Dermal blood flow response to constant pressure in healthy older and younger subjects

Tissue interface pressure and skin integrity in critically ill, mechanically ventilated patients

OBJECTIVE

To describe tissue interface pressure, time spent above critical pressure levels and the effect on skin integrity at seven anatomical locations.

DESIGN, SETTING, PATIENTS

Descriptive, longitudinal study in critically ill mechanically ventilated adults, from Surgical Trauma ICU-STICU; Medical Respiratory ICU-MRICU; Neuroscience ICU-NSICU in a Mid-Atlantic urban university medical centre. Subjects were enroled in the study within 24hours of intubation.

MEASUREMENTS

Tissue interface pressure was measured continuously using the XSENSOR pressure mapping system (XSENSOR Technology Corporation, Calgary, Canada). Skin integrity was observed at all sites, twice daily, using the National Pressure Ulcer Advisory Panel staging system, for the first seven ICU days and at day 10 and 14.

RESULTS

Of the 132 subjects, 90.9% had no observed changes in skin integrity. Maximum interface pressure was above 32mmHg virtually 100% of the time for the sacrum, left and right trochanter. At the 45mmHg level, the left and right trochanter had the greatest amount of time above this level (greater than 95% of the time), followed by the sacrum, left and right scapula, and the left and right heels. Similarly, at levels above 60mmHg, the same site order applied. For those six subjects with sacral skin integrity changes, maximum pressures were greater than 32mmHg 100% of the time. Four of the six sacral changes were associated with greater amounts of time above both 45mmHg and 60mmHg than the entire sample.

CONCLUSIONS

Maximum tissue interface pressure was above critical levels for the majority of the documented periods, especially in the sacrum, although few changes in skin integrity were documented. Time spent above critical levels for mean pressures were considerably less compared to maximum pressures. Maximum pressures may have reflected pressure spikes, but the large amount of time above the critical pressure levels remains substantial.

The Effects of Different Lying Positions on Interface Pressure, Skin Temperature, and Tissue Blood Flow in Nursing Home Residents

Background:

Although repositioning is considered an important intervention to prevent pressure ulcers, tissue response during loading in different lying positions has not been adequately explored.

Aim:

To compare the effects of different lying positions on interface pressure, skin temperature, and tissue blood flow in nursing home residents.

Method:

From May 2011 to August 2012, interface pressure, skin temperature, and blood flow at three tissue depths were measured for 1 hr over the sacrum in 30° supine tilt and 0° supine positions and over the trochanter major in 30° lateral and 90° lateral positions in 25 residents aged 65 years or older. Measurement of interface pressure was accomplished using a pneumatic pressure transmitter connected to a digital manometer, skin temperature using a temperature sensor, and blood flow using photoplethysmography and laser Doppler flowmetry.

Results:

Interface pressure was significantly higher in the 0° supine and 90° lateral positions than in 30° supine tilt and 30° lateral positions. The mean skin temperature increased from baseline in all positions. Blood flow was significantly higher in the 30° supine tilt position compared to the other positions. A hyperemic response in the post pressure period was seen at almost all tissue depths and positions.

Conclusion:

The 30° supine tilt position generated less interface pressure and allowed greater tissue perfusion, suggesting that this position is the most beneficial.

Skin blood flow response to 2-hour repositioning in long-term care residents: a pilot study

PURPOSE

The purpose of this noninvasive pilot study was to examine the changes in transcutaneous oxygen (tcO2), skin temperature, and hyperemic response in the heels, sacrum, and trochanters in a 2-hour loading-unloading condition in nursing home residents who are positioned in supine and lateral positions.

DESIGN

A 1-group, prospective, repeated-measures design was used.

SUBJECTS AND SETTING

Nine subjects (5 males, 4 females) with a mean age of 85.3 ± 10.86 years (mean ± SD) who required help in turning and positioning at a skilled nursing facility participated in the study.

