Contribution of the endotracheal tube and the upper airway to breathing workload

The influence of the endotracheal tube (ETT) during a T-piece trial remains controversial. Our aim was to compare the work of breathing of 14 successfully extubated patients at the end of a 2-h trial (T) and after extubation (E) of the trachea, and to assess, using the acoustic reflection method, the resistance of the endotracheal tube and of the supraglottic airway as well as their related work. We found that the work of breathing of the patients was identical between T and E (1.72 +/- 0.59 versus 1.63 +/- 0.45 J/L; p = 0.50 and 23.5 +/- 10.6 versus 22.6 +/- 9.7 J/min; p = 0.70). There was no significant difference between the beginning and the end of the T-piece trial (1.57 +/- 0.53 versus 1.72 +/- 0.59 J/ L, p = 0.10). The work caused by the ETT amounted to 11.0 +/- 3.9% of the total work of breathing. The supraglottic airway resistance was in the normal range and was significantly smaller than the endotracheal tube resistance (0.79 +/- 0.4 versus 1.43 +/- 0.31 cm H2O x s/L; p = 0.008, flow = 0.25 L/s). We conclude that a 2-h trial of spontaneous breathing through an endotracheal tube well mimics the work of breathing performed after extubation, in patients who pass a weaning trial and do not require reintubation.

Linear servo-controlled pressure generator for forced oscillation measurements

In respiratory input impedance measurements, the low-frequency range contains important clinical and physiological information. However, the patient's spontaneous ventilation can contaminate the data in this range, leading to unreliable results. Unbiased estimators are a good alternative to overcome this problem, provided that the generator is considered linear. This condition is not fulfilled by most existing generators as they are based on loudspeakers, which have strong nonlinearities. The present work aims to contribute to the solution of this problem, and describes a pressure generator that minimises the nonlinearities by an optical sensor placed in a position feedback loop. The static evaluation shows a high linearity for the optical system. The well known frequency response of pressure transducers is used in the dynamic evaluation of the instrument. The analysis of the generator shows that the use of position feedback improved the frequency response. The total harmonic distortion (THD) measurement shows that closed loop resulted in an effective decrease in the nonlinearities. The reduction of THD achieved by the servo-controlled generator can contribute to the practical implementation of the unbiased estimators, increasing the reliability of the impedance data, especially in the low-frequency range. This system is compared with conventional generators and with another servo-controlled system.

Incremental threshold loading: a standard protocol and establishment of a reference range in naive normal subjects

Incremental threshold loading (ITL) has been proposed as a test of inspiratory muscle strength and endurance. To date, however, there has been no standardized protocol for an ITL test, and no reference range, with different investigators using a variety of different pressure increments in small numbers of subjects. We developed an ITL test using the weighted plunger (WP) principle, which uses standard increments of pressure. In our protocol subjects inspire through the WP generating an initial threshold opening pressure of 10 cmH2O. This pressure is raised at 2 min intervals in increments of 5 cmH2O until they fail to lift the plunger on two consecutive attempted breaths. Sixty healthy volunteers (30 males and 30 females) aged 20-80 yrs performed the ITL test. Twelve subjects (six females and six males) performed the test twice to assess reproducibility and repeatability. Using stepwise multiple linear regression, we regressed the maximum threshold pressure sustained for a full 2 min (Pmax) against age, height, weight and static maximum inspiratory mouth pressure (MIP). Pmax was significantly related to age but not to either height or weight, the regression equation for males was Pmax (cmH2O)=103.8 - (1.0 x age in years), and for females was Pmax (cmH2O)=93.7 - (1.0 x age in years). The within-subject standard deviation for those repeating the ITL test was 5.4 cmH2O. Incremental threshold loading is a simple technique with good reproducibility, which most naive subjects can use without difficulty. By using standard pressure increments and performing the test in a large number of naive subjects, we have established a reference range that should be applicable wherever similar pressure increments are used.

