Vasomotion in Human Fingers

Abstract

Introduction: We describe methods by which vasomotion can be recorded in awake and anesthetized human subjects without significant interference from other spontaneous vascular oscillations.

Methods: In three separate studies, we used photoplethysmography (PPG) to record vasomotion in fingertips. In Study 1, we induced chemical sympathectomy in the studied hand of 11 awake subjects who received intravenous dexmedetomidine infusions. In Study 2, we administered four progressively increasing intravenous dexmedetomidine infusions to 16 awake volunteers. In Study 3, we recorded vasomotion simultaneously from 6 fingers of 7 patients who were under dexmedetomidine-based anesthesia. Five-minute epochs of PPG recordings that displayed slow vascular oscillations were analyzed for frequency and amplitude.

Results: In Study 1, vasomotion frequencies were 0.025 ± 0.008 Hz. In Study 2, vasomotion frequencies were 0.033 ± 0.006 Hz, and 0.032 ± 0.008 Hz during the two highest dexmedetomidine infusion steps. In Study 3, vasomotion frequencies ranged from 0.020 to 0.037 Hz and were observed in all 6 fingers, with no synchrony between the six fingers.

Conclusion: The vascular oscillations we observed without significant interference from other spontaneous oscillations are independent of neural activity (Study 1), local in nature (Study 3), and associated with alpha-2-adrenoceptor activation, consistent with known properties of vasomotion.

Keywords: Alpha-2 adrenoceptor agonist; Microcirculation; Photoplethysmography; Spontaneous vascular oscillations; Vasomotion.

Fig. 1.

Illustration of an intraoperative PPG recording that shows slow vasomotor oscillations (0.02 Hz), rhythmic mechanical ventilator induced respiratory oscillations (0.17 Hz), and cardiac oscillations (arterial pulses) (1 Hz). ADC, analog-to-digital converter counts.

Fig. 2.

Illustration of PPG DC and AC components and DC % modulation calculation. The DC value corresponds to the smallest blood volume in the finger (end diastole), when the maximum amount of light is transmitted through the finger. The AC values are due to cardiac pulses and is defined as the difference between the highest (end diastole) and lowest (end systole) light transmission values of each cardiac pulse. DC % modulation is calculated by identifying the maximum and minimum DC value for each vasomotor cycle. DC % modulation is then calculated as shown in the figure.

Fig. 3.

Spectrograms of chirp Z-trans-form analysis of a subject in Study 1. Left panel: data recorded while the subject rested in supine position prior to brachial plexus block, showing multiple vascular oscillation frequencies. At approximately 500 s, a brachial plexus block was performed, resulting in significant attenuation or disappearance of these vascular oscillation frequencies. Right panel: spectrogram recorded after the brachial plexus block during dexmedetomidine infusion revealing a single dominant frequency oscillation (vasomotion). Note the 10-fold difference in spectral power compared to the left panel.

Fig. 4.

Example of a photoplethysmography (PPG) recording from one Study 1 subject (upper panel). Changes in PPG values between minutes 15 and 22 are due to movement artefact. The black horizontal bars in the upper panel signify 5-min data segments, which are shown in more detail in the lower panels. a PPG recording from a resting subject showing typical SNS associated vasoconstrictive activity. b PPG recording of a vasodilated finger after brachial plexus neuraxial block. Note the lack of vasoconstrictive events. c Slow spontaneous vascular oscillations (vasomotion). The insert is a 7-s segment of the 100 Hz recording to illustrate that the PPG recordings are composed of cardiac pulses. d Vasomotion during L-NMMA infusion. ADC, analog-to-digital Converter counts.

Fig. 5.

Vasomotion frequencies (Hertz) of all study subjects. For Study 1 the frequencies are plotted during dexmedetomidine infusion (DEX), and after the beginning of L-NMMA infusion (L-NMMA). For Study 2, the frequencies are shown for infusion steps 3 and 4. For Study 3, frequencies from all 6 sensors for each subject are shown.

Fig. 6.

PPG recording from one Study 2 subject before dexmedetomidine infusion and during each of the four dexmedetomidine infusion steps. The black horizontal bars signify two 5-min data segments that are illustrated in more detail in Figure 7. ADC, Analog-to-Digital Converter counts.

Fig. 7.

Two 5-min PPG recordings from a subject in Study 2. The three upper panels show the original PPG signal (left), signal after filtering (lower right), and the chirp Z-transform output (CTZ) of the filtered signal from step 3 of dexmedetomidine infusion. The lower panels show similar data from step 4 of the dexmedetomidine infusion. ADC, Analog-to-Digital Converter counts.

Fig. 8.

Simultaneous 5-min 62.5 Hz PPG recordings from all 6 sensors of a subject in Study 3 (left). Middle panels show the signals after filtering, and right panels show chirp Z-transform outputs of the filtered signals. The slow oscillations are due to vasomotion, and the faster oscillations which, are best seen in the filtered signals, are due to pulse volume changes secondary to mechanical ventilation. ADC, Analog-to-Digital Converter counts.