METHODS

Oxygen and temperature sensors were placed on the heels, trochanters, and sacrum. The subject was (1) positioned lateral for 30 minutes (preload); (2) turned to the supine position with head of the bed at 30° for 2 hours (both sacrum and heels were on the bed surface) (loading); and (3) positioned lateral for 2 hours (unloading). Subjects were turned to either the right or the left side.

RESULTS

Friedman test showed no statistical differences in tcO₂ or skin temperature on the sacrum, heels, or trochanters during preload, supine, and lateral positioning (P > .5). Individual data revealed that hyperemic response was seen in 6 of the 9 subjects when the position was changed from supine to lateral. Only one-third of the subjects attained a sacral tcO₂ of 40 mm Hg or more at the end of the 2-hour lateral positioning. tcO₂ on both heels decreased within the first 30 minutes of loading.

CONCLUSION

Two hours of staying in the supine position lowered sacral oxygenation to less than 40 mm Hg, in some subjects, regardless of whether there was adequate tcO₂ at preload. Repositioning to a lateral position after 2 hours of placement in a supine position did not cause the tcO₂ to return to preload level. The efficacy of a 2-hour repositioning schedule requires further investigation. Since heel tcO₂ was reduced after 30 minutes of loading, further work is needed to determine whether the heels should be offloaded with more frequent repositioning.

Correlation of cutaneous tension distribution and tissue oxygenation with acute external tissue expansion

Today, the biomechanical fundamentals of skin expansion are based on viscoelastic models of the skin. Although many studies have been conducted in vitro, analyses performed in vivo are rare. Here, we present in vivo measurements of the expansion at the skin surface as well as measurement of the corresponding intracutaneous oxygen partial pressure. In our study the average skin stretching was 24%, with a standard deviation of 11%, excluding age or gender dependency. The measurement of intracutaneous oxygen partial pressure produced strong inter-individual fluctuations, including initial values at the beginning of the measurement, as well as varying individual patient reactions to expansion of the skin. Taken together, we propose that even large defect wounds can be closed successfully using the mass displacement caused by expansion especially in areas where soft, voluminous tissue layers are present.

Wavelet-based spectrum analysis of sacral skin blood flow response to alternating pressure

OBJECTIVES

To provide insight into the physiologic mechanisms associated with alternating pressure, using wavelet analysis of skin blood flow (SBF) oscillations, and to determine whether the application of alternating pressure induces myogenic responses, thereby enhancing SBF as compared with constant loading.

DESIGN

Repeated-measures design.

SETTING

University research laboratory.

PARTICIPANTS

Healthy, young adults (N=10; 5 men, 5 women; mean age +/- standard deviation, 30.0+/-3.1 y).

INTERVENTION

Alternating pressure for 20 minutes (four 5-min cycles with either 60 mmHg or 3 mmHg) and constant loading for 20 minutes at 30 mmHg on the skin over the sacrum.

MAIN OUTCOME MEASURES

A laser Doppler flowmeter was used to measure sacral SBF response to both alternating pressure and constant loading. Wavelet-based spectrum analysis of SBF oscillations was used to assess underlying physiologic mechanisms including endothelium-related metabolic (.008-.02 Hz), neurogenic (.02-.05 Hz), and myogenic (.05-.15 Hz) controls.

RESULTS

Alternating pressure stimulated an increase in sacral SBF of compressed soft tissues as compared with constant loading (P<.01). SBF during the high-pressure phase of 4 alternating pressure cycles showed an increasing trend. An increase in power in metabolic frequency range and a decrease in power in the myogenic frequency range during alternating pressure were observed compared with SBF prior to loading. Power increased in the myogenic frequency range during the low-pressure phase of alternating pressure and decreased during the high-pressure phase.

CONCLUSIONS

SBF control mechanisms, as assessed by the characteristic frequencies embedded in SBF oscillations, show different responses to 2 loading pressures with the same average pressure but different patterns. Our study suggests that optimization of operating parameters and configurations of alternating pressure support surfaces to compensate for impaired SBF control mechanisms in pathologic populations may be possible using wavelet analysis of blood flow oscillations.