The incidence of artery puncture with central venous cannulation using a modified technique for detection and prevention of arterial cannulation

BACKGROUND

Cannulation of the central circulation is essential for management of patients who require major surgery, and for patients who are critically ill. Arterial puncture is the most frequent complication associated with central venous cannulation, and is potentially fatal. Detection of arterial puncture can be problematic, especially in patients with cyanotic congenital heart disease.

METHODS

One thousand eleven consecutive cardiothoracic and vascular surgical patients who required central venous cannulation were studied using a new technique for detection of arterial puncture and prevention of arterial cannulation. This technique involves continuous pressure transduction of the steel introducer needle. Central venous cannulation was attempted in all patients. The sites of attempted catheterizations, number of arterial punctures and cannulations, and the number of successful catheterizations were noted. All patients were treated in accordance with standard anesthetic and surgical techniques in the institution.

RESULTS

One thousand one hundred seventy-two central venous catheters were placed. The overall success rate was 99.6%. The incidence of arterial puncture was 9.3% for central venous cannulation attempts of the internal jugular, subclavian, and femoral veins. No arterial cannulation occurred, and none of the patients had significant complications. Congenital heart disease patients had a higher incidence of arterial puncture (14.1%) and a lower rate (96.8%) of successful cannulation.

CONCLUSION

Pressure transduction of the steel needle is a useful technique for detecting arterial puncture and preventing arterial cannulation during attempts to achieve central venous cannulation.

The design and performance of an experimental external fixator with variable axial stiffness and a compressive force transducer

A unilateral external fixator has been designed for controlled experiments into the effects of micromovement on fracture healing. The experimental model used is based on a diaphyseal osteotomy of the right tibia of the sheep. The main bar has linear bearings, which allows free axial movement. This is then controlled by a spring whose stiffness can be varied. The resulting axial micromovement can be calculated from the measured compressive force and the known axial stiffness of the fixator. The transducer has limits of error of +13.3 N and -44.5 N. Preliminary measurements showed maximum micromovement at the fracture site of 0.48 mm during slow walking.

Patient-ventilator trigger asynchrony in prolonged mechanical ventilation

STUDY OBJECTIVE

To investigate patient-ventilator trigger asynchrony (TA), its prevalence, physiologic basis, and clinical implications in patients requiring prolonged mechanical ventilation (PMV).

STUDY DESIGN

Descriptive and prospective cohort study.

SETTING

Barlow Respiratory Hospital (BRH), a regional weaning center.

PATIENTS

Two hundred consecutive ventilator-dependent patients, transferred to BRH over an 18-month period for attempted weaning from PMV.

METHODS AND INTERVENTIONS

Patients were assessed clinically for TA within the first week of hospital admission, or once they were in hemodynamically stable condition, by observation of uncoupling of accessory respiratory muscle efforts and onset of machine breaths. Patients were excluded if they had weaned by the time of assessment or if they never achieved hemodynamic stability. Ventilator mode was patient triggered, flow control, volume cycled, with a tidal volume of 7 to 10 mL/kg. Esophageal pressure (Peso), airway-opening pressure, and airflow were measured in patients with TA who consented to esophageal catheter insertion. Attempts to decrease TA in each patient included application of positive end-expiratory pressure (PEEP) stepwise to 10 cm H2O, flow triggering, and reduction of ventilator support in pressure support (PS) mode. Patients were followed up until hospital discharge, when outcomes were scored as weaned (defined as >7 days of ventilator independence), failed to wean, or died.

