Computerized thermistor technique for indirect studies of esophageal blood flow

Temporal and spectral properties of esophageal mucosal blood perfusion: a comparison between normal subjects and nutcracker esophagus patients

BACKGROUND

The mechanism of esophageal pain in patients with nutcracker esophagus (NE) and other esophageal motor disorders is not known. Our recent study shows that baseline esophageal mucosal perfusion, measured by laser Doppler perfusion monitoring, is lower in NE patients compared to controls. The goal of our current study was to perform a more detailed analysis of esophageal mucosal blood perfusion (EMBP) waveform of NE patients and controls to determine the optimal EMBP biomarkers that combined with suitable statistical learning models produce robust discrimination between the two groups.

METHODS

Laser Doppler recordings of 10 normal subjects (mean age 43 ± 15 years, 8 males) and 10 patients (mean age 47 ± 5.5 years., 8 males) with NE were analyzed. Time and frequency domain features were extracted from the first twenty-minute recordings of the EMBP waveforms, statistically ranked according to four independent evaluation criterions, and analyzed using two statistical learning models, namely, logistic regression (LR) and support vector machines (SVM).

KEY RESULTS

The top three ranked predictors between the two groups were the 0.5 and 0.75 perfusion quantile values followed by the surface of the EMBP power spectrum in the frequency domain. ROC curve ranking produced a cross-validated AUC (area under the curve) of 0.93 for SVM and 0.90 for LR.

CONCLUSIONS & INFERENCES

We show that as a group NE patients have lower perfusion values compared to controls, however, there is an overlap between the two groups, suggesting that not all NE patients suffer from low mucosal perfusion levels.

Low esophageal mucosal blood flow in patients with nutcracker esophagus

Nutcracker esophagus (NE) is characterized by high-amplitude peristaltic esophageal contractions, and these patients often present with symptoms of "angina-like" or noncardiac chest pain. Tissue ischemia is a known cause of visceral pain, and the goal of our present study was to determine whether esophageal wall blood perfusion (EWBP) is reduced in patients with NE. Fourteen normal subjects (mean age 51 yr, 11 men) and 12 patients (mean age 53 yr, 9 men) with NE and noncardiac chest pain were investigated. The EWBP was measured continuously using a custom-designed laser Doppler probe tethered to a Bravo capsule, which anchored it to the esophageal wall. The baseline EWBP in normal subjects was 651 ± 27 perfusion units. In patients with NE, the baseline EWBP was significantly lower than in the normal subjects (451 ± 32 perfusion units). The EWBP decreased after injection of edrophonium (which increases muscle contractions) and increased following sublingual nitroglycerin administration (which relaxes muscle) in normal subjects, as well as in NE patients. Spontaneous pain events during the recording period were often associated with drops in the EWBP. We propose that low EWBP leads to hypoxia of the esophageal tissue, which may be a mechanism of esophageal pain in patients with NE.

Esophageal wall blood perfusion during contraction and transient lower esophageal sphincter relaxation in humans

We recently reported that esophageal contraction reduces esophageal wall perfusion in an animal study. Our aim was to determine esophageal wall blood perfusion (EWBP) during esophageal contraction and transient lower esophageal sphincter relaxations (TLESRs) in humans. We studied 12 healthy volunteers. A custom-designed laser Doppler probe was anchored to the esophageal wall, 4-6 cm above the LES, by use of the Bravo pH system so that the laser light beam stay directed toward the esophageal mucosa. A high-resolution manometry equipped with impedance electrodes recorded esophageal pressures and reflux events. Synchronized pressure, impedance, pH, and EWBP recordings were obtained during dry and wet swallows and following a meal. Stable recordings of laser Doppler EWBP were only recorded when the laser Doppler probe was firmly anchored to the esophageal wall. Esophageal contractions induced by dry and wet swallows resulted in 46 ± 9% and 60 ± 10% reduction in the EWBP, respectively (compared to baseline). Reduction in EWBP was directly related to the amplitude (curvilinear fit) and duration of esophageal contraction. Atropine reduced the esophageal contraction amplitude and decreased the EWBP reduction associated with esophageal contraction. TLESRs were also associated with reduction in the EWBP, albeit of smaller amplitude (29 ± 3%) but longer duration (19 ± 2 s) compared with swallow-induced esophageal contractions. We report 1) an innovative technique to record EWBP for extended time periods in humans and 2) contraction of circular and longitudinal muscle during peristalsis and selective longitudinal muscle contraction during TLESR causes reduction in the EWBP; 3) using our innovative technique, future studies may determine whether esophageal wall ischemia is the cause of esophageal pain/heartburn.

