Parasternal Intercostal, Costal and Crural Diaphragm Neural Activation During Hypercapnia

Background Parasternal intercostal is an obligatory inspiratory muscle working in coordination with the diaphragm, apparently sharing a common pathway of neural response. This similarity has attracted clinical interest, promoting parasternal as a non-invasive alternative to the diaphragm, to monitor central neural respiratory output. However, this role may be confounded by the distinct and different functions of costal and crural diaphragm. Given the anatomic location, parasternal activation may significantly impact chest wall via both mechanical shortening or as a "fixator" for the chest wall. Either mechanical function of parasternal may also impact differential function of costal and crural. Objectives During eupnea and hypercapnia, 1) compare the intensity of neural activation of parasternal, with costal and crural diaphragm; 2)examine parasternal recruitment and changes in mechanical action during progressive hypercapnia, including muscle baseline length and shortening. Methods In 30 spontaneously breathing canines, awake without confounding anesthetic, we measured directly both electrical activity of parasternal, costal, and crural diaphragm, and corresponding mechanical shortening of parasternal, during eupnea and hypercapnia. Results During eupnea and hypercapnia, parasternal and costal diaphragm share a similar intensity of neural activation, while both differ significantly from crural diaphragm activity. The shortening of parasternal increases significantly with hypercapnia, without change in baseline end-expiratory length. Conclusion Parasternal shares an equivalent intensity of neural activation with costal, but not crural, diaphragm. Parasternal maintains and increases its active inspiratory shortening during augmented ventilation, despite high levels of diaphragm recruitment. Throughout hypercapnic ventilation, parasternal contributes mechanically - it is not relegated to chest wall fixation.

Differential activation of the human costal and crural diaphragm during voluntary and involuntary breaths

Simultaneous electromyographic recordings from the human costal and crural diaphragm during voluntary augmented breathing and involuntary rebreathing show that the increase in inspiratory crural diaphragm activity was ~60% of the increase in costal diaphragm activity. However costal to crural diaphragm activation did not differ between the two tasks. The dissociation in the amplitude of activation of the costal and crural diaphragm becomes apparent only as the drive to breathe increases above tidal breathing.

Botox injection into the lower esophageal sphincter induces hiatal paralysis and gastroesophageal reflux

Background: Endoscopic intrasphincteric injection of Botox (ISIB) is used routinely for the treatment of achalasia esophagus and other spastic motor disorders. Studies show that the ISIB reduces the smooth muscle lower esophageal sphincter (LES) pressure. The esophageal hiatus, formed by the right crus of diaphragm, surrounds the cranial half of the LES and works like an external LES. We studied the effects of ISIB on the LES and hiatal contraction and gastroesophageal reflux (GER). Fourteen patients treated with ISIB were studied. Esophageal manometry-impedance recordings were performed before and after the ISIB. Hiatal contraction was assessed during tidal inspiration, forced inspiration, Müller’s maneuver, and straight leg raise. In 6 subjects, the manometry were repeated 6–12 mo after the ISIB. The esophagogastric junction (EGJ) pressure was measured at end expiration (LES pressure) and at the peak of maneuvers (hiatal contraction). Transdiaphragmatic pressure (pdi; force of diaphragmatic contraction) was measured at the peak of forced inspiration. GER was measured from the impedance recordings. The EGJ pressure at end expiration (LES pressure) decreased significantly after the Botox injection. The peak EGJ pressure at tidal inspiration, forced inspiration, Müller’s maneuver, and straight leg raise was also dramatically reduced by the ISIB. There was no effect of Botox on the pdi during forced inspiration. Seven of 10 subjects demonstrated GER during maneuvers following the ISIB. Six to 12 mo after ISIB, the LES and hiatal contraction pressure returned to the pre-ISIB levels. ISIB, in addition to decreasing LES pressure, paralyzes the esophageal hiatus (crural diaphragm) and induces GER. NEW & NOTEWORTHY The sphincter mechanism at the lower end of the esophagus comprises smooth muscle lower esophageal sphincter (LES) and skeletal muscle crural diaphragm (hiatus). Current thinking is that the endoscopic intrasphincteric injection of Botox (ISIB), used routinely for the treatment of achalasia esophagus, reduces LES pressure. Our study shows that ISIB, even though injected into the LES, diffuses into the hiatus and causes its paralysis. These findings emphasize the importance of esophageal hiatus as an important component of the antireflux barrier and that the ISIB is refluxogenic.

O34 A SLIGHTLY CRAZY BUT INFORMATIVE EXPERIMENT OF THE EFFECT OF THE HEAD DOWN (HD) POSTURE ON THE CHARACTERISTICS OF OESOPHAGEAL MOTILITY AND OESOPHAGOGASTRIC JUNCTION (OGJ) USING HIGH RESOLUTION OESOPHAGEAL MANOMETRY

Background It is known that posture (Supine Vs Sitting) variations can affect the dynamics and manometric characteristics of the OG junction and Oesophageal motility. Aims To study the effect of the Head Down (HD) upside down posture on the esophageal motility characteristics and dynamics of the OG junction using High resolution manometry. This would partially replicate the effect of Obesity (High Intraabdominal pressure) on the OGJ. Methods A single crazy (but sane) volunteer who had no symptoms of GORD served as the model for this unique experiment. A high-resolution manometry was performed using a solid-state transducer catheter with 36 channels. The study was performed in the sitting, supine and head down posture. Basal characteristics recording followed by wet swallows of 5ml of water and completed by rapid water swallows was done in each posture. Analysis was performed in the standard fashion using Chicago classification metrics. Further correlation of findings with a multipostural barium video oesophagogram is awaited. Results The procedure was completed satisfactorily in all the three postures. Satisfactory progression of swallows in a peristaltic sequence was obtained in all the 3 postures. However it was noted that there was a sequential change in the following parameters from the sitting to the supine to head down postures. Increased residual and contraction pressures in the Cricopharyngeal high pressure zone more pronounced in the HD position. Decreased amplitude of contraction of peristaltic sequences Decrease in slope of the peristaltic wave in the HD posture Diminished resting pressure in the HD position Exaggerated separation of the crural diaphragm (CD) and LES on the HD position Increased intragastric pressures in the HD position. Conclusion The above experiment is the first reported of Oesophageal function and OGJ dynamics in a completely unaided head down position using high resolution manometry and video fluoroscopy. The findings may serve to imitate the effect of Obesity on the OJ junction