An unanticipated effect of meditation on cardiovascular pharmacology and physiology

Abstract

T late George Harrison helped to usher in a fascination with diverse aspects of Indian culture, from sitar music to meditation. Thousands of young people embraced meditation in search of relaxation, enlightenment, or altered states of consciousness. Numerous studies examined various aspects of the physiology of meditation, and some investigators suggested that meditation was a useful adjunct in treating many medical problems such as hypertension. Meditation has been observed to decrease adrenergic receptor sensitivity and to increase cardiac parasympathetic activity. In recent years the “zeitgeist” has shifted and interest in the medical aspects of meditation has diminished. We report here a serendipitous observation of the effects of meditation to counter the effects of pharmacologic doses of the adrenergic agonist isoproterenol. As part of our institutional review board-approved studies of sympathetic nervous system regulation in hypertension, for many years we have administered intravenous isoproterenol in incremental doses as a way of gauging in vivo -adrenergic receptor sensitivity. This venerable tool in the cardiovascular physiology armamentarium has been widely used; the chronotropic (or heart rate-increasing) qualities of isoproterenol are well known. • • • A 36-year-old healthy normotensive white woman was studied using a standard isoproterenol challenge test. An intravenous catheter was placed in an antecubital vein the night before the study. On the day of study, she consumed a light non–caffeine-containing breakfast and lunch. About 1 hour after lunch, electrocardiographic electrodes were attached in the lead II configuration and she rested quietly in a supine position for 20 minutes. Isoproterenol was infused intravenously by bolus injection every 3.5 minutes at the following doses: 0, 0.1, 0.5, 1.0, 2.0, and 4.0 g. Heart rate was measured electrocardiographically 60 seconds after each bolus injection. To our surprise her heart rate diminished—plummeted even—after receiving the 0.5g dose of isoproterenol. When the test was concluded, we asked if she had noticed any unusual subjective sensations in response to the isoproterenol. Had she been feeling nauseous, dizzy, faint? She replied that she had felt fine during the infusion studies but did not really recall them very well because she had started meditating shortly after the infusions began. She indicated that for many years she had meditated as a way of quieting her mind. She did not follow any particular school of meditation but found that she could readily “enter another realm” while meditating. She reported that she routinely meditated 20 to 30 minutes at a time once a day and that her meditation involved focusing on her breathing. She noted parenthetically that her meditation was so deep that she needed an alarm clock to rouse her from meditation, lest she meditate for hours on end and miss work. Because we suspected that the isoproterenol studies were invalidated because of her meditation, we asked her to return to the hospital about 2 weeks later to repeat the isoproterenol studies—this time with the instructions to keep her eyes open and not to meditate during infusion. Figure 1 is a graph of her heart rate response on the initial occasion while meditating and on the second occasion while not meditating; for comparison purposes the figure also shows the responses observed in 93 other women studied over the years in our laboratory. In the face of a dose increment from 0 to 4.0 g, the expected response is an increase in heart rate by 21 beats/min (Figure 1). However, during meditation, her heart rate actually decreased by 17 beats/ min. When she was instructed not to meditate, her heart rate response was entirely consistent with the typical response observed in our laboratory. • • • The higher central command associated with her meditation was apparently able to override a powerful adrenergic stimulus provided by the pharmacologic infusion. Although we have no data on the precise mechanism of this unusual phenomenon, a reasonable speculation would be sizeable vagal activation. Had we obtained the electrocardiogram digitally, it would have been possible to examine vagal activity explicitly as inferred from heart rate variability. Unfortunately, the heart rate was obtained from transient electrocardiographic rhythm strips, and analysis of heart rate variability was therefore not feasible.