Influence of respiration on human sympathetic skin response.

Sympathetic skin response (SSR) is a reflexly elicited potential of the sweat glands, the afferent and efferent fibres of the reflex are cutaneous sensory fibres (if the SSR is elicited by electrical stimulus) and sympathetic sudomotor fibres respectively. Our earlier study indicated that latency, besides duration and amplitude, of SSR of a given normal individual showed significant variations between many trials of stimulation, even in a single sitting. Since deep inspiration is also an effective stimulus to elicite SSR, the present study was conducted to assess the influence of respiration on SSR. Thirty-four healthy students participated in the study. The skin of the forearm of the dominant hand was stimulated by electrical square pulse and SSR was recorded from the ipsilateral hand. SSR was elicited and recorded in each subject during the various phases of respiration, namely, end expiration (EE), end inspiration (EI), mid expiration (ME) and mid inspiration (MI). It was observed that the mean values of SSR latency during these respiratory phases (EE : 1.59, EI: 1.51, ME : 1.55, and MI: 1.56 sec) were similar, indicating that the normal respiration might not be responsible for the observed interstimulation variations in latency in any given individual.

Effect of yoga training on reaction time, respiratory endurance and muscle strength.

There is evidence that the practice of yoga improves physical and mental performance. The present investigation was undertaken to study the effect of yoga training on visual and auditory reaction times (RTs), maximum expiratory pressure (MEP), maximum inspiratory pressure (MIP), 40 mmHg test, breath holding time after expiration (BHTexp), breath holding time after inspiration (BHTinsp), and hand grip strength (HGS). Twenty seven student volunteers were given yoga training for 12 weeks. There was a significant (P < 0.001) decrease in visual RT (from 270.0 +/- 6.20 (SE) to 224.81 +/- 5.76 ms) as well as auditory RT (from 194.18 +/- 6.00 to 157.33 +/- 4.85 ms). MEP increased from 92.61 +/- 9.04 to 126.46 +/- 10.75 mmHg, while MIP increased from 72.23 +/- 6.45 to 90.92 +/- 6.03 mmHg, both these changes being statistically significant (P < 0.05). 40 mmHg test and HGS increased significantly (P < 0.001) from 36.57 +/- 2.04 to 53.36 +/- 3.95 s and 13.78 +/- 0.58 to 16.67 +/- 0.49 kg respectively. BHTexp increased from 32.15 +/- 1.41 to 44.53 +/- 3.78s (P < 0.01) and BHTinsp increased from 63.69 +/- 5.38 to 89.07 +/- 9.61 s (P < 0.05). Our results show that yoga practice for 12 weeks results in significant reduction in visual and auditory RTs and significant increase in respiratory pressures, breath holding times and HGS.

Effects of undernutrition and sex difference on skeletal muscle function in young rats.

The effects of undernutrition and sex difference on skeletal muscle contractile characteristics were studied in young albino rats. The skeletal muscle (gastrocnemius) of 8 week old pups with only one-third normal food intake (undernourished group = UN group; n = 18), as compared to free fed pups (control group = cont. group; n = 16), showed prolongation of contraction time (23.6 +/- 1.0 Vs 20.9 +/- 0.8 msec, Mean +/- SE, P < 0.05) and relaxation time (31.5 +/- 1.8 Vs 22.9 +/- 1.1 msec, P < 0.001) and retention of contraction force and endurance time. In 18 week old rats the effects of sex difference in females (n = 10), as compared to males (n = 10) were prolongation of contraction time in gastrocnemius (32.2 +/- 1.5 Vs 27.8 +/- 1.5 msec, P < 0.05), less force production in gastrocnemius (668.9 +/- 48.0 Vs 895.4 +/- 93.3 g, P < 0.05) and extensor digitorum longus (20.1 +/- 3.3 Vs 29.9 +/- 2.5 g, P < 0.05) and shorter endurance time (160.8 +/- 10.2 Vs 187.2 +/- 7.1 sec, P < 0.05) in soleus. Thus, it is concluded that early undernutrition has prolonged the contraction and relaxation times of the skeletal muscles and the effect of sex difference in the early adulthood was different in different skeletal muscles.

Effect of head-up tilting on systolic time intervals in normal young volunteers.

Systolic time intervals (STI) are sensitive indices of myocardial function. Passive tilting is a rapidly reversible and non-invasive method for inducing cardiovascular stress. The present work was conducted to study the effect of graded head-up tilt (HUT) on STI. 20 male medical students were subjected to 30 degrees, 60 degrees and 80 degrees HUT on a tilting table. ECG, phonocardiogram and carotid pulse were recorded simultaneously on Grass polygraph. Electromechanical systole (QS2), left ventricular ejection time (LVET), pre-ejection period (PEP), PEP/LEVT ratio, heart rate (HR) and corrected STI were determined immediately after and at 1, 2, 3, 4 and 5 min after each angle tilt. HUT produced a decrease in QS2 which was more pronounced at higher angle tilt. LVET decreased after 60 degrees and 80 degrees HUT. PEP and PEP/LVET ratio decreased after each angle tilt. These changes in STI can be explained on the basis of sympathetic stimulation-induced increase in the inotropic state of the heart.