In vitro airway specimens are widely used to evaluate airway ciliary function. However, the function of in vitro ciliated cells may be far different from their actual in vivo physiological conditions. Due to the lack of a valid technique, direct images of in vivo airway ciliary motion have never been captured and analyzed before. This study aims to examine nasal ciliary motion in living guinea pigs with comparison to in vitro observation. Nasal septum mucosa was exposed in anaesthetized guinea pigs and directly examined using a digital microscopy system. The study included three parts: (1) measurement of ciliary beat frequency (CBF) of nasal mucosa at room temperature in living guinea pigs and immediately after death, and in dissected mucosa specimens/cells for comparison; (2) monitoring of nasal ciliary motion, CBF, and ciliary beat distance (CBD) over 12 h in both living guinea pigs and dissected mucosa specimens/cells; and (3) measurement of ciliary motion changes in responses to temperature variations. Compared with when the animal was alive, the CBF after death and in dissected mucosa specimens/cells was lower by about 20% ( P < 0.05). CBF and CBD variation in living guinea pigs was within 10% over time. The slope of CBF/temperature profile was 0.18 ± 0.01 Hz/°C in living guinea pigs, 0.51 ± 0.02 Hz/°C for dissected mucosa specimens, and 0.48 ± 0.03 Hz/°C for isolated ciliary cells. The technique described in this study makes it feasible to study ciliary motion in living animals using the digital microscope system. Ciliary function changes immediately after death. Ciliary motion in a living animal is more stable over time and has a different response to temperature change as compared with in vitro observation results. Impact statement Cilia play an important role in the airway defense mechanism. So far, studies on ciliary function have mainly been based on in vitro methods. Images of in vivo ciliary motion are very difficult to capture. In this study, we describe a novel approach to observe and analyze nasal ciliary motion in living animals with comparison to in vitro observation. Such images of ciliary motion from living animals have not been reported to date. The result of the study indicates that in vivo ciliary physiological function differs from ex vivo and in vitro conditions in many ways, such as the stability over time and response to temperature variation. This is a good foundation for further in vivo analysis of airway ciliary physiological function in animals as well as humans.

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Due to the lack of an assessment approach, the image of in vivo nasal ciliary motion of allergic rhinitis (AR) has never been captured and analyzed to date. Here, we have used an optimized approach to analyze the nasal ciliary function in vivo in AR rats. The digital microscopy system, a method for direct observation of ciliary motion in a living AR rat model, was applied to visualize and measure ciliary motion in vivo, including ciliary beat frequency (CBF) and ciliary beat distance (CBD). The AR rat model was established by ovalbumin sensitization. Comparisons of nasal ciliary motion in vivo between the experimental group (ovalbumin sensitization, allergen, or histamine) and the control group were analyzed. In the living rat model of allergic rhinitis, CBF and CBD decreased to 57.8 and 73.1% of the control group, respectively, but were restored after administration of chlorpheniramine maleate. Ovalbumin (OVA) significantly inhibited the ciliary motion of normal mucosa in vivo. However, responding to the OVA challenge, the ciliary motion of OVA-sensitized mucosa would not decrease further and stay at a stable level. Histamine stimulated in vivo ciliary motion quickly within 30 min, but afterward, the ciliary motion gradually decreased below the baseline. These results have clarified that in vivo ciliary motion was impaired by nasal mucosal sensitization, and this impairment was most likely related to allergen challenge and histamine. In addition, the short-term stimulation and long-term inhibition effects of histamine on in vivo ciliary motion were first reported in this study.