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Pet Ownership, but Not ACE Inhibitor Therapy, Blunts
Home Blood Pressure Responses to Mental Stress
Karen Allen, Barbara E. Shykoff, Joseph L. Izzo, Jr Abstract—In the present study, we evaluated the effect of a nonevaluative social support intervention (pet ownership) on
blood pressure response to mental stress before and during ACE inhibitor therapy. Forty-eight hypertensive individuals
participated in an experiment at home and in the physician’s office. Participants were randomized to an experimental
group with assignment of pet ownership in addition to lisinopril (20 mg/d) or to a control group with only lisinopril (20
mg/d). On each study day, blood pressure, heart rate, and plasma renin activity were recorded at baseline and after each
mental stressor (serial subtraction and speech). Before drug therapy, mean responses to mental stress did not differ
significantly between experimental and control groups in heart rate (94 [SD 6.8] versus 93 [6.8] bpm), systolic blood
pressure (182 [8.0] versus 181 [8.3] mm Hg), diastolic blood pressure (120 [6.6] versus 119 [7.9] mm Hg), or plasma
renin activity (9.4 [0.59] versus 9.3 [0.57] ng · mLϪ1 · hϪ1). Lisinopril therapy lowered resting blood pressure by
Ϸ35/20 mm Hg in both groups, but responses to mental stress were significantly lower among pet owners relative to
those who only received lisinopril (PϽ0.0001; heart rate 81 [6.3] versus 91 [6.5] bpm, systolic blood pressure 131 [6.8]
versus 141 [7.8] mm Hg, diastolic blood pressure 92 [6.3] versus 100 [6.8] mm Hg, and plasma renin activity 13.9 [0.92]
versus 16.1 [0.58] ng · mLϪ1 · hϪ1). We conclude that ACE inhibitor therapy alone lowers resting blood pressure,
whereas increased social support through pet ownership lowers blood pressure response to mental stress. (Hypertension.
2001;38:815-820.)
Key Words: blood pressure Ⅲ social support Ⅲ stress Ⅲ lifestyle Ⅲ pets
Antihypertensive agents are known to reliably lower uals with pets are buffered from the impact of stressful life resting blood pressure, but most of these drugs have events and make fewer visits to physicians14; among persons little effect on blood pressure responses to physical or mental with AIDS, pet owners have a lower incidence of depression stressors.1,2 Because individuals who experience pronounced, than do those without pets.15 Finally, service dogs have a frequent, or enduring autonomically mediated cardiovascular positive influence on the well-being, self-esteem, and com- responses to stress may be at risk for the development of munity integration of persons with disabilities.16 cardiovascular disease,3,4 variables that moderate or mediate In the present study, we extended previous laboratory reactivity to stress are important to consider. Several stress-reactivity and social support research to include home laboratory- and community-based studies have focused on the data in randomly assigned pet owners administered the ACE potential role of social support in buffering reactivity to inhibitor lisinopril. We hypothesized that the acquisition of a mental stress5–9 and have found that when social support pet would reduce heart rate, blood pressure, and renin participants are perceived as supportive and nonevaluative, a responses to psychological stress among a group of hyper- tensive individuals in a high-stress profession (stockbrokers).
Although considerable attention has been devoted to the The design we used made it possible to demonstrate the definition and measurement of social support as it relates to independence of blood pressure reactivity from basal blood health,10,11 most of this literature assumes that benefits are provided only by humans. In recent years, however, severalstudies have documented that pet animals also can have an important supportive role and a positive influence on thehealth of their owners. Pet ownership is a significant predictor Participants and Setting
of 1-year survival after myocardial infarction.12,13 Relative to Participants were hypertensive patients with a high-stress occupa-tion. A pretest-posttest control group design was used17 in 48 the support of friends and spouses, the presence of a pet volunteers who had uncomplicated stage IIϩ hypertension (resting elicits significantly lower blood pressure and heart rate blood pressure Ն160/100 mm Hg). Of the 24 men (18 white and 6 reactivity during mental stress.5 In addition, elderly individ- black) and 24 women (18 white and 6 black), all were interested in Received December 26, 2000; first decision February 23, 2001; revision accepted March 26, 2001.
