Microvascular Research 52, 188-192 (1996)

Capillary Blood Cell Velocity in Human Skin Capillaries Located Perpendiculary to the Skin Surface: Measured by a new Laser Doppler Anemometer

M. Stücker, V. Baier, T.Reuther, K. Hoffmann, K. Kellam and P. Altmayer

INTRODUCTION

In general capillary loops of the skin are perpendicularly oriented to the skin surface. Only in a few areas of the human body, the lips, the nipple, or the nailfood, do the capillary loops run parallel to the skin surface. In the latter area capillary blood flow can be measured by means of modern noninvasive techniques like the so-called videocapillary microscope with frame-to-frame analysis (Böllinger et al., 1974), the flying spot technique (Tyml and Ellis, 1982), or the cross-correlation method (Fagrell et al., 1977a). However, there has been almost no technique available to measure skin blood flow in capillary loops located at a 90° angle to the skin surface until recently, when a new laser Doppler anemometer with a very small sample volume was introduced. The aim of this study was to evaluate this new device in a clinical situation, to control reproducibility, and to compare our results with results obtained from previous studies using other microscopic techniques.

MATERIALS AND METHODS

Laser Doppler Anemometer

In our investigations the laser Doppler anemometer CAM1 (KK Technology, England) was used. A technical description is given schematically in Fig. 1 (Not available on this page, Anm. d. Red.). The CAM1 includes a laser source (1.5 mW Laser Diode, wavelength 780 nm), focused by a microscope objective lens to a spot size of approximately 10 µ diameter. This results in a very small sample volume, so that the velocity in capillaries of 9.8 to 32.1 µ diameter can be singled out. A CCD camera (Model XC-75CE; Sony, Japan) is focused so that the plane and the laser focal point are the same. The output from the camera is used to identify the location of capillaries within the field of view. The operator then adjusts and maintains the position of the CAM1 so that the laser beam is positioned on a suitable capillary. An acoustic control with sounds from the Doppler shifts provides a good position for the device during the entire measurement. If a blood cell is moving with a velocity component perpendicular to the object plane then the laser radiation will be reflected with a Doppler shift. Laser radiation is also scattered by the vessel wall and surrounding tissue without beeing Doppler shifted. The CAM1 objective L2 collects some of the Doppler shifted and unshifted laser radiation. The wavelength-dependent beamsplitter BS1 seperates the collected laser radiation from the CCD image and routes it via mirrors M1 and M2 and beamsplitter BS2 to the photodetector. The photodetector detects the mixing or heterodyning of the two optical signals. The mixing produces a signal containing the sum and difference cal current in the photodetector. This is then amplified and processed, and the Doppler shift frequency detected. Since the Doppler shift is proportional to the velocity of the reflecting blood cells, the velocity is readily calculated.

Subjects

All measurements were performed in healthy volunteers. Subjects suffering from deseases influencing the microcirculation of the skin such as arterial hypertension, Raynaud's syndrome, arterial occlusive desease, atopic dermatitis or collagen vascular disease were excludd. Every measurement was caried out at the dorsal aspect of the proximal index finger. The subjects were investigated in a sitting position with the hand at heart level after acclimatization for at least 30 min. The finger under investigation was stabilized by a special finger holder. Moreover the forearm was immobilized by a cuff slightly inflated at 5 mmHg. To make the skin transparent and further minimize the reflections from the skin, surface oil was applied. The laboratory temperature was maintained at 21°.

Measurement of Resting Capillary Blood Cell Velocity

Resting capillay blood cell velocity (rCBV) was studied in 20 subjects (10 male, 10 female, mean age 28). In order to detect intraindividual differences of rCBV within a patient, resting blood velocity was measured in five capillaries in each individual.

Postocclusive Hyperamic Response (PRH)

The postocclusive hyperemic response was investigaed in 19 subjecs (9 male, 10 female, mean age 27). For this a cuff was placed at the uppe arm of each subject to perform suprasystolic arterial occlusion. At the beginning of the procedure rCBV was recorded for 3 min, after which the cuf was inflated for 3 min at 250 mmHG. When the pressure was released CBV was measured until resting blood flow could be registered. This procedure was repeated after 30 min. The percentage increase of CBV during PRH (PRH%) was calculated (Östergren and Fagrell, 1985).

Statistics

To control reproducibility a regresion analysis was performed. Differences between the values before and after the test procedures were tested using Student's t test for paired samples (SPSS for Windows, Germany).

RESULTS

Resting Blood Velocity

The mean CBV during rest was 0.47 mm/sec (SD ± 0.37 mm/sec, range 0.14 to 0.93 mm/sec). The average intraindividual difference between max rCBV and in rCBV was 0.30 mm/sec (SD ± 0.18 mm/sec). The maximum difference between the capillaries of a single subject ranged up to 0.63 mm/sec.

Postocclusive Reactive Hyperamia

In every volunteer a postocclusive hyperemic response could be observed. CBV values increased from rCBV = 0.47 mm/sec (SD ± 0.37) at rest to 0.90 mm/sec (SD ± 0.46mm/sec) peak blood cell velocity. The peak occured after 24.9 sec (tpCBV) (SD ± 9.2 sec). PRH was 118%. The reproducibility of pCBV (r = 0.67; P <= 0.002) and tpCBV (r = 0.97; P <= 0.0001) was high, but the reproducibility of PRH was weak (r = 0.09; P <= 0.002).

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