Moreover, when participants without dogs acquired them six months into the study, their average blood pressure and heart rate during stress-producing situations dropped to match that of the initial group.

Karen Allen, research scientist in the Division of Clinical Pharmacology in the School of Medicine and Biomedical Sciences, presented results of her research today at the annual meeting of the Society for Psychophysiological Research in San Diego.

"This study shows how the presence of a pet dog can diminish stress responses to real-life daily stress over which caregivers have no control," Allen stated. "It demonstrates a therapeutic role for pet dogs, especially for individuals with hypertension who live under conditions of great responsibility and stress."

Allen conducted the study over one year. It involved 60 volunteers, equally divided between men and women, who were assigned randomly to either an experimental or control group. All were caring for spouses with traumatic brain injury and were taking ACE inhibitors to control hypertension. ACE inhibitors have been shown to control blood pressure during normal daily activities, Allen noted, but not to be effective in holding down pressure during stressful situations. All participants also had to be willing to acquire a dog.

At the beginning of the study, all participants wore blood-pressure monitors for 48 hours and kept diaries of their activities. Data on blood pressure and heart rate were captured during the first day when participants were caring for their spouses. These data were labeled natural stressors. On the second day, cardiovascular readings were taken while participants performed two activities used by researchers to simulate stressful situations-giving a speech, in this case on the problems of caring for a disabled spouse, and immersing one hand in ice water for two minutes (cold pressor test).

The experimental group then adopted dogs, and cardiovascular readings were taken from all participants again at six months under the same conditions. At this point, the control group also adopted dogs, and readings were repeated once again after six months.

Results showed that before dogs entered the picture, all participants reacted similarly to natural and simulated stressful situations.

"Interestingly, although the speech and cold pressor tasks elicited large increases in blood pressure and heart rate, natural spouse interaction produced even greater increases," Allen said. "Before pets, the speech task raised systolic blood pressure by 28 mmHg (millimeters of mercury), but spouse interaction raised systolic blood pressure by 52 mmHg."

After six months, those with dogs showed only a small rise in blood pressure when caring for their spouses, while blood pressure in the control group rose nearly 40 mmHg on average. After 12 months, when all participants had dogs, once again there was little difference between the groups, results showed.