There has also been considerable research work on biochemical changes during yogic practices. The studies conducted at the Banaras Hindu University (Varanasi), showed that Six months of yoga practice increased 17-hydroxycorticosteroid excretion, reduced serum cholesterol, blood sugar and increased serum proteins (Udupa 1972, 1985). These findings (specially the increased adrenocortical activity) were interpreted as increased stress competency. Later at DIPAS Santha et al. (1981) described the biochemical changes indicating a relative hypo-metabolic state along with reduction in sympathetic activity. Investigating the role of sahaj yoga in stress, Rai and his colleagues (Rai et al. 1989) studied blood lactic acid, urinary vinyl manddic acid, blood pressure, heart rate and respiratory rate in subjects trained in sahaj yoga, and observed a significant decrease in these parameters. Galvanic skin resistance, on the other hand, significantly increased, indicating a state of relaxation.

The long-term practice of Transcendental Meditation was shown to alter pituitary hormones (e.g. TSH, LH) and cortisol responsiveness to LH-RH and insulin, respectively (Ahuja et al. 1981). A report (Sahay et al. 1982) from the Vemana Yoga Research Institute (Secunderbad) showed an increase in creatine phosphokinase and reduced pyruvate to lactate ratio following 3 months of yoga practice.

When these studies on the physiology of yoga were being carried out, research efforts were also directed to assess the therapeutic potentials of yogic practice in stress- related, psychosomatic ailments, particularly hypertension, hyperthyroidism, ischaemic heart disease, acid peptic disease and ulcerative colitis (Udupa 1976). Though Datey and his co-workers (1969) and Patel (1973, 1975) had reported their observations regarding beneficial role of yogic practices particularly shavasan in hypertension as early as in 70s, it is only recently that role of yoga specially pranayama (voluntarily regulated breathing including a period of breath-holding), meditation, shavasana and sahaj yoga have been extensively investigated in different stress-related cardiovascular disorders (Swain & Das, 1994, Sachdeva et al 1994, Talukdar 1994). In an open study comprising 23 hypertensive patients, Sachdeva et al (1994) observed reduction in systolic blood pressure from 134.5 ± 16.01 mm Hg to 125.1 ± 9.88 mm Hg and diastolic blood pressure from 88.52 ± 9.42mm Hg to 81.62 ± 6.48 mm Ug respectively after 2 months of yogic lifestyle educational program. In another study, Talukdar (1994) and his co-workers noted statistically significant changes in cell membrane enzymes after yoga practices in hyper-tensive patients. 10-12 weeks of practicing certain yogasanas significantly increased serum HDL levels, and caused a trend of reduction in serum cholesterol, triglycerides, LDL and VLDL (Bhaskaracharyulu et al. 1986). Though its beneficial role in mild hypertension seems to be fairly convincing, more in-depth studies are required to document the effect of different forms of yoga on platelet behavior, macrophages, prostaglandin system and left ventricular dysfunction particularly changes in left ventricular hypertrophy, to decide its exact place in the overall management of hypertension and /or coronary artery disease.

The effect of yoga on bronchial asthma has also been extensively studied. Pranayama has been shown to reduce clinical symptoms, reduce the need for medication and increase the PEFR, FEV₁ and FVC, though FEV₁ / FVC % did not change (Nagarathna & Nagendra 1985).

Vivekananda Kendra Yoga Research Foundation (Bangalore) has developed an integrated approach of yoga therapy which aims at correcting imbalances at all levels. It consists not only of asana, Kriyas, Pranayama, meditation, devotional sessions, but extensive coverage through lectures on the theory and philosophy of yoga. The benefits of this approach, when practiced regularly over 3 to 54 months, and compared to a control group, were a decrease in the number of asthma attacks per week, reduced intake of medication (including steroids), and improved PFR (Nagendra & Nagarathna 1985, Nagarathna et al 1991). This approach also includes a special 8-step yoga-chair breathing exercise which has proved useful for acute episodes of broncho-spasm (Nagarathna et al 1991). Singh (1987) demonstrated a particular maneuver (Kunjal) consisting of swallowing as much warm saline water as possible, first thing in the morning and then vomiting it out immediately, and it was shown to he helpful specially in asthmatics.

More recently, double-blind placebo-controlled crossover studies were done making use of a device which simulates pranayamic breathing (Singh et al. 1990). His study revealed a significant increase in the provocative dose of histamine needed to cause a 20% decrease in FEV_{1 .}

Apart from bronchial asthma, yogic practices are therapeutically beneficial in other diseases. Nine months of practicing the integrated approach of yoga therapy (described above), significantly improved the IQ and social adaptation of 45 children with varying degrees of mental retardation, compared to a matched control group who did not practice yoga (Uma et al. 1989). These, children also showed a marked improvement in their concentration and eye-hand coordination as assessed by a steadiness test, within 10 days of yoga practice (Telles et al. 1 993).

Training in yoga is also useful to cause significant reduction in visual and auditory reaction time, increase in breath holding time and hand grip strength (Mohan et al. 1992). Fortunately, certain organizations (such as the Mitra Mandal, Maharashtra) have attempted to disseminate this training for the benefit of society, by teaching yoga to jail inmates with encouraging results (Vyavahare 1991).

In conclusion, it must be mentioned that studies on physiological changes in yoga can actually be the basis for an in-depth understanding of changes in neural processes with altered states of consciousness. For example, studies on sensory cerebral evoked potentials have already revealed that specific brain areas (i.e. thalamic nuclei) are principally involved during the relaxed state and alertness maintained while practicing Pranayama (Telles et al. 1993). It can thus be seen that diverse aspects of yoga and its applications have been studied in India, and that there is an interesting and potential scope for future research.