Blood flow is directly or indirectly manipulated for mental clarity, health, increased energy, or the promotion of religious emotion through hatha yoga postures, breathing exercises, prostrations, tai chi movements, dervish dancing, and other activities associated with the contemplative traditions. Traditional teachers could not measure blood flow with scientific exactness, of course, but some of them could skillfully guide their students' practice through empathy, intuition, and kinesthetic feel, and in doing so they sometimes looked for bodily signs related to blood circulation, such as flushing of the face and chest and changes in skin tone and complexion.  The picture of meditation's effect on blood flow provided by modern studies is quite preliminary, though. Most of it comes from TM-sponsored research.
Delmonte (1984f) tested fifty-two subjects and found that meditators showed a significantly greater increase in digital blood volume during meditation than rest. Jevning, Wilson, and O'Halloran (1982) studied muscle and skin blood flow and metabolism during states of decreased activation in TM. They concluded that acute decline of forearm oxygen consumption has been observed during an acute, wakeful behaviorally induced rest/relaxation state. This change of tissue respiration was not associated with variation of rate of forelimb lactate generation. Since forearm blood flow did not change significantly during this behavior, the decline of oxygen consumption by forearm was due almost solely to decreased rate of oxygen extraction. Decreased muscle metabolism was a likely contributor to these observations.
Skin Resistance and Spontaneous GSR
Low skin resistance, as measured by the galvanic skin response test, is generally thought to be a reliable indicator of stress because it is caused in large part by anxiety-induced perspiration. Like respiration rate and muscular tension, it has been affected by meditation in many contemporary experiments. This measure of stress, we believe, fits into the general picture from both traditional and modern accounts that meditation often lowers anxiety.
Increased skin resistance, as well as lower frequency of spontaneous galvanic skin responses, has been widely reported in the TM literature or in studies of TM groups [see Delmonte (1984c), Bono (1984), Bagga and Gandhi (1983), Orme-Johnson and Farrow (1977), Farrow (1977), Laurie (1977), West (1977), T.R. Smith (1977), Orme-Johnson (1973), Wallace and Benson (1972), Wallace et al. (1971b), and Wallace (1971)]. Other researchers who concluded that meditation increases skin resistance (and sometimes lowers the frequency of spontaneous GSR fluctuations) are: Schwartz et al. (1978), Sinha et al. (1978), Pelletier and Peper (1977a), Glueck and Stroebel (1975), Walrath and Hamilton (1975), Woolfolk (1975), Benson et al. (1973a), Akishige 1970), Akishige (1968), Karambelkar et al. (1968), and Bagchi and Wenger (1957). In addition to increased skin resistance, Wenger and Bagchi (1961) found slow oscillatory skin-resistance waves in the later part of meditation for several subjects.