Asthma is a common condition seen in many acupuncturists offices.  From a Chinese perspective there are a number of underlying reasons which lead to the symptoms so proper evaluation is key.  This study published in the Journal of Asthma used TENS stimulation on acupuncture points to help children with asthma.  Researchers were from the Department of Nursing at the Ching Kuo Institute of Management and Health in Taiwan.  

Looking at 43 children with asthma, the study used pulmonary function tests, heart rate tests and the pediatric asthma qualify of life questionnaire (PAQLQ) to judge the effectiveness of treatment.  Over 8 weeks the students received treatment and at the end of the study the treatment group was found to have significant improvement in the PAQLQ scores (particularly in activity levels).

Now this study is not acupuncture and TENS stimulation is not a substitute for acupuncture.  It does, however, illustrate the effectiveness of treatment.