RESULTS

Of the 200 patients screened, 26 were excluded and 19 were found to have TA. Patients with TA were older, carried the diagnosis of COPD more frequently, and had more severe hypercapnia than their counterparts without TA. Only 3 of 19 patients (16%), all with intermittent TA, weaned from mechanical ventilation, after 70, 72, and 108 days, respectively. This is in contrast to a weaning success rate of 57%, with a median (range) time to wean of 33 (3 to 182) days in patients without TA. Observation of uncoupling of accessory respiratory muscle movement and onset of machine breaths was accurate in identifying patients with TA, which was confirmed in all seven patients consenting to Peso monitoring. TA appeared to result from high auto-PEEP and severe pump failure. Adjusting trigger sensitivity and application of flow triggering were unsuccessful in eliminating TA; external PEEP improved but rarely led to elimination of TA that was transient in duration. Reduction of ventilator support in PS mode, with resultant increased respiratory pump output and lower tidal volumes, uniformly succeeded in eliminating TA. However, this approach imposed a fatiguing load on the respiratory muscles and was poorly tolerated.

CONCLUSION

TA can be easily identified clinically, and when it occurs in the patient in stable condition with PMV, is associated with poor outcome.

Direct measurement of intra-abdominal pressure in various conditions

OBJECTIVE

To standardise a direct method for measuring intra-abdominal pressure (IAP), to correlate the results with intrarectal pressure, and to compare the results in various conditions.

DESIGN

Prospective open study.

SETTING

Teaching hospital, Egypt.

SUBJECTS

34 Subjects in 4 groups: control (n = 11), hernia (n = 8; 6 umbilical and 2 incisional), mass (n = 7; 6 enlarged spleen and 1 carcinoma of sigmoid), and obese (n = 8; a mean of 40% above expected weight).

INTERVENTIONS

Measurement of IAP with a Verres needle connected to a pressure transducer with the patient at rest, straining, supine, erect, and before and after anaesthesia. Intrarectal pressure was measured simultaneously.

MAIN OUTCOME MEASURES

Reproducibility and correlation between the two measurements.

RESULTS

The hernia group had significantly lower IAP than controls both at rest and on straining (mean (SD) 2.7 (1.5) cm H2O compared with 7.0 (5.09) and 6.1 (2.7) compared with 20.5 (7.9), p < 0.01 in each case). Neither the mass nor the obese group differed from the controls at rest, but the pressure was higher on straining (31.2 (1.4) and 33.5 (2.07) cm H2O, respectively, compared with 21.9 (7.3), p < 0.05 in each case). There was a significant drop in IAP after anaesthesia in all groups, and no significant difference between intrarectal pressure and IAP in any group.

CONCLUSION

The method of measuring IAP is reproducible. Intrarectal pressure is similar to IAP and can therefore be used instead of it.

Calibration problems encountered while monitoring stump/socket interface pressures with force sensing resistors: techniques adopted to minimise inaccuracies

Force sensing resistors (FSR) have been used to measure dynamic pressures at the interface between appliance and patient. Inaccuracies using FSRs have been reported. This paper summarises both the calibration problems encountered and the techniques adopted to minimise inaccuracies. It is considered that, by calibrating the transducers attached to the socket, and by adopting a strict test protocol, FSRs may provide a guide to the dynamic pressure distribution applied to the trans-tibial stump during gait.

[Evaluation of continuous blood pressure monitoring by arterial tonometry in the aged]

We compared tonometry systolic pressure with direct systolic pressure in 12 elderly patients (9 patients with sinus rhythm and 3 patients with atrial fibrillation) and 1 young adult patient undergoing surgical procedures in order to evaluate reliability of continuous blood pressure by arterial tonometry. In elderly patients when blood pressure fluctuated, the differences between tonometry systolic pressure and direct systolic pressure were larger compared with when blood pressure was stable. In the elderly with sinus rhythm, the correlation with stable blood pressure was 0.908; while that with fluctuating blood pressure was 0.838. In atrial fibrillation group, the differences between stable blood pressure and fluctuating blood pressure were still larger. The results indicate that it is difficult to use tonometry method as a reliable tool for blood pressure monitoring in geriatric anesthesia under circumstances of fluctuating blood pressure.

