Changes In Abdominal Pressure Research Articles

Intra-abdominal pressure and manometric data of the distal esophageal sphincter. Their relationship to gastroesophageal reflux.

Nineteen patients with abnormal gastroesophageal reflux (13 with and six without hiatal hernia) had esophageal manometry and simultaneous 24-hour monitoring of esophageal pH and intra-abdominal pressure (IAP). Only 8% of all IAP challenges induced a reflux episode. This incidence increased to 13% in patients with a distal esophageal sphincter (DES) pressure of less than 5 mm Hg and an abdominal esophageal length of less than 1 cm, whereas it was only 6% in patients with a greater DES pressure and a longer abdominal esophagus. At the same time, there was an average of 2.7 reflux episodes per hour, of which 38.7% were caused by a challenge of IAP indicating that other mechanisms, besides changes in abdominal pressure, can cause reflux. There was no difference in DES pressure, length of abdominal esophagus, and the effect of IAP challenges in patients with and those without a hiatal hernia.

Influence of Abdominal Pressure and Sympathetic Vasoconstriction on the Cardiovascular Response to Positive End-Expiratory Pressure1–3

The role of changes in abdominal pressure and sympathetically mediated vasoconstriction in the cardiovascular response to positive end-expiratory pressure was evaluated in 9 mongrel dogs. When the abdomen was widely opened, the decrease in cardiac output caused by positive end-expiratory pressure was the same as that found during control studies. When the abdomen was tightly bound, cardiac output was higher at any positive end-expiratory pressure than in control state (P less than 0.01), but the percent decrease produced by increasing positive end-expiratory pressure was the same. alpha-Adrenergic blockade with phenoxybenzamine produced a significantly greater decrease in cardiac output at any given positive end-expiratory pressure and thus appeared to inhibit the previously operative peripheral vascular adjustments to positive end-expiratory pressure. The major compensatory mechanism in the cardiovascular response to positive end-expiratory pressure thus appears to be mediated via alpha-adrenergic sympathetic factors.

Voluntary changes of thoracoabdominal shape and regional lung volumes in humans.

We measured regional lung volumes from apex to base in humans during changes in thoracoabdominal shape which we monitored with magnetometers. In erect subjects, voluntary changes of shape at FRC did not change regional volume distribution. In supine subjects, the effect of negative pressure applied to the abdomen and a similar thoracoabdominal configuration achieved by voluntary means were studied. The distribution of regional volumes in both situations was the same as that measured during relaxation at the same overall lung volumes. We concluded that neither voluntary changes in shape nor negative abdominal pressure influenced the human pleural pressure gradient. This result, which differed from findings in animals, was probably because the human chest was relatively stiff and behaved with one degree of freedom; all parts of the human rib cage changed dimensions proportionally while negative abdominal pressure distorted the rib cage of animals.

Electro-myographic investigation on the human external sphincter muscle of anus.

Using the needle electrode, the human external sphincter muscle of the anus was studied and fhe following results were obtained.A. The muscle as a whole1. Interference voltages appear with a slight increase of constriction of the muscle-a property common to the circular muscles of the mouth and eye.2. The discharge can be abolished with difficulty by a distention of the anus provoked by an intentional motive; in an electrically silent state thus caused, an interruption of the effort results in an immediate return of the discharges in many NMU.3. Disappearance of the discharge can be brought about with comparative ease when the rectum is full with feces or other artificial substitute.4. Reflex changes of the discharge may be produced by such different causes, like the change in abdominal pressure, vocalization, coughing, or lifting a heavy weight. Mechanical or heat stimulation of any skin area causes an extremely sensitive reaction, and the muscle contracts reflexively.B. Activity of individual NMU1. At a room temperature in which the subject feels no cold and under ‘at rest’ state, only the tonic discharges are obtained with spike amplitudes of about 300μV and current duration of less than 5 msec. The frequency of the discharge is of the order of 3 to 4 c.p.s.(cf. for M. soleus 8 to 10 c.p.s.). The tonic dis-charge can be led out more frequently from the deeper layer.2. Increased constriction involves kinetic discharges, with amplitudes of 600 to 800 μV (far smaller than the soleus); these discharges seem to originate in the shallower layer.3. The _??_-S curve dissolves into two distinctly different components: one has the plateau with S=8 msec. extending to 170 msec., hence ascends sharply, while the other maintains its plateau at the level of S 15 msec. and proceeds far beyond, up to 260 msec., where it makes a gradual rise. The former corre-sponds to the discharges of the kinetic NMU and the latter to the tonic ele-ments. In the _??_-S diagram the anal muscle occupies the extreme right position among the muscles so far investigated.