From the Division of Clinical Pharmacology, Department of Medicine, State University of New York at Buffalo.
Correspondence to Karen Allen, PhD, Division of Clinical Pharmacology, Department of Medicine, State University of New York at Buffalo, Millard Fillmore Hospital, 3 Gates Circle, Buffalo, NY 14209. E-mail [email protected] 2001 American Heart Association, Inc.
Hypertension is available at http://www.hypertensionaha.org
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Six-Month Results for Lisinopril and Pet Ownership: F Values for Main Effects
and Interactions With SBP, DBP, HR, and PRA
stress reduction and agreed to acquire a pet if chosen to do so.
Six months later, the data collection procedure just described was Participants were randomized to a control group without pets (nϭ24) repeated (in both the physician’s office and in the homes of or an experimental group (nϭ24) who subsequently acquired pets.
participants). Pet owners performed the second phase of the homeexperiment in the presence of their pets, which roamed freely throughout the room in which data collection took place.
All participants completed baseline mental stress sessions in theirhomes after 1 month of observation. All participants then were Data Analysis
treated with lisinopril (20 mg/d). Those assigned to the pet owner The main analysis was a repeated measures ANOVA before and group acquired their animals at the time drug therapy began. All during drug therapy, with tasks (MAT and speech) as within-subjects participants were evaluated again at 6 months with a second home factors and pet ownership status and score on self-report social mental stress session. Dependent measures were systolic blood support scale (categorized as high or low) as between-subjects pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and factors. All analyses were performed separately for SBP, DBP, HR, plasma renin activity (PRA). Participant ratings of stress and coping and PRA. Additional repeated measures ANOVAs addressed home were assessed both before and after each stressor.
versus office blood pressure values and a comparison of MATperformance before and with drug therapy and pet ownership.
Stressors
An expanded Methods section can be found in an online data Stressors included mental arithmetic task (MAT) and speech, both of supplement available at http://www.hypertensionaha.org.
which have been used in numerous laboratories18 to produce sub-stantial increases in cardiovascular response.
Physiological Recording Instrument
Physiological Responses: Experimental Findings
HR, SBP, and DBP were recorded automatically once each minute ANOVAs for SBP, DBP, and HR revealed that before throughout the experiment with a portable Propaq monitor (model individuals began drug therapy or acquired pets, there were main effects (PϽ0.01) for social support and for tasks (MATand speech), as well as for social supportϫtask interactions, Procedures
but no effects by assigned pet ownership status. Before drug After participants provided written informed consent, they wereseated in a quiet room, and the Propaq blood pressure cuff was therapy and pets, ANOVA results for PRA also revealed main attached. Resting HR, SBP, DBP, and PRA then were assessed and effects (PϽ0.01) for MAT and speech but not for social recorded. In addition, participants completed a questionnaire about social support.19 Later in the same day, participants performed 2 The Table includes SBP, DBP, HR, and PRA ANOVA psychologically stressful tasks in their homes according to a standard summary data after 6 months with lisinopril and pets; except laboratory paradigm. HR, SBP, and DBP were recorded once eachminute throughout the experiment. Renin was assessed 3 times (ie, for DBP during MAT, main effects are shown for pet after the initial rest and after each of the stressful tasks).
ownership condition as well as social support and tasks for After this home experiment, all participants in both the experi- SBP and DBP. Results for HR and PRA are similar but mental and control groups began lisinopril therapy (20 mg/d) with include no main effects for social support. In addition, the the goal of blood pressure within a normal range (Ͻ130/90 mm Hg).