Two-point calibration procedure of the forced oscillation technique

The forced oscillation technique is usually calibrated by loading the measuring device with a known impedance. A correction function is calculated, relating the measured and reference impedances at each frequency. However, this one point calibration procedure does not account for transducer asymmetry. A procedure has previously been presented to circumvent this problem: in addition to one known reference impedance, the calibration was repeated with the system occluded (infinite impedance). The aim of the present study was to evaluate a variant of this procedure, in which instead of resorting to an extreme condition imposing high requirements on the flow measuring system, two reference loads of 4 and 50 hPal-1 s were measured, thus covering the range of impedances observed in children and infants (a two-point procedure). The calibration procedure was performed with these two impedances and evaluated with a third impedance of approximately 17 hPal-1 s. The results of three calibration procedures were compared: one-point, two-point and a previously reported calibration procedure. Impedances consisted of sintered glass and mesh wire screens mounted in glass or polyvinyl tubes. For low impedance values, in the range of 4 to 17 hPal-1 s, measured and predicted values were similar for the three calibration procedures at frequencies from 4-52 Hz, although with the one point calibration procedure there was some underestimation above 44 Hz. With the highest load, especially above 32 Hz, marked discrepancies between measured and predicted values were observed with the one-point calibration procedure and the previously reported calibration procedure. Under these circumstances the two-point procedure is preferred.

A simple versatile method for measuring tail cuff systolic blood pressure in conscious rats

1. The non-invasive measurement of tail cuff systolic blood pressure in conscious rats is routinely used in long-term cardiovascular studies. There are a number of commercially available tail cuff systems, however, these apparatus are generally expensive and are dedicated for single-task operations. In the present study, a simple method for measuring systolic blood pressure, which requires only minor modifications to the existing hardware found in most cardiovascular laboratories, is described. 2. Systolic blood pressure measurements were made in the conventional manner by determining the systolic blood pressure which coincided with the restoration of the caudal artery pulse. This was achieved by using an inexpensive piezo-electric pulse transducer to detect the pulse, and this was coupled to a standard data-acquisition system (MacLab, ADInstruments) normally set up to record blood pressure. This method was compared with another established tail cuff method, as well as with direct intra-arterial recordings. 3. It was found that the results obtained using both tail cuff systems were in good agreement when systolic blood pressure was measured in Wistar-Kyoto rats and spontaneously hypertensive rats. In addition, systolic blood pressure was measured over 4 weeks in 2K1C rats and sham-operated rats, with both tail cuff methods producing similar results, which were not significantly different from direct intra-arterial recordings in the same animals. 4. Thus, in the present study, with only minor modifications, the same equipment was used for both direct and indirect determinations of systolic blood pressure. This situation differs from other conventional tail cuff systems since these items are designed for a single purpose. Therefore, the current method using piezo-electric sensor/MacLab-technology should be viewed as a relatively simple, flexible and cheap alternative method to measure tail cuff systolic blood pressure in conscious rats.

In-line pressure-flow module for in vitro modelling of haemodynamics and biosensor validation

An in-line pressure-flow module for in vitro modelling of haemodynamics and biosensor validation has been developed. Studies show that good accuracy can be achieved in the measurement of pressure and of flow, in steady and pulstile flow systems. The model can be used for development, testing and evaluation of cardiovascular-mechanical-electrical anlogue models, cardiovascular prosthetics (i.e. valves, vascular grafts) and pressure and flow biosensors.

[Feasibility of "Valsalva Leak Point Pressure". Prospective study]

OBJECTIVE

To prospectively evaluate the feasibility of determination of the Valsalva Leak Point Pressure (VLPP).

PATIENTS AND METHODS

From 1st January to 31st July 1996, 155 consecutive patients investigated for urinary incontinence with no pelvis static disorder performed Valsalva manoeuvres during cystomanometry in order to determine the VLPP. The examination was performed in the standing position at a filling volume of 200 cc with then without a vesical pressure transducer. The mean age of the patients was 54 +/- 16 years (range: 16-84 years).

