| INTRODUCTION
The nasal cycle is an ultradian rhythm with a periodicity of about two to eight hours, during which the right and left nares are alternately patent (Keuning, 1968). Forced right nostril breathing occluding the left nostril was found to increase blood glucose levels (Backon, 1988) and heart rate (Shannahoff-Khalsa & Kennedy, 1993). In a detailed review (Shannahoff-Khalsa, 1991) a number of other physiological and psychological effects of right nostril breathing were suggested, such as generalized sympathetic tonus, increased temperature and metabolic rate, and improved verbal performance. Left nostril breathing had reverse effects. Based on this, the right nostril dominant stage was correlated with the activity phase of the basic rest-activity cycle (BRAC) and with an increase in the sympathetic tone (Werntz, Bickford, Bloom & Shannahoff-Khalsa, 1983). The left nostril dominant stage was correlated with the resting phase of the BRAC and with parasympathetic dominance. Some varieties of yoga breathing (pranayama) involve inhalation and exhalation through one nostril exclusively. These yoga practices provide an opportunity to study the effects of selective nostril breathing for prolonged periods. Some of the physiological effects of a month of right nostril breathing pranayama (surya anuloma viloma or SAV), practised for ten minutes four times in a day, were found to be significantly different from the effects of a left nostril breathing pranayama (chandra anuloma viloma or CAV) and an alternate nostril breathing pranayama (nadisuddhi or NDS), when all three techniques were practiced for the same frequency and duration (Telles, Nagarathna Nagendra, 1994). SAV caused a significant increase in oxygen consumption (37%), whereas both left and alternate nostril breathing caused a nonsignificant increase in oxygen consumption (24% and 19%, respectively). With all three practices there was a significant decrease in body weight. This reduction was comparable for SAV and CAV (2.3 kg) and less for NDS (1.5 kg). With CAV alone there was a significant decrease in volar skin resistance, interpreted as a reduction in sympathetic tone. While both SAV and CAV were accompanied by a reduction in body weight, SAV alone significantly increased the oxygen consumption. The increase in OC (albeit not significant) following CAV could mean that CAV practice is not actually “cooling” as described by the ancient yoga texts, but more accurately less stimulating than SAV. Of course, the increase in skin resistance following CAV practice shows that this practice does reduce sympathetic activity at least in some divisions of innervation. The comparable reduction in body weight with both SAV and CAV suggests a possible therapeutic application in obesity for both these practices. However, the maximum increase in oxygen consumption following SAV makes this practice preferable to CAV, particularly in view of the fact that the resting metabolic rate (RMR) in kcal/kg/hour is lower in the obese and is negatively correlated with the body mass index (BMI) (Dudani, Bijlani, Gupta, Manoch & Nayar, 1986). Obesity is well known to be associated with a variety of diseases, particularly hypertension and coronary heart disease (Mayer, 1980). Hence, the present study was designed to assess the immediate effects of 45 minutes of SAV pranayama on blood pressure (BP), digit pulse volume, heart rate, breath rate, skin resistance, and oxygen consumption. This information was considered necessary to understand any possible therapeutic merits (and limitations) of this breathing technique. |