Autonomic control of the heart and peripheral vessels in human septic shock

OBJECTIVE

Circulating endotoxin impairs the sympathetic regulation of the cardiovascular system in animals. We studied the changes in the autonomic control of the heart and circulation during septic shock in humans.

DESIGN

12 patients (age 43.0 +/- 6, 17-83 years) were investigated during septic shock (mean duration: 3.5 +/- 0.5 days) and during recovery, fluctuations in R-R interval, invasive arterial pressure (AP) and peripheral arteriolar circulation (PC, photoplethysmography) were evaluated by spectral analysis as a validated noninvasive measure of sympathovagal tone. Apache II score was adopted as the disease severity index. Low frequency components (0.03-0.15 Hz) of the frequency spectra were expressed as relative to the overall variability (LFnu) for each cardiovascular variable.

RESULTS

LFnu were low or absent during shock but, in the 10 patients who recovered, increased by the time of discharge (post-shock). R-R LFnu increased from 17 +/- 6 to 47 +/- 9 (p < 0.03), AP LFnu from 6 +/- 3 to 35 +/- 4 (p < 0.02) and PC LFnu from 18 +/- 3 to 66 +/- 4 (p < 0.001). Apache II fell from 23.1 +/- 1, at admission, to 14.8 +/- 1.8 at discharge (p < 0.005). Two patients died showing no LFnu increase.

CONCLUSION

Reduced LF components of the variability of cardiovascular signals are characteristic of septic shock, confirming the presence of abnormal autonomic control. Restored sympathetic (LF) modulation seems to be associated with a favourable prognosis.

Photoplethysmography in the diagnosis of venous disease

BACKGROUND

Photoplethysmography (PPG) has become a widely used method in the diagnosis of venous disease.

OBJECTIVE

To describe briefly various aspects of PPG and its practical value.

METHODS

Standard and quantitative PPG are described as well as various evaluation procedures.

RESULTS

The refilling time is considered the most useful parameter; values higher than 22 seconds are considered normal. Quantitative PPG systems (calibrated or digital PPG) also permit evaluation of the drainage function.

CONCLUSION

While refilling time is presently the only quantitative parameter, it is expected that by introducing calibrated or digital PPG in diagnostic practice, venous function will be evaluated in a more comprehensive and quantitative form.

Optical characteristics of human extracted teeth and the possible application of photoplethysmography to the human pulp

In order to record pulp blood flow by photoplethysmography, the light transmission properties of extracted human teeth and human peripheral blood at wavelengths between 400 and 800 nm were first investigated. Transmission through peripheral blood and extracted teeth was lower at wavelengths shorter than 600 nm. Transmitted-light photoplethysmography (TLP) was applied to teeth in situ using a tungsten light, or one of two light-emitting diodes (LED) with peak wavelengths of 565 and 695 nm. A CdS-CdSe photoconductive cell was used as a detector. The LED with a peak intensity at 565 nm was the most efficient of the three light sources for recording the TLP. The results indicate that the TLP could be used to assess pulp vitality.

Toe pressure determination by audiophotoplethysmography

PURPOSE

The purpose of this study was to evaluate the performance of audiophotoplethysmography as a modality to measure toe pressure without the requirement of a recorder.

METHOD

A portable photoplethysmograph with an audio output was used to determine toe pressures, and the results were compared with those obtained by a commercial photoplethysmograph with a recorder.

RESULTS

Thirty-one measurements in control subjects and 62 measurements in patients with arterial occlusive disease were performed. The average toe pressure recorded with oscillography with standard photoplethysmography was 103.5 mm Hg +/- 14.7 SD and 95.9 mm Hg +/- 13.4 SD with audio-photoplethysmography. In the patient group the pressure recorded with a commercial photoplethysmograph was 65.3 mm Hg +/- 34.9 SD compared with 61.6 mm Hg +/- 34.8 SD obtained with audio-photoplethysmography. The difference in both groups was insignificant, and the correlation between both methods was very good.

CONCLUSION

A portable hand-held photoplethysmograph equipped with an audio output was used to measure toe pressure in control subjects and in patients with arterial occlusive disease. The results have been compared with the oscillometric method by a standard commercial photoplethysmograph connected to a recorder. The correlation was very good in the control and patient groups, and the difference between both methods was below the level of statistical significance. The fact that no recorder is needed may help in introducing toe pressure measurement into everyday office diagnostic practice.