RESULTS

The mean maximal intensity of abdominal straining pressure measured by the intravesical transducer was 72 +/- 28 cm of water. The VLPP could not be determined in 50.4% of cases, as the abdominal straining pressure during the Valsalva manoeuvre was less than 60 cm of water. No correlation was observed between abdominal straining pressure and patient age (r = 0.13; p > 0.1).

CONCLUSION

Leak Point Pressure cannot always be determined by the Valsalva method. Other techniques of progressive increase of intravesical pressure must be investigated.

[Dynamic in vivo skin pressure measurement in quality control of compression stockings]

The well-documented positive effect of compression stocking therapy on the venous macro- and microhemodynamics of the legs can only be attained if the stockings fit well. In order to determine the effective pressure exerted by compression stockings, we usually deleted in US journals. One can get this out of journal and author's address have developed a new measuring method based on piezoresistant microprobes and a microprocessor unit. With our 2-mm-thick, 5-mm diameter probe, the pressure between the compression stocking and skin can be measured at any location desired. A temporal resolution of 50 Hz makes it possible to carry out dynamic measurements while the patient is walking or performing exercises on tiptoes. Here we present 4 typical cases out of a total of over 80 which we have evaluated. We have decided empirically that the pressure exerted by a class-2 compression stocking on the skin at the height of the ankles (b-position) should not exceed 70 mm Hg while resting and a peak of 110 mm Hg while exercising on tiptoes. At the middle of the calf (c-position) these values should not exceed 60 mm Hg at rest and 80 mm Hg on tiptoes. The pressure should decrease from the distal to proximal direction in order to produce a drainage gradient. We have found empirically that a pressure gradient of 30-40% from the b to the c measurement is favorable. Too high a proximal pressure or too high a pressure on a part of the lower leg causes pain and swelling. Too low a pressure, on the other hand, does not produce the desired vascular effect and alleviation of symptoms. Although dynamic pressure measurements take about 20-30 minutes per leg, they markedly improve patient compliance with compression therapy.

Systematic and random error in repeated measurements of temporal and distance parameters of gait after stroke

OBJECTIVE

To obtain intersession estimates of error for temporal and distance (TD) parameters of gait in a sample of stroke patients undertaking inpatient rehabilitation.

DESIGN

Thirty-one stroke patients were measured with an instrumented footswitch system (after a median of 46 days poststroke; interquartile range = 26 to 63) walking over a 10-meter distance a total of four times on 3 consecutive days. Two familiarization walks provided intrasession retest data.

RESULTS

Metric estimates of systematic and random error have been provided for obtained TD parameters. Proportional indices of reliability (ICC [2,1] and Pearson's r) were generally high, ranging from .72 to .94.

CONCLUSION

By quantifying systematic and random error associated with the process of repeated measurements, criteria have been provided for evaluating change in TD variables during rehabilitation. Although error for gait velocity was small relative to individual differences in the stroke group, it was large relative to levels of change derived from measurements reported during typical periods of rehabilitation. Serial measurements of gait during rehabilitation may be better than two consecutive measurements. This study highlights the need to interpret estimates of error according to the purpose of measurement.

Determination of appropriate recording force for non-invasive measurement of arterial pressure pulses

