Autonomic Control of Skin Microvessels: Assessment by Power Spectrum of Photoplethysmographic Waves

Abstract

1. Although it is well known that the microvessels of the skin constantly undergo spontaneous variations in volume, the significance of these rhythmic changes remains uncertain. 2. In 10 healthy males and in 15 patients in intensive care, we assessed the origin of the autonomic influences on spontaneous fluctuations in the microcirculation of the skin, obtained by an infra-red photoplethysmographic device; we used spectral analysis techniques to compare these fluctuations (which were recorded simultaneously in two sites) with those of blood pressure, in order to test the presence of autonomic control of any synchronous fluctuations in these different measurements from the cardiovascular system. In order to minimize mechanical fluctuations caused by occasional slow breaths, rather than nervously mediated fluctuations in skin blood flow, respiration was controlled at 15 breaths/min (0.25 Hz). 3. Spontaneous infra-red photoplethysmographic fluctuations were observed in different body areas (left index finger and left ear lobe, right and left index finger), and all were evident at 0.1 Hz, as well as respiration-related components at 0.25 Hz. Active standing increased the power of the 0.1 Hz fluctuations (sympathetic activity) in both blood pressure (from 62.7 +/- 7.1 to 79.2 +/- 3.7 normalized units, P < 0.05) and IRP (finger: from 68.5 +/- 6.4 to 86.9 +/- 3.4 normalized units, P < 0.05; ear: from 59.0 +/- 5.9 to 88.1 +/- 2.0, P < 0.01). There was a high (> 0.5) coherence between the fluctuations obtained in blood pressure, in IRP signals obtained simultaneously at the finger and at the ear, and in R-R interval. This synchronization between the oscillations in all these signals, which were unrelated to the respiratory frequency or to the pulse rate, suggests a common neural, non-local origin. The phase between IRP and blood pressure was positive in the 0.1 Hz region (+1.65 +/- 0.41 radians, i.e. IRP was leading blood pressure, showing that 0.1 Hz fluctuations were not passively transmitted to the skin microvessels from large arteries) and negative in the 0.25 Hz region (-0.74 +/- 0.19 radians, P < 0.01 compared with phase in the 0.1 Hz region, i.e. IRP was lagging behind blood pressure, suggesting possible passive transmission to the skin microvessels of blood pressure fluctuations caused by respiration). Fluctuations at lower frequency were observed in all IRP recordings, suggesting a local origin for these. Intra-arterial and IRP fluctuations were compared in the 15 intensive care patients and gave similar results. 4. The skin microcirculation is thus not only under local control, but also reflects changes in sympathetic activity; the effect of these changes on the skin microcirculation can be easily evaluated by the spectral analysis of the IRP signal obtained simultaneously in multiple areas, in conjunction with the spectra of R-R interval and blood pressure.

Widespread depolarization during expiration: A source of respiratory drive?

“…BP oscillations of 0.1 Hz, commonly referred to as Mayer waves, are associated with sympathetic nervous activity [2,33]. In contrast, BP oscillations at a frequency of 0.25-0.3 Hz correlate with respiratory rhythms [33]. The synchronization of BP oscillations with respiration supports the theory of a baroreflex mechanism as an explanation for RSA.…”

“…Arterial BP levels throughout the body oscillate at a frequency that is dependent upon other physiological systems including heartbeat, respiration, and intrinsic myogenic vascular muscle tone. BP oscillations of 0.1 Hz, commonly referred to as Mayer waves, are associated with sympathetic nervous activity [2,33]. In contrast, BP oscillations at a frequency of 0.25-0.3 Hz correlate with respiratory rhythms [33].…”

Sympathetic mediated vasomotion and skin capillary permeability in diabetic patients with peripheral neuropathy

“…Sympathetic stimulation by postural change [17,18] and sympathetic blockade by anesthetics [17], have the largest effect on the low-frequency (LF; 0.02 to 0.14 Hz) power component of skin blood flow variability (BFV). The skin LF-BFV power has been shown to be lowered in diabetic patients [3].…”

“…Spectral analysis of skin blood flow oscillations, recorded continuously by laser Doppler flowmetry, can be used to study sympathetically mediated vasomotion [3,17,18]. Sympathetic stimulation by postural change [17,18] and sympathetic blockade by anesthetics [17], have the largest effect on the low-frequency (LF; 0.02 to 0.14 Hz) power component of skin blood flow variability (BFV).…”

“…The following spectral characteristics were obtained: the total BFV was the power in the 0.02 to 0.40 Hz frequency band (AU 2 ), the low-frequency (LF) BFV was the power in the 0.02-0.14 Hz frequency band (AU 2 ), and the high-frequency (HF) BFV was the power in the 0.15-0.40 Hz frequency band (AU 2 ). The LF-BFV was also expressed in normalized units (NU), which represents the ratio between the LF-BFV power and total BFV power [3,18]. Sodium fluorescence videodensitometry.…”