Complementary Alternative Cardiovascular Medicine
Complementary Alternative Cardiovascular Medicine
Complementary Alternative Cardiovascular Medicine
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Chapter 8 / Meditation and CVD 127<br />
unchanged in either longitudinal or acute TM studies. These include<br />
testosterone, insulin, T3, T4, and luteinizing hormone (LH) (33,35).<br />
Studies investigating the impact of meditation on neurotransmitters<br />
suggest that the regular practice of meditation has a significant impact<br />
on the sympathetic-adrenal medulla system. Michaels and colleagues<br />
first reported a nonsignificant acute decrease in catecholamine levels<br />
during TM (36). Subsequently, in an advancement of this research,<br />
Infante and colleagues conducted a controlled study of catecholamine<br />
plasma levels, which considered the impact of circadian cycles and time<br />
of day. Infante and colleagues found significantly lower morning and<br />
evening norepinephrine levels and morning epinephrine levels in the<br />
TM group than in the control subjects (37). Another controlled study<br />
investigating the urinary metabolite of serotonin, 5-hydroxyindoleaceatic<br />
acid (5-HIAA) found significant increases after 30 min of practicing TM.<br />
In addition, throughout the experiment, 5-HIAA levels were higher in<br />
meditators than they were in rest subjects (38).<br />
AUTONOMIC EFFECTS<br />
There have been numerous studies investigating the acute and longterm<br />
impact of meditation on autonomic activity. The overall results<br />
indicate decreased activation and include such findings as increased<br />
galvanic skin resistance (GSR), decreased spontaneous electrodermal<br />
response (EDR), and decreased heart rate (8,9,27,28). A meta-analysis<br />
of 31 studies comparing physiological differences between TM and rest<br />
control groups indicated that those subjects who had been practicing TM<br />
for a long time exhibited significantly lower baseline levels of spontaneous<br />
skin resistance responses, respiration rate, heart rate, and plasma<br />
lactate before meditation than comparison subjects did before rest (39).<br />
Yet another group of studies investigated the impact of meditation on<br />
recovery from stressful stimulation. Several researchers have reported<br />
significantly faster habituation or return to baseline (as measured by<br />
GSR, EDR, and heart rate) after exposure to stressful stimuli in meditators<br />
as compared to controls (40,41).<br />
HEMODYNAMIC EFFECTS<br />
Hemodynamic variables, such as systolic and diastolic blood pressures<br />
cardiac output, and total peripheral resistance (TPR) have also<br />
been a focus of study regarding how they are affected by the practice of<br />
meditation. Individuals who practice TM have lower resting systolic and<br />
diastolic blood pressures than matched controls (42–44). Because blood<br />
pressure is the product of cardiac output and TPR, changes in these<br />
variables have also been studied during meditation. An investigation of