1. Non-invasive recording techniques of the arterial pressure pulse will distort the arterial wall and may alter pulse wave measurements. We hypothesized that intersubject variability of these measurements would be reduced if recording forces were normalized to reflect individualized arterial occlusion forces. 2. In 10 normal male subjects (age 24 +/- 1 years), brachial, radial and finger arterial pressure pulses were recorded simultaneously using volume displacement pulse transducers (Fukuda TY-303) and a finger pressure monitoring system (Finapres, Ohmeda 2300) and were made at 2, 5 and 10-100% (10% increments) of the brachial arterial force associated with marked distortion of finger pulsations. Forces were applied at the brachial site in a randomized order while a constant 1.8 N force was applied at the radial artery site. Pressure pulses were analysed using the discrete fast Fourier transform. 3. Pulse amplitude, contour, wave velocity and relative transmission ratios remained relatively constant until the branchial artery recording force exceeded 59.9 +/- 0.3% of the largest recording force used in each subject (7.14 +/- 0.75 N). The finger pulse pressures (P < 0.0001), radial pulse amplitudes (P < 0.0001) and contours (harmonics 2-6, P < 0.003), pulse wave velocity (P < 0.021) and relative transmission ratios (harmonics 3-7, P < 0.01) then decreased with higher recording forces. 4. To avoid distortion, non-invasive recordings of arterial pressure pulse amplitude, contour, pressure wave velocity and relative transmission ratios along a peripheral arterial segment should use recording forces of less than 60% of the force associated with marked distortion of finger pulsations.

Simultaneous monitoring of head-to-cervix forces, intrauterine pressure and cervical dilatation during labour

In many westernized countries, the caesarean section role has now reached 15% or more, most commonly because of slow progress in labour. In order for labour to result in a vaginal delivery, the uterine cervix must dilate to allow the foetus to travel through the birth canal. This process is driven by uterine contractions, but the mechanisms by which the contractions result in cervical dilatation are still far from clear. The force exerted by the presenting part (foetal head) on the cervical tissue during contractions (head-to-cervix force, HCF) has been shown to be the variable with the best correlation with cervical dilatation. Unfortunately, the mechanism by which these two variables are related is still poorly understood. In order to investigate the relationship between head-to-cervix force, intrauterine pressure (IUP) and cervical dilatation, we have developed a system for their simultaneous and continuous monitoring during labour. The HCF is measured by using a novel intrauterine probe which is slipped alongside the foetal head so as to lie sandwiched between the latter and the cervix. The probe is fitted with six specially designed miniature force sensors, spaced 1.8 cm apart, which respond linearly and approximate the behaviour of load cells. They are interfaced with a PC by circuitry that allows auto-zeroing and drift compensation. The system enables simultaneous acquisition of intrauterine pressure and foetal heart rate (measured using a Sonicaid Meridian foetal monitor) via a serial link, together with continuous cervical dilatation measured by a caliper-like device applied to the cervix. Some preliminary data are presented, which suggest that the system can be used to investigate the role played by head-to-cervix force and intrauterine pressure in the cervix dilatation process.

Infants' suckling responses to the flavor of alcohol in mothers' milk

Contrary to medical folklore, previous research has demonstrated that alcohol consumption by lactating women diminished milk intake by their infants during breast feeding. To determine whether this decrease in milk consumption was due to the infants responding to the altered flavor of the milk that also resulted, we evaluated the infants' intake and sucking responses to alcohol-flavored human milk outside of the context of breast feeding, thereby separating the changes due to the infants response to the flavor from any other changes that could also result from acute maternal alcohol consumption such as alterations in milk ejection or the composition of milk. The testing procedure consisted of a two-bottle preference test that was composed of four, 60-sec trials in which the mother's milk flavored with alcohol was alternated with the mother's milk alone in an ABBA or BAAB design. Attached to the nipple of each bottle was a transducer that responded to pressure changes produced by the infants' suckling. There was no suppression of sucking or intake in response to the ethanol-flavored milk. Rather, the infants consumed significantly more and sucked more frequently when drinking the alcohol-flavored milk compared with the unaltered milk. That experience with the flavor of alcohol in mothers' milk modified the infants' responses to alcohol flavor is suggested by the relationship between the reported frequency of mothers' drinking during lactation and the infants' rhythm and frequency of sucking when feeding the alcohol-flavored milk. These findings indicate that infants can readily detect the flavor of alcohol in mother's milk but that the decrease in consumption at the breast after maternal alcohol consumption is apparently not due to the infants rejecting the flavor of alcohol in their mothers' milk.

