Micro-flowcell conductometric sweat analysis for cystic fibrosis diagnosis

Abstract

SUMMARY. This paper describes a device speci®cally designed to facilitate neonatal sweat testing. The components are sized appropriately for attachment to the limbs of newborns. Iontophoretic electrodes, with pilocarpine gel inserts, are latched into small holders attached by straps to the limb. The holder at the anodic site remains in place to receive and align the sensor cell, which uses a conical collecting surface to channel the sweat directly and anaerobically from the sweat ducts to the continuous ow-through conductivity cell within its body. A crib-side analysis unit incorporates an iontophoretic power supply and displays a continuous readout of sweat electrical conductivity. The average conductivity during a speci®c time interval and the initial sweating rate are automatically displayed. The method, which simpli®es sweat tests, is currently being assessed in three neonatal clinical trials to test its ability to reduce test failures in the newborn due to insuf®cient sweat.

Nanoduct® sweat testing for rapid diagnosis in newborns, infants and children with cystic fibrosis

“…The Nanoduct® sweat analysis system (Wescor Inc., Logan, Utah, USA) incorporates the classical method of inducing sweat secretion by pilocarpine iontophoreses and a conductivity measurement in one single system and one step procedure [21]. During the whole manipulation for testing, the iontophoresis device and the flow cell which measures conductivity is attached to the patient by one wire connected to the Nanoduct® inducer/analyzer central unit.…”

“…This value is approximated to a solution of sodium chloride that has the same conductivity as the sweat sample at the same temperature. The measured sweat conductivity has been shown to be about 15 mmol/L higher than the sweat chloride concentration because of additional anions such as bicarbonate and lactate [13,21]. The manufacturer of the Nanoduct® system defines a cut-off value of > 80 mmol/L to diagnose CF and a cut-off value <60 mmol/L to exclude CF in children under 16 years [21].…”

“…Nanoduct® is a new diagnostic system that induces, collects and analyzes sweat in one step while the required electrodes and sensors are attached to the patient [21]. Compared to sweat volumes between 75 to 100 μl required by other systems, this system only needs 3 μl of sweat and test results are available within half an hour [1].…”

Changes in the index of sweat ion concentration with increasing sweat during passive heat stress in humans

“…Therefore, these methods only facilitate measurement of skin surface electrolyte concentration at a given time. The amount of sweat electrolytes can also be estimated by measurement of the sweat electrical conductivity (Boisvert and Candas 1994;Heeley et al 2000;Webster and Quirante 2000). However, these methods for measuring sweat conductivity have limitations at very low levels (at the onset) of sweat and for long periods of continuous measurement, because they are used to collect sweat for particular periods (>10 min) and they sometimes fail to allow for low concentration or insufficient volumes of sweat.…”

“…To test this, we measured the index of sweat ion concentration by a new method (Shamsuddin and Togawa 1998) that is advantageous because it overcomes some of the aforementioned limitations of the earlier methods (Boisvert and Candas 1994;Heeley et al 2000;Webster and Quirante 2000) and can be used over long periods of time to obtain continuous measurement with differing sweat rates. Also, it can test the possibility that the ion reabsorption capacity could be detected continuously by using the relationship between sweat rate and sweat conductivity that may reflect the sweat ion concentration.…”