Optical detection of pulpal blood

An optical system to assess blood within the pulpal cavity was developed. The system included a light-emitting diode source, human incisor teeth, and a silicon photodiode detector. An automated syringe pump was used to flow bovine blood lengthwise through the teeth. Transmitted light intensities were recorded at a collection frequency of 20 reading/min and apparent absorbance units were calculated. The effects of blood concentration, blood flow rate, and pulp chamber size were investigated. It was found that changes in blood flow rate did not cause significant changes in transmitted light intensity. Increases in blood concentration and pulp chamber size resulted in larger absorbance values. These results suggest that photoplethysmography measurements may be sensitive to the amount of blood in the pulp chamber as it reflects the pulsatile-related expansion and contraction of capillaries within the pulp tissue.

Comparison of intraarterial with continuous noninvasive blood pressure measurement in postoperative pediatric patients

OBJECTIVE

The purpose of this study was to estimate the accuracy, bias, and frequency response of continuous blood pressure monitoring using finger photoplethysmography in children.

METHODS

To compare arterial blood pressure measured using the Finapres device with simultaneously measured intraarterial blood pressure we studied 27 randomly selected postoperative pediatric patients who were receiving a variety of inotropic and vasoactive agents at a cardiac intensive care unit in university-affiliated pediatric hospital.

RESULTS

Sixty-two of 66 attempts (94%) to obtain a noninvasive blood pressure measurement were successful. A total of 37,351 paired blood pressure measurements from 53 records were compared, revealing a measurement bias of -18.6 mm Hg for systolic blood pressure and -13.4 mm Hg for diastolic blood pressure. The measurement bias increased proportionately to blood pressure, with systolic and diastolic gains between the noninvasive and intraarterial techniques of 0.86 and 0.75 mm Hg/mm Hg, respectively. The variation bias during each recording epoch, as measured by standard deviation of bias, was low (mean sigma systolic = 2.9 mm Hg; mean sigma diastolic = 2.0 mm Hg). The frequency response between the intraarterial and noninvasive pressure waveforms was flat to 10 Hz and approximately equal to 1.

CONCLUSIONS

Substantial measurement bias exits between this noninvasive blood pressure measurement technique and intraarterial blood pressure. Measurements of the intrapatient variability and frequency response analysis suggest that the noninvasive technique accurately tracks intraarterial blood pressure over the short term. This technique may have useful applications in settings where intraarterial monitoring is undersirable or unobtainable.

Computerized photo-plethysmography of the finger

A microcomputer system for studying photo-plethysmography of the finger (PPF) was designed and applied to 50 non-premedicated healthy boys (one to ten years old) undergoing general anaesthesia (halothane in 70% N2O, with mechanical ventilation) for outpatient inguinal hernia repair. The purpose of this study was to assess the accuracy of computerized estimations of the photo-plethysmographic (arterial waves) amplitude and to evaluate whether or not PPF allows discrimination between two different surgical stimuli (skin incision, and manipulation of the spermatic cord). When anaesthesia was stable for at least five minutes (end-tidal halothane = 1.25-1.5%; PETCO2 = 32-38 mmHg; SpO2 > or = 98%; rectal temperature = 36.3-37 degrees C; ambient operating room temperature = 20-21 degrees C), and immediately before the skin incision, computerized estimations of the photo-plethysmographic (arterial waves) amplitudes (PPA) were recorded and saved for later comparison with direct (manual) measurements of the plethysmographic tracing, using an arbitrary scale of 0-255 units. Also, the values of PPA, systolic blood pressure, and pulse rate recorded immediately before the skin incision were later compared with the maximum changes in these same values recorded 30-90 sec after skin incision, and 30-90 sec after manipulation (traction+dissection) of the spermatic cord. Six boys (three to ten years old) stayed quiet enough, during induction of anaesthesia by mask, to allow regression analysis of PPA, systolic blood pressure, and pulse rate (Y) on end-tidal halothane/70% N2O (X). Computerized estimations tended to give a higher reading, by between 0.2 to 0.8 units, than direct measurements.(ABSTRACT TRUNCATED AT 250 WORDS)