Comparison of pulsatile versus nonpulsatile perfusion on the postcardiopulmonary bypass aortic-radial artery pressure gradient

OBJECTIVE

To investigate whether the type of perfusion, pulsatile (PP) or nonpulsatile (NP), has any effect on the pressure gradient that exists between the aortic root and the radial artery after cardiopulmonary bypass (CPB).

DESIGN

Prospective, randomized study.

SETTING

Tertiary care, university hospital.

PARTICIPANTS

Eighty patients undergoing elective, hypothermic coronary artery bypass graft (CABG) surgery.

INTERVENTIONS

Pulsatile perfusion with a pulse pressure of 10 to 20 mmHg and a frequency of 60 to 80 beats/min was created during the hypothermic phase of CPB. Both the radial artery and aorta were cannulated and attached to separate transducers but displayed and analyzed on the same monitor.

MEASUREMENTS AND MAIN RESULTS

Simultaneous recordings of radial artery and aortic root blood pressure were made prebypass, during CPB, and after discontinuation of CPB at 2, 5, and 10 minutes. During CPB, the PP group had a significantly higher mean pulse pressure measured at the aortic root than the NP group (15.5 +/- 8.1 v 1.7 +/- 2.7, p < 0.0001). The aortic-to-radial-artery gradient within both groups was significantly different after CPB for systolic (SBP), diastolic (DBP), and mean pressure (MAP) (p < 0.0001). There were, however, no statistically significant differences between the PP and NP groups in the aortic-to-radial-artery gradient after CPB for either SBP, DBP, or MAP.

CONCLUSIONS

Pulsatile perfusion had no effect on the aortic root radial artery blood pressure gradient after CPB in elective CABG surgery patients.

Isometric tension of cultured endothelial cells: new technical aspects

In this paper new technical aspects are discussed in the measurement of the low amount of force typically expressed in cultured endothelial cells. We illustrate how potential background noises interfere with signal acquisition. We present a new generation prototype that measures isometric tension in vitro in multiple samples and in more than on isometric vector. We report that thrombin increases isometric tension in at least two separate vectors that are directed in opposite directions. We also report that phorbol ester dibutyrate can randomly mediate a false relaxation (anisotropic contraction) in cultured PPAEC, when the force vector is directed opposite to the referenced isometric vector of the transducer. In contrast, stimulation of cultured HUVEC with the cAMP agonists, theophylline and forskolin, decreased isometric force in both vectors. Thus direction of the force vector needs to be considered when interpreting isometric tension in cultured endothelial cells.

Function of upper esophageal sphincter during swallowing: the grabbing effect

This study investigated deglutitive axial force developed within the pharynx, upper esophageal sphincter (UES), and cervical esophagus. Position and deglutitive excursion of the UES were determined using combined manometry and videofluoroscopy in eight healthy volunteers. Deglutitive clearing force was quantified with a force transducer to which nylon balls of 6- or 8-mm diameter were tethered and positioned within the oropharynx, hypopharynx, UES, and cervical esophagus. Axial force recordings were synchronized with videofluoroscopic imaging. Clearing force was dependent on both sphere diameter (P < 0.05) and location, with greater force exhibited in the hypopharynx and UES compared with the oropharynx and esophagus (P < 0.05). Within the UES, the onset of traction force coincided with passage of the pharyngeal clearing wave but persisted well beyond this. On videofluoroscopy, the persistent force was associated with the aboral motion of the ball caught within the UES. Force abated with gradual slippage of the UES around the ball. The force attributable to the combination of UES contraction and laryngeal descent was named the grabbing effect. The grabbing effect functions to transfer luminal contents distal to the laryngeal inlet at the end of the pharyngeal swallow, presumably acting to prevent regurgitation and/or aspiration of swallowed material.