Studies on Intercostal Nerve Physiology

Abstract

Summary and Conclusions

1. Stimulation of the central end of any intercostal nerve causes a reflex inhibition of respiration and effects a concomitant drop in blood pressure. 2. The lower intercostal nerves (7-12) elicit a greater response than do the upper ones. 3. Stimulation of the intercostal branches to the parietal pleura, diaphragmatic pleura, and rectus abdominis muscle give the respiratory inhibition and lowered blood pressure (approximately 25 mm of Hg.) 4. Stimulation of sensory or intercostal fibers in the diaphragm causes reflex contraction of the abdominal musculature through reflex connection with other lower intercostal nerves. 5. Among other things, these results furnish the physiological mechanisms involved in referred pain and muscular rigidity in the lower abdominal quadrant as a result of involvement of the base of the lungs, in lobar pneumonia for example. 6. Both expiration and inspiration cause the intercostal nerves to be stimulated and thereby effect reflexly respiratory inhibition, a. Inspiration more strongly inhibits respiration than does expiration, b. At the end of inspiration, the intercostal nerves aid the Hering-Breuer reflex, c. After expiration the intercostal nerves constitute a factor that determines lapse of time before the next inspiration. 7. Abnormal respiration and tightening of the abdominal musculature may be indicative of an irritation in the peripheral region of the diaphragmatic pleura.

I hereby wish to acknowledge that Dr. Arno B. Luckhardt suggested the problem and rendered valuable aid in its prosecution.