Evaluation of antidecubitus mattresses

Pressure sores are a current problem in hospitals and care of the elderly, leading to protracted hospital stays and a high care burden. The trauma for the patients is severe, and the cost of pressure sore prevention and treatment, is considerable. Antidecubitus mattresses are used for prevention and in treatment, but they also contribute to the cost of treating pressure sores. The problem highlighted in the review is that the mattresses' effectiveness in preventing and treating pressure sores has not been sufficiently evaluated. When antidecubitus mattresses are evaluated, it is often only with regard to aspects of the interface pressure and the mattresses' ability to redistribute the pressure. The review points out the important observation that, to be able to evaluate the efficacy of the antidecubitus mattress, the mattress's effect on tissue viability needs to be studied. The parameters that ought to be considered when evaluating a support surface are: interface pressure, pressure and blood flow distribution, temperature and humidity in the skin-support surface interface. The authors propose that the effect on tissue viability of external loading can be assessed by simultaneous measurement of the interface pressure and tissue perfusion.

A Comparison of Changes in Rhythms of Sacral Skin Blood Flow in Response to Heating and Indentation

OBJECTIVE

To differentiate blood flow control mechanisms associated with indentation from those associated with heating and to discern heat-induced and pressure-induced changes by comparing the effect of externally applied stress on skin blood flow (SBF) to the response to externally applied heat.

DESIGN

Repeated-measures design.

SETTING

A university research laboratory.

PARTICIPANTS

Ten healthy, young adults (5 men, 5 women; mean age +/- standard deviation, 30.0+/-3.1y). Intervention Incremental heat (35 degrees -45 degrees C, 1 degrees step/min) and pressure (0-60 mmHg, 5 mmHg step/3 min) on the sacrum using a computer-controlled indenter. Sessions for heat and pressure protocols were separated by 7+/-2 days.

MAIN OUTCOME MEASURES

We used a Laserflo Blood Perfusion Monitor 2 and Softip pencil probe to measure capillary blood perfusion and wavelet analysis to decompose the blood flow signal. The power spectrum was divided into 5 ranges corresponding to metabolic, neurogenic, myogenic, respiratory, and cardiac control mechanisms. The average relative (ie, normalized) power in each frequency range was computed to determine of the relative contribution of each control mechanism.

RESULTS

Power in the myogenic frequency range was higher after incremental pressure and lower after incremental heating, whereas power in the metabolic frequency range was lower after incremental pressure and higher after incremental heating ( P <.01). Mean blood flow decreased as pressure increased from 0 to 15 mmHg; mean blood flow increased as pressure increased from 15 to 60 mmHg.

CONCLUSIONS

SBF, as recorded by the laser Doppler, suggests that there may be a myogenic control mechanism mediating blood flow after incremental tissue loads and that a metabolic control mechanism may mediate blood flow after heat application to the tissue. The study of local blood flow control mechanisms and their response to pathomechanical perturbations may be possible using wavelet analysis of blood flow oscillations. More research is needed to establish the clinical utility of these findings in the development of support surfaces intended to reduce the risk of developing pressure ulcers.

Ischemic and pressure-induced hyperemia: a comparison

OBJECTIVE

There is reason to question whether hyperemia after pressure occlusion is caused solely by local ischemia. This study quantitatively compared the response to the two forms of occlusion on the finger.

DESIGN

Blood flow was measured by laser Doppler continuously before, during, and for 40 minutes after a 2-minute occlusion of flow at the finger dorsum and at the plantar surface of the finger tip (finger pulp), which has a much higher arteriolar density than the dorsum. Occlusion to the same low level was carried out either with a cuff at the base of the finger or by direct pressure of the laser Doppler probe head. Comparison experiments were performed with the probe head heated to 44 degrees C to elicit maximal local vasodilation.

SETTING

Outpatient clinic.

PARTICIPANTS

Eleven healthy volunteers.

MAIN OUTCOME MEASURES

Magnitude and duration of skin blood flow after occlusion.