Table shows significant 2-way interactions (between pet Black participants also received 12.5 mg/d hydrochlorothiazide. Atthe time they began drug therapy, individuals in the experimental condition and tasks and between social support and tasks) for group were instructed to acquire a pet cat or dog.
all dependent variables, as well as 3-way interactions among Allen et al
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Figure 1. SBP and DBP reactivity (mean [SEM]) in response to MAT and speech both before and during lisinopil therapy and the pres-
ence of a pet.
pet condition, social support, and tasks for all dependent ratios after participants received lisinopril and acquired pets.
Results revealed a main effect for ratio (Fϭ166.90, PϽ0.001) Figure 1 provides SBP and DBP reactivity for each task, and an interaction effect for lisinopril and pet ownership and Figure 2 provides HR and PRA (both before and during (Fϭ140, PϽ0.001.) That is, at the second data collection drug therapy). At the beginning of the study, all participants point (after the acquisition of pets), pet owners had signifi- had stage II hypertension (Ͼ160/100 mm Hg), and after 6 cantly greater improvements in their task performances than months, average blood pressures in both the lisinopril-only and the lisinopril-and-pet groups were within the normalrange. At month 1, MAT and speech elicited significant Discussion
increases in physiological responses of both groups. After 6 In the present study, we examined the effect of pet ownership months, however, relative to those without pets, individuals on cardiovascular responses to psychological stress among a with pets had significantly lower reactivity scores; their group of hypertensive individuals in high-stress professions.
On the basis of these results, we conclude that reactivity andbasal blood pressure are influenced by independent mecha- Comparisons of Office With Home Blood Pressure
nisms; that is, ACE inhibitor therapy lowers only resting Before participants received the medication and acquired blood pressure, whereas the addition of a social support pets, there was a significant difference between office and intervention lowers responses to stress. These results extend home mean SBP (Fϭ2089.36, PϽ0.001) and DBP earlier findings that ACE inhibition fails to diminish BP or (Fϭ4499.23, PϽ0.001) values. When individuals were ad- HR responses to stressful tasks1 to demonstrate a beneficial ministered medication and acquired pets, blood pressure was influence of social factors that may buffer stress responses for again higher in the office than in the home (SBP [Fϭ344.94, persons with hypertension who are treated with ACE PϽ0.001] and DBP [Fϭ1657.37, PϽ0.001]). There were no other main effects associated with these differences.
Interestingly, we found that an individual’s assessment of his or her general social environment was predictive of that Performance Data
person’s BP and HR responses to stress. Even though we did MAT performance was computed for each participant as a not investigate the effect of the presence of friends on ratio between the number of correct answers and the number reactivity, participants who perceived that they belonged to a of attempted answers. We were interested in a comparison of group and had friends to confide in had a lower reactivity to ratios before participants had received lisinopril and pets with stress than did their counterparts who reported few social 818
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Figure 2. HR and PRA reactivity (mean [SEM]) in response to MAT and speech both before and during lisinopril therapy and the pres-
ence of a pet.
contacts. These results suggest that persons with low social voluntary meeting, and all dog owners and most cat owners support systems are likely to benefit in particular from the brought their pets with them to the session. The consensus enhanced environment that pets can provide.
response with the highest rating was: “Having this pet makes Improved task performance was also associated with pet me better able to see what is really important and to put things ownership. At the beginning of the study, participants in both into perspective.” When asked about increased responsibility the control group (lisinopril only) and the experimental group and similar issues, participants responded that the positive (lisinopril and pet ownership) had 74% correct performance.
aspects far outweighed any added expense or responsibility At the second data collection point, however, participants and that they would never give up their pets. Because only with pets had 92% correct performance, whereas their coun- persons who would agree to acquire pets were eligible to terparts without pets remained at 75%. This finding is notable participate in our study, however, we cannot comment on because improved task performance suggests that participants whether individuals who are not inclined to like animals did not abandon the task because they perceived their pets to would develop similar relationships with pets.
