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"Wakeful Hypometabolic Physiologic State, A"

Wallace, Robert, Herbert Benson, and Archie Wilson

American Journal of Physiology
Volume 221, Issue 3, Pages 795-799 (1971)

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Mental states can markedly alter physiologic function. Hypermetabolic physiologic states, with increased oxygen consumption, accompany anticipated stressful situations. Hypometabolic physiologic changes, other than those occurring during sleep and hibernation, are more difficult to produce. The present investigation describes hypometabolic and other physiologic correlates of a specific technique of meditation known as "transcendental meditation." Thirty-six subjects were studied, each serving as his own control. During meditation, the respiratory changes consisted of decreased oxygen consumption, carbon dioxide elimination, respiratory rate and minute ventilation with no change in respiratory quotient. Arterial blood pH and base excess decreased slightly; interestingly, blood lactate also decreased. Skin resistance markedly increased, while systolic, diastolic, and mean arterial blood pressure, arterial oxygen partial pressure and carbon dioxide partial pressure, and rectal temperature remained unchanged. The electroencephalogram showed an increase in intensity of slow alpha waves and occasional theta-wave activity. The physiologic changes during meditation differ from those during sleep, hypnosis, autosuggestion, and characterize a wakeful hypometabolic physiologic state.

Wallace and his collaborators were one of the first American groups to publish a scientific article on the physiological modifications produced by the practice of Transcendental Meditation (TM). TM was specifically studied because the technique was easy to learn, produced consistent, significant physiologic changes, required no special environmental setting, and unlike other religious groups of meditators, TM subjects were free from special religious dietary or behavioral practices which might interfere with the study of meditation.

Thirty-six subjects without physical or mental disabilities were selected to participate in this study, each serving as his or her own control. Both genders (28 males and eight females) and ages from seventeen to forty-one were represented in the study population. The subjects had been practicing TM for an average of about two and a half years. Oxygen consumption was measured by a mask, blood chemistry was measured by a catheter inserted into the brachial artery in the arm, and electrical brain waves were measured by electroencephalography. Other measurements taken included blood pressure, heart rate, rectal temperature, and skin resistance.

After thirty minutes during which the subjects became habituated to the laboratory environment, measurements were taken at continuous intervals. The subjects first relaxed with their eyes closed for twenty minutes, then meditated for thirty minutes, followed by another fifteen minutes of relaxation. Physiological changes which occurred during the meditation period were compared with the initial measurements taken during the pre-meditation period. The post-meditation measurements were compared with those from the initial control period and from the meditation period.

One of the most dramatic changes found in this study was a decrease in oxygen consumption. During the first few minutes of meditation, the meditators recorded an immediate reduction in oxygen consumption of about seventeen percent, with a parallel reduction in the elimination of carbon dioxide. This level of reduced oxygen consumption was maintained during the entire meditation period, and returned to a normal resting level after the meditation period.

Oxygen consumption is generally regarded as a reliable index of physical activity and arousal. For example, exercise requires an increased consumption of oxygen by muscle. During this metabolic process, oxygen is converted to carbon dioxide, which is eliminated by the lungs. If the body is starved of oxygen, reduced oxygen consumption does not lead to a parallel reduction in carbon dioxide elimination because the cells continue to metabolize the remaining oxygen in the blood. Therefore, oxygen starvation causes a decrease in the concentration of oxygen and an increase in the concentration of carbon dioxide in arterial blood. The relative amount of oxygen and carbon dioxide in the blood is called the respiratory quotient. During normal respiratory processes, this quotient remains constant; in abnormal respiratory situations, however, the reduction in available oxygen and increase in carbon dioxide changes the quotient. Wallace found that during the practice of meditation the amount of carbon dioxide elimination drops in proportion to the amount of oxygen consumed; therefore, the respiratory quotient remains constant. In conclusion, the metabolic changes of meditation arise from a natural reduction in metabolic activity at the cellular level, not from a forced reduction of breathing.

Further measurements confirmed that the reduction in oxygen consumption occurred concomitantly with a decrease in the volume of air breathed and in a decrease in the rate of breathing.

Wallace also found that heart rate of meditators decreased by about three beats per minute. These decreases were hypothesized to correlate with a reduction in oxygen consumption, indicative of a state of hypometabolism. This study found that systolic, diastolic, and mean arterial blood pressures changed little during meditation. The arterial pH decreased slightly in almost all subjects during meditation, while the partial pressures of carbon dioxide and oxygen in arterial blood showed no consistent or significant changes during meditation. Mean blood lactate concentration was found to decrease during meditation and in the ten minutes following the meditation period. Rectal temperature remained constant throughout the meditation period.

Wallace further discovered a marked increase in skin resistance at the onset of meditation. After meditation, skin resistance decreased, but remained higher than before meditation. Skin resistance to electrical current provides a measure of autonomic nervous system reactivity. An increase in the skin resistance of meditators has been reported by several groups. Increase in skin resistance indicates a decrease in skin conduction and a reduction in its fluctuations. It is well established that skin resistance decreases in states of anxiety or stress, and increases during relaxation. The large increases in skin resistance of meditators found in these studies are impressive.

The EEG pattern during meditation showed increased intensity of alpha waves and occasional theta wave activity. Alpha rhythm is the classical EEG correlate for a state of relaxed wakefulness, also described as relaxed vigilance. Indeed, emotional tension attenuates or blocks the alpha rhythm. Theta activity is associated with emotional processes and indicates relative maturity of the mechanisms linking the cortex, the thalamus, and the hypothalamus; theta rhythm also occurs during a state of maximal awareness. Apparently, an alpha wave pattern is most conducive to creativity and to the assimilation of new concepts, while the theta response seems to be a stage at which the mind is capable of deep insights and intuition. It is significant to note that practiced meditators can continue to exhibit alpha and theta waves after the meditation period has ended.

Wallace et al conclude that a consistent wakeful hypometabolic state accompanies the practice of the mental technique called transcendental meditation. This study is well designed and the results are appropriately interpreted.

Annotated by: Julia Shin (April 1997)

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Topics: medical issues | other topic: meditation



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