RESULTS

Cuff occlusion at the base of the finger produced a typical, short-lived hyperemic response at both finger dorsum and finger pulp. The peak level at finger dorsum was 17.6 +/- 1.4mL/min/100g, approximately a twofold increase over the baseline flow level. The duration of the hyperemic response was 3.6 +/- 0.8 minutes. The baseline flow at the finger pulp was three times greater than at the finger dorsum, and peak flow after occlusion was also three times higher (44.3 +/- 2.6 mL/min/100g). The duration of hyperemia at finger pulp was 4.2 +/- 0.9 minutes. After pressure occlusion at the finger dorsum the hyperemic peak was higher (26.7 +/- 4.2 mL/min/100g; p < .05) and the duration of hyperemia was four times longer (16.9 +/- 2.3 minutes; p < .01) than after cuff occlusion. At the finger pulp, the pressure-induced hyperemic peak was also greater than the peak after cuff occlusion (56.3 +/- 1.7mL/min/100g; p < .05), with a longer duration than after cuff occlusion (11.1 +/- 1.1min; p < .01). Thermal stimulation significantly reduced the differences between cuff- and pressure-induced occlusion. There was a slow increase in flow over the 40-minute monitoring period. The maximal flow reached was approximately 100mL/min/100g at both finger dorsum and finger pulp. At both sites, however, the maximal flow level was attained more rapidly than the control condition without prior occlusion.

CONCLUSIONS

These results confirmed that the pressure-induced hyperemic response is greater and of longer duration than that produced by flow ischemia alone. Thermal stimulation essentially abolishes the differences, suggesting that there is a common mechanism of vasodilatation. The mechanistic differences between pressure-induced and ischemic hyperemia remain to be determined.

Impaired blood flow response following pressure load in diabetic patients with cardiac autonomic neuropathy

OBJECTIVE

An impaired blood flow response is associated with an increased risk of developing decubitus ulcers. This study investigated whether diabetic patients with autonomic neuropathy show an impaired blood flow response following pressure load, compared with healthy controls.

DESIGN

Before-after trial.

SETTING

University hospital.

PATIENTS

Eighteen patients with type I diabetes and autonomic neuropathy, and 15 healthy volunteers.

RESULTS

The blood flow response starts with a latency period, followed by a temperature increase (described by the "time constant"). The blood flow response in both groups showed significant (p < .01) differences. In diabetic patients, the latency time was 312 +/- 221 sec, the time constant was 339 +/- 149 sec, and the recovery time was 538 +/- 184 sec. In controls, latency time was 83 +/- 47 sec, time constant was 79 +/- 69 sec, and recovery time was 162 +/- 103 sec. The velocity of the blood flow response decreased with increasing duration of diabetes mellitus (p = .02).

CONCLUSIONS

Diabetic patients with autonomic neuropathy show an impaired blood flow response after pressure relief. This finding suggests that these patients have an increased risk of developing decubitus ulcers.

The effects of air mattress upon sleep and bed climate

The purpose of this study was to investigate the effects of an air mattress upon sleep and bed climate. This air mattress, which employs a pump and timer to increase or decrease the inflation pressure in order to cure and prevent decubitus was tested. Six healthy female volunteers, aged 18 to 23, served as subjects. The experiments were carried out under three conditions: using regular Futon (Futon), the air mattress with pump and timer activated (Air+) and the same mattress without pump and timer activated (Air-). Room temperature and relative humidity were controlled at 22-23 degrees C and RH 50-60% respectively. Subjects' sleep was monitored by using EEG machine throughout the night, and subject's body temperature and bed climate were also continuously checked. Subjective estimation of bed and sleep were obtained before and after the recording sessions. Sleep onset latency and wake after sleep onset tended to be reduced in Air+ compared to Futon and Air-. The time and percentage of Stage 3 was increased significantly in the middle one third of the night in Air+. A significant difference was observed in bed climate of the waist area. Temperature tended to be higher in Futon than in Air+ and Air-, while relative and absolute humidity were significantly higher in Air+ and Air-. Significant difference between Air+ and Air- was observed only during one hour after sleep recordings started. Thermal sensation in the morning was cooler and comfort sensation tended to be better in Air+ and Air-. Subjective sleep estimation was somewhat good under all conditions. These results suggest that although these air mattresses do not affect sleep, we have to be cautious in using these mattresses as relative and absolute humidity were kept higher than with Futon. Further study on materials and construction of these air mattresses to decrease the humidity is needed.