be pleasant distractions. In addition, although ACE inhibitor The issue of demand characteristics (expectations uninten- therapy has been associated with either improved or impaired tionally conveyed from the investigator to the participants) is cognitive function,20 in our study lisinopril alone did not have an important factor in behavioral research. Consequently, at any influence on cognition, and cognitive improvement the beginning of our project, we did not reveal our hypotheses occurred only when lisinopril was paired with the presence of about pets but rather said the focus of the study was on the general relationship between social factors and health. In the One explanation for our findings is that the presence of debriefing session at the conclusion of the study, we asked pets provided the kind of nonevaluative social support that is participants to identify whether they thought pets influenced critical to buffering physiological responses to stress. Social their resting blood pressure, their responses to stress, or both.
support theorists10,19 have suggested that positive feeling Except for 2 participants who answered “both,” all said that states may enhance an individual’s capacity to adapt to stress.
they believed their pets helped diminish their resting blood We believe that pets may evoke such feelings in their owners.
pressure. This was reinforced by the fact that participants This conclusion was confirmed by an exit conference in performed home monitoring over the course of the study and which the nominal group technique21 was used to structure that lisinopril therapy did in fact cause a dramatic reduction in responses to the question, “How has your pet changed your blood pressure. The pet owners, however, attributed this life?” Interestingly, all of our participants attended this reduction to a combination of drug therapy and pet owner- Allen et al
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ship. Because of this fortuitous misunderstanding on the part we cannot generalize the findings to other stressful settings, of our participants, we do not believe that demand character- such as work environments. Because differences between istics contributed to our findings about stress responses.
office and home resting blood pressures were not influenced Because the participants (both with and without pets) were by pet ownership or lisinopril therapy, it is logical to consider highly motivated to reduce their blood pressure and believed whether stress reactivity outside the home might also not be that the drug would work, however, we cannot totally rule out influenced by pets. We believe, however, that because reac- that demand characteristics as well as a placebo effect tivity and resting blood pressure are independent of each contributed to their reductions in resting blood pressure. That other, reactivity outside the home has the potential to be is, wanting to please experimenters who came to their homes, combined with a strong belief in the treatment, could have In the present study, we were able to change the social influenced responses to lisinopril, although research suggests environment of our participants by adding a pet to their lives.
that actual placebos have little effect on ambulatory blood Enhancement of social support with human friends is much pressure monitoring,22 so we believe this was unlikely.
more complex and difficult to achieve and, to our knowledge, We acknowledge that the study population sample was has not been successfully carried out in an experimental highly selected for homogeneity. We were interested in design. Because pets, unlike human friends, are perceived as looking at stress responses in a group of individuals who always being nonjudgmental and accepting of their owners, experienced similar job stress and who lived alone. Because they are ideal candidates for social support intervention.
there were many stockbrokers available who were motivated Physiologically, pets had greater influence on sympathetic to be in a behavioral study and were willing to acquire pets, responses than did ACE inhibition alone. Consequently, our we decided to focus on them. Although chronic stress may be findings suggest that higher center influences can modify associated with an elevated renin level, we did not select stress responses and that coping skills may be related to participants on this basis or for any physiological character- increased cortical inhibition of the brain stem. Although we istic other than stage II hypertension. The baseline PRA that do not advocate the substitution of pets for human compan- we report may appear higher than is often observed, but it is ionship, we conclude that for persons who like animals and consistent with a previous related study.1 In addition, our have few social contacts, pets can enhance isolated lives and work supports earlier studies that document a positive rela- tionship between psychological stress and renin reactivi-ty.23,24 In the present study, because the main interest was in Acknowledgments
a change from baseline, the reported difference in change This work was supported by Food and Drug Administration grant scores between groups is the important area of focus. How- FDT-000889 and by the Waltham Center for Pet Nutrition(Waltham-on-the-Wolds, England). We are very appreciative of ever, because it is known that individuals with high renin important contributions made to this study by the late Patrick levels often have a very positive response to ACE inhibition therapy,25 the possibility exists that our findings wouldgeneralize only to other “high-renin” individuals. Among our References
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