5 min. dog
20 min. dog
baseline
20
Figure 2
Changes in salivary cortisol over time
Salivary Cortisol
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 10203040506
Time (minutes)
Baseline Ratio
0
20 min. rest
5 min. dog
20 min. dog
baseline