Variability of short arm cast application: the influence of experience using fibreglass tape and QuickCast

A new short arm cast material which is heated to conform to the underlying limb was compared to conventional fibreglass tape. The time required for application, the pressures generated beneath the casts and the availability for digital motion were studied in three groups with varying lengths of casting experience. Results showed that the new immobilizer did not require additional time for application and provided similar interface pressures beneath the casts as compared to fibreglass tape. In addition, metacarpophalangeal joint motion was less restricted with the new casting experience. The shrinkable immobilizer thus offers an alternative to conventional fibreglass tape casts.

Pressure generation beneath a new thermoplastic cast

A new cast immobilizer that is heat-shrunk to conform to an injured extremity was examined. The purpose of these studies was to compare pressures beneath the thermoplastic cast with those beneath fiberglass casts on a laboratory model and on the forearms of human volunteers. Pressures measured beneath fiberglass casts on metal cylinders averaged 36 mm Hg. Thermoplastic casts on the smaller cylinder that allowed 42% shrinkage produced a mean pressure of 25 mm Hg; those placed on the larger cylinder that allowed 17% shrinkage produced a mean pressure of 39 mm Hg. Pressures measured on the forearms of healthy volunteers averaged 22 mm Hg beneath fiberglass casts and 31 mm Hg beneath the thermoplastic casts. These pressures were considerably less than pressures that have been shown to occlude the microcirculation of the skin. Acute compartment syndromes result from swelling within a limited space and remain a serious concern clinically when swelling is anticipated under any type of constraining cast. The results of these studies indicate that the new cast should not produce a greater risk of circulatory compromise to the limb than previously used fiberglass materials.

The effects of small shifts in body weight on blood flow and interface pressure

The purpose of this study was to (a) determine whether small shifts in body weight change pressure and blood flow under a bony prominence, and (b) identify the magnitude of change in blood flow and pressure under a bony prominence over time. Blood flow and interface pressure in two positions (lateral oblique/supine) with two small shifts in each position (thigh/rib cage) were evaluated over time in 50 nursing home residents. There was a significant decrease in interface pressure under the trochanter through the small shifts intervention, F = 5.36, p < .01. There was a significant decrease in interface pressure, F = 3.90, p < .05, and a significant increase in blood flow, F = 4.85, p < .05, under the sacrum through the small shifts intervention. Blood flow and interface pressure did not change significantly over time.

Evaluation of skin blood flow by laser Doppler flowmetry

Laser Doppler flowmetry is an excellent noninvasive technique for the measurement of cutaneous microcirculation. The list of applications of laser Doppler flowmetry in dermatology is long. It can be applied to monitor inflammation caused by various drugs, chemicals, and allergens related to blood flow. To measure certain inflammatory reactions a combination of other bioengineering measurements is desirable. Flaps can be monitored, and burn depth measured by laser Doppler flowmetry. Through blood flow measurement, the pathophysiology of various skin diseases can be verified and certain treatments can be partially monitored. Although it is not as directly applicable to daily clinical practice, except in a few cases, laser Doppler flowmetry is a very useful technique in various kinds of dermatologic research.

Age and tolerance to secondary ischemia in rat epigastric flaps

The use of microvascular procedures is increasing as the population continues to age. The purpose of this study was to observe the survival of skin flaps after ischemic injury. Skin flaps (n = 50) underwent either 3 hours of primary (1 degree) or secondary (2 degrees) venous occlusion in young (2-3 mo) and old (18-22 mo) rats. Skin flap survival was assessed on postoperative day 7. Survival rates for young and old after 3 hours of 1 degree ischemia was 100% and 90% (ns). Survival rats for young and old after 2 degrees ischemia were 67% and 47% (ns).