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We tested the hypothesis that a drop in metabolic rate (MR) causes the apneas observed in some subjects during transcendental meditation (TM). We measured O2 consumption (VO2) and CO2 production (VCO2) in three groups of experienced meditators and one group of nonmeditating controls. Measurements were made before, during, and after TM for the meditators and before, during, and after eyes-closed relaxation for the nonmeditating controls. The three groups of meditators consisted of 1) those showing little change in the frequency of ventilation (f) with meditation, 2) those showing a marked decline in f, and 3) those showing numerous apneas and a marked fall in f. There were significant trial effects but no group or interaction effects for the decline in VO2. Thus we concluded that a drop in MR is not the cause of the apneas. However, there were significant trial and interaction effects for the changes in VCO2 and the respiratory exchange ratio (R), with a significant drop in R for the meditators but not for the controls. We report additional evidence and speculate that the drop in R is a consequence of mild hypoventilation.

1. The method of controlled releases was used to obtain tension-extension curves in toad (Bufo bufo) sartorii under a variety of conditions at 0 degrees C.2. The curves obtained were approximately linear over a considerable range of force (0.4P(0) to P(0)) if the releases were given from the plateau of tetanic tension. The slope of this linear region was little affected by changes of release velocity in the range 10-120 mm/sec.3. Such changes as did occur with alterations in release velocity could be quantitatively accounted for in terms of the internal shortening predicted by A. V. Hill's two-component model.4. As the muscles were stretched above l(0), we found that the maximum stiffness of the tetanized muscles fell in much the same way as the maximum developed force, P(0).5. In another series of experiments we found a rapid change in the overall shape of the tension-extension curve during the early phase of force development in an isometric tetanus. The stiffness of the muscle increased with increasing developed force during this period.6. The force-velocity curve in these muscles was measured by two methods, both giving a similar result. Surprisingly, toad muscle appears to have about the same intrinsic speed as frog muscle at 0 degrees C. The a.b product from our experiments is considerably greater than the reported values for the maintenance heat rate at 0 degrees C in these muscles.7. The probable site of the variable compliance in active muscle is discussed. It seems most likely that this is within the A-band, perhaps in the cross-bridges themselves.

1. The increase in rate of heat production caused by stretch in the unstimulated frog's sartorius (stretch response) has been measured using a conventional thermopile technique.2. The rate of heat production was found constant between l(0) (the distance in vivo between the tendons when the legs were in a straight line) and 1.2 l(0), and rose rapidly above this length to reach 3-5 times the basal rate at 1.3 l(0). Stretching to greater lengths appeared to damage the muscles.3. The stretch response is increased by several substances which increase the duration of the active state.4. Unlike the rate of heat production at l(0), the stretch response is increased by procaine; while the presence of CO(2) greatly reduces it.5. Evidence is presented supporting the hypothesis that the stretch response is associated with the appearance of tension in the sarcolemma.