Effect of esophageal contraction on esophageal wall blood perfusion

Myocardial blood flow occurs during the diastolic phase of the cardiac cycle, because myocardial contraction during the systolic phase impedes myocardial perfusion. Using laser Doppler perfusion technique, we studied the effect of esophageal contraction on the esophageal wall perfusion. Studies were conducted in rats. A laser Doppler probe was anchored to the esophageal wall, and wall perfusion was studied under various experimental conditions. Increase and decrease in the systemic blood pressure induced by different pharmacological agents was associated with the increase and decrease in the esophageal wall perfusion, respectively. Esophageal contractions induced by electrical stimulation of the vagus nerve and electrical stimulation of the muscle directly resulted in a reduction in the esophageal wall perfusion, in a dose-dependent fashion. Esophageal wall perfusion could be monitored by placing the Doppler probe on the esophageal mucosa or on the outside of the esophageal wall. Esophageal contraction impedes entry of blood into the esophageal wall. Future studies may investigate if ischemia of the esophageal wall induced by sustained esophageal contractions/esophageal spasm is the cause of esophageal pain symptoms in humans.

The effect of edrophonium chloride-induced chest pain on esophageal blood flow and motility

BACKGROUND

It is not known to what extent patients with non-cardiac chest pain have esophageal ischemia or motor dysfunction. The aim of this study was to investigate whether chest pain provoked by intravenous edrophonium chloride could be due to esophageal ischemia or to muscular spasm.

METHODS

Sixteen patients with a history of non-cardiac chest pain took part. Ten patients (32-69 years old) who did not develop chest pain with intravenous edrophonium chloride were compared with six patients (50-71 years old) who did develop edrophonium-provoked chest pain. Esophageal motility was monitored manometrically. Changes in esophageal blood flow, assessed as the rewarming time after esophageal cooling, was measured with a thermistor technique.

RESULTS

The esophageal rewarming time after cooling was the same before and during the edrophonium test in both groups. The esophageal contraction amplitudes and contraction duration were significantly increased only in patients with edrophonium-provoked chest pain.

CONCLUSION

Strong esophageal contractions and not a decreased blood flow in the esophageal wall seem to be the cause of chest pain provoked by intravenous edrophonium chloride.

Variations in esophageal oxygen tension measured with intraluminal antimony electrodes

Monocrystalline antimony electrodes (crystallographically oriented monocrystalline antimony; COMA) are known to be sensitive to oxygen and to pH. Accordingly, it has been shown that COMA electrodes can be used for the measurement of tissue oxygen tension provided the pH remains constant or is accounted for by the simultaneous use of a glass electrode. In this study the combination of a COMA together with a glass electrode was evaluated for measurement of esophageal oxygen tension in 5 patients. The COMA electrodes showed a mean value of 2.1 pH units higher than the glass electrodes, corresponding to a pO2 level in the esophagus of 10 kPa. As the more protracted oxygen effect on the COMA electrodes was easily recognized, especially in levels of the pH above 7.8 units, they were used for indirect evaluation of intraluminal oxygen tension in the esophagus in a further 57 patients, monitored over 24 h for gastroesophageal reflux disease. The intraluminal pO2 decreased in the supine position and with increase in age. An increase in pO2 was seen after eating and during reflux periods. The changes in pO2 are interpreted as being secondary to blood flow alterations in the esophagus.