Problems in timing of respiration with the nasal thermistor technique.

When one analyzes transvalvular and venous flow velocity patterns, it is important to relate them to respiration. For this reason a nasal thermistor technique is often used, although it is known that this signal is delayed in relation to intrathoracic pressure changes. The magnitude and variation in delay have not been investigated previously and were, therefore, studied in a model experiment in 10 normal subjects, in 10 patients with obstructive, and in 10 patients with restrictive pulmonary disease. Esophageal pressure variations measured with an air-filled balloon served as a gold standard for intrathoracic pressure changes. During basal conditions there was, for both patient groups and normal subjects, a considerable delay of the thermistor signal. The average delay for all subjects was 370 msec with a wide variation (from 120 to 720 msec). At higher breathing frequencies the delay shortened to 310 msec (P < 0.01) but there was still a wide variation (ranging from 200 to 470 msec). Theoretic calculations show that the delay caused by the respiratory system accounts for only a minor portion of the total delay. Model experiments confirmed that the response characteristics of the thermistor probes limit the accuracy in timing of respiration. The total delay with the investigated thermistor technique is too long and variable to fulfil clinical demands.

Measurements of light transmission through single melanophores.

A photometrical method has been developed that allows assessment of subcellular pigment migration in melanophores of the fish cockoo wrasse (Labrus ossifagus L.) The pigment migration was studied with local light spot transmission measurements. Depending on where the light beam is placed on the melanophores it is possible to study events within an area of approximately 75 microns 2. Measuring pigment translocation in different parts of a melanophore gives new possibilities to study how cell membrane receptor-mediated signals are spread within a single cell, which will increase our understanding of how receptor activating drugs exert their cellular effect. The technique can be used in pharmacological and biophysical studies and in biosensors, pharmaceutical screens, environmental detectors, etc. The method clearly has the ability to study local and small changes in light transmission due to displacement of melanophore pigment granules. Since one melanophore on the tip of an optical fibre would be enough to obtain a measurable effect, the presented technique provides the basis for future development of biosensors small enough for in vivo applications, e.g., to monitor the catecholamine levels of circulating blood.